Polycyclic aromatic hydrocarbons (PAHs) in Chinese coal: occurrence and sorption mechanism

Elevated polycyclic aromatic hydrocarbon (PAH) concentrations were determined in different Chinese coals, with the highest concentrations in bituminous coals. Phenanthrene (Phen) was chosen as the probe compound for PAHs to study the sorption behavior of coal. No native Phen was detected in desorption experiments indicating irreversible sorption–desorption behavior of PAHs in raw coal samples. Sorption mechanism was further studied under varying conditions of pH value and ionic strength. Different ranks of coal showed different sorption behavior under acidic, neutral, and alkaline conditions. Batch experiments were further processed for the selected coals at pH values from 3 to 11 at a constant aqueous concentration. Sorption capacities of all coals decreased with increased pH except for YJ coal. Furthermore, although DOC-associated Phen mass contributed little to the total Phen mass under different pH values, the significant negative correlations between M _DOC and log K _OC values were observed for all coal samples, indicating a significant role played by DOC in the coal sorption. In addition, sorption experiments under varying ionic strength showed that the ionic strength influence was more obvious in sorption isotherms for higher rank coals with increasing ionic strength, and this effect was most significant when ionic strength increased from 0 to 0.15 M, especially at relatively low aqueous concentrations.     

Permeable reactive barriers based on natural zeolites from Kazakhstan in solving ecological problems: Mathematical model and simulation

In view of ecological problems stemming from the leakage of reservoirs with liquid radioactive wastes (LRW) and groundwater contamination with radioactive Cs⁺ and Sr²⁺, we have estimated the physicochemical (including sorption) characteristics of clinoptilolite-bearing tuff (CBT) from the Chankanai deposit in Kazakhstan. Data were obtained on the chemical and phase composition of CBT, its total cationexchange capacity, and equilibrium (exchange isotherms) and kinetic (diffusion coefficients) characteristics in sorbing radioactive Cs⁺ and Sr²⁺ from 0.07 n CaCl₂ solution (model solutions of groundwaters). We proved that CBT efficiently sorbs Cs from this solution and practically does not sorb Sr and elucidated the reasons for the low selectivity with respect to Sr²⁺. Based on the equilibrium and kinetic characteristics of the process, a mathematical model is suggested for Cs sorption under dynamic conditions. The protection lifetime of the clinoptilolite-based geochemical barrier is evaluated.     

Biosorption of lead from acid solution using chitosan as a supporting material for spore forming-fungal biomass encapsulation

Asexual spores of the filamentous fungus Rhizopus arrhizus were used as the resting biomass as they tolerate chitosan gelling for mycelia growing in chitosan beads. Biosorption of lead using the dead detergent pre-treated chitosan-immobilised and grown fungal beads was performed with initial lead (II) nitrate concentrations ranging from 9.02 to 281.65 mg/L. The adsorption data were best correlated with equilibrium adsorption isotherms in the order Redlich–Peterson, Langmuir, Freundlich and Fritz–Schlünder by non-linear regression. The biosorption kinetic model of pseudo second-order (R ² > 0.99) fitted better than pseudo first-order and modified pseudo first-order models. Among the four pseudo second-order kinetic models, the Blanchard model was the best fit for the experimental biosorption data. The rate-limiting step of biosorption of lead was shown to be intraparticle diffusion controlled according to Weber and Morris model fitting. The beads could be regenerated using 1 M nitric acid solution. This illustrated the good performance of the beads for regenerated sorption/desorption at least five cycles.     

Fluoride sorption and desorption on soils located in the surroundings of an aluminium smelter in Galicia (NW Spain)

Aluminium smelters are major sources of F emission to the environment. We studied, in laboratory experiments, the sorption and desorption of fluoride on organic and mineral horizons of soils located within 2 km from one of these factories, situated in the northern coast of Galicia (NW Spain). The soils, developed from granite, are acid (pH H₂O 3.9–5.5), rich in organic matter (4–16 % C in the A horizon) and most A horizons have high Al saturation in the exchange complex. All samples showed a notable F sorption, between 1,066 and 1,589 mg kg^?1, after adding 200 mg F L^?1, which accounts for 53–80 % of F added. The sorption was slightly higher in the A horizons than in the respective organic horizons (differences of up to 194 mg kg^?1). The fluoride sorption upon addition of 200 mg F L^?1 correlated significantly (p < 0.05) with soil pH in water (r = ?0.77), iron extracted by acid ammonium oxalate (r = 0.68), aluminium plus iron extracted by acid ammonium oxalate (r = 0.63), exchange aluminium (r = 0.52) and clay percentage in soil (r = 0.76). The F sorption fitted to both Langmuir and Freundlich models. Desorbed F accounted for only 12–22 % of sorbed fluoride and correlated (p < 0.05) negatively with non-crystalline (extracted by acid ammonium oxalate) Fe (r = ?0.51) and clay content (r = ?0.74) and positively with organic matter (r = 0.69) and with the effective cation exchange capacity of the soil (r = 0.50).     

Evaluation of Jordanian faujasite tuff by comparison with other natural and synthetic zeolites

 The evaluation of the Jordanian faujasite tuff in wastewater treatment is investigated by comparison with synthetic faujasite (13X) and clinoptilolite-rich tuff. The material used (JORD-FAUJ) is concentrated by mineral processing techniques. It has a faujasite content of 57% and phillipsite content of 35%. Thorough characterization of the JORD-FAUJ revealed the high suitability of the product for use in column operation. It either compares closely or gives better thermal stability, attrition resistance, acid resistance, cation exchange capacity (CEC) and water absorption capacity, when compared with products already recommended in column operation. The study has also revealed that the JORD-FAUJ competes efficiently in ammonium removal with the synthetic faujasite 13X and clinoptilolite-rich tuff and gives similar performance. JORD-FAUJ gave a very high performance in removing Pb, Cr, Cu, Zn, and Ni from wastewater, equivalent to 83–100% of that of faujasite 13X and much higher than the clinoptilolite-rich tuff. Received: 13 April 2000 · Accepted: 1 August 2000     

Geochemical evaluation and environmental application of Yemeni natural zeolite as sorbent for Cd<Superscript>2+</Superscript> from solution: kinetic modeling,equilibrium studies,and statistical optimization

Yemeni natural zeolite was characterized by XRD, SEM, FTIR and XRF as well as its applicability as a sorbent material for Cd²⁺ ions in aqueous solutions. The zeolitic sample is clinoptilolite-K of heulandite group with intermediate Si/Al ratio. The removal% of Cd²⁺ by natural clinoptilolite was investigated as a function of contact time, zeolite dose, pH and initial concentration of Cd²⁺ ions. Kinetic experiments indicated that sorption of Cd²⁺ follows two steps: rapid ion exchange process on the outer surface is followed by slow adsorption process on the inner surface of clinoptilolite. The equilibrium was attained after 120 min, and the results were fitted well with pseudo-second order and Elovich kinetic models. The Cd²⁺ removal% is strongly dependent on pH value and increases with the increasing pH value. Equilibrium sorption isotherm of Cd²⁺ by clinoptilolite was described well using the Langmuir, Freundlich, and Temkin isotherms models. However, the data relatively well fitted with Freundlich model (R ² = 0.97) rather than by the other models. Response surface methodology in conjunction with central composite rotatable statistical design was used to optimize the sorption process. The model F-value indicated the high significance of second-order polynomial model to represent the interaction between the operating parameters. From the Design Expert’s optimization function, the predicted optimum conditions for maximum removal% of Cd²⁺ (80.77%) are 116 min contact time, 0.27 gm dose, and pH 7 at an initial Cd²⁺ concentration of 25 mg/L.     

Biosorption of ammoniacal nitrogen from aqueous solutions with low-cost biomaterials: kinetics and optimization of contact time

The biosorption of ammoniacal nitrogen (N-NH₄ ⁺) from aqueous solutions by dead biomass of brown seaweed Cystoseira indica and Jatropha oil cake (JOC), which is generated in the process of biodiesel recovery from its seeds, was studied under diverse experimental conditions. The N-NH₄ ⁺ biosorption was strictly pH dependent, and maximum uptake capacity of C. indica (15.21 mg/g) and JOC (13.59 mg/g) was observed at initial pH 7 and 3, respectively. For each biosorbent–N-NH₄ ⁺ system, kinetic models were applied to the experimental data to examine the mechanisms of sorption and potential rate-controlling steps. The generalized rate model and pseudo-second-order kinetic models described the biosorption kinetics accurately, and the sorption process was found to be controlled by pore and surface diffusion for these biosorbents. Results of four-stage batch biosorber design analysis revealed that the required time for the 99 % efficiency removal of 40 mg/L N-NH₄ ⁺ from 500 L of aqueous solution were 76 and 96 min for C. indica and JOC, respectively. The Fourier transform infrared spectroscopy analysis before and after biosorption of ammonium onto C. indica and JOC revealed involvement of carboxylic and hydroxyl functional groups.     

Sorption of Ni on Na-rectorite studied by batch and spectroscopy methods

Sorption of Ni²⁺ on Na-rectorite as a function of contact time, temperature, pH and fulvic acid (FA)/humic acid (HA) was studied under ambient conditions. A pseudo-second-order rate equation was used to simulate the kinetic sorption. The removal of Ni²⁺ increased with increasing pH. The presence of FA/HA enhanced the sorption of Ni²⁺ at low pH values, whereas no drastic effect of FA/HA on Ni²⁺ uptake to rectorite was found at high pH values. The diffuse layer model (DLM) fitted the experimental data of Ni²⁺ sorption in the absence and presence of FA/HA very well with the aid of FITEQL 3.2. The Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were used to simulate the sorption isotherms of Ni²⁺ at different temperatures. The thermodynamic data (ΔH⁰, ΔS⁰, ΔG⁰) were calculated from the temperature dependent sorption isotherms and the results suggested that the sorption process of Ni²⁺ on rectorite was spontaneous and endothermic. The sorption and species of Ni²⁺ on rectorite in the presence and absence of FA/HA was also investigated and characterized by XPS. The spectroscopic analysis indicated no drastic structural changes of Na-rectorite and the sorption of Ni²⁺ mainly occurred on the surface and at the edge position of Na-rectorite.     

Biosorption of heavy metals by organic carbon from spent mushroom substrates and their raw materials

The use of agricultural wastes as biosorbents is gaining importance in bioremediation of heavy metal-polluted water and soils, due to their effectiveness and low cost. This work assesses the Cd, Pb and Cu adsorption capacity of the raw materials used in the production of substrates for mushroom production (Agaricus bisporus and Pleurotus ostreatus) and the spent mushroom composted (SMC), based on the functional groups of their organic carbon. The raw materials studied included agricultural wastes (wheat straw, wheat and rice poultry litter, grape pomace) and inorganic substances (gypsum and calcareous sand). Organic carbon from wastes and their composting products were characterized by CP-MAS ¹³C NMR. Langmuir adsorption isotherms of metals were plotted for each raw material, composting step, spent A. bisporus and P. ostreatus substrates and the final SMC. The maximum adsorption capacities of SMC were 40.43, 15.16 and 36.2 mg g^?1 for Cd, Pb and Cu, respectively. The composting process modified the adsorption properties of raw materials because of the enhanced adsorption of Cd and Cu and decreased adsorption capacity of Pb. CP-MAS ¹³C NMR and potentiometric titration were used to identify the functional groups of the organic carbon responsible for the metal adsorption. The content of cellulose was correlated with Pb adsorption (p < 0.001), alkyl and carboxyl carbon with Cd adsorption (p < 0.001), and N-alkyl (p < 0.001) and carboxyl (p < 0.010) groups with Cu adsorption. These results are valuable to develop new biosorbents based on agricultural wastes and demonstrate the high potential of SMC to adsorb heavy metals from polluted environments.     

Identification of potential soil adsorbent for the removal of hazardous metals from aqueous phase

The present study attempted to identify the efficient hazardous metal-removing sorbent from specific types of soil, upper and middle layer shirasu, shell fossil, tuff, akadama and kanuma soils of Japan by physico-chemical and metal (arsenic, cadmium and lead) removal characterizations. The physico-chemical characteristics of soil were evaluated using X-ray diffraction and scanning electron microscopy with energy dispersive spectroscopy techniques, whereas metal removal properties of soil were characterized by analyzing removal capacity and sorption kinetics of potential metal-removing soils. The chemical characteristics revealed that all soils are prevalently constituted of silicon dioxide (21.83–78.58 %), aluminum oxide (4.13–38 %) and ferrous oxide (0.835–7.7 %), whereas calcium oxide showed the highest percentage (65.36 %) followed by silicon dioxide (21.83 %) in tuff soil. The results demonstrated that arsenic removal efficiency was higher in elevated aluminum oxide-containing akadama (0.00452 mg/L/g/h) and kanuma (0.00225 mg/L/g/h) soils, whereas cadmium (0.00634 mg/L/g/h) and lead (0.00693 mg/L/g/h) removal efficiencies were maximum in elevated calcium oxide-containing tuff soil. Physico-chemical sorption and ion exchange processes are the metal removal mechanisms. The critical appraisal of three metal removal data also clearly revealed cadmium > lead > arsenic order of removal efficiency in different soils, except in tuff and akadama soils followed by lead > cadmium > arsenic. It clearly signified that each type of soil had a specific metal adsorption affinity which was regulated by the specific chemical composition. It may be concluded that akadama would be potential arsenic-removing and tuff would be efficient cadmium and lead-removing soil sorbents.     

Comparison of linear and nonlinear forms of isotherm models for Zn(II) and Cu(II) sorption on a kaolinite

The most appropriate method in designing the adsorption systems and assessing the performance of the adsorption systems is to have an idea on adsorption isotherms. Comparison analysis of linear least square method and nonlinear method for estimating the isotherm parameters was made using the experimental equilibrium data of Zn(II) and Cu(II) onto kaolinite. Equilibrium data were fitted to Freundlich, Langmuir, and Redlich–Peterson isotherm equations. In order to confirm the best-fit isotherms for the adsorption system, the data set using the chi-square (χ ²), combined with the values of the determined coefficient (r ²) was analyzed. Nonlinear method was found to be a more appropriate method for estimating the isotherm parameters. The best fitting isotherm was the Langmuir and Redlich–Peterson isotherm. The Redlich–Peterson is a special case of Langmuir when the Redlich–Peterson isotherm constant g was unity. The sorption capacity of kaolinite to uptake metal ions in the increasing order was given by Cu (4.2721 mg/g)?<?Zn (4.6710 mg/g).     

Lanthanide sorption on smectitic clays in presence of cement leachates

Due to their potential retention capacity, clay minerals have been proposed for use in the engineered barriers for the storage of high-level radioactive actinides in deep geological waste repositories. However, there is still a lack of data on the sorption of actinides in clays in conditions simulating those of the repositories. The present article examines the sorption of two lanthanides (actinide analogues) in a set of smectitic clays (FEBEX bentonite, MX80 bentonite, hectorite, saponite, Otay montmorillonite, and Texas montmorillonite). Distribution coefficients (K_d) were determined in two media: water and 0.02 mol L⁻¹ Ca, the latter representing the cement leachates that may modify the chemical composition of the water in contact with the clay. The K_d values of the lanthanides used in the experiments (La and Lu) varied greatly (25-50 000 L kg⁻¹) depending on the ionic medium (higher values in water than in the Ca medium), the initial lanthanide concentration (up to three orders of magnitude decrease inversely with lanthanide concentration), and the examined clay (up to one order of magnitude for the same lanthanide and sorption medium). Freundlich and Langmuir isotherms were used to fit sorption data to allow comparison of the sorption parameters among smectites. The model based on the two-site Langmuir isotherms provided the best fit of the sorption data, confirming the existence of sorption sites with different binding energies. The sites with higher sorption affinity were about 6% of the total sorption capacity in the water medium, and up to 17% in the Ca medium, although in this latter site sorption selectivity was lower. The wide range of K_d values obtained regarding the factors examined indicated that the retention properties of the clays should also be considered when selecting a suitable clay for engineered barriers.     

New insights on pressure,temperature, and chemical stability of CsAlSi<Subscript>5</Subscript>O<Subscript>12</Subscript>, a potential host for nuclear waste

A Cs-bearing polyphase aggregate with composition (in wt%): 76(1)_CsAlSi5O12 + 7(1)_CsAlSi2O6 + 17(1)_amorphous, was obtained from a clinoptilolite-rich epiclastic rock after a beneficiation process of the starting material (aimed to increase the fraction of zeolite to 90 wt%), cation exchange and then thermal treatment. CsAlSi₅O₁₂ is an open-framework compound with CAS topology; CsAlSi₂O₆ is a pollucite-like material with ANA topology. The thermal stability of this polyphase material was investigated by in situ high-T X-ray powder diffraction, the combined P–T effects by a series of runs with a single-stage piston cylinder apparatus, and its chemical stability following the “availability test” (“AVA test”) protocol. A series of additional investigations were performed by WDS–electron microprobe analysis in order to describe the P–T-induced modification of the material texture, and to chemically characterize the starting material and the run products. The “AVA tests” of the polyphase aggregate show an extremely modest release of Cs⁺: 0.05 mg/g. In response to applied temperature and at room P, CsAlSi₅O₁₂ experiences an unquenchable and displacive Ama2-to-Amam phase transition at about 770 K, and the Amam polymorph is stable in its crystalline form up to 1600 K; a crystalline-to-amorphous phase transition occurs between 1600 and 1650 K. In response to the applied P = 0.5 GPa, the crystalline-to-amorphous transition of CsAlSi₅O₁₂ occurs between 1670 and 1770 K. This leads to a positive Clapeyron slope (i.e., dP/dT > 0) of the crystalline-to-amorphous transition. When the polyphase aggregate is subjected at P = 0.5 GPa and T > 1770 K, CsAlSi₅O₁₂ melts and only CsAlSi₂O₆ (pollucite-like; dominant) and Cs-rich glass (subordinate) are observed in the quenched sample. Based on its thermo-elastic behavior, P–T phase stability fields, and Cs⁺ retention capacity, CsAlSi₅O₁₂ is a possible candidate for use in the immobilization of radioactive isotopes of Cs, or as potential solid hosts for ¹³⁷Cs γ-radiation source in sterilization applications. More in general, even the CsAlSi₅O₁₂-rich aggregate obtained by a clinoptilolite-rich epiclastic rock appears to be suitable for this type of utilizations.     

Heavy metals concentration in soils under rainfed agro-ecosystems and their relationship with soil properties and management practices

Heavy metals are governed by parent material of soils and influenced by the soil physicochemical properties and soil and crop management practices. This paper evaluates total heavy metal concentrations in rainfed soils under diverse management practices of tropical India. Vertisols (clayey soils with high shrink/swell capacity) had the highest concentrations of heavy metals. However, chromium (Cr) content was above the threshold value in Aridisol [calcium carbonate (CaCO₃)]-containing soils of the arid environments with subsurface horizon development. Concentration increased at lower depths (>30 cm). Basaltic soils showed higher concentrations of nickel (Ni), copper (Cu) and manganese (Mn). Cadmium (Cd), cobalt (Co), Cu and Mn concentrations were higher in soils cultivated to cotton, whereas Cr concentration was above the threshold level of 110 mg kg^?1 in food crop cultivated soils. As the specific soil surface is closely related to clay content and clay type, soil’s ability to retain heavy metals is more closely tied to the specific surface than to the soil cation exchange capacity. Higher positive correlations were found between heavy metal concentrations and clay content [Cd(r = 0.85; p ≤ 0.01); Co (r = 0.88; p ≤ 0.05); Ni (r = 0.87; p ≤ 0.01); Co (r = 0.81; p ≤ 0.05); Zn (r = 0.49; p ≤ 0.01); Cr (r = 0.80; p ≤ 0.05); Mn (r = 0.79; p ≤ 0.01)]. The amounts of nitrogen–phosphorus–potassium applied showed a positive correlation with Co and Ni (r = 0.62; p ≤ 0.05). As several soils used for growing food crops are high in Ni, Cr and Mn, the flow of these metals in soil–plant–livestock/human chain needs further attention.     

Biogenic silver nanoparticles on carbonaceous material from sewage sludge for degradation of methylene blue in aqueous solution

Silver nanoparticles (Ag NPs) were synthesized in situ, using a one-step green methodology with Camellia sinensis (green tea) aqueous extract as reducing agent, and supported on a carbonaceous material (Ag-CM), originated from the pyrolysis of sewage sludge. UV–Vis spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Brunauer–Emmet–Teller were used to characterize the nanocomposite. Ag-CM composite exhibited very good catalytic activity in the degradation process of methylene blue (MB) dye in aqueous solution without using sunlight or UV radiation. Batch kinetic and isothermal experiments, using 30 mg/L MB solution, showed that Ag-CM composite removed near to 91 % of MB in 9 h, whereas the carbonaceous material alone removed only 60 % in 30 h. Experimental data were adjusted to different kinetic and isotherms models, where both materials fit the second-order and Langmuir–Freundlich models, respectively; therefore, a chemisorption mechanism probably occurs in these heterogeneous materials.     

Assessment of drought frequency, duration, and severity and its impact on pasture production in Mongolia

Drought frequency, duration, and severity and its impact on pasture productivity in the four main vegetation zones of Mongolia were analyzed using meteorological, soil moisture, and vegetation data during the growing season (April–August) of 1965–2010. Meteorological and pasture drought characteristics were explored using the Standardized Precipitation Index (SPI), the soil moisture anomalies percentile index (W _p), and Palmer Drought Severity Index (PDSI) on 1-month timescale. Generally, 35–37 (15–16 %) by SPI for meteorological drought while 27–29 (12–13 %) by W _p, and 16–21 (7–9 %) by PDSI for pasture drought with different durations were identified over the four vegetation zones during the study period. Most of these droughts (80 % by SPI and 50–60 % by both W _p and PDSI) observed during the entire events occurred on a 1-month duration with moderate intensity. Drought frequencies were not significantly (p > 0.05) different within the four zones. The frequency of the short-term meteorological droughts was observed relatively greater than pasture droughts; however, pasture droughts were more persistent and severe than meteorological droughts. The three indices show that the frequency and severity of droughts have slightly increased over the 46 years with significant (p < 0.05) dry conditions during the last decade of 2001–2010 in the four zones (except in the high mountain). The results showed the W _p was more highly significantly correlated with the precipitation anomalies (r = 0.68) and pasture production (r = 0.55) than PDSI (r = 0.51, p < 0.05 and r = 0.38, p < 0.10, respectively). A statistical model, based on pasture production and the W _p, suggested that the consecutive drought months contribution during the growing season was 30 % (p < 0.05) and that pasture production was more sensitive to the occurrence of droughts during June–August (R ² = 0.32, p < 0.05) as seen in 2000–2002 and 2007. We concluded that a greater severity and frequency of growing-season droughts, during the last decade of 2001–2010, have driven a reduction in pasture production in Mongolia.     

Use of Tunisian raw clay to remove dye from aqueous solution

This paper presents the first attempt to investigate the potential of Tunisian palygorskite-rich clay (Pal-clay) on the effectiveness of a textile dye “Direct orange 34” (DO34) removal. Important parameters which affect adsorption, such as initial solution pH, contact time, adsorbent mass, initial dye concentration, and temperature, were investigated. The raw Pal-clay was characterized using X-ray diffractometer (XRD), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), cation exchange capacity (CEC), specific surface area (SSA) analysis, and point of zero charge (PZC) determination. The results showed that the Pal-clay has a high selectivity for DO34 and had maximum removal efficiency reaching up to about 91 %. The highest adsorption capacity was obtained at 25 °C and pH of 2. The dye uptake process fitted well to the pseudo-second-order kinetic expression and was best described by the Langmuir and Freundlich isotherms. Intra-particle diffusion studies showed that the adsorption mechanism was not exclusively controlled by the diffusion step and was more likely to be governed by external mass transfer. Thermodynamic parameters such as change in free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were also calculated. The parameters revealed that the adsorption of dye by the raw clay is spontaneous and exothermic. The results indicate that the Pal-clay has a moderate adsorption capacity towards anionic dye.     

Removal of arsenic and iron from mine-tailing leachate using chitosan hydrogels synthesized by gamma radiation

Mine residue and leachate were sampled from an acid mine drainage site near Arroyo San Pedro, which is one of the oldest abandoned mine districts in San Luis Potosi, Mexico, and characterized by X-ray diffraction and inductively coupled plasma-optical emission spectroscopy, confirming the presence of Fe, As, and SO₄ ^2?. To address this problem, chitosan network (net-CS) and chitosan network-N-vinylcaprolactam/N–N-dimethylacrylamide (net-CS)-g-NVCL/DMAAm hydrogels were synthesized and used as adsorbents of the different ions present in the aforementioned leachate by batch equilibrium procedure. Kinetics, isotherms, and ions dissolved in leachate were evaluated. The gels showed the highest adsorption capacity for As and Fe ions. The adsorption capacity of the net-CS hydrogels for As (V) and Fe(III) was 0.786 and 76.85 mg/g, respectively, attained after 50 h. The surface of the hydrogels was investigated by scanning electron microscopy and Fourier transform infrared spectroscopy, before and after the adsorption process, where the presence of a bond between the hydrogels and heavy metals ions, which is commonly observed in organic groups, was observed. In addition, Freundlich and Langmuir adsorption isotherms constants were determined for the As and Fe ions, and it was found that the Freundlich isotherm, with a first-order pseudo model, better fitted the adsorption process, indicating heterogeneous sorption, and the retention process occurred by chemisorption. The results from the Geochemist´s Workbench (GWB) software program revealed that arsenates, such as H₃AsO₄, H₂AsO₄ ^?, as well as Fe⁺⁺, FeSO₄(aq) and FeOH⁺ were the common aqueous species found in the leachate at pH = 2.9.     

Fate and transport of zinc in a sand tank model: monitoring of 2-D plume using TDR method

Sorption is a well-known phenomenon that may cause the retardation effect of zinc in the subsurface environment. In this study, the governing process for zinc sorption during transport was investigated by conducting 2-D plume tests in a laboratory scale sand tank model using the time domain reflectometry (TDR) method. Tracer solutions of NaNO₃ and ZnSO₄ were applied at a constant flow rate as a pulse type to capture the plumes of both solutes based on TDR-measured resistance. It was revealed that the observed zinc sulfate plume showed no retardation relative to sodium nitrate with a retardation factor of R ≈ 1. Instead of retardation, a prominent reduction of zinc sulfate mass occurred during transport through the tank model due to the irreversible sorption as well as longitudinal dispersion. This indicates that the controlling factor for the sorption process of zinc sulfate in the sand tank model is kinetic rather than equilibrium. These hydrogeological parameters would provide valuable information on the prediction of the fate of zinc in sandy aquifer materials.     

Utilization of ochre as an adsorbent to remove Pb(II) and Cu(II) from contaminated aqueous media

The ability of ochre to remove Pb(II) and Cu(II) from aqueous media has been studied by batch sorption studies varying the contact time, initial metal concentration, initial solution pH and temperature to understand the adsorption behaviour of these metals through adsorption kinetics and isotherms. The pH of the solution and the temperature controlled the adsorption of metal ions by ochre and rapid uptake occurred in the first 30 min of reaction. The kinetics of adsorption followed a pseudo-second-order rate equation (R ² > 0.99) and the isotherms are well described by the Freundlich model. Adsorption of metals onto ochre is endothermic in nature. Between the two metals, Pb(II) showed more preference towards the exchangeable sites on ochre than Cu(II). This study indicates that ochre is a very effective adsorbent in removing Pb(II) and Cu(II) from the aqueous environment with an adsorptive capacity of 0.996 and 0.628 mg g^?1 and removal efficiency of 99.68 and 62.80 %, respectively.