Abstract

A method for the re-cycling of chrome-tanning liquors is proposed in which the spent liquor is used as a basis for preparation of the pickle liquor for the following pack of hides to be tanned. This method, which can be used with a short pickling time, is considered to be preferable to the previously proposed re-cycling method based on an equilibrium pickle system. In the present work, the only adjustments made to the spent liquor were first the addition of the normal amount of acid used in pickling and then, after the desired pickling time, the addition of the calculated amount of chrome reagent necessary to give the normally required total Cr₂O₃ content. Two pickling systems were tested in which either formate was omitted or was added before pickling with the pickle acid but in an amount reduced in proportion to the amount of added chrome reagent. Both systems were successfully operated over 12 cycles and it is considered that this method is feasible for commercial application.