Metal Precipitants

Metal Precipitants for Industrial Wastewater Treatment

Industrial facilities that discharge wastewater containing dissolved heavy metals — nickel, copper, zinc, lead, cadmium, chromium, mercury, silver, and others — are subject to strict permit limits under the Clean Water Act. Metal precipitation converts soluble metal ions into insoluble solids that can be removed by settling or filtration. It is the most widely used and cost-effective metal removal method for industrial wastewater.

The primary precipitation chemistries are hydroxide (caustic soda or lime), sulfide (sodium sulfide or hydrosulfide), and organic precipitants including TMT-15 and dithiocarbamate (DTC) compounds. Hydroxide precipitation is standard practice but fails in the presence of chelating agents. Sulfide and organic precipitants handle chelated metals and can achieve lower effluent concentrations, though each comes with handling and safety considerations. Hexavalent chromium requires a chemical reduction step before it can be precipitated.

pH control is the most critical variable in any metal precipitation program. Each metal has an optimal precipitation range, and operating outside it leaves dissolved metal in the effluent.

Read the full technical guide in our Knowledge Center

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