Identification of selective ion-exchange resin for fluoride sorption

The defluoridation capacity (DC) of a chelating resin, namely Indion FR 10 (IND), and Ceralite IRA 400 (CER), an anion-exchange resin, were compared under various equilibrating conditions for the identification of selective sorbent. The results showed that chelating resin is more selective than an anion-exchange resin for fluoride removal. The fluoride sorption was reasonably explained using Freundlich and Langmuir isotherms. The surface morphology of resins before and after fluoride sorption was observed using scanning electron microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) was used for the determination of functional groups responsible for fluoride sorption. Various thermodynamic parameters such as DeltaG0, DeltaH0, DeltaS0, and Ea have been calculated to understand the nature of sorption. The sorption kinetic mechanism was studied with reaction-based and diffusion-based models. The sorption process was found to be controlled by pseudo-second-order and particle diffusion models. The performance of the resins studied has been tested with field samples collected from a fluoride-endemic area.

Defluoridation chemistry of synthetic hydroxyapatite at nano scale: equilibrium and kinetic studies

This study describes the advantages of nano-hydroxyapatite (n-HAp), a cost effective sorbent for fluoride removal. n-HAp possesses a maximum defluoridation capacity [DC] of 1845 mg F(-)/kg which is comparable with that of activated alumina, a defluoridation agent commonly used in the indigenous defluoridation technology. A new mechanism of fluoride removal by n-HAp was proposed in which it is established that this material removes fluoride by both ion-exchange and adsorption process. The n-HAp and fluoride-sorbed n-HAp were characterized using XRD, FTIR and TEM studies. The fluoride sorption was reasonably explained with Langmuir, Freundlich and Redlich-Peterson isotherms. Thermodynamic parameters such as DeltaG degrees , DeltaH degrees , DeltaS degrees and Ea were calculated in order to understand the nature of sorption process. The sorption process was found to be controlled by pseudo-second-order and pore diffusion models. Field studies were carried out with the fluoride containing water sample collected from a nearby fluoride endemic area in order to test the suitability of n-HAp material as a defluoridating agent at field condition.

Removal of fluoride from aqueous solution using protonated chitosan beads

In the present study, chitosan in its more usable bead form has been chemically modified by simple protonation and employed as a most promising defluoridating medium. Protonated chitosan beads (PCB) showed a maximum defluoridation capacity (DC) of 1664mgF-/kg whereas raw chitosan beads (CB) possess only 52mgF-/kg. Sorption process was found to be independent of pH and altered in the presence of other co-existing anions. The sorbents were characterized using FTIR and SEM with EDAX analysis. The fluoride sorption on PCB follows both Freundlich and Langmuir isotherms. Thermodynamic parameters, viz., DeltaG degrees , DeltaH degrees DeltaS degrees and Ea indicate that the nature of fluoride sorption is spontaneous and endothermic. The sorption process follows pseudo-second-order and intraparticle diffusion kinetic models. 0.1M HCl was identified as the best eluent. The suitability of PCB has been tested with field samples collected from a nearby fluoride-endemic area.

Uptake of fluoride by nano-hydroxyapatite/chitosan, a bioinorganic composite

A bioinorganic composite namely nano-hydroxyapatite/chitosan (n-HApC) composite which could be employed for technology development was prepared and studied for its defluoridation efficiency. It has been observed that there was a slight enhancement in the defluoridation capacity (DC) of n-HApC composite (1560mgF(-)/kg) than nano-hydroxyapatite (n-HAp) which has a DC of 1296mgF(-)/kg. The sorbents were characterized with XRD and TEM studies. The fluoride sorption was explained with Freundlich and Langmuir isotherms. Thermodynamic parameters such as DeltaG degrees , DeltaH degrees , DeltaS degrees and Ea were calculated in order to understand the nature of sorption. The sorption process was found to be controlled by pseudo-second-order and pore diffusion models. Field studies were carried out with the fluoride containing water sample collected from a fluoride-endemic area in order to test the suitability of the sorbents at field conditions.

Enhanced fluoride sorption by mechanochemically activated kaolinites

Kaolinite clay obtained from the mines was processed and studied for its fluoride sorption capacity. The surface area of the clay mineral was increased from 15.11 m(2)/g (raw) to 32.43 m(2)/g (activated) by mechanochemical activation. Batch adsorption studies were conducted to optimize various equilibrating conditions like the effect of contact time, dosage, pH for both raw and micronized kaolinites (RK and MK). The effect of other interfering anions on the defluoridation capacity (DC) of the sorbents was studied. Sorption of fluoride by the sorbents was observed over a wide pH range of 3-11. The studies revealed there is an enhanced fluoride sorption on MK. FTIR and XRD were used for the characterization of the sorbent. The surface morphology of the clay material was observed using SEM. The adsorption of fluoride was studied at three different temperatures, viz., 303, 313 and 323 K. The sorption data obtained at optimized conditions were subjected to Freundlich and Langmuir isotherms. Sorption intensity (1/n) (0.770-0.810) has been evaluated using Freundlich isotherm, whereas the values of sorption capacity Q(0) (0.609, 0.714 and 0.782 mg/g) and binding energy b (0.158, 0.145 and 0.133 L/mg) at three different temperatures have been estimated using Langmuir isotherm. Adsorption process was found to be controlled by both Freundlich and Langmuir isotherms. Thermodynamic studies revealed that the sorption of fluoride on MK is endothermic and a spontaneous process. The kinetic studies indicate that the sorption of fluoride on MK follows pseudo-first-order and intraparticle diffusion models.

Defluoridation of water using magnesia/chitosan composite

Magnesia (MgO) is a well-known adsorbent showing extremely high defluoridation capacity (DC). In order to over come the limitations of MgO for field applications, an attempt has been made to modify magnesia with abundant biomaterial chitosan to form magnesia/chitosan (MgOC) composite in a usable form and its merits over conventional magnesia and raw chitosan is established. Removal of fluoride from aqueous solution with MgO and MgOC composite was studied with batch equilibrium experiments. At equilibrium, MgOC composite has a DC of 4440 mg F(-)/kg while for magnesia it is only 2175 mg F(-)/kg. The physicochemical properties of the synthesised MgOC composite were analyzed with FTIR and SEM with EDAX studies. The equilibrium data were fitted with isotherm and kinetic models. Thermodynamic parameters viz, Delta G degrees, Delta H degrees and DeltaS degrees were calculated to understand the nature of sorption. Field studies were carried out to find the suitability of these sorbents at field conditions.

Fluoride sorption by nano-hydroxyapatite/chitin composite

In this study the fluoride adsorption potential of novel nano-hydroxyapatite/chitin (n-HApCh) composite was explored. The sorbent was characterized using FTIR studies. The effects of pH, interfering anions and contact time were studied. The sorption data obtained under optimized conditions were subjected to Langmuir and Freundlich isotherms. Kinetic studies indicate that the rate of sorption of fluoride on n-HApCh composite follows pseudo-second-order and pore diffusion patterns. n-HApCh composite possesses higher defluoridation capacity (DC) of 2840 mg F(-)kg(-1) than nano-hydroxyapatite (n-HAp) which showed a DC of 1296 mg F(-) kg(-1). Field trials were conducted with the sample collected from a nearby fluoride endemic area.

Enriched fluoride sorption using alumina/chitosan composite

Alumina possesses an appreciable defluoridation capacity (DC) of 1566 mg F(-)/kg. In order to improve its DC, it is aimed to prepare alumina polymeric composites using the chitosan. Alumina/chitosan (AlCs) composite was prepared by incorporating alumina particles in the chitosan polymeric matrix, which can be made into any desired form viz., beads, candles and membranes. AlCs composite displayed a maximum DC of 3809 mg F(-)/kg than the alumina and chitosan (52 mg F(-)/kg). The fluoride removal studies were carried out in batch mode to optimize the equilibrium parameters viz., contact time, pH, co-anions and temperature. The equilibrium data was fitted with Freundlich and Langmuir isotherms to find the best fit for the sorption process. The calculated values of thermodynamic parameters indicate the nature of sorption. The surface characterisation of the sorbent was performed by FTIR, AFM and SEM with EDAX analysis. A possible mechanism of fluoride sorption by AlCs composite has been proposed. Suitability of AlCs composite at field conditions was tested with a field sample taken from a nearby fluoride-endemic village. This work provides a potential platform for the development of defluoridation technology.

Development of chitosan supported zirconium(IV) tungstophosphate composite for fluoride removal

A new biocomposite was prepared by incorporating inorganic ion exchanger namely zirconium(IV) tungstophosphate (ZrWP) into the chitosan biopolymeric matrix. The sorption behaviour of fluoride from aqueous solutions by this ZrWP/chitosan (ZrWPCs) composite has been investigated by batch technique. The fluoride sorption was studied as a function of contact time, pH, initial fluoride concentration, competing co-ions and temperature. The defluoridation capacity (DC) of the adsorbent was found to be 2025 mg F(-) kg(-1). The composite was characterized using FTIR and SEM with EDAX analysis. The equilibrium sorption data were fitted to Freundlich and Langmuir isotherms. The kinetics of sorption was found to follow pseudo-second-order and intraparticle diffusion models. The values of thermodynamic parameters indicate the nature of sorption is spontaneous and endothermic. The biocomposite was successfully used for the removal of fluoride from the field water taken in a nearby fluoride endemic village.

Role of metal ion incorporation in ion exchange resin on the selectivity of fluoride

Indion FR 10 resin has sulphonic acid functional group (H(+) form) possesses appreciable defluoridation capacity (DC) and its DC has been enhanced by chemical modification into Na(+) and Al(3+) forms by loading respective metal ions in H(+) form of resin. The DCs of Na(+) and Al(3+) forms were found to be 445 and 478 mg F(-)/kg, respectively, whereas the DC of H(+) form is 265 mg F(-)/kg at 10 mg/L initial fluoride concentration. The nature and morphology of sorbents are characterized using FTIR and SEM analysis. The fluoride sorption was explained using the Freundlich, Langmuir and Redlich-Peterson isotherms and kinetic models. The calculated thermodynamic parameters such as DeltaG degrees, DeltaH degrees, DeltaS degrees and sticking probability (S(*)) explains the nature of sorption. Comparison was also made by the elution capacity of these resins in order to select a cost effective material. A field trial was carried out to test the suitability of the resins with fluoride water collected from a nearby fluoride-endemic area.

Preparation and characterization of La(III) encapsulated silica gel/chitosan composite and its metal uptake studies

Lanthanum loaded silica gel/chitosan composite (LaSiCS) was prepared by mixing silica gel, LaCl(3) · 7H(2)O and chitosan which was then cross-linked with glutaraldhyde. The LaSiCS composite was characterized using FT-IR, SEM-EDAX, XRD and BET. The adsorption of chromium(VI) ions onto LaSiCS composite has been investigated. The LaSiCS composite was found to have excellent chromium adsorption capacity than the silica gel/chitosan composite (SiCS), silica gel (Si) and chitosan (CS). The sorption experiments were carried out in batch mode to optimize various parameters viz., contact time, pH, initial chromium ion concentration, co-ions and temperature that influence the sorption. Langmuir and Freundlich adsorption models were applied to describe isotherm constants. Equilibrium data agreed very well with the Langmuir model. Thermodynamic studies revealed that the nature of chromium sorption was spontaneous and endothermic. The LaSiCS composite removes chromium by electrostatic adsorption coupled reduction/ion-exchange.