EPA R2-72-043
„ . „„ Environmental Protection Technology Series
September 1972
Control of Mercury Pollution
in Sediments
\
'
Office of Research and Monitoring
U.S. Enviionmental Protection Agenr
Washington, O.C. 20460
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were"established to facilitate further
development and appliceition of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
degradation from point and non-point sources of
pollution. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards..
-------
EPA-R2-72-OU.3 '
September 1972
CONTROL OF MERCURY POLLUTION
IN SEDIMENTS
Contract No. 68-01-008?
Project 16080 HTY
Project Officer
Dr. Curtis C. Harlin, Jr.
Robert S. Kerr Water Research Center
P.O. Box 1198
Ada, Oklahoma 74820
Prepared for
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20^60
For sale by the Superintendent ol Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price 75 cents
-------
EPA Review Notice
This report has been reviewed by the Environmental
Protection Agency, and approved for publication.
Approval does not signify that the contents
necessarily reflect the views and policies of
the Environmental Protection Agency, nor does
mention of trade names or commercial products
constitute endorsement or recommendation for
use.
11
-------
ABSTRACT
Methods are needed for controlling pollution from mercury-laden sediment
deposits on the bottom of streams and lakes. The results of exploratory
studies to develop such methods are reported here.
Five sediment samples containing from 6 ppm to 500 ppm mercury were in-
vestigated. Two samples were taken from the St. Glair River below the out-
fall of a chloroalkali plant; one sample from the Detroit River below a
chloroalkali plant; one sample from a stream which empties into the San
Francisco Bay; and one sample from an industrial holding pond used for
disposing of waste from a chloroalkali plant.
The geochemical nature of these sediments varied considerably from sample
to sample. The major differences were in organic content, sand or sili-
cate content, carbonate content and particle size distribution. Although
no effort was specifically directed to determining the chemical form of
mercury in the sediment samples, the results of these studies indicate that
mercury is present in a variety of chemical forms. These forms likely in-
clude mercuric sulfide; complexes with organic materials (proteinaceous or
folic acids); and insoluble double salts such as mercury aluminates or
mercury ferrates, and adsorbed on particulate matter. The relative amounts
of various chemical forms of mercury in a specific sediment depend on what
is available in the sediments. Sulfides and organic materials form extremely
stable compounds with mercury, and will be the predominant forms of mercury
present in the water or sediment. Materials capable of forming double salts
are excellent mercury scavengers; however, the compounds are labile and will
readily give up mercury in the presence of sulfides or organic complexing
agents.
The use of an iron overlay in the form of crushed automobile bodies topped
with sand should, on the basis of results developed on this program, be an
inexpensive and effective method of isolating mercury-containing sediments
from a water overlayer. An important attraction of using iron as an overlay
is its ability to reduce methylmercury ions as well as mercuric ions to
elemental mercury.
A variety of methods for recovering the mercury values from dredged sedi-
ments were explored. Density fractionation, particle size fractionation,
flotation, roasting and leaching were the methods studied. Roasting and
chemical leaching afford the greatest promise for inexpensive removal and
recovery of the mercury. A possible method for in-place leach of sediment
deposits is presented.
Field tests of the iron overlay and the chemical leach method are recommended.
111
-------
This report was submitted in fulfillment of Project No. 16080 HTY, Contract
No. 68-01-0087, under the sponsorship of the Environmental Protection
Agency.
iv
-------
CONTENTS
Section Page
I CONCLUSIONS 1
II RECOMMENDATIONS 3
Method 1 - Hypochlorite Leach of In-Place Sediment . . 3
Method 2 - Iron Overlay 4
III INTRODUCTION 5
IV EXPERIMENTAL DESIGN AND RATIONALE 9
Descriptions of Sediment Samples Studied ....... 9
Experimental Rationale 11
Analytical Procedures 14
V EXPERIMENTAL RESULTS 17
Overlay of Mercury-Laden Sediments with Iron 17
Mercury Recovery from Sediment 26
VI DISCUSSION 39
Iron Overlay 39
Mercury Recovery from Sediment 40
VII ACKNOWLEDGEMENTS 43
VIII REFERENCES 45
Appendix - Demonstration of Hypochlorite Leach of In-Place
Sediment 47
-------
FIGURES
No. Page
1 SCHEDULE FIELD TEST OF HYPOCHLORITE LEACH OF SEDIMENT 49
2 SCHEDULE FIELD TEST IRON-SAND OVERLAY 53
VI
-------
TABLES
No.. Page
1 SEDIMENT SAMPLES 10
2 MERCURIC ION REDUCTION BY IRON 18
3 REDUCTION OF CH3Hg+ BY IRON 22
4 CONVERSION OF CE^&+ TO (CH3)2Hg BY IRON 24
5 MERCURY CONTENT OF WATER OVER SEDIMENT 27
6 PARTICLE SIZE AND ORGANIC DISTRIBUTION IN ST. CIAIR RIVER
SEDIMENT (SAMPLE 1) 50 G OF WET SEDIMENT SCREENED ... 28
7 PARTICLE SIZE AND ORGANIC DISTRIBUTION IN SAN FRANCISCO
BAY SEDIMENT (SAMPLE 4) 30 G OF WET SEDIMENT SCREENED . 28
8 PARTICLE SIZE DISTRIBUTION, PERCENT ORGANIC AND
MERCURY CONTENT 29
9 MERCURY CONTENT OF SPECIFIC GRAVITY FRACTIONS OF SEDIMENT
SAMPLE 1 31
10 MERCURY CONTENT OF SPECIFIC GRAVITY FRACTIONS OF SEDIMENT
SAMPLE 5 31
11 FLOTATION OF SEDIMENT 32
12 MERCURY RECOVERY FROM SEDIMENT SAMPLE 1 BY THERMAL
TREATMENT 33
13 LEACHING STUDIES ON SEDIMENT SAMPLES 35
VI1
-------
SECTION I
CONCLUSIONS
Mercury lost to streams, rivers and lakes accumulates in bottom sediments.
Fish and plants which occupy waters covering these sediments often have a
mercury content which approaches the maximum acceptable level for safe
consumption by man.
This report describes a method for insulating mercury-laden sediment from
its water overlayer, methods for recovering the mercury values from dredged
sediment so that it could be used as a safe landfill or returned to the
water body, and a possible method for recovering mercury from in-place sedi-
ment deposits.
Laboratory studies have shown that scrap iron will rapidly and efficiently
remove divalent mercuric ions and methylmercury ions from water by convert-
ing these soluble forms to elemental mercury. Hydrated iron oxide which
forms when mercury is reduced is an effective precipitating agent for
mercury ions. Iron, perhaps as crushed automobile bodies, covered with
4 to 6 in. of sand or other finely divided inert material to prevent erosion
and shifting of the iron should serve as an inexpensive yet very effective
covering for mercury-laden sediment.
A large fraction of the cost of solving the problem by dredging the mercury-
laden sediments would be incurred in transport of the sediment to a site
where runoff or leaching of the sediment would not recontaminate a water
body, or in the cost of construction of a suitable disposal site. Even if
such sites were found or constructed, there would always be a potential
hazard posed by these relocated deposits. An inexpensive treatment of the
dredgings to recover the mercury value and to sanitize the sediment so that
it could be used as a safe landfill or even returned to the water body is
desirable.
Roasting, the most commonly used process for recovering mercury from ore,
could be used to remove mercury from sediments. Sediments could be roasted
without grinding or crushing. Air drying of the sediment prior to roasting
would result in a considerable energy saving. Rotary cement kilns are
widely distributed and would often be favorably located for sediment treat-
ment. It would be necessary to equip such a kiln with suitable mercury
condensation equipment.
Leaching with 1% hypochlorite solution at a pH of 6.0 to 6.5 was found to
be very effective for solubilizing the mercury in all but one of the
sediments studied. The one exception was the sediment from the San
Francisco Bay area, which had a very high organic content. Recovery of
mercury from dredgings using this leaching medium appears practical.
-------
Sinkable barges could be used as temporary water-tight cofferdams. A
large fraction of the water could be pumped out of the impoundment. The
sediment within this impoundment would then be treated with the hypochlorite
leach liquid to solubilize the mercury. Mercury would be recovered by re-
ducing with an active metal, by sulfide precipitation or by carbon
adsorption.
If in-place treatment proves to be impractical, the portable cofferdam could
be used to prevent sediment from being broadly dispersed during dredging.
The dredgings could be leached, returned to the water and allowed to settle
before moving to the next dredging site.
-------
SECTION II
RECOMMENDATIONS
Two methods are recommended for controlling pollution for mercury-laden
bottom deposits. The first method uses a solution of hypochlorite ions
(pH 6.0 to 6.5) to leach mercury from dredged sediment or from in-place
sediment. The second method uses an iron overlay (crushed or shredded
automobile bodies) covered with sand to prevent diffusion of mercuric and
methylmercury ions from the sediment into the water overlayer.
Following are specific recommendations for demonstrating each of the methods
at a field site.
Method 1 - Hypochlorite Leach of In-Place Sediment
It is recommended that a field demonstration be conducted to:
(1) Demonstrate that hypochlorite solution will solubilize a large fraction
of the mercury compounds in natural sediment,
(2) Determine the optimum concentration and pH of the hypochlorite solution
for leaching in-place sediments,
(3) Determine the rate of leaching and the amount of sediment agitation re-
quired to achieve efficient leaching, and
(4) Develop and evaluate methods for recovering the mercury- from the
leachate.
A site should be selected where the water level, the water inflow and the
water outflow can be controlled. An industrial holding pond would be an
appropriate site. Recovery from dredged sediment could be substituted for
in-place recovery.
A detailed outline for a field test of this method is attached to this
report as an Appendix. Preliminary estimates of the cost of recovering
mercury by this method vary from $5,000 to $10,000 per acre depending on
the site.
-------
Method 2 - Iron Overlay
It is recommended that a field demonstration be conducted to: (1) demon-
strate that an iron overlay covered with sand is an effective barrier and
will prevent mercury from diffusing out of the sediment into the water,
and (2) determine the long-range environmental effects of an iron-sand
overlay on the flora and fauna of the water body.
A site to field test this method must be carefully selected. The water in-
flow should be essentially mercury-free. The flora and fauna of the water
body must not contact sediment not covered with the overlay. A control
site must be operated under identical conditions to demonstrate the effec-
tiveness of the treatment.
It is recommended that ponds be constructed specifically for this study.
These pond bottoms will be covered with 4 to 6 in. of mercury-spiked natural
sediment for demonstration purposes. The sediment in one pond would be
covered with 4 to 6 in. of iron and then with 4 to 6 in. sand; in a second
pond the sediment would be covered only with sand. A control pond would
contain only spiked sediment.
The ponds would be filled with fresh water, appropriate flora and fauna in-
troduced into the ponds and monitored for mercury accumulation over an ex-
tended time interval. These same ponds could be used to study the uptake
of other heavy metals or pesticides by the flora and fauna of a water body.
A detailed program outline for a field test is contained in the Appendix.
Preliminary estimates of the cost of treating mercury-laden sediment by
this method is $2,500 to $3,000 per acre.
-------
SECTION III
INTRODUCTION
Midwest Research Institute has been conducting studies to develop methods
for controlling pollution from mercury-laden sediment by isolating or de-
contaminating sediments present in the bottom of lakes and rivers. These
sediments are potentially serious health hazards since they are believed
to be the source of mercury found in fish inhabiting the waters overlaying
these sediments. It is further believed that the highly toxic methylmercury
found in fish tissue is formed by organisms present in the sediments. This
program, funded under EPA Contract No. 68-01-0087, was initiated to evaluate
methods for isolating mercury-laden sediments from the water overlayer, for
decontaminating sediments in place, and for recovery of mercury from sedi-
ments removed from the bottoms of water bodies.
Two attractive approaches for treating these sediments have been investigated:
(1) An iron overlay (perhaps using crushed automobile bodies) covered with
sand, clay, or other environmentally acceptable material to prevent mercury
from entering the water overlayer was evaluated. The results of these
studies showed that iron will remove soluble mercury from water by convert-
ing it to elemental mercury. Iron also reduces toxic methylmercury ion to
elemental mercury, and should function as an effective barrier preventing
any methylmercury formed in the sediment from entering the water overlayer
and contaminating the flora and fauna of the water body. (2) A method using
a hypochlorite leaching solution (pH 6.0 to 6.5) for removing mercury from
dredged sediments was investigated. This treatment would allow the treated
dredgings to be returned to the water body or used as landfill without
fear of contamination. Design and construction of portable cofferdams would
allow the sediments to be treated in place to remove and recover the mercury.
Following is background information relevant to experimental studies of
methods for coping with the mercury pollution problem.
Approximately 83,000 tons of mercury have been consumed in the United States
during this century.i' However, little information is available on how and
where it entered the environment. The largest source of industrial mercury
pollution in 1968 was chloroalkali plants.— By 1970, the levels of mercury
emissions from these plants had decreased by 86%. Similar improvements have
been made by other industries in reducing mercury effluents. Of the total
of 2,865 tons of mercury purchased in the U.S., in 1968, 76% or 2,160 tons
were lost to the environment. This loss does not include that amount
emitted to the atmosphere during mercury ore refining (approximately 31
tons/year), or mercury emitted as a by-product of tin, zinc, copper and
gold production. Mercury emissions from coal combustion, probably the
-------
largest source of mercury emission into the air, is estimated at anywhere
from 275-1,800 tons/year. From these major sources, some 2,500-4,000 tons
of mercury were lost to the environment in 1968. The reduction in losses
from various industries since 1968 would reduce this figure; however, con-
sumption of coal by electrical industries has increased. The majority of
this mercury eventually ends up in the sediment of lakes, rivers and oceans.
Other sources of mercury in the environment can be traced to mercury ore
deposits and brackish water runoff from oil fields. These sources often
result in high natural background levels of mercury in the affected areas.
Alkylmercury salts, in general, and methylmercury, in particular, are the
most hazardous forms of mercury in the environment; the inorganic forms of
mercury are much less hazardous. All serious incidents of mercury-poisoning
can be traced to losses of man-made alkylmercury compounds to the
environment.
It is generally accepted, although poorly documented, that methylmercury is
biologically formed in the sediments which contain mercury. It is postulated
that methylmercury thus formed is absorbed by microscopic plants and animals,
and then works its way up the food chain. It is also probable that methyl-
mercury present in water would be absorbed directly through the gills of
fish.
Homogenized fish tissue has been used as a source of organisms that will
methylate mercury. It has also been demonstrated that chickens can methylate
mercury in vivo.— It therefore seems probable that fish are capable of
methylating mercury in vivo. The mercury can be made available for methyla-
tion by ingestion, adsorption in the gills, or absorption on the outer surface
of the fish. Absorption of inorganic mercury on the intestine walls or on
other fish surfaces is thennodynamically probable since proteinaceous mate-
rial forms very stable coordination compounds with divalent inorganic mercury.
Hence, an important consideration which will determine the usefulness of a
mercury decontamination method is whether methylmercury found in fish is
primarily obtained from the food they eat or by in vivo methylation.
Although much more information is needed to describe the metabolic processes
responsible for methylmercury accumulation in fish tissue, two facts are in-
controvertible: (1) mercury is present in substantial quantities in the
sediment in some water bodies; and (2) fish in these same water bodies con-
tain abnormally large quantities of mercury.
The chemical composition and physical properties of sediments are known only
in a very general manner. They contain varying quantities of igneous rock,
sedimentary rock and other geophysical products. Individual particles range
from submicron to multicentimeter in dimension. Sediment contains, in
-------
addition, particles of waste solids, and liquids that have been added by
industrial operations and other human factors. In short, each sediment
bed is a peculiar mixture of materials. In a technical sense, each sediment
bed is a raw material which may require a unique series of processes and
operations to remove mercury.
The chemical forms of mercury contained in sediment have been deduced from
isolated chemical examinations of relatively simple systems in the labora-
tory. The factors that affect the state of mercury in contaminated sedi-
ments, however, are poorly understood at this time, primarily because little
attention has been directed to defining the chemistry of these types of
materials.
Based on this information, the hazard of mercury contaminated sediment
could be reduced by: (1) Isolation of the mercury-laden sediment from the
water overlayer. This method of dealing with the mercury problem is probably
a holding action at best and is most applicable to situations where mechani-
cal disturbance or erosion of the sediment is expected to be minimal. (2) Re-
moval of mercury compounds from the bulk of materials in the sediment removed
(dredged) from the water body or recovering the mercury compounds from the
sediment in place, perhaps by treating one section of the system at a time.
The second method could utilize modified forms of metallurgical processes
now used in recovering metal values from ores, or in some instances, sea-
water and brines. It follows that the technology of mercury hydrometallurgy
can be adapted, with appropriate modifications dictated by the nature of the
raw material, to the problems encountered in handling and processing mercury-
laden deposits.
New and more subtle methods for dealing with mercury-laden sediments may
present themselves as additional information on physical, chemical and
biological processes operative in the sediments, the water, and in aquatic
life is developed.
-------
SECTION IV
EXPERIMENTAL DESIGN AND RATIONALE
The experiments conducted and the rationale behind these experiments were
based on our understanding of the mercury contamination problem. Experimental
studies were sometimes modified during this program as new insight into the
nature of the problem was developed.
Following are descriptions of the sediments studied, a discussion of the ex-
perimental rationale, and details of methods of analysis.
Descriptions of Sediment Samples Studied
The results of work in this program are based on information about the
states of mercury in sediment for five sources: two from the St. Clair
River; and one each from the Detroit River, the Islais Creek which flows
into the San Francisco Bay, and an industrial waste impoundment.
One sample from the St. Clair River and the sample from the Detroit River
were supplied by the EPA Grosse lie Laboratory. A sample from Islais Creek
was supplied by the Corps of Engineers, and the remaining two samples were
furnished by private industries. Table 1 contains information on the
samples.
The major portion of the effort was devoted to Samples 1 and 5 because of
their high mercury content. Sample 2, which was obtained late in the pro-
gram, received very limited attention.
Samples 1 and 3 were collected and shipped as individual grab-samples.
Since more than one grab-sample was required to complete a series of
mercury recovery studies, all the grab-samples were combined into one
large sample. The initial studies conducted on St. Clair Sample 1 were
an exception. A single grab-sample containing approximately 37 ppm mercury
was used. That sample is designated Sample la throughout this report.
The combined grab-samples (Sample 1) had an average mercury content of
127 ppm.
All samples were thoroughly mixed before studies were initiated.
-------
TABLE 1. SEDIMENT SAMPLES
Sample Source
Sample
Number
Sampling Method Sample Size
Remarks
St. Glair River
33.5-mile point
St. Glair River
Detroit River
Islais Creek, 4
San Francisco Bay
Peterson Dredge 9 - grabs
(~ 3 gal.)
Unknown
Peterson Dredge
Unknown
5 gal.
5 - grabs
(~ 1.5 gal.)
5 gal.
Near Canadian shore
407, ooze, 40% silt, 20% clay
Considerable variation (37 - 130 ppm)
in mercury content between grab samples.
Near Canadian shore
Mercury content ~ 25 ppm.
Sample taken 20 ft from U.S. shore at
13.1-mile mark. Mercury content 6.5 ppm.
Mercury content 6.9 ppm.
Industrial Pond
Unknown
5 gal.
Mercury content > 500 ppm.
-------
Experimental Rationale
Iron Overlay. The rationale behind using iron as an overlay for mercury-
contaminated sediment to prevent mercury entry into the water overlayer
was based on both chemical and biological considerations. In the chemical
sense, iron is sufficiently active to reduce mercurous, mercuric and methyl-
mercury ions. The electrochemical potentials for these reactions are ex-
pressed as the Gibbs free energy (,A>G) for the reactions. (No free energies
of formation for the methylmercury ion could be found.)
3 Hg+2 + 2 Fe° > 2 Fe+3 + 3 Hg° AG = -123.2 Kcal/mole
3 (Hg)2+2 + 2 Fe° > 2 Fe+3 + 6 Hg° &G = -113.8 Kcal/mole
Although the free energies values indicate the driving force for the reac-
tions, the rates of reaction are equally important and must be determined
experimentally. Hence, preliminary in-house studies were conducted to
demonstrate that the rate of reaction was sufficient to warrant using iron
as an overlay. Preliminary studies also demonstrated that iron would re-
move methylmercury ions from water.
The reduction of methylmercury greatly increased the attractiveness of the
iron overlay since it is widely believed that methylmercury is formed in
the sediment and then works itself into the biota of the water body.
The product of reduction by iron is hydrated ferric oxide. This oxide is
a good coprecipitator of mercuric ions. Hydrated ferric oxide is relatively
insoluble, is widely distributed in water, and is not considered to be an
environmental hazard. Municipal water treatment methods commonly remove
most iron salts from water. Discarded automobile bodies are plentiful and
inexpensive, and are suggested as the overlay iron source. Within funding
and time limitations imposed on this program, it was determined that program
objectives could best be met by determining the efficiency and the rate of
iron reduction of mercuric and methylmercury ions and by identifying factors
which affect the reduction such as pH, light, oxygen and the presence of
interfering compounds. Studies were therefore designed to generate this
information.
Mercury Recovery from Sediment. Removal of mercury from contaminated
sediment has been suggested in a number of cases as the most desirable solu-
tion to the problem. Dredging has been suggested as a plausible solution
to a few specific problems; however, an in-place treatment would offer many
obvious advantages if a practical method could be devised.
11
-------
This report does not address itself to the environmental consequences of
dredging, and definitive studies addressed to this issue are recommended
before widespread dredging is initiated to alleviate the mercury problem.
Total mercury removal may be the only answer in situations where bottom
agitation would make an overlay impractical. A variety of physical and
chemical methods for separating mercury from the sediment were investigated.
Following are descriptions of physical and chemical separation methods
investigated.
Particle Size Separation. Size grading is a commercially practiced method
used widely by mineral processing and food industries. Size grading to
-325 mesh is routine. There has been considerable speculation that mercury
in sediment is primarily associated with the fine particles. If a large
fraction of the mercury were in these fines, then sieving might be used to
concentrate the mercury in a small fraction of the sediment. Hence,
Samples Nos. 1, 3, and 4 were separated into, four particle-size fractions
by sieving. Each fraction was weighed and its mercury content determined.
Gravity Separation. There are many examples of purification processes
based on transport and settling of particles of different densities.
Placer mining for gold recovery is a prime example. In modified forms the
technique has been adapted to numerous industrial processes, particularly
those in which water can be utilized.
There has been isolated evidence-^' that mercury is concentrated in a high-
density fraction of the sediment. Hence, density fraction offered a possi-
bility for separating the mercury-containing fraction. If the mercury were
predominantly in the high density fraction, then perhaps agitation of the
sediment and subsequent settling would result in stratification, with the
mercury in the bottom strata covered by relatively clean sediment. Such a
condition might effectively insulate the mercury from the water overlayer.
Sediment Samples Nos. 1, 3, 4, and 5 were divided into a number of specific
gravity fractions by placing wet sediment samples in centrifuge tubes con-
taining mixtures of carbon tetrachloride and tetrabromoethane. By varying
the proportions of the two liquids, a range of specific gravities from 1.6
(pure CCl^) to 3.0 (pure C^-^^l^ was obtained. Wet sediment was agitated
violently with the solutions and the mixtures then centrifuged for several
minutes at 2,000 rpm. The material more dense than the liquid settled to
the bottom, and the less dense material floated. Beginning at the low
density end, successive specific gravity fractions were collected and analyzed
for total mercury.
12
-------
Flotation. Air flotation is a standard method used in mercury mining for
upgrading the mercury sulfide ore from 0.2-0.5% to 55-607,,. It has been
postulated that mercuric sulfide is the principal form of mercury present
in the sediment of rivers and lakes. As a consequence, flotation was in-
vestigated for removing mercury from sediment. Two reagents (Roccal and
Zephiran) are commonly used in flotation of mercuric sulfide.
Approximately 1 Ib of sediment was placed in a Denver Sub-A 500-g flotation
cell. The cell was Teflon coated prior to initiating these studies to mini-
mize reduction of any water soluble mercury ions on the walls of the flota-
tion cell.
A variety of activators, promoters, and frothers were investigated. These
include Zephiran, Roccal, pine oil, aerosol OT and Saratoga chips. The
floats were collected, weighed and analyzed for mercury.
Pyrometallurgy. The most commonly used process for recovering mercury from
ore is roasting. The process consists of heating cinnabar to reduce and
volatilize the metal followed by condensation of the vapor. Either mechani-
cal furnaces or retorts are used to roast the mercury-bearing materials.
The process is continuous in a mechanical furnace, and batch in a retort.
Roasting is so efficient for recovering mercury that beneficiation prior to
roasting is needed only for low grade ores. Ore taken from open cast mines
commonly contains 0.1-0.15% mercury. Since some isolated sediments have
mercury contents approaching this level, it may be economically feasible
to decontaminate such sediments by roasting.
A limited number of roasting studies were conducted to determine whether
mercury would be efficiently reduced and volatized from sediments without
beneficiation. Treatment of dredged sediment by this method might be
feasible where surplus kilns (such as a large rotary kiln from a cement
plant) could be equipped with a suitable mercury condenser and used locally
to treat sediments.
Sediments were roasted both in the presence and absence of air, and then
analyzed for total mercury.
Chemical Leaching. Hydrometallurgical processing has not been used ex-
tensively to extract mercury from cinnabar. However, one accepted process
uses a solution of sodium sulfide and sodium hydroxide which solubilizes
metallic mercury or cinnabar. The mercury is generally believed to be
present in sediment as a sulfide. However, a significant fraction is
present as a complex with organic materials (amino acids or folic acid) or
adsorbed on particulate material, either organic or inorganic. Mekhonina—
reported the distribution of Mercury II between phases in organic matter-water
13
-------
and mineral matter-water systems as a function of pH. His studies indicated
that a large fraction of mercury in sediment might exist as a complex with
both organic and mineral matter. These complexes would reportedly dissociate
at a low pH (6.3) to yield water soluble mercury.
Studies were conducted to determine whether mercury in the sediment samples
studied on this program could be solubilized. The effectiveness of hydro-
chloric, sulfuric, and nitric acids were investigated as a function of pH
and temperature. Hydrochloric acid affords the added advantage of chloride
O
ions which allow formation of the water soluble HgCl^ complex. Nitric
acid was studied because of its oxidizing potential, and sulfuric acid be-
cause it is most economical. The effect of adding chloride, as sodium
chloride, to sulfuric acid was determined. A hydrometallurgical process
using hypochlorous acid (pH 6-6.5) for extracting mercury from low grade
ore was investigated. The effectiveness was determined as a function of
pH, hypochlorite concentration and leach time.
The sediments were dispersed in the appropriate solutions and the solutions
agitated. Samples of the leachate were taken at various intervals and
centrifuged to remove suspended solids. The clear supernatant was digested
in aqua regia and analyzed for total mercury. At the end of each leaching
study the sediment was digested and analyzed for total remaining mercury.
Analytical Procedures
The step-by-step procedures used in analyzing for total mercury, methyl-
mercury and dimethylmercury are:
Total Mercury.
(1) Twenty milliliters of aqua regia slowly added to ^ 5 g of wet sediment
in a 100-ml beaker.
(2) Allow the mixture to stand at ambient temperature until no evidence of
reaction can be detected.
(3) Boil sample for 2 min.
(4) Cool sample and transfer to polyethylene centrifuge tube.
(5) Mix with vortex.
(6) Centrifuge and then decant liquid into 100-ml volumetric flask.
14
-------
(7) Wash sediment with 20 ml of water, centrifuge and combine liquid
with (6).
(8) Repeat (7).
(9) Dilute sample to 100 ml.
(10) Add 2 ml SnCl2 (107o solution) to a suitable aliquot of (9).
(11) Aspirate sample through 10-cm AA cell.
The instrument used for these analyses was a Varian AA-5 Atomic Absorption
Spectrometer.
Water samples to be analyzed for mercury were treated by the same procedure
as sediment. The purpose of the treatment was to free the mercury from
suspended solids that may have been in the liquid. Steps (7) and (8) were
omitted in water analyses.
Methylmercury. Methylmercury analyses are more difficult. The amount of
methylmercury which can be recovered from a sample is very dependent on the
chemical nature of the sample. Fish tissue and some sediments seem to hold
methylmercury tenaciously. The procedure for extracting methylmercury and
the workup for analysis used in this laboratory is as follows:
(1) Add acidified KBr (5 ml) solution to sample to free methylmercury.
(This solution contains 100 g concentrated 112804, 310 g KBr in 1 liter
of solution.)
(2) Extract with 35 ml of toluene and centrifuge.
(3) Freeze aqueous layer and pour off toluene.
(4) Extract toluene with aqueous cysteine. (This solution contains 10 g
cysteine, 7 g sodium acetate and 125 g sodium sulfate in 1 liter of
solution.)
(5) Repeat step (4).
(6) Add 0.6 ml of 3 molar KI to extract.
(7) Extract water solution with 2 ml of benzene.
(8) Store in dark freezer if analysis is delayed.
(9) Analyze by gas chromatography.
15
-------
The GC conditions for methylmercury analysis were:
(1) Column 3 to 4 ft, 0.25-in. glass column.
(2) Packing - 0V 17 (1.5%)/QF-1 (1.957o) on Supelcoport 100/120 mesh.
(3) Carrier - Nitrogen, approximately 70 ml/min.
(4) Temperature - Inlet - 180°C
- Column - 115°-130°C depending on column length
- Detector - 165°C
(5) Detector - Electron capture (tritium foil), polarizing voltage 12 V.
DimethyImercury. DimethyImercury is analyzed as methylmercury. Samples
suspected of containing dimethyImercury must be stored in the dark be-
cause of its sensitivity to light. DimethyImercury is not likely to be
found in samples containing mercuric ions since the two rapidly dispropor-
tionate to form methylmercury.
(1) Extract sample with toluene.
(2) Reflux while stirring equal volumes of toluene and aqueous HgB^-KBr
solution. (This solution consists of 15 g HgBr and 100 g KBr in 1 liter
of solution.)
16
-------
SECTION V
EXPERIMENTAL RESULTS
The experimental program was divided into two phases: (1) overlay of
mercury-laden sediment with iron; and (2) recovery of mercury from sediment.
Studies were designed to identify the important variables and to optimize
the conditions for each of these methods of treating hazardous mercury-laden
sediments.
Overlay of Mercury-Laden Sediments with Iron
The use of an iron overlay to prevent water soluble inorganic or methyl-
mercury ions from entering water over a mercury-contaminated sediment was
based on studies that had been conducted at MRI prior to this program which
showed that both types of ions were effectively reduced by iron turnings.
The Gibbs free energy for the reduction of the methylmercury ion was unknown.
The rate of the reduction was not known for either inorganic or methylmercury
ions.
Iron Reduction of Mercuric Ions. Studies of the reduction of mercuric ions
(mercuric nitrate) in an aqueous media were conducted under a variety of
conditions which might exist in nature. These conditions included variations
in pH; reduction in the presence of interfering substances, such as chloride
ions which form the stable complex HgCl^; and reduction in the presence and
absence of oxygen. The results of studies of mercuric ion reduction by iron
are shown in Table 2.
Methylmercury reduction by iron turnings was studied at pH values of 7.3,
6.0, 4.0, and 2.6 in the presence and absence of oxygen, and in the presence
and absence of light. High initial concentrations of mercuric and methyl-
mercury ions in water (> 100 ppm) were used in early studies. In later
studies, starting concentrations of 5-7 ppm were used. In all these studies
approximately 10 g of iron turnings (1/6 in. x 1/4 in. x 1 in.) was placed
in a round-bottom flask. The iron filings were cleaned first with acetone,
washed with distilled water and then with 5% nitric acid, and again with
distilled water. The mercury solution was prepared by diluting a 500-ppm
mercury solution to the desired volume (1 liter) adjusting the pH by adding
sodium hydroxide or nitric acid, then adding any desired foreign ions or
compounds.
17
-------
TABLE 2. MERCURIC ION REDUCTION BY IRON
00
Experiment pH
l'a' 6.3
6.3
6.3
6.3
6.2
6.3
6.3
2(a) ' 9.6
9.6
9,6
9.6
9.6
9.6
9.2
-
3 8.1
8.1
8.1
8.0
7.6
7.6
6.7
6.8
-
Reaction
Time
(min)
0
2
5
12
25
45
105
0
2
5
11
25
45
90
185
0
1
5
11
26
60
120
180
1,200
Total Kg"1"1"
in Water
(ppm)
69.0
67.0
51.0
34.0
34.0
46.0
46.0
78.0
63.0
59.0
52.0
49.0
47.0
55.0
58.0
80.0
55.0
58.0
45.0
39.0
40.0
40.0
38.0
0.2
Percent Hg
Removed
_
3.0
26.0
50.7
50.7
33.4
33.4
_
19.3
24.4
33.4
37.2
39.9
29.5
25.7
_
31.3
27.5
43.8
51.3
50.0
50.0
52.5
99.8
Remarks
On Atmosphere
02 Atmosphere
G£ Atmosphere
Agitation sto
after 180 m
-------
TABLE 2 (Concluded)
Experiment pH
4 4.0
5.4
5 4.0
-
6 4.0
-
7(b) 2.5
-
-
Reaction
Time
(min)
0
16
134
1,108
0
150
0
55
125
0
15
240
Total Hg"1"*
in Water
(ppm)
117.0
48.0
6.6
0.56
0.68
0.40
78.75
0.4
0.515
10.0
4.2
0.8
Percent Hg
Removed
59.0
94.4
99.5
—
41.2
99.5
99.4
_
58.0
92.0
Remarks
02 Atmosphere
With 1% Cl"
Agitation stopped
after 134 min
02 Atmosphere
N2 Atmosphere
(a) Solutions found to contain dispersed elemental mercury.
(b) Solution passed through a 1.25 in.x 9.25 in. column packed with iron turnings.
-------
The solution was placed in a 2-liter, 3-necked round-bottom flask and the
iron turnings added. When studies were conducted in an oxygen-free
atmosphere, the reactor was purged for 1 hr with nitrogen, while being stirred
with motor-driven polyethylene paddles. A number of interesting observa-
tions regarding the reduction of mercuric ions by iron were made during
these studies. The amount of mercuric ions reduced and removed from the
water during Experiments 1 and 2 were considerably below the amount which
had been removed in earlier in-house studies. The only significant differ-
ence between the experimental procedures was the amount of agitation of the
reaction system. In the earlier studies, the mixture was gently agitated
on a rocker. In Experiments 1 and 2, the reaction media were vigorously
stirred with a polyethylene paddle at 350 rpm. This rather violent agita-
tion was apparently sufficient to cause the elemental mercury condensed on
the iron to be redispersed, since 50-707,, of the mercury in the water at the
end of these experiments was determined to be elemental mercury. Finely
divided elemental mercury is very susceptible to air oxidation. Continuous
reoxidation of this finely dispersed elemental mercury by air probably
accounted for the unexpectedly large amount of ionic mercury present in the
water phase at the end of the experiment. When agitation of the reaction
medium was stopped and the dispersed particles allowed to settle as shown
in Experiment No. 3, the mercury content of the water dropped dramatically.
Hydrated iron oxide is an excellent coprecipitator for heavy metals such
as mercury. A significant fraction of the mercury found in the aqueous
phase in Experiments 1 and 2 may have been associated with finely divided
hydrated iron oxide. Beginning with Experiment No. 3, all samples were
centrifuged to remove finely divided suspended material. In all succeeding
studies the samples were centrifuged before analysis, and all contained
< 1 ppm mercury at the end of the experiment.
Solubility and thermodynamic considerations indicated that 0.2-0.8 ppm
mercury was more than should have been present in these samples. It
therefore seems likely that a significant fraction of the < 1 ppm mercury
found in water at the end of the experiments was present as either solubil-
ized elemental mercury, colloidally suspended elemental mercury, or colloid-
ally suspended hydrated iron oxide containing absorbed mercury.
A large fraction of the remaining mercury (0.2-0.8 ppm level) was removed
when the water was passed through micropore filters. However, these
filters absorb mercuric ions, and the results of this analysis still do not
indicate whether the approximately 0.5 ppm of mercury was present as sus-
pended particulates containing mercury or as solubilized mercuric ions.
Lower initial concentrations of mercury in water did not significantly
affect the final mercury content of the water. There is some indication
that the efficiency of mercury removal is better at a pH of 8 (Experiment 3)
than at lower pH values.
20
-------
When the results of Experiment 4 (run in an air environment), and Experiment
6 (run under a nitrogen atmosphere) are compared, it appears that oxygen
reduces the rate of mercury removal. Thus, it appears that an anaerobic
condition in the region of the iron overlay might be beneficial in preventing
mercury from diffusing from the sediment, through the iron overlay into the
water overlayer.
Iron Reduction of Methylmercury Ions. The same procedure was used for bo'th
mercuric ion and methylmercury ion reduction studies. However, in later
studies of methylmercury, the purging gas was passed through toluene traps
to collect any dimethyImercury formed. The results of studies of methyl-
mercury reduction by iron are shown in Table 3. Table 4 shows the amount
of methylmercury converted to dimethyImercury.
The amount of reduction which had occurred was determined by analyzing the
water for total mercury. A 20-ml aliquot of water was taken from the
reaction vessel. The sample was centrifuged for 2 min at 2,000 rpm to pre-
cipitate suspended solids. An aliquot of the supernatant was then carefully
collected and digested in boiling aqua regia before being submitted for
analysis by atomic adsorption spectroscopy. Investigators at Dow Chemical
Company recommended using micropore filters to remove suspended solids from
water samples before analysis. Studies conducted in this laboratory in-
dicated that those filters will absorb microgram quantities of mercury from
dilute aqueous solutions.
All samples taken for analysis were stored under acid conditions in acid-
washed polyethylene bottles to minimize mercury absorption on the walls
of the storage vessel.
The results of studies reported in Table 3 indicate that the reduction will
occur either under aerobic or anaerobic conditions. The reduction was
studied both in the presence and absence of oxygen since either conditions
could exist at a water-sediment interface, and because Keevay and Hansen^'
had observed that oxygen increased the rate of degradation of methylmercury
by acid by a factor of 10 . No attempt was made to obtain good rate data
on this degradation. It was felt that methylmercury formed in nature would
have to diffuse through the iron overlay, and would therefore be in contact
with the iron several hours or days. Based on the results of these studies,
such contact time appears to be adequate to reduce and degrade the methyl-
mercury .
Dimethylmercury is decomposed by ultraviolet radiation.—' Experiment 6
was conducted in the dark because of the possibility of light affecting
the reduction of methylmercury by iron and because little or no light would
be present at the sediment-iron interface where the reduction of methyl-
mercury would occur. The results indicated that the reaction does not
require photoexcitation.
21
-------
TABLE 3. REDUCTION OF C^Hg"1" BY IRON
Reaction Time
Experiment pH Atmosphere (hr)
1 4.0 Air 0.0
0.1
0.4
1.0
2.8
29.4
2 6.0 Air 0.0
0.1
0.4
1.4
2.4
25.8
3 4.0 N2 0.0
2.8
18.4
18.7
4 2.6 N2 0.0
2.0
16.0
2.6 Air 16.5
20.0
24.5
24.5
5 4.0 N2 0.0
1.0
3.0
6.0
6(b) 4.0 N2 0.0
0.5
4.0
20.2
7 7.3 N2 0.0
0.5
2.0
4.0
19.5
8 7.3 Air 0.0
0.6
2.0
4.1
21.5
Total Hg
(ppm)
77.0
40.0
11.0
9.8
16.8
0.56
101.5
35.0
13.0
35.0
0.96
0.11
103.0
110.0
112.0
107.0
230.0
50.5
9.3
3.4
2.2
1.4
6.5
95.5
10.3
12.5
19.0
34.5
3.6
3.0
1.5
8.8
8.2
5.9
2.5
1.9
8.6
5.0
4.6
6.0
4.6
Hg Removed
a>
_
48.1
85.8
87.3
78.9
99.3
_
65.6
87.2
65.6
99.1
99.9
-
-
78.1
96.0
98.6
99.1
99.4
97.2
-
89.3
87.0
80.2
-
89.6
91.4
95.7
-
6.9
33.0
71.6
78.5
.
41.9
46.6
30.3
46.6
22
-------
TABLE 3. (Concluded)
Reaction Time
Experiment pK Atmosphere (hr)
9 7.3 Air 0.0
0.5
2.1
3.7
67.0
91.0
116.0
124.0
142.0
10 - Air 0.0
20.0
92.0
116.0
140.0
164.0
188.0
11 - N2 0.0
32.0
56.0
80.0
152.0
176.0
200.0
Total Hg
(ppm)
7.9
7.0
7.3
7.1
6.1
4.9
2.8
0.9
0.54
7.56
0.56
0.06
0.076
0.041
0.066
7.4
0.39
0.057
0.036
0.034
0.034
0.017
Hg Removed
a)
•
11.4
7.6
10.2
22.8
38.0
-
67.8
80.8
,
92.6
99.3
99.0
99.5
99.2
-
94.8
99.2
99.5
99.5
99.5
99.8
(a) Sample not centrifuged before analysis.
(b) 12 ppm Cysteine hydrochloride added to system.
(c) Experiment shielded from light.
23
-------
TABLE 4. CONVERSION OF CH3Hg+ TO (CKtf2HS BY
Experiment
7
8
9
10
11
pH Atmosphere
7.3 N2
7.3 Air
7.3 Air
Air
N2
Total CH3Hg+
(Mg)
2,700
2,700
2,578
2,700
2,700
(CH3)2Hg Formed
(Mg)
175
75
75
385
300
Percent
Theoretical
13.0
5.6
6.1
28.5
22.2
-------
Reducing agents and strong complexing agents are known to convert alkyl-
mercury ions to dialkylmercury. Since the atmosphere over these reactions
was controlled by passing either air or nitrogen through the reactor, this
carrier gas was simply passed through toluene traps to collect any dimethyl-
mercury being formed.
In Experiments 7, 8, 9, 10, and 11, dimethylmercury was found in the trap.
The reaction to form dimethylmercury is:
6CH3Hg4 + 2Fe =» 3(CH3)2Hg 4- 3Hg + 2Fe+3
However, any mercuric ion present in the system will undergo a dispropor-
tionation reaction with dimethylmercury to convert it back to methylmercury.
This reaction is rapid and quantitative.
(CH3)2Hg + Hg+2 > 2CH3Hg+
In all of the experiments, 307o or less of the methylmercury was converted
to dimethylmercury (theoretical is 50%).
Although a relatively large fraction of the methylmercury was converted to
dimethylmercury in these concentrated reaction systems, formation of dimethyl-
mercury in nature should not be a problem since only very small equilibrium
quantities of methylmercury would be present and because the reaction in-
volves a methyl transfer, that is, it requires two methylmercury ions coming
together simultaneously to affect the methyl transfer. There would likely
be sufficient divalent mercury present to react with any dimethylmercury
and convert it to methylmercury.
Laboratory Evaluation of Iron Overlay of Sediments. A seriTes of experiments
was conducted to evaluate the effectiveness of the iron overlay. Sediment
Samples 1, 3, 4, and 5 were studied as follows:
(1) Approximately 1 Ib of each sediment was placed in each of three 1-gal.
wide-mouth glass jars.
(2) One sample of each sediment was covered with distilled water.
(3) A second sample of each sediment was covered with approximately 1 in.
of iron turnings and then with distilled water. These turnings were
several feet long and were compressed into a loose overlay.
(4) The third sample of each sediment was covered with 1 in. of iron turn-
ings, 1 in. of mercury-free sand, and then with distilled water. The
25
-------
samples were rocked gently through an arc of about 30 degrees at a rate of
10 rocks/min. These conditions were used to simulate wave motion over a
sediment in the bottom of a lake.
Samples of water were taken at various intervals and analyzed for mercury.
The results of these analyses are shown in Table 5.
The concentrations of mercury in all the water samples analyzed were in the
0.5 to 15 ppb range. These concentrations are approaching the limits of
sensitivity of the analytical method, which accounts for some of the scatter
in the data. The mercury content of water overlaying sediments having high
mercury content (1,000 ppm) does not normally exceed a few parts per billion.
The general trends indicate that iron is effective and the iron-sand is more
effective in reducing the mercury content of water covering mercury-laden
sediments.
Mercury Recovery from Sediment
A variety of methods for recovering mercury from in-place sediment or from
dredged sediments was evaluated. These methods included size grading,
gravity separation, flotation, roasting and leaching. A description of the
methods used and the results obtained are described below.
Particle Size Separation. Sediment Samples Nos. 1 and 4 were divided into
seven particle-size fractions using brass sieves. These fractions were
analyzed for organic material by ashing samples of dried sediment. The re-
sults of these ashing studies and the calculated organic content of each
particle size fraction are shown in Tables 6 and 7. It was subsequently
determined that carbonates present in the sediments were being degraded
during ashing, and that the calculated organic content was therefore too
high. The organic content based on carbon and hydrogen analysis was sub-
sequently shown to be: Sample 1 < 1%; Sample 3 ~ 5% and Sample 4 ~ 10%.
Since brass screen might reduce and amalgamate any water-soluble mercury
present in the sediments or amalgamate any free mercury, bolting cloth
sieves were used to separate sediment fractions to be analyzed for mercury.
Sieve sizes of 60, 200 and 325 mesh were used to separate the sediment into
four fractions: + 60 mesh; -60 to + 200 mesh; -200 to + 325 mesh; and -325
mesh. The fraction of sediment that passes through the 325-mesh bolting
cloth sieve agreed very closely with the fraction that passed through the
325-mesh brass sieve. The percent of total solids, total mercury in each
particle-size fraction and the present mercury in each particle—size fraction
are shown in Table 8.
26
-------
TABLE 5. MERCURY CONTENT OF WATER OVER SEDIMENT
NJ
•vl
Sediment
Sample 1
Sample 3
Sample 4
Sample 5
Overlay
None
Iron
Iron and Sand
None
Iron
Iron and Sand
None
Iron
Iron and Sand
None
Iron
Iron and Sand
Initial
Hg Cone.
(ppm)
0.000
0.001
0.002
0.000
0.000
00002
0.010
0.006
0.002
0.067
0.011
0.007
30-Day
Hg Cone.
(ppm)
0.000
0.000
0.000
0.184
0.000
0.002
0.000
0.000
0.003
-
60-Day
Hg Cone.
(ppm)
0.010
0.010
0.005
0.010
0.009
0.005
0.007
0.004
0.009
-
90-Day
Hg Cone.
(ppm)
0.014
0.010
0.003
0.009
0.012
0.0052
0.0045
0.0326
0.0033
0.0020
0.0030
0.0017
180-Day
Hg Cone.
(ppm)
0.0015
0.0035
0.0017
0.0013
0.0034
0.0034
0.0004
0.0005
0.0017
-
-------
TABLE 6. PARTICLE SIZE AND ORGANIC DISTRIBUTION IN ST. CLAIR RIVER
SEDIMENT (SAMPLE 1) 50 G OF WET SEDIMENT SCREENED
Mesh Size
> 20
20 to 60
60 to 100
100 to 200
200 to 270
270 to 325
< 325
Dry Weight
(g)
0.087
0.775
1.019
1.441
1.114
0.479
17.463
Percent of
Solids
0.39
3.46
4.57
6.46
5.00
2.14
78.1
Weight of Ash
(g)
0.039
0.540
0.882
1.279
0.964
0.398
15 . 943
(a\
Organic v '
(%)
55.20
30.30
13.42
11.23
13.44
16.90
8.71
(a) Based on weight lost during ashing.
TABLE 7. PARTICLE SIZE AND ORGANIC DISTRIBUTION IN SAN FRANCISCO BAY
SEDIMENT (SAMPLE 4) 30 G OF WET SEDIMENT SCREENED
Mesh Size
> 20
20 to 60
60 to 100
100 to 200
200 to 270
270 to 325
< 325
Dry Weight
(g)
0.205
0.205
0.601
1.069
0.480
0.203
4.834
Percent of
Solids
2.19
2.19
6.43
11.45
5.14
2.17
51.70
Weight of Ash
(g)
0.138
0.138
0.470
0.799
0.379
0.165
4.089
Organic ^
(%)
32.6
32.6
21.8
25.3
21.0
18.7
15.4
(a) Based on weight lost during ashing.
28
-------
TABLE 8. PARTICLE SIZE DISTRIBUTION, PERCENT ORGANIC AND MERCURY CONTENT
NJ
Sample Size
Sample (dry wt-g)
Sample 1 22.38
Sample 3 11.10
Sample 4 9.35
Particle Size
(mesh)
> 60
60 to 200
200 to 325
< 325
> 60
60 to 200
200 to 325
< 325
> 60
60 to 200
200 to 325
< 325
Percent of
Total Solids
3.7
11.0
7.1
78.2
5.3
11.7
3.2
79.8
23.1
17.9
7.3
51.7
Total Mercury
(Ag)
37.5
95.2
43.8
639.0
6.73
22.71
5.55
116.34
23.8
24.9
7.2
31.9
Percent of
Total Mercury
4.6 "1
11.7
5.4
78.3 J
4.4 ^
15.0 1
3.7
76.9 J
27.1 ")
28.4 I
8.2 [
36.3 J
Percent^
Organic
< 1%
~ 5%
~ 10%
(a) Organic content based of carbon., hydrogen analysis.
-------
Results of the analyses of the four particle-size fractions showed
little difference in mercury content in any of the fractions of sediment
Samples 1 and 3. There was a small variation in the mercury content of the
various fractions of Sample 4 but not enough to justify sieving as a benefi-
ciation method.
The results indicated that no significant beneficiation of sediment could
be affected by size grading.
Gravity Separation. Samples Nos. 1 and 5 were separated into density frac-
tions, and the fractions analyzed for total mercury.
Separation was accomplished by placing wet sediment samples in centrifuge
tubes containing mixtures of carbon tetrachloride and tetrabromethane. By
varying the ratios of the two liquids, densities were varied from 1.6 for
pure carbon tetrachloride to 3.0 for pure tetrabromethane.
Wet sediment samples were agitated and centrifuged for several minutes at
2,000 rpm. The fraction less dense than the liquid floated and was separated
for analysis. The fraction which sank was transferred to a tube containing
the next higher density liquid, and the fractionation was repeated.
The percent of the sediment and the percent of the mercury found in each of
the specific gravity fractions are shown in Tables 9 and 10. Sediment dried
in an oven or dried by repeated extractions with acetone agglomerated.
These agglomerated particles, even when ground, were difficult to fractionate.
Since drying would be impractical in a treatment method, studies with dry
material were not pursued.
Analysis of the different fractions showed that the mercury was almost
uniformly distributed throughout all the density fractions. Since a signif-
icant fraction of the mercury could not be concentrated in a relatively small
fraction of the sediment, it does not appear that levigation processes, which
take advantage of density and particle-size distribution, could be used
practically in beneficiating mercury-laden sediments.
Flotation: Flotation studies were carried out on sediment Samples 1 and 5.
A total of seven flotation reagents were used in the experimental flotation
work. Mercury removal from sediment by flotation was not successful. Separa-
tions were achieved, but the concentration of mercury in either fraction,
float or sink, was not appreciably different from the original concentration
of mercury in the sediment (Table 11).
Leaching studies and results of specific gravity and particle size fractiona-
tion experiments indicate that mercury is present in sediments in a variety
30
-------
TABLE 9. MERCURY CONTENT OF SPECIFIC GRAVITY FRACTIONS
OF SEDIMENT SAMPLE 1
Specific
Gravity
< 2.1
2.1-2.2
2.2-2.3
2.3-2.4
2.4-2.5
> 2.5
Weight of
Fraction (g)
0.009
0.006
0.006
0.012
0.028
0.506
?„ of Fraction
1.7
1.0
1.0
2.1
4.9
89.3
Hg Content
(ug/g)
825
466
384
350
285
99
%• Hg in
Fraction
9.9
3.7
3.1
5.6
10.7
67.0
(a) Average concentration of mercury.
TABLE 10. MERCURY CONTENT OF SPECIFIC GRAVITY FRACTIONS
OF SEDIMENT SAMPLE 5
Specific
Gravity
2.0-2.3
2.3-2.5
2.5-2.61
2.61-2.75
2.75-3.0
> 3.0
Weight of
Fraction (g)
0.0019
0.0549
0.3193
0.0680
0.0003
0.0017
7. of
Fraction
0.3
12.2
72.0
15.2
< 0.1
0.3
Hg Content
(ug/g)
890
602
336
38
467 -
225
% Hg in
Fraction
1.3
22.6
73.8
1.7
0.1
0.4
31
-------
TABLE 11. FLOTATION OF SEDIMENT
Sample
Number Reagent
1 None
Zephiran
1 None
Roccal
1 None
Pine Oil
Aerosol OT and Saratoga Chips
Pine Oil
Aerosol OT and Saratoga Chips
Aerosol OT
Roccal
Xanthate and Dow Froth 250
5^a) Xanthate and Dow Froth 250
Roccal
Pine Oil
Aerosol OT and Saratoga Chips
7o Sediment
Floated
5.2
9.3
14.5
18.2
1.1
19.3
13.9
8.5
22.6
45.0
15.2
17.1
9.1
3.4
4.6
49.4
7.75
1.55
7.1
14.9
31.3
?<> Hg
in Float
12.8
17.6
30.4
37.5
3.2
40.7
35.0
17.2
19.2
71.4
18.3
15.4
15.3
7.4
12.9
69.3
23.6
5.1
12.0
10.5
51.2
(a) Sediment aerated before flotation study.
32
-------
of physical and chemical forms. To reduce the number of chemical degrees of
freedom and consequently increase the chances for separating the mercury by
flotation, the sediment was treated with H2S and (NH^)2S in an attempt to
convert all the mercury into the sulfide. No significant increase in separa-
tion efficiency was noted. Oxidation of the sediment with air prior to flota-
tion likewise was not useful in improving the separation efficiency.
The state of the art of hydrometallurgical beneficiation of mercury-containing
materials has not advanced to the point that a variety of chemical forms '
of mercury can be separated simultaneously. The known flotation reagents,
promoters, collectors, frothers, modifiers, activators, flocculents and de-
pressants are specific for sulfides, oxides, or metals. An extensive pro-
gram of research and development would be needed to find reagents for the
forms of mercury present in the sediment.
Pyrometallurgy. Experiments were conducted to ascertain whether mercury
could be recovered from sediment Sample No. 1 by:
(1) Steam distillation
(2) Heating in a retort
(3) By heating to approximately 400°C in a reducing atmosphere of a yellow
gas flame.
The treated sediments were tested for residual mercury. The results as
shown in Table 12 indicate that roast conditions similar to those employed
in extracting mercury ores would be required for sanitizing sediments.
This practice would entail either inexpensive but time-consuming air dryings
for water removal before roasting or a relatively expensive heat drying
operation in conjunction with roasting.
TABLE 12. MERCURY RECOVERY FROM SEDIMENT SAMPLE 1
BY THERMAL TREATMENT
Treatment Mercury Recovered (%)
Steam Distillation 1
Heating in a Retort 90
Heating in a Reducing Atmosphere 99
33
-------
These preliminary studies demonstrate that conventional roasting methods
used for mercury ore could be used to recover mercury from sediment. Be-
cause of the finely divided nature of the sediment, there would be no need
for crushing or other preroasting treatment other than drying to minimize
energy costs.
Chemical Leaching. A variety of leaching solutions was evaluated for re-
covering mercury from sediment. The rationale for the liquids chosen for
these leaching studies was presented in Section IV. Leach liquids and the
variables affecting leaching such as time, temperature and pH together with
the results are shown in Table 13.
Leaching with sulfuric acid at ambient temperature did not solubilize a
large fraction of the mercury in any of the sediment samples even when the
pH was reduced to 1.0 or less. Hydrochloric acid was a more effective
leachant, because chloride ions assist solubilization by reacting with
o
mercury to form the soluble HgCl^ ion. A large fraction of the mercury,
957o or more, was recovered from sediment Sample 5 by leaching with 3.57,
hydrochloric acid at 100°C. Hot hydrochloric acid was not as effective
a leachant for some of the other sediments. A large fraction of the acid
was consumed by carbonates present in Sample 1 sediment, and in significant
but lesser amounts by the other sediments studied.
It appears that a hot hydrochloric acid leach might be practical for recover-
ing the mercury value of sediments which contain little carbonate. Equipment
for hot acid leaching is available and widely used by the foods industry.
Hypochlorite solution (pH 6.0-6.5) was found to be an effective leachant for
all but sediment Sample 4. This leaching agent acts very rapidly, is effec-
tive at ambient temperature, solubilizes all forms of mercury in the sediment
and should be relatively inexpensive when used in the vicinity of chloroalkali
plants. Only sediment Sample 4, which has a large organic content, was not
efficiently leached by a 1% hypochlorite solution.
Mercury leached from sediments by this process can be recovered from the
leach media by metal reduction (iron), absorption on carbon, precipitation
with aluminum, sulfide precipitation, or by other recently developed re-
covery methods, Hypochlorite is widely used in water treatment and is
relatively innocuous to the aquatic environment.
34
-------
TABLE 13. LEACHING STUDIES ON SEDIMENT SAMPLES
Leach
Liquid
5% H2S04
57. H2S04 + 0.1% NaCl
57, H2S04 + 1.0% NaCl
7.5% NaCl
5% H2S04
3.5% HC1
3.5% HN03
3.5% HN03(a)
3.5% HC1
5% NaOCl
5% NaOCL
Leach Leach
Time Temperature % Hg
(jnin) (°C) pH Solubilized
Sample No.
60
60
60
4 hours
20 hours
120
30
60
120
10
10
20
30
15
15
30
30
30
30
60
120
30
60
120
1
25
25
25
25
25
25
100
100
100
25
100
100
100
25
100
100
100
100
25
25
25
25
25
25
21.4
27.0
26.2
4.4
11.5
< 1.0
< 1.0
< 1.0
11.7
0.0
49.2
56.9
76.3
0.0
15.5
32.4
70.3
28.6
12 64.0
12
12 70.8
6 97.3
6 97.8
6 98.6
35
-------
TABLE 13. (Continued)
Leach
Liquid
17. NaOCl
47o NaOCL
5% H2SC>4
57. H2S04 + 0.1% NaCl
57. H2S04 -f 1.07. NaCl
7.57» NaCl
1% NaOCl
4% NaOCl
5% H2S04
57o H2S04 + 0.17o NaCl
5% H2S04 + 1.0% NaCl
1% NaOCl
4% NaOCl
17, NaCl
2% NaCl
47= NaCl
57. H2S04
57. H2S04 - 1% NaCl
57. H2S04
Leach Leach
Time Temperature % Hg
(min) (°C) pH Solubilized
Sample No.
10
10
Sample No.
60
60
60
4 hours
20 hours
10
10
Sample No.
60
60
60
10
10
Sample No.
30
30
30
30
30
120
30
60
120
2
25
25
3
25
25
25
25
25
25
25
4
25
25
25
25
25
5
100
100
100
100
100
25
100
100
100
6.2 81.7
6.3 94.9
0.05 0.0
0.10 0.0
0.0
0.01 6.0
0.01 13.0
6.0 85.8
6.4 92.2
0.2 0.0
0.01 0.0
0.01 0.0
6.3 0.5
5.5 88.2
< 2.0
< 2.0
< 2.0
4.7
23.3
< 1.0
4.7
7.2
12.8
36
-------
TABLE 13. (Concluded)
Leach
Liquid
3.5% HC1
3.5% HNC-3
3.5% HClW
3.5% HN03(a)
3.5% HN03(b)
3.5% HCl
5% NaOCl
5% NaOCl
3% NaOCl
1% NaOCl
Leach
Time
(min)
30
30
30
30
30
30
30
60
120
30
60
120
2
5
10
20
2
5
10
20
Leach
Temperature
100
100
100
100
100
100
25
25
25
25
25
25
25
25
25
25
25
25
25
25
PH
_
_
-
-
_
-
12
12
12
6
6
6
6
6
6
6
6
6
6
6
% Hg
Solubilized
97.0
98.0
94.0
3.0
98.0
2.0
47.9
50.6
51.2
97.3
98.5
97.7
97.0
97.0
95.0
95.0
95.0
97.0
-
97.0
(a) Consecutive leaches of the same sediment sample using first HC1
then HN03.
(b) Consecutive leaches of the same sediment sample using first HN03
the HC1.
37
-------
In summary the hypochlorite solutions (pH 6.0 to 6.5) appear to be effective
leaching agents for removing mercury from sediments. Mercury solubilization
is rapid and efficient with this leachant. Thus, if portable water-tight
cofferdams were available so that the water level over a sediment could be
reduced to a practical level (1 to 2 ft) then it would be practical to
treat sediment in place.
38
-------
SECTION VI
DISCUSSION
A discussion of the experimental results and their significance relative to
the problem posed by mercury in sediment is presented in this section of the
report.
Iron Overlay
Iron, an abundant element in nature, is not considered to be a health hazard.
It is in fact noteworthy that iron anemia is more common in the United States
than in many other countries because of the extra care taken in this country
to cleanse food intended for human consumption. As a consequence, no ad-
verse fcnviri.uanG'HL'64. effects would be expected if iron was used as an overlay
to prevent mercury diffusion from sediment into the water.
These studies demonstrate that iron effectively and efficiently reduces
mercuric ions and methylmercury ions to elemental mercury. In aqueous solu-
tions a fraction of the methylmercury disproportionates in the presence of
iron to form dimethylmercury. Such a conversion would be less probable in
a natural environment because of: (1) the low steady-state concentration
of methylmercury ions found in nature, and (2) the low probability of two
methylmercury ions coming together simultaneously on the iron surface to
accomplish methyl transfer. If dimethylmercury were formed it would react
rapidly and quantitatively with mercuric ions to form methylmercury.
Hydrated iron oxide, formed when mercury is reduced, is an effective pre-
cipitator of mercuric ions and would aid in retaining mercury at the
sediment-overlay interface. Consequently, the results of these studies
together with consideration of the chemistry of iron and mercury compounds
indicate that iron would be very effective in isolating mercury-laden
sediment from water.
Sand or other inexpensive overlay materials act as physical barriers and
are partially effective as sediment insulators. The effectiveness of the
iron would be increased if the iron were covered with such a material.
Sand would reduce the rate of diffusion of mercury thus allowing more time
and opportunity for the mercury to contact the iron and be reduced. Sand
would also prevent metallic mercury condensed on iron and the mercury
ferrate from being redispersed by agitation.
39
-------
Iron overlay has some disadvantages. Crushed automobile bodies would hinder
subsequent dredging of a site treated by this method. Swift watercourses
where mechanical disturbance of the sediment occurs could not be effectively
treated by this method.
In summary the chemistry and the thermodynamics of the reactions of iron
with soluble mercury are favorable. The results of these studies show that
the rate of the reaction is sufficient so that an iron overlay covered with
sand should be an effective barrier against mercuric ion diffusing out of
the sediment into the water overlayer. The sand covering the iron should
help to maintain an anaerobic condition around the iron which is apparently
beneficial. The sand should prevent agitation of the iron layer, thus
minimizing the chances of redispersing elemental mercury which condenses on
the iron or precipitated mercury salts of hydrated iron oxide. This treat-
ment method would be most applicable to industrial holding ponds, lakes or
watercourses which are subjected to little or no bottom agitation.
4 Mercury Recovery from Sediment
Removal of mercury-laden sediment or the recovery of the mercury from the
sediment may be determined to be a necessary action in some incidents of
heavy mercury contamination. A drastic action such as dredging would seem to
be premature at this time for a number of reasons. The most modern dredging
equipment recovers only about 70% of the sediment. Unrecovered sediment
would be dispersed over a much larger area and would likely result in an
increase in the mercury content of the flora and fauna of the watercourse
for perhaps several years. Dredged sediment could not be piled along the
shore of the watercourse, but would have to be transported to a suitable
disposal site. A lined excavation might have to be constructed for disposal.
Future recontamination of surface or groundwater even then could occur from
such a site. A second problem is disposal of the large amount of water
associated with the dredged sediment. In most cases the water will not meet
water quality standards and will require treatment before it can be returned
to the watercourse.
Regardless of the problems, dredging may be judged to be an appropriate
course of action. A variety of methods were screened for recovering the
mercury value from sediments so that it could be used as a sterile landfill
or returned to the watercourse.
Particle size fractionation and gravity separation were not effective in
separating mercury from the bulk of the sediment. It does not appear that
either of these commercially practiced methods for beneficiating ores could
be used to recover the mercury value of sediment. Some concentrating of the
mercury was achieved by flotation. However, because of the many chemical
40
-------
forms of mercury in sediment and because the chemical forms vary from sedi-
ment to sediment, a new flotation scheme would probably be needed for each
situation. Development of a scheme would be expensive and difficult to
justify.
Sediment could be roasted using conventional equipment and methods to recover
the mercury value. The energy costs would be excessive if the sediments
were not dewatered before roasting. Costs of transportation of the sediment
to a refinery or of constructing a facility at the site would be prohibitive.
Portable mercury recovery equipment used as an accessory to a locally avail-
able cement kiln would reduce the capital equipment costs. A facility of
this nature would make roasting a more attractive treatment method.
Chemical leaching is the most attractive method evaluated for recovering
mercury. Hot hydrochloric acid was effective in recovering 957» or more of
the mercury from sediment. However, a large fraction of the acid would be
consumed by carbonate which is often present in the sediment. Hypochlorite
solution (pH 6.0-6.5) was found to be even more efficient than hydrochloric
acid. This leaching agent is rapid and effective at ambient temperature and
does not react with carbonate. Mercury solubilized by this method could be
recovered from the leachate using methods used to treat chloroalkali plant
effluent. Spent leachate could be returned to the watercourse. Hypochlorite
solution is inexpensive and readily available in the vicinity of chloroalkali
plants where many mercury-laden sediment deposits occur.
Dredged sediment could be pumped into a pond or other treatment compound,
leached, and the solubilized mercury recovered by passing the leachate through
the chloroalkali plant mercury-recovery facility. The sediment could then
be used for landfill. A wastewater clarifier equipped with some form of
agitation would be appropriate as a leach tank.
In situations where that part of the watercourse containing the mercury-
laden sediment could be isolated from the remainder of the watercourse,
sediment could be leached in place. The water containing the mercury could
be treated to recover the mercury. By isolating the sediment there would
be no fear of contaminating a larger area of the water body. In-place
treatment might be particularly attractive for recovering mercury from
industrial holding ponds.
41
-------
SECTION VII
ACKNOWLEDGEMENTS
The project leader was Dr. Ivan C. Smith. The major contributors to the
program were Mr. E. P. Shea, Mr. C. J. Wiegand, Mr. T. Ferguson, Mr. D.
Wapplehorst, Mr. R. Wantack, and Mrs. C. Weis. Dr. J. Spigarelli and
Mrs. Carol Green were responsible for the analytical results. Our thanks
to Dr. Robert Moolenaar, Dow Chemical Company; Mr. William Oppold, Olin
Corporation; and Dr. Sam Upchurch, Michigan State University, who served
as consultants on this program.
The assistance of the Grosse lie Laboratory, the Corps of Engineers, Dow
Chemical Company, and Olin Corporation in supplying sediment samples is
gratefully acknowledged.
We thank Dr. Curtis C. Harlin, Jr., Robert S. Kerr Water Research Center, EPA,
who served as Project Officer and provided considerable insight and guidance
through this program.
43
-------
SECTION VIII
REFERENCES
1. Abelson, P. H. , Science. J£9, No. 3942, July 1970.
2. Wallace, R. A., et al. , Oak Ridge National Laboratory, ORNL-NSF-EP-,1.
3. Hammond, A. L. , "Mercury in the Environment: Natural and Human Factors,'
Science. 171, No. 3973, 788-9, February 26, 1971.
4. Private Communication — Dr. Sam Upchurch, Department of Geology,
Michigan State University.
5. Mekhonina, G. A., Pochvovendenie, No. 11, 116-120 (1969).
6. Kelvay, M. M. , and R. L. Hansen, J. Phys. Chem. . 65, 1055 (1961).
7. Nesmeyanov, A. N. , and K. A. Kocheshkov, Series-Methods of Electro-
organic Chemistry, 4, North Holland Publishing Company (1967) .
45
-------
APPENDIX
DEMONSTRATION OF HYPOCHLORITE LEACH OF IN-PLACE SEDIMENT
A site will be selected or constructed which allows the water level, the
water inflow and water outflow to be controlled. This site would preferably
be approximately 1 acre in area and situated close to a chloroalkali plant.
Following are major features and operations to be used in conducting the
feasibility study.
Engineering Operations
(1) The water level of the test site will be dropped to 1 ft or to the
lowest depth possible, to conserve and minimize chlorine use.
(2) Chlorine will be mixed with the water covering the test site using
conventional chlorination equipment used in municipal chlorination operations.
Varying concentrations of hypochlorite ion beginning at 0.057o hypochlorite
will be used for leaching.
(3) The sediment will be agitated to a depth dictated by the depth of the
mercury deposit. Agitation will be accomplished using a dragline and a
device such as a subsoiler used in many farming operations.
Mercury Recovery from Leachate. Two parallel methods for recovering mercury
from the water will be evaluated.
(1) The first stage in mercury recovery will employ metal reduction. The
leach stream will be split. Half of the stream will be passed through a
bed of iron, the second half through a zinc bed.
Iron is more environmentally acceptable, and the hydrated ferric oxide formed
by mercury reduction or air oxidation is an excellent coprecipitator of
mercury.
Zinc is a more efficient and rapid reducing agent for mercury and forms
mercury amalgams. Its environmental acceptability is being questioned.
(2) The leachant will pass from the metal reduction through an iron pyrite
bed to precipitate residual mercury as the sulfide.
(3) The leachant will then be passed through a sand filter to remove any
residual particulate material.
47
-------
(4) The final step in mercury recovery will involve passing the leachant
through an activated carbon bed.
(5) The clean water, which may contain residual chlorine, will be diluted
to an appropriate level and returned to a stream.
Water containing residual chlorine would, in actual practice, be returned for
processing more sediment.
Sampling and Analysis. The following samplings and analyses would be con-
ducted in support of the field test.
(1) The sediment to be leached will be core sampled and analyzed for mercury
to obtain an accurate measure of the mercury content of the sediment to be
treated.
(2) The mercury content of the water covering the sediment will be
determined.
(3) Leaching will be initiated with 0.05% hypochlorite. The mercury con-
tent of the water will be monitored continually, with leaching to continue
until the mercury content of the water reaches a constant level. A mercury
mass balance will determine how much mercury has been solubilized. Addi-
tional chlorine will be added in stepwise increments until an acceptable
fraction of the mercury is in solution.
(4) Water processing will commence when an acceptable fraction of the
mercury has been solubilized. The water will be analyzed for mercury con-
tinuously as it passes through each treatment. Water will be recycled for
further treatment if the mercury content exceeds maximum allowable levels.
(5) At the completion of the treatment the sediment will again be core
sampled and analyzed for mercury to determine the effectiveness of the
treatment.
(6) A biologist will monitor the water body treated and the stream into
which the treated water is discharged to assess the environmental impact
of the treatment.
The recommended field test is divided into three phases. The tasks to be
performed during each phase are described. A schedule showing the duration
and manpower requirement for each task is shown in Figure 1.
48
-------
SCHEDULE
FIELD TEST OF HYPOCHLORITE LEACH OF SEDIMENT
PHASE/TASKS
Phase 1
• Prepare Site
• Procure Equipment and
Materials
• Construct Water Treating
Facilities
• Conduct Sediment and
Water Analyses
• Obtain Background Biological
Data
Phase II
• Conduct Leaching and
Water Treatment
• Analyze Water and
Sediment
• Conduct Biological
Tests
Phase III
• Analyze Results
• Program Management
• Reports
1
•MM
2
••
3
4
t
5
k
MO
6
NTH
7
8
i
9
k
10
11
12
t
Effort (Me
Sr. Pers.
1.0
0.5
0.5
1.0
0.5
3.5
1.0
1.0
5.0
4.0
k
18
in-Month)
Technician
1.0
1.5
4.0
1.0
0.5
8.0
1.5
0.5
1.0
19
Figure 1
-------
Phase I - Preparation of Site and Facilities. Preliminary estimates of
the time required to complete Phase I are 4 montha Following are the
tasks to be performed during this phase of the program.
Task 1 - Prepare Site. A temporary earthen cofferdam will be constructed
around the area to be treated, by a local contractor. A pipeline will be
laid over ground from the treatment pond to the Tombigbee River.
Task 2 - Procurement of Equipment and Materials. Chlorination equipment,
pumps, sediment agitation equipment, and water treatment materials will be
acquired, assembled and tested.
Task 3 - Construct Water Treatment Facility. Two parallel treatment
processing facilities and associated pumps and piping will be designed and
constructed. Each treatment process will consist of the following steps:
metal reduction, sulfide precipitation, filtration and carbon adsorption.
Each step of this treatment will be conducted in a 4 ft x 4 ft x 4 ft box
constructed of marine plywood.
Task 4 - Water and Sediment Analysis. Water overlying the sediment will
be analyzed for mercury. The sediment will be core sampled to obtain a total
mercury inventory of the pond to be treated.
Task 5 - Background Biological Data. Background data on the biota of the
pond to be leached and on the river which will receive the effluent of the
treatment will be obtained.
Phase II - Leaching Studies. Preliminary estimates of the time required to
complete Phase II are 4 months. The following tasks will be performed dur-
ing Phase II.
Task 1 - Conduct Leaching Operation and Water Treatment. Leaching will
be conducted by successive additions of 0.05% hypochlorite (pH 6.5) until
> 95% of the mercury in the sediment has been solubilized. When leaching
is completed, water treatment to recover the mercury will commence.
Task 2 - Water and Sediment Analysis. The initial water and the water
after passing through each step of the treatment will be analyzed for total
mercury content. Effluent which does not meet water quality standards will
be returned to the pond.
At the completion of the test the sediment will again be analyzed for total
mercury.
50
-------
Task 3 - Biological Tests. Biological tests will be conducted on the
water body treated and on the Tombigbee River below the effluent outfall to
determine whether the biota was adversely affected. These studies will
extend into Phase III.
Phase III - Analysis of Results. This phase of the program, together with
the preparation of a final report, will require 4 months. The results of
the tests and recommendations for more extensive testing or field use will
be recommended.
Proposed Field Test of Iron Overlay
A site selected for field testing the iron- sand overlay for isolating mercury-
laden sediment must, for the purposes of a demonstration, have the following
physical and chemical features.
(1) The water should have a depth of 6 ft or greater.
(2) The area of the water body would preferably be less than 10 acres.
(3) There should not be a continuous inflow of new mercury, even at
levels of 0.01 ppb.
(4) The water body must not be situated downwind from a fossel fuel com-
bustion plant.
(5) The water must contain plant and animal life.
(6) The water body should be available for extended studies, lasting
approximately 3 years.
(7) There should be no plans to dredge the water body during the study
period.
Although these conditions are necessary to demonstrate the effectiveness of
iron overlay in preventing pollution of the plants and fish by mercury in
sediment, it is doubtful that all these conditions can be satisfied in a
natural site.
It is therefore recommended that three 1/2-acre ponds be constructed. The
bottoms of both ponds would be covered to a depth of 4 in. with mercury-
contaminated sediment dredged from a river or lake bottom and shipped to
the ponds or by spiking a real or synthetic sediment with mercury.
Matr-rial;; P?lonpr To: ' '^
OPi'I «...; ,rr.rv
51 -
.'asn?rigton, DC ±j46'
-------
Water used to fill these ponds would come from the overflow of a spring-fed
lake.
Following are the major features of this demonstration study.
(1) Three 1/2-acre earthen dam ponds would be constructed for use in ex-
tended studies of mercury pollution (the ponds could find future use in
studying pollution by other heavy metals, pesticides, etc). One pond
would be used as a control (no treatment), the second to determine the
effectiveness of an iron-sand overlay, and the third pond would contain
a sand overlay. The ponds could be filled by channeling part of the over-
flow of a lake into the ponds. The water would be treated, if necessary,
to reduce its mercury content. A bypass would carry any heavy overflow
around the ponds. A dike would surround the ponds to prevent natural
runoff from entering the ponds. A flood gate would be installed in the
dam of each pond so that the water level could be varied and the pond
drained for removal of the mercury contaminated sediment at the end of the
study.
(2) The bottom of each pond would be covered with 4 to 6 in. of mercury-
laden sediment dredged from a contaminated lake or river bottom or synthet-
ically prepared. These sediments should contain 10 ppm mercury or more.
The sediment in one pond would be covered with 4 to 6 in. of shredded auto-
mobile bodies, in turn covered with 4 in. of sand. The sediment in the
second pond would be covered with 4 to 6 in. of sand. The third pond would
act as a control. All three ponds would then be filled to the desired depth
and stocked with a variety of fish and plants.
(3) The mercury content of the water, fish and plants of the ponds will be
monitored at regular intervals to determine the effectiveness of the iron-
sand overlay. These studies should continue for 1 to 2 years, to obtain
statistically reliable results.
(4) If after 2 years, the iron-sand overlay continues to function as a
mercury barrier, the bottom of the control pond will be covered with the
iron-sand overlay and the rate of decrease of mercury levels in the fish
and plants monitored.
Work Statement
This field demonstration is divided into three phases. The tasks to be
conducted during each phase are described. A schedule showing the duration
of, and the manpower required, to perform each task is shown in Figure 2.
52
-------
SCHEDULE
FIELD TEST IRON-SAND OVERLAY
PHASE / TASKS
Phase 1
• Pond Construction
• Construct Water Treatment
Facility
• Prepare Pond Bottom
• Fill and Stock Pond
Phase II
• Anal/sis of Water,
Plants and Fish
• Feed Fish and Plants
• Iron-Sand Overlay
Control Pond
Phase III
• Cleanup
• Analysis of Results
• Program Management
• Reports
2
4
•••
••
A
6
••
i
8
k
Du
10
A
ratioi
12
4
lof S
14
i
tudy
16
A
(Mon
18
t
ths)
20
i
22
A
24
t
26
.
28
t
Man-A,
Eff
Senior
1.0
1.0
0.5
0.5
3.0
1.0
1.0
6.0
3.0
i
17
Aonths
ort
Technician
1.0
3.0
1.0
1.0
12.0
3.0
2.0
23
Ul
Figure 2
-------
Phase I - Construction and Preparation of Facilities. It is estimated
that 5 months will be required to complete Phase I.
Task 1 - Construction of Ponds. The major items of the construction
will include the earthen dams, the water gates, the channel which feeds the
ponds, a dike to prevent runoff into the ponds, and water treatment facil-
ities. The area will be fenced to prevent accidental contamination. Given
suitable weather the construction of the ponds, dike and feed canal should
be completed in 2 months.
Task 2 - Water Treatment Facility. Water fed to each pond will be
treated as follows:
(1) The water will filter through a 4-ft bed of shredded iron to reduce
the ionic mercury to elemental mercury.
(2) It will then pass through a bed of iron pyrite to convert residual
mercury to the sulfide.
(3) The water will then be passed through a sand filter to remove
particulates.
This water will be analyzed continually to assure that no mercury is being
added to the ponds.
Task 3 - Pond Preparation. Sediment will be dredged from a heavily
sedimented lake adjacent to the pond sites. This sediment will be pumped
directly to the ponds. Approximately 400 yards of sediment will be required
to cover the bottoms of each pond to a depth of 6 in. This sediment will
be spiked with approximately 10 ppm mercuric nitrate and mixed with a roto
tiller.
One pond bottom would be covered with shredded iron and then sand, the
second with only sand and the third will serve as a control.
Task 4 - Fill and Stock Ponds. The ponds would then be filled with
water and stocked with a variety of fish and plants. Care will be taken to
select mercury-free fish and plants.
Phase II - Monitoring of Water. Plants and Fish. This phase of the program
is expected to require 1 to 1.5 years to complete.
54
-------
Task 1 - Analysis of Water. Plants and Fish. Water, plant and fish
samples will be taken for mercury analyses at weekly intervals during the
early stages of these studies. As trends develop, these intervals will be
adjusted to obtain statistically reliable data at the least expense.
Task 2 - Feeding of Fish and Plants. Mercury-free synthetic feed will
be used for feeding fish to assure that external mercury contamination does
not occur. A single large batch of feed will be prepared for this purpose.
Task 3 - Iron-Sand Overlay of Control Pond. If iron-sand overlay
proves to be effective, the control pond will be similarly treated. The
fish and plants in the newly treated pond will be monitored for mercury
content at regular intervals to determine the rate of mercury loss.
Phase III - Cleanup and Analysis of Data. It is estimated that 3 months
will be required for this phase.
Task 1 - Drainage and Disposal of Sediment. At the conclusion of these
studies, the ponds will be drained and the sediments removed. .These sedi-
ments will be disposed of by methods judged suitable at that time.
Task 2 - Analysis of Results. Three months will be required for analysis
of results and preparation of a final report. The report will contain results
and recommendations for further testing or for field use.
55
-------
SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
!. RepfTtKo.
w
CONTROL OF MERCURY POLLUTION IN SEDIMENTS
Ivan C. Smith
MIDWEST RESEARCH INSTITUTE
12. Sponsoring Organization
S. Perforating Organ:?atioa
RtffOTtJfo.
16080 HTY
68-01-0087
13. Type c ' Repot • and
Period Covered
Environmental Protection Agency report
number EPA-R2-72-(A-3, September 1972.
Methods are needed for controlling pollution from mercury-laden sediment deposits
in the bottoms of streams and lakes. This report contains the results of exploratory
studies conducted to develop control methods. Sediment samples containing 6-500 ppm
mercury were collected from the St. Clair River, the Detroit River, the San Francisco
Bay and an industrial holding pond. The geochemical nature of these sediments varied
considerably amongst the samples. Density and particle-size fractionation, flotation,
roasting and leaching were evaluated for recovering the mercury value from the sedi-
ments. Only leaching and roasting appear to have merit. Studies were also conducted
to determine the rate and efficiency of the removing mercury from water by reducing
mercuric and methylmercury ions with iron. Field tests for controlling mercury pollu-
tion by (1) overlaying sediments with iron and sand.and (2) by recovering the mercury
by leaching with a hypochlorite solution were recommended.
17a. Descriptors
Mercury,* Sediments,* Gravity Fractionation, Particle Size Fractionation Flotation,
Leaching, Iron Reduction, Methylmercury, Dimethylmercury, Analytical Methods*
17b- Identifiers
Sediment Treatment, Mercury Recovery, Mercury Pollution
19. Security C*f
(Report)
20.
Security Class.
(Page)
21. Ko. of
Pages
22. Pnc«
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C. 2OZ4O
------- |