Abstract

It has been shown that lime-sulphide unhairing liquors can be recycled more than 20 times, perhaps indefinitely. The only treatments necessary before re-use are temperature adjustment and replenishment with lime, sulphide and water, preferably as washings from the previous unhairing. For 20 cycles the average consumptions based on green-hide weight were 1.5% lime, 2.2% sodium sulphide and 40-55% water; the higher water usage occurred when solids were removed before each use, a procedure which has advantages. Salted hides can be unhaired satisfactorily in re-used liquors if they first have an adequate soak to reduce their salt content. Recycling of lime liquors has no apparent effect on leather quality or yield even though, when compared with conventional unhairing, it results in a decrease in hide swelling and an uptake of proteins or their degradation products. This method could be developed as a no-effluent system of unhairing if liquors can be cycled indefinitely or, after a certain number of cycles, can be utilised as a source of protein. Even if the liquors are discharged after 20 uses there can be overall a 20-fold reduction in water consumption and effluent sulphide, and a seven-fold reduction in effluent lime and protein.