The tanning industry is one of the oldest industries in the world and is known for the production of a wide variety of toxic waste (aqueous and solid) containing chromium salts and other heavy metals. Solid waste is produced during the conversion of putrescible collagen fibres into finished non-putrescible leather products. In this process, the use of a variety of chemicals during the fleshing or trimming phases, results in different hazardous waste, such as wet blue leather, crust leather, chrome shaving, finished leather off-cuts, and unusable chrome spilt.
In the present study, we deal with the treatment of these hazardous leather sludge and the recovery of heavy metals contained in them. The leather sludge was pyrolyzed in a torch plasma reactor at a temperature of 1,400-1,500 °C producing an inert solid residue. However, the high temperatures involved induce the volatilization of some metals, which condense to form hazardous dusts (21.8% Zn, 0.70% Cr, 4,080 ppm Pb and 123 ppm Cd) that have to be properly dealt with. Numerous leaching tests have been conducted to maximize the amount of the individual components solubilized from the powder. Then, different treatment strategies have been combined for the recovery of the main metals: precipitation for Pb and Zn, and adsorption on chitosan for Cd.