Use of laterite for the removal of fluoride from contaminated drinking water

The effects of different operational variables on the mechanistic function of laterite in removal of fluoride have been investigated. Thermodynamic parameters such as free energy change, enthalpy, and entropy of the process, as well as the sorption isotherm, were evaluated. The extent of solute removal is determined by initial solute concentration, operational conditions, laterite dose, and solution pH. For a fixed set of experimental conditions, a model equation is developed from which the percent removal corresponding to each load of fluoride is determined. The mechanism of fluoride adsorption is governed by the zero point charge of laterite and follows a first-order rate equation. pH has a vital role influencing the surface characteristics of laterite. To simulate the flow dynamics, fluoride solution was run through a fixed bed column. The pattern of breakthrough curves for different influent fluoride concentration, pH, and column bed height was characterized. The column efficiency was tested from the bed depth-service time model. The elution of the retained fluoride was studied and the effectiveness of column operation was determined by the retention-elution cycles.     

Removal of fluoride from fluoride contaminated industrial waste water by electrolysis

Wastewater containing fluoride are generally treated with lime or calcium salt supplemented with aluminium salts. Wastewater generated from different industries does not always behave in the same way due to the presence of interfering contaminants. A number of techniques have been developed and studied for the removal of excessive fluoride. Most of these are based on use of aluminium salt. In alum coagulation the sorption properties of product of hydrolysis of aluminium salts and capacity of fluoride for complex formation plays a very important role. These hydrolysis products of aluminium can be produced by passing direct current through aluminium electrode. The text presented in the paper deals with the various aspect of removal of fluoride by electrolysis using aluminium electrode from fluoride chemical based industrial wastewater.     

Removal of diphenhydramine from water by swelling clay minerals

Frequent detection of pharmaceuticals in surface water and wastewater attracted renewed attention on studying interactions between pharmaceuticals and sludge or biosolids generated from wastewater treatment. Less attention was focused on studying interactions between pharmaceuticals and clay minerals, important soil and sediment components. This research targeted on investigating interactions between diphenhydramine (DPH), an important antihistamine drug, and a montmorillonite, a swelling clay, in aqueous solution. Stoichiometric desorption of exchangeable cations accompanying DPH adsorption confirmed that cation exchange was the most important mechanism of DPH uptake by the swelling clay. When the solution pH was below the pK(a) of DPH, its adsorption on the swelling clay was less affected by pH. Increasing solution pH above the pK(a) value resulted in a decrease in DPH adsorption by the clay. An increase in d(001) spacing at a high DPH loading level suggested interlayer adsorption, thus, intercalation of DPH. The results from this study showed that swelling clays are a good environmental sink for weak acidic drugs like DPH. In addition, the large cation exchange capacity and surface area make the clay a good candidate to remove cationic pharmaceuticals from the effluent of wastewater treatment facilities.     

Solid phase extraction-spectrophotometric determination of fluoride in water samples using magnetic iron oxide nanoparticles

A new, sensitive, fast and simple method using magnetic iron oxide nanoparticles (MIONs), as an adsorbent has been developed for extraction, preconcentration and determination of traces of fluoride ions. The determination method is based on the discoloration of Fe(III)-SCN complex with extracted fluoride ions which was subsequently monitored spectrophotometrically at λ_max = 458 nm. Various parameters affecting the adsorption of fluoride by the MIONs have been investigated, such as pH of the solution, type, volume and concentration of desorbing reagent, amount of adsorbent and interference effects. A linear response for the determination of fluoride was achieved in the concentration range of 0.040-1.250 μg mL⁻¹. The limit of detection (LOD) and limit of quantification (LOQ) for fluoride based on 3 times and 10 times the standard deviation of the blank (3S_b, 10S_b) were 0.015 and 0.042 μg mL⁻¹ (n = 20) for fluoride ion, respectively. A preconcentration factor of 50 was achieved in this method. The proposed procedure has been applied for determination of fluoride concentration in various water samples. The results obtained from this method were successfully compared with those provided by standard SPADNS method.     

Synthesis of La-incorporated chitosan beads for fluoride removal from water

In this study, lanthanum incorporated chitosan beads (LCB) were synthesized using precipitation method and tested for fluoride removal from drinking water. The effect of various parameters like complexation and precipitation time, lanthanum loading and ammonia strength on fluoride removal have been studied. It is observed that the parameters for the synthesis of LCB have significant influence on development of LCB and in turn on fluoride removal capacity. The optimal condition for synthesis of LCB includes lanthanum loading: 10 wt%, complexation time: 60 min, precipitation time: 60 min, drying temperature: 75 °C for 72 h. The maximum fluoride adsorption capacity of LCB was found to be 4.7 mg/g and negligible release of lanthanum ion was observed. XRD analysis shows the presence of lanthanum hydroxide and amorphous nature of LCB. SEM of LCB shows the presence of oval lanthanum hydroxide particles spread over the chitosan matrix. Fluoride adsorption capacity has been calculated by applying Langmuir and Freundlich isotherms. The comparative study suggests that LCB shows four times greater fluoride adsorption capacity than the commercially used activated alumina.     

Microcoulometric measurement of water in minerals

A DuPont Moisture Analyzer is used in a microcoulometric method for determining water in minerals. Certain modifications, which include the heating of the sample outside the instrument, protect the system from acid gases and insure the conversion of all hydrogen to water vapor. Moisture analyzer data are compared to concurrent data obtained by a modified Penfield method. In general, there is a positive bias of from 0.1 to 0.2% in the moisture analyzer results and a similarity of bias in minerals of the same kind. Inhomogeneity, sample size, and moisture pick-up are invoked to explain deviations. The method is particularly applicable to small samples.     

Volumetric microdetermination of water in minerals

Summary A new technique for the determination of water in minerals is described. As in theBrush andPenfield technique, the water is evolved by ignition, condensed, and collected. This step is conducted in aPregl micromuffle bearing a special collecting tube. The final step in the determination of the water, however, is volumetric, rather than gravimetric. For this purpose, theKarl Fischer reagent, dispensed from a microburette, is used. The titration is conducted in a cell designed for external magnetic stirring and with provision for the electrometric determination of the end point.The method is quite rapid. In general, one operator could conduct both the ignition and titration steps faster than a second operator could weigh out the next sample. The precision of duplicate determinations is of the order of 0,5%, and the accuracy of the method is usually better than 1%.With 2 figures.     

Removal of fluoride from water by electrocoagulation using Mild Steel electrode

Electrocoagulation process was used for defluoridation of synthetic fluoride containing water. In the process Mild Steel (MS) was used as sacrificial electrode and experiments were performed with different varying parameters such as pH and current density (CD). The fluoride removal efficiency was found to be maximum at pH 6 and CD 75.44 A/m² (2 A). At these conditions fluoride concentration reduces from initial concentration of 50 ​mg/dm³ to 5.2 ​mg/dm³. Kinetic study of electrocoagulation process revealed that the order of the reaction was in the range 1.61–1.64 with respect to fluoride concentration. It was observed that fluoride removal efficiency of the present MS electrode is comparable to the other electrodes used in electrocoagulation process available in the literature.     

Removal of mercury and fluoride from aqueous solutions by three-dimensional reduced-graphene oxide aerogel

Research on Chemical Intermediates - Three-dimensional reduced-graphene oxide (3-D RGO) hydrogel was synthesized by hydrothermal method from graphene oxide, de-ionized water, and oxalic acid...     

Preferential adsorption of extracellular polymeric substances from bacteria on clay minerals and iron oxide

The adsorption of extracellular polymeric substances (EPS) from Bacillus subtilis on montmorillonite, kaolinite and goethite was investigated as a function of pH and ionic strength using batch studies coupled with Fourier transform infrared (FTIR) spectroscopy. The adsorption isotherms of EPS on minerals conformed to the Langmuir equation. The amount of EPS-C and -N adsorbed followed the sequence of montmorillonite>goethite>kaolinite. However, EPS-P adsorption was in the order of goethite>montmorillonite>kaolinite. A marked decrease in the mass fraction of EPS adsorption on minerals was observed with the increase of final pH from 3.1 to 8.3. Calcium ion was more efficient than sodium ion in promoting EPS adsorption on minerals. At various pH values and ionic strength, the mass fraction of EPS-N was higher than those of EPS-C and -P on montmorillonite and kaolinite, while the mass fraction of EPS-P was the highest on goethite. These results suggest that proteinaceous constituents were adsorbed preferentially on montmorillonite and kaolinite, and phosphorylated macromolecules were absorbed preferentially on goethite. Adsorption of EPS on clay minerals resulted in obvious shifts of infrared absorption bands of adsorbed water molecules, showing the importance of hydrogen bonding in EPS adsorption. The highest K values in equilibrium adsorption and FTIR are consistent with ligand exchange of EPS phosphate groups for goethite surface. The information obtained is of fundamental significance for understanding interfacial reactions between microorganisms and minerals.     

Removal of fluoride from water through ion exchange by mesoporous Ti oxohydroxide

In our previous study, we found that Ti(OH)(4) exhibited fluoride ion exchange properties. In order to improve the ion exchange capacity, mesoporous Ti oxohydroxide (TiOx(OH)y) had been prepared by using dodecylamine as template. Zirconia and silica had been introduced into the mesoporous Ti oxohydroxide to enhance the ion exchange capacity. The mesoporous structure and the morphology of the mesoporous materials obtained were confirmed using XRD and SEM, respectively. A fluoride ion exchange study was done on each sample. Results showed that mesoporous Ti oxohydroxide containing zirconia exhibited the highest fluoride ion exchange capacity, as it has the smallest particle size, with high uniformity among the mesoporous materials prepared.     

Adsorption of fluoride from water by amorphous alumina supported on carbon nanotubes

A new candidate for fluoride adsorption from water, amorphous Al₂O₃ supported on carbon nanotubes (Al₂O₃/CNTs), is reported in this Letter. The adsorption isotherms show that the best fluoride adsorption of Al₂O₃/CNTs occurs at a pH range of 5.0–9.0. The adsorption capacity for Al₂O₃/CNTs is about 13.5 times higher than that of AC-300 carbon, 4 times higher than that of γ-Al₂O₃ at equilibrium fluoride concentration of 12 mg/l. The broad range of the pH values and high adsorption capacity of Al₂O₃/CNTs make it very suitable for potential applications in fluoride removal from water.     

Dissolution rates of silicate minerals in water from a subcritical to a supercritical state: effect of solvent properties

Hydrothermal reaction experiments of silicate minerals (actinolite, pyroxene, etc.) were carried out using flow-through reactors in the temperature range from 25 to 400 °C at 23 MPa. The dissolution in water of a multi-oxide silicate mineral, for example actinolite or pyroxene may require the breaking of more than one type of metal?Coxygen bond. Differences between the rates at which these bonds break are often sufficiently large for dissolution to be non-stoichiometric. Dissolution rates (of Si) for actinolite and pyroxene in water were found to increase with increasing T from 25 to 300 °C, and then decrease with increasing T from 300 to 400 °C. The maximum release rates of Si are reached at 300 °C. The different metals in the minerals often have different release rates at a fixed temperature. At T < 300 °C the release rates of Na, Ca, Mg, Fe, and Al from minerals are usually higher than that of Si. In contrast, release rates of Si are higher than those of the others at T ?? 300 °C. The hydrolysis of Si?CO?CSi bonds and metal ion-H⁺ exchange reactions at T < 300 °C are different from reactions at T ?? 300 °C, at 23 MPa, because the solvent properties of water (decreasing density and dielectric constant in the region from sub-critical to supercritical state) affect reaction rates. log r (dissolution rates of Si) increases with 1/dielectric constant, as the temperature rises to close to 300 °C (or up to 374 °C) and at the critical pressure.     

Adsorption of Pseudomonas putida on clay minerals and iron oxide

Adsorption of Pseudomonas putida on minerals including montmorillonite, kaolinite and goethite was studied. The adsorption isotherms of P. putida on the examined minerals conformed to the Langmuir equation. The amount of P. putida adsorbed followed the order: goethite > kaolinite > montmorillonite. A greater extent of P. putida adsorption on minerals was observed in the range of temperature from 15 to 35 °C. The adsorption of P. putida on minerals decreased with the increase of pH from 3.0 to 10.0. Magnesium ion was more efficient than sodium ion in promoting P. putida adsorption on minerals. The results suggest that electrostatic interactions play a vital role in P. putida adsorption by soil colloidal factions. The information obtained in this study is of fundamental significance for the understanding of the survival and transport of bacteria in soil systems.     

Preparation and properties of rare-earth containing oxide fluoride glasses

The preparation of the rare earth containing oxide fluoride glasses LnF₃ (Ln; Y through Lu)-BaF₂-AlF₃-GeO₂ in which the nominal content of LnF₃ reached 60 mol% in maximum and their basic properties such as density, refractive index and glass transition temperature were investigated and summarized in detail. Especially, in order to discuss the local structure around the rare earth ion in the glass, the Judd-Ofelt analysis (discussion with Ω parameters) of the HoF₃-BaF₂-AlF₃-GeO₂ glasses was carried out. The unique fluorescent behavior and the magnetic properties of LnF₃-BaF₂-AlF₃-GeO₂ glasses (Ln = Tb and/or Sm) were also studied.     

Spectrophotometric determination of fluoride in fluoride-bearing minerals after decomposition by fusion with sodium hydroxide

The decomposition of highly insoluble minerals (fluorspar and cryolite) by fusion with molten alkali-metal hydroxides is studied. The introduction of additives such as aluminium compounds or sodium peroxide to obtain total liberation of fluoride from calcium fluoride samples, is tested. The fusion is done in a silver crucible with a Bunsen burner. The cooled melt is easily soluble, giving solutions suitable for spectrophotometric fluoride determination by the Zr(IV)-fluoride-Erichrome Cyanine R method.