Optimization of kinetic data for two-stage batch adsorption of Pb(II) ions onto tripolyphosphate-modified kaolinite clay

BACKGROUND: Most adsorption studies consider only the adsorption of pollutants onto low cost adsorbents without considering how equilibrium and kinetic data can be optimized for the proper design of adsorption systems. This study considers the optimization of kinetic data obtained for the removal of Pb(II) from aqueous solution by a tripolyphosphate modified kaolinite clay adsorbent. RESULTS: Modification of kaolinite clay with pentasodium tripolyphosphate increases its cation adsorption capacity (CEC) and specific surface area (SSA) from 7.81 to 78.9 meq (100 g)(-1) and 10.56 to 13.2 m(2) g(-1) respectively. X-ray diffraction patterns for both unmodified and tripolyphosphate-modified kaolinite clay suggest the modification is effective on the surface of the clay mineral. Kinetic data from the batch adsorption of Pb(II) onto the tripolyphosphate-modified kaolinite clay adsorbent were optimized to a two-stage batch adsorption of Pb(II) using the pseudo-second-order kinetic model. Mathematical model equations were developed to predict the minimum operating time for the adsorption of Pb(II). Results obtained suggest that increasing temperature and decreasing percentage Pb(II) removal by the adsorbent enhanced operating time of the adsorption process. The use of two-stage batch adsorption reduces contact time to 6.7 min from 300 min in the single-stage batch adsorption process for the adsorption of 2.5 m(3) of 500 mg L-1 Pb(II) under the same operating conditions. CONCLUSION: Results show the potential of a tripolyphosphate-modified kaolinite clay for the adsorption of Pb(II) from aqueous solution and the improved efficiency of a two-stage batch adsorption process for the adsorption of Pb(II) even at increased temperature. (C) 2009 Society of Chemical Industry