Keywords: COD, chemical oxygen demand, laboratory waste, waste management, chemistry laboratories, ionic metals, wastewater treatment, toxic metals, metal removal, chromium, mercury, silver
Removal of ionic metals from wastewaters of COD determinations
Chemical Oxygen Demand (COD) determinations generate highly disruptive waste streams with chromium, mercury and silver. These should follow specific waste management approaches in search of environmental and economical benefits, for which this work reports simple chemical procedures allowing toxic metal removal. Chromium(VI) is reduced to chromium(III) and total chromium is precipitated with sodium hydroxide. Silver is precipitated with chloride and mercury with iodide. Enhanced reduction of mercury levels is achieved by adsorption to activated carbon. Treated wastewaters have Cr, Ag and Hg levels of 225, 410 and 2.25 ppb, respectively, and the purity of the produced solids is always >80%.