Print version Updated: 31 March 2020 Lecture #36 Precipitation and - PowerPoint PPT Presentation

Print version Updated: 31 March 2020 Lecture #36 Precipitation and Dissolution: Other Metal Hydroxides (Stumm & Morgan, Chapt.7) Benjamin; Chapter 8.7-8.15 David Reckhow CEE 680 #36 1

Impact of pH on alum coagulation 9 450 Control (no alum) 400 8 7 350 Soluble Manganese ( µ g/L) 24 mg/L dose 6 300 48 mg/L dose DOC (mg/L) 5 250 4 200 96 mg/L dose 3 150 Manganese 2 100 Rennes IV Raw Water Mn precipitation (France) 11/19/84 1 50 Reckhow & Bourbigot (unpublished data) 0 0 4 5 6 7 8 9 10 11 12 pH

0 H + -1 OH - Al(OH) 3 -2 -3 - Al(OH) 4 Al Total -4 -5 Morgan’s fig. 6.8a, pg.273 -6 Al(OH) 3 Log C  Compare to Stumm & -7 -8 +5 Al 3 (OH) 4 -9 +7 Al 13 O 4 (OH) 24  Al solubility -10 AlOH +2 -11 + Al(OH) 2 Al +3 -12 -13 -14 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 pH David Reckhow CEE 680 #36 3

0 ZnOH + Zn +2 -1 Zn Total H + Zn(OH) 2 -2 -3 Zn(OH) 2 (aq) -4 Zn 2 (OH) +3 -5 Morgan’s fig. 6.8c, pg.273 -6 -2 Log C Zn(OH) 4  Compare to Stumm & -7 -2 Zn 2 (OH) 6 -8 -9 OH - - Zn(OH) 3  Zn solubility -10 -11 -12 -13 -14 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 pH David Reckhow CEE 680 #36 4

Chromium Hydroxide I  Thermodynamic Data  Although “metastable”, the Cr(OH) 3 (s) is Stumm & thought to control solubility in Morgan, 1996, wastewaters pg. 365 David Reckhow CEE 680 #36 5

Chromium Hydroxide II Stumm & Morgan, 1996, Figure 7.4, pg. 366 David Reckhow CEE 680 #36 6

Aqueous Silica  Thermodynamics  SiO 2 (s,quartz) + 2H 2 O = Si(OH) 4 log K = -3.7  SiO 2 (s,am.) + 2H 2 O = Si(OH) 4 log K = -2.7 - + H +  Si(OH) 4 = SiO(OH) 3 log K = -9.46 - = SiO 2 (OH) 2 -2 + H +  SiO(OH) 3 log K = -12.56 -2 + 2H +  4 Si(OH) 4 = Si 4 O 6 (OH) 6 log K = -12.57 + 4H 2 O David Reckhow CEE 680 #36 7

Stumm & Morgan, 1996, Figure 7.5, pg. 368 David Reckhow CEE 680 #36 8

 To next lecture David Reckhow CEE 680 #36 9