Enhanced fluoride removal from drinking water by magnesia-amended activated alumina granules

This paper describes the fluoride removal potential of a novel sorbent, magnesia-amended activated alumina (MAAA) from drinking water. MAAA, prepared by calcining magnesium hydroxide impregnated alumina at 450 °C has shown high fluoride sorption potential than activated alumina from drinking water. Batch sorption studies were performed as a function of contact time, pH, initial fluoride concentration, and adsorbent dose. Studies were also performed to understand the effect of various other co-existing ions present in real ground water samples. X-ray powder diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray (EDAX) and a gas adsorption porosimetry analyses were used to characterize the physicochemical properties of MAAA. More than 95% removal of fluoride (10 mg l⁻¹) was achieved within 3 h of contact time at neutral pH. Sorption of fluoride onto MAAA was found to be pH dependant and a decrease in sorption was observed at higher pHs. Among the kinetic models tested, pseudo-second-order model fitted the kinetic data well, suggesting the chemisorption mechanism. Among the various isotherm model tested, Sips model predicted the data well. The maximum sorption capacity of fluoride deduced from Sips equation was 10.12 mg g⁻¹. Most of the co-existing ions studied have negligible effect on fluoride sorption by MAAA. However, higher concentrations of bicarbonate and sulfate have reduced the fluoride sorption capacity.     

Removal of metal ions from aqueous solution by adsorption onto activated carbon cloths: adsorption competition with organic matter

Activated carbon cloths are recent adsorbents whose adsorption properties are well known for monocomponent solutions of organics or metal ions. However, to treat wastewaters with these materials, their performance has to be determined in multicomponent solution. This work studies adsorption competition between metal ions (Cu²⁺, Pb²⁺) and organic matter (benzoic acid). The first part investigates adsorption equilibrium of monocomponent metal ions solutions and shows the dependence of adsorption capacities on adsorbent porosity and metal ions chemical properties (molecular weight, ionic radius and electronegativity). The influence of pH is also demonstrated. The second part focuses on adsorption competition: (1) between both metal ions (a decrease of adsorption capacities is observed, whose value is related to adsorption kinetics of metal ions); (2) between metal ions and organic matter, in solution or adsorbed onto the activated carbon cloth (a strong influence of pH is shown: when benzoic acid is under benzoate form, in both cases adsorption is increased due to the formation of ligands between adsorbed benzoate ions and metals).     

Removal of excess fluoride ions from Saharan brackish water by adsorption on natural materials

Water supply for people in the Sahara region is mainly assured by poor quality ground water which has excessive minerals, hardness and high concentration of fluoride. This leads to many teeth and bones diseases such as fluorosis. The purpose of this study is to eliminate the excess of fluorides from the El Oued Souf City water supply located in the South East of the Algerian Sahara by retention process onto montmorillonite clay using potentiometric method. Two types of natural clays were tested. The first one contains a higher percentage of calcium (AC) and the second one without calcium (ANC). These adsorbents were activated chemically and thermally with temperatures ranging between 200 and 500 °C. Experimental results showed that chemical activation proved effective adsorption reaching up to 88% whereas the thermal activation is ineffective and reached only around 5%. Moreover, the acidity of the medium and the alkalinity affect the adsorption considerably. The retention predicted from the adsorption isotherms is in agreement with Langmuir's model. The kinetic analysis of the reactions indicates that reaction is slow with diffusional control. The low values obtained for the heat of adsorption mean that the adsorption is exothermic with no specific type. An ionic mechanism exchange for fluoride removal is proposed in this study.     

Effect of ZnO loading to activated carbon on Pb(II) adsorption from aqueous solution

The effect of zinc oxide loading to granular activated carbon on Pb(II) adsorption from aqueous solution was studied in comparison with zinc oxide particles and oxidized activated carbon. Cu(II), Cd(II) and nitrobenzene were used as reference adsorbates to investigate the adsorption. The BET surface area and point of zero charge (pH_PZC) in the aqueous solution were measured for the adsorbents. The adsorption isotherms were examined to characterize the adsorption of heavy metals and organic molecules. The heavy metal adsorption was improved by both the zinc oxide loading and the oxidation of activated carbon. In contrast, the adsorption of nitrobenzene was considerably reduced by the oxidation, and slightly decreased by the zinc oxide loading. The zinc oxide loading to the activated carbon was found to be effectively used for the Pb(II) adsorption whereas only a part of surface functional groups was used for the zinc oxide particles and the oxidized activated carbon. From the experimental results, the surface functional groups responsible for the Pb(II) adsorption on the zinc oxide loaded activated carbon were considered to be hydroxyl groups that formed on the oxide, while those on the oxidized activated carbon were considered to be carboxylic groups.     

Mathematical modelling of styrene drying by adsorption onto activated alumina

This work is focused on the analysis and modelling of styrene drying, raw material in the manufacture of synthetic rubber, by means of adsorption onto activated alumina. Equilibrium experiments, carried out under isothermal conditions at 10°C, correlated to the equation q (kg/kg)=2.659×10⁻⁴ C (mg/kg). Fixed bed column experiments were performed working with different flow rates and using different bed lengths in order to obtain experimental breakthrough curves. A mathematical model that considers the influence of both film and pore mass transfer resistances described satisfactorily well the experimental results. Finally a value of D_p=6.101×10⁻⁹ m²/s was obtained from correlation of experimental data to simulated curves and using the minimum weighted standard deviation as optimisation criterion.     

Removal of elemental mercury from coal combustion flue gas by chloride-impregnated activated carbon

In this work, adsorption of vapour-phase elemental mercury (Hg⁰) from pulverised-coal combustion flue gas by commercially available granular activated carbons treated with zinc chloride (ZnCl₂) impregnation was investigated. The experiment results showed that ZnCl₂ impregnation significantly enhanced the adsorptive capacity for mercury vapour, but decreased the specific surface area of the activated carbon. This could be explained by the occurrence of chemisorption, which was confirmed by adsorption tests over a wide range of temperatures. The influence of ZnCl₂ solution concentration on the mercury removal performance was also studied. Mechanisms of mercury adsorption onto the Cl-impregnated activated carbon were proposed.     

Removal of the persistent pollutant chlorobenzene by adsorption onto activated montmorillonite

The potential of activated bentonite was assessed for adsorption of chlorobenzene from aqueous solution. The bentonite used was treated by chemical and thermal activation over 100–500 °C. The thermal activation increased the adsorption capacity more strongly than chemical activation which consists to acid and hydrogen peroxide treatment. The removal is dominated by adsorption at low initial concentrations and low temperatures and favourable in acidic media. The dependence of the adsorption on pH appears to be related to the solubility of chlorobenzene. Thermodynamic parameters such as ΔH°, ΔS°, ΔG° and Ea have been calculated. The adsorption process is spontaneous and exothermic in nature. The Freundlich isotherm described the adsorption data over the concentration range (20–270 °C).     

Removal of dibenzothiophenes in kerosene by adsorption on rice husk activated carbon

The capacity of rice husk activated carbon (RHAC) to adsorb refractory sulfur compounds of dibenzothiophenes (DBTs) from commercial kerosene was evaluated in terms of their textural and chemical characteristics. Rice husk activated at 850 °C for 1 h showed an acceptable adsorption capacity for DBTs, despite a much lower specific surface area (473 m²/g) and total pore volume (0.267 cm³/g), when compared to micro-porous activated carbon fiber with a large specific surface area (2336 m²/g) and total pore volume (1.052 cm³/g). The volumes of ultramicropores acting as DBTs adsorption sites, and of mesopores leading DBTs into the ultramicropores were closely related to the DBTs adsorption capacity of the RHACs.     

Use of chemically activated cotton nut shell carbon for the removal of fluoride contaminated drinking water:Kinetics evaluation☆

Chemically activated cotton nut shell carbons (CTNSCs) were prepared by different chemicals and they were used for the removal of fluoride from aqueous solution. Effects of adsorption time, adsorbent dose, pH of the solution, initial concentration of fluoride, and temperature of the solution were studied with equilibrium, ther-modynamics and kinetics of the adsorption process by various CTNSC adsorbents. It showed that the chemical y activated CTNSCs can effectively remove fluoride from the solution. The adsorption equilibrium data correlate well with the Freundlich isotherm model. The adsorption of fluoride by the chemical y activated CTNSC is spon-taneous and endothermic in nature. The pseudo first order, pseudo second order and intra particle diffusion kinetic models were applied to test the experimental data. The pseudo second order kinetic model provided a better correlation of the experimental data in comparison with the pseudo-first-order and intra particle diffusion models. A mechanism of fluoride adsorption associating chemisorption and physisorption processes is presented allowing the discussion of the variations in adsorption behavior between these materials in terms of specific surface area and porosity. These data suggest that chemically activated CTNSCs are promising materials for fluoride sorption.     

Adsorption and desorption characteristics of 2-methyl-4-chlorophenoxyacetic acid onto activated carbon

Adsorption and desorption characteristics of the 2-methyl-4-chlorophenoxyacetic acid (MCPA) from aqueous solution onto the activated carbon (GAC, F-400) were studied. Adsorption equilibrium capacities of the MCPA increased with decreasing pH and temperature of the solution. Adsorption equilibrium of the MCPA could be represented by the Sips equation. The internal diffusion coefficients were determined by comparing the experimental concentration decay curves with those predicted from surface diffusion model and pore diffusion model. The adsorption model based on the linear driving force approximation (LDFA) was used for simulating the adsorption behavior of the MCPA in a fixed bed. Over ninety five percent desorption of the MCPA could be obtained using distilled water.     

Removal of fluoride ions from water by adsorption onto carbonaceous materials produced from coffee grounds

Carbonaceous material for the removal of fluoride ions from water was prepared from coffee grounds (CGs) by calcination and subsequent HCl treatment. The characteristics of the CGs, including the surface area, mean pore diameter, pore volume, and surface functional groups were determined, and the morphological characteristics were evaluated using scanning electron microscopy. The adsorption isotherms, saturated amount of fluoride ions adsorbed, and the effect of contact time and temperature on the adsorption of fluoride ions were investigated for a sample of tap water. The specific surface area of CG calcined at 600° (CG600) was larger than that of CGs calcined at 400, 800, and 1000°. Phenolic, lactonic, and carboxyl groups were detected on the CG600 surface. The adsorption capacity of the carbonized CGs for fluoride was ranked in the order CG400 < CG1000 < CG800 < CG600 (where the numeral indicates the carbonization temperature), whereas virgin CG and CG600-NAT (not treated with hydrochloric acid solution) did not exhibit any adsorption ability for fluoride ions. The amount of fluoride ions adsorbed onto CG600 increased with increasing temperature and was consistent with chemical adsorption. The mechanism of adsorption of fluoride ions onto CG600 proceeded via ion exchange with chloride ions (1:1) present on the surface of CG600. The adsorption isotherms were fitted to the Freundlich and Langmuir equations. Moreover, CG600 showed an acceptable adsorption capacity for fluoride ions present in tap water.     

Influence of solvent type on dibenzothiophene adsorption onto activated carbon fiber and granular coconut-shell activated carbon

The adsorption behavior of dibenzothiophene (DBT) on an activated carbon fiber (ACF) and a granular coconut-shell activated carbon (GCSAC) in the solvents n-hexane, n-decane, toluene, and mixture of n-decane and toluene was investigated. The DBT adsorption onto both samples was more active in n-hexane than in n-decane. The lowest DBT adsorption was observed in toluene. Regardless of the type of activated carbons and solvents, all the isotherms fit the Freundlich equation better than the Langmuir equation. At low equilibrium concentrations of <2 mass ppm-S, GCSAC displayed greater capacity for DBT adsorption than did ACF in all the tested solvents. The adsorption kinetics of ACF and GCSAC in all the tested solvents were governed by a pseudo-second-order model.     

Nonionic surfactants adsorption onto activated carbon. Influence of the polar chain length

The adsorption of a nonionic surfactants series characterized by a different length of the hydrophilic tail on an activated carbon has been studied over a wide concentration range. Adsorption isotherms show two steps limited by the critical micelle concentration (c.m.c.) of the surfactants. The adsorption extension depends on the oxyethylenic chain length, in such way that the amount adsorbed decreases with increasing the chain length, although the effect is much lower for the longest polar chains. In the concentration range below the c.m.c. of the surfactants, the molecules are adsorbed by direct interactions with the activated carbon surface, but with different configuration of the polyoxyethylene chain (POE) directed to the aqueous phase. For concentrations above the c.m.c., the adsorption takes place by the interactions between the adsorbed surfactants molecules and differences related to the length of the hydrophilic chain are also found.     

The defluoridation of water by acidic alumina

Fluoride is considered as a major inorganic pollutant present in drinking water. To remove this excess fluoride, defluoridation was done by alumina. In the present study, alumina used was acidic in nature and hence considered as a good fluoride removing adsorbent. Characterization of the adsorbent was done by XRD, SEM, BET and FTIR with BET surface area of 144.27 m²/g. Systematic adsorption experiments were carried out with different process parameters such as contact time, adsorbent mass, pH, temperature and stirring speed. Fluoride adsorption by alumina was highly pH dependent. Maximum fluoride was removed from water at pH 4.4. At very low and very high pH, fluoride removal efficiency was affected. The study of thermodynamic parameters inferred that physical adsorption was dominant with activation energy of 95.13 kJ/mol and endothermic behavior of the process. The kinetics study concluded that pseudo second order kinetics was followed by the adsorption process. Adsorption equilibrium was studied with Langmuir and Freundlich isotherm models. The adsorption process followed Langmuir isotherm with an adsorption capacity of 8.4 mg/g. A regeneration study was proposed in order to reuse the adsorbent for better economy of the process. Finally, a process design calculation was reported to know the amount of adsorbent required for efficient removal of fluoride from aqueous medium.     

Effect of pH on adsorption of 2,4-dinitrophenol onto an activated carbon

The adsorption characteristics of 2,4-dinitrophenol from water onto a granular activated carbon, F-400, were studied at pH 4.3, 7 and 10. Adsorption equilibria of 2,4-dinitrophenol on GAC could be represented by Sips equation. Equilibrium capacity increased with decreasing pH. The differences in the rates of adsorption are primarily attributable to the differences in the equilibrium at the various pHs. Intraparticle diffusion was explained by surface diffusion mechanism. An adsorption model based on the linear driving force approximation (LDFA) was used for simulating the adsorption behavior of 2,4-dinitrophenol in a fixed bed adsorber. Presented at the Int’l Symp. on Chem. Eng. (Cheju, Feb. 8-10, 2001), dedicated to Prof. H. S. Chun on the occasion of his retirement from Korea University.     

A review of the effects of covapors on adsorption rate coefficients of organic vapors adsorbed onto activated carbon from flowing gases

Published breakthrough time, adsorption rate, and capacity data for components of organic vapor mixtures adsorbed from flows through fixed activated carbon beds have been analyzed. Capacities (as stoichiometric centers of constant pattern breakthrough curves) yielded stoichiometric times τ, which are useful for determining elution orders of mixture components. Where authors did not report calculated adsorption rate coefficients k_v of the Wheeler (or, more general, Reaction Kinetic) breakthrough curve equation, we calculated them from breakthrough times and τ. Ninety-five k_v (in mixture)/k_v (single vapor) ratios at similar vapor concentrations were calculated and averaged for elution order categories. For 43 first-eluting vapors the average ratio (1.07) was statistically no different (standard deviation 0.21) than unity, so that we recommend using the single-vapor k_v for such. Forty-seven second-eluting vapor ratios averaged 0.85 (standard deviation 0.24), also not significantly different from unity; however, other evidence and considerations lead us to recommend using k_v (in mixture)=0.85k_v (single vapor). Five third- and fourth-eluting vapors gave an average of 0.56 (standard deviation 0.16) for a recommended k_v (in mixture)=0.56k_v (single vapor) for such.     

改性活性氧化铝除氟性能研究

通过静态实验,研究了改性活性氧化铝(MAA)对F-的吸附性能,考察了吸附时间、改性活性氧化铝的用量对除氟性能的影响,并与新型除氟树脂的除氟性能进行了比较.研究结果表明:活性氧化铝的用量为4 g时,除氟效率最高,为94.57%;活性氧化铝与含氟水的最佳接触时间为3 h;MAA在较低用量(＜4 g)时,除氟效率不如除氟树脂高,但是在较高用量(≥4 g)下,MAA则高于树脂的除氟效率.     

Removal of fulvic acid from aqueous media by adsorption onto modified vermiculite

Clay minerals are low cost materials that can be structurally modified and exploited for removal of natural organic matter from freshwaters. The present study shows that vermiculites modified by ion exchange with hexadecyltrimethylammonium or intercalation with poly(hydroxy iron) cations are potential adsorbents for removal of fulvic acid, whereas the adsorption on the raw clay mineral is negligible. The efficiency of the modified vermiculite was evaluated by measuring adsorption isotherms by the batch technique using initial fulvic acid concentrations between 2.5 and 50.0 mg L^− 1, with one hour of contact time. At least 94% of the fulvic acid initially present in a 20 mg L^− 1 solution was sorbed onto either the intercalated poly(hydroxy iron) cations or the organically modified vermiculite. Up to an initial concentration of 5.0 mg L^− 1 the adsorption is irreversible, and no quantifiable fulvic acid was measured in the desorption experiments. For initial fulvic acid concentrations between 10.0 and 50.0 mg L^− 1, desorption was between 2.3% and 4.9% for Fe(III) intercalated vermiculite, and between 1.4% and 9.2% for the organoclay. The adsorption percentages on intercalated poly(hydroxy iron) cations increased upon lowering pH and increasing the ionic strength, indicating the occurrence of strong binding mechanisms such as ligand exchange. Adsorption percentage of fulvic acid onto the organoclay also increased with lowering of pH, but in this case the adsorption percentages showed a small decrease at high ionic strength, suggesting that electrostatic attraction plays an important role in the adsorption process.