Monocrystalline MnZn ferrite dissolution in aqueous H3PO4-HCl solutions

The dissolution of monocrystalline MnZn ferrite in H₃PO₄-HCl aqueous solutions has been studied at temperatures varying from 30 to 110° C. The dissolution rate determined for the two crystal orientations {1 0 0} and {1 1 1} is found to increase with higher H₃ P0₄ concentration and higher temperatures with an activation energy of 62 to 77 kJ mol^–1. The dissolution is shown to be kinetically controlled, and the rate is determined by the absorption of H₃ PO₄ molecules on the surface. At H₃ P0₄ concentrations above 10 M, H⁺ ions accelerate the dissolution. The dissolution rate of the {100} orientated surface is a factor of four larger than for the {111} orientated surface. Temperature and acid concentration do not have a significant influence on the anisotropy, which indicates a similar reaction mechanism for both orientations. When the ferrite surface is partly masked (e.g. by an SiO₂ film) the anisotropy in the dissolution rate yields etched regions which are bordered by planes with the lowest dissolution rates. By properly aligning the masks this results in three-dimensional structures such as V-grooves.     

Removal of cadmium from aqueous solutions by adsorption onto orange waste

The use of orange wastes, generated in the orange juice industry, for removing cadmium from aqueous solutions has been investigated. The material was characterized by Fourier transform infrared spectroscopy and batch experiments were conducted to determine the adsorption capacity of the biomass. A strong dependence of the adsorption capacity on pH was observed, the capacity increasing as pH value rose. Kinetics and adsorption equilibrium were studied at different pH values (4-6). The adsorption process was quick and the equilibrium was attained within 3h. The maximum adsorption capacity of orange waste was found to be 0.40, 0.41 and 0.43 mmol/g at pH 4-6, respectively. The kinetic data were analysed using various kinetic models - pseudo-first order equation, pseudo-second order equation, Elovich equation and intraparticle diffusion equation - and the equilibrium data were tested using four isotherm models - Langmuir, Freundlich, Sips and Redlich-Peterson. The data were fitted by non-linear regression and five error analysis methods were used to evaluate the goodness of the fit. The Elovich equation provides the greatest accuracy for the kinetic data and the Sips model the closest fit for the equilibrium data.     

Removal of phosphate from aqueous solution by biochar derived from anaerobically digested sugar beet tailings

Biochar converted from agricultural residues or other carbon-rich wastes may provide new methods and materials for environmental management, particularly with respect to carbon sequestration and contaminant remediation. In this study, laboratory experiments were conducted to investigate the removal of phosphate from aqueous solution by biochar derived from anaerobically digested sugar beet tailings (DSTC). Batch adsorption kinetic and equilibrium isotherm experiments and post-adsorption characterizations using SEM-EDS, XRD, and FTIR suggested that colloidal and nano-sized MgO (periclase) particles on the biochar surface were the main adsorption sites for aqueous phosphate. Batch adsorption experiments also showed that both initial solution pH and coexisting anions could affect the adsorption of phosphate onto the DSTC biochar. Of the mathematical models used to describe the adsorption kinetics of phosphate removal by the biochar, the Ritchie N_th-order (N=1.14) model showed the best fit. Two heterogeneous isotherm models (Freundlich and Langmuir-Freundlich) fitted the experimental isotherm of phosphate adsorption onto the biochar better than the Langmuir adsorption model. Our results suggest that biochar converted from anaerobically digested sugar beet tailings is a promising alternative adsorbent, which can be used to reclaim phosphate from water or reduce phosphate leaching from fertilized soils. In addition, there is no need to regenerate the exhausted biochar because the phosphate-laden biochar contains abundance of valuable nutrients, which may be used as a slow-release fertilizer to enhance soil fertility and to sequester carbon.     

海枣核CO2活化和磷酸活化制备活性炭及其结构、吸附性能（英文）

由于具有很大的吸附容量,多孔炭材料是优良的吸附剂。笔者试图比较海枣核分别经CO2活化和磷酸活化所制活性炭的结构和吸附性能。活化过程和工艺条件对炭的物理化学性质影响较大,根据文献报道的结果选取了优化的工艺参数。基于氮气吸附等温线、SEM、FT-IR等分析结果,评估了活性炭的结构特征,吸附性能则由亚甲蓝吸附值表示。CO2活化得到了微孔活性炭,产率为44%、BET比表面积是666 m2·g-1;磷酸活化得到了产率为14.8%的中孔活性炭,BET比表面积为725 m2·g-1。CO2活化活性炭的平均孔径是1.51 nm,磷酸活化活性炭的则为2.91 nm。活性炭的亚甲蓝吸附等温线分别用Langmuir等温线和Freundlich等温线进行了验证,在优化工艺条件下制备的CO2活化炭和磷酸活化炭的亚甲蓝w单分子吸附容量分别为110 mg·g-1和345 mg·g-1。然而,磷酸活化产生的亚甲蓝吸附值最高达455 mg·g-1。     

Removal of phenol from aqueous solutions by adsorption onto activated carbon prepared from biomass material

Activated carbon derived from rattan sawdust (ACR) was evaluated for its ability to remove phenol from an aqueous solution in a batch process. Equilibrium studies were conducted in the range of 25–200 mg/L initial phenol concentrations, 3–10 solution pH and at temperature of 30 °C. The experimental data were analyzed by the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherm models. Equilibrium data fitted well to the Langmuir model with a maximum adsorption capacity of 149.25 mg/g. The dimensionless separation factor R_L revealed the favorable nature of the isotherm of the phenol-activated carbon system. The pseudo-second-order kinetic model best described the adsorption process. The results proved that the prepared activated carbon was an effective adsorbent for removal of phenol from aqueous solution.     

Determination of the adsorption capacity of activated carbon made from coffee grounds by chemical activation with ZnCl2 and H3PO4

In order to evaluate the adsorptive capacities of granular activated carbon produced from coffee grounds by chemical activation, the adsorption of different phenols and acid and basic dyes, has been carried out. The comparison with a commercial activated carbon has been made. Adsorption isotherms of phenols and dyes (acid and basic) onto produced and commercial granular activated carbons were experimentally determined by batch tests. Both Freundlich and Langmuir models are well suited to fit the adsorption isotherm data. As a result, the coffee grounds based activated carbon may be promising for phenol and dye removal from aqueous streams.     

The corrosion of tantalum in oxidizing sub- and supercritical aqueous solutions of HCl, H2SO4 and H3PO4

The corrosion of tantalum was investigated in sub- and supercritical oxidizing solutions of hydrochloric, sulfuric and phosphoric acid at temperatures between 360 and 500 °C. The corrosion rates in HCl and H₂SO₄ increased strongly above the critical temperature of water, which was attributed to a phase transformation from vitreous to crystalline Ta₂O₅. Corrosion rates in H₃PO₄ were low at all temperatures due to the formation of a top phosphate layer.     

Adsorption of cadmium from aqueous solutions by perlite

The present study examined the use of perlite for the removal of cadmium from aqueous solutions. The effects of pH and contact time on the adsorption process were examined. The optimum pH for adsorption was found to be 6.0. Residual cadmium concentration reached equilibrium in 6h and the rate of cadmium adsorption by perlite was rapid in the first hour of the reaction time. Ho's pseudo-second-order model best described the kinetics of the reaction. Batch adsorption experiments conducted at room temperature (22+/-1 degrees C) showed that the adsorption pattern followed the Freundlich isotherm model. The maximum removal of cadmium obtained from batch studies was 55%. Thomas model was used to describe the adsorption data from column studies. The results generally showed that perlite could be considered as a potential adsorbent for cadmium removal from aqueous solutions.     

Removal of cadmium from aqueous solutions by palygorskite

The sorption characteristics of palygorskite with respect to cadmium were studied with the aim of assessing its use in water purification systems. Using a batch method the influence of time (0.5-48 h), initial Cd concentration (5-150 mg/l or 0.044-1.34 mmol/l), ionic strength ([Ca(II)]: 0-0.1 mol/l), pH (3-7) and mineral dose (1-20 g/l) on Cd removal was evaluated. The sorption of Cd on palygorskite appeared as a fast process, with equilibrium being attained within the first half an hour of interaction. This process could be described by the Langmuir model and gave a maximum Cd sorption of 4.54 mg/g. This sorption capacity value was greatly affected by both pH and ionic strength. Thus, Cd sorption decreased as initial pH lessened, especially at proton concentrations similar to those of Cd, at which competition for variable charge sites (silanol groups on palygorskite surface) appeared to be important. High competing electrolyte concentrations also decreased significantly (close to 60%) the amount of sorbed Cd, suggesting a great contribution of replacement of exchange cations in this metal removal by palygorskite. The increase of mineral dose provoked a Cd removal raise; removal values in the range 85-45% were attained for Cd initial concentrations of 10-150 mg/l (0.089-1.34 mmol/l) when a palygorskite dose of 20 g/l was employed. Column studies were also performed in order to estimate the potential of palygorskite to be used in continuous flow purification systems, showing the effectiveness of this mineral to purify down to the legal limit of waste moderate volumes of Cd-containing solutions with a similar concentration (50mg/l or 0.445 mmol/l) to those mostly found in the upper range of concentrations usually present in industrial wastewaters.     

Removal of cadmium (II) from aqueous solutions by adsorption on agricultural waste biomass

This paper reports the feasibility of using various agricultural residues viz. sugarcane bagasse (SCB), maize corncob (MCC) and Jatropha oil cake (JOC) for the removal of Cd(II) from aqueous solution under different experimental conditions. Effect of various process parameters, viz., initial metal ion concentration, pH, and adsorbent dose has been studied for the removal of cadmium. Batch experiments were carried out at various pH (2-7), adsorbent dose (250-2000 mg), Cd(II) concentration (5-500 mg l(-1)) for a contact time of 60 min. The maximum cadmium removal capacity was shown by JOC (99.5%). The applicability of Langmuir and Freundlich isotherm suggests the formation of monolayer of Cd(II) ions onto the outer surface of the adsorbents. Maximum metal removal was observed at pH 6.0 with a contact time of 60 min at stirring speed of 250 rpm with an adsorbent dose of 20 g l(-1) of the test solution. The maximum adsorption of cadmium (II) metal ions was observed at pH 6 for all the adsorbents viz; 99.5%, 99% and 85% for JOC, MCC, and SCB, respectively. Order of Cd(II) removal by various biosorbents was JOC>MCC>SCB. JOC may be an alternative biosorbent for the removal of Cd(II) ions from the aqueous solution. FT-IR spectra of the adsorbents (before use and after exhaustion) were recorded to explore number and position of the functional groups available for the binding of Cd(II) ions on to studied adsorbents. These results can be helpful in designing a batch mode system for the removal of cadmium from dilute wastewaters.     

Equilibrium and kinetics of cadmium adsorption from aqueous solutions using untreated Pinus halepensis sawdust

Untreated Pinus halepensis sawdust has been investigated as an adsorbent for the removal of cadmium from aqueous solutions. Batch experiments were carried out to investigate the effect of pH, adsorbent dose, contact time, and metal concentration on sorption efficiency. The favorable pH for maximum cadmium adsorption was at 9.0. For the investigated cadmium concentrations (1–50 mg/L), maximum adsorption rates were achieved almost in the 10–20 min of contact. An adsorbent dose of 10 g/L was optimum for almost complete cadmium removal within 30 min from a 5 mg/L cadmium solution. For all contact times, an increase in cadmium concentration resulted in decrease in the percent cadmium removal (100–87%), and an increase in adsorption capacity (0.11–5.36 mg/g). The equilibrium adsorption data were best fitted with the Freundlich isotherm (R² = 0.960). The kinetics of cadmium adsorption was very well described by the pseudo-second-order kinetic model (R² > 0.999).     

Removal of Acid Violet 17 from aqueous solutions by adsorption onto activated carbon prepared from sunflower seed hull

The adsorption of Acid Violet 17 (AV17) was carried out using various activated carbons prepared from sunflower seed hull (SSH), an agricultural solid waste by-product. The effect of parameters such as agitation time, initial dye concentration, adsorbent dosage, pH and temperature were studied. The Langmuir and Freundlich isotherm models were applied and the Langmuir model was found to best report the equilibrium isotherm data. Langmuir adsorption capacity was found to be 116.27 mg/g. Kinetic data followed pseudo-second-order kinetics. Maximum colour removal was observed at pH 2.0. It was observed that the rate of adsorption improves with increasing temperature and the process is endothermic. The adsorbent surface was analysed with a scanning electron microscope. The results indicate that activated sunflower seed hull could be an attractive option for colour removal from dilute industrial effluents.     

Removal of catechol from aqueous solutions by adsorption onto organophilic-bentonite

Organophilic-bentonite, produced by exchange of cetyltrimethylammonium cation for metal cations on the bentonite, was exploited as adsorbent for removal of catechol from aqueous solutions using batch technique. The dependence of removal on various physico-chemical parameters, such as contact time (1–250 min), concentration (0.8–15.3 mmol L⁻¹), temperature (30, 40, 50 ± 1 °C) and pH (5–12) of the adsorptive solution were investigated. Obtained results show that catechol could be removed efficiently (100%) at pH values ≥9.9. The uptake process follows first-order rate kinetics and the equilibrium data fit well into the Langmuir and Freundlich adsorption isotherms over a wide range of concentration (1–10 mmol L⁻¹). The magnitude of change of free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) were determined.     

Defluoridation from aqueous solutions by nano-alumina: characterization and sorption studies

The present study was conducted to evaluate the feasibility of nano-alumina (Al(2)O(3)) for fluoride adsorption from aqueous solutions. The nature and morphology of pure and fluoride-sorbed nano-alumina were characterized by SEM with EDX, XRD, and FTIR analysis. Batch adsorption studies were performed as a function of contact time, initial fluoride concentration, temperature, pH and influence of competing anions. Fluoride sorption kinetics was well fitted by pseudo-second-order model. The maximum sorption capacity of nano-alumina for fluoride removal was found to be 14.0 mg g(-1) at 25°C. Maximum fluoride removal occurred at pH 6.15. The fluoride sorption has been well explained using Langmuir isotherm model. Fluoride sorption was mainly influenced by the presence of PO(4)(3-), SO(4)(2-) and CO(3)(2-) ions.     

Li1.3Al0.3Ti1.7(PO4)3的溶胶-凝胶法制备及其性质研究

采用溶胶凝胶法及固相反应法合成锂离子固体电解质Li1.3Al0.3Ti1.7(PO4)3,用X射线衍射检测合成产物的物相,用循环伏安及交流阻抗技术测试产物的电化学窗口及离子电导率等电化学性质。研究表明溶胶凝胶法合成的Li1.3Al0.3Ti1.7(PO4)3的电化学窗口为2.4V。与固相反应法相比,溶胶凝胶法合成的Li1.3Al0.3Ti1.7(PO4)3具有更好的结晶性,其烧结片具有较高的离子电导率和较小的活化能。     

Preparation of cadmium telluride nanoparticles from aqueous solutions by sonochemical method

Cadmium telluride nanoparticles with sizes between 8 and 13 nm have been synthesized via a sonochemical route using cadmium sulfate hydrate (CdSO₄·8/3H₂O), cadmium chloride (CdCl₂) and elemental Te as precursors and aqueous solutions of NaOH and EDTA as solvents. The qualitative characterization and estimation of nanoparticle size were carried out by using X-ray powder diffraction (XRD). The morphology of nanoparticles was analyzed by transmission electron microscopy (TEM). Changes of physical and chemical properties of the prepared CdTe nanoparticles at increased temperature were studied by thermal analysis (TGA, SDTA). A probable mechanism for the sonochemical formation of CdTe is proposed.     

Immobilisation of TiO2-nanoparticles on sewage sludge and their adsorption for cadmium removal from aqueous solutions

In this study, pure TiO₂-nanoparticles and TiO₂/sewage sludge (TS) as biomass material were synthesised via a sol–gel method. The adsorption potential of nanosized TiO₂ and TS for removal of Cd(II) was investigated in a batch system. The prepared adsorbents were characterised using X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The XRD analysis showed that pure TiO₂ is in amorphous phase before calcination and in anatase phase at annealing temperature of 400 °C. TiO₂/sewage sludge that calcined at 400 °C (TS⁴⁰⁰) was found to be the best adsorbent for cadmium removal from aqueous solution. Kinetic and isotherm studies were carried out by considering the parameters, pH, initial concentration and contact time. The optimum pH value for Cd(II) adsorption onto TS⁴⁰⁰ was found to be 6. Langmuir isotherm showed better fit than Freundlich isotherm and the maximum adsorption capacity was found to be 29.28 mg/g which is higher than that of many other adsorbents reported in literature. The sorption kinetic data were well fitted with a pseudo-second-order model. These results demonstrated that TS⁴⁰⁰ was readily prepared and is the promising and effective solid material for the removal of Cd(II) from aqueous solutions.     

Hydrolysis of tetracalcium phosphate in H3PO4 and KH2PO4

The activity product of tetracalcium phosphate (TTCP, Ca₄(PO₄)₂O), was determined at 37°C, and the hydrolysis of TTCP was investigated in 0.01–0.1 mol l^–1 H₃PO₄ and KH₂PO₄ solutions by means of calcium and phosphorus analyses, X-ray diffraction and infrared analysis. The activity product, defined as K _sp=(Ca²⁺)⁴ (PO ₄ ^3– )² (OH^–)², was 37.36 as pK _sp, which was smaller than that previously reported (42.4). TTCP easily hydrolysed to form calcium-deficient apatite (Ca-def OHAp, Ca_5–x (HPO₄) _x (PO₄)_3–x (OH)_1–x ), or dicalcium phosphate dihydrate (DCPD, CaHPO₄2H₂O), depending on the initial phosphate concentration. With 0.1 mol l^–1 H₃PO₄, TTCP hydrolysed to form DCPD within several minutes. In 0.025 mol l^–1 H₃PO₄ and 0.1 mol l^–1 KH₂PO₄, TTCP hydrolysed to form Ca-def OHAp through DCPD. In the latter solution, a small amount of octacalcium phosphate (OCP, Ca₈(H₂PO₄)₂(PO₄)₄5H₂O), was detected as an intermediate product. In 0.025 mol l^–1 KH₂PO₄, TTCP hydrolysed directly to form Ca-def OHAp. In 0.01 mol l^–1 H₃PO₄, hydrolysis of TTCP was not completed, although Ca-def OHAp was only a product. Thus the final product and the degree of hydrolysis depended on the pH and the overall Ca/P ratio in the reaction system. The rate of Ca-def OHAp formation seemed to be controlled by the dissolution rate of TTCP rather than the crystallization rate of the OHAp.