Abstract

A simple recycling system was used in the preparation of wet-blue leathers, with the residual chrome tanning liquor being replenished with acid and salt before being used for pickling the next batch of bated hide. Chrome tanning powder was added to the liquor on completion of pickling, to give a total offer of the required amount, with the wet blues thus produced being compared to those prepared by a conventional process. Two series of experiments were carried out to give either “low chrome” (1.8% Cr₂O₃, dry weight basis) or “normal chrome” (2.5% Cr₂O₃) wet blues. Within each series, the initial properties and storage behaviour were unaffected by the use of recycled, rather than fresh, chrome tanning liquors. Low chrome and normal chrome samples displayed similar stability under the storage conditions used, with neither set showing deterioration of the measured properties after the prescribed holding time. Colour measurements on the wet-blues before and after storage showed that the leathers from recycled liquors did not undergo changes greater than those of the control samples, and that between-batch colour differences should not be a problem in practical application. Wastage of chrome tanning salt, and hence concentration of chrome in the effluent, was reduced by approximately 90% by recycling the residual tanning liquor, rather than discarding it as in a normal process. Overall consumption of chrome tanning salt was reduced by 13% (low chrome series) and by 24% (normal chrome series) compared to that of similar, conventional processes.