Page 82 - Membranes for Industrial Wastewater Recovery and Re-Use

62 Membranes for lndustrial Wastewater Recovery and Re-use

Table 2.14 Solubility products for some common scalants at 20°C
~
Salt Formula Solubility product, K,
Aluminium hydroxide 8.5 x 10-23
Barium sulphate 9.2 x lo-"
Calcium carbonate 4.8 x 10-9
Calcium fluoride 3.2 x lo-''
Calcium hydrogen phosphate 2.0 x 10-7
Calcium hydroxide 8 x
Calcium sulphate 2.3 x 10-4
Cadmium sulphide 1.4 x
Cobalt sulphide 3.0 x
Chromium hydroxide 2.9 x
Copper sulphide 1.0 x 10-44
Dolomite 6.8 x 10-l8
Ferrous hydroxide 4.8 x lo-''
Ferric hydroxide 3.8 x 10-38
Ferrous sulphide 4.0 x 10-19
Lead sulphide 5.0 x 10-29
Manganese hydroxide 4.0 x 10-14
Manganese sulphide 1.4 x 10-15
Magnesium ammonia phosphate 2.2 x 10-13
Magnesium carbonate 1.0 x 10-5
Magnesium hydroxide 3.4 x 10-1'
Mercuric bromide 5.2 x 10-23
Mercuric chloride 3.5 x 10-1*
Mercuric sulphide 1.0 x 10-45
Nickel hydroxide 8.7 x lo-"
Nickel sulphide 7.7 x l0-l3
Silver chloride 1.5 x 10-1"
Silver sulphide 1.6 x 10-49
Zinc hydroxide 1.0 x 10-17
Zinc sulphide 1.0 x 10-23

for which the equilibrium constant is:

Kl = [H+][COi-]/[HCO,] (2.34)

and so:
[COf-] = K2[HC0,]/[Ht] (2.35)

Equations (2.31) and (2.35) can be combined to give:
[H'] = K2 [Ca2+] [HCO:]/K, (2.36)

Thus:
pH, = (pK2 - pK,) + pCa + pAlk (2.37)