Proceeding for waste treatment of chemical oxygen demand analysis

Abstract

Analysis of the chemical oxygen demand (COD) is commonly employed in environmental control and effluent analysis. The COD analysis generates an extremely acid residue containing heavy metals such as silver, chromium, and mercury. Therefore, disposal of this residue without any previous treatment is forbidden. Some proposed treatments lead to the formation of solid residues containing chromium and mercury, which should thuerefore be disposed of in suitable industrial wasteland, which is expensive. Besides that, there is formation of sulfidric acid, which is toxic. The present work reports on a method that allows recovery of silver and mercury, but does not lead to the formation of H2S. The COD residue is treated with sodium chloride to yield silver precipitation from the solution. After removal of silver chloride, metallic zinc is added, leading to mercury reduction and the formation of an amalgam. The residue is then neutralized with sodium hydroxide, leading to the separation of chromium in its hydroxide form. A reduction of 99.99%, 99.99%, and 99.25% in the concentrations of mercury, silver, and chromium can be observed. Keywords: waste, COD, mercury, waste management.