Time evolution of a natural clinoptilolite in aqueous medium: conductivity and pH experiments

The chemical behavior in an aqueous medium of a natural zeolitic material, NZ (mainly consisting in crystals of the zeolites clinoptilolite/heulandite) has been studied through electrochemical techniques, complemented by atomic absorption spectrometry. The time dependence of the conductivity of the aqueous medium in the presence of NZ, showed a steep increase at the beginning followed by a slower increase for longer times until saturation of the system is reached. The release of the ions present in the zeolitic material at different times, was followed by means of atomic adsorption spectroscopy, which indicated that the sodium ion is the main responsible for the conductivity response. The interaction of NZ with the aqueous medium revealed a pH increase in the weakly acid region and a decrease in the basic region. The correlation between conductometric and pH-metric studies suggests that an ion-exchange mechanism takes place within the very first minutes of the interaction of NZ with the aqueous medium, followed by the temperature-dependent dissolution of minority phases up to several days. Finally, a comparative study between NZ and a modified form of this zeolite with sodium carbonate (NZ1), showed a faster pH increase with time for NZ1.     

Removal of Fe(III) ion from aqueous solution by adsorption on raw and treated clinoptilolite samples

Iron (III) adsorption from aqueous solutions onto raw and pretreated clinoptilolite was investigated here. Various parameters for iron removal; initial solution pH, contact time and metal ion concentration were optimized. The equilibrium data were modeled by both the Langmuir and Freundlich adsorption isotherms at optimal conditions. Adsorption capacities of raw samples and those pretreated with Na₂S₂O₈ at 20 °C , 70 °C and with HNO₃ at 20 °C were all similar but samples pretreated with HNO₃ at 70 °C were significantly different; iron (III) removal from samples pretreated with HNO₃ decreased with increasing pretreatment temperature. Tests with Fe⁺³ solutions containing phenol, CsCl or KCl, indicated the continued presence of these ions in zeolite which either promoted or retarded the adsorption of iron. The Fe⁺³ adsorption capacity of clinoptilolite pretreated with HNO₃ at 70 °C was about two times greater with, than without, CsCl and KCl. The kinetics of iron adsorption from aqueous solution were also investigated using the first-order Lagergren equation and a pseudo-second-order model.     

Microwave effect on ion-exchange and structure of clinoptilolite

The effect of microwave irradiation on the ion exchange degree and structure of clinoptilolite mineral has been examined in comparison with the conventional heat treatment in waterbath. Clinoptilolite-rich mineral from the Western Anatolia, Bigadiç region was used for the experimental study. The mineral was mainly clinoptilolite (80–85%) and additionally, quartz (5–10%), and analcime + mordenite (< 5%) were found as co-existing minerals. The mineral was stable towards dehydration and maintains its original structure up to 800 °C. The BET and Langmuir surface areas of the sample were found to be 22 and 17 m²/g for N₂ adsorption and 28 and 22 m²/g for Ar adsorption, respectively. For the exchange experiments, clinoptilolite rich mineral was treated with 1 N NaCl salt solution both in a microwave unit and waterbath for 10 min, 1 h and 2 h at 80 °C. The waterbath treatment with the same conditions was continued for two additional weeks. The chemical composition of the parent and Na-exchanged forms of the clinoptilolite rich minerals were analyzed by using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). Microwave treatment was found to be more rapid and effective for ion exchange compared to conventional waterbath treatment. Additionally, the XRD results reveal that microwave irradiation has zero effect on the structure of the clinoptilolite rich mineral.     

Transformation of Cs-exchanged clinoptilolite to CsAlSi5O12 by hot-pressing

Dense CsAlSi₅O₁₂ was successfully obtained by hot pressing of Cs-exchanged clinoptilolite at 900 °C. Simultaneous application of high temperature and mechanical pressure allowed formation of CsAlSi₅O₁₂ at temperature considerably lower than 1150 °C which was the lowest reported temperature of CsAlSi₅O₁₂ formation in pressureless sintered Cs-exchanged clinoptilolite. CsAlSi₅O₁₂ formation was preceded by complete amorphisation of Cs-exchanged clinoptilolite in temperature range between 700 and 900 °C. Bearing in mind that clinoptilolite possesses high affinity for Cs cation it is believed that hot pressing of Cs-exchanged clinoptilolite might be an efficient way to immobilize radioactive Cs by its incorporation into crystal lattice of stable CsAlSi₅O₁₂. The samples sintered at 950 °C had relative density about 84% of theoretical density and open porosity of only 6% which is expected to result in low Cs leaching rate.     

Few-layered graphene oxides as superior adsorbents for the removal of Pb(II) ions from aqueous solutions

Few-layered graphene oxides (GOs) were successfully synthesized from graphite using Hummers’ method. The synthesized GOs were characterized in detail by SEM, AFM, XRD, and FTIR spectroscopy. The prepared GOs were used as adsorbents to preconcentrate Pb(II) ions from large volumes of aqueous solutions. The effects of pH, ionic strength and temperature on the removal of Pb(II) ions from solution to GOs were investigated. The sorption of Pb(II) on GOs was dependent on pH values and independent of ionic strength, which suggested that Pb(II) sorption on GOs was mainly dominated by strong inner-sphere surface complexation. The maximum adsorption capacities (C _smax ) of Pb(II) on GOs were calculated to be 344 mg/g at 293 K, 487 mg/g at 308 K, and 758mg/g at 333 K, respectively. The C _smax values are the highest sorption capacities of today’s materials for the sorption of Pb(II) ions from aqueous solutions. The thermodynamic parameters were calculated from the temperature-dependent sorption isotherms, and the results indicated that Pb(II) sorption on GOs was spontaneous and endothermic. The results suggested that the GOs were promising materials for the preconcentration of Pb(II) and other kinds of heavy metal ions from aqueous solutions in environmental pollution cleanup in real work.     

Removal of Pb(II) from aqueous solution by adsorption using activated tea waste

A basic investigation on the removal of Pb(II) ions from aqueous solutions by using activated tea waste was conducted in batch conditions. An inexpensive and effective adsorbent was developed from waste tea leaves for the uptake of Pb(II) from aqueous solution. The influence of different experimental parameters—shaking time, particle size, adsorbent dose, initial pH, temperature, etc.—on lead uptake was evaluated. Lead is adsorbed by the developed adsorbent up to maximum of 99.7%. The initial Pb(II) concentrations were 5, 10, 15 and 20 mg/l in the experiment. The adsorption was found to be exothermic in nature. The Langmuir, Freundlich and Tempkin isotherm models were tried to represent the equilibrium data of Pb(II) adsorption. The adsorption data was fitted very well to the Langmuir isotherm model in the studied concentration range of Pb(II) adsorption. Isotherms have been used to determine thermodynamic parameters of the process: free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°). Column experiments were performed to study the practical applicability of the system. The kinetics and the factors controlling the adsorption process were also discussed. Activated tea waste is a better adsorbent compared to other adsorbents available in literature.     

Biosorption of cadmium(II) and lead(II) from aqueous solutions using Pleurotus ostreatus immobilized on bentonite

The purpose of this work was to evaluate the potential of a white rot fungi (P. ostreatus) immobilized on bentonite, in a continuous flow removal of trace heavy metals. The procedure is based on the biosorption of Cd(II) and Pb(II) ions on a column of bentonite loaded with dried, dead fungi components prior to their determination by atomic absorption spectroscopy (AAS). Cd(II) and Pb(II) were determined with a relative error of less than 5%. Various parameters such as “pH, amount of adsorbent, eluent type and volume, flow rate of the solution and matrix interference effect” on the retention of the metal ions were investigated. This procedure was applied to Cd(II) and Pb(II) determination in aqueous solutions, including tap water system. The optimum experimental parameters were determined to be pH 5, concentration of 10 mg/L, contact time of 30 min and 0.2 g of adsorbent for a quantitative adsorption of the metals. The optimum flow rate was found to be 2.5 mL/min for all metal ions. Each column can be used up to 20 successive analyses without considerable change in recoveries of metal ions.

The proposed method is excellent as regards simplicity, sensitivity, selectivity, precision, accuracy and column stability.     

Removal of phenol from aqueous solutions by adsorption onto polymeric adsorbents

Phenolic compounds are one of the most representative pollutants in industrial wastewater, and efficient removals of them have attracted significant concerns. In this study, several commercial and new synthetic polymers (acrylonitrile, 1,3‐butadiene, and styrene copolymer (ABS), styrene, acrylonitrile copolymer (SAN), poly(vinyl chloride) (PVC), poly(methyl methacrylate) (PMMA), poly(tert‐butyl acrylate) (ptBA)) with special functionalities were evaluated for their ability to remove phenol from an aqueous solution. Equilibrium studies were conducted in the range of 20–100 mg/L initial phenol concentrations, 3–11 pH solutions, and a temperature range of 25–65°C. The results showed that (styrene, 1,3‐butadiene) copolymer (SAN) gave the best adsorption capacity among all of the polymers tested. The solution temperature, phenol concentration, and agitation rate played a significant role in influencing the capacity of the adsorbents toward phenol molecules. An increase in solution temperature led to a significant increase in the adsorption capacity of SAN. The percentage of adsorption decreased when initial concentration of phenol increased. However, the percentage removal of phenol was observed to increase with agitation. Removal of phenol using polymeric microbeads is difficult to investigate under high and low pH values because it requires a lot of acid or base to adjust the pH values in the adsorption media. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Removal of lead (II) and cadmium (II) from aqueous solutions using spent Agaricus bisporus

The sorption of Pb and Cd from aqueous solutions by spent Agaricus bisporus was investigated. The effects of contact time, pH, ionic medium, initial metal concentration, other metal ions presence and ligands were studied in batch experiments at 25°C. Maximum sorption for both metals was found to occur at an initial pH of around 5.5. The equilibrium process was well described by the Langmuir isotherm model, with maximum sorption capacities of 0.2345 and 0.1273 mmol g^?1 for Pb and Cd respectively. Kinetic data followed the pseudo‐second‐order kinetic model. The presence of NaCl and NaClO₄ caused a reduction in Cd sorption, while Pb sorption was not remarkably affected. The presence of other metals did not affect Pb removal, while the Cd removal was much reduced. HCl or EDTA solutions were able to desorb Cd from the spent Agaricus bisporus (SAB) completely, while an approximately 60% and 15% desorption yield was obtained for Pb when HCl 0.01 mol L^?1 or EDTA 0.001 mol L^?1 were used, respectively. The results of FTIR, SEM and EDX analysis indicated that other mechanisms, such as surface complexation and electrostatic interactions, must be involved in the metal sorption in addition to ion exchange. © 2012 Canadian Society for Chemical Engineering     

Potentiality of the porous geopolymer sphere in adsorption of Pb (II) from aqueous solutions: Behaviors and mechanisms

In this study, a porous geopolymer sphere (PGS) was developed that comprised a mixture of coal gasification fly ash, steel slag, metakaolin and an alkaline activator (SiO₂/Na₂O molar ratio = 1.33) (44.89 wt%, 20.10 wt%, 2.01 wt% and 33 wt%) using an 8.5 wt% hydrogen peroxide foaming agent. The micro characteristics of the PGS were tested using X-ray CT, BET, XRD, and FT-TR. The mechanism to Pb adsorption was revealed via adsorption isotherm, adsorption kinetics, thermodynamics, and adsorbent characterization. Results indicated that the PGS was a mesoporous structure (the most accessible pore sizes was 9.31 nm) and the main crystalline phases in the PGS were ZK-5 zeolite, vaterite, calcium silicate, and wustite. Batch experiments showed that the adsorption of Pb by the PGS was best described by pseudo-second-order kinetics and the Langmuir isotherm model, indicating that the adsorption process was dominated by chemical adsorption. Moreover, the maximum adsorption capacity of the PGS could reach 59.31 mg/g. The mechanism of Pb(II) adsorption using the PGS mainly involves: (1) ion exchange, (2) a complexation reaction between Pb and the PGS, (3) lattice immobilization of Pb and in the ZK-5 zeolite and zeolite-like phase, (4) physical adsorption by the PGS.     

Removal of copper ions from aqueous solution by adsorption using LABORATORIES-modified bentonite (organo-bentonite)

Equilibrium, kinetic and thermodynamic aspects of the adsorption of copper ions from an aqueous solution using linear alkylbenzene sulfonate (LABORATORIES) modified bentonite (organo-bentonite) are reported. Modification of bentonite was performed via microwave heating with a concentration of LABORATORIES surfactant equivalent to 1.5 times that of the cation exchange capacity (CEC) of the raw bentonite. Experimental parameters affecting the adsorption process such as pH, contact time and temperature were studied. Several adsorption equations (e.g., Langmuir, Freundlich, Sips and Toth) with temperature dependency were used to correlate the equilibrium data. These models were evaluated based on the theoretical justifications of each isotherm parameter. The Sips model had the best fit for the adsorption of copper ions onto organo-bentonite. For the kinetic data, the pseudo-second order model was superior to the pseudo-first order model. Thermodynamically, the adsorption of copper ions occurs via chemisorption and the process is endothermic (ΔH⁰>0), irreversible (ΔS⁰>0) and nonspontaneous (ΔG⁰>0).     

Arsenic (V) removal from aqueous solutions using natural clay ceramic monoliths

Abstract

An adsorbent material arranged in a ceramic monolith (CM) obtained by extrusion technique using natural bentonite and alumina (as raw materials) is presented. Ceramic and raw materials were characterized by X-ray fluorescence, thermal analysis, X-ray diffraction, and textural analysis (with N₂ adsorption–desorption at 77?K and Hg intrusion–extrusion porosimetry) to determine their chemical and physical properties. Then, As (V) adsorption capacity of the CM at different pH (3–9) using arsenic aqueous solution (with 2000?µg As (V) L^?1) was evaluated. Additionally, studies of kinetics and equilibrium of As (V) adsorption on CM were performed. It was found that: (i) the As (V) removal capacity is favored at acidic pH, reaching an average value of 15?µg As (V) per gram of CM; (ii) from kinetic studies, As (V) adsorption on CM occur in two stages, the first of them reaching a lower As uptake in a short time period, followed by an slow second stage with a subsequent higher As uptake, which continued for a longer time period, reaching equilibrium conditions in approximately 24?h; and (iii) the As (V) adsorption isotherm is a type-Langmuir, indicating that the CM present an homo quantity of fixed sites to adsorb the As (V).     

Adsorption performance of Al-pillared bentonite clay for the removal of cobalt(II) from aqueous phase

In this research, the natural bentonite clay collected from Ashapura Clay Mines, Gujarat State, India, was utilized as a precursor to produce aluminium-pillared bentonite clay (Al-PILC) for the removal of cobalt(II) [Co(II)] ions from aqueous solutions. The original bentonite clay and Al-PILC were characterized with the help of chemical analyses, methylene blue (MB) adsorption isotherm, powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared spectroscopy (IR), while the thermal stability of the samples were studied using thermogravimetry (TG). Surface charge density of the samples as a function of pH was investigated using potentiometric titrations. Adsorption experiments were conducted under various conditions, i.e., pH, contact time, initial concentration, ionic strength, adsorbent dose and temperature. The most effective pH range for the removal of Co(II) ions was found to be 6.0–8.0. The maximum adsorption of 99.8% and 87.0% took place at pH 6.0 from an initial concentration of 10.0 and 25.0 mg l⁻¹, respectively. Kinetic studies showed that an equilibrium time of 24 h was needed for the adsorption of Co(II) ions on Al-PILC and the experimental data were correlated by either the external mass transfer diffusion model for the first stage of adsorption and the intraparticle mass transfer diffusion model for the second stage of adsorption. The intraparticle mass transfer diffusion model gave a better fit to the experimental data. The Arrhenius and Eyring equations were applied to the data to determine the kinetic and thermodynamic parameters for explaining the theoretical behaviour of the adsorption process. The equilibrium isotherm data were analyzed using the Langmuir, Freundlich and Scatchard isotherm equations and the adsorption process was reflected by Freundlich isotherm. The efficiency of the Al-PILC was assessed by comparing the results with those on a commercial ion exchanger, Ceralite IRC-50. The suitability of the Al-PILC for treating Co(II) solutions was tested using simulated nuclear power plant coolant samples. Acid regeneration was tried for several cycles with a view to recover the adsorbed Co(II) and also to restore the adsorbent to its original state.     

Removal of Cu(II) from aqueous solutions by chelating starch derivatives

Two chemically modified starch derivatives, crosslinked amino starch (CAS) and dithiocarbamates modified starch (DTCS), were prepared and used for the removal of Cu(II) from aqueous solutions. CAS was found to be effective for the adsorption of Cu(II), which tended to form a stable amine complex. Adsorption of Cu(II) onto DTCS was higher than that onto CAS. Experiments showed that the adsorption processes of Cu(II) on both CAS and DTCS were endothermic, and followed Freundlich isothermal adsorption. For both adsorbents, dynamic modeling of their adsorption showed that the first‐order reversible kinetic model described the adsorption process. The adsorption rate constants of CAS and DTCS were 1.578 and 10.32 h^?1, respectively. From the results of the thermodynamic analysis, free energy ΔG, enthalpy ΔH, and entropy ΔS of the adsorption process were calculated. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3881–3885, 2004     

Removal of Cu(II) from aqueous solutions by recycled tire rubber

A batch adsorption system was applied to study the adsorption of Cu(II) ions from aqueous solutions by crumb rubber. The effects of pH ranging from 1.5 to 7.0, contact time ranging from 6 to 96 h and initial metal concentration ranging from 1 mg L^− 1 to 50 mg L^− 1 on the removal of Cu(II) were studied. Results show that adsorption of Cu(II) is pH-dependent and the best results are obtained at pH = 6.0. Results also show that copper uptake is accompanied by displacement of zinc and therefore probably involves an ion exchange type mechanism. Langmuir and Freundlich adsorption models were applied to describe the isotherms and isotherm constants. Equilibrium data agreed very well with the Langmuir model. Results clearly show that crumb rubber is an effective adsorbent for the removal of Cu(II) from aqueous solutions.     

Removal of arsenic(III) from aqueous solution by concrete-based adsorbents

The present paper investigates the adsorption of arsenic(III) (As(III)) onto 2 concrete-based low-cost materials, i.e., Aerocrete and Vermiculite impregnated by ferric oxyhydroxide. Adsorption experiments were performed to study the effect of initial pH, initial concentration of As(III), contact time, and ions usually present in water. No significant effect of the initial pH on the adsorption of As(III) by Aerocrete and Vermiculite was observed at the pH range of 4–8. The As(III) removal efficiency decreased at a high initial pH (i.e., 10). The Langmuir isotherm showed that the maximum As(III) adsorption capacity of Aerocrete and Vermiculite is 15.15 and 13.51 mg/g, respectively, which is higher than that observed using titanium dioxide (i.e., 3.52 mg/g), at pH 7 and 24 ±1 °C. A pseudo-second order kinetic model fitted well the experimentally obtained kinetic data. This suggests that chemisorption most probably controls the adsorption of As(III) on Aeroctere and Vermiculite. Significantly, As(III) (1 mg/L) could be removed almost completely by both Aeroctere and Vermiculite (1 g/L) in 30 and 60 min, respectively at pH 7 and 24 ±1 °C. Importantly, Ca²⁺, Mg²⁺, Na⁺, HCO₃⁻, SO₄²⁻, and Cl⁻ ions had no significant effect on the adsorption of As(III) on Aeroctere and Vermiculite. The results showed that the proposed concrete-based adsorbents have the potential to remove As(III) from water.     

Cadmium(II) removal from aqueous solution using microporous titanosilicate ETS-10

In this work, the removal of Cd²⁺ ions from aqueous solution using microporous titanosilicate ETS-10 was investigated in order to assess its potential as decontaminating agent in tertiary treatments. Accordingly, batch stirred tank experiments were carried out to study the ion exchange kinetics and equilibrium. Results show that pH affects considerably the ion exchange capability of ETS-10: at pH 4 it is 1.567 × 10² eq m⁻³, at pH 6 it is 3.629 × 10³, and no further increment was observed at pH 8. This is an extremely important observation since pH of industrial effluents and other wastewaters rounds 6. Both Langmuir and Langmuir–Freundlich isotherms were fitted to the experimental data measured. The second model performs slightly better as the calculated absolute average deviations show: AAD_L = 2.94% and AAD_LF = 2.40%. Concerning the kinetic behavior, the ion exchange was successfully represented by a Nernst–Planck based model (AAD = 11.9%).     

Removal of zinc ions from aqueous solution using a cation exchange resin

The present study is concerned with the mass transfer and kinetics study of zinc ions removal from aqueous solution using a cation exchange resin packed in a rotating cylindrical basket reactor. The effect of various experimental parameters on the rate of zinc ion removal, such as initial zinc ion concentration, packed bed rotation speed and temperature has been investigated. In addition to find a suitable equilibrium isotherm and kinetic model for the zinc ion removal in a batch reactor. The experimental isotherm data were analyzed using the Langmuir, Freundlich and D–R equations. The equilibrium data fit well in the Langmuir isotherm. The experimental data were analyzed using four sorption kinetic models, pseudo-first and second-order equations, the Elovich and the intraparticle diffusion model equation, to determine the best fit equation for the biosorption of zinc ions onto purolite C-100 MH resin. Results show that the Elovich equation provides the best correlation for the biosorption process.     

Removal of chromium (III) and cadmium (II) from aqueous solutions

Chromium and cadmium are toxic heavy metals present in wastewaters from a variety of industries. A strong cationexchange resin, Amberlite IR 120, was used for the removal of chromium and cadmium. The resin was prepared in two different cationic forms, as Na⁺ and H⁺. The optimum conditions were concentration, pH, stirring time and resin amount. The concentration range was between 2–50 mg/L, pH range between 2–10, stirring time between 5–60 min, and the amount of resin was from 50–1000 mg. Exchange capacities, moisture content and optimum conditions of this resin were determined in a batch system. The stirring speed was 2000 rpm during all of the batch experiments. The initial and final chromium and cadmium amounts were determined by atomic absorption spectrophotometry. The optimum conditions were found to be a concentration of 20 mg/L, pH of 5.5, stirring time of 20 min and 100 mg of resin. The results obtained show that the Amberlite IR 120 strong cation-exchange resin performed well for the removal and recovery of chromium and cadmium.     

Removal of hydrogen sulfide by clinoptilolite in a fixed bed adsorber

Due to its toxic and corrosive nature, H₂S should be safely removed from the gases produced in gasification or combustion processes. In this study, adsorption of hydrogen sulfide was investigated on a natural zeolite, namely clinoptilolite. H₂S adsorption characteristics of Western Anatolian clinoptilolite was studied in a fixed-bed system at different temperatures between 100 and 600 °C at atmospheric pressure. H₂S adsorption capacity of clinoptilolite was found to be about 0.03 g S/g clinoptilolite at 600 °C. A deactivation model considering concentration dependence of activity term was applied to experimental results and adsorption rate constant and activation energy values were evaluated. Good agreement of the experimental breakthrough curves with the model predictions was observed.