Extraction and recovery of chromium from electroplating sludge

This work reports a study of the extraction and recovery of chromium from the wastes (class I dangerous) generated by a galvanic manufacturer. Commercial HCl at room temperature was employed, and the conditions of the extraction process were optimized according to a sequential experimental design, which also included the acid concentration and contact time as variables. The best extraction conditions (80% v/v; 30 min; 97.6% Cr) for the chromic sludge were chosen in order to make the recovery process economically feasible. After each extraction, the residue was submitted to leaching essays, to assess environmental risks. It was found that sludge could be characterized as no longer dangerous. In the recovery study, a simple and low-cost technique was evaluated for selectivity based on an oxidation step with hydrogen peroxide. A 23 factorial design to assess the influence of oxidation time (min), temperature (°C) and peroxide amount (mol/L) was employed. The best conditions, yielding a chromium recovery of about 92%, were a time of 60 min, a temperature of 60 °C and 2.1 mol/L peroxide. Additional essays revealed that the same result could be obtained with more economic conditions (40 min, 1.4 mol/L peroxide and 60 °C). This technique proved not only effective in comparison with existing alternatives, but also low costing.