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

CEE 680 Lecture #32 3/25/2020 Print version Updated: 25 March 2020 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 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 1

CEE 680 Lecture #32 3/25/2020 Algae and Copper  Fresh and salt water algae  Depends on Cu +2 ion: 10 ‐ 7 M seems to work for most 𝜈 % 𝜈 ��� McKnight et al., 1983; Environmental Management 7(4)311-320 Add CuSO 4 Smith et al., 2015, Applied Geochemistry 57:55 2

CEE 680 Lecture #32 3/25/2020 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 See: Knud-Hansen Paper  NTA: nitrilotriacetate  Used as a substitute “builder” in place of phosphate CH 2 COOH  Good example of moderately N CH 2 COOH strong ligand  Research interests: 70’s & 80’s CH 2 COOH  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] David Reckhow CEE 680 #32 6 3

CEE 680 Lecture #32 3/25/2020 Cu ‐ NTA II  Thermodynamics (20ºC)  Acid/Base  H 3 NTA = H + + H 2 NTA ‐ pK 1 = 1.6  H 2 NTA ‐ = H + + HNTA ‐ 2 pK 2 = 3.0  HNTA ‐ 2 = H + + NTA ‐ 3 pK 3 = 10.3  Cu complex  Cu +2 + NTA ‐ 3 = CuNTA ‐ p  1 = ‐ 13.0  Others are rather weak  CuHNTA David Reckhow CEE 680 #32 7 From: Snoeyink & Jenkins, 1980 David Reckhow CEE 680 #32 8 4

CEE 680 Lecture #32 3/25/2020 Cu ‐ NTA III  Specific problem  Cu T = 10 ‐ 4 M 6.35 mg/L  NTA T = 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 David Reckhow CEE 680 #32 9 Cu ‐ NTA IV  Mass Balance Equations  Cu T = [Cu +2 ] + [ CuNTA ‐ ]  NTA T = [CuNTA ‐ ] + [H 3 NTA] + [H 2 NTA ‐ ] + [HNTA ‐ 2 ] + [NTA ‐ 3 ]  Definition: total free concentration (TF) is that which is unbound to any metal except H +  NTA T = [CuNTA ‐ ] +NTA TF David Reckhow CEE 680 #32 10 5

CEE 680 Lecture #32 3/25/2020 Cu ‐ NTA V  Equilibria  3 [ NTA ]    Acid/base 3 NTA TF  1      2 3 [ H ] [ H ] [ H ]  Complexation       1   K K K K K K   3 2 3 1 2 3  [ CuNTA ]   1   2 3 [ Cu ][ NTA ] David Reckhow CEE 680 #32 11 Cu ‐ NTA VI  Substitute mass balance and alpha equations into the beta equation    2 [ CuNTA ] Cu [ Cu ]    T 1     2 3 2 [ Cu ][ NTA ] [ Cu ] NTA 3 TF   2 Cu [ Cu ]  T     2   [ Cu ] NTA [ CuNTA ] 3 T   2 Cu [ Cu ]  T     2    2 [ Cu ] NTA ( Cu [ Cu ]) 3 T T David Reckhow CEE 680 #32 12 6

CEE 680 Lecture #32 3/25/2020 Cu ‐ NTA VII  Now solve, noting that Cu T = NTA T   2 Cu [ Cu ]   T   1   2    2 [ Cu ] NTA ( Cu [ Cu ]) 3 T T   2 Cu [ Cu ]  T    2 2 [ Cu ] [ Cu ] 3  Which gives us a quadratic which can be solved for a given pH        2 2 2 [ Cu ] [ Cu ] Cu 0 3 1 T David Reckhow CEE 680 #32 13 Cu ‐ NTA VIII  Then determine other species from the free copper     [ CuNTA ] Cu [ Cu 2 ] T    NTA NTA [ CuNTA ] TF T  3 ]   [ NTA NTA 3 TF  Can use a spreadsheet to calculate  3 versus pH, and then calculate the other species David Reckhow CEE 680 #32 14 7

CEE 680 Lecture #32 3/25/2020 1e-3 CuNTA - 1e-4 1e-5 Cu ‐ NTA IX 1e-6 Cu +2 1e-7  Figure shows 1e-8 Concentration (moles/L) impact of 1e-9 ligand 1e-10 NTA -3 speciation on 1e-11 extent of 1e-12 complexation 1e-13 1e-14  Same thing 1e-15 happens with 1e-16 fulvic acid 1e-17 1e-18 1e-19 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 David Reckhow CEE 680 #32 15 pH -3 CuNTA - -4 -5 CuNTA X -6 Cu +2 -7 -8 Log Concentration (moles/L) -9 -10 -11 NTA -3 -12 -13 -14 -15 -16 -17 -18 -19 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 David Reckhow CEE 680 #32 16 pH 8

CEE 680 Lecture #32 3/25/2020 -3 CuOHNTA -2 CuNTA - Cu +2 -4 -5 NTA -3 CuNTA XI Cu(OH) 2 (aq) -6 -7 -8 Log Concentration (moles/L) -4 -9 Cu(NTA) 2 CuOH + -10 -11 -12 -13 - -14 Cu(OH) 3 -15 -16 -2 Cu(OH) 4 -17 +2 Cu 2 (OH) 2 -18 -19 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 David Reckhow CEE 680 #32 17 pH  To next lecture David Reckhow CEE 680 #32 18 9