Mechanisms Of Cd Sorption Research Articles

Sorption mechanism of cadmium on soils: A combination of batch experiment, path analysis, and EXAFS techniques

• The sorption mechanism of Cd(II) in 49 soils was fully explored. • Cd(II) sorption capacities were closely related to soil physicochemical properties. • Cd in soils was mainly bound to metal (hydro)oxides or existed as CdCO 3 . Soil cadmium (Cd) contamination has emerged as an alarming environmental issue worldwide. Chemical reactivity and bioavailability of Cd in soils are highly dependent on soil properties. However, the sorption mechanism of Cd(II) on soils is not yet fully explored. For this purpose, batch sorption experiments, statistical analysis, and extended X-ray absorption fine structure (EXAFS) spectroscopy were integrated to elucidate the Cd(II) sorption mechanism by investigating the Cd(II) sorption behaviors in 49 soils with contrasting physicochemical characteristics and to figure out the influence of soil properties on Cd(II) sorption in soils. The outcomes of this study revealed that the soils from different areas had large differences in their abilities to adsorb Cd(II), while the differences were closely related to the physicochemical properties of soils. Cd(II) sorption capacities were controlled together by pH, metal (hydro)oxides, organic matter, and cation exchange capacity. The soil pH was the most critical factor in connecting Q max with soil properties. EXAFS results indicated that Cd(II) adsorbed on soils was mainly bound with metal (hydro)oxides or existed as CdCO 3 precipitate. The findings of this study provide a theoretical basis for predicting the risk of soil Cd contamination.

Performance and mechanisms of immobilization remediation for Cd contaminated water and soil by hydroxy ferric combined acid-base modified sepiolite (HyFe/ABsep)

In order to simultaneously improve the remediation capability of Cd contaminated water and soil, hydroxy iron-ABsep (HyFe/ABsep) was synthesized by a two-step modified (acid-base composite treatment, and hydroxy group was by using NaOH and Fe (NO3)3·9H2O). Results showed that HyFe/ABsep had developed pores and a rougher surface morphology, and the salt-soluble ion content was increased, surface-loaded iron species was mainly composed of FeOOH. Adsorption process of Cd2+ by HyFe/ABsep conformed best to the preudo-second-order model and Redlich-Paterson models, respectively. The behavior over a whole range of adsorption was consistent with chemical adsorption being the rate-controlling step and the theoretical maximum adsorption capacity obtained for the HyFe/ABsep was 220.9 mg·g−1 at 298 K, which was 4.87 times than Sep. HyFe/ABsep also had a more excellent passivation effect on available Cd in soil, being 36.83%–48.46% under the treatments of 0.5%–4% HyFe/ABsep, The structure and morphology of HyFe/ABsep were characterized through SEM-EDS, TEM, FTIR, XRD and XPS indicated that the mainly mechanisms of Cd sorption may include precipitates, ion exchange and complexation of active silanol groups. Therefore, HyFe/ABsep can employ as an effective agent for immobilization remediation of Cd contaminated water and soil.

Effect of biochar artificial ageing on Cd and Cu sorption characteristics

The present investigation was carried out to optimize the artificial ageing process of biochar by the hydrogen peroxide method. For the optimization of three oxidation parameters (concentration of oxidizing agent, reaction time, temperature) the Box–Behnken Design under Response Surface Methodology was effectively applied. As a response, the sorption capacity of aged biochar for Cd and Cu was studied. The results demonstrate the crucial effect of hydrogen peroxide concentration on sorption capacity for both studied metals. For Cd sorption capacity a positive effect was detected whereas the sorption efficiency of aged biochar for Cu decreased with increasing concentration of the oxidizing agent. The effects of reaction time and temperature had lower statistical significances. Differences in sorption mechanism of Cd and Cu by biochar-based sorbent were detected. ANOVA analysis as well as 3D surface plots revealed that maximum sorption capacity of aged biochar-based sorbents for Cd was obtained at CH2O2=14.9997%, t=5.99998h, T=20.0°C and for Cu at CH2O2=5.05%, t=2.00h, T=59.5°C. The results confirm that RSM represents an excellent tool for predicting optimal parameters of chemical engineering processes like the hydrogen peroxide oxidation of biochar to optimize its sorbent behaviour. The application of BBD under RSM could reduce the number of required experiments from 39 to 17.

Sorption Mechanism of Cd(II) and Zn(II) onto Modified Palm Shell

A series of adsorbents were prepared from palm shell powder (PSP) at different thermochemical conditions. APSP was prepared by treating PSP with H2SO4, PAPSP by further modification of APSP with K2S2O8 at 150 °C and 9AAC by thermal activation of APSP at 900 °C. Fourier transform infrared spectroscopy analysis revealed similarity of functional groups in PSP, APSP and PAPSP, suggesting that functional groups are retained during chemical or physical treatment of PSP at 150 °C. A wide pH range (3-8) was found suitable for cadmium and zinc adsorption. The adsorption of Cd2+ and Zn2+ was found to be feasible, spontaneous, exothermic, and could be described by the pseudo-second-order kinetic model as well as by Langmuir and Freundlich isotherm models. The maximum adsorption capacity was found to be 363.636 and 238.095 mg/g for Cd2+ and Zn2+, respectively, using PAPSP. Desorption was achieved using HCl and EDTA for Cd2+ and Zn2+, respectively.

Sorption mechanism of Cd(II) from water solution onto chicken eggshell

The mechanism and capacity of eggshell for sorbing Cd(II) from aqueous solution was examined in detail. The eggshell was characterized by several techniques. The eggshell was mainly composed of Calcite (CaCO3). The surface charge distribution was determined by acid–base titration and the point of zero charge (PZC) of the eggshell was found to be 11.4. The sorption equilibrium data were obtained in a batch adsorber, and the adsorption isotherm of Langmuir fitted the data quite well. The sorption capacity of eggshell increased while raising the pH from 4 to 6, this tendency was attributed to the electrostatic interaction between the Cd2+ in solution and the surface of the eggshell. Furthermore, the sorption capacity was augmented by increasing the temperature from 15 to 35°C because the sorption was endothermic. The sorption of Cd(II) occurred mainly onto the calcareous layer of the eggshell, but slightly on the membrane layer. It was demonstrated that the sorption of Cd(II) was not reversible, and the main sorption mechanisms were precipitation and ion exchange. The precipitation of (Cd,Ca)CO3 on the surface of the eggshell was corroborated by SEM and XRD analysis.

Efficiency of Cd(II) removal from aqueous media using chemically modified polystyrene foam

The removal of Cd(II) using polystyrene foam chemically modified with 2,2′-bipyridine has been investigated. The modified polystyrene foam has been characterized by FT-IR spectroscopy, thermogravimetry, elemental analysis and scanning electron microscopy. The solid was employed as a Cd(II) adsorption from aqueous solutions at room temperature. The effects of several variables (pH, shaking speed, agitation time, metal concentration and presence of other ions in the medium) have been studied using batch technique. Flame atomic absorption spectrometry was used to determine the Cd(II) ion concentration in the filtrate after the adsorption process. Maximum sorption ⩾90% was achieved at pH 7 after 30min of shaking time. Sorbed metal ions have been desorbed with 5ml of 2M HNO3 with the detection limit of 16.7ng ml−1. The Langmuir, Freundlich and D–R isotherm equation were used to describe partitioning behavior of the system at room temperature. Kinetic and thermodynamic behavior of modified polystyrene foam for Cd(II) ion removal was also studied. Br−, PO43−, Pb2+, Ni2+ and Cr(VI) suppress the sorption to some extent. The possible sorption mechanism of Cd(II) ions onto modified sorbent is also discussed. Method was utilized to remove Cd(II) ions from aqueous media.

Sorption of cadmium on humic acid: Mechanistic and kinetic studies with atomic force microscopy and X-ray absorption fine structure spectroscopy

Humic acids (HA) constitute a major fraction of the organic matter in soils and sediments. Little is known about the kinetics and mechanisms of Cd sorption by HAs, especially those pertaining to the surface features and structure of the Cd-humate complexes. We investigated Cd sorption by HA using the conventional batch method, N2-BET method, atomic force microscopy (AFM), and extended X-ray absorption fine structure (EXAFS) spectroscopy to gain a better understanding of the kinetics and mechanisms. Cadmium sorption by HA can be described by the parabolic diffusion equation. The increase in the apparent diffusion coefficient with an increase in the initial Cd concentration was less pronounced at higher initial Cd concentrations, apparently due to an enhancement in aggregation of the Cd-humate complexes. The HA before and after Cd sorption at Cd concentrations ≤ 10–6 M in different reaction times was spheroidal in shape. The Cd-humate complexes formed at 10–4 and 10–3 M Cd gradually changed to resemble the shape of a bean with increasing reaction time, thereby substantially decreasing their specific surface. Cadmium ions raveled the spheroidal HA particles into a bean-like structure by coordinating to six O atoms from the functional groups of HA, with a Cd-O distance of 2.297(2) Å. The Cd-O bond strength decreased with increasing initial Cd concentration. Key words: Cadmium, humate complexes, conformation, atomic force microscopy, EXAFS