Abstract

Trials have been performed on both laboratory and commercial scales to determine the feasibility of re-cycling of used chrome liquors in the hide tanning industry. Re-cycling has been successfully carried out using commercially available chrome-tanning powders and concentrated liquors, adopting a system in which the chrome liquor was reused for successive tanning runs after adjustment of the float and Cr₂O₃ content to the desired values; the amount of Na₂CO₃ normally used for basification was reduced in proportion to the amount of added chrome reagent. In this way, chrome liquors were reused for up to 13 cycles and an equilibrium was established in the liquors after no more than 3 cycles, such that the initial and final pH of the liquor and the residual concentrations of Cr, NaCl, and Na₂SO₄ remained constant in successive cycles; it appeared that the liquor could be reused indefinitely. The additional Na₂SO₄, which is taken up by the leather during tanning was shown to be removed during subsequent wet-processing in the commercial trials. There was no significant effect produced by re-cycling on either the subjective or physical properties of the resultant leather. Re-cycling has been shown to be capable of saving more than 25% in the cost of chrome-tanning reagents and has the added advantage of reducing the amount of chromium discharged in the tannery effluent to a minimum.