United States
                   Environmental Protection
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
                   Research and Development
EPA/600/S2-88/005  Mar. 1988
c/EPA         Project Summary
                   Copper  Dump  Leaching and
                   Management Practices That
                   Minimize the Potential for
                   Environmental Releases
                   Robert L. Hearn and Robert Hoye
                     The full report presents  a
                   description  of the magnitude and
                   distribution  of copper  dump
                   leaching, the design and operation of
                   leaching facilities, the potential for
                   environmental  impact,   and
                   management practices that can be
                   used, to minimize environmental
                   releases. The information contained
                   in the report was obtained through
                   searches  of  published  and
                   unpublished literature and  through
                   contact  with  knowledgeable
                   individuals involved in the dump
                   leaching  industry. Ten leaching
                   operations were visited to acquire
                   firsthand knowledge and  site-
                   specific information.
                     Seepage frqm  leach  dumps and
                   process solution  collection systems
                   is the most significant potential
                   mechanism for the release of
                   contaminants. These solutions have
                   low pH and  high concentrations of
                   metals and  total dissolved solids
                   (TDS). Ground-water impacts have
                   been documented. The application
                   and efficiency of standard waste
                   management practices at dump
                   leach operations are site specific
                   and are limited by the magnitude of
                   these facilities.
                     This Project  Summary  was
                   developed by EPA's Hazardous Waste
                   Engineering Research  Laboratory,
                   Cincinnati, OH,  to announce key
                   findings of the  research project that
is fully documented in a separate
report of the same title (see Project
Report ordering Information at back).

  Dump leaching refers to percolation
leaching of copper from run-of-mine
low-grade ores that have been piled on
native ground. These dumps typically
cover hundreds of acres and contain
millions of tons of low-grade  ore.  The
leaching cycle covers a span of many
years. The percentage of  copper
produced by leaching operations  has
increased and this trend is expected to
continue.  Currently, there are  18
commercially active  copper  leaching
operations in the  United States with a
total production capacity of 280,000
metric tons of copper per year. Fourteen
of these sites are in Arizona. There are
about  23  inactive  and abandoned
leaching sites.
  Sections 8002(f)  and (p) of  the
Resource Conservation and Recovery
Act (RCRA) and its amendments require
the  U.S. Environmental Protection
Agency (EPA) to conduct studies on the
"adverse effects on  human health  and
the environment of the disposal  and
utilization of solid  wastes  from  the
extraction, beneficiation, and processing
of ores and minerals." The EPA
submitted  a report  to Congress on
December 31, 1985, that  indicated
concern with the low pH and  the
potentially high concentration of metals

found in leachates  and leach material
associated with copper dump  leaching.
The  EPA  subsequently  issued  a
regulatory determination on July 3, 1986,
that expressed continued  concern about
mining   wastes  having  high   acid-
generation  potential.  Also in  this
determination, the EPA indicated that it
would develop a regulatory program for
mining wastes under Subtitle D of RCRA
and collect additional information  on the
nature  of  mining  wastes   and
management practices and the potential
for  exposure to  these wastes. The full
report addresses  these  issues  with
regard to the  development, operation,
and  closure activities associated with
copper dump leaching operations.

General Characteristics
  Although the number of active mines
in the United  States  has decreased  in
recent years, the percentage of primary
copper   produced  by  leaching has
increased.  Low copper  prices have
resulted in the closing of many mining,
milling, and  smelting  operations.
Although  many   of the   leaching
operations associated with  these  sites
also  have  been closed,  a significant
number  are  still active because  of the
relatively low operating costs associated
with dump leaching. The result has been
an increase in  the percentage of  copper
produced by leaching operations  in the
United States. Estimates indicate that by
1990 approximately 30  percent  of the
copper  produced in this country  will be
recovered by  some  type  of leaching
  The areas in which copper leaching is
practiced  are similar in  general
characteristics. Most of the  active U.S.
copper  dump  and  heap  leaching  sites
are  in the Southwest. The climate  in
these areas ranges from arid to semi-
arid.  The topography of these  areas
varies  from  gently rolling hills  to
mountainous  terrain.  Vegetation  is
sparse.  The active leaching operations in
Utah and northern  and eastern Arizona
tend to  be located in  more mountainous
terrain than those  in southern Arizona
and western  New  Mexico.  The land
surrounding  many of the  active leaching
operations consists  primarily of sparsely
populated and undisturbed vacant land.
Some of the active leaching operations,
however,  are  relatively  close  to
residential and urban areas.
   Very little surface water is found near
active leaching  sites  in the  Southwest.
The depth to ground water, which is the
principal source of  water most of these
mines,  varies. In the  more mountainous
environments, however, the amounts of
surface-water runoff and ground water
are greater because  of winter snow

Operating Practices
   Copper leach dumps typically cover
hundreds of hectares,  are  more than a
hundred meters  high,  and  contain
millions of metric tons of leach  ore.
Copper leach  piles  as  small as  8
hectares (Cyprus Johnson) and as large
as 850 hectares (Bingham Canyon) were
observed during this study. Estimates
indicate that more than  5.5 billion metric
tons of leach ore  now exist in copper
leach dumps scattered around the United
States and in excess of 40 million metric
tons of  new material is being added to
these dumps annually.
   Dump leaching and heap leaching are
distinguished by the use of liners. Dump
leaching refers  to  the  leaching of  low-
grade  ore  that has  been  deposited
directly  on the ground. The  pregnant
leach solution  is  typically  collected in
unlined natural  drainage basins. In
contrast, heap  leaching  refers to the
leaching of ore  that has been  deposited
on specially  prepared  pads.  Dump
leaching   operations  are  always
constructed in  the  immediate vicinity of
the mine site. Leach sites are selected to
minimize haulage costs and to utilize the
natural  drainage patterns of the native
terrain  for  collection  of the  pregnant
liquor solutions.
   Leaching of copper from  massive
dumps  of sulfide ore  is accomplished
bacterial activity  and,  often,  by the
addition of sulfuric  acid. Ferric sulfate,
the major, lixiviant, forms in the presence
of oxygen  and bacterial  activity.  The
bacteria generate acid in situ, which
provides   acid for acid-consuming
reactions,  including oxygen reduction.
Frequently, only makeup water is needed
in copper dump operations because the
oxidation  of   the sulfide  minerals
generates sufficient acid to dissolve the
copper  and maintain an active bacterial
population. More  effective   leaching
reagents have been identified, but  they
are generally much more expensive and
their impact on the  environment  is
   Copper  is recovered from  pregnant
leach liquors either by cementation or
by solvent extraction/electrowinning.
These processes remove  copper  from
solution and   allow  other dissolved
substances to accumulate. The recovery
process itself may add other substances
to the leach solutions.  The cementation
process uses  scrap  iron to precipital
copper from the pregnant solution.  Th
iron replaces copper in solution, and thi
iron-rich  solution  is subsequent!
recycled to the top of the  leach dum|
Upon exposure to the atmosphere, th
dissolved iron  oxidizes to form insolubl
salts, which precipitate on the surface  c
the dump and restrict the flow of solutiot
Solvent extraction  uses a complexatio
mechanism whereby  copper is chelatec
the copper is then  stripped  from  th
organic carrier by a strong acid solutior
Kerosene is a common carrier used  i
most solvent extraction operations, and
may appear in small  quantities in th
raffinate recirculated the dump.

Environmental  Impact

   Seepage from  leach  dumps  ani
solution collection  systems is  the  moj
significant potential mechanism for thi
release of contamination into the groum
water. One of the primary criteria in sitini
leaching operations is proximity to thi
mine.  In dump leach operations,  thi
ground surface is  neither  lined  no
treated  in  any  manner  to reduci
seepage. Because  the leaching solution:
are in direct contact with the earth, somi
continuous solution loss results. Release;
can  also  result from pipe and  dan
failures equipment  malfunctions,  an<
overflows due to severe storm events.
   The solutions  generated in  coppe
dump  and heap  leaching  operation:
usually have  a lower pH  and highe
concentrations  of metals and  tola
dissolved solids than  the natural water:
surrounding the site. Leach ores contair
pyrites and other naturally occurring
metal sulfides  that oxidize to generate <
low-pH solution when exposed  to aii
and microbial  activity.  The solven
extraction process also reduces the pH o
the solution by ion exchange before it i;
distributed on the leach dump.  Generally
acidic  solutions increase  the  solubility
and bioavailability  of heavy  metal:
contained in the leach material and  rock
surrounding the dump.
   The water quality around severa
active  copper  dump leaching operations
has  been affected by leachates that have
seeped into  the  ground water.  The
available ground-water monitoring data
indicate that some degradation of the
ground water has occurred around
several  copper  dump  leaching
operations. Some  seepage of leachates
into the  ground beneath  copper leach
dumps is  inevitable.  The  amount  ol
seepage and its impact depend on  site-
specific factors.

Management Practices
  Most  active  copper  leaching
operations have implemented a system
of management practices that includes
one  or  more  mitigative  measures
designed to minimize solution losses.
Historically, such management practices
were implemented solely for economic
reasons- (to improve copper recoveries).
As  the  potential for  ground-water
contamination problems associated with
leaching  became  apparent,  these
practices  were implemented  for
environmental reasons  as well.  The
measures  used at  a  particular site
depend on various site-specific factors,
the  most significant  of  which are  the
geology,  hydrogeology, topography, and
meteorology of  the site. The  land use
and  population  density of  the area
surrounding  the  operation  are also
considered, as is the cost of constructing
and/or  installing  each  potential mitigative
  The application and efficiency  of
standard waste management practices at
copper  leaching   operations  are
frequently limited by the size  of  the
dump and environmental characteristics
of the  site. Copper leaching operations
are  massive;  thus,   management
practices required for adequate control of
potential ground-water  contamination
from leaching operations also must be on
a very large  scale.  The  geologic and
hydrogeologic evaluation required  to
design and  implement an effective
surface-water  and  ground-water
control system is complex,  and  the
required  control systems must  cover
several   hundred  hectares. The
environment of the site may necessitate
a system to divert surface water resulting
from the  torrential  rains periodically
experienced in  the region, but  annual
precipitation may  not be adequate  to
sustain revegetation efforts. The  size of
the  leaching  operation  and  its
surrounding environment often combine
to make both lining of new facilities and
capping economically  impractical.
  The  cost of  implementing  and
maintaining  an effective system  of
management practices  to  minimize
solution  loss and  reduce  potential
ground-water contamination depends
on  site-specific  factors. Traditional
management  practices tend  to be very
expensive  to implement at  copper
leaching operations because of the size
of the operations   and the  natural
characteristic  of the  site. Nevertheless,
several of these practices have been
implemented  economically at or  around
one or more leaching operation. Proper
planning  and design procedures  are
required to  select the most appropriate
management practices and  to minimize

  Robert L Hearn and Robert Hoye are with PEI Associates, Inc., Cincinnati, OH
  S. Jackson Hubbard  is the EPA Project Officer (see below).
  The  complete report, entitled "Copper Dump  Leaching and Management
    Practices That Minimize the Potential for Environmental Releases" (Order No.
    PB 88  J55 114IAS;  Cost: $19.95,  subject to change) will  be available only
       National Technical Information Service
       5285 Port Royal Road
       Springfield, VA 22161
       Telephone:   703-487-4650
  The EPA Project Officer can be contacted at:
       Water Engineering Research Laboratory
       U.S. Environmental Protection Agency
       Cincinnati, OH 45268
United States
Environmental Protection
Center for Environmental Research
Cincinnati OH 45268
Official Business
Penalty for Private Use $300


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                                                                            ft- U.S. GOVERNMENT PRINTING OFFICE: 1988648-013/8701