Abstract
Abstract Copper, chromium, nickel, and zinc are frequently found in high concentrations in industrial waste water and can be removed by precipitation. Typical precipitation processes do not allow each metal to be precipitated separately, and hence selective metal recovery is not possible. It is desirable to recover each metal separately to allow recycling of metals and to satisfy waste minimization requirements. Chelation can be utilized to selectively remove metals from aqueous solution, since chelation can be controlled by pH. A study has been undertaken to determine the pH optima for removal of copper, nickel, and zinc by chelation with dithiozone. A similar study will be initiated to determine the pH optimum for removal of chromium by chelation with Aliquat 336, a high molecular weight amine. Percent extraction of metal was measured as a function of metal solution pH. Two dithiozone solvents, chloroform and carbon tetrachloride, were investigated. The preliminary results indicate that the optimum pH for extraction of copper with dithiozone—chloroform solution is near pH 3. As a solvent, chloroform allows more copper extraction than carbon tetrachloride. Carbon tetrachloride was rejected as a solvent due to the low solubility of dithiozone in carbon tetrachloride. The chelation reaction must be performed in a pH-buffered solution to maintain a constant pH. The results of this study will be utilized to design a process to selectively recover metals from industrial waste water.
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