Ni Sorption Research Articles

Effect of Carbonates and Organic Matter in Retention and Release of Nickel by a Central Italy Soil

To improve the prediction and management of problems associated with toxicity in nickel (Ni)-contaminated soils, a better understanding of their sorptive and desorptive behavior is required. In this research, the sorptive and desorptive behavior of Ni in a clay loam soil (Fluventic Xerochrept), typical of central Italy, was measured using a stirred-flow reactor where the desorption products are continuously removed from solution. In addition, the effects of the presence of carbonates (calcite) and organic matter on Ni adsorption and desorption by the soil were investigated. For this purpose, samples obtained depriving the whole soil (S) of carbonates (S-C) and, successively, organic matter (S-C-OM) or only organic matter (S-OM) were prepared. In the samples containing carbonates, Ni adsorption was characterized by a fast initial reaction in which all the Ni added to the stirred-flow chamber was sorbed; following this, a slower and incomplete sorption occurred. This Ni adsorption process was totally nonreversible. This behavior enables hypothesizing the formation of a complex Ni calcite that can be considered to be mainly responsible for Ni sorption in calcareous soils. When the pH of the whole soil was lowered, depriving the soil of carbonates, its Ni sorptive capacity was significantly reduced and the Ni sorption process became partially reversible. The removal of organic matter decreased both the adsorbed and the desorbed Ni percentage only in the soil samples previously deprived of carbonates.

Impact of environmental conditions on the removal of Ni(II) from aqueous solution to bentonite/iron oxide magnetic composites

The sorption of radionuclide 63Ni(II) on bentonite/iron oxide magnetic composites was investigated by batch technique under ambient conditions. The effect of contact time, solid content, pH, coexistent electrolyte ions, fulvic acid, and temperature on Ni(II) sorption to bentonite/iron oxide magnetic composites was examined. The results demonstrated that the sorption of Ni(II) was strongly dependent on pH and ionic strength at pH <8.0, and was independent of pH and ionic strength at high pH values. The sorption of Ni(II) was dominated by outer-sphere surface complexation or ion exchange at low pH, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The experimental data were well fitted by Langmuir model. The thermodynamic parameters (∆G°, ∆S°, ∆H°) calculated from the temperature-dependent sorption isotherms indicated that the sorption of Ni(II) on bentonite/iron oxide magnetic composites was an endothermic and spontaneous processes. The results show that bentonite/iron oxide magnetic composites are promising magnetic materials for the preconcentration and separation of radionickel from aqueous solutions in environmental pollution.

Kinetics of Ni Sorption in Soils: Roles of Soil Organic Matter and Ni Precipitation

The kinetics of Ni sorption to two Delaware agricultural soils were studied to quantitatively assess the relative importance of Ni adsorption on soil organic matter (SOM) and the formation of Ni layered double hydroxide (Ni-LDH) precipitates using both experimental studies and kinetic modeling. Batch sorption kinetic experiments were conducted with both soils at pH 6.0, 7.0, and 7.5 from 24 h up to 1 month. Time-resolved Ni speciation in soils was determined by X-ray absorption spectroscopy (XAS) during the kinetic experiments. A kinetics model was developed to describe Ni kinetic reactions under various reaction conditions and time scales, which integrated Ni adsorption on SOM with Ni-LDH precipitation in soils. The soil Ni speciation (adsorbed phases and Ni-LDH) calculated using the kinetics model was consistent with that obtained through XAS analysis during the sorption processes. Under our experimental conditions, both modeling and XAS results demonstrated that Ni adsorption on SOM was dominant in the short term and the formation of Ni-LDH precipitates accounted for the long-term Ni sequestration in soils, and, more interestingly, that the adsorbed Ni may slowly transfer to Ni-LDH phases with longer reaction times.

Effect of humic acid on nickel(ii) sorption to Ca-montmorillonite by batch and EXAFS techniques study

The influence of humic acid (HA) on Ni(II) sorption to Ca-montmorillonite was examined by using a combination of batch sorption experiments and extended X-ray absorption fine structure (EXAFS) spectroscopy technique. The sorption of Ni(II) on HA-montmorillonite hybrids is strongly dependent on pH and temperature. At low pH, the sorption of Ni(II) is mainly dominated by Ni-HA-montmorillonite and outer-sphere surface complexation. The EXAFS results indicate that the first coordination shell of Ni(II) consists of ∼6 O atoms at the interatomic distances of ∼2.04 Å in an octahedral structure. At high pH, binary Ni-montmorillonite surface complexation is the dominant sorption mechanism. EXAFS analysis indicates the formation of mononuclear complexes located at the edges of Ca-montmorillonite platelets at pH 7.5, while a Ni-Al layered double hydroxide (LDH) phase at the Ca-montmorillonite surface formed with pH 8.5. At pH 10.0, the dissolved HA-Ni(II) complexation inhibits the precipitation of Ni hydroxide, and Ni-Al LDH phase forms. The rise of temperature increases the sorption capacity of Ni(II), and promotes Ni-Al LDH phase formation and the growth of crystallites. The results are important to evaluate the physicochemical behavior of Ni(II) in the natural environment.

Investigation of radionuclide 63Ni(II) sequestration mechanisms on mordenite by batch and EXAFS spectroscopy study

The sorption behavior and microscopic sequestration mechanisms of radionuclide 63Ni(II) on mordenite as a function of aging time, ionic strength, initial 63Ni(II) concentrations, solid content and coexistent electrolyte ions were investigated by the combination of batch and EXAFS techniques. Macroscopic experiment results show that the sorption of 63Ni(II) is dependent on ionic strength at pH 7. The sorption percentage of 63Ni(II) on mordenite increases with increasing solid content, while the sorption capacity decreases as solid content increases. The presence of different electrolyte ions can enhance or inhibit the sorption of Ni(II) on mordenite in various degrees. EXAFS analysis results of the samples under three different ionic strengths suggest that the retained 63Ni(II) in these samples exists in an octahedral environment with six water ligands. In the initial period of rapid uptake, the sorption of 63Ni(II) is dominated by the formation of inner-sphere surface complexes. As aging time increases, 63Ni(II) sequestration behavior tends to be mainly controlled by the formation of Ni phyllosilicate co-precipitates and/or Ni(OH)2(s) precipitates. Results for the second shell fit of the sample prepared at an initial 63Ni(II) concentration of 100 mg/L indicate the possible formation of Ni polynuclear surface complexes. Both the macroscopic sorption data and the molecular level evidence of 63Ni(II) surface speciation at the mordenite/water interfaces should be factored into better predictions of the mobility and bioavailability of 63Ni(II) in environment mediums.

Sorption of Ni and Eu in a Multi-element System

Laboratory studies on the retardation of radionuclides in the far-field of a radioactive waste repository are often performed using a single metal in the presence of the solid surfaces in solution. However, in the event of failure in the engineered barrier system (EBS), groundwater flowing pass the EBS will likely contain more than one long live radionuclide. The aim of this paper is to understand sorption in systems containing more than one radionuclide in solution. The work presented is carried out to understand how the presence of Ni or Eu in solution will affect the sorption of each other. Static batch sorption experiments of Ni and Eu sorption to different granitic materials have been performed. Radiometric analysis was done using Cobra (II) Auto gamma for 152Eu and TriCarb liquid scintillation for Ni63. Experimental results were described initially using the empirical models from which Rd values were obtained for sorption in single systems of Ni and Eu, and of multi-element systems of Ni and Eu. The experimental data was fitted to the surface complexation using JChess Geochemical Code to obtained complexation constants for the interactions between Ni and Eu and the solid surfaces. The effect on sorption in a multi-element system was expressed by the ratio of the sorption capacity of one metal ions in the presence of the other metal ions Qmix to the sorption capacity of same metal ions when it is present alone in solution Qsing. s in 1 m ix g Q Q > , the sorption is promoted by the presence of other metal ions, whereas if: sin 1 mix g Q Q = , there appears to be no observable effect, and if: s in 1 m ix g Q Q < , it would indicate that sorption is suppressed by the presence of other metal ions in solution. Results obtained showed that sorption was suppressed in systems containing Eu and Ni. Ratios of Qmix and Qsing were calculated as approximately 1and Eu sorption to Muscovite Mica and for Ni sorption to Plagioclase Feldspar, showing that there was no effect on the sorption capacity. The ratio was calculated as < 1 for Eu sorption to Granite Adamellite, Rose Quartz, Plagioclase Feldspar and Muscovite Mica, showing that sorption of Eu in the presence of both Ni was suppressed. Results also showed suppression of Ni sorption in the presence of Eu with the most suppression occurring with for Ni sorption to Rose Quartz in the presence of Eu with a mixed/single ratio << 1. A correlation between the Rd and determined surface complexation constant is determined for the granitic minerals.

Impact of environmental conditions on the sorption behavior of radionuclide 63Ni(II) onto hierarchically structured γ-MnO2

A novel hierarchically structured γ-MnO2 has been synthesized using a simple chemical reaction between MnSO4 and KMnO4 in aqueous solution without using any templates, surfactants, catalysts, calcination and hydrothermal processes. As an example of potential applications, hierarchically structured γ-MnO2 was used as adsorbent in radionuclide 63Ni(II) treatment, and showed an excellent ability. The effects of pH, ionic strength, temperature, humic acid (HA) and fulvic acid (FA) on the sorption of radionuclide 63Ni(II) to hierarchically structured γ-MnO2 have been investigated by using batch techniques. The results indicated that the sorption of 63Ni(II) on γ-MnO2 is obviously dependent on pH values but independent of ionic strength. The presence of HA/FA strongly enhances the sorption of 63Ni(II) on γ-MnO2 at low pH values, whereas reduces 63Ni(II) sorption at high pH values. The sorption of 63Ni(II) on γ-MnO2 is attributed to inner-sphere surface complexation rather than outer-sphere surface complexation or ion exchange. The thermodynamic parameters (ΔH 0, ΔS 0, ΔG 0) are also calculated from the temperature dependent sorption isotherms, and the results suggest that the sorption of 63Ni(II) on γ-MnO2 is a spontaneous and endothermic process.

Sorption/desorption of radionickel on/from Na-montmorillonite: kinetic and thermodynamic studies

In this work, Na-montmorillonite was used as a novel adsorbent for the sorption of Ni(II) from aqueous solutions. The sorption and desorption of Ni(II) on Na-montmorillonite was investigated as the function of pH, ionic strength, Ni(II) concentrations and temperature. The results indicated that the sorption of Ni(II) on Na-montmorillonite was strongly dependent on pH, ionic strength and temperature. The sorption of Ni(II) increases slowly from 22.1 to 51.4% at pH range 2–6.5, abruptly at pH 6.5–9, and at last maintains high level with increasing pH at pH > 9 in 0.1 mol/L NaNO3 solutions. The Ni(II) kinetic sorption on Na-montmorillonite was fitted by the pseudo-second-order model better than by the pseudo-first-order model and the experimental data implies that Ni(II) sorption on montmorillonite were mainly controlled by the film diffusion mechanism. The Langmuir, Freundlich and D–R models were used to simulate the sorption data at three different temperatures (298.15, 318.15 and 338.15 K) and the results indicated that Langmuir model simulates the experimental data better than Freundlich and D–R models. The sorption–desorption isotherm of Ni(II) on montmorillonite suggested that the sorption is irreversible. The irreversible sorption of Ni(II) on montmorillonite indicates that montmorillonite can be used to pre-concentration and solidification of Ni(II) from large volumes of solution and to storage Ni(II) ions stably.

Role of Bacterial Biomass in the Sorption of Ni by Biomass-Birnessite Assemblages

Birnessites precipitated by bacteria are typically poorly crystalline Mn(IV) oxides enmeshed within biofilms to form complex biomass-birnessite assemblages. The strong sorption affinity of bacteriogenic birnessites for environmentally important trace metals is relatively well understood mechanistically, but the role of bacterial cells and extracellular polymeric substances appears to vary among trace metals. To assess the role of biomass definitively, comparison between metal sorption by biomass at high metal loadings in the presence and absence of birnessite is required. We investigated the biomass effect on Ni sorption through laboratory experiments utilizing the birnessite produced by the model bacterium, Pseudomonas putida. Surface excess measurements at pH 6-8 showed that birnessite significantly enhanced Ni sorption at high loadings (up to nearly 4-fold) relative to biomass alone. This apparent large difference in affinity for Ni between the organic and mineral components was confirmed by extended X-ray absorption fine structure spectroscopy, which revealed preferential Ni binding to birnessite cation vacancy sites. At pH ≥ 7, Ni sorption involved both adsorption and precipitation reactions. Our results thus support the view that the biofilm does not block reactive mineral surface sites; instead, the organic material contributes to metal sorption once high-affinity sites on the mineral are saturated.

A nickel availability study in serpentinised areas of Portugal

The factors that control Ni availability and adsorption in serpentine soils from the northeast of Portugal, which developed under temperate climacteric conditions, were investigated following characterisation of the soils' selected physicochemical properties. Ni bioavailability was assessed through complementary extractions. The results showed that surface-bound Ni in serpentine soils is primarily specifically adsorbed. The influence of the soils' physicochemical characteristics and of the Ni-bearing oxides on Ni bioavailability (EDTA-extractable Ni) was examined using correlation analysis. Our study revealed that most of the variability in Ni bioavailability in the Portuguese serpentine soils can be linked to hydrous manganese oxide. Surface affinity for exogenous Ni was evaluated by adsorption studies on soil suspensions followed by voltammetric titrations at pH 7.Sorption data was fitted to a Langmuir isotherm assuming the formation of one-to-one Ni complexes with the soil surface binding sites. Conditional surface formation constants and the concentration of surface groups for Ni binding were determined. The results showed that serpentine soils have potential available sites for further Ni adsorption. Hydrous Mn oxides existing in these serpentine soils determine the Ni sorption capacity.

The influence of Fe(II) competition on the sorption and migration of Ni(II) in MX-80 bentonite

► We model the diffusion of Ni(II) through bentonite using different sorption models. ► We examine sorption competition of Fe(II) and Ni(II) at different concentrations. ► Ni(II) breakthrough is 15 times earlier with Fe(II) sorption competition. ► Ni(II) sorption is non-linear and depends on the Fe(II) concentration levels. ► Sorption competition is important and has to be modelled by reactive transport codes. The results from batch sorption experiments on montmorillonite systems have demonstrated that bivalent transition metals compete with one another for sorption sites. For safety analysis studies of high level radioactive waste repositories with compacted bentonite near fields, the importance of competitive sorption on the migration of radionuclides needs to be evaluated. Under reducing conditions, the bentonite porewater chosen has a Fe(II) concentration of ∼5.3 × 10 −5 M through saturation with siderite. The purpose of this paper is to assess the influence of such high Fe(II) concentrations on the transport of Ni(II) through compacted bentonite, Ni(II) was chosen as an example of a bivalent transition metal. The one-dimensional calculations were carried out at different Ni(II) equilibrium concentrations at the boundary (Ni(II) EQBM ) with the reactive transport code MCOTAC incorporating the two site protolysis non electrostatic surface complexation/cation exchange sorption model, MCOTAC-sorb. At a Ni(II) EQBM level of 10 −7 M without Fe(II) competition, the reactive transport calculations using a constant K d approach and the MCOTAC-sorb calculation yielded the same breakthrough curves. At higher Ni(II) EQBM (10 −5 M), the model calculations with MCOTAC-sorb indicated a breakthrough which was shifted to later times by a factor of ∼5 compared with the use of the constant K d approach. When sorption competition was included in the calculations, the magnitude of the influence depended on the sorption characteristics of the two competing sorbates and their respective concentrations. At background Fe(II) concentrations of 5.3 × 10 −5 M, and a Ni(II) EQBM level of 10 −7 M, the Ni(II) breakthrough time was ∼15 times earlier than in the absence of competition. At such Fe(II) concentrations the Ni(II) breakthrough curves at all source concentrations less than 3.5 × 10 −5 M (fixed by the NiCO 3,S solubility limit) are the same i.e. Ni(II) exhibits linear (low) sorption. Competitive sorption effects can have significant influences on the transport of radionuclides through compacted bentonite i.e. reduce the migration rates. Since, for the case considered here, the Fe(II) concentration in the near field of a high-level radioactive waste repository may change in time and space, the transport of bivalent transition metal radionuclides can only be properly modelled using a multi-species reactive transport code which includes a sorption model.

Soil Solution Ni Concentrations over which K d is Constant in Japanese Agricultural Soils

The soil-soil solution distribution coefficient (K d) is one of the most important parameters required by the models used for radioactive waste disposal environmental impact assessment. The models are generally based on the assumption that K d is independent of the element concentration in soil solution. However, at high soil solution concentrations, this assumption is not valid. Since the sorption of most radionuclides in soil is influenced by their stable isotope concentrations, it is necessary to consider if the range in the naturally occurring stable isotope concentrations in the soil solution is within the range over which K d is valid. The objective of this study was to determine if the K d for nickel (Ni) can be assumed to be constant over the ranges of stable Ni concentration in five main Japanese agricultural soil types. To obtain Ni sorption isotherms for five Japanese soils, two types of batch sorption tests were carried out using radioactive 63Ni as a tracer. The concentration at which the relationship between soil and soil solution concentration became nonlinear was determined using the two types of sorption isotherms: the Langmuir and Henry isotherms. The result showed that the Ni concentration in the soil solution at which the assumption of a constant K d becomes valid is at least ten times higher than the natural Ni concentrations in solutions of Japanese agricultural soils. This value is sufficient to treat K d for Ni as constant for environmental impact assessment models for the disposal of radioactive waste.

Sorption study of radionickel on attapulgite as a function of pH, ionic strength and temperature

Sorption of radionickel on attapulgite is studied as a function of contact time, ionic strength, pH and temperature. The results indicate that the sorption of Ni(II) on attapulgite is strongly ionic strength-dependent at pH 8. Outer-sphere surface complexation or ion exchange contributes to Ni(II) sorption on attapulgite at pH 8. The sorption of Ni(II) on attapulgite increases with increasing temperature, and the thermodynamic parameters (ΔH 0, ΔG 0 and ΔS 0) calculated from the temperature dependent sorption isotherms suggest that the sorption of Ni(II) on attapulgite is a spontaneous and endothermic process. The high sorption capacity of attapulgite suggests that attapulgite is a suitable material for the preconcentration and solidification of radionickel from large volumes of aqueous solutions.

Kinetic and equilibrium modeling of Cu(II) and Ni(II) sorption onto physically pretreated Rosa centifolia distillation waste biomass

The removal of Cu(II) and Ni(II) from aqueous solution by physically pretreated (boiled, heated and autoclaved) Rosa centifolia distillation waste biomass was conducted in batch conditions. The obtained results revealed that initial metal ion concentration, kinetics, and temperature affected the adsorption capacity of the physically pretreated R. centifolia distillation waste biomass. The Cu(II) and Ni(II) equilibrium sorption data agreed well to Langmuir isotherm model and the sorption kinetics were accurately described by pseudo second order kinetic model. The Cu(II) and Ni(II) uptake capacities (mg g-1) of physical pretreated R. centifolia distillation waste biomass were in following order: boiled (66.91) > heated (52.51) > autoclaved (49.82) > native (42.68) and boiled (67.55) > heated (65.19) > autoclaved (58.09) > native (45.19), respectively. The nature of R. centifolia distillation waste biomass surface functionalities was analyzed by FTIR spectroscopy. Keywords: Cu(II), Ni(II), isotherms, kinetics, pretreatment, Rosa centifolia.

Kinetic Testing and Sorption Studies by Modified Weathering Cells to Characterize the Potential to Generate Contaminated Neutral Drainage

Techniques developed for acid mine drainage (AMD) prediction might not be suitable for contaminated neutral drainage (CND) generating sites. The Tio mine waste is known to generate Ni contaminated neutral drainage in some of the piles, but humidity cell tests fail to generate the Ni concentrations observed in the field. Weathering cell tests (small-scale humidity cell tests) were performed on fresh and weathered (produced 25 years ago) waste rock samples from the Tio mine containing various levels of hemo-ilmenite ore, and results were compared to humidity cell results on similar samples. The main constituents of the waste rock are the hemo-ilmenite ore and the plagioclase gangue; these minerals were purified from the waste rocks and the purified fractions were also submitted to weathering cell tests. The fresh waste rock samples were also submitted to sorption cells (modified weathering cells), which showed that the waste rocks have an important Ni sorption potential and that the sorbed phases are stable under weathering cell conditions. Even though the Ni concentrations obtained from the laboratory tests remain significantly lower than those obtained in field conditions (from field test pads and from waste rock piles), the results from the present study give important insight into the geochemical processes implicated in CND generation.

Iron-Modified Sepiolite for Ni2+ Sorption from Aqueous Solution: An Equilibrium, Kinetic, and Thermodynamic Study

Sepiolite was used for the synthesis of the sepiolite−iron oxide system to obtain a sorbent suitable for the removal of Ni2+ from aqueous solution. The modified material, Fe-sepiolite, was characterized by X-ray diffraction analysis, Fourier transform infrared spectroscopy, differential thermal/thermogravimetric analysis, and point of zero charge (pHpzc) determination. The sorption experiments were performed as a function of the initial metal concentration, equilibration time, and temperature using the batch method. The Fe-sepiolite had a higher sorption capacity than the natural sepiolite sample due to a higher specific sorption and a higher ion exchange with Mg2+ ions from the sepiolite surface. Thermodynamic parameters, such as enthalpy, Gibbs energy, and entropy, were calculated from the temperature-dependent sorption isotherms, and these values showed that the sorption of Ni2+ onto sepiolites was endothermic. Pseudo-second-order kinetic models provide the best correlation of the experimental kinetic data.

Thermodynamic and Kinetic Studies for the Adsorption of Fe(III) and Ni(II) Ions From Aqueous Solution Using Natural Bentonite

In this study, the adsorption behavior of natural bentonite with respect to Fe(III) and Ni(II) has been studied in order to consider its application to purity metal finishing wastewaters. During the adsorption process, batch technique is used, and the effects of pH, bentoite amount, temperature, heavy metal concentration, bentonite treatment (calcinations of natural bentonite at 700°C, washing by deionized water to remove the excess salt from bentonite surface), and agitation time on adsorption efficiency are studied. The washed and calcined bentonite samples were labeled by WB and CB, respectively. The pH-dependence of Fe(III) and Ni(II) sorption on the bentonite is significantly more noticeable, indicating a major contribution of surface complexation at the edge sites. It was determined that adsorption of Fe(III) and Ni(II) is well fitted by the second order reaction kinetic. Furthermore, the sorption rate of Fe(III) was higher than the sorption rate of Ni(II). Adsorption of Fe(III) and Ni(II) on NB appeared to follow Langmuir isotherm. In addition, calculated and experimental adsorbed amounts of Fe(III) by the unit NB mass are very higher than Ni(II). The paper also discusses the thermodynamic parameters of the adsorption (the Gibbs free energy, entropy, and enthalpy). Our results demonstrate that the adsorption process was spontaneous and endothermic under natural conditions. Also the adsorption capacity of bentonite for Fe(III) Ni(II) and increases with increased bentonite dose. According to the equilibrium studies, the selectivity sequence can be given as Fe(III) > Ni(II). The adsorbed amount of Fe(III) and Ni(II) on washed bentonite (WB) were very higher compared to NB and CB. Our results show that bentonite could especially WB be considered as a potential adsorbent for Fe(III) and Ni(II) removal from aqueous solutions.

Predicting Geochemical Behaviour of Waste Rock with Low Acid Generating Potential Using Laboratory Kinetic Tests

Prediction of contaminated neutral drainage using laboratory kinetic tests designed for acid mine drainage prediction is challenging because of the low metal concentrations generated by low sulfide oxidation rates. Fresh and weathered samples from the Tio mine waste rock piles were submitted to humidity cell tests. The waste rocks were demonstrated to be non-acid generating in the long term, as interpreted by conservative oxidation-neutralization curves. The results demonstrate that even though the main neutralizing minerals react differently after 25 years of natural weathering (with regard to Ca, Mg, Al, and Si release), the response of the fresh waste rocks during humidity cell leaching was very similar to those of the weathered waste rocks, when considering all the elements related to silicate dissolution, including those implicated in secondary phase precipitation. However, Ni generation was greater in the weathered waste rocks even though sulfide oxidation rates were similar, as Ni sorption properties reach saturation. Although the Ni concentrations from the leachates of humidity cell tests remain below regulated values, they are bound to increase with continued weathering if no preventive or control measures are undertaken at the site.

Solution chemistry effects on sorption behavior of radionuclide 63Ni(II) in illite–water suspensions

In this work, a naturally occurring illite was characterized by using FTIR and XRD to determine its chemical constituents and crystal structure. A series of batch experiments were carried out to investigate the effect of various environmental factors such as contact time, pH, ionic strength, foreign ions, coexisting humic substances and temperature on the sorption behavior of illite towards radionuclide 63Ni(II). The sorption of 63Ni(II) on illite was strongly dependent on pH and ionic strength. A positive effect of HA/FA on 63Ni(II) sorption was found at pH < 6.5, whereas a negative effect was observed at pH > 6.5. The Langmuir, Freundlich, and D-R models were used to simulate the sorption isotherms of 63Ni(II) at three different temperatures of 293, 313 and 333 K. The thermodynamic parameters (Δ H 0, Δ S 0 and Δ G 0) of 63Ni(II) sorption on illite were calculated from the temperature dependent sorption isotherms, and the results indicated that the sorption of 63Ni(II) on illite was endothermic and spontaneous. At low pH, the sorption of 63Ni(II) was dominated by outer-sphere surface complexation and ion exchange with Na +/H + on illite surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. From the experimental results, it is possible to conclude that illite has good potentialities for cost-effective treatments of 63Ni(II)-contaminated wastewaters.

Investigation of radionuclide 63Ni(II) sorption on ZSM-5 zeolite

The sorption of 63Ni(II) from aqueous solution using ZSM-5 zeolite was investigated by batch technique under ambient conditions. ZSM-5 zeolite was characterized by point of zero net proton charge (PZNPC) titration. The sorption was investigated as a function of shaking time, pH, ionic strength, foreign ions, humic acid (HA), fulvic acid (FA) and temperature. The results indicate that the sorption of 63Ni(II) on ZSM-5 zeolite is strongly dependent on pH. The sorption is dependent on ionic strength at low pH, but independent of ionic strength at high pH values. The presence of HA/FA enhances 63Ni(II) sorption at low pH values, whereas reduces 63Ni(II) sorption at high pH values. The sorption isotherms are simulated by Langmuir model very well. The thermodynamic parameters (i.e., ∆H0, ∆S0 and ∆G0) for the sorption of 63Ni(II) are determined from the temperature dependent sorption isotherms at 293.15, 313.15 and 333.15 K, respectively, and the results indicate that the sorption process of 63Ni(II) on ZSM-5 zeolite is spontaneous and endothermic.