Removal of silver and mercury from COD waste solutions

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Virginia Polytechnic Institute and State University


Ion exchange and precipitation technologies were examined for the selective separation and recovery of silver and mercury from COD waste solutions. Batch equilibrium studies were conducted to determine ion exchange selectivity of several commercial and regenerated resins. Resin capacity and metal ion recovery efficiency were evaluated in continuous-flow column studies. Solubility studies were included to determine if metal ions could be selectively separated and included in a treatment regime for removal and recovery of silver and mercury from the waste solution. Reduction of waste volume was also an important consideration for precipitation of metal ions.

The results indicated that ionic strength considerations dictate overall treatment and recovery efficiency. Silver and mercury ions were removed by ion exchange while iron and chromium uptake did not occur. Highest removal efficiencies were observed for a mercury-specific resin and an anionic resin compared to cationic or mixed resins. Column capacity was severely impacted by the acidic, high strength, waste solution. Additional studies showed that the solution ionic strength and dissolved solids concentration were more important than solution pH in determining ion exchange preference and column capacity. Reuse of column regenerant solutions in the COD test procedure indicated the strength of sulfuric acid was critical in obtaining complete oxidation of a synthetic waste solution.