An integrated membrane process for the recovery of chromium salts from tannery effluents

The aim of this study was to identify a technically viable method for recovering chromium salts from exhausted tanning liquors. At this purpose an integrated process based on a preliminary ultrafiltration (UF) treatment of the exhausted liquor followed by a nanofiltration (NF) process of the UF permeate was studied on laboratory scale. The UF process permitted to obtain a remarkable reduction of suspended solids and fat substances. A tanning solution with a chromium (III) concentration of about 10 g/l was obtained in the NF process. The NF retentate seems to guarantee improved characteristics of tanned skins with respect the control group treated with conventional chromium solutions. The process permitted also the reuse of the NF permeate in the pickling step on the bases of its high content of chlorides. The proposed process permits to rationalize the tanning cycle of the leather industry through a simplification of the cleaning-up process of wastewaters, easy reuse of sludges, saving of chemicals and water.