Competitive sorption of arsenate and phosphate on aluminum mining by-product

Abstract

Studies concerning competitive sorption of anions on oxidic materials eligible to be used as soil amendments are crucial for a better understanding of the adsorbent’s effectiveness and ion mobility/availability in the environment. This study evaluated mono-/multi-element adsorption of phosphate and arsenate on aluminum (AMB) and iron mining by-products (IMB; used for comparison) and measured the effect of pH and thermal pretreatments on P and As adsorption on AMB and IMB. We also evaluated whether the desorption of As previously adsorbed on AMB and IMB increases with the addition of increasing doses of P. For adsorption, each adsorbent was reacted at selected pHs with solutions containing As and P individually or in combination. Non-competitive desorption was performed with 30 mmol L−1 NaCl. Arsenate displacement was evaluated by reaction of the adsorbents containing previously adsorbed As with P-containing solutions. The competition between P and As decreased the adsorption of these anions by 2.7 and 23.2 %, respectively. Increasing pH decreased adsorption of both As and P, whereas the thermal pretreatment increased P adsorption by 40 % and As adsorption by 15 %. Phosphate in solution increased As desorption, with each millimoles per kilogram of adsorbed P desorbing as much as 2.3 ± 1.1 mmol kg−1 of As.