Chromium(III) salts recovery process from tannery wastewaters

Abstract

Chromium(III) salts are the most widely used chemicals for tanning processes [1], but only 60% of the total chromium salt reacts with the hides. Therefore, about 40% of the chromium amount remains in the solid and liquid wastes (especially spent tanning solutions). The presence of chromium(III) and salts in the sludges of both the wastewater biological treatment plants or the chemical plants for recycling spent tanning liquors, represents an inconvenience for the safe reuse of these sludges and a cost forming factor for their disposal. Among the several proposed methods for chromium recovery [1–6], lime or sodium hydroxide precipitation and filter-pressing of the chromium hydroxide is the usual way to recover chromium salts from spent process solutions or from leaching solutions of residues of hides. However, usually the chromium salts quality must be improved for their reuse in tanning processes [7]. The integration of membranes in the treatment process for chromium recovery reduces the environmental impact, favours the reuse of both the protein residue and the biological plant sludges, reduces the consumption of chemicals and decreases the costs of waste disposal.