Gelatin processing from chrome tanned trimmings and shavings

Abstract

The chromium toxicity of solid waste created by the tannery industries is a subject of worldwide concern. Solid tannery waste is high in protein, yet it is dumped in the environment also putting human health at risk. Chromium exists in different oxidation states, having Cr3+ and Cr6+ being the most prevalent and stable in nature. Trivalent chromium is considered vital for human health in trace amounts, whereas Cr6+ is a recognized carcinogen and hazardous compound. The current study shows that utilizing a combined hydrolysis process, industrial grade gelatin can be extracted from chrome-tanned leather trimmings and shavings by dechroming the leather and used in a variety of industrial applications. The isolated shavings gelatin has 1.1 mg/kg chromium and trimmings gelatin have 7.2 mg/kg chromium that were below the standard limit 10 mg/kg making it suitable for use as industrial grade gelatin. Hydrolysis of chrome tanned leather waste was tested under atmospheric pressure and alkaline-acidic conditions to obtain dechromed leather for gelatin extraction. To obtain the required dechroming degree, four steps of combined hydrolysis operations were performed. Dose studies, time effects, and temperature effects were applied to improve various steps. Chemical analysis techniques and experimental procedures (AAS, FTIR, Viscosity test, SEM, XRF, TCLP) were utilized to characterize dechromed leather, gelatin extracts, dry gelatin and chrome cakes. The SEM analysis helped to ensure the dechromed condition of tanned leather waste and the FTIR analysis evaluated the chemical bonding of the dechromed leather trimmings and shavings. Gelatin samples recovered in this study met a variety of gelatinous properties including 99.95% and 99.99% Chromium free level with 68% and 64% aqueous yield, had no Pb, were better at gel formation, had a suitable viscosity and contained low levels of Cd, Zn and other heavy metals after dechroming optimization.