Removal of Cadmium (II) Ions from Aqueous Solution Using Zebediela Kaolin, Limpopo Province, South Africa

Abstract

Water is central to the life of human beings and the ecosystem, thus, access to clean and safe water for the overall wellbeing of a nation cannot be over-emphasised. In this study, raw kaolin from Zebediela was used to adsorb cadmium (II) ions from aqueous solution. Mineralogical characterization (X-ray diffractometry, Fourier transform infrared spectrophotometry), morphological characterization (scanning electron microscope-energy dispersive using X-ray) and chemical characterization (X-Ray Fluorescence) were done to determine and quantify the minerals present, their morphologies and the elemental composition of the kaolin sample. The mineralogical analyses revealed that the sample was predominantly made up of kaolinite. Morphological analysis showed that the kaolin sample had well developed kaolinite books and stacks with relatively porous aggregates. Furthermore, chemical analysis demonstrated that the kaolin sample is predominantly composed of silica (SiO2 = 58.39 %), alumina (Al2O3 = 28.04 %) and titanium dioxide (TiO2 = 2.26 %). Batch adsorption experiments were done to investigate the effect of pH, sorbent dose, contact time and metal ion concentration on the removal of cadmium (II) ions from aqueous solution using Zebediela kaolin. An optimum pH of 7 was observed and was used as the working pH for the other adsorption experiments. Increased adsorption was noted at lower sorbent doses (0.25 - 1 g), however, there was a decline in adsorption at higher sorbent doses (1 – 1.5 g). The adsorption process was initially very fast, and equilibrium was reached after 40 minutes. In addition, there was a rise in percentage removal of Cd (II) ions as initial concentration increased which was followed by a decline after equilibrium was attained. Adsorption isotherm and kinetic models illustrated the adsorption of Cd (II) ions onto the Zebediela kaolin which followed Langmuir isotherm and pseudo second order mechanism, respectively. This study, therefore revealed that raw Zebediela kaolin has the potential to be used as an adsorbent of cadmium (II) ions from aqueous solution.