CEE 680 Lecture #32 3/25/2020 Print version Updated: 25 March - - PDF document

CEE 680 Lecture #32 3/25/2020 1

Lecture #32 Coordination Chemistry: Case Studies: NTA (cont.)

(Stumm & Morgan, Chapt.6: pg.317‐319)

Benjamin; Chapter 8.1‐8.6

David Reckhow CEE 680 #32 1

Updated: 25 March 2020

Print version

Biotic ligand model of the acute toxicity of metals. 2. Application to acute copper toxicity in freshwater fish and Daphnia

Environmental Toxicology and Chemistry, Volume: 20, Issue: 10, Pages: 2397-2402

CEE 680 Lecture #32 3/25/2020 2

Algae and Copper

McKnight et al., 1983; Environmental Management 7(4)311-320

% 𝜈 𝜈

 Fresh and salt water algae  Depends on Cu+2 ion: 10‐7M seems to work for most

Add CuSO4

Smith et al., 2015, Applied Geochemistry 57:55

CEE 680 Lecture #32 3/25/2020 3

Modeling the Fate of Metal Concentrates in Surface Water

Environmental Toxicology and Chemistry, Volume: 38, Issue: 6, Pages: 1256- 1272, First published: 23 March 2019, DOI: (10.1002/etc.4417)

Copper – NTA problem

 NTA: nitrilotriacetate

 Used as a substitute “builder”

in place of phosphate

 Good example of moderately

strong ligand

 Research interests: 70’s & 80’s

 General Review

 Perry et al., 1984 [Wat. Res., 18(3)255]

 Other Aspects

 Photochemistry: e.g., Langford et al., 1973 [ES&T 7(9)820]  Biodegradation: e.g., Kuhn et al., 1987 [Wat. Res. 21(10)1237], Vanbriesen

et al., 2000 [ES&T 34(16)3346]

 Bioavailability of bound metals: e.g., Bressan & Brunetti, 1988 [Wat.

• Res. 22(5)553]

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N CH2COOH CH2COOH CH2COOH See: Knud-Hansen Paper

CEE 680 Lecture #32 3/25/2020 4

Cu‐NTA II

 Thermodynamics (20ºC)

 Acid/Base

 H3NTA = H+ + H2NTA‐

pK1 = 1.6

 H2NTA‐ = H+ + HNTA‐2

pK2 = 3.0

 HNTA‐2 = H+ + NTA‐3

pK3 = 10.3  Cu complex

 Cu+2 + NTA‐3 = CuNTA‐

p1 = ‐13.0

 Others are rather weak

 CuHNTA David Reckhow CEE 680 #32 7 David Reckhow CEE 680 #32 8

From: Snoeyink & Jenkins, 1980

CEE 680 Lecture #32 3/25/2020 5

Cu‐NTA III

 Specific problem

 CuT = 10‐4 M

6.35 mg/L

 NTAT = 10‐4 M

19.1 mg/L

 Notes:

 this is a much higher concentration of NTA than is

generally found, but it can be used to represent background natural organic matter

 Copper concentrations may sometimes be this high

when used as an algicide

 We are ignoring other complexes such as copper

hydroxides or carbonates

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Cu‐NTA IV

 Mass Balance Equations

 CuT = [Cu+2] + [ CuNTA‐]  NTAT = [CuNTA‐] + [H3NTA] + [H2NTA‐] + [HNTA‐2] +

[NTA‐3]  Definition: total free concentration (TF) is that which

is unbound to any metal except H+

 NTAT = [CuNTA‐] +NTATF

David Reckhow CEE 680 #32 10

CEE 680 Lecture #32 3/25/2020 6

Cu‐NTA V

 Equilibria

 Acid/base  Complexation

David Reckhow CEE 680 #32 11 1 3 2 1 3 3 2 2 3 3 3

] [ ] [ ] [ 1 ] [

    

             K K K H K K H K H NTA NTA

TF



] ][ [ ] [

3 2 1   

 NTA Cu CuNTA 

Cu‐NTA VI

 Substitute mass balance and alpha equations into the

beta equation

David Reckhow CEE 680 #32 12

   

]) [ ( ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] ][ [ ] [

2 3 2 2 3 2 2 3 2 2 3 2 1           

          Cu Cu NTA Cu Cu Cu CuNTA NTA Cu Cu Cu NTA Cu Cu Cu NTA Cu CuNTA

T T T T T TF T

   

CEE 680 Lecture #32 3/25/2020 7

Cu‐NTA VII

 Now solve, noting that CuT = NTAT  Which gives us a quadratic which can be solved for

a given pH

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 

] [ ] [ ] [ ]) [ ( ] [ ] [

2 3 2 2 2 3 2 2 1      

      Cu Cu Cu Cu Cu Cu NTA Cu Cu Cu

T T T T

  

] [ ] [

2 2 2 1 3

  

  T

Cu Cu Cu  

Cu‐NTA VIII

Then determine other species from the free

copper

Can use a spreadsheet to calculate 3 versus

pH, and then calculate the other species

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] [ ] [

2  

  Cu Cu CuNTA

T

] [



  CuNTA NTA NTA

T TF

TF

NTA NTA

3 3]

[  



CEE 680 Lecture #32 3/25/2020 8

Cu‐NTA IX

 Figure shows

impact of ligand speciation on extent of complexation

 Same thing

happens with fulvic acid

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pH 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Concentration (moles/L) 1e-19 1e-18 1e-17 1e-16 1e-15 1e-14 1e-13 1e-12 1e-11 1e-10 1e-9 1e-8 1e-7 1e-6 1e-5 1e-4 1e-3 Cu+2 NTA-3 CuNTA-

CuNTA X

David Reckhow CEE 680 #32 16

pH 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Log Concentration (moles/L)

• 19
• 18
• 17
• 16
• 15
• 14
• 13
• 12
• 11
• 10
• 9
• 8
• 7
• 6
• 5
• 4
• 3

Cu+2 NTA-3 CuNTA-

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CuNTA XI

David Reckhow CEE 680 #32 17

pH 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Log Concentration (moles/L)

• 19
• 18
• 17
• 16
• 15
• 14
• 13
• 12
• 11
• 10
• 9
• 8
• 7
• 6
• 5
• 4
• 3

Cu+2 NTA-3 CuNTA- CuOH+ Cu(OH)2(aq) Cu(OH)3

• Cu(OH)4
• 2

CuOHNTA-2 Cu(NTA)2

• 4

Cu2(OH)2

+2

To next lecture

David Reckhow CEE 680 #32 18