title: Fluoride removal from groundwater by limestone treatment in presence of phosphoric acid.
abstract: Fluoride removal from groundwater has been studied by addition of dilute phosphoric acid (PA) to the influent water before limestone treatment through laboratory plug-flow column experiments and bench-scale plug-flow pilot tests. In this PA-enhanced limestone defluoridation (PAELD) technique, fluoride is removed from 0.526 mM to 0.50-52.60 μM in 3 h with near neutral final pH. The presence of PA increases the fluoride removal capacity of limestone to 1.10 mg/g compared to 0.39 mg/g reported in its absence. The changes in fluoride removal with variation in initial PA concentration, initial fluoride concentration and the final pH have been found to be statistically significant with p < 0.05. The estimated recurring cost is US$ ≈0.58/m(3) water. Simple scrubbing and rinsing is a preferable method for regeneration of limestone as it is almost equally effective with lime or NaOH. Sorption of fluoride by calcium phosphates produced in situ in the reactor is the dominant mechanism of fluoride removal in the PAELD. Precipitation of CaF2 and sorption of fluoride by the limestone also contribute to the fluoride removal. High efficiency, capacity, safety, environment-friendliness, low cost and simplicity of operation make the PAELD a potential technique for rural application.
authors.affiliation: Department of Chemical Sciences, Tezpur University, Napaam, Tezpur 784028, Assam, India. Electronic address: sgogoi4@tezu.ernet.in.
authors.forename: Sweety
authors.initials: S
authors.lastname: Gogoi
authors.affiliation: Department of Chemical Sciences, Tezpur University, Napaam, Tezpur 784028, Assam, India. Electronic address: suresh@tezu.ernet.in.
authors.forename: Suresh K
authors.initials: SK
authors.lastname: Nath
authors.affiliation: Department of Chemical Sciences, Tezpur University, Napaam, Tezpur 784028, Assam, India. Electronic address: sh_momy@tezu.ernet.in.
authors.forename: Shreemoyee
authors.initials: S
authors.lastname: Bordoloi
authors.affiliation: Department of Chemical Sciences, Tezpur University, Napaam, Tezpur 784028, Assam, India. Electronic address: robind@tezu.ernet.in.
authors.forename: Robin K
authors.initials: RK
authors.lastname: Dutta
mesh_terms: D002119:Calcium Carbonate / Q000737:chemistry*; D052918:Environmental Restoration and Remediation / Q000379:methods*; D005459:Fluorides / Q000737:chemistry*; D060587:Groundwater / Q000032:analysis*; D010756:Phosphoric Acids / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D014877:Water Pollution, Chemical / Q000517:prevention & control*
chemical_list: D010756:Phosphoric Acids; D014874:Water Pollutants, Chemical; C030242:phosphoric acid; D002119:Calcium Carbonate; D005459:Fluorides
keywords: Calcium fluoride; Calcium phosphate or hydroxyapatite; Defluoridation; Limestone; Phosphoric acid