Enhanced Heavy Metal Removal from Wastewater Produced by Chemical Analysis Laboratory Using Calcium Oxide Precipitation: pH Improvement and Characterization of Precipitated Phases

Abstract

This article presents research results on the precipitation of heavy metals: Aluminum (Al), arsenic (As), cadmium (Cd), zinc (Zn), iron (Fe), chromium (Cr), copper (Cu), nickel (Ni), vanadium (V), and molybdenum (Mo) from wastewater generated in mining chemical analysis laboratory. Calcium oxide was used as the precipitating agent. The efficiency of heavy metal removal was achieved by increasing the dosage of precipitating reagent (8-28 g/L). Efficiencies greater than 90% are achieved. The efficiency of chemical precipitation depends on the pH of the process. Over a wide pH range from 6-11, the removal efficiency of zinc, iron, cadmium, and arsenic were approximately 99.9%. The optimum pH range for the removal of most elements was found to be between 8 and 11, where the removal efficiency of heavy metal ions reached up to 99%. Furthermore, X-ray diffraction results indicated that the metals in the wastewater precipitated in various forms as mentioned in Table 7, and not just as hydroxides, due to the presence of different ions in the solution.