Activated charcoal mediated purification of Yellow Sodium Sulphate: a green process to utilize a hazardous by-product of the leather chemical industry

Abstract

Basic Chrome Sulphate (BCS) is an important industrial chemical, which is predominantly used in the leather tanning process. During the production of BCS, huge amounts of non-utilizable, hazardous by-product, Yellow Sodium Sulphate (YSS), are generated which is basically Na₂SO₄ contaminated with ∼1% Na₂Cr₂O₇. Huge accumulation of this YSS has become a matter of concern for BCS manufacturers particularly due to its severe pollution potential. The present study showed that contaminated Cr(VI) could be completely reduced to less toxic Cr(III) when the YSS solution was treated with Activated charcoal at pH ≤ 2. Thereafter, Cr(III) was successfully separated from the solution by precipitating at pH ∼ 12; subsequently 99% pure Na₂SO₄ with 98.5% yield (with respect to YSS) was recovered from the filtrate. A recycling study indicated that the efficiency of activated charcoal for the treatment of Cr(VI) in YSS remained unaffected up to five times of reuse. The purified Na₂SO₄ and the separated Cr(III) residue both may be utilized again for their respective purposes.