Heavy metal removal by olive pomace: biosorbent characterisation and equilibrium modelling

This paper concerns with metal biosorption onto an agricultural waste, olive pomace. Experimental tests of adsorbent characterisation (potentiometric titration, IR analyses, selective extractions) and titration modelling (accounting for adsorbent heterogeneity by the introduction of a two-peak proton affinity distribution function) evidence that carboxylic and phenolic groups are the main active sites involved in metal removal. Potentiometric titration and single metal system biosorption tests (Pb, Cu, Cd) onto native and treated olive pomace samples are represented by an equilibrium model describing the competition among heavy metals and hydrogen ions in solution.     

Synthetic carbons activated with phosphoric acid: I. Surface chemistry and ion binding properties

Synthetic activated carbons were prepared by phosphoric acid activation of a styrene-divinylbenzene copolymer at various temperatures in the 400-1000 °C range. The resulting carbons were characterized by elemental analysis, cation-exchange capacity measurement, infrared spectroscopy, potentiometric titration with calculation of proton affinity spectra, and copper adsorption from solution. The results indicate that the synthetic carbons obtained possess acidic character and show cation-exchange properties similar to those of oxidized carbons. However, the acidic compounds arising from treatment with phosphoric acid are tightly bound to the carbon lattice and are chemically and thermally more stable than those introduced by oxidative treatments. The largest amount of cation-exchange surface groups is introduced after activation at 800 °C. Infrared investigations showed that phosphorus compounds may be polyphosphates bound to the carbon lattice. Proton affinity distribution curves calculated from potentiometric titration experiments showed four types of surface groups on synthetic phosphoric acid activated carbons. Among them phosphorus-containing groups are the most important for the adsorption of heavy metal ions (copper) from acid solutions. Thus, carbons activated with phosphoric acid may be regarded as prospective cation-exchangers for the removal of heavy metals from water solutions.     

Cleaning Water Contaminated with Heavy Metal Ions Using Pyrolyzed Biochar Adsorbents

The extraction of pollutants from water using activated biochar materials is a low cost, sustainable approach for providing safe water in developing countries. The adsorption of copper ions, Cu(II), onto pyrolyzed and activated dried banana peel was studied and compared with the adsorption of copper ions onto a commercial activated carbon, F-400. Both the physical and chemical properties of the banana peel and activated carbon were measured. Pyrolysis of dried banana peels resulted in the formation of a large, porous surface area adsorbent with strongly negative surface charges.

Screening studies, which were designed to evaluate the effect of the mass of the adsorbent, pH of the solution, tumbling time, and initial Cu(II) concentration were conducted for each adsorbent. Equilibrium adsorption data were also analyzed, and the Freundlich isotherm resulted in a better fit than the Langmuir isotherm. The degree of favorability of adsorption of Cu(II) ions and adsorption capacity were 1.25 and 351.1 mg/g for pyrolyzed banana peel, respectively. The sorption kinetics fit a pseudo-second order equation. The mechanism of adsorption of metal ions on pyrolyzed banana peel followed ion exchange and electrostatic interactions resulting in the complexation of adsorbed ions.     

O-carboxymethyl functionalization of chitosan: Complexation and adsorption of Cd (II) and Cr (VI) as heavy metal pollutant ions

Chitosan (CHI) is a biopolymer that can be used on complexation and adsorption of heavy metals in water. Chitosan can be chemically functionalized to modulate the pH range of solubility and favoring the complexation and adsorption processes with metal ions. Thus, in this study, it was investigated the synthesis and characterization of carboxymethyl-chitosan (CMC) as well as its application for the complexation and adsorption of Cd(II) and Cr(VI) ions at different pH conditions and compared to pristine chitosan. The properties of the synthesized derivative were extensively characterized by potentiometric titration, Fourier transform infrared spectroscopy (FTIR) and ultraviolet–visible (UV–vis) spectroscopy. The complexation and adsorption behaviors of CHI and CMC were assessed using atomic absorption spectrometer (AAS) and zeta potential analysis. The results demonstrated that O-carboxymethylation of chitosan has occurred with a degree of functionalization higher than 50% leading to the formation of CMC soluble in alkaline medium. In addition, the effective incorporation of carboxylic groups in the chitosan chain (CMC) has significantly altered the complexation and adsorption responses towards heavy metal cations (Cd^2 +) and anions (chromates) as compared to CHI. Therefore, these systems offer an attractive alternative as biosorbents for the removal of heavy metal pollutants from the wastewater.     

Synthesis and characterization of polyacrylamide‐grafted coconut coir pith having carboxylate functional group and adsorption ability for heavy metal ions

The present investigation was undertaken to evaluate the effectiveness of a new adsorbent prepared from coconut coir pith (CP), a coir industry‐based lignocellulosic residue in removing metal ions from aqueous solutions. The adsorbent (PGCP‐COOH) having a carboxylate functional group at the chain end was prepared by grafting polyacrylamide onto CP using potassium peroxydisulphate as an initiator and in the presence of N,N′‐methylenebisacrylamide as a crosslinking agent. The adsorbent was characterized by infrared (IR) spectroscopy, thermogravimetry (TG), X‐ray diffraction (XRD) patterns, scanning electron microscopy (SEM), and potentiometric titration. The adsorbent exhibits very high adsorption potential for the removal of Pb(II), Hg(II), and Cd(II) ions from aqueous solutions. The optimum pH range for metal ion removal was found to be 6.0–8.0. The adsorption process follows a pseudo‐second‐order kinetic model. The adsorption capacities for Hg(II), Pb(II), and Cd(II) calculated using the Langmuir isotherm equation were 254.52, 189.49, and 63.72 mg g^?1, respectively. Adsorption isotherm experiments were also conducted for comparison with a commercial carboxylate form cation exchanger. Different industry wastewater samples were treated by the PGCP‐COOH to demonstrate its efficiency in removing heavy metals from wastewater. The reusability of the PGCP‐COOH was also demonstrated using 0.2M HCl. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3670–3681, 2007     

Heavy metals adsorption on some iminodiacetate chelating resins as a function of the adsorption parameters

The adsorption properties of some novel chelating resins (CRs) bearing iminodiacetate groups for removal of heavy metal ions like: Cu(II), Co(II) and Ni(II) from aqueous solutions comparative with the commercial resin Amberlite IRC-748 have been studied in this work by a batch equilibrium technique. Quantitative analysis for adsorption was conducted using UV–vis spectroscopy to investigate the kinetics, adsorption isotherm and thermodynamics of the removal process considering equilibration time, pH, metal ion concentration and temperature as controlling parameters. The metal adsorption capacities, at pH 5, were in the order Cu(II) > Ni(II) > Co(II), for both the CR with 10 wt.% DVB (CR-10) and the commercial resin Amberlite IRC-748. The adsorption capacities on CR-10 were higher for Ni(II) and Co(II) ions, but lower for Cu(II) ions compared with Amberlite IRC-748. Both Freundlich and Langmuir isotherms well fitted on the adsorption results of Cu(II), Ni(II) and Co(II) ions on all iminodiacetate resins.     

蛭石在重金属离子废水处理中的应用

蛭石是黏土矿物的一种,具有较大的比表面积和较强的阳离子交换容量,能有效去除废水中的重金属。文章总结了近年来蛭石吸附Cu2+、Cd2+、Ni2+、Pb2+等重金属离子的研究状况,发现其去除重金属离子的机理主要是离子交换和表面络合作用。分析了溶液pH值、吸附时间、蛭石粒径、蛭石投加量、溶液浓度对吸附效果的影响。指出应进一步加深对蛭石吸附机理和吸附后处置技术的研究,以及蛭石在实际工程上的应用推广。     

Modeling of cadmium(II) adsorption on kaolinite-based clays in the absence and presence of humic acid

Cadmium adsorption on kaolinite-based clays in the absence and presence of humic acid was modeled with the aid of the FITEQL 3.2 computer program using a modified Langmuir approach for capacity calculations. Formation of surface–metal ion and surface–humate–metal ion complexes was assumed using the DLM approach. As Cd(II) adsorption was ionic strength-dependent, the adsorption experiments were carried out in solutions containing two different concentrations of an inert electrolyte (0.1 M and 0.005 M NaClO₄). The surface sites responsible for the adsorption were assumed to be the permanent charges, ≡S₁OH silanol groups and carboxyl groups having pK_a values close to that of the silanol groups, and ≡S₂OH aluminol groups and phenol groups with pK_a values close to that of the aluminol groups, because the studied clays (partly composed of clay soil) contained organic carbon. Cd²⁺ ions were assumed to bind to the surface in the form of outer-sphere X₂²⁻ Cd²⁺ and inner-sphere ≡SOCd⁺ monodentate complexes. When humic acid was added, Cd(II) adsorption was modeled using a multi-site binding model by the aid of FITEQL3.2. The fit between model and experimental values was excellent in each case. Since the stability of the ternary surface complexes in the presence of humic acid was higher than that of the corresponding binary surface–cadmium ion complexes, the adsorption vs. pH curves were much steeper (and distinctly S-shaped) compared to the tailed curves observed in binary clay–cadmium ion systems. The clay mineral in the presence of humic acid probably behaved more like a chelating ion-exchanger for heavy metal ions than as a simple inorganic ion exchanger.     

Chitosan functionalized with 2[-bis-(pyridylmethyl) aminomethyl]4-methyl-6-formyl-phenol: equilibrium and kinetics of copper (II) adsorption

The complexation agent 2[-bis-(pyridylmethyl) aminomethyl]-4-methyl-6-formyl-phenol (HL) was immobilized in chitosan in order to obtain a new adsorbent material to be employed in studies on adsorption and pre-concentration of Cu(II). The chitosan modified by the complexation agent was characterized by infrared spectroscopy, DSC and TGA. The studies were conducted as a function of the pH of the medium and the mechanism of Cu(II) adsorption in the solid phase was analyzed utilizing several kinetic models. The parameters for the adsorption of Cu(II) ions by chitosan-HL were determined with a Langmuir isotherm, the maximum saturation capacity of the monolayer being 109.4 mg of Cu(II) per gram of polymer. Electron paramagnetic resonance spectroscopy revealed that Cu^II ions coordinate to the donor atoms of the HL ligand anchored to the surface of the polymer forming a stable chelate complex in the solid state.     

Adsorption performance and physicochemical mechanism of MnO2-polyethylenimine-tannic acid composites for the removal of Cu(II) and Cr(VI) from aqueous solution

In this work, an adsorbent, which we call MnPT, was prepared by combining MnO₂, polyethylenimine and tannic acid, and exhibited efficient performance for Cu(II) and Cr(VI) removal from aqueous solution. The oxygen/nitrogen-containing functional groups on the surface of MnPT might increase the enrichment of metal ions by complexation. The maximum adsorption capacities of MnPT for Cu(II) and Cr(VI) were 121.5 and 790.2 mg·g⁻¹, respectively. The surface complexation formation model was used to elucidate the physicochemical interplay in the process of Cu(II) and Cr(VI) co-adsorption on MnPT. Electrostatic force, solvation action, adsorbate–adsorbate lateral interaction, and complexation were involved in the spontaneous adsorption process. Physical electrostatic action was dominant in the initial stage, whereas chemical action was the driving force leading to adsorption equilibrium. It should be noted that after adsorption on the surface of MnPT, Cr(VI) reacted with some reducing functional groups (hydroxylamine-NH₂) and was converted into Cr(III). The adsorption capacity declined by 12% after recycling five times. Understanding the adsorption mechanism might provide a technical basis for the procedural design of heavy metal adsorbents. This MnPT nanocomposite has been proven to be a low-cost, efficient, and promising adsorbent for removing heavy metal ions from wastewater.     

Synthesis and Surface Modification of Mesoporous Silicate SBA‐15 for the Adsorption of Metal Ions

Abstract

In this study surface modified SBA‐15, coated with octadecyltrichlorosilane (C18), is considered as an alternative adsorbent for metal ions in water. The SBA‐C18 was loaded with Bis(2,4,4-trimethylpentyl) phosphinic acid (cyanex 272) as the metal ion extractant. The adsorption characteristics of phosphinic acid loaded SBA‐C18 were evaluated for Cu(II) and Zn(II) ions in aqueous solution. Adsorption tests indicated that a contact time of 1 hour was sufficient for adsorption equilibrium to occur. The pH_1/2 values of Zn(II) and Cu(II) onto SBA‐C18, were found to be similar to published data for levextrel ion exchange resins and around 1 pH unit lower than published solvent extraction data for cyanex 272 in xylene.     

Adsorption of Cr(III), Ni(II), Zn(II), Co(II) ions onto phenolated wood resin

In this study, phenolated wood resin was used an adsorbent for the removal of Cr(III), Ni(II), Zn(II), Co(II) ions by adsorption from aqueous solution. The adsorption of metal ions from solution was carried at different contact times, concentrations and pHs at room temperature (25°C). For individual metal ion, the amount of metal ions adsorbed per unit weight of phenolated wood resin at equilibrium time increased with increasing concentration and pH. Also, when the amounts of metal ions adsorbed are compared to each other, it was seen that this increase was order of Cr(III) > Ni(II) > Zn(II) > Co(II). This increase was order of Cr(III) > Ni(II) > Co(II) > Zn(II) for commercial phenol–formaldehyde resin. Kinetic studies showed that the adsorption process obeyed the intraparticle diffusion model. It was also determined that adsorption isotherm followed Langmuir and Freundlich models. Adsorption isotherm obtained for commercial phenol–formaldehyde resin was consistent with Freundlich model well. Adsorption capacities from Langmuir isotherm for commercial phenol–formaldehyde resin were higher than those of phenolated wood resin, in the case of individual metal ions. Original adsorption isotherm demonstrated the monolayer coverage of the surface of phenolated wood resin. Adsorption kinetic followed the intraparticle diffusion model. The positive values of ΔG° determined using the equilibrium constants showed that the adsorption was not of spontaneous nature. It was seen that values of distribution coefficient (K_D) decreasing with metal ion concentration in solution at equilibrium (C_e) indicated that the occupation of active surface sites of adsorbent increased with metal ions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2838–2846, 2006     

Adsorptive removal of sulfamethoxazole with shell-core chitosan immobilized metal ion

Immobilized metal ion affinity chromatography (IMAC) for adsorptive removal of sulfamethoxazole (SMX) was investigated. Shell-core chitosan was applied as a support for metal ions and could successfully immobilize copper via ion-exchange ability of chitosan. The copper-immobilized shell-core chitosan has adsorption ability for SMX at pH = 4–6, due to the complexation between copper on the adsorbent and sulfonamide group of the SMX. The adsorbent was also applicable for chromatographic operation for removal of SMX. The SMX adsorbed was successfully eluted with deionized water, although a small amount of copper was also eluted from the adsorbent together with the SMX.     

Removal of heavy metal ions with water-insoluble amphoteric sodium tertiary amine sulfonate starches

The removal of heavy metal ions (Pb⁺², Cu⁺² and Zn⁺²) from solutions with high crosslinked amphoteric starch containing the sulfonate anionic group and the tertiary ammonium cationic group was investigated. The adsorption capacity of sodium tertiary amine sulfunate starch is 0.050 meq/g. The adsorption process has been found to be concentration and pH dependent and exothermic, and follows the Langmuir isothermal adsorption. The heat of adsorption (H) of Pb⁺², Cu⁺² and zn⁺² ions is equal to –10.85. –16.20 and –20.00 Kcal/mole, respectively. The amount of adsorbed metal ions on the adsorbent decreases when NaCl or Na₂SO₄ is added to the solution.     

Adsorption equilibria between dye and surfactant in single and binary systems onto geological materials

Adsorption characteristics of cationic dyes and surfactants onto clay and sandstone from a single component system were studied using toluidine blue (TB) and cetyl trimethylammonium bromide (CTAB). Equilibrium data of TB and CTAB in the single solute systems fit well to the Langmuir and the Freundlich adsorption isotherms. Competitive adsorption was observed between dye and surfactant cations. The effect of sodium chloride on dye and surfactant adsorption was studied in TB–NaCl and CTAB–NaCl binary systems. Equilibrium adsorption for binary systems was analyzed by using the extended Langmuir and the extended Freundlich models. Adsorption results for the TB–CTAB system onto both adsorbents were also well described by the Sheindorf–Rebuhn–Sheintuch (SRS) model for multi-component systems. Free energy changes for adsorption systems were calculated using thermodynamic equilibrium constants evaluated from selectivity coefficients of the binary systems. The site distribution functions estimated using Freundlich model parameters gave valuable information about the ratio of the adsorption sites on adsorbent surface having different affinity for competing cations.     

Smectite organofunctionalized with thiol groups for adsorption of heavy metal ions

The structural characteristics as well as the binding capacity of the functionalized bentonite from Campina Grande (PB), Brazil, were investigated. The sample was modified by acid treatment followed by immobilization of ligands containing thiol (–SH) groups by covalent grafting with surface and interlayer silanol groups. The modification was carried out under anhydrous conditions with (3-mercaptopropyl)trimethoxysilane. The functionalization process changed the hydrophilic nature of the clay mineral into hydrophobic. X-ray diffraction indicated that their original structure had been preserved. The DRIFT spectra demonstrated the presence of organic chains and thiol groups. The BET results indicated decreased porosity and specific surface area after grafting. Organic loading, calculated from TG data was 1.76 mmol g^− 1 of bentonite. The thiol-functionalized bentonite presented binding capacity of Ag⁺ ions about ten times higher compared to the ungrafted sample. These results support a mechanism of adsorption involving primarily ion complexation by the thiol groups (specific) instead of cation exchange (unspecific). The accessibility to the reactive centers was 60–75%. Thus, the adsorption capacity of bentonite can be enhanced by surface modification using organo-functional silane coupling agents. This new hybrid organic–inorganic material may be a good alternative for separation and pre-concentration of heavy metal ions.     

载铜树脂处理高含盐氨氮废水的性能

针对高含盐氨氮废水,选择具有不同功能基团的树脂为载体,进行负载Cu2+改性制得载铜树脂并对其处理高含盐氨氮废水的性能进行研究。在筛选出最佳载铜树脂的基础上,研究pH及Na+浓度、树脂投加量、反应时间对载铜树脂处理高含盐氨氮废水效果的影响,通过对吸附氨氮前后的载铜树脂进行SEM和EDS表征分析并构建吸附动力学模型以进一步探究配位吸附的过程。结果表明,Cu2+可与螯合树脂D751稳定结合且在宽pH值下均表现出耐盐性和良好的氨氮吸附效果;在室温(25℃)、pH=11及Na+浓度4 g/L、树脂投加量8 g/L、反应时间60 min的条件下,D751载铜树脂对氨氮的去除率为34.8%。D751载铜树脂吸附氨氮后其表面出现明显的晶状结构物质,该物质可能为铜氨络合物。D751载铜树脂对高含盐氨氮的吸附符合准二级动力学模型。     

Surface Charge of Variable Porosity Al2O3(s) and SiO2(s) Adsorbents

The surface charge properties of two SiO₂ and three Al₂O₃ mineral adsorbents with varying degrees of framework porosity were investigated using discontinuous titration and ion adsorption methodologies. Points of zero net charge (p.z.n.c) for porous and non-porous SiO₂ were <2.82 and for Al₂O₃ minerals ranged from 6.47–6.87. Silica surfaces possessed very slight negative charge in the acid pH range (pH < 7) and significant dissociation of silanol groups occurred at pH > 7. Variation of surface charge density with aqueous proton concentration was nearly identical within a mineral type (i.e., SiO₂ or Al₂O₃) irrespective of the degree of framework porosity, indicating that the densities of dissociable surface sites are equivalent, when normalized to surface area. The results suggest that the use of titration methods alone may be insufficient for thorough surface charge characterization, particularly at low and high pH. Proton titrations should be coupled with concurrent ion adsorption measurements to confirm surface charge development. Discontinuous proton titration and ion adsorption data, which were in agreement in the slightly acidic through slightly basic pH range, both indicated that p.z.n.c. was equal to the point of zero net proton charge (p.z.n.p.c.) for the variable charge minerals investigated.     

Removal of metal ions from aqueous solution by adsorption onto activated carbon cloths: adsorption competition with organic matter

Activated carbon cloths are recent adsorbents whose adsorption properties are well known for monocomponent solutions of organics or metal ions. However, to treat wastewaters with these materials, their performance has to be determined in multicomponent solution. This work studies adsorption competition between metal ions (Cu²⁺, Pb²⁺) and organic matter (benzoic acid). The first part investigates adsorption equilibrium of monocomponent metal ions solutions and shows the dependence of adsorption capacities on adsorbent porosity and metal ions chemical properties (molecular weight, ionic radius and electronegativity). The influence of pH is also demonstrated. The second part focuses on adsorption competition: (1) between both metal ions (a decrease of adsorption capacities is observed, whose value is related to adsorption kinetics of metal ions); (2) between metal ions and organic matter, in solution or adsorbed onto the activated carbon cloth (a strong influence of pH is shown: when benzoic acid is under benzoate form, in both cases adsorption is increased due to the formation of ligands between adsorbed benzoate ions and metals).     

A systematic study and proposed model of the adsorption of binary metal ion solutes in aqueous solution onto activated carbon produced from pecan shells

Adsorption isotherms of a number of binary solute systems have been obtained. The adsorption behavior of these cations in the presence of other metal ions that display strong or intermediate affinities for adsorption sites has been systematically investigated. In this investigation the following factors have been considered: (1) metal ion site competition; (2) charge accumulation near the carbon surface; and (3) speciation of the metal ions. Two multicomponent adsorption models are proposed, and the results are compared to two models presented in the literature. The performance of these models is evaluated by an analysis of error. It is found that models with three interaction parameters generally provide a better fit of the data. In most cases, the proposed two-parameter model gives acceptable results.