Sorption studies of cadmium and lead ions on hybrid polysaccharide biosorbents

The sorption of lead and cadmium ions on hybrid pectin-based biosorbents containing gellan, carob, and xanthan gum has been studied. The rate constant of the metal ions’ sorption on hybrid P + X beads (analyzed with the two kinetic models: pseudo-first-order and pseudo-second–order models) is at least two times higher than obtained on other pectin-based sorbents. The Langmuir equation fits experimental data better than Freundlich model. A greater equilibrium constant B for lead(II) than cadmium(II) indicates a stronger bond between Pb(II) and pectin-based beads. Prepared hybrid materials are promising biosorbents for heavy metals’ removal from waste waters.     

Removal of Cadmium from Aqueous Solution using Wheat Stem,Corncob, and Rice Husk

Three kinds of agricultural by-products, wheat stem, corncob, and rice husk, were tested as biosorbents for cadmium removal from aqueous solution. The study was focused on the evaluation and comparison of the potential of the agriculture by-products as biosorbents of cadmium with the sorption isotherms determination. The impact of solution pH and kinetic study was also discussed. The result indicated that cadmium removal was strongly dependent on solution pH and the optimum pH range is 4.5 ～ 6.0. The sorption process was fast, and the sorption equilibrium can be attained within 60 min. The kinetic process fit well with the pseudo-second-order kinetic model. For the three kinds of biosorbents, the initial sorption rate as well as the maximum sorption capacity q _max calculated from the Langmuir isotherm equation showed the following tendency: rice husk > wheat stem > corncob. The maximum sorption capacity of the three kinds of biosorbents enhanced after being base treated, especially for wheat stem and corncob. This study indicated that wheat stem, corncob, and rice husk displayed the potential to be used as biosorbents for cadmium removal from aqueous solution.     

Adsorption of cadmium(II) from aqueous solution by surface oxidized carbon nanotubes

Carbon nanotubes (CNTs) were oxidized with H₂O₂, KMnO₄ and HNO₃. Their physicochemical properties were investigated by BET N₂ adsorption, laser particle examination, Boehm’s titration, zeta potential measurement and cadmium(II) adsorption. The experimental results suggest that cadmium(II) adsorption capacities for three kinds of oxidized CNTs increase due to the functional groups introduced by oxidation compared with the as-grown CNTs. The cadmium(II) adsorption capacity of the as-grown CNTs is only 1.1 mg g⁻¹, while it reaches 2.6, 5.1 and 11.0 mg g⁻¹ for the H₂O₂, HNO₃ and KMnO₄ oxidized CNTs, respectively, at the cadmium(II) equilibrium concentration of 4 mg l⁻¹. Adsorption of cadmium(II) by CNTs was strongly pH-dependent and the increase of adsorption capacities for HNO₃ and KMnO₄ oxidized CNTs is more obvious than that of the as-grown and H₂O₂ oxidized CNTs at lower pH regions. The experiments of CNT dosage effect on the cadmium(II) adsorption show that the adsorption capacity for KMnO₄ oxidized CNTs has a sharper increase at the CNT dosage from 0.03 to 0.08 g per 100 ml than the as-grown, H₂O₂ and HNO₃ oxidized CNTs and its removal efficiency almost reaches 100% at CNT dosage of 0.08 g per 100 ml. Analysis revealed that the KMnO₄ oxidized CNTs hosted manganese residuals, and these surely contributed to cadmium sorption to a yet-undefined extent.     

Preparation of poly(vinyl alcohol)/tetraethyl orthosilicate hybrid membranes modified with TMPTMS by sol-gel method for removal of lead from aqueous solutions

Poly(vinyl alcohol)/tetraethyl orthosilicate (PVA/TEOS) ion exchange hybrid membranes modified with 3-mercaptopropyltrimethoxysilane (TMPTMS) were prepared by the sol-gel method, and their applications for the removal of lead ions from aqueous solutions in a batch sorption process were studied. The functional groups of the hybrid membranes were characterized by FTIR. Batch adsorption studies such as TMPTMS content, pH, adsorbent dose, contact time, initial concentration and temperature were evaluated. The maximum adsorption capacity of lead ions was found to be 61.62mg g^?1, respectively. The kinetic data were analyzed by pseudo-first-order and pseudo-second-order kinetic models. The Freundlich and Langmuir isotherm models were applied to describe the equilibrium data. Thermodynamic parameters indicated that the lead adsorption onto the membrane is an endothermic and spontaneous process. The PVA/TEOS/TMPTMS hybrid membrane is regenerated by 0.5M HNO₃/0.1 M HCl in equal ratio solution and the adsorption capacity did not change remarkably after five sorption-desorption cycles.     

Acid modified bamboo‐type carbon nanotubes and cup‐stacked‐type carbon nanofibres as adsorbent materials: cadmium removal from aqueous solution

BACKGROUND: Nitrogen‐doped multi‐walled carbon nanotubes (CN_x) and cup‐stacked‐type carbon nanofibres (CST) were modified with nitric acid, at 85 °C, for 1–3 h to enhance their cation adsorption capacity, and were used for cadmium removal from aqueous solutions. These carbon nanostructures were characterized by SEM, EDX, FTIR, BET surface area, TGA and acid/base titrations. In addition, cadmium adsorption experiments were carried out at different pH values and constant temperature. RESULTS: EDX and FTIR revealed a 0.4 times increase in oxygen content after acid treatment, which was reflected in an increment of up to 1.93 mmol g^?1 of acid sites and in a shift of about two units of the zero point charge to lower pH values. The BET surface area, in general, decreased as the oxidation time increased. Finally, batch sorption experiments indicated that CN_x are more effective than CST to sequester Cd²⁺ at pH 7; the sorption capacities of these materials increased as pH rose. CONCLUSIONS: The results obtained indicate that it is feasible to modify both physical and chemical properties of the carbon nanostructures CN_x and CST by HNO₃ in such a way that they can be used to adsorb cations present in aqueous solutions. Copyright © 2008 Society of Chemical Industry     

Kinetics of cadmium(II) sorption by an iminodiacetic ion exchanger in the presence of a nonionic surfactant

The kinetics of cadmium(II) sorption from separate solutions and from the mixtures with nonionic surfactant Lutensol AO-10 (oxyethylated alkohols) in hydrogen form of chelating iminodiacetic ion exchanger Purolite S-930 has been investigated: kinetic curves and breakthrough curves have been obtained, determining the concentration of nonionic surfactant spectrophotometrically, and that of cadmium(II) complexometrically. The kinetic coefficients (B_t), the coefficients of the intraparticle diffusion (D, m²s⁻¹), the effective kinetic coefficients of the external mass transfer (β, s⁻¹), the overall rate constants (k₀, s⁻¹) and the distribution coefficients (K_d) have been calculated. Cadmium(ll) sorption from the separate solutions and from the mixtures with AO-10 is controlled by the intraparticle diffusion at pH 5 and pH 7.6. Reducing the initial solution acidity from pH 5 to pH 7.6, the coefficients of intraparticle diffusion (D) for cadmium(II) increase, although they decrease as the cation exchanger saturation increases. The equilibrium sorption of cadmium(II) is slightly higher at pH 7.6 than at pH 5 both without and with the surfactant. The performance of Purolite S-930 packed column with respect to cadmium(II) is better in the absence than in the presence of the surfactant: the action of AO-10 interferes with the removal of cadmium(II). The sorption of AO-10 is negligible both in the absence and in the presence of cadmium(II). Regeneration of Purolite S-930 using 0.7 M HCl for both the removal of cadmium(II) and the conversion into hydrogen form enables the 100% recovery of the sorptive capacity. The rate of the cadmium(ti) intraparticle diffusion, its negligible concentration at the breakthrough, sufficiently high equilibrium sorption and the ability to restore the sorptive capacity refer to the possibility of the hydrogen form of Purolite S-930 practical use, including the purification of plating rinse water for its recycling, preventing the environmental contamination with cadmium(II).     

Novel imino diacetamide grafted styrene divinyl benzene resin for separation and recovery of palladium from simulated high level liquid waste

Imino diacetamide styrene divinyl benzene resin was evaluated for separation of palladium from simulated high level liquid waste (HLLW). The kinetics of sorption was found to be fast, and the kinetic data were fitted well to the pseudo-second-order kinetics model. Very high K_d (~10³) were obtained for Pd for feed solutions having acidity from 0.25 M to 4.0 M HNO₃. The loading studies of the resin showed the maximum sorption capacity of 54 mg/g. Back extraction studies showed that sorbed Pd can be effectively back extracted using 0.01 M thiourea in 0.2 M HNO₃. Studies with simulated HLLW showed preferential sorption of Pd over other metal ions.     

Cadmium Recovery from HCl Solutions Using Cyanex 301 and Cyanex 302 Immobilized in Alginate Capsules (Matrix-Type vs. Mononuclear-Type Mode of Encapsulation)

Cyanex 301 and Cyanex 302 have been immobilized in alginate capsules by two methods: the matrix-type process immobilizes the extractant as homogeneous-dispersed vesicles while the mononuclear mode consists of encapsulation of the extractant drop by an alginate layer. The influence of HCl concentration on Cd(II) removal is discussed as a function of acid concentration and extractant. The sorption isotherms are fitted by the Langmuir model; maximum sorption capacities reach up to 42 mg Cd g^?1 in 0.1 M HCl. Uptake kinetics are controlled by resistance to intraparticle diffusion. Cadmium is desorbed using either 1 M HNO₃ or 1 M thiourea/1 M HCl solutions.     

Polyethyleneimine-containing sol-gels as novel sorbents for the removal of cadmium from aqueous solutions

The removal of cadmium ions from aqueous solutions is described using polyethyleneimine (PEI) entrapped in sol-gel matrices. The process is optimized with respect to operating conditions and both sorption and desorption are considered. The sorption process followed the Langmuir isotherm, and the corresponding Langmuir constants q_max and K_dwere found to be 80.64 mg Cd2⁺/g PEI and 236.36 mg/L, respectively, using the immobilized PEI polymer. More than 90% of the cadmium could be recovered in 2 h using 2 M NaCl solutions. This technique has potential applications in the recovery of cadmium in aqueous waste streams.     

Potassium hexacyanocobalt ferrate and ammonium molybdophosphate sorption bags for the removal of 137Cs from aqueous solutions and a simulated waste

In the present study, the removal and immobilization of ¹³⁷Cs from aqueous waste solutions and a simulated waste was investigated. Two inorganic ion‐exchange complexes: di‐potassium hexacyanocobalt(II)‐ferrate(II), K₂CoFe(CN)_6·xH₂O (KCFC), and ammonium‐12‐molybdophosphate [(NH₄)₃PMo₁₂O_40·aq] (AMP), were charged separately into porous nylon bags (sorption bags) of 5 µm pore diameter. The first complex (KCFC) was prepared in our laboratory. The second (AMP) was used for comparison. Easy handling and increased potential for reuse characterize the sorption bag technique. The KCFC complex was investigated by thermal gravimetric analysis (TGA) and differential thermal analysis (DTA), porosity, infra‐red (IR) and X‐ray powder diffraction (XRD). The chemical and structural investigations revealed that the KCFC complex has adequate ion‐exchange capacity and high affinity for ¹³⁷Cs. The sorption bag technique showed promising results for the removal of ¹³⁷Cs from aqueous waste solutions. The KCFC bags showed the highest ¹³⁷Cs removal (～0.91 g g^?1), at pH 8.5; AMP bags gave the highest ¹³⁷Cs removal (～0.97 g g^?1) in 0.1 N HNO₃ and 1.5 N HNO₃, both with a waste: sorbent ratio of 80 cm³ g^?1. Sorption data for both KCFC and AMP revealed a good fit to the Freundlich sorption isotherm. To assess the potential of sorption bags, the used bags were regenerated in different leachants and reused in further sorption investigations. ¹³⁷Cs recovery from the used sorbents was ～0.46 g g^?1 using 6 N HCl as leachant for AMP, compared with ～0.253 g g^?1 for KCFC using 6 N NaCl. These results indicated stronger cesium immobilization in the KCFC complex. Copyright © 2003 Society of Chemical Industry     

Effect of pH,flow rate and concentration on the sorption of Pb and Cd on montmorillonite: I. Experimental

Continuous column adsorption of lead (Pb) and cadmium (Cd) was studied using pH adjustment and calcium‐saturated montmorillonite in a short stainless steel column. Changing either pH or flow rate, while keeping inlet concentration of the ions constant, led to considerable changes in effluent concentrations and breakthrough curves (BTCs). At low pH values (2–4), H⁺ ions competed strongly with lead and cadmium ions; at intermediate pH (4–6), ionic size played the major role in adsorption and ion exchange and at high pH (6–9) precipitation was the major process taking place especially for lead sorption. At low flow rates less than 0.5 cm³ min⁻¹, sorption of both lead and cadmium increased due to the long retention time in the column. When both lead and cadmium ions were present in the feed, adsorption remained the same while that of cadmium decreased compared with single ion experiments. © 1999 Society of Chemical Industry     

Potential of carbon nanomaterials for removal of heavy metals from water

Heavy metals, such as, cadmium, lead, nickel and zinc can be removed from water using sorbents. The rate and extent of removal may be enhanced by choice of appropriate sorbents. In this study heavy metal sorption was studied on indigenously synthesized carbon nanomaterials (CNMs). Two CNMs differing in surface morphology were synthesized using turpentine oil in a chemical vapour deposition (CVD) setup by varying the process parameters. Activation and catalyst removal were achieved by post-treatment with HNO₃ and KOH. Characterization of the CNMs produced revealed that both comprised of graphitic amorphous carbon, however, while the nanocarbon (NC) produced using cobalt catalyst in N₂ atmosphere comprised of varying grain sizes indicative of soot, the nanoporous carbon (NPC) produced using silica catalyst in H₂ atmosphere had a distinctive uniformly porous surface morphology. Comparative sorption studies with cadmium, lead, nickel and zinc also revealed greater sorption on NPC compared to NC. Batch isotherms for the various heavy metals using NPC and a commercial activated carbon (AC) widely used for metal sorption revealed that NPC is characterized by significantly higher metal sorption capacity and more favourable sorption energetics. The superior performance of NPC as a sorbent may be due to its unique nanoporous structure.     

Sorption and desorption of cadmium and lead on pectin-based biosorbents – batch and column studies

ABSTRACT

The hybrid pectin-based beads containing carob, gellan and xanthan gum were studied to be suitable for removing the Cd(II) and Pb(II) from aqueous solution in column system. Desorption of the ions from studied materials was also determined in batch and continuous studies. It was possible to remove the Cd(II) and Pb(II) ions from solution of concentration ca. 130 and 250 mg/L, respectively, to the level permissible by law. Both ions may be completely removed from our biosorbents using mineral acid solutions (confirmed by mass balance). The minimal lifetime of sorbent was also determined to be at least 10 cycles.     

Sorption of Rare-Earth Elements and Ac on UTEVA Resin in Different Acid Solutions

The distribution of some rare-earth elements (REEs) on Uranium and TEtraValent Actinides (UTEVA) resin was determined from different concentrations of inorganic (HCl, HNO₃, HClO₄, HPF₆) and one organic acid – CCl₃COOH. Low sorption of all REEs in the range of 1 M–5 M HNO₃ was observed. In more concentrated HNO₃, a rapid increase of the distribution coefficients (K_d) was noticed with an increase in the atomic number of the lanthanides as well as in Y and Sc. The system UTEVA–CCl₃COOH showed a higher selectivity for Eu(III). Chromatographic elution profiles were checked in order to confirm the obtained K_d values.     

Adsorptive Removal of Lead from Battery Wastewater by Coconut Coir

The sorption behavior of lead ions on coconut coir has been investigated to decontaminate lead ions from aqueous solutions. Various physico-chemical parameters were optimized to simulate the best conditions in which this material can be used as an adsorbent. Maximum adsorption was observed at 0.0001 to 0.001 mol L^?1 of acid solutions (HNO₃, HCl and HClO₄) using 0.4 g of adsorbent for 4.83 × 10^?5 mol L^?1 lead concentration in ten minutes equilibration time. The adsorption of lead was decreased with the increase in the concentrations of all the acids used. The kinetic data indicated an intraparticle diffusion process with sorption being pseudo-second order. The determined rate constant k₂ was 8.8912 g mg^?1 min^?1. The adsorption data obeyed the Freundlich isotherm over the lead concentration range of 2.41 × 10^?4 to 1.45 × 10^?3 mol L^?1. The characteristic Freundlich constants i.e., 1/n = 0.44 ± 0.02 and K = 0.184 ± 0.0096 m mol g^?1 have been computed for the sorption system. The sorption mean free energy from the Dubinin-Radushkevich isotherm is 10.48 ± 0.72 kJ mol^?1 indicating the ion-exchange mechanism of chemisorption. The uptake of lead increases with the rise in temperature (293–333 K). Thermodynamic quantities i.e., ΔG, ΔS, and ΔH have also been calculated for the system. The sorption process was found to be endothermic. The proposed procedure was successfully applied for the removal of lead from battery wastewater samples.     

Studies on the Sorption of Palladium using Cross‐Linked Poly (4‐Vinylpyridine‐Divinylbenzene) Resins in Nitric Acid Medium

Various cross‐linked (4, 8, and 12%) gel‐type weak‐base poly(4‐vinylpyridine) (PVP) resins were studied for palladium recovery from nitric acid medium. The sorption of palladium was found to decrease with an increase in cross‐linkage of the resin. 8 and 12% PVP resins exhibited maximum D _Pd(II) values at 2–6 M HNO₃, whereas 4% PVP resin showed maximum D _Pd(II) values at lower acidities (0.1 M HNO₃). FT‐IR, SEM, and XPS techniques were used for the characterization of palladium‐loaded resins. Detailed studies were carried out with the resin of modest cross‐linkage i.e., 8% PVP resin. The sorption isotherm studies revealed that the maximum palladium loading approaches the theoretical capacity of the resin, presuming the sorption of palladium as divalent anion at 4 M HNO₃. The pseudo‐second order kinetics model yielded the best fit for the experimental data of sorption kinetics. An increase in temperature accelerates the rate of palladium extraction and also the addition of chloride ions increases the palladium uptake. Column studies were performed using 4 and 8% PVP resins in 2 and 4 M nitric acid concentrations. The loaded palladium could be eluted efficiently with acidic thiourea solution.     

Adsorptive removal of alizarin dye from wastewater using maghemite nanoadsorbents

ABSTRACT

This is an investigation of the adsorptive removal of anthraquinone dyes, resembled by Alizarin, by utilizing maghemite iron oxide (γ-Fe₂O₃) nanoparticles in aqueous media. The adsorption process was affected by several parameters such as solution pH, adsorbent amount, contact time, and temperature. After optimizing the parameters affecting the adsorption, the process was successful in removing Alizarin dye with an efficiency exceeding 95%. Best adsorption results were achieved at a pH of 11 and contact time of 60 min. The adsorption was shown to follow the Langmuir model suggesting a monolayer and homogeneous coverage. The maximum adsorption capacity (q_m ) was found to be 23.2 mg/g at pH = 11. A thermodynamic study showed that the adsorption process is exothermic and spontaneous at room temperature. The Gibbs free energy of adsorption (-6.79 kJ/mol) obtained in this study suggests a physisorption process. This finding has facilitated the regeneration of the Fe₂O₃ nanocatalyst. Both NaOH and HNO₃ at dilute levels were tested for the regeneration of the nanocatalyst. Regeneration with HNO₃ was successful up to four successive removal cycles with an efficiency >80%. Photodegradation experiments utilizing a UV light were also successful in maximizing the adsorption removal efficiency. A sorption mechanism based on the results obtained in this work is also proposed.     

Sorption of Cadmium from Aqueous Solution with a Highly Effective Sorbent – B-Doped g-C3N4

B-doped g-C₃N₄ was prepared in the laboratory via heating a mixture of melamine and boric acid. The synthesized material was characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) analysis, which revealed the high specific surface area and large amount of active groups on the surface of B-doped g-C₃N₄. The sorption of cadmium from aqueous solutions by B-doped g-C₃N₄ was studied under equilibrium conditions in the concentration range of 0.01?5.0 mmol/L. The pH of the solution was varied over a range of 2?6. The sorption of cadmium on the material was determined to be pH-dependent, and the Lagergren-second-order kinetic model was suitable to simulate the sorption process. The maximum sorption capacity from the Langmuir model was determined to be 1.4162 mmol/g (about 159.2 mgCd/g). XPS and FTIR data suggest that cadmium ions were mainly attached to the N-H and O-H groups on the surface of B-doped g-C₃N₄.     

Use of three types of magnetic biochar in the removal of copper(II) ions from wastewaters

Three types of magnetic biochars (MBC1, MBC2, and MBC3) were synthesized from biochar using NaBH₄ as a reducing agent of Fe(II) to Fe(0) to remove copper(II) ions from different wastewaters. Based on the research it was found that removal of copper(II) ions by MBC1 occurs with a yield of 99.8% for the concentration 50 mg/dm³ and decreases to 71.7% at 200 mg/dm³. The maximum pH sorption was found at pH 5. The highest correlation coefficient values (65.55 mg/g) were obtained for the Langmuir isotherm model. Application of 0.5 mol/dm³ HNO₃ as a desorbing agent gives the highest desorption percentage 98.92%.     

Biosorption of silver from aqueous solutions using wine industry wastes

The potential of wine industry wastes (grape peel, seed, and stem) as alternative biosorbents to remove Ag from aqueous media was investigated in this work. Wine industry wastes were washed, lyophilized and pulverized to obtain the biosorbents. The powdered biosorbents were characterized in detail and several batch experiments were performed to found the most suitable conditions for Ag biosorption. Kinetic, equilibrium, and thermodynamic studies were also performed. The interactions Ag-biosorbent were elucidated by analyses before and after the biosorption. For all wastes, the maximum removal percentages were found using a biosorbent dosage of 3.0?g?L^?1 at pH of 7.0. The kinetic data were well represented by the pseudo-first-order model. The equilibrium was satisfactorily represented by the Sips model. The maximum biosorption capacities, found at 298?K, were: 41.7, 61.4, and 46.4?mg?g^?1 for grape peel, seed, and stem, respectively. Thermodynamically, the biosorption was a spontaneous, favorable, exothermic, and enthalpy-controlled process. The magnitude of ΔH⁰ indicated a physical sorption. These results showed that the wine industry wastes can be considered alternative efficient, low-cost, and eco-friendly biosorbents to remove Ag from aqueous media.