Abstract

This study concerns the re-cycling of used sulphide-lime unhairing liquors in order to reduce pollution, save fresh water and minimize the cost of the liming process. Chemical analyses of the used liquor indicated that a considerable amount of sulphide (2100 mg/l) was present. As lime has a limited solubility (0.125%), un-dissolved lime is always present. This un-dissolved lime will dissolve when its equilibrium solubility is disturbed by recycling. It has been observed that the unhairing power of an old lime liquor was greater than that of a fresh liquor.

Wet salted sheepskins were processed according to the normal recipe and the once-used lime solution was analysed for lime and sulphide content, its composition was adjusted with a make-up fresh lime-sulphide liquor and recycled. The same was repeated for eight cycles, each time the recycled liquor analyses were adjusted with a fresh make-up.

The average savings were 65% sodium sulphide, 33% lime and 90% water. The limed-unhaired pelts from each cycle were further processed through tannage, retannage, drying, and finishing. The physical and chemical properties were satisfactory. The leather produced is normal, soft, of good tensile strength, full and of good quality.

We recommended this process to all tanneries, its application is simple. It requires a collection pit, a filter, a pump and a pipeline to and from the drums.