Removal of fluoride from water by carbon nanotube supported alumina

Understanding fluoride adsorption from groundwater by alumina modified with alum using PHREEQC surface complexation model

Fluoride is recognized as a vital ion for human and animal growth because of the critical role it plays in preventing skeletal and dental problems. However, when it is ingested at a higher concentration it can cause demineralization of teeth and bones resulting in fluorosis, therefore, the production of high-adsorptive capacity material which is also cost-effective is necessary for the treatment of fluorides. In this study, aluminium foil is valorised into alumina nanoparticles. The as-prepared alumina was modified with alum in two different ratios of 1:0.5 and 1:1 (alumina to alum w/w%) and later used as adsorbents for the removal of fluoride from groundwater. The adsorbents were characterized by Fourier transform infrared spectroscopy, point of zero charge and X-ray diffraction. Different factors that influence the removal efficiency of fluorides such as pH, initial concentrations, contact time and adsorbent dosage were studied and optimized using a simulated fluoride solution. The optimum conditions obtained were used to test real groundwater. The static experiment conditions were used to calibrate a PHREEQC geochemical model which was later used to simulate the fluoride sorption onto the modified alumina at different conditions. PHREEQC was also coupled with parameter estimation software to determine equilibrium constants for the surface reactions between the fluoride species and the adsorbent in a way that the simulations accurately reflect the outcomes of laboratory experiments. Isotherm studies were carried out on the adsorbents. Both Langmuir and Freundlich's non-linear models fitted well for the equilibrium data. However, with a higher coefficient of regression and low chi-square test values, the adsorption process was more of chemisorption on a monolayer surface. Kinetic studies were also carried out by using the non-linear equations from the pseudo-first-order and pseudo-second-order models. The pseudo-second-order model fitted well for the equilibrium data. The mechanism for the fluoride ion adsorption was also studied by the intraparticle (IP) diffusion model and was found that IP was not the rate-determining factor, and therefore the most plausible mechanism for the sorption process was ion exchange or attraction of fluoride ions to the sorbent surface. The findings obtained from this research show that readily available aluminium waste could be valorised into a useful product that could be employed in the removal of fluoride from water samples, including groundwater, that may contain too much fluoride and pose a risk to the general public's health.

Synthesis of high quality boehmite and γ-alumina for phosphorus removal from water works sludge by extraction and hydrothermal treatment

Alum sludge from water treatment was calcined and extracted to synthesize high quality boehmite and γ-alumina for phosphate removal. Synthesized boehmite and γ-alumina were able to remove phosphate quickly and effectively. Boehmite (hydrothermal treatment at 60 °C) showed maximum phosphate removal (adsorption) of 61 mg P/g followed by γ-alumina (50 mg P/g) and the boehmite hydrothermally treated at 120 °C (41 mg P/g). The degree of crystallinity gave more effect on phosphate adsorption of boehmite than that of γ-alumina. The lower the pH, the more phosphate adsorbed on the boehmite and γ-alumina (adsorb phosphate more than 4 times at pH 3 than at pH 11). Spectroscopic analysis (SEM-EDS and FTIR) indicates that phosphate are removed by ligand exchange, electrostatic attraction, and surface precipitation on the synthesized boehmite and γ-alumina.

Advances in nanomaterial based approaches for enhanced fluoride and nitrate removal from contaminated water

Various nanomaterials for fluoride and nitrate removal from contaminated water.

Fluoride removal from water using high-activity aluminum hydroxide prepared by the ultrasonic method

Ultrasonically prepared Al(OH)₃ has a high defluoridation capacity and a low residual aluminum concentration in drinking water after defluoridation.

Synthesis and characterization of a chitosan/montmorillonite/ZrO2 nanocomposite and its application as an adsorbent for removal of fluoride

Removal of fluoride by CTS/MMT/ZrO₂ nanocomposite as adsorbent was investigated. Adsorbent was characterized by BET, FTIR, SEM and XRD. Effect of molar ratio, pH, temperature on adsorbent capacity and model of kinetics and isotherm was investigated.

Defluoridation of drinking water using adsorption processes

Excessive intake of fluoride (F), mainly through drinking water, is a serious health hazard affecting humans worldwide. There are several methods used for the defluoridation of drinking water, of which adsorption processes are generally considered attractive because of their effectiveness, convenience, ease of operation, simplicity of design, and for economic and environmental reasons. In this paper, we present a comprehensive and a critical literature review on various adsorbents used for defluoridation, their relative effectiveness, mechanisms and thermodynamics of adsorption, and suggestions are made on choice of adsorbents for various circumstances. Effects of pH, temperature, kinetics and co-existing anions on F adsorption are also reviewed. Because the adsorption is very weak in extremely low or high pHs, depending on the adsorbent, acids or alkalis are used to desorb F and regenerate the adsorbents. However, adsorption capacity generally decreases with repeated use of the regenerated adsorbent. Future research needs to explore highly efficient, low cost adsorbents that can be easily regenerated for reuse over several cycles of operations without significant loss of adsorptive capacity and which have good hydraulic conductivity to prevent filter clogging during the fixed-bed treatment process.

Review of fluoride removal from drinking water

Fluoride in drinking water has a profound effect on teeth and bones. Up to a small level (1-1.5mg/L) this strengthens the enamel. Concentrations in the range of 1.5-4 mg/L result in dental fluorosis whereas with prolonged exposure at still higher fluoride concentrations (4-10mg/L) dental fluorosis progresses to skeletal fluorosis. High fluoride concentrations in groundwater, up to more than 30 mg/L, occur widely, in many parts of the world. This review article is aimed at providing precise information on efforts made by various researchers in the field of fluoride removal for drinking water. The fluoride removal has been broadly divided in two sections dealing with membrane and adsorption techniques. Under the membrane techniques reverse osmosis, nanofiltration, dialysis and electro-dialysis have been discussed. Adsorption, which is a conventional technique, deals with adsorbents such as: alumina/aluminium based materials, clays and soils, calcium based minerals, synthetic compounds and carbon based materials. Studies on fluoride removal from aqueous solutions using various reversed zeolites, modified zeolites and ion exchange resins based on cross-linked polystyrene are reviewed. During the last few years, layered double oxides have been of interest as adsorbents for fluoride removal. Such recent developments have been briefly discussed.

Fluoride Wastewater Treatment by Adsorption onto Metallurgical Grade Alumina

The adsorption of fluoride onto metallurgical grade alumina (to produce Al) was investigated under different conditions: pH, contact time and adsorbent concentration. Data were evaluated with the aim of developing an alternative treatment technology for washing wastewater arising from an Aluminum can production plant. Kinetics and adsorption isotherms data have been also produced Sorption is greatly affected by pH and the best condition for fluoride removal are obtained at pH 5-6 and alkalinity competes successfully with fluoride ions for the exchange sites. Experiments with fixed beds indicate that fluoride is removed from wastewater by metallurgical-grade alumina with a capacity of 12.21 mg of F per gram and adsorption increases of about 25% at appropriate pH. The Mass Transfer Zone at 5% of the breakthrough occupies 70.6% of the total column length. The optimization of aluminum precipitation by pH adjustment and with different precipitant agents has been done.