Removal of Copper (II) Ions from Aqueous Solutions using Na‐mordenite

Abstract

The potential to remove copper (II) ions from aqueous solutions using Na‐mordenite, a common zeolite mineral, was thoroughly investigated. The effects of relevant parameters solution pH, adsorbent dose, ionic strength, and temperature on copper (II) adsorption capacity were examined. The sorption data followed the Langmuir, Freundlich, and Dubinin‐Radushkevich (D‐R) isotherms. The maximum sorption capacity was found to be 10.69 mg/g at pH 6, initial concentration of 40 mg/dm³, and temperature of 40°C. Different thermodynamic parameters viz., changes in standard free energy (ΔG⁰), enthalpy (ΔH⁰), and entropy (ΔS⁰) have also been evaluated and the results show that the sorption process was spontaneous and endothermic in nature. The dynamics of the sorption process were studied and the values of rate constant of adsorption, rate constant of intraparticle diffusion were calculated. The activation energy (E_a) was found to be 11.25 kJ/mol in the present study, indicating a chemical sorption process involving weak interactions between sorbent and sorbate. The interaction between copper (II) ions and Na‐mordenite is mainly attributable to ion exchange. The sorption capacity increased with the increase of solution pH and the decrease of ionic strength and adsorbent dose. The Na‐mordenite can be used to separate copper (II) ions from aqueous solutions.     

Hybrid Properties of Alginate‐PEI Adsorbent for Chromium (VI) Removal from Aqueous Solutions

Abstract

An adsorbent consisting of polyethyleneimine (PEI) immobilized in calcium alginate gel beads was synthesized and evaluated for Cr⁶⁺ removal. An evaluation of the synthesis process showed the importance of the PEI molecular weight on the immobilization efficiency. Polyethyleneimine of 70,000 Da molecular weight displayed the highest immobilization percentage at 52%. Batch kinetics and equilibrium tests showed that alginate‐PEI (APEI) resin displayed considerable affinity for negatively charged Cr⁶⁺ complexes at low pH conditions ranging from pH 1.5‐pH 3. The results also indicated the reduction of Cr⁶⁺ to less toxic Cr³⁺ species by the APEI adsorbent. The column adsorption experiments showed the ability of APEI resin to treat a 10 mg/L Cr⁶⁺ solution with pH influent adjustment from pH 1.5 to pH 3 to concentrations that satisfy effluent standards for Cr⁶⁺ (<0.1 mg/L) and total Cr (<0.5 mg/L). Finally, comparisons with a highly aminated commercial resin Chitopearl CS‐03 highlighted the unique ability of the hybrid APEI beads with its amine and carboxylic groups for the adsorption of Cr⁶⁺ as well as the retention of generated Cr³⁺ ions.     

Fluoride Removal from Aqueous Solutions by Magnesium,Nickel, and Cobalt Calcined Hydrotalcite‐like Compounds

Abstract

Magnesium, nickel and cobalt hydrotalcite‐like compounds (MgHT, NiHT, and CoHT), with similar M²⁺:Al³⁺ ratios were synthesized and characterized by XRD. It was confirmed from XRD that the materials have hydrotalcite‐like structure. MgHT, NiHT, and CoHT were calcined and treated with fluoride solutions in a batch system. F^? ions were determined in the remaining solutions using a fluoride ion selective electrode. The kinetics of the fluoride ions sorption on calcined hydrotalcite‐like compounds (CHT) was best described by the pseudo‐second order model and the equilibrium was reached in less than 300 minutes in all cases (MgCHT, NiCHT, and CoCHT). The sorption isotherms of the fluoride by hydrotalcite like compounds can be explained by the Langmuir‐Freundlich model and, the highest fluoride sorption capacity was obtained for NiCHT (1.202 mgF/gCHT). The fluoride removal from aqueous solutions by calcined hydrotalcite‐like compounds depends on the adsorption properties of the thermal decomposition products and the regeneration reaction mechanism of the hydrotalcite‐like compounds.     

Applications of the Biosorption Process for Nickel Removal from Aqueous Solutions – A Review

Wastewaters and contaminants released to the aqueous environment increase due to developing industrialization and technology. These wastewaters should be treated before being discharged to water bodies. Also, reusable materials in wastewaters must be recovered by appropriate techniques. Discharge limits required by the authorities become more stringent with updated legislations. Nickel ions can be reusable by recovering it after the biosorption process. So, this will prevent the loss of raw materials in industries and it also affects the economy in a positive way. Conventional heavy metal removal processes may be costly and inadequate to meet the desired discharge limits and they exhibit low efficiencies. Eco-friendly and economical treatment technologies gain great importance in the removal and recovery of nickel from wastewaters. In this study, biosorption which is the subject of numerous studies and one of the heavy metal removal methods will be investigated, and nickel removal by this technique and the biosorption mechanism will also be elaborated with data from literature studies.     

Kinetic Aspects of Copper‐LIX ® Extraction from Nitrate/Nitric Acid Aqueous Solutions

Abstract

A comparative kinetic study of the extraction of copper from nitrate/nitric acid aqueous solutions by different classes of LIX ^® reagents (LIX 984N, LIX 860N‐I, LIX 84‐I, LIX 65N) was performed. Using a Rotating Diffusion Cell, the rate constants of the chemical reactions (forward and reverse) were estimated and compared. In the case of the mixed extractant LIX 984N, a synergistic effect was observed. The values of the forward reaction constants of all the extractants were found to be an order of magnitude higher than those of the reverse reaction. The relatively low E _a ‐values prove the substantial influence of the diffusion on the extraction kinetics under the experimental conditions studied.     

Equilibrium and Fixed Bed Adsorption of 1‐Butene,Propylene and Propane Over 13X Zeolite Pellets

Abstract

Propylene‐propane separation is one of the most difficult and demanding energetic operation currently practiced using cryogenic distillation. Extensive studies on various alternatives showed that cyclic adsorption processes, and particularly pressure swing adsorption (PSA), might be an option to replace the traditional distillation. In spite of the promising results of the PSA process, much attention is currently being paid to the simulated moving bed technology (SMB) for gas‐phase separations. The ingenious principle of this process is based on the choice of an adequate adsorbent‐desorbent couple. Thus, in the present work 1‐butene has been studied as an interesting desorbent to displace adsorbed propylene‐propane mixture on 13X zeolite. The measurements of pure 1‐butene adsorption isotherms over 13X zeolite were performed with a gravimetric experimental device for pressure ranging from 0 to 110 kPa and at temperature of 333, 353, 373, and 393 K. The experimental adsorption data were correlated using Toth model. The heat of adsorption at zero coverage and the maximum loading capacity of 1‐butene were found to be 54.4 kJ/mol and 2.10 mol/kg, respectively. The adsorption and desorption of 1‐butene on 13X zeolite packed on a fixed bed initially saturated either by a propane‐propylene mixture or a pure C₃ hydrocarbon has been studied. The performance of 1‐butene has been compared with isobutane that was previously proposed to be a highly effective desorbent for C₃H₆/C₃H₈ separation. A model based on a double LDF approximation for the mass transfer combined to a heterogeneous energy balance taking into account a variable velocity of the gaseous bulk phase, has been used to describe the breakthrough curves obtained experimentally at 373 K and 110 kPa.     

Adsorption of CO2 on Hydrotalcite‐like Compounds in a Fixed Bed

Abstract

The reduction of carbon dioxide emission from flue gases can be achieved using post‐combustion technologies, such as adsorption employing efficient solid sorbents. In this work, the adsorption of CO₂ on hydrotalcite‐like Al‐Mg compounds partially carbonated was studied using dynamic and static methods. The breakthrough curves were obtained at different flow gas rates in the range 60 to 100 mL/min and total pressure 1.0 atm. Different mixtures of CO₂ diluted in helium were used (3–20% v/v) at temperatures in the range 29 to 350°C. The experimental equilibrium data were described according to a Langmuir‐like equation. The capacity of adsorption presented a weak dependence on the temperature due to opposite effects of increasing of entropy and increasing of MgO (non‐carbonated) content in the adsorbent at high temperatures. The linear driving force model was suitable to describe the breakthrough curves. The dispersion and mass transfer coefficients were calculated by theoretical correlations and the model described quite very well the adsorption of CO₂ on hydrotalcite‐like compounds in a fixed bed in any temperature.     

Removal of Parabens from Aqueous Solution Using β-Cyclodextrin Cross-Linked Polymer

The removal of four parabens, methyl-, ethyl-, propyl-, and benzyl-paraben, by β-cyclodextrin (β-CD) polymer from aqueous solution was studied. Different β-CD polymers were prepared by using two cross-linkers, i.e., hexamethylene diisocyanate (HMDI) and toluene-2,6-diisocyanate (TDI), with various molar ratios of cross-linker. β-CD-HMDI polymer with molar ratio of 1:7 and β-CD-TDI polymer with ratio 1:4 gave the highest adsorption of parabens among the β-CD-HMDI and β-CD-TDI series, and were subsequently used for further studies. The adsorption capacity of β-CD-HMDI is 0.0305, 0.0376, 0.1854 and 0.3026 mmol/g for methyl-, ethyl-, propyl-, and benzyl-paraben, respectively. β-CD-TDI have higher adsorption capacities compared with β-CD-HMDI, the adsorption capacity are 0.1019, 0.1286, 0.2551, and 0.3699 mmol/g methyl-, ethyl-, propyl-, and benzyl-paraben respectively. The parameters studied were adsorption capacity, water retention, and reusability. Role of both cross-linker in adsorption, hydrophobicity of polymers, and adsorption capacity of different parabens were compared and discussed. All experiments were conducted in batch adsorption technique. These polymers were applied to real samples and showed positive results.     

Pseudo‐Hydroxide Extraction in the Separation of Sodium Hydroxide from Aqueous Solutions Using Alkyl Phenols

Abstract

Pseudo‐hydroxide extraction of sodium hydroxide from aqueous solution using four alkyl phenols of nearly identical molecular weight in 1‐octanol at 25°C was examined to understand the effect of alkyl substituents. The order of extraction strength among the four alkyl phenols tested was 4‐tert‐octylphenol>3,5‐di‐tert‐butylphenol>2,4‐di‐tert‐butylphenol>2,6‐di‐tert‐butyl‐4‐methylphenol. A good correlation with phenol pK _a was observed, indicating that extraction strength is determined by phenol acidity, as modified by steric effects in proximity to the phenol –OH group. The effective partition ratios (P _eff) of two phenols from 1 M NaOH solution were determined, showing that the phenols remain predominantly in the 1‐octanol phase even when converted to their sodium salts. However, the hydrophobicity of the tested phenols may not be sufficient for process purposes. The equilibrium constants for the governing extraction equilibria were determined by modeling the data using the program SXLSQI, supporting the cation‐exchange extraction mechanism. The proposed mechanism consists of two simple sets of equilibria for

1. Ion‐pair extraction to give Na⁺OH^? ion pairs and corresponding free ions in 1‐octanol the phase and

2. Cation exchange by monomeric phenol molecules (HAs) to form monomeric organic‐phase Na⁺A^? ion pairs and corresponding free organic‐phase ions.

Ultrafiltration of Aqueous Solutions of PVA‐Cu(II) Macromolecular Complex

Abstract

The hydrodynamic behavior of aqueous solutions of poly(vinyl alcohol) and poly(vinyl alcohol)–cupric complex and its effect on the performance in the concentration of the macromolecular cupric complex by ultrafiltration is considered in this study which implements various synthetic membranes in polyethersulfone. The polyelectrolyte–like behavior of poly(vinyl alcohol) is highlighted. This behavior disappears in the case of the macromolecular complex. The disappearance of the polyelectrolyte–like effect is explained by the modification of the macromolecular conformation induced by the formation of the complex which takes up a tightly packed conformation. The study of the effect of the variation of the pH and the ionic strength made it possible to observe that the increase of the pH is accompanied by the reduction of the medium viscosity and the increase of the flux through the ultrafilters and the increase of the ionic strength of the medium is accompanied by the increase of the thickness of the adsorbed solute layer. The study of the effect of the nature of the ionic species in solution on the hydrodynamic behavior of the aqueous solutions of the macrocomplex leads to the conclusion that the use of the cupric chloride salt, instead of the nitrate or the sulphate salts, in the preparation of the macrocomplex improves the hydrodynamic properties of the solution and enhances the performance of its treatment by means of the ultrafiltration process.     

Breakthrough Data Analysis of Adsorption of Toluene Vapor in a Fixed‐Bed of Granular Activated Carbon

Abstract

Toluene vapor was adsorbed in a laboratory‐scale packed‐bed adsorber using granular activated carbon (GAC) at constant pressure (101.3 kPa). The adsorber was operated batchwise with the charge of GAC in the range of 2–4 g to obtain the breakthrough curves of toluene vapor. Experiments were carried out at different adsorption temperatures (25–50°C), sparger temperatures (20–30°C), and the flow rates of nitrogen (80–150 cm³/min) to investigate the effects of these experimental variables on the breakthrough curves. The deactivation model was tested for these curves by combining the adsorption of toluene vapor and the deactivation of adsorbent particles. The observed values of the adsorption rate constant and the deactivation rate constant were evaluated through analysis of the experimental breakthrough data using a nonlinear least squares technique. The experimental breakthrough data were fitted very well to the deactivation model than the adsorption isotherm models in the literature.     

Modification of Malonamide Ion-Exchange/Chelating Resins Using the Fields–Kabatschnik Reaction and Their Application to Metal Ion Removal from Aqueous Solutions

A resin containing 2-aminoethyl-substituted amides of malonic acid was modified in the Fields–Kabatschnik reaction using diethyl phosphite. The resultant ion-exchange/chelating resins have aminomethylphosphonate groups. Modification proceeds almost quantitatively, giving a resin with P=1.97 mmol/g, N=4.20 mmol/g, and water regain of 0.44 g/g. It can be selectively hydrolyzed by treatment with trimethylchlorosilane/potassium bromide in dry acetonitrile. Both acidic and ester forms of the resin were used in the removal of Cu(II), Cd(II), Ni(II), and Zn(II) from their diluted 1×10^–4 N solutions in 0.2 M acetate buffer at pH 3.7 and 5.6. The affinity of the resin in an acid form toward divalent metal cations is high, and at pH 5.6 the log K _d is 7.54, 3.97, 3.41, and 3.98, respectively. The resins are selective and the presence of an excess of sodium ions does not influence the uptake of metal ions. The type of complexes formed between the resins and Cu(II) ions was studied using EPR spectroscopy. The ester form of the resin was used in the removal of tetrachloroaurate anions from hydrochloric acid solution. It has been found that the log K _d is in the range of 3.14–3.94 for the uptake of AuCl^– ₄ from 5.0–0.5 M HCl solutions.     

Synthesis of Novel Chelating Adsorbents for Boron Uptake from Aqueous Solutions

Two kinds of novel chelating adsorbents have been synthesized to separate boron from aqueous solutions. One is the boron-specific chelating resin, synthesized by the functionalization of macroporous poly (glycidyl methacrylate-co- trimethylolpropane trimethacrylate), with N-methylglucamine. The other is the organic-inorganic hybrid mesoporous SBA-15 with polyol functional groups, prepared by a two-step post-grafting method. The resin can adsorb boron in almost all pH range, and its maximum uptake capacity reaches 1.15 mmol/g. The present study of the polyol-functionalized SBA-15 shows that the post-grafting is successful and the resulting adsorbent has the uptake capacity of 0.63 mmol/g.     

Thermodynamic Data of 6-(4′-Aminobutylamino)-6-deoxycellulose Sorbent for Cation Removal from Aqueous Solutions

The natural biopolymer cellulose was first modified with thionyl chloride, followed by reaction with 1,4-diaminebutane to yield 6-(4′-aminobutylamino)-6-deoxycellulose. From 1.85% of nitrogen incorporated in the polysaccharide backbone, the amount of 0.66 ± 0.11 mmol of this molecule was anchored per gram of the chemically modified cellulose. The resulting chemically immobilized surface was characterized by elemental analysis, infrared spectroscopy, and nuclear magnetic resonance of the carbon nucleus in the solid state and thermogravimetry. The newly synthesized biopolymer gave maximum sorption capacities of 0.32 ± 0.03, 0.29 ± 0.01, 0.26 ± 0.03 and 0.25 ± 0.02 mmol g^?1 for divalent copper, cobalt, nickel, and zinc cations, using the batch method, whose data were fitted to different sorption models. The thermal effects obtained from a calorimetric titration procedure gave favorable thermodynamic data for cation sorption from aqueous solutions at the solid/liquid interface, suggesting the use of this anchored biopolymer for cation removal from the environment.     

Study of the Fixed‐Bed Adsorption Behavior of Phenylalanine on Solvent Impregnated Resins,Part III

Abstract

The implementation of the SIR technique for the amino acid separation from diluted aqueous solutions in a fixed‐bed column is presented and a mathematical model for the prediction of the adosrption behavior is developed. Independently determined equilibrium and kinetic parameters are used for the calculation of the breakthrough curves. Fixed‐bed parameters, such as axial dispersion and bed porosity, are determined experimently and compared with correlations. Analysis of the Biot and Bodenstein number reveal that the mass transfer through the film liquid around the particles, as well as the axial dispersion in the column, could be neglected at the studied experimental conditions. A simplified mathematical model was found to give the best prediction to the experimental breakthrough curves over a wide range of feed concentrations and flow rates.     

Flowsheet Modeling and Testing of Pseudohydroxide Extraction from Aqueous Sodium Hydroxide Solutions with 3,5‐di‐tert‐Butylphenol in Isopar® L Modified with Exxal® 8

Abstract

A conceptual counter‐current process flowsheet was developed for sodium hydroxide recovery from alkaline solutions via pseudohydroxide extraction (PHE). PHE relies on a simple sodium ion/proton exchange mechanism at elevated pH using a weak organic acid extractant. The contact of the sodium‐loaded organic phase with water results in the reconstitution of the extractant in the organic phase and sodium hydroxide in the aqueous phase. In this work, the 3,5‐di‐tert‐butylphenol (35‐DTBP) cation exchanger was used in the Isopar^® L diluent modified with isooctyl alcohol Exxal^® 8. Equilibrium isotherms determined for PHE from pure sodium hydroxide solutions and simulated radioactive waste leachate were used to develop a semi‐empirical model that could be used for designing PHE process flowsheets. Using this model, a conceptual PHE flowsheet was developed for recovering NaOH from solutions generated by caustic leaching of radioactive tank sludges. The flowsheet consists of the extraction, scrub, and strip processes, each employing four equilibrium stages. The modeling of this flowsheet indicates 97% recovery of the sodium hydroxide from the waste leachate feed solution. An experimental demonstration, performed with a simulated radioactive waste leachate using batch contacts in a co‐current analog of the counter‐current flowsheet, confirmed the potential for practical application of PHE technology.     

Effect of the Alkyl Chain Length in N,N‐Dialkylpyridine‐3‐carboxamides upon their Extraction of Copper(II) from Aqueous Chloride Solutions

Abstract

Three nicotinamide derivatives with two butyl, hexyl, or octyl alkyl chains at amide nitrogen were synthesized. These model individual compounds were used for copper(II) extraction from acidic chloride solutions at constant ionic strength I = 1.0. It was found that during the extraction N,N‐dialkylpyridine‐3‐carboxamides form two complexes with copper(II) and chloride ions; these can transfer into the organic phase. In these complexes the molar ratio of copper:chlorine:extractant = 1:2:2 or 1:2:3. The obtained stability constants of N,N‐dihexyl‐ and N,N‐dioctylpyridine‐3‐carboxamides complexes with copper(II) chloride in water are comparable, but N,N‐dibutylpyridine‐3‐carboxamide complexes stability constants are significantly lower. The partition constants of these complexes in toluene–water system depend on amide hydrophobicity, increasing with increasing carbon chain length in N,N‐dialkylpyridine‐3‐carboxamides.     

Adsorption and Thermal Desorption of Volatile Organic Compounds in a Fixed Bed – Experimental and Modeling

Adsorption and thermal desorption dynamics of acetone in fixed-bed silica gel were studied experimentally and theoretically. The effect of process factors on adsorption and desorption performances was established. Acetone adsorption from air stream was performed by the dynamic (flowing gas) method in a laboratory setup at two levels of air superficial velocity (0.7 and 1.7 cm s^?1), temperature (30 and 40°C), and adsorbent particle diameter (0.21 and 0.54 cm). The values of saturation adsorption capacity (0.147–0.270 g g^?1) increased up to 78% and 36%, respectively, with a decrease in air velocity and adsorption temperature. Acetone thermal desorption from spent silica gel was studied in a thermobalance at three levels of process temperature (60, 70, and 80°C) and two values of particle size (0.21 and 0.54 cm). Equilibrium desorption efficiency (63–81%) was up to 14% larger for finer particles and increased with the desorption temperature. Kinetic models with relevant parameters adjusted based on experimental data were adopted to predict the dynamics of acetone adsorption and thermal desorption. The models simulated well the real conditions and could be applied to scale up and operate the adsorption columns used for air remediation.     

Pseudohydroxide Extraction from Aqueous Sodium Hydroxide Solutions with 3,5‐di‐tert‐Butylphenol in Isopar® L Modified with 1‐Octanol

Abstract

Pseudohydroxide extraction (PHE) was investigated for recovering sodium hydroxide (NaOH) from alkaline process solutions. PHE relies on the deprotonation of a lipophilic weak acid by hydroxide ion with concomitant transfer of sodium ion into an organic phase. Contact of the sodium‐loaded organic phase with water results in the reconstitution of the extractant in the organic phase and NaOH in the aqueous phase, thus leading to a process in which NaOH equivalents are transferred from an alkaline feed solution to an aqueous stripping solution. In this work, we investigated PHE using a process‐friendly diluent—Isopar^® L. The lipophilic cation exchanger 3,5‐di‐tert‐butylphenol (35‐DTBP) was used as the extractant. The Isopar^® L diluent was modified with 1‐octanol to improve its solvation properties and the solubility of 35‐DTBP so that practical Na⁺ concentrations could be achieved in the process solvent. The PHE mechanism at process‐relevant conditions was explored by Raman and Fourier transform infrared spectroscopic measurements. Complementary electrospray ionization mass spectrometry studies were also performed. Equilibrium computer modeling suggested that the Na⁺ extraction behavior can be largely explained by the formation of 1∶1 and 1∶2 Na/35‐DTBP species in the organic phase. Extraction isotherms obtained using simulated caustic leaching solutions indicate the potential utility of this approach for recycling NaOH from complex alkaline mixtures.