Print version. Lecture #30 Coordination Chemistry: case studies. Benjamin; Chapter (Stumm & Morgan, Chapt.6: pg )

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1 Updated: 30 March 2018 Print version Lecture #30 Coordination Chemistry: case studies (Stumm & Morgan, Chapt.6: pg ) Benjamin; Chapter David Reckhow CEE 680 #30 1

2 Summary of a few general rules At the intersection of sequential alphas, i and i+1 : At the peak of an intermediate alpha, i, where 0, -max value LogK x -LogK x+1 This peak is also usually near intersection of the previous and following alphas (i.e., i 1 and i+1 ), and its maximum height is estimated from: David Reckhow CEE 680 #30 2

3 Cadmium Complexes Bisulfide Ligand Species log K Log Beta CdL Log K 1 = Log 1 = CdL 2 Log K 2 = 6.36 Log 2 = CdL 3 Log K 3 = 2.18 Log 3 = CdL 4 Log K 4 =2.19 Log 4 = Cyanide Ligand Species log K Log Beta CdL Log K 1 = 5.32 Log 1 = 5.32 CdL 2 Log K 2 = 5.05 Log 2 = CdL 3 Log K 3 = 4.46 Log 3 = CdL 4 Log K 4 =3.46 Log 4 = David Reckhow CEE 680 #30 3

4 1.2 Cd-HS system Alpha Log [L] David Reckhow CEE 680 #30 4

5 David Reckhow CEE 680 #30 5 Log [L]

6 1.2 Cd-HS system Alpha Log [L] David Reckhow CEE 680 #30 6

7 Cd + CN 0.9 Alpha David Reckhow CEE 680 #30 Log [L] 7

8 Cadmium Bisulfide Species log K Log Beta CdL Log K 1 = Log 1 = CdL 2 Log K 2 = 6.36 Log 2 = CdL 3 Log K 3 = 2.18 Log 3 = CdL 4 Log K 4 =2.19 Log 4 = Specific Problem 5 x 10 4 M Cd total 10 3 M HS total David Reckhow CEE 680 #30 8

9 1.2 Cd-HS system Alpha Log [L] David Reckhow CEE 680 #30 9

10 5x10-4 M Cd Total M HS Total n-bar (equ) Alpha n-bar (mass balance) n-bar David Reckhow CEE 680 #30 Log [L] 10

11 5x10-4 M Cd Total + 2.5x10-4 M Cu Total M HS Total n-bar (equ) 3.5 Alpha n-bar n-bar (mass balance) David Reckhow CEE 680 #30 Log [L] 11

12 Cadmium Cyanide Species log K Log Beta CdL Log K 1 = 5.32 Log 1 = 5.32 CdL 2 Log K 2 = 5.05 Log 2 = CdL 3 Log K 3 = 4.46 Log 3 = CdL 4 Log K 4 =3.46 Log 4 = Specific Problem 10 5 M Cd total 2.5 x 10 5 M CN total David Reckhow CEE 680 #30 12

13 Cd + CN 0.9 Alpha David Reckhow CEE 680 #30 Log [L] 13

14 10-5 M Cd Total + 2.5x10-5 M CN Total n-bar (equ) Alpha n-bar (mass balance) n-bar David Reckhow CEE 680 #30 Log [L] 14

15 10-5 M Cd Total + 2.5x10-5 M CN Total n-bar (equ) Alpha n-bar (mass balance) n-bar David Reckhow CEE 680 #30 Log [L] 15

16 Zinc Cyanide Species Betas ZnL Log 1 = 5.7 ZnL 2 Log 2 = 11.1 ZnL 3 Log 3 = 16.1 ZnL 4 Log 4 = 19.6 Specific Problem 10 4 M Zn total 5 x 10 4 M CN total David Reckhow CEE 680 #30 16

17 Zn + CN 0.9 as 0.7 Alpha David Reckhow CEE 680 #30 Log [L] 17

18 10-4 M Zn Total + 5x10-4 M CN Total n-bar (mass balance) n-bar (equ) Alpha n-bar David Reckhow CEE 680 #30 Log [L] 18

19 Complexation 10-4 M Zn Total + 5x10-4 M CN Total n-bar (mass balance) n-bar (equ) Alpha n-bar David Reckhow CEE 680 #30 19 Log [L]

20 Complexation Hg Cl 1.2 example M Hg Total + 3x10-2 M Cl Total Alpha Log [L] David Reckhow CEE 680 #30 20

21 Ag Br 1.2 example Complexation 10-2 M Ag Total M Br Total Alpha Log [L] David Reckhow CEE 680 #30 21

22 Aluminum Fluoride system Significance Aluminum in natural waters Aluminum in coagulation Thermodynamic Values: Smith & Martel (Benjamin) Log K 1 = 6.16 (7.01) Log K 4 = 2.71 (2.70) Log K 2 = 5.05 (5.74) Log K 5 = 1.46 (8) Log K 3 = 3.91 (4.27) Log K 6 = 0 ( 0.3) Now calculate alpha s [ M ] n ] CM 2 n 1 [ L] [ L] [ L 1 [ ML ] 0 [ L] n n n n David Reckhow CEE 680 #30 CM 22

23 Aluminum Fluoride Aluminum Fluoride: alphas alone Alpha n-bar Log [L] David Reckhow CEE 680 #30 23

24 Aluminum Fluoride Aluminum Fluoride alpha diagram n-bar (equ) Alpha n-bar The pk s Log [L] David Reckhow CEE 680 #30 24

25 n-bar (equ) Alpha n-bar The pk s Log [L] David Reckhow CEE 680 #30 25

26 Natural Fluoride Figure 1.4, pg. 9 in Benjamin, 2015 Figure 15.1, pg.873 in Stumm & Morgan, 1996 David Reckhow CEE 680 #30 26

27 Fluoride addition Balance between Dental Caries and Fluorosis Recommended dose 0.7 to 1.2 mg/l, Based on temperature Fig from Water Quality & Treatment, 1999 (5 th edition) David Reckhow CEE 680 #30 27

28 Al F Problems & Discussion Typical WT Situation Alum dose = 33 mg/l Total Fluoride = 1.9 mg/l High Fluoride pulse & high alum dose Alum dose = 660 mg/l Total Fluoride = 190 mg/l Impacts of OH complexation? David Reckhow CEE 680 #30 28

29 n-bar (equ) Alpha AlF +2 AlF 2 + AlF n-bar David Reckhow CEE 680 #30 Log [L] 29

30 Iron Thiocyanate system Significance Metal plating wastewaters Used in colorimetric analysis of iron Thermodynamic Values Log K 1 = 2.11 Log K Log K 2 = = 0 Log K Log K 3 = 0 5 = 0.1 Log K Now calculate alpha s 6 = 0.9 [ M ] n ] CM 2 n 1 [ L] [ L] [ L 1 [ ML ] 0 [ L] n n n n David Reckhow CEE 680 #30 CM 30

31 n-bar (equ) Alpha Fe +3 FeSCN +2 Fe(SCN) n-bar The pk s Log [L] David Reckhow CEE 680 #30 31

32 Specific problem Total concentrations C M = 0.1 M C L = 0.1 M Mass based equation N bar = 1 10[SCN ] Solution: n bar = 5 [Fe +3 ]=28M [FeSCN +2 ] = 57M [Fe(SCN) 2+ ] = 14M David Reckhow CEE 680 #30 32

33 Fe S problem Below are the equilibria for the Fe +2 HS system as listed in Benjamin s book. Note that are no equilibria for FeL, as this species is never significant. Prepare a graph of alpha values (vs log[hs ]) for the this system. Using this graph determine the complete ferrous iron speciation in groundwater where the total sulfide concentration is mm and total ferrous iron is 0.1 mm. Assume the ph of the groundwater is about 8. Species Ligand HS PO 3 4 FeL FeL FeH 2 L Log ß values (From Table 8.3 ; pg 374) David Reckhow CEE 680 #30 33

34 Thorium concentrations Surface concentration David Reckhow CEE 680 #30 34

35 Thorium example I In pure water C Th = 1 µg/l Temp = 25ºC From: Langmuir, 1997; Fig. 3.12a, Original source: Langmuir & Herman, 1980; Geochim. Et Cosmochim. Acta 44(11) David Reckhow CEE 680 #30 35

36 Thorium example II In pure water with sulfate C SO4 = 100 mg/l C Th = 1 µg/l Temp = 25ºC From: Langmuir, 1997, Fig. 3.12b Original source: Langmuir & Herman, 1980; Geochim. Et Cosmochim. Acta 44(11) David Reckhow CEE 680 #30 36

37 Model groundwater without organics C Th = 1 µg/l & Temp = 25ºC Groundwater composition Total fluoride = 0.3 mg/l Total chloride = 10 mg/l Total phosphate = 0.1 mg/l Total sulfate = 100 mg/l Thorium example III From: Langmuir, 1997; Fig. 3.13a, Original source: Langmuir & Herman, Geochim. Et Cosmochim. Acta 44(11) David Reckhow CEE 680 #30 37

38 Model groundwater with organics Same inorganic groundwater composition With organics Total oxalate = mg/l Total EDTA = 0.1 mg/l Thorium example IV From: Langmuir, 1997; Fig. 3.13b, Original source: Langmuir & Herman1980; Geochim. Et Cosmochim. Acta 44(11) David Reckhow CEE 680 #30 38

39 End To next lecture David Reckhow CEE 680 #30 39

40 Fe S problem Below are the equilibria for the Fe +2 HS system as listed in Benjamin s book. Note that are no equilibria for FeL, as this species is never significant. Prepare a graph of alpha values (vs log[hs ]) for the this system. Using this graph determine the complete ferrous iron speciation in groundwater where the total sulfide concentration is mm and total ferrous iron is 0.1 mm. Assume the ph of the groundwater is about 8. Species Ligand HS PO 3 4 FeL FeL FeH 2 L Log ß values (From Table 8.3 ; pg 374) David Reckhow CEE 680 #30 40

41 Calculations Log ß values (From Table 8.3 ; pg 374) calculations. Species Ligand HS PO 3 4 FeL FeL FeH 2 L David Reckhow CEE 680 #30 41

42 a Alpha 0.7 n-bar (equ) n-bar n-bar (mass balance) David Reckhow CEE 680 #30 42 Log [L]

43 a Alpha n-bar n-bar (mass balance) n-bar (equ) David Reckhow CEE 680 #30 43 Log [L]

44 Species Conc (M) Log C HS 5.37E Fe E Fe(HS) o E Fe(HS) 3 0 H + 0E 08 8 OH 0E 06 6 H 2 S 5.75E S E David Reckhow CEE 680 #30 44