Adsorption of arsenic(III) and arsenic(V) from groundwater using natural siderite as the adsorbent

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 mL of 1000 μg/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 μg/g for As(V) and As(III), respectively. Column studies show that effluent As was below 1.0 μg/L after a throughput of 26,000 pore volumes of 500 μg/L As water, corresponding to about 2000 μg/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 HCO−3 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.

SEM images of the pristine siderite (A) and the used siderite (B), and TEM image of the used siderite (C) and EDS spectra for the Fe-oxide coating (D).Figure optionsDownload as PowerPoint slide