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.     

Separation of Cu<Superscript>2+</Superscript> and Pb<Superscript>2+</Superscript> by tetraethylenepentamine-modified sugarcane bagasse fixed-bed column: selective adsorption and kinetics

Tetraethylenepentamine-modified sugarcane bagasse (SCB) was prepared to improve its adsorption capacity and selectivity toward Cu²⁺. Adsorption performances of the modified sorbent for Cu²⁺ were studied in batch system. Separation of Cu²⁺ from Pb²⁺ by the modified sorbent fixed-bed column were studied under dynamic system with initial molar concentration ratio \(\left( {C_{0}^{\text{Cu}} /C_{0}^{\text{Pb}} } \right)\) ranging from 1:1 to 1:100. The amount of Cu²⁺ and Pb²⁺ adsorbed on the saturated column was calculated by the elution curve. Batch experimental results showed that the adsorption capacity of the sorbent for Cu²⁺ increased from 0.12 to 0.21 mmol g^?1 after modification. Dynamic adsorption results showed that the modified SCB had higher adsorption affinity toward Cu²⁺ than Pb²⁺. 0.07 mmol g^?1 of adsorbed Pb²⁺ was pushed off by Cu²⁺ during the competitive adsorption process at \(C_{0}^{\text{Cu}} /C_{0}^{\text{Pb}} = {\text{1:1}}.\) The breakthrough curves and adsorption kinetics of Cu²⁺ in the column could be fitted well by the Yoon–Nelson and modified Yoon–Nelson model, respectively. According to the elution curve, the amount of Cu²⁺ adsorbed on the fixed-bed column were 0.16, 0.16 and 0.15 mmol g^?1, while that of Pb²⁺ were 0.0016, 0.0051 and 0.0094 mmol g^?1 when \(C_{0}^{\text{Cu}} /C_{0}^{\text{Pb}}\) increased from 1:1 to 1:10 and 1:100. Cu²⁺ could be selectively adsorbed and separated from Pb²⁺ by using the modified sorbent fixed-bed column.     

Assessment of raw clays from Maghnia (Algeria) for their use in the removal of Pb<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript> ions from industrial liquid wastes: a case study of wastewater treatment

Homogenized samples of raw clays resulting from two (2) different lots of natural clays from Maghnia (Algeria) have been assessed for their potential use in the removal of Pb²⁺ and Zn²⁺ ions from industrial liquid wastes (LW). Raw and acid-activated samples have been characterized by powder X-ray diffraction, FT-IR spectroscopy, electron microscopy (SEM), and X-ray fluorescence (XRF) and used as adsorbents for the removal of Pb²⁺ and Zn²⁺ ions from aqueous system using adsorption method under different conditions. The effect of factors including contact time, pH, and dosage on the adsorption properties of Pb²⁺ and Zn²⁺ ions onto clays was investigated at 25 °C. The obtained results revealed that the removal percentages of Pb²⁺ and Zn²⁺ ions, from both aqueous solution (AS) and LW, were varying between 90 and 98% for 40 min and optimal pH values ranged from 5 to 6 for Pb²⁺ and Zn²⁺ ions, respectively. The kinetics of both Pb²⁺ and Zn²⁺ ion adsorption fitted well with the pseudo-second-order model. Langmuir, Freundlich, and Temkin adsorption isotherms were used, and their constants were evaluated. The values of thermodynamic parameters, ΔH°, ΔS°, and ΔG° indicated that the adsorption of Pb²⁺ and Zn²⁺ ions was spontaneous and exothermic process in nature. The adsorption and desorption isotherms indicated that Pb²⁺ and Zn²⁺ adsorption to raw clays was reversible. The experimental results obtained showed that the raw clays from Maghnia (Algeria) had a great potential for removing Pb²⁺ and Zn²⁺ ions from industrial liquid wastes using adsorption method.     

Influence of operating conditions on the removal of Cu, Zn, Cd and Pb ions from wastewater by adsorption

Nile Rose Plant was used to study adsorption of several cations (Cu²+, Zn²+, Cd²+ and Pb²+) from wastewater within various experimental conditions. The dried leaves of Nile Rose Plant were used at different adsorbent/ metal ion ratios. The influence of pH, contact time, metal concentration, and adsorbent loading weight on the removal process was investigated. Batch adsorption studies were carried out at room temperature. The adsorption efficiencies were found to be pH dependent, increasing by increasing the pH in the range from 2.5 to 8.5 exept for Pb. The equilibrium time was attained within 60 to 90 min. and the maximum removal percentage was achieved at an adsorbent loading weight of 1.5 g/50 mL mixed ions solution. Isothermal studies showed that the data were best fitted to the Temkin isotherm model. The removal order was found to be Pb²⁺> Zn²⁺> Cu²⁺> Cd²⁺. The surface IR-characterization of Nile rose plant showed the presence of many functional groups capable of binding to the metal cations.     

Biosorption characteristics of heavy metals (Ni2+, Zn2+, Cd2+, Pb2+) from aqueous solution by Hizikia fusiformis

Heavy metal ions (Pb²⁺, Cd²⁺, Ni²⁺, and Zn²⁺) were biosorbed by brown seaweed (Hizikia fusiformis), which was collected from Jeju Island of South Korea. The metal adsorption capacity of H. fusiformis improved significantly by washing with water or by base or acid treatments. The maximum sorption by NaOH-pretreated biomass was observed near a slightly acidic pH (pH 4?6) for Pb²⁺, Cd²⁺, Ni²⁺, and Zn²⁺. This result suggests that the treatment of H. fusiformis biomass with NaOH helped increase the functional forms of carboxylate ester units. Kinetic data showed that the biosorption occurred rapidly during the first 60 min, and most of the heavy metals were bound to the seaweed within 180 min. The maximum metal adsorption capacities assumed by a Langmuir model were on the order of Pb²⁺ > Cd²⁺ > Ni²⁺ > Zn²⁺. Equilibrium adsorption data for the heavy metal ions could fit well in the Langmuir model with regression coefficients R ² > 0.97.     

Adsorption characteristics of phenol and heavy metals on biochar from <Emphasis Type="Italic">Hizikia fusiformis</Emphasis>

The objective of the present study is to evaluate the absorption efficacy of H. fusiformis biochar (HFB) for the removal of phenol and heavy metals from single and mixed solute systems of these species under different experimental conditions. The effects of contact time, pH change, initial phenol concentration, and heavy metal concentration on the adsorption capacity of HFB were investigated. The kinetics and equilibrium models of sorption of the components of the single and mixed solute systems on HFB were also studied. The experimental data were fitted to kinetic and equilibrium models. The batch experiments revealed that 360 min of contact time was sufficient to achieve equilibrium for the adsorption of both phenol and heavy metals. The adsorption of phenol and nickel by HFB followed the pseudo-second-order kinetic model, which was quite adequate for describing the adsorption mechanism. The equilibrium data for the adsorption of phenol and heavy metals fit well to the Langmuir model with regression coefficients of R ² > 0.819. The maximum Langmuir adsorption capacities were 10.39, 12.13, 22.25, 2.24, 2.89, and 22.03 mg/g for phenol, Ni²⁺, Zn²⁺, Cu²⁺, Pb²⁺, and Cd²⁺, respectively. Moreover, HFB exhibited optimal sorption under slightly acidic conditions at pH 6. The HFB used in the present study exhibited higher adsorption capacity for the removal of phenol and heavy metals from aqueous solutions compared to documented sorbents. These results demonstrate that HFB is potentially useful for alleviating the harmful effects of phenol and heavy metal in wastewater treatment systems.     

Readily dispersible clay and its role in the mobility of transition metals Cd2+, Cu2+ and Zn2+ in an alkaline alluvial soil

Readily dispersible clay is the part of the clay fraction in soils that potentially disperses in water when a small amount of mechanical energy is applied to soil. Column and batch experiments were conducted to identify the effect of readily dispersible clay on the mobility of some metal ions in a disturbed soil sample. The clay fraction (<0.002 mm) was separated from an alkaline Vertisol from the Nile River Delta. X-ray diffraction technique was used to identify minerals present in the clay fraction. Clay suspensions and deionized H₂O solutions of Cd²⁺, Cu²⁺, and Zn²⁺ were prepared and used as influents in soil columns. Adsorption capability of the studied soil among the three metal ions was investigated. The results showed high adsorption capacity of Cd²⁺, Cu²⁺, but not Zn²⁺ for the studied soil. Cu²⁺ was the highest adsorbed metal by soil and its sorption increased at small equilibrium concentrations compared with Cd²⁺ and Zn²⁺. For the three studied metal ions, Langmuir model represented the best fit to the adsorption data. The concentration of Zn²⁺ and Cd²⁺ in leachates increased as the leaching solution volume increased, while Cu²⁺ showed a homogeneous distribution throughout the soil column. According to DTPA extractable metals, Zn²⁺ was appeared at greater depths than Cd²⁺, while Cu²⁺ had homogeneous distribution through the soil column.     

The impacts of common ions on the adsorption of heavy metal

Researches on the impact of common ions onto sediments are of great importance for the study of the heavy metal adsorption mechanisms. Considering the surface sediments from the relatively clean reach in the Baotou section of the Yellow River as the adsorbent, this work presents the impacts of common ions (Na⁺, Mg²⁺, K⁺, Ca²⁺, Cl⁻, SO₄ ²⁻, and NH₄ ⁺) on heavy metals (Cu²⁺, Zn²⁺, Cd²⁺, and Pb²⁺) adsorption. The experimental results reveal that the adsorptive capacities of the heavy metals are controlled by different adsorption mechanisms in different ion concentration ranges. With the increase of the ionic strength, the adsorption of the heavy metals increases for the compression of the electric double layer, whereas decreases for the decreasing of the ionic activities of the heavy metals. The competitive adsorption and complexations between the heavy metals and common ions are also important factors controlling the heavy metal adsorption. According to the experimental results and the real concentration of common ions in the Baotou section of the Yellow River, the increase of the concentrations of Na⁺, Mg²⁺, K⁺, and Ca²⁺ would cause the increase of Zn²⁺ adsorption and reduce the Zn pollution. The NH₄ ⁺ from the industrial discharge of the tributaries has a strong impact on the heavy metal adsorption.     

Experimental Study on Surface Reactions of Heavy Metal Ions With Quartz—Aqueous Ion Concentration Dependence

Adsorption of divalent metal ions, including Cu²⁺, Pb²⁺, Zn²⁺, Cd²⁺ and Ni²⁺, on quartz surface was measured as a function of metal ion concentration at 30°C under conditions of solution pH= 6. 5 and ion strength I = 0. 1mol/L. Results of the experimental measurements can be described very well by adsorption isotherm equations of Freudlich. The correlation coefficients (r) of adsorption isotherm lines are > 0. 96. Moreover, the experimental data were interpreted on the basis of surface complexation model. The experimental results showed that the monodentate-coordinated metal ion surface complex species (SOM⁺) are predominant over the bidentate-coordinated metal ion surface complex species [(SO)₂M] formed only by the ions Cu²⁺, Zn²⁺ and Ni²⁺. And the relevant apparent surface complexation constants are lgK_M = 2.2–3.3 in order of K_Cd≥K_Pb > K_Zn > K_Ni≥K_Cu, and lgβ_M = 5.9-6.8 in order of β_Ni > β_Zn > β_Cu. Therefore, the reactive ability of the ions onto mineral surface of quartz follows the order of Cd > Pb > Zn > Ni> Cu under the above-mentioned solution conditions. The apparent surface complexation constants, influenced by the surface potential, surface species and hydrolysis of metal ions, depend mainly on the Born solvation coefficient of the metal ions. This project was financially supported by the National Natural Science Foundation of China (No. 49572091).     

In situ formation of AgNPs on <Emphasis Type="Italic">S. cerevisiae</Emphasis> surface as bionanocomposites for bacteria killing and heavy metal removal

Novel bionanocomposites, S. cerevisiae–AgNPs, were synthesized by in situ formation of AgNPs on S. cerevisiae surface using fulvic acids as reductants under simulated sunlight. S. cerevisiae–AgNPs were characterized using UV–Vis spectroscopy, scanning electron microscope, transmission electron microscope and Fourier transform infrared spectroscopy. These analyses showed that AgNPs were distributed on the surface of S. cerevisiae. The application of S. cerevisiae–AgNPs in bacteria killing and heavy metal removal was studied. S. cerevisiae–AgNPs effectively inhibited the growth of E. coli with increasing concentrations of S. cerevisiae–AgNPs. E. coli was killed completely at high concentration S. cerevisiae–AgNPs (e.g., 100 or 200 µg mL^?1). S. cerevisiae–AgNPs as excellent heavy metal absorbents also have been studied. Using Cd²⁺ as model heavy metal, batch experiments confirmed that the adsorption behavior fitted the Langmuir adsorption isotherms and the Cd²⁺ adsorption capacity of S. cerevisiae–AgNPs was 15.01 mg g^?1. According to adsorption data, the kinetics of Cd²⁺ uptake by S. cerevisiae–AgNPs followed pseudo second-order kinetic model. Moreover, S. cerevisiae–AgNPs possessed ability of different heavy metals’ removal (e.g., Cr⁵⁺, As⁵⁺, Pb²⁺, Cu²⁺, Mn²⁺, Zn²⁺, Hg²⁺, Ni²⁺). The simulated contaminated water containing E. coli, Cd²⁺ and Pb²⁺ was treated using S. cerevisiae–AgNPs. The results indicated that the bionanocomposites can be used to develop antibacterial agents and bioremediation agents for water treatment.     

Removal of heavy metal ions from drinking water by alginate-immobilised <Emphasis Type="Italic">Chlorella sorokiniana</Emphasis>

This paper investigates the potential of alginate-immobilised Chlorella sorokiniana for removing Cu²⁺, Ni²⁺ and Cd²⁺ ions from drinking water solutions. The effects of initial metal concentrations, contact times and temperatures on the biosorptions and removal efficiencies of the tested metals were investigated at initial pH values of 5, and pH effects were studied within the range of 3–7. When studying the effects of initial metal concentrations, the highest experimental removal yields achieved for Cu²⁺, Ni²⁺ and Cd²⁺ ions were 97.10, 50.94 and 64.61 %, respectively. The maximum biosorption capacities obtained by the Langmuir isotherm model for the biosorptions of Cu²⁺, Ni²⁺ and Cd²⁺ ions by alginate-immobilised C. sorokiniana were found to be 179.90, 86.49 and 164.50 mg/g biosorbent, respectively. The experimental data followed pseudo-second-order kinetics. At an initial metal concentration of 25 mg/L, immobilised algae could be used in at least 5 successive biosorption–desorption cycles. SEM and EDS analyses revealed that the metals bonded to the biosorbent. Bi- and multi-metal systems of Cu²⁺, Ni²⁺ and Cd²⁺ were investigated at initial metal concentrations of 30, 50 and 100 mg/L. The removal of Cd²⁺ as well as Ni²⁺ in such systems was negatively affected by the presence of Cu²⁺. The removal efficiency for Cu²⁺ in multi-metal systems decreased by 5–7 %, whilst in the cases of Cd²⁺ and Ni²⁺ the efficiencies decreased by up to 30 %. Nevertheless, the results obtained show that alginate-immobilised C. sorokiniana can efficiently remove the metals tested from polluted drinking water sources.     

Predicting the activity of Cd and Zn in soil pore water from the radio-labile metal fraction

Cadmium and zinc were added at 3 and 300 mg kg⁻¹, respectively, to 23 soils and incubated at 16°C and 80% field capacity for 818 d. Following addition of metal, changes in the radio-labile concentrations of both elements were examined on seven separate sampling occasions over 818 d. At each sample time, soil pore water was extracted using Rhizon soil solution samplers, and concentrations of Cd, Zn, dissolved organic carbon, and major cations and anions were determined. The chemical speciation program WHAM 6 was used to determine free metal ion activity, (M²⁺). Similar measurements were made on a set of historically contaminated soils from old mining areas, sewage sludge disposal facilities, and industrial sources. The two data sets were combined to give a range of values for p(Cd²⁺) and p(Zn²⁺) that covered 5 and 4 log₁₀ units, respectively. A pH-dependent Freundlich model was used to predict Zn²⁺ and Cd²⁺ ion activity in soil pore water. Total and radio-labile metal ion concentration in the solid phase was assumed to be adsorbed on the “whole soil,” humus, or free iron oxides to provide alternative model formats. The most successful models assumed that solubility was controlled by adsorption on soil humus. Inclusion of ionic strength as a model variable provided small improvements in model fit. Considering competition with Ca²⁺ and between Zn²⁺ and Cd²⁺ produced no apparent improvement in model fit. Surprisingly, there was little difference between the use of total and labile adsorbed metal as a model determinant. However, this may have been due to a strong correlation between metal lability and pH in the data set used. Values of residual standard deviation for the parameterized models using labile metal adsorbed on humus were 0.26 and 0.28 for prediction of p(Cd²⁺) and p(Zn²⁺), respectively. Solubility control by pure Zn and Cd minerals was not indicated from saturation indices. However there may have been fixation of metals to non-radio-labile forms in CaCO₃ and Ca-phosphate compounds in the soils in the higher pH range. Independent validation of the Cd model was carried out using an unpublished data set that included measurements of isotopically exchangeable Cd. There was good agreement with the parameterized model.     

Mg2+ removal in the system Mg2+—amorphous SiO2—H2O by adsorption and Mg-hydroxysilicate precipitation

Two chemical processes can remove Mg²⁺ from suspensions containing amorphous silica (am-SiO₂) at low temperatures: adsorption and precipitation of a Mg-hydroxysilicate resembling sepiolite. Mg²⁺ removal from am-SiO₂ suspensions was investigated, and the relative role of the two removal processes evaluated, as a function of: pH, ionic strength, Mg²⁺ concentration, and temperature.The extent of Mg²⁺ adsorption onto am-SiO₂ decreases with increasing NaCl concentration due to displacement of Mg²⁺ by Na⁺. At NaCl concentrations of 0.05 M and above, adsorption occurs only at pH values above 8.5, where rapid dissolution of am-SiO₂ gives rise to high concentrations of dissolved silica, resulting in supersaturation with respect to sepiolite. Removal of Mg²⁺, at concentrations of 40 to 650 μM, from am-SiO₂ suspensions in 0.70 M NaCl at 25 °C occurs at pH 9.0 and above. Experiments show that under these conditions adsorption and Mg-hydroxysilicate precipitation remove Mg²⁺ at similar rates. For 0.05 M Mg²⁺, at 0.70 M ionic strength and 25 °C, measurable Mg²⁺ removal occurs down to ca. pH 7.5 but is primarily due to Mg-hydroxysilicate precipitation. For the same solution conditions at 5°C, Mg²⁺ removal occurs above pH 8.0 and is primarily due to adsorption.Assuming that increasing pressure does not greatly enhance adsorption, Mg²⁺ adsorption onto am-SiO₂ is an insignificant process in sea water. The surface charge of pristine am-SiO₂ in sea water is primarily controlled by interactions with Na⁺. The principal reaction between Mg²⁺ and am-SiO₂ in marine sediments is sepiolite precipitation.The age distribution of sepiolite in siliceous pelagic sediments is influenced by temperatures of bottom waters and by geothermal gradients.     

腐植酸改性强化磁铁矿吸附水体中铅镉的实验研究

磁铁矿是一种绿色廉价的矿物材料,对水体中重金属离子具有良好的吸附性,但吸附容量低,选择性差,易团聚,通过改性可以克服该缺点并提高其吸附性能。本文以腐植酸为改性剂,采用常温水相反应制备了腐植酸改性磁铁矿吸附材料。通过傅里叶红外光谱(FTIR)、扫描电镜(SEM)和X射线光电子能谱(XPS)表征研究其表面形貌和微观结构。采用静态平衡实验考察了pH、吸附时间等因素对铅、镉吸附性能的影响,探讨了吸附动力学规律,拟合了吸附等温线。结果表明:腐植酸上的羧基、羟基被成功地接枝到了磁铁矿表面。在室温下,溶液初始pH对Pb~(2+)的吸附率几乎无影响,对Cd~(2+)的影响较大,当pH=7时,Pb~(2+)和Cd~(2+)吸附率均达到了95%。对初始质量浓度为10mg/L的Pb~(2+)、Cd~(2+)最佳吸附平衡时间为360min,吸附过程符合准二级动力学方程。吸附等温线实验得到的竞争吸附顺序为Pb~(2+)Cd~(2+),由Langmuir等温吸附模型得到Pb~(2+)、Cd~(2+)饱和吸附容量分别为39.27mg/g、28.95mg/g,显著大于磁铁矿的饱和吸附容量,表明磁铁矿经腐植酸改性后增强了对水中铅镉的吸附能力。     

Luminescence of Eu<Superscript>2+</Superscript> in feldspars from muscovite pegmatites

The data on photoluminescence (PL) that precisely detects Eu²⁺ centers and X-ray luminescence (XL) were compared for plagioclases and potassium feldspars in 21 samples from muscovite pegmatites of the Mama region. The Eu contents determined in 10 samples vary from 10^?4 to 10^?6 wt %. Europium occurs mainly as bivalent species that replaces Sr²⁺, Ca²⁺, and Ba²⁺. Eu is gained in the products of early crystallization, and its relative amounts decrease by an order of magnitude in the course of pegmatite formation down to complete disappearance in late generations of feldspars. It is shown that Eu²⁺ can be detected in XL spectra, and the Eu²⁺ content can be determined in qualitative terms, for instance, by the intensity of radiation band 400–420 nm in plagioclase.     

Adsorption of lead, zinc and cadmium ions from contaminated water onto Peganum harmala seeds as biosorbent

Peganum harmala seeds were assessed as biosorbent for removing Pb²⁺, Zn²⁺and Cd²⁺ ions from aqueous solutions. The effects of various parameters such as the aqueous solution pH, the contact time, the initial metal concentration and the amount of adsorbent in the process were investigated. The adsorption efficiencies increased with pH. It was found that about 95 % of lead, 75 % of zinc and 90 % of cadmium ions could be removed from 45 ml of aqueous solution containing 20 mg l^?1 of each cation with 2 g of adsorbent at pH 4.5 after 15 min. The quantitative desorption of cadmium from adsorbent surface was achieved using 10 ml of a 0.5 M nitric acid solution. This condition was attained for lead and zinc ions with 10 ml of 1 M hydrochloric acid solution. Kinetic investigation of the process was performed by considering a pseudo-second-order model. This model predicts the chemisorption mechanism of the process. Langmuir, Freundlich, Temkin and Dubinin–Radushkevich models were tested for describing the equilibrium data. It was found that the Freundlich model describes the experimental data resulting from the adsorption of lead ions. However for cadmium and zinc ions, the adsorption equilibria were interpreted with the Langmuir model.     

Effects of strong network modifiers on Fe<Superscript>3+</Superscript>/Fe<Superscript>2+</Superscript> in silicate melts: an experimental study

The effect of CaO, Na₂O, and K₂O on ferric/ferrous ratio in model multicomponent silicate melts was investigated in the temperature range 1450–1550?°C at 1-atm total pressure in air. It is demonstrated that the addition of these network modifier cations results in an increase of Fe³⁺/Fe²⁺ ratio. The influence of network modifier cations on the ferric/ferrous ratio increases in the order Ca?<?Na?<?K. Some old controversial conceptions concerning the effect of potassium on Fe³⁺/Fe²⁺ ratio in simple model liquids are critically evaluated. An empirical equation is proposed to predict the ferric/ferrous ratio in SiO₂–TiO₂–Al₂O₃–FeO–Fe₂O₃–MgO–CaO–Na₂O–K₂O–P₂O₅ melts at air conditions.     

Heavy metal biosorption potential of a Malaysian Rhodophyte (<Emphasis Type="Italic">Eucheuma denticulatum</Emphasis>) from aqueous solutions

Biosorption is a promising technology for the removal of heavy metals from industrial wastes and effluents. In the present study, biosorption of Pb²⁺, Cu²⁺, Fe²⁺ and Zn²⁺ onto the dried biomass of Eucheuma denticulatum (Rhodophyte) was investigated as a function of solution pH, contact time, temperature and initial metal ion concentration. The experimental data were evaluated by Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherm models. The sorption isotherm data followed Langmuir and Freundlich models, and the maximum Langmuir monolayer biosorption capacity was found as 81.97, 66.23, 51.02 and 43.48 mg g^?1 for Pb²⁺, Cu²⁺, Fe²⁺ and Zn²⁺, respectively. The sorption kinetic data followed pseudo-second-order and intraparticle diffusion models. Thermodynamic study revealed feasible, spontaneous and endothermic nature of the sorption process. Fourier transform infrared analysis showed the presence of amine, aliphatic, carboxylate, carboxyl, sulfonate and ether groups in the cell wall matrix involved in metal biosorption process. A total of nine error functions were applied in order to evaluate the best-fitting models. We strongly suggest the analysis of error functions for evaluating the fitness of the isotherm and kinetic models. The present work shows that E. denticulatum can be a promising low-cost biosorbent for removal of the experimental heavy metals from aqueous solutions. Further study is warranted to evaluate its potential for the removal of heavy metals from the real environment.     

Sorption of Cd<Superscript>2+</Superscript> ions onto zeolite synthesized from perlite waste

In this work, the studies on the formation of zeolites from expanded perlite waste and their use in the sorption process of Cd²⁺ ions will be reported. Such approach is innovative and has not been investigated elsewhere. The results of the synthesis of zeolites from aluminosilicate waste using hydrothermal method were presented. By-product from the process production of expanded perlite was used as the starting material. Theoretical and practical aspects of Cd²⁺ ions sorption process onto material synthesized in selected conditions (a material with good sorption capacity can be obtained by 24 h reaction of 1 g of perlite waste in 10 mL of 4.0 M NaOH solution with at 70 °C) will be presented. The atomic absorption spectroscopy has been used as the main method, from which the effective cation exchange capacity as well as the proportion of ion exchange to chemisorption in the sorption process have been determined. Structural analyses of the sample before and after sorption process have been also carried out by the mid-infrared spectra measurement, especially pseudolattice range of the spectra was analyzed in detail in which changes caused by ion exchange of non-tetrahedral ions have been observed.     

Removal of Lead,Copper, Zinc and Cadmium from Water Using Phosphate Rock

Removal of Pb^2＋, Cu^2＋, Zn^2＋ and Cd^2＋ from aqueous solutions by sorption on a natural phosphate rock （FAP） was investigated. The effects of the contact time and initial metal concentration were examined in the batch method. The percentage sorption of heavy metals from solution ranges generally between 50% and 99%. The amount of sorbed metal ions follows the order Cu〉Pb〉Cd〉Zn. Heavy metal immobilization was attributed to both surface complexation of metal ions on the surface of FAP grains and partial dissolution and precipitation of a heavy metal-containing phosphate. The very low desorption ratio of heavy metals further supports the effectiveness of FAP as an alternative and low-cost material to remove toxic Pb^2＋, Cu^2＋, Zn^2＋ and Cd^2＋ from polluted waters.