Elimination of Cu (II) and Zn (II) ions in mono-element and the bi-element aqueous solutions by adsorption on natural clay of Bikougou (Gabon)

Abstract

This work was undertaken to evaluate the potential of the clay of Bikougou to remove copper (II) and zinc (II) ions (Cu²⁺ and Zn²⁺) in  mono-element and binary aqueous solutions. The experiments were
carried out by employing the batch technique through the variations of pH, clay mass, ionic strength, concentration in metal, temperature and contact time. The quantity of ions coppers (II) or zinc (II) adsorbed increases when the pH increases up to pH=5 and beyond, there is precipitation of the metal hydroxides; the quantity of metal ions adsorbed decreases when the clay mass or the ionic force increases. The average adsorption energies of copper (II) and zinc (II) ions are indicative of endothermic reactions. The modeling of the experimental results is better achieved by application of
Freundlich adsorption isotherm and Langmuir adsorption isotherm  concerning the adsorption of Cu (II) ions with correlation coefficients of 0.98 and 0.93, respectively. The Langmuir adsorption isotherm and Freundlich adsorption isotherm are all applicable for describing the experimental result of isotherm adsorption of Zn (II) ions with correlation coefficient respectively, 0.99 and 0.96. The kinetic which shows more clearly the observed phenomenon is that of the pseudo-second order with the coefficients of correlation close to 0.99. In the binary system copper (II) - zinc (II) the adsorption of copper (II) is favoured compared to that of zinc (II). All these results have shown efficiency as adsorbent of the
clay from Bikougou to eliminate Cu2+and zinc (II) ions in mono-element or bi-element aqueous solutions. In the mono-element solution, the adsorption rate varied from 98.59 to 94.41% for the Cu(II) ions and from 86.76 to 53.80% for Zn (II) ions.

Key words: System of bi-element, copper and zinc, adsorption, technique in batch, natural clay mixture.