Thermodynamics of Chromium(VI) Anionic Species Sorption onto Surfactant-Modified Montmorillonite Clay

Adsorption of Pb, Cu, and Ni Ions on Activated Carbon Prepared from Oak Cupules: Kinetics and Thermodynamics Studies

Agricultural residue-activated carbon and biochar, inexpensive and environmentally friendly adsorbent materials, have recently received significant research attention. This study investigated the potential use of oak cupules in activated carbon form to remove widespread heavy metals (Pb2+, Cu2+, and Ni2+) from wastewater. The oak-activated carbon was prepared from oak cupules and activated with phosphoric acid. Oak-activated carbon was characterized using FTIR, BET analysis, energy-dispersive X-ray spectrometry (EDS), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The Freundlich, Langmuir, and Temkin isotherm models were used to assess the equilibrium data. The impact of various parameters, including pH effect, temperature, adsorbent dose, and contact time, was estimated. The Freundlich model was the most agreeable with Pb2+ adsorption by oak-based activated carbon, and Langmuir was more compatible with Cu2+ and Ni2+. Under optimum conditions, the average maximum removal was 63% Pb2+, 60% Cu2+, and 54% Ni2+ when every ion was alone in the aqueous solution. The removal was enhanced to 98% Pb2+, 72% Cu2+, and 60% Ni2+ when found as a mixture. The thermodynamic model revealed that the adsorption of ions by oak-based activated carbon is endothermic. The pseudo-second-order kinetic best describes the adsorption mechanism in this study; it verifies chemical sorption as the rate-limiting step in adsorption mechanisms. The oak-activated carbon was effective in removing Pb2+, Cu2+, and Ni2+ from wastewater and aqueous solutions.

Modification of ultrasound-pretreated montmorillonite using poly(diallyldimethylammonium chloride) for W and Mo separation and the sequential application in removal of heavy metals

The use of a resin to selectively separate thiomolybdate from a tungsten (W) feed solution is a well-known protocol for achieve high-purity W products; however, the regeneration of saturated resin is laborious. In this study, poly(diallyl dimethyl ammonium chloride) (PDADMA) was used to modify ultrasound-pretreated montmorillonite (Mt) for W and molybdenum (Mo) separation for the first time, and the resultant tetrathiomolybdate (MoS42-)-loaded composite was further tested to remove heavy metals instead of regeneration. Among the three variables of ultrasound pretreatment, that is, Mt concentration, ultrasound power, and treatment time, the Mt concentration exhibited the most significant influence followed by ultrasound power on the separation performance of W and Mo. Compared to the distance of the interlayer space and the surface charge of the modified Mt, the PDADMA content showed a closer correlation with the W/Mo separation coefficient. Assisted by Box-Behnken design, with Mt concentration of 6.9 g/L, ultrasound power of 593.8 W, and treatment time of 13.8 min, the composite with the greatest separation coefficient was obtained. The adsorption of Cu(II) on the optimal W/Mo separation-derived composite was ascribed to the formation of Cu-S complexes, while that of Pb(II) was attributed to complexation and surface precipitation. In contrast, ion exchange with the initially loaded anions, reduction by sulfide to Cr(III), and formation of Cr(III)-S complexes accounted for Cr(VI) removal. The adsorption of Cu(II) and Pb(II) equilibrated faster and showed higher acid-resistance than that of Cr(VI). The adsorption capacities for Cu(II), Pb(II), and Cr(VI) were 0.535, 1.398, and 0.882 mmol/g, respectively. Applying PDADMA to modify Mt as a reagent for W/Mo separation was feasible, and the derived composite was capable of removing cationic and anionic heavy metals.

Preparation and Characterization of Modified Kaolin by a Mechanochemical Method

A mechanochemical approach was utilized to prepare modified kaolin, and the hydrophobic modification of kaolin was realized. The study aims to investigate the changes in particle size, specific surface area, dispersion ability, and adsorption performance of kaolin. The structure of kaolin was analyzed using infrared spectroscopy, scanning electron microscopy, and X-ray diffraction, and the alterations to the kaolin microstructure were thoroughly researched and discussed. The results demonstrated that this modification method can effectively improve the dispersion and adsorption capacities of kaolin. Mechanochemical modification can increase the specific surface area of kaolin particles, reduce their particle size, and improve their agglomeration behavior. The layered structure of the kaolin was partially destroyed, the degree of order was debased, and the activity of its particles was enhanced. Furthermore, organic compounds were adsorbed on the surface of the particles. The appearance of new infrared peaks in the modified kaolin's infrared spectrum suggested that the kaolin has undergone a chemical modification process, introducing new functional groups.

Comparison of Adsorption Capacity and Removal Efficiency of Strontium by Six Typical Adsorption Materials

The rapid development and application of nuclear technology have been accompanied by the production of large amounts of radioactive wastes, of which Sr is a typical nuclide. In this study, six typical materials with strong adsorption properties, namely activated carbon, kaolin, montmorillonite, bentonite, zeolite, and attapulgite, were selected. Their adsorption mechanisms were investigated by analyzing their adsorption isotherms, adsorption kinetics, micromorphologies, element contents, specific surface areas, crystal structures, and functional groups. The results showed that the adsorption efficiency of Sr by the six adsorbents can be ranked as zeolite, bentonite, attapulgite, montmorillonite, activated carbon, and kaolin, among which the maximum adsorption capacity of zeolite was 4.07 mg/g. Based on the adsorption kinetic and thermodynamic fitting results, the adsorption of Sr by zeolites, bentonite and attapulgite is consistent with Langmuir model, the pseudo-first-order and pseudo-second-order model, and the adsorption process of Sr (II) by montmorillonite, activated carbon and kaolinite is consistent with the Freundlich model and corresponds to non-uniform adsorption. The main mechanisms of the six materials are physical adsorption, ion exchange and complexation. In summary, zeolite, bentonite, and attapulgite, especially zeolite, are highly effective for the treatment of radioactive wastewater containing strontium and have great application value in the treatment of radioactive wastes.

Natural water defluoridation by adsorption on Laponite clay

Safe drinking water is a necessity for every human being, but clean water is scarce and not easily available due to natural geochemical factors or industrial pollutant activity. Many issues involving water quality could be greatly improved using clays as adsorbents. We highlight for the first time, the uptake of fluoride from natural water by Laponite, synthetic hectorite clay, in raw and modified state. A series of batch adsorption experiments were carried out to evaluate the adsorption potential of the different parameters. The optimized parameters were: contact time, adsorbent dose and pH. It was found that fluoride uptake from natural water was better using raw Laponite and inorganic-modified Laponite than using organic-modified Laponite clays. Adsorbents were characterized before and after fluoride adsorption by X-ray diffraction, X-ray fluorescence, FTIR, thermo gravimetric analyses and ¹⁹F solid state NMR spectroscopy. The experimental data showed that both Langmuir and Freundlich models fitted an adsorption isotherm well. Thermodynamic parameters such as Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were calculated. These parameters indicated that fluoride adsorption onto Laponite was nonspontaneous and endothermic in temperature range between 25 and 45 °C.

Thermodynamic study of the adsorption of acridinium derivatives on the clay surface

In this study, the adsorption behavior of mono-cationic acridinium derivatives on a synthetic clay mineral (Sumecton SA) was investigated. The acridinium derivatives were adsorbed on the clay surface without aggregation, as found from the changes in the absorption spectra of the acridinium derivatives with SSA and without SSA represented by two-component equilibrium systems of adsorbed and non-adsorbed components. Following the Langmuir isotherm analysis, the adsorption equilibrium constants and maximum adsorption amounts were determined for acridinium derivatives, and the Gibbs free energy change (ΔG) was calculated to be in the range of −33.8 to 40.0 kJ mol⁻¹ from the adsorption equilibrium constants. These results indicated that the adsorption of acridinium derivatives on the clay surface was an exergonic reaction. Moreover, thermodynamic parameters such as enthalpy change (ΔH) and entropy change (ΔS) were obtained from the temperature effect experiments. For all acridinium derivatives, ΔH (from −7.82 to −26.0 kJ mol⁻¹) and ΔS (0.047–0.088 kJ mol⁻¹ K⁻¹) were found to be negative and positive, respectively. It was suggested that not only electrostatic interactions, but also van der Waals forces and hydrophobic interactions played an important role in the adsorption of cationic aromatic molecules on the clay surface. Because these thermodynamic parameters showed a strong correlation with the molecular cross-sectional area of acridinium derivatives, it was suggested that the contribution of hydrophobic interactions became smaller as the molecular cross-sectional area became larger.

Thermodynamic studies indicate that van der Waals and hydrophobic interactions contribute to the adsorption of mono-cationic acridinium derivatives on the clay surface.

The Simultaneous Removal of Zinc and Cadmium from Multicomponent Aqueous Solutions by Their Sorption onto Selected Natural and Synthetic Zeolites

Natural and synthetic aluminosilicate minerals, in particular zeolites, are considered to be very useful in remediation processes, such as purification of waters polluted with heavy metals. That is due to their unique and outstanding physico-chemical properties, rendering them highly efficient, low-cost, and environmentally friendly sorbents of various environmental pollutants. The aim of this study was to examine the sorption capacity of four selected zeolites: A natural zeolite and three synthetic zeolites (3A, 10A, and 13X), towards zinc and cadmium present in multicomponent aqueous solutions, in relation to identified sorption mechanisms. It was stated that synthetic zeolites 3A and 10A were the most efficient in simultaneous removal of zinc and cadmium from aqueous solutions. Additionally, zeolite 10A was demonstrated to be the mineral best coping with prolonged pollution of water with those elements. The mechanism of sorption identified for tested minerals was physisorption.

Highly effective removal of Pb2+ in aqueous solution by Na-X zeolite derived from coal gangue

The present study aimed to synthesize Na-X zeolite from coal gangue powder (CGP) via the alkali fusion hydrothermal method. The optimal synthetic conditions were investigated, the mass ratio of CGP/NaOH(s) was 1:1.25, and crystallization reaction time was 12 h. X-ray powder diffraction, scanning electron microscopy energy-dispersive X-ray spectrum, and Fourier transform infrared spectrometer techniques were used to test the properties of resultant zeolite product, which was highly identical to that of commercial zeolite. The efficiencies of the synthetic zeolite for Pb²⁺ adsorption were analyzed on factors including solution pH, adsorbent dosage, temperature, and contact time. Compared with the pseudo-first-order, Elovich, Freundlich, and Temkin models, the pseudo-second-order and Langmuir models were fitted more satisfactorily with the dynamic data and adsorption equilibrium data, respectively. The maximum Pb²⁺ adsorption capacity of synthetic zeolite (457 mg/g) could be reached when the pH, contact time, temperature, and initial Pb²⁺ concentration was 6, 40 min, 45 °C, and 200 mg/L. The adsorption capacity was higher than many of the natural and synthetic zeolites reported in previous literature.

A review on functional polymer-clay based nanocomposite membranes for treatment of water

Water is essential for every living being. Increasing population, mismanagement of water sources, urbanization, industrialization, globalization, and global warming have all contributed to the scarcity of fresh water sources and the growing demand of such resources. Securing and allocating sufficient water resources has thus become one of the current major global challenges. Membrane technology has dominated the field of water purification due to its ease of usage and fabrication with high efficiency. The development of novel membrane materials can hence play a central role in advancing the field of membrane technology. It is noted that polymer-clay nanocomposites have been used widely for treatment of waste water. Nonetheless, not much efforts have been put to functionalize their membranes to be selective for specific targets. This review was organized to offer better insights into various types of functional polymer and clays composite membranes developed for efficient treatment and purification of water/wastewater. Our discussion was extended further to evaluate the efficacy of membrane techniques employed in the water industry against major chemical (e.g., heavy metal, dye, and phenol) and biological contaminants (e.g., biofouling).

Preparation of ionic liquids/montmorillonite composites and its application for diclofenac sodium removal

Ionic liquid (IL) is an environment friendly organic solvent, which has a relatively low vapor pressure. This work focuses on adsorption of montmorillonite (Mt) to IL as well as removal of diclofenac sodium (DS), an anionic contaminant in water, by IL-modified Mt. The experiment shows absorption of DS increased by increasing IL dosage in modifying Mt. As a result, to modified Mt. with a concentration of IL of 200% cationic exchange capacity (CEC), its static absorption of modified Mt. to DS is 310 mmol/kg, with a rapid rate (reaching balance in 5 min). In dynamic column experiment, absorption of DS reaches balance after 24 h, which absorption amount is 2490 mmol/kg. It can be inferred that modification of IL change surface charge of Mt. and renders intercalation of DS into Mt. interlayers, thus increasing adsorption capacity to DS. These features could further expand the application of ILs and enable IL-modified Mt. to be used as inexpensive sorbents for the removal of chromate and other oxyanions from water.

Elimination of pesticides by natural and modified clays

The objective of this study is the variation of natural and modified clays and their use in industrial waste treatment. For this purpose, we carried out several elimination tests of the effluents by adsorption by using two natural clays from different deposits, namely bentonite located in Maghnia and Djabel Debbagh of Ain Berbar and bentonite coupled with cellulose. The adsorption test was performed on a Decis pesticide. The clays that we tested, in the natural state and in the modified state, are the object of a mineralogical and physicochemical characterization by various techniques of analysis: X-ray diffraction, chemical composition, spectroscopy infrared, cation exchange capacity, scanning electron microscopy, measurement of specific surface area, and various adsorption tests concerning kinetics and capacity, as well as kinetic and thermodynamic modeling and adsorption isotherms. The results showed the practical use of clays for the decontamination of waters contaminated by organic pollutants.

Removal of hexavalent chromium using mackinawite (FeS)-coated sand

This study investigates the feasibility of mackinawite (FeS)-coated sand in permeable reactive barrier applications to treat Cr(VI)-contaminated groundwater under anoxic conditions. For this, Cr(VI) sorption experiments were conducted using both coated and uncoated sands. Solution-phase Cr speciation and Cr K-edge X-ray absorption near-edge structure (XANES) analysis indicated the complete reduction of Cr(VI) to Cr(III) by coated sand. At pH 4.7, substantial amounts of Cr(III) remained in solution due to its unfavorable cationic adsorption at acidic pH. At pH 7.1 and 9.8, it was quantitatively immobilized by forming Cr(III)-bearing precipitates. In contrast, uncoated sand showed the decreasing Cr(VI) sorption with pH. In uncoated sand, magnetite impurities would mediate the partial reduction of Cr(VI). Thus, the pH-dependent sorption by uncoated sand was due to both unfavorable anionic Cr(VI) adsorption and its lesser reduction to Cr(III) with pH. Compared to uncoated sand, coated sand showed significantly increased Cr(VI) sorption at neutral to basic pH. By Fe K-edge XANES analysis, FeS was mainly responsible for Cr(VI) reduction by coated sand, with a green rust-like phase being the major Fe product. Since Fe(OH)₃ is not thermodynamically stable under the redox conditions favoring formation of green rust, Fe(III)-substituted Cr(OH)₃ likely represents a Cr(III)-bearing phase.

Removal of vanadium from wastewater using surface-modified lignocellulosic material

Palm fruit husk, a lignocellulosic material, is an agricultural solid waste. Since raw palm fruit husk does not adsorb V (V), it was subjected to surface modification with a cationic surfactant cetyl trimethyl ammonium bromide (CTAB). The surface-modified palm fruit husk showed adsorption capability for V (V). The maximum adsorption of V (V) takes place at pH 4. Adsorption equilibrium data were fitted to Langmuir, Freundlich, and Dubinin Radushkevich (D-R) isotherm models. Kinetic studies showed that the adsorption data fit second-order kinetic model better than first order. Desorption of V (V) proved that it is feasible to recover V (V) from the spent adsorbent. Effect of coexisting anions like Molybdate, sulfate, nitrate, phosphate, and thiocyanate on the adsorption of V (V) was also studied and the foreign ions compete for the adsorption sites with V (V) anionic species. Quantitative removal of V (V) was achieved from synthetic wastewater.

Rare Earth Elements Removal from Water Using Natural Polymers

Adsorption of rare earth metals, Eu (III) and Nd (III) was investigated on a new environmental friendly material, thiourea functionalized cellulose. Before usage, the synthesized material was characterized by Fourrier Transform Infrared spectroscopy and energy dispersive X-ray analysis. The influence of adsorption parameters (adsorbent dosage, time, temperature and initial metal concentration) on adsorption capacity was investigated. Experimental data were fitted by using the pseudo-first-order and pseudo-second-order kinetic models. Simultaneously thermodynamic and equilibrium studies have been carried out using Langmuir, Freundlich and Sips isotherm. Maximum adsorption capacities were reached in 30 minutes at 298 K having the value of 27 mg/g for Eu (III) and 73 mg/g for Nd (III).

Chromium(VI) sorption efficiency of acid-activated banana peel over organo-montmorillonite in aqueous solutions

In the present study, we examined sorption of chromate (Cr(VI)) to acid-activated banana peel (AABP) and organo-montmorillonite (O-mont) as a function of pH, initial Cr(VI) concentration at a sorbent dose of 4 g L^-1 and at 20 ± 1°C in aqueous solutions. In sorption edge experiments, maximum Cr(VI) removal was obtained at pH 3 after 2 hours by AABP and O-mont (88% and 69%). Sorption isotherm data showed that the sorption capacity of AABP was higher than O-mont (15.1 vs. 6.67 mg g^-1, respectively, at pH 4). Freundlich and Langmuir models provided the best fits to describe Cr(VI) sorption onto AABP (R² = 0.97) and O-mont (R² = 0.96). Fourier transform infrared spectroscopy elucidated that for AABP mainly the -OH, -COOH, -NH₂, and for O-mont intercalated amines and -OH surface functional groups were involved in Cr(VI) sorption. The scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDX) analyses, although partly, indicate that the (wt. %) proportion of cations (e.g., Ca, Mg) in AABP decreased after Cr(VI) sorption. This may be due to ion exchange of chromite (Cr(III)) (produced from Cr(VI) reduction) with cationic elements in AABP. Also, Cr(VI) desorption (using phosphate solution) from AABP was lower (29%) than that from O-mont (51%) up to the third regeneration cycle. This bench scale comparative study highlights that the utilization of widely available and low-cost acid-activated biomaterials has a greater potential than organo-clays for Cr(VI) removal in aqueous media. However, future studies are warranted to precisely delineate different mechanisms of Cr(VI) sorption/reduction by acid-activated biomaterials and organo-clays.

Sorption of Cr(III) and Cr(VI) to K2Mn4O9 nanomaterial a Study of the effect of pH, time, temperature and interferences

A Rancieite type material (K₂Mn₄O₉) nanomaterial was synthesized and tested for the removal of chromium (III) and chromium (VI) from aqueous solutions. The synthesized nanomaterial was characterized using powder XRD and SEM. XRD showed weak diffraction peaks at only at the angles associated with K₂Mn₄O₉. The SEM corroborated that the nanoparticles were present; however, the nanoparticles were clustered into larger aggregates. Batch studies were performed to determine the optimum pH, capacity, time dependency, interferences, and the thermodynamics of the binding. The optimum pH for the binding of Cr(III) and Cr(VI) were determined to be pH 5 and pH 2, respectively. Isotherm studies were performed at temperatures of 4 , 25 , and 45 for Cr(III) and Cr(VI) and showed binding capacities of 21.7 mg/g, 36.5 mg/g, 41.8 mg/g for Cr(III). The Cr(VI) binding capacities were 4.22 mg/g, 4.08 mg/g, and 3.25 mg/g at the respective temperatures. The thermodynamic studies showed that the binding processes for the reactions were spontaneous and endothermic, with a ΔH was 17.54 kJ/mol for Cr(III) and 6.05 kJ/mol for Cr(VI). The of sorption for Cr(III) were determined to be -3.88 kJ/mol, -5.83 kJ/mol and -7.03 kJ/mol at the aforementioned temperatures. The ΔG values for the Cr(VI) sorption were determined to be -4.89 kJ/mol, -5.64 kJ/mol, and -6.05 kJ/mol. In addition, the ΔS values for Cr(III) and Cr(VI) were determined to be 77.92 J/mol and 39.49 J/mol, respectively. The thermodynamics indicate that the binding of Cr(III) and Cr(VI) is spontaneous and endothermic.

Characterization of biochar prepared from slow pyrolysis of Jordanian olive oil processing solid waste and adsorption efficiency of Hg2+ ions in aqueous solutions

Solid waste from Jordanian olive oil processing (OOSW) was used to prepare biochar samples by slow pyrolysis at terminal temperatures of 350, 450, 550 and 630 °C; henceforth known as BC-350, BC-450, BC-550 and BC-630, respectively. These samples were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray diffraction, ash content, moisture content and surface area. The ability of the biochar to remove Hg²⁺ ions from aqueous solutions was investigated in laboratory scale batch experiments. The kinetics, effect of pH and temperature were studied. The optimum pH value for Hg²⁺ adsorption was 5. Dubinin-Radushkevich (D-R) isotherm model was the best fit for the experimental results. Based on the D-R model, the maximum adsorption capacities at 25 °C were 84.93, 94.48, 96.11 and 104.59 mg.g^-1, for BC-350, BC-450, BC-550 and BC-630, respectively. The pseudo-second-order kinetic model was a good fit for the experimental data. The calculated change in free energy ΔG and enthalpy ΔH indicated that the adsorption process was spontaneous and exothermic in nature. The positive value of ΔS showed increased randomness of the solid/solution interface during the adsorption. The results indicated that biochar derived from OOSW can be a good adsorbent for treatment of water contaminated with Hg²⁺.

Effective adsorption of phosphate from wastewaters by big composite pellets made of reduced steel slag and iron ore concentrate

In order to remove phosphate from wastewater, a large plastic adsorption column filled with big phosphate-adsorbing pellets with diameters of 10 mm, heated by electromagnetic induction coils, was conceived. It was found that the prepared big pellets, which were made of reduced steel slag and iron ore concentrate, contain magnetic Fe and Fe3O4. The thermodynamics and kinetics of adsorption of phosphate from synthetic wastewaters on the pellets were studied in this work. The phosphate adsorption on the pellets followed three models of Freundlich, Langmuir and Dubinin-Kaganer-Radushkevick. The maximum phosphate adsorption capacity Qmax of the pellets were 2.46, 2.74 and 2.77 mg/g for the three temperatures of 20°C, 30°C and 40°C, respectively, based on the Langmuir model. The apparent adsorption energies were -12.9 kJ/mol for the three temperatures. It implied that ion exchange was the main mechanism involved in the adsorption processes. The adsorbed phosphate existed on the pellet surface mainly in the form of Fe3(PO4)2. A reduction pre-treatment of the pellet precursor with H2 greatly enhanced pellet adsorption for phosphate. The adsorption kinetics is better represented by a pseudo-first-order model. The adsorbed phosphate amounts were similar for both real and synthetic wastewaters under similar adsorption conditions. The percentage of adsorbed phosphate for a real wastewater increased with increasing pellet concentration and reached 99.2% at a pellet concentration of 64 (g/L). Some specific phosphate adsorption mechanisms for the pellets were revealed and the pellets showed the potential to efficiently adsorb phosphate from a huge amount of real wastewaters in an industrial scale.

Illite spatial distribution patterns dictate Cr(VI) sorption macrocapacity and macrokinetics

This work examines the largely unexplored role of illite spatial distribution patterns in dictating the sorption of Cr(VI), a ubiquitously occurring contaminant. Flow-through experiments were carried out at 0.6, 3.0, and 15.0 m/day using columns packed with the same illite and quartz mass however with different spatial patterns and permeability contrasts. Column-scale sorption macrocapacity and macrorates were found to decrease with transport connectivity, a quantitative measure of heterogeneity characteristics. At 0.6 and 3.0 m/day, well-connected low permeability illite zones oriented in the flow-parallel direction lead to diffusion-controlled mass transport limitation for accessing sorption sites. This results in up to 1.4 order of magnitude lower macrocapacity and macrorates compared to those in minimally connected columns with well-mixed illite and quartz. At 15.0 m/day, effects of spatial heterogeneities are less significant (up to a factor of 2.8) owing to the close to chemical kinetics-controlled condition. Although the column-scale macrocapacity can reach full sorption capacity under low flow conditions, the macrorates are 10(-1) to 10(-3) of the microrates measured in well-mixed reactors. Insights gained here bridge gaps between laboratory observations and field applications and advance predictive understanding of reactive transport processes in the naturally heterogeneous subsurface.

Thermodynamics, Kinetics, and Activation energy Studies of the sorption of chromium(III) and chromium(VI) to a Mn3O4 nanomaterial

In this study, a manganese oxide, Mn₃O₄ was used to remove chromium(III) and chromium(VI) from aqueous solutions. The Mn₃O₄ nanomaterial was synthesized through a precipitation method, and was characterized using XRD, which confirmed the material had a crystal structure similar to hausmannite. In addition, using Scherrer's equation it was determined that the nanomaterial had an average grain size of 19.5 ± 1.10 nm. A study of the effects of pH on the binding of chromium(III) and chromium(VI) showed that the optimum binding pH was 4 and 3 respectively. Batch isotherm studies were performed to determine the binding capacity of chromium(III), which was determined to be 18.7 mg/g, 41.7 mg/g, and 54.4 mg/g respectively for 4°C, 21°C, and 45°C. Chromium(VI) on the other hand had lower binding capacities of 2.5 mg/g, 4.3 mg/g, and 5.8 mg/g for 4°C, 21°C, 45°C, respectively. Thermodynamic studies performed indicated the sorption process was for the most part controlled by physisorption. The ΔG for the sorption of chromium(III) and Chromium(VI) ranged from -0.9 to -13 kJ/mol, indicating a spontaneous reaction was occurring. The enthalpy indicated a endothermic reaction was occurring during the binding and show ΔH values of 70.6 and 19.1 kJ.mol for chromium(III) and Chromium(VI), respectively. In addition, ΔS for the reaction had positive values of 267 and 73 J/mol for chromium(III) and chromium(VI) which indicate a spontaneous reaction. In addition, the sorption process was found to follow pseudo second order kinetic and the activation energy studies indicated the binding process occurred through chemisorption.

Rapid removal of copper with magnetic poly-acrylic weak acid resin: quantitative role of bead radius on ion exchange

A novel magnetic weak acid resin NDMC was self-synthesized for the removal of Cu(2+) from aqueous solutions. NDMC showed superior properties on the removal of Cu(2+) compared to commercial resins C106 and IRC-748, which was deeply investigated by adsorption isotherms and kinetic tests. The equilibrium adsorption amount of Cu(2+) onto NDMC (267.2mg/g) was almost twice as large as that onto IRC-748 (120.0mg/g). The adsorption kinetics of Cu(2+) onto the three resins fitted well with the pseudo-second-order equation. The initial adsorption rate h of NDMC was about 4 times that of C106 and nearly 8 times that of IRC-748 at the initial concentration of 500mg/L. External surface area was determined to be the key factor in rate-controlling by further analyzing the adsorption thermodynamics, kinetics parameters and physicochemical properties of the resins. NDMC resin with the smallest bead radius possessed the largest external surface and therefore exhibited the fastest kinetics. The adsorption amount of Cu(2+) onto NDMC was not influenced as the concentration of Na(+) increased from 1.0 to 10.0mM/L. Dilute HCl solution could effectively desorb Cu(2+). NDMC demonstrated high stability during 10 adsorption/desorption cycles, showing great potential in the rapid removal of Cu(2+) from wastewater.