2.1.2. Weak Acid Dissociable Cyanide (WAD) Weak cyanide complexes, or WAD, can dissociate in solution and release environmentally significant concentrations of free cyanide. These complexes include cadmium, copper, nickel, zinc, and silver cyanide complexes. CYANIDE WAD → CYANIDE FREE Zn (CN)4 -2, Cd (CN) 4 -2, Cu CN) 4 -2 Ni (CN) 4 -2 Ag (CN) 2 - → HCN, CN- The degree of dissociation of WAD cyanides depends on solution pH, temperature, light intensity, dissolved solids, and the concentration of weak complexes. 2.1.3. Strongly Complexed Cyanides Strong cyanide complexes degrade much more slowly compared to WAD cyanides. Iron, cobalt, and gold cyanide complexes are strong and stable in solution. STRONGLY COMPLEXED → CYANIDE FREE Fe (CN)6 -4, Co (CN) 6 -4, Au (CN) 2 - → HCN, CN- 3. CARO’S ACID PROCESS Peroxymonosulfuric acid was first described by Heinrich Caro (1834–1910), who prepared it in 1898. Laboratory-scale preparation involves the combination of chlorosulfuric acid and hydrogen peroxide. H2O2 + ClSO2OH ↔ H2SO5 + HCl (2) Large-scale production is usually carried out in situ due to its instability. According to Martin’s patent, peroxymonosulfuric acid is produced by reacting sulfuric acid >85% with hydrogen peroxide >50% H2SO4 + H2O2 ↔ H2SO5 + H2O (3) Maximum efficiency is obtained with a molar ratio: H2SO4 / H2O2 from 1.5 to 3.0
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