Optimization of Leaching Recovery of Zinc, Iron and Manganese from Selected Solid Waste Ashes in Zaria, Kaduna State, Nigeria

The increasing environmental burden of toxic heavy metal-concentrated ash from solid waste incineration, particularly from burnt tires and contraband drugs, poses significant challenges for waste management and resource recovery. This study aims to optimize the leaching recovery of zinc, iron, and manganese from these solid waste ashes in Zaria, Kaduna State, Nigeria, using Response Surface Methodology (RSM). The ashes were analyzed for their metal content using atomic absorption spectroscopy (AAS), with additional characterization by X-ray diffraction (XRD) and X-ray fluorescence (XRF). Among the leaching agents tested, hydrochloric acid (HCl) exhibited the highest efficiency, particularly under optimized conditions determined through central composite design (CCD). The optimal conditions for leaching from burnt tire ash were found to be 2.97 mol/l acid concentration, 97.7 minutes leaching time, and 68.85°C temperature, yielding recoveries of 32,009 mg/kg zinc, 4,553 mg/kg iron, and 137 mg/kg manganese. For contraband drug ash, the optimal conditions were 2.83 mol/l acid concentration, 97.7 minutes leaching time, and 68.85°C temperature, resulting in recoveries of 70.55 mg/kg zinc, 5,771 mg/kg iron, and 676 mg/kg manganese. This study successfully developed a multiple linear regression model to express the relationship between the leaching parameters and metal recovery, providing a reliable and sustainable method for metal recovery from solid waste ashes. The findings offer valuable insights into waste management practices, contributing to the circular economy and reducing the environmental impact of waste disposal.