Removal of arsenic from water by porous charred granulated attapulgite-supported hydrated iron oxide in bath and column modes

Clays are increasingly used as hosting materials to develop cost-effective adsorbents for pollutant removal from water. This is especially urgent for arsenic purification in rural and undeveloped areas. However, the fine powder form of modified clay cannot be used directly in water treatment due to the separation difficulty. Herein, a simple and easy method was used to prepare a low-cost arsenic adsorbent through loading hydrated iron oxide into porous charred granulated attapulgite. The results show that iron impregnation can increase the Brunauer-Emmett-Teller surface area and micropore volume of charred granulated attapulgite, which was possibly caused by the nano-sized iron formed in the channel of charred granulated attapulgite. Batch studies indicate that As(III) (arsenite) and As(V) (arsenate) sorption on the prepared adsorbent fit well with the Langmuir equation as the maximum sorption capacities were 3.25 and 5.09 mg/g, respectively, which were higher than the reported low-cost arsenic adsorbent. The arsenic sorption rate on the iron impregnated sorbents varied with initial arsenic concentrations, but all can be described by a pseudo-second-order model. The iron modified charred granulated attapulgite performed well with a wider pH value (5-9). However, inhibition effects of arsenic sorption by coexisting ions SO42-, HCO3- and PO43- increased with the increase of their concentrations. Of these, PO43- exerted the largest effect. The arsenic adsorbed sorbent can be regenerated by 0.5 mol/L NaOH four times with an approximate 11.3% and 25.6% sorption capacity lost for As (V) and As (III), respectively. A fixed bed column experiment showed that iron-modified charred granulated attapulgite can treat 397 BV for As (V) and 175 BV for As (III) of arsenic contaminated water below 10 mu g/L. These results indicated that the first reported low-cost iron modified charred granulated attapulgite is very promising for arsenic contaminated water purification in rural and developing area. (C) 2017 Elsevier Ltd. All rights reserved.