Chromium recovery from tannery sludge by bioleaching and its reuse in tanning process

Abstract

Bioleaching has been demonstrated as a feasible and effective technology for removing Cr(III) from tannery sludge, but the recovery of bioleachate derived from tannery sludge by bioleaching is rarely reported. The purpose of this study was therefore to figure out the components of bioleachate and develop a chromium-iron tanning agent using the bioleachate and reuse it in tanning process. Component analysis indicated that the bioleachate contained high concentrations of Cr and Fe, as well as small quantities of other elements. The dissolved organic matter in the bioleachate was detected to be less than 1000 mg/L, which was mainly composed of polysaccharide, aliphatic or aromatic carboxylic acid compounds. A chromium-iron tanning agent was then prepared using the bioleachate, iron and chromium salts in a suitable ligand environment, and reused for tanning. In the tanning experiments, the pickled pigskins were tanned with this prepared tanning agent and the results indicated that chromium-iron tanned crust leather presented comparable physical and mechanical properties as well as air permeability when compared with conventional chromium tanned crust leather, but the thermal shrinkage temperature was about 4 °C lower than that of the chromium tanned crust leather. Therefore, this study provides not only a reuse route for tannery sludge bioleachate but also a clean tanning agent for leather processing.