Adsorption of tannic and gallic acids on a new polymeric adsorbent and the effect of Cu(II) on their removal.

In this paper, a new polymeric adsorbent WJN-09 for adsorbing and removing tannic and gallic acids from water was prepared, and its adsorption capacities for these two natural organic acids were tested by using the commercial resins XAD-7, XAD-4 and NDA-7 as references. The adsorption capacities of WJN-09 for tannic and gallic acids were higher than those of XAD-4, XAD-7 and NDA-7 at 303 K, which may be attributed to its amino function groups, pore structure and Zeta potential. The adsorption enthalpy changes DeltaH exhibited that the adsorption of tannic acid by WJN-09 was a chemical and endothermic process. Furthermore, batch kinetic studies indicated that the tannic acid adsorbed to WJN-09 could be fitted well by both pseudo-first-order and pseudo-second-order adsorption equations, but the intra-particle diffusion played a dominant role in the adsorption of gallic acid. Changes of resin's Zeta potential and acids' average molecular size were observed when Cu(II) was added in solutions, which could explain the significant increase in WJN-09's adsorption capacity for tannic and gallic acids in the presence of Cu(II).