New Method for Electrical Conductivity Temperature Compensation

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A New Method for Electrical Conductivity Temperature Compensation Richard Blaine McCleskey Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/es402188r • Publication Date (Web): 29 Jul 2013 Downloaded from http://pubs.acs.org on August 5, 2013

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Environmental Science & Technology

ACS Paragon Plus Environment


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A New Method for Electrical Conductivity

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Temperature Compensation

3

R. Blaine McCleskey

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US Geological Survey, 3215 Marine St., Suite E. 127, Boulder, CO 80303, USA

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KEYWORDS: Electrical conductivity, temperature compensation, specific conductance

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8

ABSTRACT

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Electrical conductivity (κ) measurements of natural waters are typically referenced to 25 °C (κ25)

10

using standard temperature compensation factors (α). For acidic waters (pH 12. However, researchers studying basic waters should carefully check

23

electrical conductivity measurements by measuring κ at 25 °C. 4



1

The existing temperature compensation factors for natural waters do not account for the

2

unique mobility of H+. Consequently, the κ25 reported for natural waters with a pH < 4 often

3

have large errors. Furthermore, the uncertainty increases as the temperature departs from 25 °C.

4

Low-pH waters generated from acid rock and geothermal sources are particularly susceptible to

5

having erroneous κ25 reported. The low-pH waters from acid rock and geothermal sources are

6

primarily derived from the oxidation of pyrite and sulfur, respectively, which generates sulfuric

7

acid.

8 9

The κ25 is a frequently measured water-quality parameter, but the δκ25 for acidic waters can be excessively large using existing α. Because many waters of environmental concern are

10

acidic (i.e. acid mine and geothermal waters), a method that can be used to accurately predict κ25

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at pH values as low as 0.5 and temperatures of 0 to 100 °C is essential. In this paper a new

12

electrical conductivity temperature compensation factor is proposed that is applicable for acidic

13

waters and also works well for most natural water up to pH 11. The new temperature

14

compensation factor can be utilized by multimeters that measure pH, temperature, and κ or it can

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be calculated after these measurements are made and used to calculate κ25.

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EXPERIMENTAL DETAILS

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Field and laboratory measurements. The κ of laboratory solutions and natural waters

18

was determined by using commercially available conductivity meters and probes, and the

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following equation: κ Κ G 4

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where Κcell is the conductivity cell constant (in cm-1) and G is the conductance (in S). The Κcell is

21

the ratio of the distance between two plates (d) and their area (A). Laboratory κ measurements

22

were made with a bench-top conductivity meter (YSI, Inc., model 3200) equipped with a dip-

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style conductivity cell having a cell constant of 1.0 cm-1 (YSI, Inc., model 3253). Field κ

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measurements were made using a handheld conductivity meter (WTW 3300i) with a probe

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having a cell constant of 0.475 cm-1 and a temperature sensor. The Κcell for each conductivity cell

4

was determined using equation 4 and KCl solutions of known conductivity.30 For laboratory

5

temperature measurements, a digital thermometer (VWR International, LLC) with a resolution of

6

0.001 °C and an uncertainty of ± 0.01 °C between 0 and 100 °C was used for all temperature

7

measurements. The thermometer conforms to the International Temperature Standard (ITS-90)

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and was calibrated by the manufacturer to standards provided by NIST. A refrigerating/heating

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water bath circulator (Thermo Scientific NESLAB, model RTE-7) was used to control the

10

temperature of all solutions measured in the laboratory. The temperature stability of the water

11

bath, reported by the manufacturer, was ± 0.01 °C. The electrolyte solution was allowed to

12

thermally equilibrate with the water bath before its conductance was measured.

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Measurement solutions were placed in 50 mL high-density polyethylene (HDPE) vessels

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containing the conductivity and temperature probe. The measurement vessels and the

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conductivity probes were cleaned by soaking in HCl (0.6 M) for at least 24 h and rinsing three

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times with deionized water (18 MΩ·cm). The lid containing the probes was tightly sealed to

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minimize evaporation.

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Forty solutions were prepared in the laboratory containing various concentrations and

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mixtures of H2SO4 (0, 0.0001, 0.0005, 0.001, 0.005, 0.01, 0.05, 0.1 and 0.2 M) and NaCl (0,

20

0.001, 0.01, 0.1, and 0.5 M). These solutions were used to develop temperature compensation

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factors by measuring κ from 5 to 90 °C. The H2SO4 concentration was determined by Gran

22

titration using standardized NaOH,31 and the NaCl was gravimetrically prepared (Sartorius

23

R160P analytical and GP5202 5 kg top-loading balances). The water used in all preparations was

6



1

passed through a deionizing system (18 MΩ·cm). The deionized water used in all preparations

2

was allowed to equilibrate with atmospheric CO2 for several days before use.

3

In addition to the laboratory solutions, the new temperature compensation method was

4

applied to 65 natural water samples (Table 1). Twenty-one of the samples were acid rock/mine

5

waters (AMW). These samples were collected from Questa, NM, Summitville, CO, Iron

6

Mountain, CA, and Handcart Gulch, CO. For the AMW samples, the pH ranged from 0.88 to 3.8,

7

the κ25 from 460 to 76,200 µS/cm, and the Fe concentration from 0.05 to 17,000 mg/L. Because a

8

visible Fe precipitate formed in several of the samples above about 50 °C, laboratory

9

measurements were limited to 5, 10, 25, 35, and 45 °C. Furthermore, 47.1 °C was the highest

10

underground temperature found at Iron Mountain, which has the lowest known pH (-3.6) of any

11

water in the environment.32 Twenty-four samples were collected from acidic geothermal sources

12

in Yellowstone National Park. The pH of this group ranged from 1.3 to 4.8 and the κ25 from

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1,100 to 23,000 µS/cm. The remaining twenty samples were circumneutral pH. They were

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collected from rivers and springs in Yellowstone, WY, several rivers in CO, and sea water from

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San Diego, CA. The pH of this group ranged from 6.8 to 8.7 and the κ25 from 69 to 50,800

16

µS/cm.

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Measurements of pH, both in the field and laboratory, were made with an Orion 3 Star

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pH meter with an Orion Ross combination electrode and temperature probe. The temperature

19

probe, pH electrode, and calibration buffers were equilibrated to sample temperature prior to

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calibration and measurement. The system was calibrated using at least two bracketing standard

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buffers (chosen from among 1.68, 4.01, 7.00, or 10.00) corrected to their values at the sample

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temperature. After calibration, the pH electrode was placed in the sample water and monitored

23

until no change in temperature (± 0.1 °C) or pH (± 0.01 standard unit) was detected for at least

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30 seconds. For laboratory solutions with pH < 1.7, the pH was calculated by charge balance

2

using the geochemical computer program PHREEQCI.33, 34

3

Temperature Compensation Factor. Since κ is the sum of the products of the ion

4

concentrations and ionic conductivities (equation 1), the solutions' α should be equal to a

5

weighted average of each ion's α. Except for H+, most ions have similar α because their mobility

6

is dependent on the solution's viscosity. Because the H+ ion migrates via a proton jump from one

7

water molecule to the next as H3O+ and its α is not as dependent on the viscosity,19 the following

8

α was developed in this study to be used in combination with equation 2 to calculate κ25:

9 α T$ α$ T∗ α∗ 5

10

where TH is the H+ transport number, αH is the H+ temperature compensation factor, T∗ is the sum

11

of all transport numbers excluding H+ (i.e. T∗ 1 T$ ), and α∗ is a temperature compensation

12

factor representative of all ions except H+. The transport number (T) is the relative contribution

13

of a given ion to the overall electrical conductivity and is defined as the fraction of the current

14

carried by a given ionic species.19 Therefore, the transport numbers of all ions in solution sum to

15

unity. The transport number of individual ions (Ti) can be determined in natural waters using:

16 T

17 18 19

λ C & ∑'( λ C

κ 6

κ

where κi is the conductivity of the ith ion. To determine α (equation 5) first measure the solution's κ, temperature (t), and pH. Then determine κH: -. / 0 (.( 1$2 03.(,(-4 /5 2 6.6 ,(-7 / 2 .88

κ$ 10(. (,(

8

7



1

where t is temperature in °C. Once κH is determined, calculate TH (as Ti) using equation 6 and the

2

measured κ. The H+ temperature compensation factor (αH) can be determined using the following

3

equations:

4

For pH > 2.1: α$ 5.70 , 100 pH 2.63 , 1008 t 8.73 , 1008 pH 1.14 , 100 8

5

For pH < 2.1: α$ 5.53 , 100 pH 3.27 , 100 t 3.40 , 1003 pH 7.04 , 1003 pH 1.36 , 100 9

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Finally, determine α∗ : α∗ 5.37 , 100 t 1.85 , 100 10

7

and then determine κ25 from equation 2.

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It is important to note, that for pH>5, α∗ ≈ α because TH ≈ 0. A spreadsheet with example

9

calculations of κH, TH, T*, α$ , α∗, α, and κ25 are provided in the Supporting Information.

10 11

RESULTS AND DISCUSSION Method Development and Temperature Compensation of Laboratory Solutions. The

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forty laboratory solutions containing various concentrations and mixtures of H2SO4 and NaCl

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along with the λH presented by McCleskey et al.15 were used to develop equations 7 to 9. Using

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conductivity data reported by McCleskey26, α∗ (Figure 2) was determined at 5, 10, 25, 35, 45,

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70, and 90 °C for many important electrolytes found in natural waters (KCl, NaCl, NH4Cl,

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CaCl2, MgCl2, Na2SO4, K2SO4, KHCO3, K2CO3, NaHCO3, KF, KNO3). The median α∗ at each

17

temperature was used to determine equation 10. Besides viscosity, the degree of hydration and

18

equilibrium constants are affected by temperature, which accounts for some of the variation in

19

α∗ . The α is also shown for H2SO4 solutions (0.0001 to 0.5 M),26 which are lower than α∗ for all

20

temperatures (Figure 2). 9


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The TH for 1593 natural water samples including acid mine waters, geothermal waters,

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seawater, dilute mountain waters, and river water affected by municipal wastewater reported by

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McCleskey et al.15 are shown in Figure 3. For samples with pH 0.1) for many natural water samples. The largest TH for this sample set was 0.81 for a sample

5

with a pH 1.8. The TH for the 40 laboratory solutions and the 65 natural waters used in this study

6

are also shown in Figure 3. The H+ has a large effect on κ for acidic waters and its unique

7

temperature compensation needs to be accounted for. However, for waters with pH > 5 the TH ≈

8

0 and α can be determined using only equation 10.

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Figure 4 shows plots of ∆α (∆α = α – αm) determined using the ISO-788821 method, a

10

constant α (0.019), and the new α method (equations 5) for the 40 laboratory solutions studied.

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The measured temperature compensation factor (αm) was determined at each temperature (5, 10,

12

25, 35, 45, 70, and 90 °C) using the following equation by rearranging equation 2:

13 α>

14 15

κ κ > 11

κ > t 25 °C

where κ25m is the electrical conductivity of the solution measured at 25 °C. The new method better predicts the α than either of the commonly used approaches.

16

Thus, the κ25 determined using the new method is a substantial improvement over the κ25 found

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with commonly used α. The error (δκ25) between the calculated (κ25) and measured (κ25m)

18

electrical conductivity was determined using the following equation:

19 δκ %

κ κ > , 100 12

κ >

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The difference between κ25 and κ25m may not always be zero because temperature adjustment to

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25°C may cause precipitation of some electrolytes, equilibrium shifts which may change the

10



1

distribution of dissolved species, and changes in the degree of hydration of some electrolytes.

2

However, δκ25 provides a reasonable estimate of the error resulting from temperature

3

compensation. The δκ25 for the 40 laboratory solutions using the new method ranged from -8.8 to

4

4% (Figure 4), which is a much narrower range compared to the constant α and ISO-788821

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approaches. The δκ25 for the ISO-788821 method ranged from -52 to 27% and δκ25 for the

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constant α (0.019) ranged from -41 to 25%. For the two commonly used α approaches, the

7

largest errors were for the samples with the largest TH. Furthermore, the δκ25 is greater than

8

±10% for t < 15 °C and t > 35 °C.

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To correct κ25 measurements that were made with a conductivity meter that incorporates

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the commonly used α, the κ must be determined using equation 2. The α utilized is likely in the

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instrument manual or can be determined using equation 11 and standard conductivity solutions.30

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To determine α using equation 11, κ25m is the electrical conductivity of the standard solution at

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25 °C. For non-constant α, κ must be determined at several temperatures and the α–t correlation

14

determined.

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Temperature Compensation of Natural Waters. The goal of this study was to develop

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an electrical conductivity temperature compensation technique that would accurately predict κ25

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of a wide range of natural waters, including low-pH waters. To confirm that the new α method

18

accurately predicts κ25, 65 natural water samples including acid mine waters (21 samples),

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geothermal waters (24 samples), and circumneutral pH waters (20 samples) were tested. The

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range of electrical conductivity, pH, temperature, and the maximum solute concentration for the

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major ions for the natural waters tested are shown in Table 1. The samples have a wide range of

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pH (0.88 to 8.71) and solute concentrations. Figure 5 is a ternary plot showing equivalent

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fractions of Cl, HCO3, and SO4 for the waters tested. The major ion composition encompasses

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several water types, thus providing a good test of the new α.

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The accuracy of calculated κ25 for the natural waters determined using the new α method

4

was compared to the ISO-788821 and constant α (0.019) methods. For the 21 acid mine waters

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tested (Figure 6A–6C), the δκ25 for the new method ranged from -8.4 to 3.5% (Figure 6C), which

6

is a substantial improvement compared to the ISO-788821 and constant α (0.019) methods. The

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δκ25 for the ISO-788821 method ranged from -21 to 27% (Figure 6A) and δκ25 for the constant α

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ranged from -17 to 25% (Figure 6B). Note that the temperature of AMW could be close to 0 °C

9

during the winter, increasing the δκ25 for the ISO-7888 21 and constant α methods. For the 24

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geothermal waters tested (Figures 6D–6F), the δκ25 for the new method ranged from -11 to 5.2%

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(Figure 6F), a substantial improvement over the common ISO-7888 21 and constant α methods.

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The δκ25 for the ISO-788821 method ranged from -53 to 27% (Figure 6D) and δκ25 for the

13

constant α ranged from -42 to 25% (Figure 6E). For the circumneutral pH waters (Figures 6G–

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6I), the new method performed as well or better than the other two methods. The δκ25 for the

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new method ranged from -9.5 to 9% (Figure 6I) whereas the ISO-788821 method ranged from -16

16

to 4% (Figure 6G) and δκ25 for the constant α ranged from -9 to 23% (Figure 6H). Figure 7

17

contains box plots of the δκ25 for the 65 natural waters tested using the α methods compared

18

here. For the 413 measurements, the δκ25 (mean ± 1s) for the new method was -0.8 ± 2.7%

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whereas the ISO-788821 was -3.5 ± 13.3% and δκ25 for the constant α was 0.1 ± 11.2%.

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Accurately predicting the κ25 for all natural waters is challenging because α is not the

21

same for all waters since temperature adjustment to 25 °C may cause precipitation of some

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electrolytes, equilibrium shifts changing the distribution of dissolved species, and changes in the

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degree of hydration of some electrolytes. Consequently, a generalized approach for calculating

12



1

κ25 may not work perfectly for all natural waters. Nonetheless, the new method accounts for the

2

unique mobility of the H+, which has a large effect on α, and as a result is a more reliable method

3

for determining κ25 for natural waters than the commonly used α methods.

4

SUPPORTING INFORMATION AVAILABLE

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An Excel spreadsheet with example calculations is provided. This information is

6

available free of charge via the Internet at http://pubs.acs.org.

7

ACKNOWLEDGEMENTS

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I would like to thank Bill Evans, Kirk Nordstrom, Deb Repert, Mark Dornblaser, Kate

9

Campbell, and Randall Chiu for their constructive comments and reviews. This study would not

10

have been possible without the support of the National Research Program of the USGS. The use

11

of trade, product, industry, or firm names is for descriptive purposes only and does not imply

12

endorsement by the U.S. Government.

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REFERENCES

14

1.

15

1980, 5 (1), 3-8.

16

2.

17

Prof. Pap. 700-D 1970, D272-D280.

18

3.

19

determination. J. Mar. Res. 1954, 13 (2), 228-231.

Lewis, E. L. The practical salinity scale 1978 and its antecedents. IEEE J. Oceanic Eng.

Lind, C. J. Specific conductance as a means of estimating ionic strength. U.S. Geol. Surv.

Pollak, M. J. The use of electrical conductivity measurements for chlorinity

13


Page 14 of 27

Page 15 of 27


1

4.

McNeil, V. H.; Cox, M. E. Relationship between conductivity and analysed composition

2

in a large set of natural surface-water samples, Queensland, Australia. Environ. Geol. 2000, 39

3

(12), 1325-1333.

4

5.

5

conductivity. Ind. Eng. Chem. Anal. Ed. 1939, 11, 355.

6

6.

7

dissolved solids and specific conductance, Susquehanna River and New York. U.S. Geol. Surv. J.

8

Res. 1978, 6, 541-545.

9

7.

Gustafson, H.; Behrman, S. Determination of total dissolved solids in water by electrical

Lystrom, D. G.; Rinella, R. A.; Knox, W. D. Definition of regional relationships between

NWIS National Water Information System: USGS Water-Quality Data for the Nation.

10

http://waterdata.usgs.gov/wy/nwis/.

11

8.

12

sludge plant by conductivity and pH measurement. J. Text. Inst. 2000, 91 (4), 523-529.

13

9.

14

wastewater for fast determination of metal ion concentration. Russ. J. Appl. Chem. 2001, 74 (8),

15

1321-1324.

16

10.

17

effects of mountaintop coal mining: comparing biological conditions using family-and genus-

18

level macroinvertebrate bioassessment tools. J. N. Am. Benthol. Soc. 2008, 27 (3), 717-737.

19

11.

20

valley fills on aquatic ecosystems of the Central Appalachian Coalfields; EPA/600/R-10/023F;

21

Office of Research and Development, National Center for Environmental Assessment,

22

Washington, DC, 2011.

Binkley, J.; Simpson, J. A.; McMahon, P. Characterisation of textile aerobic-activated

Prieto, F.; Barrado, E.; Vega, M.; Deban, L. Measurement of electrical conductivity of

Pond, G. J.; Passmore, M. E.; Borsuk, F. A.; Reynolds, L.; Rose, C. J. Downstream

U.S. EPA (Environmental Protection Agency). The effects of mountaintop mines and

14



1

12.

U.S. EPA (Environmental Protection Agency). A field-based aquatic life benchmark for

2

conductivity in central Appalachian streams; EPA/600/R-10/023F; Office of Research and

3

Development, National Center for Environmental Assessment, Washington, DC, 2011.

4

13.

5

Heasler, H.; Huebner, M. A. Solute and geothermal flux monitoring using electrical conductivity

6

in the Madison, Firehole, and Gibbon Rivers, Yellowstone National Park. Appl. Geochem. 2012,

7

27 (12), 2370-2381.

8

14.

9

Orlando, 1982; Vol. I. Inorganic Species, Part 1, pp 137-161.

McCleskey, R. B.; Clor, L. E.; Lowenstern, J. B.; Evans, W. C.; Nordstrom, D. K.;

Hem, J. D. Conductance: A collective measure of dissolved ions. Academic Press, Inc.:

10

15.

McCleskey, R. B.; Nordstrom, D. K.; Ryan, J. N.; Ball, J. W. A new method of

11

calculating electrical conductivity with applications to natural waters. Geochim. Cosmochim.

12

Acta. 2012, 77, 369-382.

13

16.

14

Methods. 2008, 6, 489–501.

15

17.

16

calculation methods for natural waters. Limnol. Oceanogr.: Methods. 2012, 10, 952-967.

17

18.

18

Reinhold Publishing Corporation: New York, 1958.

19

19.

20

Limited: London, 1965.

21

20.

22

field manual for the collection of water-quality data: U.S. Geol. Surv. Tech. Water-Res. Invest.,

23

book 9, chaps. A1-A9, available online at http://pubs.water.usgs.gov/twri9A, 2005.

Pawlowicz, R. Calculating the conductivity of natural waters. Limnol. Oceanogr.:

McCleskey, R. B.; Nordstrom, D. K.; Ryan, J. N. Comparison of electrical conductivity

Harned, H. S.; Owen, B. B. The Physical Chemistry of Electrolyte Solutions. 3rd ed.;

Robinson, R. A.; Stokes, R. H. Electrolyte Solutions. 2nd ed.; Butterworths Publications

Radtke, D. B.; Davis, J. V.; Wilde, F. D. 6.3 Specific electrical conductance. In National

15


Page 16 of 27

Page 17 of 27


1

21.

ISO-7888 Water quality - determination of electrical conductivity; International

2

Organization for Standardization: 1985.

3

22.

4

for natural waters. Anal. Chem. 1987, 59 (13), 1594-1597.

5

23.

6

dependence of electrical conductance for river waters. Water Res. 1990, 24 (10), 1295-1304.

7

24.

8

1962, 7 (3), 330-334.

9

25.

Sorensen, J. A.; Glass, G. E. Ion and temperature dependence of electrical conductance

Talbot, J. D. R.; House, W. A.; Pethybridge, A. D. Prediction of the temperature

Smith, S. H. Temperature correction in conductivity measurements. Limnol. Oceanogr.

Endoh, S.; Tsujii, I.; Kawashima, M.; Okumura, Y. A new method for temperature

10

compensation of electrical conductivity using temperature-fold dependency of fresh water.

11

Limnol. 2008, 9, 159-161.

12

26.

13

to 90) °C. J. Chem. Eng. Data. 2011, 56 (2), 317-327.

14

27.

15

London, 1956; p 884-1043.

16

28.

17

tension. In Chemistry, The Central Science, Sixth edition ed.; Prentice Hall: Englewood Cliffs,

18

NJ, 1994; pp 382-383.

19

29.

20

conductivity and the fluidity of sodium chloride solutions. Philos. Mag. 1902, 6 (3), 487-498.

21

30.

22

standards of electrolytic conductivity. Pure Appl. Chem. 2001, 73 (11), 1783-1793.

McCleskey, R. B. Electrical conductivity of electrolytes found in natural waters from (5

Glasstone, S. Textbook of Physical Chemistry. 2nd ed.; Macmillan and Co. Limited:

Brown, T. L.; Lemay, H. E.; Bursten, B. E. Properties of liquids: viscosity and surface

Lyle, T. R.; Hosking, R. The temperature variations of the specific molecular

Pratt, K. W.; Koch, W. F.; Wu, Y. C.; Berezansky, P. A. Molality-based primary

16



1

31.

Barringer, J. L.; Johnsson, P. A. Theoretical considerations and a simple method for

2

measuring alkalinity and acidity in low-pH waters by Gran titration; Water-Resources

3

Investigations Report 89-4029; U.S. Geological Survey: 1996.

4

32.

5

extremely acidic mine waters from Iron Mountain, California. Environ. Sci. Technol. 1999, 34

6

(2), 254-258.

7

33.

8

geochemical model PHREEQC; U. S. Geol. Surv. Fact Sheet FS-031-02; 2002.

9

34.

Nordstrom, D. K.; Alpers, C. N.; Ptacek, C. J.; Blowes, D. W. Negative pH and

Charlton, S. R.; Parkhurst, D. L. PHREEQCI--A graphical user interface to the

Parkhurst, D. L.; Appelo, C. A. J. User's guide to PHREEQC (Version 2) - A computer

10

program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical

11

calculations; U. S. Geol. Surv. Water-Resour. Invest. Rep. 99-4259; 1999.

12

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TABLES

2

Table 1. Ranges of pH and electrical conductivity (κ) and the maximum solute concentration in

3

the 65 natural waters studied

pH

Field -measured properties 0.88 - 8.71

69 - 76200 κ25 (µS/cm) Maximum solute concentration (mg/L) Ca 480 Mg 1200 Na 10000 K 410 HCO3

4

340

SO4 Cl

55000 18000

SiO2

670

NH4 Al Cu Fe(T) Fe(II) Mn

27 780 200 17000 17000 45

5

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1

LIST OF FIGURES

2

Figure 1. The κ25 calculated using a constant (0.019) and ISO 788821 α for a 0.00944 m H2SO4

3

solution reported by McCleskey.26 The dashed line is the κ of the solution measured at 25 °C.

4

Figure 2. Temperature compensation factors for environmentally important electrolytes (α∗ ) and

5

H2SO4 (α$5 AB. ). The dashed line corresponds to equation 10.

6

Figure 3. The H+ transport number (TH) for 1593 natural water samples reported by McCleskey

7

et al.15 (solid circles), 40 laboratory solutions containing various concentrations and mixtures of

8

H2SO4 and NaCl (open circles), and 65 natural waters samples studied in this investigation (open

9

triangles).

10

Figure 4. The ∆α and the resulting δκ25 are shown for the 40 laboratory solutions determined

11

using (A and B) the ISO-788821 method, (C and D) a constant α (0.019), and (E and F) the new α

12

method. The dashed lines (B, D, and F) are at ±10% for reference.

13

Figure 5. Ternary plot showing the equivalent fraction of HCO3, Cl, and SO4 for the 65 natural

14

waters tested.

15

Figure 6. The δκ25 determined for the 65 natural waters tested using the ISO-788821 method, the

16

constant α (0.019), and the new α method are shown for (A-C) 21 acid mine waters (AMW), (D-

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F) 24 geothermal waters, and (G-I) 20 circumneutral pH waters.

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Figure 7. Box plots showing the electrical conductivity error (δk25) for the 65 natural water

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samples studied using the new α method, the constant α (0.019), and ISO-788821 methods.

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Figure 3

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Figure 4

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Figure 5

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Figure 6

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Figure 7

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New Method for Electrical Conductivity Temperature Compensation

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