Equilibrium and kinetic studies on free cyanide adsorption from aqueous solution by activated carbon

Adsorption equilibrium and kinetics of free cyanide onto activated carbon were investigated in the batch tests, and the effects of contact time (1–72 h) and initial cyanide concentrations in the range of 102–532 mg/L were studied. Linear regression was used to determine the best fit of equilibrium and kinetics expressions. The two-parameter models including Freundlich, Dubinin–Radushkevich, Temkin and four different linearized forms of Langmuir and three-parameter models including Redlich–Peterson and Koble–Corrigan were employed for fitting the equilibrium data and it was found that, three-parameter models fitted the data better than the two-parameter models and among the three-parameter models the equilibrium data are best represented by Koble–Corrigan model. A number of kinetic models including fractional power, zero order, first order, pseudo-first order, Elovich, second order, intraparticle diffusion and four different linearized forms of pseudo-second order models were tested to fit the kinetic data. The latter was found to be consistent with the data. Intraparticle diffusion plots show that the adsorption process of free cyanide is a two steps process. In the first step, the adsorption of cyanide is fast while in the second step, cyanide adsorption slows down.     

Degradation of malachite green in aqueous solution by Fenton process

In this study, advanced oxidation process utilizing Fenton's reagent was investigated for degradation of malachite green (MG). The effects of different reaction parameters such as the initial MG concentration, initial pH, the initial hydrogen peroxide concentration, the initial ferrous concentration and the reaction temperature on the oxidative degradation of MG have been investigated. The optimal reacting conditions were experimentally found to be pH 3.40, initial hydrogen peroxide concentration=0.50mM and initial ferrous concentration=0.10mM for initial MG concentration of 20mg/L at 30 degrees C. Under optimal conditions, 99.25% degradation efficiency of dye in aqueous solution was achieved after 60 min of reaction.     

Chromium removal from aqueous solution by the ferrite process

This research summarises the results of the study on the removal of chromium by applying the ferrite process to the solutions obtained from two different Cr(VI) reduction processes utilising sodium sulphite and ferrous sulphate as reducing agents. For both solutions containing trivalent chromium ions, the optimum treatment conditions were determined. The generated sludges were characterised by XRD analysis and physical tests. In addition, to explore the dissolution properties of the sludges obtained, they were contacted with the solutions of sulphuric, citric, tartaric, oxalic and ascorbic acids and EDTA. Also, the sludge samples were subjected to standard toxicity characterisation leaching procedure (TCLP) test of USEPA in order to determine the pollution potential. An efficient Cr(III) removal (about 100%) in the solution from the Cr(VI) reduction process utilising sodium sulphite as reducing agent was achieved when the solution was treated at pH 9 and 50 degrees C for 60 min in the presence of Fe2+/Cr3+ weight ratio of 16. For the other Cr(III) solution prepared from Cr(VI) reduction by ferrous sulphate, a Fe2+/Cr3+ weight ratio of 17.9 at the same conditions was found to produce complete removal of Cr(III). It was determined that the spynel chromium-iron compounds obtained in the process were in the form of chromite (Cr2FeO4). Dissolution experiments and TCLP tests show that the concentrations of the chromium dissolved from both sludges were below the limit given as 5 mg l(-1) by USEPA. The results showed that Cr(III) removal through ferrite process provides the advantages that the sludges generated are non-voluminous, easily separable and environmentally stable.     

Degradation of 2,4-dichlorophenol in aqueous solution by a hybrid oxidation process

A hybrid photoelectroreaction system has been developed in this study, which consists of three functional electrodes: a TiO2/Ti sheet as the anode, a steel (Fe) sheet as another anode in parallel and a piece of graphite felt (GF) as the cathode. While an electrical current is applied between the Fe anode and GF cathode and UV light is irradiated on the surface of TiO2/Ti anode, both of E-Fenton reaction and photoelectrocatalytic (PEC) reaction are involved simultaneously. The integration of E-Fenton and PEC reactions was evaluated in terms of 2,4-dichlorophenol (2,4-DCP) degradation in aqueous solution. In the meantime, the current distribution between two anodes and pH influence on the 2,4-DCP degradation were studied and optimized. Experimental results confirmed that 2,4-DCP in aqueous solution was successfully degraded by 93% and mineralized by 78% within 60 min in such a hybrid oxidation process. When a current intensity of 3.2 mA was applied, the current efficiency for H2O2 generation on the GF cathode was determined to be 61%. Furthermore, the experiments demonstrated that combination of E-Fenton reaction with photocatalytic reaction let the process be less pH sensitive and would be more favorable to water and wastewater treatment in practice.     

Synthesis of multi-walled carbon nanotube/silver nanocomposite powders by chemical reduction in aqueous solution

Carbon nanotube (CNT)/silver nanocomposite powders with different volume fractions of CNTs 2.5, 5 and 10?vol.% were prepared by chemical reduction in solution. Multi-walled CNTs underwent surface modifications for functionalisations by acid treatments. The acid-treated CNTs were investigated by FT-IR and X-ray photoelectron spectroscopy. The spectroscopic investigations of the acid-functionalised CNTs detected that several kinds of functional groups attached with the graphene structure as well as produced short and de-caped CNTs. Acidic stannous chloride solution was used to sensitise the surface of the functionalised CNTs. Silver was deposited on the surface of sensitised CNTs with chemical reduction reaction of alkaline silver nitrate solution by formaldehyde at room temperature and pH?～?9. The morphology of the produced CNT/silver nanocomposite powder was investigated by high-resolution SEM and TEM. It was observed that the produced CNT/silver nanocomposite powders have decorated type of spherical silver particle size 2–5?nm deposited on the surface of CNTs as well as the CNTs were implanted in large spherical silver nanoparticles of particle size ～200?nm. The chemical analysis of the produced powder indicates that some oxygen content is included in the prepared powders which can be reduced by heat treatment at temperatures between 300°C and 400°C under hydrogen atmosphere.     

PVP水溶液中纳米Pd粒子的生长过程及形貌控制

在微量聚乙烯吡咯烷酮(PVP)存在下,超声还原氯化钯水溶液,合成纳米Pd粒子,利用透射电镜、紫外-可见吸收光谱、X射线光电子能谱等技术对纳米Pd粒子的生长过程进行了研究。考察了PVP用量对纳米粒子形貌的影响。结果表明,当PVP与PdCl2的质量比为10∶1、超声反应50min时,得到规则的单分散球型纳米Pd粒子,粒径大约8nm左右。根据紫外-可见特征吸收波峰和X射线光电子能谱中结合能的变化,提出了纳米粒子的稳定分散是借助于纳米Pd与PVP之间的配位作用来实现的。     

Removal of heavy metals from aqueous solution by chelating resin in a multistage adsorption process

Copper and zinc removal from aqueous solution by chelating resin was investigated theoretically and experimentally in the present study. A multistage process was proposed as an alternative for enhancement of the heavy removal of the single-stage process. Heavy metal mass balance equations with empirical Freundlich adsorption isotherm were developed to represent the multistage process and the theoretical model permits determination of the inter-stage heavy metal concentrations and the total amount of chelating resin required for achieving a desired level of heavy metal removal. Optimization of the linearized theoretical model shows that equal division of the total amount of chelating resin among all stages of the multistage process yields the best results in terms of saving of chelating resin for a given heavy metal removal or enhanced heavy metal removal for a given total amount of chelating resin. Experimental tests were also conducted to establish the equilibrium adsorption of heavy metal by the chelating resin and to empirically verify the advantages of the multistage adsorption process.     

Recovery of cyanide in gold leach waste solution by volatilization and absorption

In this study, the effects of pH, time and temperature in regeneration of cyanide in the leaching waste solution of gold production from disseminated gold ore by cyanidation process were investigated and the optimum conditions, consumptions and cyanide recovery values were determined. The sample of waste solution containing 156 mg/l free CN- and 358 mg/l total CN-, that was obtained from Gümü?hane-Mastra/Turkey disseminated gold ores by cyanidation and carbon-in-pulp (CIP) process under laboratory conditions was used in the experiments. Acidification with H2SO4, volatilization of hydrogen cyanide (HCN) with air stripping and absorption of HCN in a basic solution stages were applied and under optimum conditions, 100% of free cyanide and 48% of complex cyanide and consequently 70% of the total cyanide in the liquid phase of gold leach effluent are recovered.     

The preparation of YBCO epitaxial superconducting films by a chemical solution deposition process

The utility of a chemical precursor solution for the production of YBa₂Cu₃O_7-x superconducting films has been investigated. The homogeneous precursor solution made of metal acetates, 1,3-bis(dimethylamino) -2-propanol, and acetic acid was applied to [1 0 0] MgO substrates via spin-coating. Subsequent heating and sintering removed the organic components. The best epitaxial film obtained by this chemical solution deposition method has a T_c of 78 K.     

硝酸银容量法快速测定水质中氰化物

经蒸馏得到的碱性馏出液,用硝酸银标准溶液滴定。本方法重现性好,回收率满意,采用两种方法检验结果无显著性差异,检出限为0·0026mg/l,本法简便、快速、准确,能满足水质卫生标准要求,可适用于基层单位对水质中氰化物的测定,具有一定的实用价值。     

苯丙氨酸和天冬氨酸水溶液的纳滤分离及其过程模拟

选择苯丙氨酸和天冬氨酸水溶液进行了纳滤分离过程研究,讨论了不同pH下氨基酸的透过特性,并就该体系的浓缩分离进行了模拟计算。     

Optimum synthesis conditions of nanometric Fe50Ni50 alloy formed by chemical reduction in aqueous solution

In the present article, various nanometric Fe₅₀Ni₅₀ alloys were synthesized by chemical reduction of the corresponding metal ions, with hydrazine in an aqueous solution. Process variables of reaction temperature, pH of the hydrazine solution and concentration of metal ions were varied in order to determine the optimum synthesis conditions regarding quality, productivity and cost. It is found that pH of hydrazine solution, at low concentration of metal ions, is the most crucial variable affecting the reaction rate, average crystallite and particle sizes of the synthesized nanometric Fe₅₀Ni₅₀ alloy, followed by the total concentration of metal ions. Thus, increase of pH of hydrazine solution acts as an efficient stabilizer in reducing the particle size. On the contrary, at high concentration of metal ions, the structural characteristics of the nanometric Fe₅₀Ni₅₀ alloy are almost insensitive to reaction temperature and pH of hydrazine solution, but the reduction rate is remarkably sensitive to reaction temperature. Based on these results, it is decided that a reaction temperature of 80 °C, pH of the hydrazine solution of 12·5 and concentration of metal ions of 0·6 M represent the optimum synthesis conditions. The role of pH of hydrazine solution in reducing the alloy’s average particle size as well as efficient stabilizer confirms tremendous effect of synthesis conditions on the alloy structure and therefore, the importance of this study for industrial production of nanometric Fe₅₀Ni₅₀ alloy.     

Low temperature preparation of nanocrystalline solid solution of strontium barium niobate by chemical process

Sr_xBa_1-xNb₂O₆ (with x = 0.4, 0.5 and 0.6) powders have been prepared by thermolysis of aqueous precursor solutions consisting of triethanolamine (TEA), niobium tartarate and, EDTA complexes of strontium and barium ions. Complete evaporation of the precursor solution by heating at ∼ 200°C, yields in a fluffy, mesoporous carbon rich precursor material, which on calcination at 750°C/2 h has resulted in the pure SBN powders. The crystallite and average particle sizes are found to be around 15 nm and 20 nm, respectively.     

Degradation of amoxicillin,ampicillin and cloxacillin antibiotics in aqueous solution by the UV/ZnO photocatalytic process

The study examined the effect of operating conditions (zinc oxide concentration, pH and irradiation time) of the UV/ZnO photocatalytic process on degradation of amoxicillin, ampicillin and cloxacillin in aqueous solution. pH has a great effect on amoxicillin, ampicillin and cloxacillin degradation. The optimum operating conditions for complete degradation of antibiotics in an aqueous solution containing 104, 105 and 103 mg/L amoxicillin, ampicillin and cloxacillin, respectively were: zinc oxide 0.5 g/L, irradiation time 180 min and pH 11. Under optimum operating conditions, complete degradation of amoxicillin, ampicillin and cloxacillin occurred and COD and DOC removal were 23.9 and 9.7%, respectively. The photocatalytic reactions under optimum conditions approximately followed a pseudo-first order kinetics with rate constant (k) 0.018, 0.015 and 0.029 min^?1 for amoxicillin, ampicillin and cloxacillin, respectively. UV/ZnO photocatalysis can be used for amoxicillin, ampicillin and cloxacillin degradation in aqueous solution.     

The growth process of regular radiated nanorod bundles hydroxyapatite formed by thermal aqueous solution approach

Nanorod bundles of hydroxyapatite (nrHA) with ordered radiated structure was successfully prepared through hydrothermal treatment, with the hexadecyltrimethylammonium bromide (CTAB) and sodium citrate as surfactant and crystal modifier, respectively. The results showed that the citrate and CTAB played an important role in assembly of nanorods. Moreover, the pH value of the original solution also can influence the final morphology of products. The possible formation mechanism of nanorod bundle structure was discussed in detail.     

Separation of fluoride from aqueous solution by electrodialysis: effect of process parameters and other ionic species

Removal of fluoride from aqueous solution by electrodialysis was studied. Applied voltage, feed flow rate, fluoride concentration in the solution and effect of the other anions as sulfate, chloride were investigated as experimental parameters on fluoride removal from aqueous solution. The separation performance was evaluated in terms of mass transfer and energy consumption. It was obtained that the separation performance increased when the initial concentration of fluoride in the feed solution increased. Percent removal of fluoride increased as the applied potential increased. However, the effect of feed flow rate was not apparent in the range of applied feed flow rate. Separation of fluoride was influenced by chloride but not by sulfate ions.     

Formation process of silver nanoparticles in DTAB/SDBS/PVP aqueous solution

Silver nanoparticles were prepared from the nitrate silver solution in dodecyl trimethyl ammonium bromide (DTAB)/sodium dodecylbenzenesulfonate (SDBS)/polyvinyl pyrrolidone (PVP) complex solution with hydrazine as the reductant. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV–Vis spectroscopic analysis were conducted to investigate the role of anionic–cationic surfactants on the growth process of silver particles. The results showed that, before the formation of spherical silver nanoparticles, the cube and then tetrakaidecahedrons of AgBr were initially formed. It is concluded that the selective interaction of bow-like electric double-layer structure of anionic–cationic surfactants with certain crystallographic planes of crystals dominated the morphology evolvement of the reaction products. In addition; the PVP coverage finally encouraged the formation of well-dispersed spherical silver nanoparticles.     

Physical, chemical and optical properties of aqueous L-arginine phosphate (LAP) solution

The mathematical modelling of the solution growth of high quality single crystals requires a good understanding of the fluid properties. In addition to the physical and mechanical properties a detailed knowledge of the optical parameters is required to study the dynamics of the crystal growth process. Measurements of polarizability, refractive index, optical dispersion, solubility, pH, viscosity, and density were performed on aqueous L-Arginine phosphate (LAP) solutions. The index of refraction was measured with an Abbe refractometer at four different wavelengths. Optical dispersion was calculated using the Cauchy's equation. Effects of the density and kinematic viscosity of the LAP solution are discussed in terms of the dimensionless Grashof and Reynolds number allowing a better understanding of the benefits of operating under the micro-g conditions of space for the solution growth of single crystals. The Cauchy's formula and Sellmeier formula of the refractive index have been used to determine both the gradients dn/dc and dn/dT as a function of wavelength and the polarizability of the LAP solution. The polarizability of the LAP crystal, ₂, was found to be 14.50 cm³/mol and this value was in good agreement with experimental data obtained and analyzed using the well-known Lorentz-Lorenz formula.     

Degradation of 17alpha-ethinylestradiol in aqueous solution by ozonation

This study investigates the ozonation of 17alpha-ethinylestradiol (EE(2)) in aqueous solution. The affecting factors on the degradation of EE(2) were studied and described in details, such as initial EE(2) concentration, initial pH value and ozone concentration. In addition, some parameters such as pH, electrical conductivity, mineralization efficiency and degradation products were monitored during the process. The mineralization efficiency of EE(2) could reach 53.9%. During the ozonation process the rapid decrease of pH and the sharp increase of electrical conductivity indicated the formation of acidic by-products, small fragments and ions which were confirmed by high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC/MS) analysis. Results showed that there were intermediate products of smaller molecule with higher polarity produced during the course of EE(2) degradation. Then a possible reaction pathway for EE(2) degradation involving all intermediates detected is proposed. During the ozonation process EE(2) was first oxidized into hydroxyl-semiquinone isomers which were subsequently degraded into low molecular weight compounds such as oxalic acid, malonate, glutarate, and so on. Furthermore, these organic acids are easily oxidized by ozone into carbon dioxide (CO(2)). This work shows that ozonation process is promising for the removal of EE(2). The results can provide some useful information for the potential treatment of EE(2) by ozonation in aqueous solution.     

染料水溶液纳滤脱盐和浓缩的过程模拟

分析了工业生产的NT染料水溶液的纳滤脱盐和浓缩过程中NaCl组分在膜液界面处浓差极化现象，将NaCl组分的传质系数与渗透流率关联起来，建立了适合于描述应用卷式纳滤膜作NT染料水溶液的纳滤脱盐和浓缩过程的简洁的模型方程。该模型的预测与实验结果具有良好的一致性，为应用纳滤技术进行相应的工艺预测和工种优化设计提供了新的方法。