Silver recovery from waste X-ray films using alkaline protease from aspergillus wentii and its antibacterial studies

Abstract

Fungal proteases are of particular importance in food, pharmaceuticals, waste management and decomposing gelatin coating of X-rays for silver recovery. Alkaline protease from Aspergillus wentii was used to strip the silver from waste X-ray films. The enzyme worked efficiently at pH 8.0 and gelatin layer was completely hydrolyzed at 50°C within 20 min. The slurry containing silver was dried in an oven overnight and subjected for smelting to obtain crude silver ash. This ash was converted to its respective salts-silver nitrate and silver chloride. Silver, 1.94% was obtained from waste X-ray films. Generally, used X-ray films contain 1.5-2.0% of silver by weight. The metal impurities (Cu, Mo, Co, Zn, Cr, Ni, Mn, Mg etc.) in the recovered silver were determined using mass spectroscopic method. Further, the antibacterial activity of these silver compounds was also tested. Antibacterial results with recovered silver nitrate showed encouraging results.