Removal of As(III) ions from aqueous systems using modified natural sorbents (Hazelnut and walnut shell)

Arsenic can occur in the environment in several oxidation states but in natural waters it is mostly found in inorganic form as oxyanions of trivalent arsenite [As(III)] or pentavalent arsenate [As(V)]. As(III) is more toxic to biological systems than As(V). The major technologies for arsenic removal include precipitation-coagulation, membrane separation, ion exchange, and adsorption. Adsorption techniques are generally considered to be promising method and have been shown to be an economically feasible alternative method for removing heavy metals from wastewater and water supplies. In this study, natural adsorbents were used to remove as As(III) ions from artificially prepared solutions. For this, hazelnut shell and walnut shell were used as sorbents after modifications with FeCl3 and FeCl3+NaOH to remove As(III) ions. Adsorbtion studies were carried out using a batch method and adsorbtion parameters such as time, pH, temperature, As(III) concentration were researched to have the maximum absorbsion. As(III) amount at the beginning and unadsorbed As(III) amount left in the solution after treatment were determined by using hydride generation atomic absorbtion spectrophotometer (HG-AAS) with air-acetylene flame. When the effects of time on adsorption performance is analyzed, the maximum adsorption observed as optimum contact time, for hazelnut shell modified with FeCl3 is 4 hours, nut shell modified with NaOH+FeCl3 is 2 hours, walnut shell modified with FeCl3 is 1 hour, walnut shell modified with NaOH+FeCl3 is 4 hours. The optimum temperature was found 20° C and optimum pH was found 9 for all of the adsorbents. Maximum adsorption was observed on hazelnut shell which modified with FeCl3 and NaOH and the adsorption capacity was found 11.84 mg As(III) /g adsorbent. For hazelnut shell modified with FeCl3 capacity is 4.37 mg of As (III) / g adsorbent, for walnut shell modified with FeCl3 is 6.17 mg of As (III) / g adsorbent and walnut shell modified with FeCl3+NaOH is 5.74 mg of as (III) / g of adsorbent.