Source of Anion
Sulfate (SOD Hydroxide (OH") Carbonate (CO32") Chromate (CrOf")
Sulfide (S2") Sulfite (SO2")
Spent chrome plating bath or chrome plating rinse Sodium sulfide Sulfur dioxide require removal. Therefore, a given treatment method may also remove other substances, and a treatability study is needed before selecting a treatment method.
Expected effluent quality in terms of lead concentration for batch or continuous flowthrough treatment is reported to be 0.5 mg/l, whereas that for integrated treatment is 0.01 mg/l.
The amphoteric nature of lead compounds requires careful control of pH for both precipitation and handling (dewatering) of sludges resulting from treatment. Each stage requires a different operating pH control range. As with all precipitation reactions, nucleation and crystal growth are important, although the high molecular weight of lead aids in particulate settling.
Physical methods such as electrodialysis, ion exchange, and reverse osmosis can also remove lead from waste-waters. Lead may also be removed by deliberately introducing the wastewater to acclimated biological treatment plants for complexing with biologically formed organic substances. A combination of chemical and biological methods, the in process treatment, can be used, with the lead chemically complexed and removed from the biological process.
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