Lipid adsorption capacities of magnesium silicate and activated carbon prepared from the same rice hull

This study is a comparison of the lipid adsorption capacities of synthetic magnesium silicate and activated carbon produced from rice hulls of the same origin. The lipids examined were the free fatty acids, diacylglycerols and monoacylglycerols of frying oils. Pure oleic acid, an unused sunflower frying oil and a used sunflower frying oil were used in the experiments. The produced adsorbents, magnesium silicate and activated carbon, have surface areas of 680 and 43 m²/g, respectively. The lipid adsorption capacity of the produced magnesium silicate was found as 644 mg polar compounds/g adsorbent and it is higher than the capacities of the industrial adsorbents, Magnesol XL and activated carbon. This value is only 368 mg polar compounds/g adsorbent for the activated carbon produced from the same‐origin rice hull.     

Adsorption of chromium (III) ion from aqueous solution using rice hull ash

Rice hull was calcined to rice hull ash (RHA) at 500 °C under 20 mL air/s for 50 min. The RHA thus prepared has been found to be able to remove chromium (III) ion from aqueous solution, though not very efficient. The experiments indicated that the rate of removal of Cr³⁺ and the removal of Cr³⁺ at equilibrium was increased upon decreasing the RHA dosage. The removal could also be enhanced upon increasing the initial chromium concentration, or adsorption temperature. However, pH in the range of 2.5-5.4 or stroke speed higher than 120 stroke/min could not change the removal. The dependence of the RHA dosage and the initial chromium concentration on the removal have been found to be strong, while that of adsorption temperature is mild. An empirical equation correlating the relationship between the removal of Cr³⁺ and the adsorption time was determined.     

Adsorptive potential of Acacia nilotica based adsorbent for chromium(VI) from an aqueous phase

The objective of this research was to enhance adsorption capacity of Acacia nilotica (keekar) sawdust for the abatement of chromium bearing wastewater and to investigate the effect of process parameters on adsorption capacity. The sawdust was activated by acid wash and functionalized subsequently with formaldehyde. Functionalization of activated sawdust raised its chromium removal efficiency of almost 10% as compared to its adsorption removal efficiency of HCl treated sawdust in a batch adsorption study. Adsorption kinetic data provided better fitting with pseudo second order model. Maximum adsorption capacity calculated through the best fitting Langmuir model was 6.34 mg·g^-1 and 8.2 mg·g^-1 for HCl treated and formaldehyde functionalized sawdust adsorbents, respectively. The adsorption of Cr(VI) was endothermic when studied by varying temperature from 20℃ to 50℃ for both activated and functionalized adsorbents.     

Thermodynamics,kinetics, and isotherms studies for gold(III) adsorption using silica functionalized by diethylenetriaminemethylenephosphonic acid

A novel hybrid material silica gel chemically modified by diethylenetriaminemethylenephosphonic acid GH-D-P has been developed and characterized. The results of the adsorption thermodynamics and kinetics of the as-synthesized GH-D-P for Au(III) showed that this high efficient inorganic–organic hybrid adsorbent had good adsorption capacity for Au(III), and the best interpretation for the experimental data was given by the Langmuir isotherm equation, the maximum adsorption capacity for Au(III) is 357.14 mg/g at 35 °C. Moreover, the study indicated the adsorption kinetics of GH-D-P could be modeled by the pseudo-second-order rate equation wonderfully, and the adsorption thermodynamic parameters ΔG, ΔH and ΔS were −20.43 kJ mol⁻¹, 9.17 kJ mol⁻¹, and 96.24 J K⁻¹ mol⁻¹, respectively. Therefore, the high adsorption capacity make this hybrid material have significant potential for Au(III) uptake from aqueous solutions using adsorption method.     

Study of the adsorption of phenol by two soils based on kinetic and isotherm modeling analyses

Various natural adsorbents, which have been in used for removal of pollutants, in general, and phenol, in particular, are mostly directed towards improving the adsorption capacity of the adsorbents by various pretreatments (chemical, thermal or biological), which necessarily lead to increase in the cost as well as in the level of difficulties in regeneration/disposal of the adsorbent. The present studies, on the other hand, are aimed towards evaluating the feasibility of using two common soils as potential low-cost adsorbents for the removal of phenol from its aqueous solution, in their natural forms (i.e., without any pretreatment). Accordingly, experiments were carried out (in batch mode) for optimization of the adsorption parameters (such as pH, contact time, equilibrium time and adsorbent dosage), for varying initial phenol concentrations. The results showed that the maximum phenol adsorption capacity was found at pH ~6, under a constant temperature of 30 ± 2 °C (at 6-hour equilibrium period). Several kinetic models (viz. Lagergren first-order, pseudo-second-order, Elovich and intra-particle diffusion) as well as isotherm models (Langmuir, Freundlich, Redlich and Peterson and Sip) were applied to the experimental data. The pseudo-second-order model was found to be the most suitable model describing the adsorption of phenol by two soils (which indicated this adsorption as a chemisorption process). On analysis of equilibrium isotherms for the adsorption of phenol by two soils, Redlich-Peterson and Sip isotherms were found to be the best representative for phenol-sorption on two selected, soil adsorbents.     

Synthesis and characterization of carbon/AlOOH composite for adsorption of chromium(VI) from synthetic wastewater

In this work, flake like carbon/AlOOH composite has been synthesized and evaluated as a new adsorbent for the removal of Cr(VI) from synthetic wastewater. Different characterization tools such as, SEM, EDAX, XRD and XPS were performed to characterize the composite material. Batch adsorption studies for Cr(VI) removal were performed under the influence of various operational parameters such as solution pH, contact time, initial solution concentration and temperature. Results obtained revealed that adsorption of Cr(VI) onto carbon/AlOOH composite followed the pseudo-second order kinetics and Freundlich isotherm model. Thermodynamic results suggests that adsorption of Cr(VI) onto carbon/AlOOH composite was spontaneous and endothermic in nature.     

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.     

The effects of picolinic acid and pH on the adsorption of Cu(II) by activated carbon fibers

The adsorption characteristics of Cu(II) on activated carbon fibers (ACFs) from simulated wastewater was investigated in the picolinic acid concentration range from 0.15 to 15 mM by varying pH from 2 to 8. When pH is below 4, the removal fraction of Cu(II) ions decreased with the decrease of pH. The removal fraction of Cu(II) ions is almost constant above pH 4. The removal efficiency of Cu(II) ions increased as the molar ratio of picolinic acid to Cu(II), specific surface area of ACFs and pH of the solution increased. In the case of [Pic]/[Cu(II)]=10, complete adsorption of Cu(II) was performed on ACF, even at pH 2.     

Preparation, characterization and Methylene Blue adsorption of phosphoric acid activated carbons from globe artichoke leaves

Activated carbons were prepared by the pyrolysis of artichoke leaves impregnated with phosphoric acid at 500 °C for different impregnation ratios: 100, 200, 300 wt.%. Materials were characterized for their surface chemistry by elemental analysis, “Boehm titrations”, point of zero charge measurements, infrared spectroscopy, as well as for their porous and morphological structure by Scanning Electron Microscopy and nitrogen adsorption at 77 K. The impregnation ratio was found to govern the porous structure of the prepared activated carbons. Low impregnation ratios (~ 100 wt.%) led to essentially microporous and acidic activated carbons whereas high impregnation ratios (> 100 wt.%) gave essentially microporous-mesoporous carbons with specific surface areas as high as 2038 m²·g^− 1, pore volume as large as 2.47 cm³·g^− 1, and a slightly acidic surface. The prepared activated carbons were studied for their adsorption isotherms of Methylene Blue at pH = 3 and pH = 9. The supermicroporous structure of the material produced at 200 wt.% H₃PO₄ ratio was found to be appropriate for an efficient adsorption of this dye controlled by dispersive and electrostatic interactions depending on the amount of oxygen at the surface.     

Kinetics and equilibrium of dissolved oxygen adsorption on activated carbon

The macroscopic adsorption behavior of dissolved oxygen on a coconut shell-derived granular activated carbon has been studied in batch mode at 301 and 313 K for initial dissolved oxygen concentrations of 10-30 mg/l and oxygen/carbon ratios of 2-180 mg/g. BET (Brunauer, Emmett, and Teller) surface area, micropore volume, and pore size distribution were determined from N₂ isotherm data for fresh and used samples of carbon. The surface groups were characterized using Boehm titrations, potentiometric titrations, and FTIR study. The material is characterized by its high specific surface area , microporocity (micropore volume ), its basic character ( total basic groups) and its high iron content (15,480 ppm Fe). BET n-layer isotherm describes adsorption equilibrium suggesting cooperative adsorption and important adsorbate-adsorbate interactions. Kinetic data suggest a process dependent on surface coverage. At low coverage a Fickian, intraparticle diffusion rate model assuming a local equilibrium isotherm (oxygen dissociation reaction) adequately describes the process. The calculated diffusion coefficients (D) vary between and for initial oxygen concentration of 10 and 20 mg/l, respectively. Sensitivity analysis shows that the oxygen dissociation equilibrium constant determines the equilibrium concentration, whereas the diffusion coefficient controls the kinetic rate of the adsorption process having no effect at the final equilibrium concentration. A combined kinetic mass transfer model with concentration-dependent diffusion (parabolic form) has been developed and successfully applied on the dissolved oxygen adsorption system at high surface coverage. For equilibrium uptake of the estimated mean mass transfer coefficient and adsorption rate constant are and , respectively.     

Behavior of Ni(II) and Mn(II) in single and binary aqueous solutions in the adsorption process by rice hull ashes (RHA)

The retention of nickel and manganese by calcined rice hull ashes (RHA) in single and binary solutions was determined as a function of metal concentration and time. The maximum adsorptions of RHA for Ni(II) and Mn(II) were 7.27 and 6.45 mg/g from monocomponent solutions, and 4.6 and 3.8 mg/g from bicomponent solutions, respectively. The kinetic experimental data best fit a pseudo-second-order model. The k₂ is higher for Mn(II) than Ni(II) considering the monocomponent solutions and this parameter is similar between them if the bicomponent solution is considered. The metallic species were partially desorbed from RHA by water.     

Calcined tetrabutylammonium kaolinite and montmorillonite and adsorption of Fe(II), Co(II) and Ni(II) from solution

Kaolinite and montmorillonite were modified with tetrabutylammonium (TBA) bromide, followed by calcination. The structural changes were monitored with XRD, FTIR, surface area and cation exchange capacity measurements. The modified clay minerals were used for adsorption of Fe(III), Co(II) and Ni(II) ions from aqueous solution under different conditions of pH, time and temperature. The uptake of the metal ions took place by a second order kinetics. The modified montmorillonite had a higher adsorption capacity than the corresponding kaolinite. The Langmuir monolayer capacities for the modified kaolinite and montmorillonite were Fe(III): 9.3 mg g^− 1 and 22.6 mg g^− 1; Co(II): 9.0 mg g^− 1 and 22.3 mg g^− 1; and Ni(II): 8.4 mg g^− 1 and 19.7 mg g^− 1. The modified kaolinite interacted with Co(II) in an endothermic manner, but all the other interactions were exothermic. The decrease of the Gibbs energy in all the cases indicated spontaneous adsorption.     

直接耐酸性枣红在脱硅稻壳活性炭上的吸附热力学与动力学特性

以稻壳为原料,磷酸为活化剂制备了脱硅稻壳活性炭.探讨了浸渍比、磷酸浓度、活化温度和活化时间对活化效果影响.结果表明,制备脱硅稻壳活性炭的合适工艺条件为:浸渍比为2:1,磷酸浓度为50%,活化温度为500℃、活化时间为1 h.通过X射线衍射、比表面、Fourier红外光谱、X射线能谱和高分辨透射电子显微镜等技术对脱硅稻壳...     

Study of adsorption behavior using activated carbon for removal of colored impurities from 30% caprolactam solution produced by means of SNIA-toluene-technology

We studied the adsorption removal of the colored impurities from caprolactam solution by granular activated carbons. It was observed that removal was favored at lower pH (pH 3.84 or below) and higher temperature. The effects of concentration, dosage of activated carbons, contact time have been also reported. Uptake of colored impurities was very rapid in the first 100 minutes and reached equilibrium after 24 h. The batch adsorption kinetics was found to follow the pseudo-second-order model and the rate constants of adsorption for all these kinetic models have been calculated. Three isotherm expressions Langmuir, Freundlich and Trinomial were shown to fit with the experimental results successfully. The mass transfer coefficientβ and the effective diffusion coefficient in aqueous phase Deff was calculated under a temperature 35–80 °C. The value of the mean free energy of adsorption E signifies that the adsorption of colored impurities onto activated carbon has a physical nature.     

Removal of lead(II) from water using activated carbon developed from jujube stones,a low-cost sorbent

The preparation of activated carbon from jujube stones with H₂SO₄ activation and its ability to remove lead from aqueous solutions were reported in this study. The surface structure of the activated carbon was characterized by various physico-chemical methods. Sorption studies were carried out by varying the initial metal ion and the pH: the amount of sorbed Pb(II) ions increased with increasing pH and initial Pb(II) ions concentration. The removal of lead ions was rapid and the kinetic of sorption can be well described by pseudo-second order modelling. The Langmuir model conveniently fits the data of isotherm experiments and the monolayer sorption capacity of Pb(II) ions was determined as 71.43 mg/g at pH 6.0 and 25°C. These results showed that activated carbon prepared from jujube stones could be considered for application as a potential sorbent for the removal of lead from wastewaters.     

Comparison of textile dyeing effluent adsorption on commercial activated carbon and activated carbon prepared from olive stone by ZnCl2 activation

Adsorption of Remazol Red B on activated carbon prepared from olive stone and commercial activated carbon from aqueous solutions was compared. Different activating agent (ZnCl₂) amounts and adsorbent particle size were studied to optimize adsorbent surface area. The adsorptive property of commercial activated carbon and activated carbon prepared from olive stone were investigated in terms of adsorbent dose, temperature, equilibrium time and pH. Then the obtained results were compared for all parameters, According to the results, the equilibrium time, optimum pH, adsorbent dosage were found 60 min, pH < 3–4 and 1.0 g/50 ml respectively. Lower adsorption capacity for RRB on activated carbon prepared from olive stone was found. The kinetic data for both adsorbents supports pseudo-second order model (r² > 0.99) and intra-particle model (r² > 0.95) but the first order kinetic model did not adequately fit to the experimental values (r² < 0.76). The equilibrium adsorption data were interpreted using Langmuir and Freundlich models. The adsorption of Remazol Red B was better represented by the Langmuir equation. In addition, the thermodynamic parameters, standard free energy (ΔG°), standard enthalpy (ΔH°), standard entropy (ΔS°) of the adsorption process were calculated for both adsorbents. To reveal the adsorptive characteristics of the produced active carbon, surface area measurements were carried out and structural analysis was performed using SEM-EDS.     

Removal of Zn(II) from aqueous solution with natural Chinese loess: Behaviors and affecting factors

The Chinese loess was proved a promising adsorbent for Zn(II) removal from aqueous solution with adsorption capacities at 70.2-83.2 mg g^− 1 at 15-45 °C. Batch tests were conducted to evaluate the factors affecting the removal efficiency, of which the pH, temperature and initial Zn concentration all found in positive relevance to the increase of Zn(II) removal efficiency except for the slurry concentration. The uptake of Zn(II) on Chinese loess was considered as ion-exchange adsorption based on the calculated adsorption energy at − 12.8 to − 16.18 kJ mol^− 1 by D-R isothermal adsorption model. The adsorption kinetics follows the pseudo-second-order kinetics and the equilibrating duration was found to be > 24 h. Thermodynamic investigation shows that the enthalpy and entropy changes during adsorption are in the range of 18.27-47.83 kJ mol^− 1 and 52.7-129.6 J mol^− 1 K^− 1, respectively. The predicted Gibb's free energies were in the range of − 5.97-3.09 kJ mol^− 1, indicating that the adsorption was in favor of higher temperature and lower initial Zn(II) concentration. The optimal Zn(II) removal efficiency could be obtained under the following conditions: low or intermediate Zn(II) concentration, long reaction time, high temperature and initial pH > 3.0.     

Analysis of equilibrium,kinetic, and thermodynamic parameters for biosorption of fluoride from water onto coconut (Cocos nucifera Linn.) root developed adsorbent

Drinking water with higher fluoride levels results in serious irremediable health problems that have attained a startle all over the world.Researches focused towards deflouridation through the application of biosorbents prepared from various plants are finding greater scope and significance.Present research is done on Cocos nucifera Linn.(coconut tree) one of the very commonly available plants throughout Kerala and around the globe.An adsorbent developed from the root portion of C.nucifera Linn.is used in the present study.Equilibrium study revealed that the fluoride uptake capacity is quite significant and linearly increases with initial adsorbate concentration.The adsorption data is analyzed for Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models at varying initial adsorbate concentrations(2–25 mg·L~(-1)).It is found that the adsorption of fluoride onto C.nucifera Linn.root adsorbent follows Langmuir isotherm.Langmuir isotherm constants "a" and "b" obtained are 2.037 mg·g~(-1) and 0.823 L·mg~(-1) at an adsorbent dose of 8 g·L~(-1) and temperature(26 ± 1) ℃.The mean free sorption energy, E obtained, is 9.13 kJ ·mol~(-1) which points out that the adsorption of fluoride onto C.nucifera Linn.root adsorbent is by chemisorption mechanism.The kinetic study also supports chemisorption with adsorption data fitting well with a pseudo-second-order kinetic model with an estimated rate constant K_2 of 0.2935 g·mg~(-1) min at an equilibrium contact time of 90 min.The thermodynamic study indicated the spontaneous and endothermic nature(ΔH =12.728 kJ·mol~(-1)) of fluoride adsorption onto the C.nucifera Linn.root adsorbent.Scanning Electron Microscopy(SEM), BET, FTIR, and EDX methods were used to analyze the surface morphology of adsorbent before and after fluoride adsorption process.Experiments on deflouridation using C.nucifera Linn.root adsorbent application on fluoride contaminated ground water samples from fields showed encouraging results.     

Statistically modeled adsorption isotherms for the multilayer gas molecules adsorbed on non-porous solid adsorbents of two and three groups sites

The adsorption isotherms with each saturation vapor pressure factor (c_s1, c_s2 or c_s3) for two groups of sites in two cases of the multilayer and for three groups of sites in one case of the multilayer are derived statistically in heterogeneous non-porous solid adsorbents without interactions among the adsorbed molecules. When some sites of BET isotherm are substituted by less energetic sites, the two-group isotherm obtained by the substitution shows less adsorption over the whole range of relative pressure than the BET isotherm prior to the substitution, at any combined values of f₁ with M₁ of the two-group isotherm with the same saturation vapor pressure factor. A method to get the monolayer sites (v_m) from the ratios of the experimental isotherm to the theoretical isotherm at the whole relative vapor pressure minimizing the standard error is suggested. Our two- or three-group isotherms calculated through many experimental adsorption isotherm data selected appropriately provide larger values of v_m than those obtained from BET isotherms. Differential heat vs. v/v_m and Bose-Condensation heat are mentioned.