Defluoridation of Groundwater Using Raw Bauxite: Kinetics and Thermodynamics

Abstract

High concentration of fluoride in drinking water causes dental and skeletal fluorosis, a slow, progressive and incurable disease. Removal of fluoride from water (defluoridation) offers a viable remedy to high fluoride content in water and fluorosis where other domestic water treatment solutions are not practicable. Conventional defluoridation technologies are either inefficient or require significant financial and technological investment. Therefore studies in developing countries have focused on local defluoridating agents for abating high fluorides and fluorosis. This study therefore investigated the efficiency of using raw bauxite in defluoridating groundwater through batch equilibrium studies. The bauxite exhibited defluoridation efficiency of up to 96.1% for groundwater with a fluoride concentration of 6.17 mg/L at a bauxite dosage of 0.120 kg/L. High fluoride uptake capacity of up to 275 mg/kg was obtained for the raw bauxite. Gibbsite which is the main constituent of the raw bauxite was responsible for the fluoride removal. The intraparticle diffusion model revealed that fluoride sorption by the raw bauxite occurred through both surface complexation and penetrative diffusion. Ion exchange resulting in the precipitation of insoluble AlF3 might add to the fluoride removal. Fluoride sorption was spontaneous and showed first order kinetics. The activation energy and enthalpy of reaction were determined as 19.6 and 126.5 kJ/mol, respectively.

Factors Governing the Performance of Bauxite for Fluoride Remediation of Groundwater

“…Although several studies have observed fluoride adsorption on bauxite, 20 29 but very few studies have focused on the adsorption of fluoride (F − ) on pure gibbsite 16 or on its composite bauxite ore. 27,23 More generally, the adsorption behavior of composite mineral assemblages such as bauxite is not well understood because published surface complexation and spectroscopic studies have primarily focused on surface interactions with pure mineral phases. Specifically, the effect on fluoride removal of non-Al minerals present in bauxite (e.g., hematite, goethite, kaolinite, calcite, etc.…”

Addressing technical barriers for reliable, safe removal of fluoride from drinking water using minimally processed bauxite ores

“…Previous work in our group ( Cherukumilli et al, 2017a ) and by others has demonstrated that raw bauxite ore from a variety of locations (including Iran ( Malakootian et al, 2014 ), Ghana ( Buamah et al, 2013 ), India ( Das et al, 2005 ), Malawi ( Kayira et al, 2014 ; Sajidu et al, 2008 ), and Turkey ( Dilek et al, 2013 )) can be used to remove fluoride from drinking water at significantly lower costs than activated alumina. Bauxite ore is composed largely of aluminum hydroxides, along with significant or trace quantities of iron-, silicon-, and sometimes calcium- and titanium-oxides.…”

“…With regards to co-occurring ions, we explore the impacts of phosphate and sulfate as potentially competitive co-occurring ions on the adsorption of fluoride onto both raw and thermally activated Vizag bauxite, building on our previous work ( Cherukumilli et al, 2017b ). We also test gibbsite, widely postulated to be the active adsorbent material in bauxite, in the presence of nitrate, silicic acid, phosphate and sulfate ( Habuda-Stanic et al, 2014 ; Kayira et al, 2014 ; Sujana and Anand, 2011 ), to provide fundamental understanding in a simpler model system. Due to the lack of observed interference of nitrate and silicic acid in fluoride adsorption in gibbsite, these were not studied as competitors to fluoride adsorption on either raw or thermally activated bauxite.…”

Adsorption of F on Bio-Filter sorbent: kinetics, equilibrium, and thermodynamic study

“…Thermodynamic parameters associated to the adsorption process were determined using the following equations [43,44]: …”