Characterizing the reactivity of metallic iron for water defluoridation in batch studies.

Abstract

The suitability of metallic iron (Fe(0)) for water defluoridation is yet to be understood. Fluoride removal ([F-]0\u202f=\u202f20.0\u202fmg\u202fL-1) and Orange II discoloration ([Orange II]0\u202f=\u202f10.0\u202fmg\u202fL-1) by Fe(0)/H2O batch systems are compared herein. A steel wool (SW) and a granular iron (GI) are used as Fe(0) specimens. Each essay tube contains 0.5\u202fg sand and 0.1\u202fg of the used Fe(0). Investigated systems were: (i) SW/sand at pH 5.0, (ii) GI/sand at pH 5.0 and (iii) SW/sand at pH 8.0. Prior to contaminant addition, Fe(0) was allowed to pre-corrode within the systems for up to 46 days. The systems were then equilibrated for 30 days with a mixture of the two model contaminants. Result confirmed (i) the higher efficiency of SW over GI in removing both contaminants, (ii) the higher efficiency of Fe(0) for Orange II discoloration and (iii) the positive impact of initial low pH values on the efficiency of Fe(0)/H2O systems. The major output of this research is that conventional Fe(0)/H2O systems are not suitable for quantitative water defluoridation. It is suggested that ways to avoid defluoridation using Fe0 must be explored. One affordable opportunity is blending fluoride-polluted water with carefully harvested rainwater.