Batch and column tests were performed utilizing natural siderite to remove As(V) and As(III) from water. One hundred milligrams of siderite was reacted at room temperature for up to 8 days with 50 rnL of 1000 mu g/L As(V) or As(III) in 0.01 M NaCl. Arsenic concentration decreased exponentially with time, and pseudoequilibrium was attained in 3 days. The estimated adsorption capacities were 520 and 1040 mu g/g for As(V) and As(III), respectively. Column studies show that effluent As was below 1.0 mu g/L after a throughput of 26,000 pore volumes of 500 mu g/L As water, corresponding to about 2000 mu g/g of As load in the filter. Results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) reveal that high As retention capacity of the filter arose from coprecipitation of Fe oxides with As and subsequently adsorption of As on the fresh Fe oxides/hydroxides. Arsenic adsorption in the filter from As-spiked tap water was relatively lower than that from artificial As Solution because high HCO3- concentration restrained siderite dissolution and thus suppressed production of the fresh Fe oxides on the siderite grains. The TCLP (toxicity characteristic leaching procedure) results suggest that these spent adsorbents were inert and could be landfilled. (c) 2007 Elsevier Inc. All rights reserved.