lecture #53 redoxchemistry: arsenic ii, geochemistry · 2019-05-02 · lecture #53. redoxchemistry:...

Lecture #53Redox Chemistry: Arsenic II, Geochemistry

(Stumm & Morgan, Chapt.8 )

Benjamin; Chapter 9

David Reckhow CEE 680 #53 1

Updated: 2 May 2019 Print version

http://www.ecs.umass.edu/cee/reckhow/courses/680/680l53/680l53print.pdf

Arsenic Geology 20th in Abundance in Earth’s Crust Typically Associated with Igneous or Sedimentary

Rocks Arsenic Concentrations Tend to be High in Igneous

Rocks Containing Iron Oxides Often Associated with Sulfidic Ores


From presentation by Philip Brandhuber (2001)

Geology (cont.) Approximately 245 Arsenic Bearing Minerals have

been Identified Some Common Arsenic Bearing Minerals

Realgar (AsS) Orpinent (As2O3) Arsenopyrite (FeAsS) Scorodite (FeAsO4 . H2O)



National Distribution of Arsenic in Groundwater

David Reckhow CEE 680 #53 4Welsh et al. 2000


Arsenic Mobility Theoretically As(III) tends to be more Mobile

than As(V) As(V) will Strongly Sorb to Iron Oxides To a lesser Extent, As(V) will Sorb to Manganese

Oxides However, As(VI) Associated with Iron Oxides

may be Transported (Colloidal As) Changes in Redox Conditions may Mobilize

Arsenic



Arsenic Size Distribution


0

20

40

60

80

100

G1 G2 G3 G4 G5 G6 G7 G8Ground Water

% o

f Tot

al A

s

0

20

40

60

80

100

S1 S2 S3 S4 S5 S6 S7 S8Surface Water

% o

f Tot

al A

s

Size < 3K Dalton 0.45u > Size > 3K Dalton Size > 0.45u

Reference: Brandhuber and Amy 1998From presentation by Philip Brandhuber (2001)


From: Hering & Elimelech, 1996; AWWARF Report

Arsenic Eh - pH Diagram in Pure Water


0

p H12 14100 2 4 6

.250

.500

1.000

.750

0

-.250

-.500

-.750

-1.00

H2O UnstableO2 (g)

H2O Unstable

H2 (g)

H3AsO4H2AsO4

-

HAsO42-

AsO43-

H2AsO3-

H3AsO3

HAsO32-

As

8

Eh(V)

AsH3

Reference: Ferguson and Garvis (1972)

H O

O = As - OH O H

Arsenate

ArseniteH O

As O O H H


AsH3

3

2

-

Eh

(V)

1

4

12

1

0

8

H

p

6

4

2

0

0

0

.

0

-

1

0

.

5

7

-

0

0

.

5

-

5

0

.

2

-

0

0

.

0

1

5

0

7

.

0

0

.

5

0

5

4

AsO

H

3

AsO

3

H

4

AsO

2

H

(g)

O

O Unstable

2

H

-

2

4

HAsO

3-

4

AsO

-

2

3

HAsO

-

3

AsO

2

H

O Unstable

2

H

(g)

2

H

As

2

.

0

As and S Ferguson & Gavis,

1972 [Wat. Res. 6:1259] AsT = 10-5 M ST = 10-3 M Solids in ()


From: Evangelou, 1998, Environmental Soil and Water Chemistry, Wily Publ.

Regulatory Dates I 1942, Public Health Service Establishes 50 ppb

Standard 1975, EPA formalizes 50 ppb Standard 1989, EPA misses the First of Several Deadlines

for Revising Rule June 22, 2000, EPA Proposes MCL of 5 ppb January 22, 2001, EPA Publishes Final Rule, MCL

of 10 ppb



Regulatory Dates II March 20, 2001, EPA Announces it will “Reassess” Costs

and Scientific Issues, Delay Rule 60 Days April 23, 2001, EPA Announces Additional Delay of Nine

Months May 22, 2001, EPA Announces Delay Until February 22,

2002 July 19, 2001, EPA Request Comment on MCL’s of 20, 5

and 3 as Alternative to 10 ppb October 31, 2001, EPA announces that As standard will

be 10 ppb (effective 2006?)


From presentations by Brandhuber (2001) & Kempic (2001)

New regulated contaminants UCMR: 12 months of sampling within window

1212

98 99 00 0201 03 04 05 0706 08Year

CCL1

UCMR1Monitoring

PossibleExtension

CCL2

1009 12 1311 14 15

UCMR3Monitoring

CCL3

InitialList

FinalList

50 10

429

chemicalsmicrobials

10612

28 & 2L1: 12 & 0L2: 15 & 1

L1: 10 & 0L2: 15 & 0

UCMR2Monitoring

Preliminary Regulatory

Determination

Final Regulatory

Determination

Proposed Rule

Final Rule

Not actualSchedule

Hea

lthO

ccur

renc

e

Rulemaking Process

Other new or revised rules expected Revised TCR

E. coli in; fecal coliforms out

A “simple” view of what’s happening

14

2014

UCMR3 Proposal(3/2011)

CCL3 Final(10/2009)

2012 2013 2015 2016Reg Det 3

Final(

Impact to Utilities, Alternative MCL’s


0

1

2

3

4

5

6

7

8

9

10

3 5 10 20

# C

WS

Impa

cted

(10

00s)

Alternative MCL (ug/L)

GW SW

EPA: Federal Register 65(121):38888From presentation by Philip Brandhuber (2001)

Key Features of Arsenic’s Chemistry in Water Present in two Oxidation States Behaves as an Acid

Arsenate (As(V)) H3AsO4 => H2AsO4- => HAsO42- => AsO43-

Arsenite (As(III)) H3AsO3 => H2AsO3- => HAsO32-



Coagulation

As(V) is much better removed than As(III)



Coagulation

Alum vs Ferric Fe(III) is clearly

better Why?



Oxidize - Cl2 - MnO4- - O3

Treat - RO/NF - Coagulation/MF - Activated Alumina -

Ion Exchange - Greensand - Iron media (GFH) Dispose of Residual

- POTW - Dewater - Landfill



Ferrous Arsenite Initial Arsenite:Fe ratio of 1:1

From GEO-CHEM-PC


From: Evangelou, 1998, Environmental Soil and Water Chemistry, Wily Publ.

To next lecture


DAR

http://www.ecs.umass.edu/cee/reckhow/courses/680/680l54/

CEE 680: Water ChemistryArsenic GeologyGeology (cont.)National Distribution of Arsenic in GroundwaterArsenic MobilityArsenic Size DistributionSlide Number 7Arsenic Eh - pH Diagram in Pure Water�As and SRegulatory Dates IRegulatory Dates IINew regulated contaminants Other new or revised rules expectedA “simple” view of what’s happeningImpact to Utilities, Alternative MCL’sSlide Number 16CoagulationCoagulationSlide Number 19Ferrous ArseniteSlide Number 21

lecture #53 redoxchemistry: arsenic ii, geochemistry · 2019-05-02 · lecture #53. redoxchemistry:...

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