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Recovery of Chromium from Spent Plating Solutions by a Chromyl Chloride Process

by Subbarao L. Guddati,
Thomas M. Holsen,
J. Robert Selman,



Document Type: Proceeding Paper

Part of: Critical Issues in Water and Wastewater Treatment

Abstract:

A novel chromyl chloride process has been investigated for the recovery of hexavalent chromium from spent plating solutions. In this process chromium is converted to chromyl chloride by reacting it with concentrated hydrochloric acid and then separated as a heavy underlayer, or alternatively, extracted into a solvent as follows: H₂CrO₄ + 2 HCl qq CrO₂Cl₂ + 2 H₂O Purified chromyl chloride is then hydrolyzed and the resulting solution dried and chromium trioxide recovered. H₂CrO₄ [+ 2 HCl] qq CrO₃' + H₂O? [+ 2 HCl?] In preliminary experiments more than 98% of the chromium has been separated as chromyl chloride (without using any solvent) from an aqueous solution which originally contained 200 g/L chromic acid. Temperature and reactant concentrations were found to greatly affect the stability and the yield of chromyl chloride respectively. Equilibrium conditions have been identified using a geochemical equilibrium speciation model. A statistical analysis of experimental results has been performed to quantify the effects of various parameters on the yield of chromyl chloride.

Subject Headings: Chloride | Chromium | Thermal analysis | Mathematical models | Solvents | Parameters (statistics) | Equilibrium

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