Development of cost-effective and eco-friendly adsorbent by direct physical activation of Tanzanian Malangali kaolinite for efficient removal of heavy metals

Abstract

The occurrence, toxicity and hazardous nature of heavy metals have prompted researchers to search for affordable and efficient adsorbents for their removal from the environment. Malangali kaolin clay is an abundant and eco-friendly local adsorbent material which can offer sustainable and cost-effective solution towards heavy metal remediation. Raw kaolin clay has the ability to scavenge heavy metals by improvement to its surface chemistry and adsorption capacity through modification. In this study, the feasibility of physically activated Tanzanian Malangali kaolin clay to sequester cobalt and cadmium ions from simulated wastewater was examined under batch process. The physical activation of pristine kaolin clay was carried out by thermal treatment at 300 °C to influence its adsorption efficiency and physicochemical properties. The clay sample was characterized by Fourier Transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray fluorescence (XRF), Nitrogen adsorption–desorption and chemical analysis by atomic absorption spectrometer (AAS). After thermal treatment of the pristine kaolinite, the specific pore volume and surface area amplified significantly from 0.454 − 0.813 cc/g and 78.69–83.046 m2/g, respectively. The heavy metal removal efficiency of thermally activated Malangali kaolinite (TAMK) was evaluated by investigating cobalt (Co2+) and cadmium (Cd2+) ions as potential water pollutants. The results obtained from batch experiments showed the elimination of heavy metal ions is greatly influenced by the initial concentration, adsorbent amount, contact time and solution pH. Adsorption isotherm studies revealed that Langmuir isotherm (R2 = 0.988 for Cd2+ and 0.979 for Co2+) presented the best fit to the equilibrium data than Freundlich isotherm (R2 = 0.965 for Cd2+ and 0.953 for Co2+) with cadmium ions being favourably adsorbed on TAMK compared to cobalt ions. Owing to improved surface area and porosity characteristics, TAMK displayed higher removal efficiency for both Co2+ and Cd2+ ions in simulated polluted water.