Processing of chrome-tanned solid waste generated in the leather industry:Recovery of proteins and synthesis of a pigment for paint

Between the beginning of the tanning of the skins and the delivery of finis hed leather articles, there is a series of operations that produce a signif icant quantity of waste. Unfortunately, this waste is only very little reus ed. Environmental concerns and escalating landfill costs have prompted envi ronmentalists, scientists and research people to look for ways to convert t his waste material into more valuable co-products. The objectives of this study are to: evaluate the quantity of wastes genera ted by the operations involved in the transformation of hides into leather, and revalue the most significant category of tanned wastes, namely chrome shavings and tanned splits. The quantitative study of solid waste showed that the tanning industry prod uces a high percentage of waste (about 38 percent of the weight of salted h ides). The alkaline digestion of tanned waste with calcium hydroxide allows the separation of the proteins and the metallic salts. The proteins are in the aqueous phase and the metallic salts in the solid phase. Solid protein s are recovered after lyophilization of the liquid. The solid residue is in cinerated under precise conditions of temperature with a large initial exes s of oxygen in order to oxidize the trivalent chromium and transform them i nto hexavalent state. The dissolution of recovered ash by a dilute solution of nitric acid allows regeneration of a concentrated bichromate solution w hose chromium is recovered in the form of solid yellow chromate by the reac tions of complexation and precipitation using a solution of lead(II) nitrat e. The crystal structure of the precipitate was identified by x-ray diffrac tion.