Oxyanion removal and recovery using silica polyamine composites.

Modified silica polyamine composites (SPC) made from silanized amorphous nano-porous silica gel and polyamines have been used for the selective removal and recovery of oxyanions of heavy metals such as As and Se in the presence of excess sulfate. The SPCs were functionalized with phosphorus acid using the Mannich reaction, resulting in a phosphonic acid modified composite (BPAP) on which Zr(IV) was immobilized by complexation to the phosphonic acid group. Tungstate and molybdate anions strongly adsorbed on the ZrBPAP composite over a broad pH range of 2–10. The sorption mechanism is believed to be a complexation between the tungstate and/or molybdate and Zr(IV) immobilized-phosphonic acid complex of BPAP. However, complete regeneration of the composite was not successful. A second composite modeled after polymer based adsorbents containing tetraalkyl ammonium groups was synthesized by exhaustive alkylation of the poly(allylamine) composite, BP-1. This composite, BPQAM, composite shows a higher selectivity for tungstate over molybdate at a pH of 6 (WO42 −/MoO42 − = 3/1). Using 2MH2SO4 as the strip solution provided selectivity for molybdate (~ 90% purity). The significance of the observed selectivity is discussed in terms of the chemical properties of the oxyanion and the nature of the interactions with the immobilized metal site. Attempts to separate molybdate from nickel and vanadium using solution concentrations modeled after a contaminated creek in Western Australia are also reported. The use of ZrBPAP and the aminoacetate modified SPC, WP2, resulted in the efficient separation of molybdate but the separation of the nickel from vanadium proved more difficult. [Copyright &y& Elsevier]