Simultaneous adsorption of Ni(II) and Mn(II) ions from aqueous solution unto a Nigerian kaolinite clay

An unmodified Nigerian kaolinite clay (UAK) was utilized as a low-cost adsorbent for the removal of Ni(II) and Mn(II) ions from a binary solution of both metal ions. Batch adsorption methodology was used to evaluate the effect of solution pH, initial metal ion concentration, sorbent dose, particle size, contact time, temperature and ligand on adsorption. FTIR, XRD and SEM analysis were used to characterize the adsorbent. The equilibrium isotherm data were analyzed using the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich (D–R) isotherm model. The Freundlich isotherm model provided the best fit to the experimental data for both metal ions as indicated by the values of the regression coefficient. The Langmuir monolayer maximum adsorption capacities for Ni(II) and Mn(II) ions are 166.67 mg/g and 111.11 mg/g, respectively. The kinetic data were analyzed using the pseudo-first order, pseudo-second order equations, the Elovich equation and intraparticle diffusion rate equation. The Elovich equation gave the best fit to the experimental data for both metal ions. The presence of intraparticle diffusion mechanism was indicated, although it was not the sole rate determining step. Thermodynamic studies indicated an endothermic, spontaneous and a physisorption process between both metal ions and UAK. The results showed that the kaolinite can be utilized as a low-cost adsorbent for the removal of Ni(II) and Mn(II) ions from solution.