Detoxification process for a ferric chloride etching waste
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The purpose of this study was to determine an economically feasible method for treating a ferric chloride etching solution contaminated with nickel and chromium. The major factors in determining the optimum method of treatment for the etching waste were effectiveness in the conversion of the liquid waste to a solid form and in the conversion of the hazardous waste to a nonhazardous form. Ferric chloride etching waste is a listed hazardous waste according to state of Missouri regulations; however, federal regulations do not list etching solutions as hazardous wastes. A number of treatment methods were tested to determine the most effective method of neutralizing the waste. Drying tests were conducted to study the possibility of removing the water from the waste and thereby producing a solid. Aeration tests were also performed in an effort to learn if the metals could be precipitated as crystalline oxides or hydroxides. Neutralization (hydroxide precipitation) tests were also conducted using three bases, sodium hydroxide, calcium hydroxide, and water treatment plant sludge. The most effective and economic method of treating the ferric chloride etching waste is with hydrated lime. Approximately 0.7 kilogram of calcium hydroxide per liter of waste is necessary to convert the liquid waste stream to a hydroxide sludge. This sludge was evaluated by the standard extraction procedure (EP) toxicity test for hazardous levels of chromium and nickel. The Cr and Ni leachate concentrations are at part per billion levels, thus the sludge qualifies for delistment as a hazardous waste. For this purpose, a practical treatment process has been designed and developed.
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This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License.