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Table 1 Experimental conditions and resultsa

From: Speciation of arsenic in sulfidic waters

    

Fractional abundances

Exp.

pH

log ΣH2S

log ΣAs

As(III)

As(V)

S : As

1 : 1

S : As

2 : 1

S : As

3 : 1

S : As

4 : 1

1

7.24

-7.51

-4.82

0.998

0.002

0.000

0.000

0.000

0.000

2

7.30

-5.49

-4.87

0.988

0.005

0.001

0.005

0.002

0.000

3

7.20

-4.96

-4.87

0.917

0.015

0.012

0.032

0.024

0.000

4

7.01

-4.28

-4.93

0.102

0.011

0.005

0.072

0.811

0.000

5

7.20

-3.85

-4.90

0.007

0.001

0.001

0.027

0.962

0.003

6

7.12

-3.51

-4.91

0.009

0.002

0.007

0.139

0.838

0.005

7

7.04

-3.49

-4.91

0.011

0.003

0.004

0.094

0.865

0.023

8

7.17

-2.97

-4.85

0.000

0.004

0.000

0.063

0.847

0.086

9

7.16

-3.50

-5.63

0.000

0.004

0.004

0.078

0.902

0.012

10

7.00

-3.00

-5.55

0.000

0.012

0.006

0.125

0.805

0.053

11

6.79

-5.96

-4.85

0.994

0.010

0.000

0.000

0.000

0.000

12

7.24

-5.47

-4.88

0.973

0.016

0.002

0.004

0.000

0.000

13

7.05

-4.96

-4.87

0.960

0.005

0.014

0.021

0.000

0.000

14

7.20

-4.66

-4.91

0.896

0.011

0.038

0.054

0.001

0.000

15

7.30

-4.48

-4.94

0.748

0.030

0.026

0.089

0.095

0.000

16

9.13

-5.73

-4.88

0.942

0.033

0.012

0.005

0.009

0.000

17

10.02

-4.99

-4.94

0.840

0.000

0.114

0.045

0.003

0.000

18

9.83

-4.48

-4.89

0.650

0.132

0.127

0.185

0.009

0.000

19

9.80

-3.80

-4.89

0.290

0.035

0.024

0.198

0.454

0.000

20

10.90

-3.57

-4.86

0.054

0.034

0.041

0.251

0.620

0.000

21

9.51

-4.54

-4.96

0.800

0.000

0.124

0.063

0.005

0.000

22

9.67

-4.24

-4.87

0.710

0.000

0.200

0.090

0.000

0.000

23

9.20

-3.96

-4.94

0.470

0.050

0.071

0.221

0.184

0.000

  1. aConcentrations in M. Concentrations of ΣH2S were calculated based on gravimetric mixing ratios of the stock NaHS and arsenite solutions, and the measured thioarsenite speciation; ΣH2S concentration in the stock NaHS solution was determined from the average of quadruplicate analyses using the methylene blue colorimetric method. Concentrations of ΣAs were determined by inductively coupled plasma-optical emission spectroscopy on unacidified samples. Precision of measurements: pH ~ 0.03; ΣH2S ~ 5%; ΣAs ~ 5%; species fractional abundance (F) ~5% for F > 0.1, ~10% for 0.1 > F > 0.01, ~20% for F < 0.01.