Adsorption of Heavy Metals from Steel Processing Effluent on Sodium Hydroxide Modified Nigerian Kaolinite

Abstract

This study investigated the quality level of heavy metal-laden effluent discharge (wastewater) from a steel processing plant in Ilorin, Kwara State, Nigeria and the utilization of NaOH treated Nigerian kaolinite clay as low-cost adsorbent for remediation of the effluent. Physicochemical analysis of the wastewater was carried out and the clay adsorbent was characterized using X-Ray Diffractometry (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy coupled with Electron Dispersive Spectroscopy (SEM/EDS). From the results obtained, XRD reflection peaks of the 63 μm fractions obtained after purification revealed the clay as kaolin. FTIR absorption bands at 3689.64 and 3619.67 cm^-1 represent surface -OH stretching of the octahedral and inner -OH between the tetrahedral and octahedral sheets. The EDS spectra of the kaolin following treatment with NaOH showed an increase in silica and alumina content from 15.92% to 24.81% and 13.36% to 15.58% respectively. Physicochemical parameters of the raw effluents were above the recommended limits set by National Environmental Standards and Regulations Enforcement Agency (NESREA) of Nigeria for industrial discharge. The metal ion concentrations were 309.0, 20.50, 40.40 and 10.90 mg/L for Fe²⁺, Pb²⁺, Zn²⁺ and Cr⁶⁺ ions respectively. Successive reuse of the treated clay in four adsorption cycles recorded removal efficiency of 99.77, 99.95, 98.91 and 99.91% for Fe²⁺, Pb²⁺, Zn²⁺ and Cr⁶⁺ ions respectively and decrease in the physicochemical parameters to permissible level. The Water Quality and Metal Pollution Indices (WQI/MPI) of the effluent after adsorption showed the treated wastewater fulfilled environmental requirement for industrial discharge. The study concluded that NaOH treated clay offered potential for remediation of heavy metal-laden industrial effluents.

Keywords: Adsorption, Clay, Effluents, Heavy metals, Steel