| Contents Notes |
"Precipitation behavior of heavy metals (Ni, Co, Cd, Cu, and Zn) was studied extensively in single and multi-metal systems. Kinetic studies showed that NiS oxidation (as a function of pH, oxygen, and reaction time) caused the dissolution of NiS. CoS precipitation behavior was similar to NiS. Effective NiS (or CoS) precipitation would require high pH, short detention times, or closed reactors (under N2 atmosphere). In the multi-metal systems without nickel, CdS and ZnS precipitation were the same as in their single-metal systems; however, the precipitations were affected in nickel-containing systems because of NiS oxidation. Results of CuS precipitation from multi-metal systems (with or without nickel) were substantially better than the single-metal case. The use of ultrafiltration proved that the particle size of CdS was influenced by pH. A higher pH (greater than 8) favored the formation of colloidal precipitates. The settling characteristics of precipitate were improved significantly by the addition of coagulants (anionic polymer or calcium). The effectiveness of the polymer was controlled by polymer type, pH, and polymer concentration. Freshly prepared CaS slurries were quite successful in supplying both sulfide source and coagulant." |
