Section 313, Emergency Planning
and community Right-to~Know Act
Estimating Releases for Mineral Acid
Discharges Using pH Measurements
June, 1991
U.S. Environmental Protection Agency
Office of Toxic Substances
Economics and Technology Division
-------
6-12-91 ESTIMATING BEL1ASES FOR MINERAL ACID
DISCHARGES USIHG pB MEASUREMENTS
The mineral acids currently listed on the section 313 toxic chemical
list ar* commonly used throughout the manufacturing sector as product
ingredients, reactantB, and chemical processing aids. Currently, inorganic
bases ar* not listed on the section 313 toxic chemical list and, SB a result*
this directive focuses on mineral acids. The guidance in this directive
applies only to these mineral acids listed below;
Namo
Sulfuric Acid ' 7664~i3~9 HjSO4
Mitric Acid 7697-37-2 HSOj
Hydrochloric Acid 7S47-01-0 HC1
Phosphoric Acid 7664-38-2 HjP04
Hydrofluoric Acid 7664-39-3 HF
These mineral acids may be present In aqueous waste streams that are
sent to GA-mLt* neutralization or arc discharged to a FOTW or other of £ site
treatment facility, Qn-site acid neutralization and it* efficiency must bo
reported in Part III, section 7 of Form R (Waste Treatment and Efficiency
Section) . For purposes of reporting on Form R, EPA considers a waste mineral
acid at * pH 6 or higher to be effectively neutralized* That is, the
treatment efficiency of the neutralization can be considered 100% and water
discharge* to streams or POTWs can be reported as zero. It i« important to
note that this interpretation applies only to mineral acids, not other Section
313 chemicals. If the treatment . ef f icieney is not equal to 1QQ percent (pS is
las* than 6), the amount of the. li-.«te4^J»l«i«>r*l -,*<5iA ifosaaifltLng in the waste
stream which is released to the environment on-site must be reported in Part
III «»etion 5 of Form H. if the waste stream Lm *«nt oxf-site for further
treatment, tti* amount; of mineral acid remaining in the waste stream must be
reported in Fart III section 6-
Mineral
In the case of m. listed mineral acid, the pH -of the waste stream can be
used to calculate th* amount of acid in a waste stream and th» efficiency of
the neutralization. The pH is a coctwonly available measure of the acidity or
alkalinity of a waste stream and can be obtained using & pa jaeter or pH
sensitive paper. The pH scale itself varies from 0 to 14.
The total mineral acid concentration (ionized and unionized) in
pounds /gallon can be derived by using the pH value of the solution, the
molecular weight and ionizatioa constant of the acid, and- appropriate
conversion factor*. The total acid concentration for each mineral acid for
different pH values is listed in Table 1. the derivation of this table is
discussed in a separate addendum to this directive, gajbJjBaA&no Releases for
Mineral Reid D^pcharoes Paino oH Meagurogtentg - Addendum, and is available
from the XfCRA Hotline, USEPX, 401 K Street, S» (OS-120) , Washington DC
20460; telephone (800) 535-O202 or (703} 920-9877.
The approach outlined in this directive can only b* «*«d for o: taineral
acid in a solution. Also, reloaoe estimates for a listed mineral aci s)
based solely on pa calculations provide only a rough estimate. The estimates
can ba mad* for a wasteotreaa with a steady pH below 6 or for one whor- • pK
temporarily drops to below pH 6. Facilities should use their beat eng sering
judgement and knowladge of the solution to evaluate the reasonableness of the
-------
• TABLE 1
MINERAL ACID CONCENTRATION VS pH
Concentration in Ibs/gallo**
pH
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
2.2
2.4
2.6
2.8
3
3.2
3.4
3-6
3.8
4
4.2
4.4
4.6
4.8
S
5.2
5.4
5.6
5.3
€
T
HsSO,
0.8200000
0.5200000
0.3300000
0.21OOOOQ
0.1300000
0.0820000
0.0520000
0.0330000
0.0210000
0.0130000
0.0082000
O.OOS20OO
0-0033QOQ
0.0021000
0.0013000
0.0008200
0.0005200
0.0003300
0-0002100
0.0001300
0.0000820
O.OOOOS20
0.0000330
0.0000210
0.0000130
0.0000082
O.OGQOOS2
0.0000033
0.0000021
0.0000013
0.0000008
HNOj
0.5200000
0.3300000
0.2100000
0.1300000
0.0830000
0.0520000
0.0330000
0.0210000
0.0130000
0.0083000
0.0052000
0.0033000
0.0021000
0.0013000
0.0008300
Q.OOQS2QO
0.0003300
0-0002100
0.0001300
0.0000830
0.0000520
0.0000330
0.0000210
0.0000130
0.0000083
O.OOOOOS2
0.0000033
0.0000021
0.0000013
o.ooooooa
o.oooooos
HC1
0.3000000
0.1900000
0.1200000
0.0760000
0.0480000
0.0300000
0.0190000
0.0120000
0.0076000
0.0048000
0.0030000
0.0019000
0.0012000
O. 0007 600
0.0004800
0.0003000
0.0001900
0.0001200
0.0000760
0.0000410
0.0000300
0.0000190
0.0000120
O.OQGOQ76
0.0000048
0.0000030
0.0000019
0.0000012
0.0000008
0,0000005
0.0000003
H*PQ«
**********
**********
**********
7.0700000
2.8600000
1.1700000
0.4800000
0.2000000
0.0890000
0.0400000
0.0190000
0.0095000
0.0050000
0.0027000
1 0.0016000
O.OQ092QO
O.OOOS600
0.0003400
0.0002100
0.00013OO
0.0000830
0.0000520
0.0000330
0.0000210
0.0000130
0.0000082
0. 00000 S 2
0.0000033
0.0000021
0.0000013
0 . 0000008
HP
**********
**********
**********
**********
**********
4.8000000
1.9100000
0.7600000
0.3OOOOOO
0.1200000
O.O490000
0-0200000
0.0082000
0-QG34000
0.0015000
0. 0006400
0.0002900
0,0001400
0-OO00720
0.0000380
0.0000214
0.0000120
0.0000074
0.0000045
0.0000028
0.0000017
0.0000011
0.0000007
O.OO00004
0.0000003
0-0000002
********* dianotaa ft pH value
lonization.
not panaibla for thia acid because of
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1: In a calendar year, a facility transfers 1.3 million
gallons of a solution containing hydrofluoric acid (HF), at pH 4, ±o
a POT». Uaing Table 1, a pH of 4 corresponds to a, concentration of
0.000021 lisa HF/gallon of Bplution. The weight of HP transferred
can be estimated using the equation:
Transfer of HC1 - (concentration of HF) x (effluent flow rate)
Substituting the values into the above equation yields:
Transfer of HCL = 0.000021 Ibs HP x 1,300,000 gal solution
gal yr
« 27 ibs/yr
Example 2: A facility had an episodic release of hydrochloric acid
(HCl) in which the wasta stream was temporarily below pH 6. During
the episode, the waste water {pB 1.6) was discharged to a riv*r for
10 minutes at n rate of 106 gallons per minute, using Table 1, a pR
of 1.6 for HCl represents a concentration of 0.0076 Ibs BCl/gallon
of solution. The amount of the HCl released can be estimated using
the following equation;
Release of HCl • (concentration of HCl) x (affluent flowrats)
...--Substituting the valusa in the above equations
.Releaso of HCl
0..0076 Ibs it 106 gal x 10 rain
gal sain
8 Ibs/yr
Treataant
ftcid
Mineral acid solutions that are neutralized to a pH of .6 or above have a
treatment .efficiency of 100 percent. If a, mineral acid io neutralized to a pH
is leas than 6, then the reportable treatment efficiency is somewhere between
0 and 100 percent, it is possible to estimate the neutralization treatment
efficiency using the mineral acid concentration values directly from Table 1
in the equation below. The concentrations correspond with the pH values
before and after treatment.
Treatment Efficiency « (I-g> x 100
I
where I « acid concentration before treatment
S - acid concentration after treatment
31 An H,po4 acid wastestreara of pH 2,4 is newtraliaed to pH
4.6. Using Table 1, the initial acid concentration is 0,005
mol/liter and the final concentration ie 0.000021 rool/liter.
Substituting these values -into the equation for treatment
efficiency:
Treatment Efficiency
0.005 - O.OOOO21 x
0.005
95.6 percent
100
-------
can
For .trong acid. only (H^O,, HHO,, and H d ) . tb.
o estimate the efficiency by
Tho following table eun-arlze. traatment
changes. Soo« PH Ihang^ result in tto w t
^^
Treatment Efficiencies for Varioua pH unit Changea
for Sulfurie, Nitric, or H
4$ If a HNO3 wAeteatream of pH 2 in treated to pH 4, the pH
change ifi 2 units, tfsing Table 2 above, the treatment: efficiency
ie given as 99-0 percent.
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Section 313, Emergency Planning
and Community Right-to-Know Act
Estimating Releases for Mineral Acid
Discharges Using pH Measurements - Addendum
June, 1991
U.S. Environmental Protection Agency
Office of Toxic Substances
Economics and Technology Division
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6-12-91
ESTIMATING RELEASES FOR MINERAL ACID
DISCHARGES USING pH MEASUREMENTS
ADDENDUM
•Introduction
This addendum explains the derivation of tables in Estimating Releases
for Mineral Acid Discharges Using pH Measurements. In that document, Table 1
shows the acid concentration in Iba/gallon derived from pH values for the
mineral acids listed below. Also, the derivation of Table 2, which relates
neutraliztion treatment efficiency to the change in pH for neutralization of
strong mineral acids, is given.
Name
• • Sul'furic Acid
• Nitric Acid
« Hydrochloric Acid
« Phosphoric Acid .
» Hydrofluoric Acid
Section 313 Mineral Acids
CAS Number Formula
7664-93-9
7697-37-2
7647-01-0
7664-38-2
7664-39-3
HZS04
HNOj
HC1
H,P04
HF
Molecular
Weic
98.08
63.01
36.46
98.00
20.01
Relationship jgetween pH and hydrogen ion concentration
The pH or hydrogen ion activity is a measure of the acidity or
alkalinity of a solution. The pH'is determined by the hydrogen.ion
concentration [H*]- when an acid or alkaline solution dissociates into ita
charged ionic parts. Acids such as hydrochloric acid disso'ciate as follows:
[HC1J
The equation indicates that an equilibrium exists between the hydrochloric
acid and the hydrogen and chloride ions, although the equilibrium lays far^to
the right. The pH Lm a. logarithmic measure of the hydrogen ion concentration:
pH = -logw[H+]
which can be rearranged for [H"1"] to yield:
where [H+] » concentration of hydrogen ions in moles per liter.
The following table summarizes [H*] values in moles/liter corresponding
to various pH values:
-------
A2
TABLE Air [H+l Values Corresponding to Various pH Values in Moles/Liter
EH
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
EH
3.0
3.1
3.2
3.3
3.4
3.5
3.6
3.7.
3.8
3.9
fH+l
1.0
0.79
0.63
0.50
0.40
0.32
0.25
0.20
0.16
0.12
riri
0.001
0.00079
0.00063
0.00050
0.00040
0.00032
0.00025
0.00020
0.00016
0.00012
EH [H+1
1.0
1.1
1.2
1.3-
1.4
l.S
1.6
1.'7
1.8
I-9
EH
4.0
4.1
4.2 .
4.3
4.4
4.5
4.6
4.7
4.8
4.9
0.1
0.079
0.063
0.050
0.040
0.032
0.025
0.020
0.016
0.012
fH+1
0.0001
0.000079
0.000063
0.000050
0.000040
0.000032
0.000025
0.000020
0.000016
0.000012
pH rn+i
•2.0
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
,2.9
, Ei
5.0
5.1
5.2
5.3
5.4
5.5
' 5.6
5.7
5.8 '
' 5.9
0.01
0.0079
0.0063 '
0.0050
0.0040
0.0032
0.0025
0.0020
0.0016
0.0012
fH+1
0.00001
0.0000079
0.0000063
0.0000050
0.0000040
0.0000032
0.0000025
0.0000020
0.0000016
0.0000012
Strong acid dissociation
Strong acida such as hydrochloric, sulfuric, and nitric acid dissociate
almost completely thus the total molar concentration of the acid is equal^ to
the [H+] concentration. Since every mole of [H+] represents a mole of acid,
one can just multiply the hydrogen ion concentration (moles/liter) by the
molecular weight.of the acid (gram/mole) to get the acid concentration. To
convert the acid concentration from grain/liter to Ibs/gallon,. additional
conversion factors are used. Thus the values of acid concentration (Ibs/gal)
in Table 1 for H2SO4, HNQ3 and HCl were obtained from the following .equation.
Acid concentration Ibs * IP"1*1 mol x
gal L
Iba x 3.78 L
454g gal
where M - molecular weight of the acid.
Using [H*J values directly from Table Al yields equation_A1:
Equation Al: Acid concentration Ibs = H* mol x M o x
Acid concentration Ibs
gal
H* mol x
L
lbg_ x 3.78 I.
454g gal '
Exmapl* Ms A solution contains hydrochloric acid (HCl), a listed
section 313 toxic chemical at pH 3. The concentration of [H+] of
0.001 mole/liter is obtained from Tabla Al. Using Equation Al, the
acid concentration in Ibs/gallon is estimated.
HCl concentration Ibs
gal
0.001 mol x
L
36.46 g X Ibs x 3V78 L
mol
454g
gal
0,003 Ibs HCl/gallon solution
-------
- A3
Weak acid dissociation
Weak acids, »uch as phosphoric and hydrofluoric acid, do not dissociate
completely and an equilibrium . ia reached in which the concentration of the
undissociated acid is much greater than zero. Aa a result, the total acid
molar concentration must be calculated as the sum of the undissociated and the
dissociated acid. Because every mole of hydrogen ion represents one mole of
dissociated acid, the hydrogen ion concentration is used as a measure of the
dissociated acid concentration. By substituting the hydrogen, ion
concentration for the dissociated acid concentration, the total acid molar
concentration is given by Iquation A2:
Equation A2: Total acid molar - Concentration of + Hydrogen ion
concentration undissociated acid concentration
Hydrofluoric acid
For hydrofluoric acid, the dissociation is expressed as:
.HP < ------ > H* + r
The total acid molar concentration for hydrofluoric acid is given by Equation
A3:
Equation A3: Total hydrofluoric acid = [HF] •*• [H+]
molar concentration
In order to determine the concentration of undissociated acid,' [HF], the
equilibrium constant, which represents the degree of dissociation of the acid,
must be used. The equilibrium constant, X,, for HF is given by Equation A4:
Eqmution A4: K, - f_H*1
[HF]
Since' every mole of dissociated' hydrogen ion produces one mole of
fluoride ion, then [H+] = [F]. The K, for hydrofluoric acid is 3.5 x ICT*
(CRC). Substituting these values into Equation A4 yields:
3.5 x 10"1 - [H*12
[HF]
Solving for [HFJ, the aquation becomes: • - .
[HF] « fH+12 _
3.5 X 10" • "
Thi« valu* for {HP] can be substituted into Iquation A3 and, -therefore,
the total acid molar concentration for hydrofluoric acid is given by Equation
A5:
Equation AS: Total hydrofluoric acid mol - fH*12 + JH*]
molar concentration L 3.5x10
-The [H*] concentration for a given pH can be found using Table A, the
total acid' molar concentration -calculated and then converted into Ibs/gallon
using the similar approach as for the strong acids by equation A6:
Equation A6:
Total Acid Concentration Lbs - Acid Cone, mol x M
-------
A4
where M - add molecular weight
See the summary equations on page A7,
Exaaftl* A2: A' solution of 'hydrofluoric acid has a pH of 5.
Using'Table Al, the value of [H+J. IB 0.00001 moles/liter. For HF,
use equation A5 to" "calculate the total acid molar concentraton
(moles/1iter}.
Total hydrofluoric acid
molar concentration
.3.5 x 10-4
= (0.00001.1*
0.00035
[H+]
0.00001
= 0.00001 moles HF/liter solution
Now use equation AS to convert the concentration into Lbs/gallon.
The" molecular weight of HP ' ia 20.01.'-.
Total HF Acid Cone.Iba
gal
Acid Cone, mol x M_g_ x Ibs- x 3.78 L
L mol 454g gal
= O.QQ001 mol x 20.01 a x j.bs : x 3.78 L
L mol 4S4g gal
« 1.7x10^ or 0.0000017 j.ba HF
gal solution
Because hydrofluoric acid is a weak acid and does not dissociate
completely, there exists & lower pH limit, denoted by ***** in Table 1. This
limit can be estimated by using a theorectical maximum acid concentration,
equation AS and pH, » -logffl[H*]. For HF, the maximum possible concentration
"approaches 100% since the acid is infinitely soluble in water. At 100%
concentration, the density of HF is.0.9576 g/ml at 25°C (Kirk-Othmer).
Therefore the concentration of HF in mol/L can be calculated as follows:
Q._9_576_q: x 1000 ml x mole HF - 47.86 mol - Total HF concentration
ml L 20.01 g L
Iqaution AS- can be rearranged to give equation A6:
Equation AS: Total hydrofluoric acid mol
molar concentration I*
3.5 x 10"
Equation *6 i [H+]2 + (S-SxlO^HH*] - (3.5x10'') (Total HF cone.) » 0
Substituting Total HF concentration - 47.86 mol/L gives:
[H*]2 + (S^xlO^JtH"1"] - (1.68xlO"2) * 0
where [H+] is equal to 0.13 moles/L. Therefore!
pH * -Iog10 {H*3 - -logM (0.13) - 0.88
Therefore, a pH of '0.88 is the theorectical lowest pH that can be measured for
a HF solution.
-------
AS
Phosphoric icid
Three dissociations exist for phosphoric acid:
{!) HjP04 < > H+ + HjPCV.
(2) H3P04- < > H* + HPO/
(3) -HPO^ < > H* + PO43-
'second and third dissociations are very small and are considered to be
negligible compared to the first dissociation of phosphoric acid. Because
their contribution to the hydrogen ion concentration ia expected to be too
small to affect the results, only the first dissociation of phosphoric' acid
will be considered when calculating the total acid molar concentration.
Thus for phosphoric acid, the total acid molar concentration is given by
Equation AS. -
Equation A8: Total phosphoric acid - [H3PO4] + [H*]
molar concentration
For the first dissociation of phosphoric 'acid, the equilibrium constant,
K,, is given by Equation Ai. ,
Equation A9: K. » |H*J f H,PO4'1
(H,P04]
where K, - 7.5 x 10'* (CRC) and
[H2P04-] « [H*J
Substituting these values into Equation A9 yields:
7.5 x 1CT3 = [BfLlJ
[H,F04]
Solving for [H3PO4], Equation A9 becomes?
(H3P04] - [H4-]2
7.5 X 10"3
This value for [HjPO4J can be substituted into Equation AS and,
therefore, the total phosphoric acid molar concentration is given by Equation
AID.
Equation JU.O; Total phosphoric acid moj. - fH*12 + [H+]
molar concentration L 7.5 x 10"3
Similarly, as was done for hydrofluoric acid, the values of [H+] can be
obtained froo fable Al and then the resulting phosphoric acid molar_
concentration can be converted to pounds per gallon by using Equation A6.
See the summary equations on page A7.
Because phosphoric acid is a weak acid and does not dissociate
completely, there exist a low pH limit. Assuming a maximum concentration of
85.5% HjPO4 in water with a solution density of 1.70 g/ol (Lange's), the molar
concentration of H}PO4 would be:
1.70 g x 1000 ml x 0.855 a H,PO.. x mole H,PO, - = |4.8 mol
ml L g solution 98 g L
Using this concentration, equation A10, and pH - -log [H*3, and similar
calculations as was done for hydrofluoric acid, the lower limit pH ia
calculated as 0.48, with [H*] = 0.33 mol/L.
-------
A6
•3. Keutraliiatlon Treatment Efficiencies for Acid Solutions
For neutralization of acid solutions, the treatment efficiencies can be
expressed as the mass percentage of the listed acid that has been neutralized.
The calculation follows Equation All.
Equation All: Treatment Efficiency = (I-EJ x 100
I •
where Z = acid concentration before treatment
£ = acid concentration after treatment
For strong mineral acids such as .sulfuric, nitric and hydrochloric acid,
the acid concentration is directly proportional to the [H*] concentration
which is directly related to pH. This can be illustrated by using the [H*]
values directly from Table Al for the pre- and post-treatment pH values.
Example A3: A sulfuric acid wastestream of pH 2 ia treated with a
mild base to raise the effluent to pH 3. Therefore', the pHtafeB = 2,
and the pH^ = 3. Using Table 1, the following [H*] values are
obtained;
[H*]w» = 0.01 mol
L
[H*].** « 0.001 mol
L
Substituting these values into _Equat ion All, the treatment
efficiency ia given by:
Treatment Efficiency-= 0.01 - 0.001 x 100
0.01
= 90.0 percent
Example A4; An HC1 acid waste stream of pH 2 is neutralized to pH
4. Therefore, the pH^,,. - 2, and the pH^, » 4. Using Table 1, the
following [H*] value* are obtained:
0.01 mol
L
* O'.OOOl mol
L
Substituting these values into Equation All, the treatment
efficiency is given by:
Treatment Efficiency - 0.01 - 0.0001 x 100
0.01
« '99.0 percent
-------
A7
As illustrated in the 'above examples/ a small change in the pH of a
solution results in a large treatment efficiency due to the logarithmic nature
of the pH »c*l». Specifically, a pH change of one unit results in a treatment
efficiency of 90 percent, whether the pH change ia from pH 1 to pH 2 or from
pH 4 to pH 5. Table 2 in- the previous document was developed by calculating
various treatment efficiencies for different pH changes using (H*] values from
Table Al. Table 2 was developed for strong mineral acids. ' ,
For weak mineral acids such as phosphoric acid and' hydrofluoric acid,
the efficiency values.in Table 2 are closely approximate, but not exact, since
the acid concentration is not linearly proportional to (H4"] or pH. For
example, in Example 3 in the previous document, a phosphoric acid stream whose
pH changed from 2.4 to 4.6 had a treatment efficiency of 99.85%. If Table 2
is used (for-a pH change of-2.2), the treatment efficiency is estimated at
99.4%.
Summary of Equations -Used to Develop Table 1
Note: 1Q-*41 - [H+]
Sulfurie Acid H2SO4
Ibs - IP** x 98.08 x 3,78
gal 454
or
Ibs - fH*1 x 98.08 x .3.78 '
gal 454 .
Nitric Acid HNOj
Ibs = W**1 x 63.01 x 3.78
gal 454
or
Ibs - [H*.] x 63.01 x 3.78
gal 454
Hydrochloric Add HCl
•' Ibs - IP-**1 x 36.46 x 3.78
gal 454
or
Iba - [H*1 x 36.46 x 3.78
gal 454
Phosphoric Acid H3PO4
1M- '{ flO*"!* + 10"1*1 } x 98.0 x 3.78
gal 0.0075 4i4
, or
- • Ibs- { fH*l2 + [H*]' } x 98.0 x 3.78
gal 0.0075 454
-------
AS
*
Hydrofluoric Acid HF
lbs= { flO^2 + 10-*" } x 20.01 x 3.78
gal 0.00035 454
or
lb_s= { [H+l* + [H+] } x 20.01 x 3_.:78
gal 0.00035 454
REFERENCES:
CRC Handbook of Chemistry and Physics. 1988-89. 69th edition. CRC Press, inc.
Boca Raton, FL. Pgs. B-94, B-113, D-163.
Kirk-Othiner Encyclopedia of Chemical Technology. Third Edition. Volume 10.
Fluorine Compounds, Inorganic. 1980. John Wiley & Sons, New York, NY. Pg.
734.
Lange'a Handbook of chemistry. Thirteenth Edition. 1985. McGraw-Hill Book Co.,
New York, NY. Pg. 11-27
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