Methods for arsenic removal from aqueous solutions

Pirgalıoğlu, Saltuk
In the last few decades, one of the major environmental problems that world has been facing is limited access to clean water and depletion of water resources. Scarcity of clean water started to compel municipals to use waters which must be separated from contaminants. One of the major contaminants in water sources is arsenic which poses a challenge for separation. This study is an effort to find a feasible method for the removal of arsenic from water. Arsenic is a mineral found in rocks and soil, which can contaminate ground waters and surface waters used as public water resources. Due to adverse effect of arsenic on human health and plants allowable arsenic concentration in drinking waters was determined as10 µg/L by the World Health Organization (WHO). In this study, arsenic removal problem was approached with two different arsenic removal methods based on the use of two different types of polymers. High porosity cationic hydrogels synthesized via crosslinking co-polymerization of diallyldimethylammonium-chloride (DADMAC) with N,N’-tetraallylpiperaziniumdichloride (TAP) was used in batch and fixed colum adsorption studies; on the other hand, water soluble linear diallyldimethylammonium chloride (DADMAC) – vinyl pyridine (P(4-VP)) co-polymers were used in polymer enhanced ultrafiltration (PEUF) studies. DADMAC hydrogels can be regarded as the most efficient hydrogels reported in literature for arsenate removal in terms of applicable pH range, arsenic removal capacity and contact time required. In this study, hydrogels synthesized showed high affinity for arsenate anions (As (V)) at a wide pH range of 6 to 10. Arsenic removal efficiency of 99 percent was obtained when arsenic solutions having concentrations of 1000 µg/L (100 mL) were treated with 0.1 g hydrogel with a contact time less than 15 minutes; regeneration and re-usability studies of hydrogels were also conducted. Ultrafiltration experiments conducted with commercially available Polyether Sulfone (PES) membranes resulted in arsenate (As (V)) retention values around 80-85 percent in the pH range of 7 to 10, while DADMAC- P(4-VP) co-polymer addition increased this value up to 98 percent. In PEUF, polymer concentrations of 0.01 g/L were enough for successful separations without membrane fouling. On the other hand arsenite (As(III)) removal by PEUF resulted in merely as high as 50 percent only due to the poor interaction of polymer with arsenic ions. Highest retention value obtained in ultrafiltration experiments for As(III) was also recorded as 40%.