Comparative Column Studies of Chemically Modified Ion Exchange Resin with Agglomerated Adsorbents for Fluoride Removal

The present study is aimed to prepare three different granular adsorbents and applying on fluoride removal in column operations. Commercially available powdered adsorbents activated alumina (PAA) and tri-calcium phosphate (PTCP) is agglomerated to obtain granular polymer agglomerated alumina (GPAA) and granular polymer agglomerated tri-calcium phosphate (GTCP). Agglomeration was carried out using powdered adsorbents with neutral and non-toxic polymer Poly (vinyl acetate) to granular form of 20-50 mesh size. Plain Amberlite IRA 400 anion exchange resin (PR) was chemically modified (CMR) through phosphorylation by alum impregnation and investigated for fluoride removal as a third adsorbent. Column studies were carried out using 1.5 cm diameter columns to find out the suitability of the material for large scale applications. Solutions containing 5 mg L^-1 of fluoride adjusted to pH 7.0 were allowed to percolate through the column at known flow rates. Under optimum conditions of flow rate 10 mL min^-1 and bed height of 31 cm (25 g) of GPAA, 36 cm (20 g) of GTCP and 42 cm (20 g) of CMR respectively. The amount of fluoride removed were 1.948 mg g^-1, 2.1005 mg g^-1, and 2.3325 mg g^-1 of the respective adsorbent. The effects of co-existing anions were also studied in column experiments. Column regeneration studies were also carried out for all the adsorbents with Al₂(SO₄)₃ solutions. The cyclic regeneration experiments indicated that all the three adsorbents could be completely regenerated and used for repeated cycle. Ground water sample was collected from a village in Dharmapuri district of South India. The defluoridation capacity of the wet resin (6.80 mg g^-1) was found to be three times more than dried resin. CMR potentially can be the best adsorbent for fluoride removal. (author)