Recycling of Unhairing –Liming Solution in Leather Industry

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Kamal Eldin Abu EL Fatah, Mohamed
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University of Khartoum
This work was undertaken to utilize the used sulphide-lime unhairing liquor in order to reduce these caustic chemicals in the effluent, save the fresh water and minimize the cost of the liming processes. The chemical analyses of the used liquor indicated that a considerable amount of sulphide (2100 mg/l) was present. As the lime has a limited solubility of 0.125%, undissolved lime always remains in the solution. This undissolved lime will dissolve when its equilibrium solubility is disturbed by recycling. It was observed that the unhairing power of the old lime liquor was more effective than the fresh liquor. This is due to the fact that the disulphide link of the hair is broken and dissolved during the liming process and consequently the sulphide content will build up through recycling. Wet salted sheepskins were processed with the normal recipe and the once-used lime solution was analyzed for lime and sulphide content, its composition was leveled by a make-up fresh lime-sulphide liquor and recycled. The same was repeated for seven cycles, each time the recycling flow rate was leveled 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 was normal, soft, of good tensile strength, full and of good quality. This process is recommended to be applied in all tanneries. Its application is simple. It requires a collection pit, a filter, a pump and a pipe line to and from the drums.
pit;filter;pump;Leather Industry;water;sodium