Enhancement of Limestone Defluoridation of Water by Acetic and Citric Acids in Fixed Bed Reactor

Abstract

Limestone defluoridation by fixed bed reactor has been studied with water pre-acidified with edible organic acids, viz. acetic acid (AA) and citric acid (CA). The study has been carried out by varying acid concentration, contact time (t), number of repeated use of the same limestone bed (n), and chip size of the crushed limestone using fixed fluoride concentration of 10 mg/L in distilled water and groundwater amended to that concentration of fluoride. The presence of both the acids considerably improved the fluoride removal and the removal increased with increase in the acid concentration. Fluoride removal to less than 0.5 and 1.0 mg/L from initial 5 and 10 mg/L, respectively, have been achieved by the method on treatment with single reactor. The mechanism of fluoride removal in the process thought to be the increase in Ca 2þ activity by dissolution of limestone, which precipitates as CaF 2 . XPS analysis reveals that adsorption also contribute to the fluoride removal along with precipitation. The final pH of water remained within acceptable range for drinking water. Initial concentration of fluoride, effects the removal ability of the limestone particles only to some extent. The influence of other anions on fluoride removal process has a little influence which follows the order phosphate > sulfate > bromide > chloride > nitrate.

Effect of acid on morphology of calcite during acid enhanced defluoridation

“…So it is a challenge to decrease the fluoride from lower strength, i.e., from 10 to 20 mg/ L to drinking water level by precipitation method without the need of pH correction. To meet this challenge we have done the experiment using edible acids and obtained promising results [32,33]. Use of the edible acids, viz., acetic acid (AA) and citric acid (CA) for the acid enhanced limestone defluoridation has been found to reduce the fluoride to below 1.5 mg/L which has been considered as a potential technique for rural groundwater defluoridation applications [33].…”

“…To meet this challenge we have done the experiment using edible acids and obtained promising results [32,33]. Use of the edible acids, viz., acetic acid (AA) and citric acid (CA) for the acid enhanced limestone defluoridation has been found to reduce the fluoride to below 1.5 mg/L which has been considered as a potential technique for rural groundwater defluoridation applications [33]. An investigation of the mechanism of fluoride removal when citric acid and acetic acid were used revealed the removal to be a combined result of precipitation of calcium fluoride by the calcium ion generated by dissolution of calcium carbonate and adsorption of fluoride on limestone surface [33].…”

Behavior of Fluoride Removal by Aluminum Modified Zeolitic Tuff and Hematite in Column Systems and the Thermodynamic Parameters of the Process

“…Diverse water defluoridation techniques have been used for treatment of fluoride-contaminated water. These techniques include chemical additions to cause precipitation/coagulation (Turner et al 2005;Nath and Dutta 2010), ion exchange (Meenakshi and Viswanathan 2007;Solangi et al 2009), electrochemical (Cui et al 2012), adsorption (Loganathan et al 2013), and membrane processes (Amor et al 2001;Tahaikt et al 2007). Each technique has advantages and disadvantages that limit its use (Onyango et al 2004).…”

Removal of Fluoride from Aqueous Solutions by Adsorption Using a Siliceous Mineral of a Kenyan Origin

“…These adsorbents are normally characterized by high F adsorption capacities due to their porous structures and large surface areas but their application is limited due to high costs and they require frequent regeneration which complicates the process. Because the adsorbents are nonbiodegradable and tend to persist in the environment for long periods of time [19], the spent waste from the process must carefully be disposed of. Because of these limitations a lot of unconventional adsorbents including various biosorbents [20][21][22][23] and a number of low-cost carbons [24][25][26] have been studied widely for use as substitute inexpensive adsorbents.…”

“…Certain clays and soil minerals [17,18,[27][28][29] have attracted a lot of research interest in the recent past as alternative adsorbents for F removal from water due to their attractive properties which include: ready and abundant availability, chemical stability, good natural adsorptive properties, ease of preparation for use, uncomplicated regeneration after use, and general environment passiveness [30][31][32]. In the present work, defluoridation capacity of a siliceous mineral from Kenya, M1, was studied in batch simulation tests.…”