Alkaline Hydrolysis of Chromium Tanned Leather Scrap Fibers and Anaerobic Biodegradation of the Products

Abstract

Chromium tanned leather wastes fibers are difficult to manage by chemical and biological processes due to the strong bonds established between collagen and chromium. Therefore, it is of great interest to develop treatments that disrupt recalcitrant bonds and may open new perspectives to materials valorization. A temperature and pressure-assisted alkaline hydrolysis method has been studied. The effects of sodium hydroxide concentration, temperature, holding time and leather fibers to solution ratio on organic matrix destruction, chromium dissolution and anaerobic biodegradability of hydrolyzates obtained are reported. The more suitable conditions found are leather fibers treatment at 423 K for 1.5 h with NaOH 4 mol/L solution and solid to liquid (S/L) ratio (w/w) of 0.15 or 0.2. Under these conditions, more than 98 % of the leather and 85 % of chromium were dissolved. The hydrolyzates may be used in the leather process and show anaerobic biodegradability mostly in the range of 20-30 %. This work establishes an alternative route of treatment that promotes fast destruction of chromium tanned leather scrap, and may avoid its landfilling, contributing to recover part of resources contained in leather waste.