Uptake of trivalent chromium ions from aqueous solutions using kaolinite

The sorption of Cr(III) from aqueous solutions on kaolinite has been studied by a batch technique. We have investigated how solution pH, ionic strength and temperature affect this process. The adsorbed amount of chromium ions on kaolinite has increased with increasing pH and temperature when it has decreased with increasing ionic strength. The sorption of Cr(III) on kaolinite is endothermic process in nature. Sorption data have been interpreted in terms of Freundlich and Langmuir equations. The adsorption isotherm was measured experimentally at different conditions, and the experimental data were correlated reasonably well by the adsorption isotherm of the Langmuir, and the isotherm parameters (q(m) and K) have been calculated as well. The enthalpy change for chromium adsorption has been estimated as 7.0 kJ mol(-1). The order of enthalpy of adsorption corresponds to a physical reaction.     

Removal of chromium ions from aqueous solutions by polymer-enhanced ultrafiltration

This study deals with the removal of chromium species from aqueous dilute solutions using polymer-enhanced ultrafiltration (PEUF) process. Three water soluble polymers, namely chitosan, polyethyleneimine (PEI) and pectin were selected for this study. The ultrafiltration studies were carried out using a laboratory scale ultrafiltration system equipped with 500,000 MWCO polysulfone hollow fiber membrane. The effects of pH and polymer composition on rejection coefficient and permeate flux at constant pressure have been investigated. For Cr(III), high rejections approaching 100% were obtained at pH higher than 7 for the three tested polymers. With chitosan and pectin, Cr(VI) retention showed a slight increase with solution pH and did not exceed a value of 50%. An interesting result was obtained with PEI. The retention of Cr(VI) approached 100% at low pH and decreased when the pH was increased. This behavior is opposite to what one can expect in the polymer-enhanced ultrafiltration of heavy metals. Furthermore, the concentration of polymer was found to have little effect on rejection. Permeate flux remained almost constant around 25% of pure water flux.     

Removal of copper ions from aqueous solutions by hazelnut shell

There is a great potential of woody hazelnut shell to use in some applications. Sorption studies are one of these. For this reason in this paper, batch adsorption of Cu(2+) ions onto hazelnut shells was studied. The capacity of the adsorption for the removal of copper ions from aqueous solution was investigated under different conditions such as solution contact time (1-360 min), particle size (0-75, 75-150 and 150-200 microm), temperature of solution (25-60 degrees ) and solution pH (3-7). Moreover, zeta potential of particles at different initial pHs (2-10) was measured. The equilibrium data were processed according to Langmuir and Freundlich's models and higher adsorption capacity values towards Cu(2+) ions were shown. The adsorption kinetics was investigated and the best fit was achieved by a second-order equation.     

Application of DNA condensation for removal of mercury ions from aqueous solutions

DNA has a unique character that allows it to combine with various chemical substrates at the molecular level, and the DNA binding with chemical pollutants can cause serious damage to the organism. The purpose of this research was to apply the strong bonding character of DNA for the removal of mercury ions. In this research, we used DNA condensation promoted by the action of DNA condensing agents, such as cetyltrimethylammonium bromide and a commercially available combination flocculant made of zeolite, to precipitate out the DNA bound with mercury ion in an aqueous solution. When solutions of mercury at 0.02–100 ppm (parts per million) concentrations at a pH range of 2–11 were treated with double-stranded DNA followed by the condensing agent, more than 95% of the mercury ions could be removed after simple filtration or sedimentation.     

Removal of metal ions from aqueous solutions by sorption onto rice bran

A new sorbent (raw rice bran) was investigated for heavy metal ions removal from aqueous solutions. Rice bran characterisation was carried out in order to identify the functional groups possibly involved in the metal binding. The binding process was studied in terms of binding capacity and metal affinity. The adsorption equilibrium was well described by the Freundlich isotherm model. The negative Gibbs free energy values obtained in this study with rice bran confirm the feasibility of the process and the spontaneous nature of sorption.     

Effective removal of zinc ions from aqueous solutions using crab carapace biosorbent

The carapace of the crab (Cancer pagurus), a waste material disposed of by the seafood industry, has recently been shown to have potential as a biosorbent for the removal of metals from aqueous media. Crab carapace in the particle size ranges 0.25-0.8mm and 0.8-1.5mm were used to investigate the effects of agitation speed, contact time, metal concentration and initial pH on the removal of Zn(2+). In sequential-batch process Zn(2+) uptakes of 105.6 and 67.6 mg/g were recorded for 0.25-0.8 mm and 0.8-1.5 mm particles, respectively, while values of 141.3 and 76.9 mg/g were recorded in fixed-bed column studies. Binary-metal studies showed that the presence of Cu(2+) or Pb(2+) significantly suppressed Zn(2+) uptake. This study confirms that crab carapace may be considered a viable and cost-effective alternative to commercial activated carbon or ion-exchange resins for the removal of metals from aqueous media.     

Removal of heavy metal ions from aqueous solutions using various low-cost adsorbents

The removal of single heavy metals Co and Zn from aqueous solutions using various low-cost adsorbents (Fe(2)O(3), Fe(3)O(4), FeS, steel wool, Mg pellets, Cu pellets, Zn pellets, Al pellets, Fe pellets, coal, and GAC) was investigated. Experiments were performed at different solution pH values (1.5-9) and metal concentrations (0.67-333 mg/l). The effect of solution pH on metal adsorption using Fe(2)O(3) and Fe(3)O(4) was significant, but was negligibly small using steel wool, Mg pellets, Fe pellets, and Al pellets over the entire pH range. Steel wool and Mg pellets were the most excellent adsorbents; for example, the removal of Zn and Co from dilute solutions (<35 mg/l) was greater than 94% at an adsorbent dose of 1.7 g/l. A mass transfer model, which involves two parameters tau (50% breakthrough time) and k (proportionality constant), was proposed to describe breakthrough data of Co in the fixed beds packed with steel wool and Mg pellets. The calculated breakthrough curves agreed well with the measured data (standard deviation < 6%). The value of tau decreased with increasing the flow rate. The effects of flow rates on the value of k and adsorption capacity are discussed.     

Removal of copper ions from aqueous solutions by kaolinite and batch design

The removal of copper ions from aqueous solutions by kaolinite was investigated by using a batch-type method. Effects of factors such as pH, ionic strength, temperature, acid-activation and calcination on copper adsorption were investigated. The uptake of copper was determined from changes in concentration as measured by atomic absorption spectrometry. The extent of copper adsorption increased with increasing pH and temperature and with decreasing ionic strength, acid-activation and calcination temperature. The Langmuir and Freundlich adsorption models were used to determine the isotherm parameters associated with the adsorption process. The results provide support for the adsorption of copper ions onto kaolinite. Thermodynamic parameters indicated the endothermic nature of copper adsorption on kaolinite. The experimental results were applied a batch design. As a result, the kaolinite may be used for removal of copper ions from aqueous solutions.     

Use of cellulose-based wastes for adsorption of dyes from aqueous solutions

Low-cost banana and orange peels were prepared as adsorbents for the adsorption of dyes from aqueous solutions. Dye concentration and pH were varied. The adsorption capacities for both peels decreased in the order methyl orange (MO) > methylene blue (MB) > Rhodamine B (RB) > Congo red (CR) > methyl violet (MV) > amido black 10B (AB). The isotherm data could be well described by the Freundlich and Langmuir equations in the concentration range of 10-120 mg/l. An alkaline pH was favorable for the adsorption of dyes. Based on the adsorption capacity, it was shown that banana peel was more effective than orange peel. Kinetic parameters of adsorption such as the Langergren rate constant and the intraparticle diffusion rate constant were determined. For the present adsorption process intraparticle diffusion of dyes within the particle was identified to be rate limiting. Both peel wastes were shown to be promising materials for adsorption removal of dyes from aqueous solutions.     

An evaluation of hydroxyapatite-based filters for removal of heavy metal ions from aqueous solutions

Three hydroxyapatite(HA)-based materials have been investigated with respect to their potential for removing heavy metal ions from aqueous solutions. The materials have been evaluated as both loose powders and in the form of ceramic foams. The results have shown that all three grades of HA were found to be capable of removing a number of different ionic species although the more impure grades generally yielded the best performance. It is believed that the increased impurity levels resulted in increased numbers of lattice defects which were ideal adsorption/exchange sites. 100% removal could be achieved for some ions under the correct experimental conditions. For the ceramic foam filters, the optimum filtration parameters were found to be a high surface area, long filtration times, a low pH and a high filtrate temperature. Ion adsorption was positively detected as a mechanism of ion removal. Ion exchange was not observed but could not be completely ruled out.     

Adsorption of zinc from aqueous solutions to bentonite

The adsorptive properties of natural and Na-enriched bentonite in zinc rich aqueous environment have been studied. The results show that adsorption behavior of both bentonites was strongly depending on the pH. At low pH values, the mechanisms that govern the adsorption behavior of bentonites are dissolution of crystal structure and competition of the metal ions with the H+. Between pH 4 and 7, the basic mechanism is an ion exchange process. The alkaline and alkaline earth metals located in the exchangeable sites of bentonites are replaced with Zn2+ cations present in the aqueous solution. At higher pH values (i.e. pH 8), formation of zinc hydroxyl species may result either participation to the adsorption or precipitation onto the bentonites. Therefore, a rapid increase in the equilibrium removal of zinc was obtained above pH 7. Increase in the initial metal ion concentration led to the increase in equilibrium adsorption to a certain degree; then, a plateau was obtained at higher concentrations. The rate of zinc removal depends also on the solid concentration of the suspension. Reducing the slurry concentration allows particles to get in the more dispersed form, resulting higher available sorption sites for zinc. As a result, the adsorption performance of Na-enriched bentonite is better than the natural bentonite in all physical and chemical changes. The data were fitted both Langmuir and Freundlich isotherms.     

Removal of heavy metal ions from aqueous solutions using carbon aerogel as an adsorbent

The removal of Cd(II), Pb(II), Hg(II), Cu(II), Ni(II), Mn(II) and Zn(II) by carbon aerogel has been found to be concentration, pH, contact time, adsorbent dose and temperature dependent. The adsorption parameters were determined using both Langmuir and Freundlich isotherm models. Surface complexation and ion exchange are the major removal mechanisms involved. The adsorption isotherm studies clearly indicated that the adsorptive behaviour of metal ions on carbon aerogel satisfies not only the Langmuir assumptions but also the Freundlich assumptions, i.e. multilayer formation on the surface of the adsorbent with an exponential distribution of site energy. The applicability of the Lagergren kinetic model has also been investigated. Thermodynamic constant (K(ad)), standard free energy (DeltaG(0)), enthalpy (DeltaH(0)) and entropy (DeltaS(0)) were calculated for predicting the nature of adsorption. The results indicate the potential application of this method for effluent treatment in industries and also provide strong evidence to support the adsorption mechanism proposed.     

Selective removal of cesium ions from aqueous solutions using different inorganic metal hexacyanoferrate-prepared sorbents

Mg-Fe–hexacyanoferrate (MgFeCF) and Ni-Fe–hexacyanoferrate (NiFeCF) were prepared and characterized using X-ray diffraction, Fourier-transform infrared spectroscopy spectra, and thermal analysis. The isotherm study showed that the sorption data fit with the Langmuir and Freundlich isotherms at 25?±?1°C. The sorption capacities of the prepared sorbents for MgFeCF and NiFeCF were found to be 154.32 and 180.83?mg?g^?1, respectively. The adsorption of cesium by MgFeCF and NiFeCF is exothermic and spontaneous processes. Kinetic study indicated that the adsorption of cesium on MgFeCF and NiFeCF fits with the pseudo-second-order kinetic model. Desorption tests indicated that the sorption process is relatively stable. The new sorbents are promising efficient materials for cesium removal from aqueous solutions and sea water. The possibility of reusing the sorbents after stripping the metal ions was studied using 0.5?M HCl, and its efficiency for cesium removal was found to be 98% after five runs.     

Sorption profile of Cd(II) ions onto beach sand from aqueous solutions

Sorption of traces of Cd(II) ions onto beach sand is investigated as a function of nature and concentration of electrolyte (10(-4) to 10(-2)M nitric, hydrochloric and perchloric acids, pH 2-10 buffers and deionized water), shaking time 5-40min, shaking speed 50-200strokes/min, dosage of sand (50-1000mg/15cm(3)), concentration of sorbate (1.04x10(-6) to 1.9x10(-4)M) and temperature (293-323K). Maximum sorption of Cd(II) ions (approximately 66%) is achieved from deionized water using 300mg/15cm(3) sand in 20min. The data are successfully tested by Langmuir, Freundlich and Dubinin-Redushkevich (D-R) sorption isotherms. The values for characteristic Langmuir constants Q=13.31+/-0.20micromol/g and of b=(6.56+/-0.53)x10(3)dm(3)/mol, Freundlich constants A=2.23+/-1.16mmol/g and 1/n=0.70+/-0.05 of (D-R) constants beta=-0.005068+/-0.000328kJ(2)/mol(2), X(m)=46.91+/-11.91micromol/g and energy E=9.92+/-0.32kJ/mol have been estimated. Kinetics of sorption has been studied by applying Morris-Weber, Richenberg and Lagergren equations. The sorption follows first order rate equation resulting 0.182+/-0.004min(-1) The thermodynamic parameters DeltaH=32.09+/-2.92kJ/mol, DeltaS=111.0+/-9.5J/molK and DeltaG=-1.68+/-0.02kJ/mol are evaluated. The influence of common ions on the sorption of Cd(II) ions is also examined. Some common ions reduce the sorption while most of the ions have very little effect. It can be concluded that beach sand may be used as an alternative for the expensive synthetic sorbents.     

Extraction of metal ions from aqueous solutions of mineral acids with crown ether-ionic liquid systems

The extraction of U(VI), Sr, and Cs from solutions of mineral acids (HNO₃, HCl) with a crown ether, cis-syn-cis-dicyclohexyl-18-crown-6 (DCH18C6-A), dissolved in ionic liquids (ILs), 1-butyl-3-methyl-imidazolium derivatives (bmimPF₆, bmimBF₄, bmimTf₂N), was studied. The best physicochemical characteristics (solubility in the aqueous phase, viscosity, hydrophobicity, etc.) are exhibited by a solution of DCH18C6-A in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (bmimTf₂N). The metal distribution ratios (D _M) in the extraction with a 0.01 M DCH18C6-A solution are 80 for CsNO₃, 78 for CsCl, and 162 for Sr(NO₃)₂. With an increase in the HNO₃ and HCl concentrations, D _M decreases, and with 1 M acids it does not exceed 1. The U(VI) extraction from nitric acid solutions with a 1 M solution of DCH18C6-A in bmimTf₂N initially increases with an increase in the aqueous phase acidity, with D _U(VI) reaching 5.4 in 4 M HNO₃, but then decreases in the interval 4–8 M HNO₃, whereas in the extraction with a 1 M solution of tributyl phosphate (TBP) in bmimTf₂N D _U(VI) monotonically increases with an increase in the HNO₃ concentration to 8 M. From hydrochloric acid solutions, U(VI) is extracted with solutions of DCH18C6-A in bmimTf₂N with the D _U(VI) values characteristic of solutions of DCH18C6-A in nonpolar organic diluents. On the whole, ILs as solvents exhibit unusual properties in the extraction of alkali and alkaline-earth elements from neutral solutions and of U(VI) with TBP from concentrated nitric acid solutions.     

Kinetic and equilibrium studies in removing lead ions from aqueous solutions by natural sepiolite

The capacity of sepiolite for the removal of lead ions from aqueous solution was investigated under different experimental conditions. The Langmuir and Freundlich equations, which are in common use for describing sorption equilibrium for wastewater-treatment applications, were applied to data. The constants and correlation coefficients of these isotherm models for the present system at different conditions such as pH, temperature and particle size were calculated and compared. The equilibrium process was well described by the Langmuir isotherm model and the maximum sorption capacity was found to be 93.4 mg/g for the optimal experimental condition. The thermodynamic parameters (DeltaG(o), DeltaH(o) and DeltaS(o)) for lead sorption on the sepiolite were also determined from the temperature dependence. The influences of specific parameters such as the agitation speed, particle size and initial concentration for the kinetic studies were also examined. The sorption kinetics were tested for first order reversible, pseudo-first order and pseudo-second order reaction and the rate constants of kinetic models were calculated. The best correlation coefficients were obtained using the pseudo-second order kinetic model, indicating that lead uptake process followed the pseudo-second order rate expression.     

Application of dolochar in the removal of cadmium and hexavalent chromium ions from aqueous solutions

Dolochar, a waste material generated in sponge iron industry, is processed and put to test as an adsorbent for removal of Cd(II) and Cr(VI) ions from aqueous solutions. The dolochar samples were characterised to determine the different phases and their distribution by reflection microscopy. The analysis indicated that the sample consists of metallic iron, fused carbon, and Ca-Mg bearing phases (Ca-Mg-silicate-oxide) along with lots of voids and pores. The fixed carbon (FC) content of the material is 13.8% with a Langmuir surface area of 81.6 m²/g and micropore area of 34.1 m²/g. Batch adsorption experiments have been conducted to study the sorption behaviour of Cd(II) and Cr(VI) ions on dolochar as a function of particle size, contact time, adsorbent dosages, pH and temperature. It is observed that higher pH and temperature enhances sorption of Cd(II) ions. In contrast, the adsorption for Cr(VI) is found to be better in acidic pH in comparison to alkaline media. The equilibrium adsorption isotherm data are tested by applying both Langmuir and Freundlich isotherm models. It is observed that Langmuir isotherm model fitted better compared to the Freundlich model indicating monolayer adsorption. The thermodynamic parameters such as ΔG°, ΔH° and ΔS° indicate the effectiveness of dolochar to remove Cd(II) and Cr(VI) ions from aqueous solution. The kinetics of adsorption is found to better fit to pseudo second order reaction.     

Adsorption characteristics of heavy metal ions onto a low cost biopolymeric sorbent from aqueous solutions

In this study, the adsorption conditions of Cu(II), Pb(II) and Cd(II) metal ions onto sporopollenin have been studied. The different variables effecting the sorption capacity such as pH of the solution, adsorption time, initial metal ion concentration and temperature have been investigated. Adsorption isotherms correlated well with the Freundlich type adsorption isotherm and adsorption capacities were found to be 0.0195, 0.0411 and 0.0146 mmol g(-1) for Cu(II), Pb(II) and Cd(II) metal ions, respectively. Experimental data were also evaluated to find out kinetic characteristics of the adsorption process. Adsorption processes for three target heavy metal ions were found to follow pseudo-second order type adsorption kinetics. Intraparticle diffusion was found to take part in adsorption processes but it could not be accepted as the primary rate-determining step. The mean free energies of adsorption (E) were found to be between 8 and 16 kJ mol(-1) for the metal ions studied and therefore adsorption mechanism for the adsorbent was explained as an ion-exchange process. But it was observed that chelating effect is also playing an important role in the adsorption of metal ions onto sporopollenin. Thermodynamic parameters, DeltaH degrees , DeltaS degrees and DeltaG degrees were also calculated from graphical interpretation of the experimental data. Standard heats of adsorption (DeltaH degrees ) were found to be endothermic and DeltaS degrees values were calculated to be positive for the adsorption of Cu(II), Pb(II) and Cd(II) ions onto the adsorbent. Negative DeltaG degrees values indicated that adsorption process for these three metal ions onto sporopollenin is spontaneous.     

Nucleation of solid solutions crystallizing from aqueous solutions

The study of nucleation and growth mechanisms of salts from aqueous solutions, as a function of supersaturation, is described using both macroscopic and microscopic experiments. In situ observations in a fluid cell in an atomic force microscope (AFM) reveal phenomena not accounted for in standard crystal-growth theories, specifically on the role of the crystal structure of the substrate in controlling spiral growth and two-dimensional nucleation. As a model example, the crystallization of two isostructural salts, BaSO(4) and SrSO(4), is described. The growth of solid-solution crystals is considerably more complex. The supersaturation of a given aqueous solution relative to a solid solution is different with respect to each solid composition, and it leads to the possibility that different compositions can simultaneously grow by different mechanisms on the same crystal face. Oscillatory compositional zoning is another consequence of the interplay between the thermodynamics and the kinetics of nucleation. The factors which control nucleation and growth of the solid solution (Ba,Sr)SO(4) from an aqueous solution are described. The predictions made from the theory are compared with direct observations of crystal growth in an AFM.     

Removal of Pb(II) ions from aqueous solutions by sulphuric acid-treated wheat bran

Sulphuric acid-treated wheat bran (STWB) was used as an adsorbent to remove Pb(II) ions from aqueous solution. It was observed that the adsorption yield of Pb(II) ions was found to be pH dependent. The equilibrium time for the process was determined as 2h. STWB gave the highest adsorption yield at around pH 6.0. At this pH, adsorption percentage for an initial Pb(II) ions concentration of 100mg/L was found to be 82.8 at 25 degrees C for contact time of 2h. The equilibrium data obtained at different temperatures fitted to the non-linear form of Langmuir, Freundlich and Redlich-Peterson and linear form of Langmuir and Freundlich models. Isotherm constants were calculated and compared for the models used. The maximum adsorption capacity (q(max)) which was obtained linear form of Langmuir model increased from 55.56 to 79.37mg/g with increasing temperature from 25 to 60 degrees C. Similar trend was observed for other isotherm constants related to the adsorption capacity. Linear form of Langmuir isotherm data was evaluated to determine the thermodynamic parameters for the process. Thermodynamic parameters show that adsorption process of Pb(II) ions is an endothermic and more effective process at high temperatures. The pseudo nth order kinetic model was successfully applied to the kinetic data and the order (n) of adsorption reaction was calculated at the range from 1.711 to 1.929. The values of k(ad) were found to be 5.82x10(-4) and 21.81x10(-4)(min(-1))(mg/g)(1-n) at 25 and 60 degrees C, respectively. Activation energy was determined as 29.65kJ/mol for the process. This suggest that the adsorption Pb(II) ions by STWB is chemically controlled.