The recovery of chromium from galvanic wastewater sludge

The recovery of chromium from prepared (mixed and co-precipitated) sludge, generated during the neutralisation process of galvanic wastewater was investigated. Studied sludge contained hydroxide and oxide mixtures of various metals including chromium(III) hydroxide. The recovery procedure included precipitation of hydroxides and their dissolution, oxidation of chromium(III) to chromium(VI) and final extraction and reextraction of chromium(VI). The recovery of chromium from the mixed and co-precipitated sludge was limited by the sludge solubility in the sodium hydroxide solution. The yield of chromium recovery did not exceed 36%, which suggests that sludge should not be mixed after neutralisation [1, 2]. The recovery of chromium from the co-precipitated sludge was about 18% of its initial amount. This group of sludges should be managed according to the method proposed in papers [3, 4].