Selective adsorption of arsenate and antimonate from phosphate-rich waters

The similarity of arsenic (As), antimony (Sb) and phosphorus (P) originates in their identical periodicity, which results in the formation of the same inorganic species, analogical binding properties etc. While As and currently also Sb denote permanent environmental risk originating in their toxicity and carcinogenic properties, P as the biogenic element is obviously desired in water for its fertilizing effects. As, Sb and P oxyanions, which are abundant in natural systems, mostly behave as the competitors to binding positions in surface complexation. Three manganese-based adsorbents (birnessite, Mn²⁺ modified zeolite and Mn²⁺ modified biochar) were tested for selective adsorption of arsenate (As^V) and antimonate (Sb^V) in presence of phosphate (P^V). Birnessite and Mn-modified biochar were excellent for the removal of individual oxyanions (80–95% of P^V, 93–100% of As^V, and ~85% of Sb^V was removed), while a preferential As^V/Sb^V adsorption only for birnessite was observed (86% of As^V with 32% of P^V, and 68% of Sb^V with 7% of P^V were removed).