Development of valonia and quebracho tannin resins for the adsorption of precious and heavy metals

In this study, tannin resins were prepared by reactions of hydrolysable (Valonia) and condensed tannins (Quebracho) with formaldehyde. The adsorption of heavy and precious metal ions (Cr6+, Cu2+, Pb2+, Cd2+, Ni2+, Au3+ and Ag+) from aqueous solutions was studied using these resins and recovery of adsorbed heavy and precious metal ions was investigated. In the adsorption studies; particle size, agitation rate, initial pH, temperature and initial metal concentration parameters were changed. So, the optimum conditions for maximum metal adsorption were determined. Selective adsorption of metal ions from multiple metal systems was also investigated. The time for attaining adsorption equilibrium of metals 180 min. BET surface areas and zeta potentials of prepared tannin resins were measured, and their SEM photographs and IR spectra were taken. The optimal pH for the adsorption of Cr6+, Cu2+, Pb2+, Cd2+, Ni2+, Au3+ and Ag+ ions was found to be pH:5, pH:7, pH:5, pH:4, pH:4, pH:2 and pH:5, respectively. It was found that agitation rate has not very much effect on adsorption. Conformity of experimental results to different adsorption isotherms were examined using the Langmuir, Freundlich, Dubinin-Raduskevich and Temkin isotherm equations, and properties of isotherms were explained. The adsorption kinetic data of the Cr6+, Cu2+, Pb2+, Cd2+, Ni2+, Au3+ ve Ag+ metal ions are well fitted by the pseudo-second-order model. When the isotherm constants were examined, it was seen that adsorption process fits Langmuir model for Cd2+, Ag+, Cu2+, Cr6+, Pb2+ and Au3+ ions, Freundlich model for Ni2+ very well. In addition, desorption studies of Cr6+, Cu2+, Pb2+, Cd2+, Ni2+, Au3+ and Ag+ ions were also performed.