CEE 680 Lecture #29 3/11/2020 Print version Updated: 11 March 2020 Lecture #29 Complexation: Speciation in Fresh Waters (Stumm & Morgan, Chapt.6: pg.289 ‐ 305) Benjamin; Chapter 8.1 ‐ 8.6 David Reckhow CEE 680 #29 1 Cadmium Batteries & electroplating Very high ratio of abundance to toxicity Like Pb, Hg, As EPA Standards 0.005 g/L in drinking water Concern over kidney damage Click here for more on Cd Cadmium is of no use to the human body and is toxic even at low levels. The negative effects of cadmium on the body are numerous and can impact nearly all systems in the body, including cardiovascular, reproductive, the kidneys, eyes, and even the brain. • Cadmium affects blood pressure. • Cadmium affects prostate function and testosterone levels. • Cadmium induces bone damage (Itai-ltai). • Exposure to cadmium can affect renal and dopaminergic systems in children. David Reckhow CEE 680 #29 2 1
CEE 680 Lecture #29 3/11/2020 David Reckhow CEE 680 #29 3 Flux in 10 7 M/yr From: Morel & Malcolm, “ The Biogeochemistry of Cadmium ”, Chapt 8 in Metal Ions in Biological Systems, Vol 43 Sigel, Sigel & Sigel, eds. David Reckhow CEE 680 #29 4 2
CEE 680 Lecture #29 3/11/2020 CdCl Example Consider the speciation of cadmium and chloride -value First the four beta’s Cd +2 + Cl ‐ = CdCl + 21 Cd +2 + 2Cl ‐ = CdCl 2 166 204 Cd +2 + 3Cl ‐ = CdCl 3 ‐ 71.5 Cd +2 + 4Cl ‐ = CdCl 4 ‐ 2 Now plot the alpha curves David Reckhow CEE 680 #29 5 Cadmium Chloride From: Butler, 1964; pg.268 Reproduced in Langmuir, 1997; pg.96 Similar to: Butler, 1998; pg.241 David Reckhow CEE 680 #29 6 3
CEE 680 Lecture #29 3/11/2020 CdCl Example Calculate the concentration of all species for the following solution 0.01 M Cd(NO 3 ) 2 + 1 M HCl Use the equilibrium equations [ M ] 1 2 n 1 [ L ] [ L ] [ L ] 0 1 2 n C M [ ML ] 0 n n [ L ] n n C M But what do you use for [L]? David Reckhow CEE 680 #29 7 Cadmium Chloride From: Butler, 1964; pg.268 Reproduced in Langmuir, 1997; pg.96 Similar to: Butler, 1998; pg.241 David Reckhow CEE 680 #29 8 4
CEE 680 Lecture #29 3/11/2020 Cadmium Chloride (cont.) Butler, 1964; pg.269 David Reckhow CEE 680 #29 9 Cadmium Chloride (cont.) Pankow, 1991; pg.375 David Reckhow CEE 680 #29 10 5
CEE 680 Lecture #29 3/11/2020 Ligand Number Definition The average number of bound ligands per atom of metal Significance Defines Mixture Can be analytically determined Used to evaluate ’s Can be calculated via 2 independent ways and used to solve problems, if you know the free ligand concentration Mass balance equations Equilibrium equations Thus, we have 2 independent equations and two unknowns (free L, and n ‐ bar), so we can solve David Reckhow CEE 680 #29 11 Determination of Ligand # Equilibrium constant approach [ ML ] 2 [ ML ] 3 [ ML ] n [ ML ] 2 3 n n C M [ ML ] [ ML ] [ ML ] [ ML ] 2 2 3 3 n n C C C C M M M M 2 3 n 1 2 3 n And substituting in for the apha’s 2 3 n n [ L ] 2 [ L ] 3 [ L ] n [ L ] 0 1 0 2 0 3 0 n 2 3 n [ L ] 2 [ L ] 3 [ L ] n [ L ] 0 1 2 3 n David Reckhow CEE 680 #29 12 6
CEE 680 Lecture #29 3/11/2020 Determination of ligand # Mass balance approach C M = [M]+[ML]+[ML 2 ]+[ML 3 ]+ +[ML n ] C L = [L]+[ML]+2[ML 2 ]+3[ML 3 ]+ +n[ML n ] [ ML ] 2 [ ML ] 3 [ ML ] n [ ML ] n 2 3 n C M C [ L ] L C M David Reckhow CEE 680 #29 13 Take alpha diagram For CdCl x Next add n ‐ bar curves One based on equilibria Other based on mass balances David Reckhow CEE 680 #29 14 7
CEE 680 Lecture #29 3/11/2020 Cadmium Chloride alpha diagram 1.2 6.0 1.1 5.5 1.0 5.0 0.9 4.5 0.8 4.0 n-bar (equ) 0.7 3.5 Alpha n-bar 0.6 3.0 0.5 2.5 0.4 2.0 0.3 1.5 0.2 1.0 0.1 0.5 0.0 0.0 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 David Reckhow CEE 680 #29 Log [L] 15 In ‐ Class Problems Class problems with CdCl x Sea Water: C L =5 x 10 ‐ 1 , C M =1 x 10 ‐ 9 Contaminated Sea Water: C L =5 x 10 ‐ 1 , C M =1 x 10 ‐ 1 Desal Brine: C L =15 x 10 ‐ 1 , C M =3 x 10 ‐ 9 RO conc. of Cont. Sea Water: C L =15 x 10 ‐ 1 , C M =3 x 10 ‐ 1 𝑜 �� � 𝐷 � � 𝑀 𝐷 � David Reckhow CEE 680 #29 16 8
CEE 680 Lecture #29 3/11/2020 Cadmium Chloride problem 1.2 6.0 𝑜 �� � 𝐷 � � 𝑀 1.1 5.5 𝐷 � 1.0 5.0 0.9 4.5 0.8 4.0 n-bar (equ) 0.7 3.5 Alpha n-bar 0.6 3.0 0.5 2.5 0.4 2.0 0.3 1.5 0.2 1.0 Sea Water: C L =5 x 10 -1 , C M =1 x 10 -9 0.1 0.5 0.0 0.0 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 David Reckhow CEE 680 #29 Log [L] 17 Cadmium Chloride problem 2 1.2 6.0 𝑜 �� � 𝐷 � � 𝑀 1.1 5.5 𝐷 � 1.0 5.0 0.9 4.5 0.8 4.0 n-bar (equ) 0.7 3.5 Alpha n-bar 0.6 3.0 0.5 2.5 0.4 2.0 0.3 1.5 Contaminated Sea Water: 0.2 1.0 C L =5 x 10 -1 , C M =1 x 10 -1 0.1 0.5 0.0 0.0 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 David Reckhow CEE 680 #29 Log [L] 18 9
CEE 680 Lecture #29 3/11/2020 Cadmium Chloride problem 3 1.2 6.0 𝑜 �� � 𝐷 � � 𝑀 1.1 5.5 𝐷 � 1.0 5.0 0.9 4.5 0.8 4.0 n-bar (equ) 0.7 3.5 Alpha n-bar 0.6 3.0 0.5 2.5 0.4 2.0 0.3 1.5 Desal Brine: C L =15 x 10 -1 , 0.2 1.0 C M =3 x 10 -9 0.1 0.5 0.0 0.0 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 David Reckhow CEE 680 #29 Log [L] 19 Cadmium Chloride problem 4 1.2 6.0 𝑜 �� � 𝐷 � � 𝑀 1.1 5.5 𝐷 � 1.0 5.0 0.9 4.5 0.8 4.0 n-bar (equ) 0.7 3.5 Alpha n-bar 0.6 3.0 0.5 2.5 0.4 2.0 0.3 1.5 RO conc. of Cont. Sea 0.2 1.0 Water: C L =15 x 10 -1 , C M =3 x 10 -1 0.1 0.5 0.0 0.0 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 David Reckhow CEE 680 #29 Log [L] 20 10
CEE 680 Lecture #29 3/11/2020 Speciation in Natural Waters From: Morel & Malcolm, “ The Biogeochemistry of Mostly Cl complexes in Cadmium ”, Chapt 8 in Metal Ions in Biological Systems, Vol 43 Sigel, Sigel & Sigel, eds. sea water David Reckhow CEE 680 #29 21 Cellular metabolism of Cd gg From: Morel & Malcolm, PCs are “ The Biogeochemistry of Cadmium ”, Chapt 8 in phytochelatins; metal Metal Ions in Biological binding proteins that Systems, Vol 43 Sigel, Sigel help regulate Cd & Sigel, eds. concentrations David Reckhow CEE 680 #29 22 11
CEE 680 Lecture #29 3/11/2020 1.2 4.0 1.1 3.5 1.0 K 1 =10 6 , 0.9 3.0 0.8 2.5 0.7 K 2 =10 2 Alpha n-bar (equ) n-bar 0.6 2.0 0.5 1.5 0.4 0.3 1.0 0.2 0.5 0.1 1.2 0.0 4.0 0.0 K 1 =10 4.5 , 1.1 -8 -6 -4 -2 0 3.5 1.0 Log [L] 0.9 3.0 K 2 =10 3.5 0.8 2.5 0.7 Alpha n-bar (equ) n-bar 0.6 2.0 0.5 1.5 0.4 0.3 1.0 0.2 0.5 0.1 0.0 0.0 -8 -6 -4 -2 0 Note: as K’s get closer, so do the Log [L] intersections, and the middle alpha’s get compressed with diminished height David Reckhow CEE 680 #29 23 1.2 4.0 1.1 3.5 1.0 0.9 3.0 0.8 2.5 K 1 =10 4 , K 2 =10 4 0.7 Alpha n-bar (equ) n-bar 0.6 2.0 0.5 1.5 0.4 0.3 1.0 0.2 0.5 0.1 0.0 1.2 4.0 0.0 K 1 =10 3.5 , 1.1 -8 -6 -4 -2 0 3.5 1.0 Log [L] K 2 =10 4.5 0.9 3.0 0.8 2.5 0.7 Alpha n-bar (equ) n-bar 0.6 2.0 0.5 1.5 0.4 0.3 1.0 0.2 0.5 0.1 0.0 0.0 -8 -6 -4 -2 0 Log [L] David Reckhow CEE 680 #29 24 12
CEE 680 Lecture #29 3/11/2020 Features of alpha diagrams Intersection point for adjacent curves Occur at: log [L] = pK’s E.g., first intersection occurs where: 0 = 1 which is where: [M]=[ML] And in general, intersection of adjacent curves will occur where: [ML (i ‐ 1) ]=[ML (i) ] So at these intersection points, the metal terms in the equations for K will cancel each other out and: [ ML ] [ ML ] K i K i 1 [ ML ][ L ] [ M ][ L ] ( i 1 ) or 1 1 [ L ] [ L ] K K 1 i log[ L ] pK log[ L ] pK 1 i David Reckhow CEE 680 #29 25 Features (cont.) An alpha curve will reach its maximum at the point where the preceding alpha and the following alpha intersect (i.e., i ‐ 1 and i+1 ), Consider the intersection of i ‐ 1 and i+1 [ ML ] [ ML ] The two K equations are: K i 1 K i i 1 i [ ML ][ L ] [ ML ][ L ] ( i ) ( i 1 ) [ ML ] K K i 1 And their product gives us: i i 1 2 [ ML ][ L ] ( i 1 ) Once again, we can cancel 1 [ L ] metal concentrations to get: K K i i 1 log[ L ] 0 . 5 ( pK pK ) i i 1 David Reckhow CEE 680 #29 26 13
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