Adsorption of Copper (II), Cobalt (II) and Nickel (II) on Minim-Martap Bauxite, Cameroon: A Kinetic and Equilibrium based Study Approach

Abstract

The freshwater that is available for use in drinking, agriculture, industry, sanitation, food, recreation and transportation is <1% of the total water on earth. Unfortunately, some 2 million tons of waste containing heavy metals, which are persistent in the environment, toxic in trace amounts, ability to induce severe oxidative stress and bioaccumulate in organisms are disposed of within these scarce receiving waters per day without treatmet. Therefore this study is aimed at investigating the influence of different parameters on the kinetics of Cu (II), Co (II) and Ni (II) ions adsorption on Cameroon bauxite, a local adsorbent. The bauxite was characterized using X-ray diffraction (XRD), Electric conductivity (EC), and Fourier transform infrared spectroscopy (FTIR) techniques. The influence of particles size, stirring speed, contact time, pH and temperature on the kinetics of the removal process was studied. The experiments results show that Cu (II), Co (II) and Ni (II) were significantly retained at a pH value of 5, 8 and 9 respectively, with corresponding removal efficiency of 97% for Cu (II), 99% for Co (II) and the 98% for Ni (II) 98%.  Furthermore, the adsorption increases with decreasing particles size and increasing stiring speed. The Langmuir separation factor SL, shows a more favourable adsorption of the three heavy metals on bauxite The Temkin constant, BT, related to the heat of sorption for three metal ions were all less than 8 kJmol-1, indicating a physical removal mechanism. The adsorption of Cu (II) and Ni (II) on bauxite is endothermic while adsorption of Co (II) is exothermic. Cobalt removal was faster with pseudo-second order rate constant K2 (μmolg1min-1) of 0.861 compared to, 0.316 for both Cu (II) and Ni (II), and more favourable as given by the Langmuir equilibrium constant, KL(Lmmol-1) of 0.032 for cobalt, 0.007 for Nickel and 0.0011 for copper. Results of this study shows that different heavy metals simultaneously present in wastewater can effectively be removed with bauxite, particularly Cameroonian bauxite, a low cost material with over 95% efficiency for each metal.