Adsorption of copper and nickel on Na-bentonite

The removal of copper and nickel from aqueous solution on the Na-bentonite has been studied under static conditions. Experiments were carried out as a function of solution pH, dosage of Na-bentonite, contact time and temperature. The adsorption equilibrium for nickel and copper onto Na-bentonite is reached in 200 min. The adsorption of copper and nickel is pH dependent in the pH range 2–9. The kinetic process of adsorption can be described by the pseudo-second-order kinetic equation excellently and the adsorption isotherm be fitted to the Langmuir model by means of regression analyses very well. The adsorption capacities follow the order of Cu²⁺ > Ni²⁺ in single-component systems and competitive adsorption capacities in order decreasing is Cu²⁺ > Ni²⁺ in binary-component systems.     

Zero valent nano-sized iron/clinoptilolite modified with zero valent copper for reductive nitrate removal

Nitrates constitute one of the main toxic contaminants of groundwater. On the other hand, groundwater may be considered anoxic (oxygen concentration less than 9 μg L^?1). This fact justifies the use of nano zero valent metals for nitrate removal. In such conditions, zero valent metals are quite stable against oxidation due to the very low level of dissolved oxygen concentration. It has been shown that the performance of zero valent iron coated clinoptilolite zeolite for the reduction of nitrate anion in un-buffered conditions may be enhanced by coating small amounts of Cu⁰ onto the freshly prepared Fe⁰/zeolite composite. An optimum loading of Cu⁰ exists for which the rate of nitrate removal is maximal. For this optimal composition, the nitrite anion production curve with time passes through a maximum. Nitrite production, however, is slightly higher for the Cu modified zeolite. It has been shown that the nitrate removal process is only slightly dependent on the initial solution pH. In the temperature range of 20–60 °C, the process is controlled by both the liquid phase mass transfer and intrinsic reaction rate resistances. FESEM analysis of the zero valent metal/zeolite composite showed that upon the metal reduction reaction, an egg-shell distribution of zero valent metal in the zeolite agglomerate particle is produced.     

Growing Carbon Nanotube on Aluminum Oxides: An Inherently Safe Approach for Environmental Applications

Using micron-sized Al₂O₃ particles as carriers to grow carbon nanotubes (CNTs) under 700°C atmosphere of methane and hydrogen after pre-planted catalysts of Fe–Ni nanoparticles, those composite CNTs (CCNTs) have demonstrated several unique properties compared to CNTs—medium specific surface area and zeta potential, high adsorption capacity for metal ions, high recovery rate by acids, low decomposition heat for exothermal reaction, and so on. The adsorption behaviours of Pb²⁺, Cu²⁺ and Cd²⁺ in aqueous solutions by CCNTs are in good agreement with the Langmuir adsorption isotherm and second order kinetic model with maximum individual adsorption capacities of 67.11, 26.59 and 8.89 mg g⁻¹. The individual and competitive adsorption behaviours indicated that the preference order of adsorption were Pb²⁺ > Cu²⁺ > Cd²⁺ for aluminum oxides, activated carbon, commercial CNTs, and CCNTs as well as other researchers’ CNTs. We suggest that future development of CNTs to combine with metals and/or other materials, such as TiO₂, should consider attached to carriers or surface in order to avoid concerns on environment, health and safety. Thus, growing CNTs on Al₂O₃ particles to form CCNTs is an inherently safe approach for many promising environmental applications.     

Study on decomposition of hydroxylamine/water solution

The risk evaluation of decomposition of hydroxylamine(HA)/water solution was studied experimentally. The thermal property of HA/water solution was studied from the calorimetric data obtained using the differential thermal analysis (DTA). The intensity of decomposition was studied on the basis of the results of the mini closed pressure vessel test (MCPVT) and the pressure vessel test (PVT) in addition to the steel tube test.The thermal property of HA/water solution was evaluated on the basis of results of the DTA. The heat-release onset temperatures using the no-treated stainless steel cells were more than 70 K below those measured using the GSC. This result implies that the heat-release onset temperature depends on the materials of sample cell. On the other hand, the heat of reaction did not depend on the materials of sample cell.The intensity of the thermal decomposition was investigated on the basis of results of the MCPVT, the PVT and the steel tube test. The intensity of the thermal decomposition increased as the HA concentration increased in the MCPVT. The intensity of the thermal decomposition increased greatly when the HA concentration was beyond 80wt.% in the MCPVT. It was elucidated that the thermal decomposition of HA 70wt.%/water solutions was very violent in the PVT. In addition, HA/water solutions of more than 80wt.% concentration could detonate in the steel tube test. HA 80 wt.% water/solution was easily detonated by a detonator without RDX in the steel tube test.In addition, the decomposition hazard of HA/water solution by the metal ion and the iron powder was studied in this paper. The thermal stability of HA85%/water solution with the iron ion or the iron powder was discussed on the basis of the heat-release onset temperature by the DTA. The heat-release onset temperatures decreased when the concentration of the iron ion or the iron powder increased in the DTA measurements. The reactiveness of HA/water solution with the metal ion of iron, manganese, nickel, chromium and copper was examined by measuring the mass loss of HA/water solution after the metal ion was added to HA/water solution at room temperature. The reactiveness of HA/water solution with the iron powder was also studied in this paper. The ferrous ion, the ferric ion and the iron powder reacted with HA/water solution. Ignition automatically began when the 0.2wt.% ferric ion solution was added to HA85wt.%/water solution. The mass loss rate depended on the HA concentration greater than the iron ion concentration. The mass loss rate increased when an amount of the iron powder increased. On the other hand, the decomposition reaction of HA85wt.%/water solution with Cu²⁺ was calm compared to that of the iron ion. HA/water solution did not react with Mn²⁺, Ni²⁺ and Cr³⁺ at room temperature.     

Removal of Zn and Ni by adsorption in a fixed bed of wheat straw

Zn⁺² and Ni⁺² in a solution were removed by biosorption in a fixed bed of wheat straw Triticum aestivum. The removal rate and the mass transfer coefficient for Zn⁺² and Ni⁺² were found to be proportional to the liquid superficial velocity to the power of 0.31 for the range of the particle Reynolds number from 18 to 445 (equivalent liquid rates of 0.00070–0.0175 m³ m⁻² s⁻¹). This agrees well with reported literature for mass transfer in a packed bed of solid particles under a laminar flow regime. Effect of the solution pH, temperature and the particle size (0.5, 1.0, 1.5 and 2.0 in.) on biosorption of Zn⁺² and Ni⁺² was also investigated. Biosorption of both Zn⁺² and Ni⁺² increased significantly with the solution pH from 4.0 to 7.0. On the other hand, Zn⁺² and Ni⁺² removal appeared to be insensitive to liquid temperature from 25 to 30 °C. Nevertheless, a 25% increase in the percentage removal of metal ions was observed with further increase of liquid temperature from 30 to 35 °C. However, the biosorbent particle size did not seem to have a systematic effect on the biosorption of Zn⁺² and Ni⁺². In addition, biosorption of Zn⁺² was not affected considerably by co-adsorption of the bimetal solution while biosorption of Ni⁺² decreased about 14%.     

Electro-Fenton degradation of cationic red X-GRL using an activated carbon fiber cathode

We reported the study of the degradation of the azo dye cationic red X-GRL by the electro-Fenton process using an activated carbon fiber cathode. The electrogeneration of hydrogen peroxide in solution using different material cathodes fed with air was investigated, and the results revealed that the activated carbon fiber cathode was more effective compared to the graphite cathode. The decolorization and mineralization of cationic red X-GRL were also determined. The effect of the operating parameters, such as the initial Fe²⁺ concentration, temperature and initial dye concentration, was investigated. The optimum Fe²⁺ catalyst concentration values for the degradation of cationic red X-GRL was found to be 5 mM. The rate of decolorization and mineralization of dye could be accelerated by increasing the temperature. In addition, the decolorization and total organic carbon (TOC) removal efficiency decreased with the increasing initial dye concentration, while the TOC removal increased. Two different transition metal ions (Cu²⁺ and Mn²⁺) were applied as substitutes for ferrous sulfate for evaluating catalytic effect. The results indicated that Cu²⁺ and Mn²⁺ were more effective than Fe²⁺ in catalyzing the degradation of the dye.     

改性沸石吸附氨氮及电化学再生研究

研究了改性沸石对氨氮的吸附效能、动力学机制以及电化学再生效果。间歇和连续试验结果表明:沸石经改性后,能高效去除水中的氨氮,其吸附等温式更符合Langmuir模型,沸石、改性沸石的饱和吸附量分别为8.09 mg/g和13.55 mg/g,沸石的钠型改性能显著提高吸附容量约40.3%;颗粒内扩散是改性沸石吸附氨氮的控制性步骤,可以利用Vermeulen的内扩散模型进行描述;利用电化学再生吸附饱和后的沸石,再生液为NaCl溶液,阳极涂覆RuO2-Ti,再生时间为3h,可高效地再生沸石,无二次污染物排出,对环境冲击较小。     

Adsorptive efficacy analysis of lignocellulosic waste carbonaceous adsorbents toward different mercury species

Adsorptive efficacy of lignocellulosic waste char (LW-CHAR) and activated carbon (LW-AC) toward inorganic (Hg²⁺) and organic (MeHg⁺) mercury ions was studied. The LW-CHAR and LW-AC were, respectively, prepared by carbonization and KOH activation processes of lignocellulosic waste (LW) carried out at 700 °C. The Hg²⁺ adsorption onto the LW-CHAR was lower than LW-AC, however, an opposite result was observed for the MeHg⁺ indicating the nature of the surface interactions of both mercury ions to respective adsorbent surfaces was significantly different. The adsorption data analysis of both mercury ions was found however to only follow the Langmuir isotherm and pseudo-second order kinetic models whereby a combination of chemisorption and diffusional process was the governing mercury ions adsorption mechanism.     

新疆某石化污水库周边土壤对锶的吸附特征研究

以新疆某石化污水库周边土壤为例,采用静态吸附试验法研究土壤对Sr2+的吸附特征。通过单因素法研究初始pH值、反应温度、离子强度、时间、Sr2+初始质量浓度等因素对土壤吸附Sr2+的影响,并对吸附机理进行了初步探讨。结果表明,供试土壤对Sr2+有较强的吸附能力,溶液pH值对土壤吸附Sr2+的影响较显著。在3 h左右供试土壤对Sr2+的吸附量达到最大值,3 h后吸附量略有下降,并逐渐稳定。供试土壤对Sr2+的吸附量随溶液离子强度的增加而减小;但当离子浓度大于0.2 mol/L时,土壤对Sr2+的吸附量又呈增加趋势。试验数据拟合结果表明,供试土壤对Sr2+的吸附符合Henry和Fre-undlich方程;在吸附3 h内供试土壤对Sr2+吸附基本可以用一级动力学方程描述。     

磁性CoFe2O4/MgAl-LDH的制备及对水中刚果红的去除

采用水热法制备了CoFe_2O_4,采用化学共沉淀法将镁铝水滑石(Mg Al-LDH)覆盖在CoFe_2O_4上,制成磁性CoFe_2O_4/Mg Al-LDH复合材料,用于去除水中阴离子染料刚果红。考察了溶液p H值、吸附时间、共存阴离子等对吸附过程的影响,研究了CoFe_2O_4/Mg Al-LDH对刚果红吸附动力学、吸附等温线。结果表明,溶液p H值、共存离子对CoFe_2O_4/Mg Al-LDH去除刚果红效果的影响较小。吸附剂对刚果红的吸附过程符合准二级动力学模型,且在吸附时间180 min内基本达到吸附平衡。吸附等温线符合Langmuir等温吸附模型,CoFe_2O_4/Mg Al-LDH对刚果红的理论最大吸附容量为610.8 mg/g。     

Novel materials for environmental remediation of tailing pond waters containing naphthenic acids

A nanofiltration strategy for tailing pond waters (TPWs) that utilizes cyclodextrin (CD)-based polymeric materials as supramolecular sorbents is proposed. Naphthenic acids (NAs) from the Athabasca TPWs are investigated as the target sorbate molecules.The sorption properties of several supramolecular porous materials were characterized using equilibrium sorption isotherms in aqueous solution wherein electrospray ionization mass spectrometry was used to monitor the concentration of NAs in aqueous solution. The characterization of the supramolecular sorbents was performed using ¹³C NMR and IR spectroscopy, while nitrogen porosimetry was used to estimate their surface area and pore structure properties. Independent estimates of surface area were obtained using a chromophore dye adsorption method in aqueous solution.The sorption results for NAs in solution were compared between a commercially available standard; granular activated carbon (GAC) and three types of synthetic materials. The sorption capacities for GAC ranged from 100 to 160 mg NAs/g of material whereas the polymeric materials ranged from 20 to 30 mg NAs/g of material over the experimental conditions investigated. In general, differences in the sorption properties between GAC and the CD-based sorbents were observed and related to differences in the surface areas of the materials and the chemical nature of the sorbents. The CD-based supramolecular materials displayed sorption capacities ranging from 36.2 to 657 m²/g as compared to that for GAC (795 m²/g).     

A generalized differential method to calculate lumped kinetic triplet of the nth order model for the global one-step heterogeneous reaction using TG data

Computing kinetic triplet is of importance for the process safety of combustion/gasification industries to establish the chemical reaction scheme and to assess the hazardous risk. Few approaches have been capable of calculating lumped kinetic triplet at one time efficiently, which might be attributed to the fact that the analytical solution for the nonlinear ordinary differential equation (NNODE) for the n^th order reaction model has not been found yet. This paper presents an analytical solution of NNODE to compute kinetic triplet. Results showed that the proposed method (mass fraction curve-fitting error ϕ = 1.49%–2.07%) is more efficient to compute kinetic triplet of the n^th order reaction model, comparing to genetic algorithm (GA) optimization (ϕ = 1.43%–1.81%), Coats-Redfern (ϕ = 2.36%–3.16%), peak-shape, and isoconversional methods. A compensation effect between lnA and E_a is observed due to heating rates. Effects of exported data quality and smooth processing on computation of kinetic triplet are discussed. It is the first time that an analytical solution of NNODE (n^th order model) for global one-step heterogeneous reaction is derived for computing kinetic triplet. This work may help to search for analytical solutions of power-law and Avrami-Erofeev models in the future to efficiently calculate kinetic triplet for accelerating and sigmoidal reaction systems.     

Artificial neural network modelling of As(III) removal from water by novel hybrid material

The present study reported a method for removal of As(III) from water solution by a novel hybrid material (Ce-HAHCl). The hybrid material was synthesized by sol–gel method and was characterized by XRD, FTIR, SEM–EDS and TGA–DTA. Batch adsorption experiments were conducted as a function of different variables like adsorbent dose, pH, contact time, agitation speed, initial concentration and temperature. The experimental studies revealed that maximum removal percentage is 98.85 at optimum condition: pH = 5.0, agitation speed = 180 rpm, temperature = 60 °C and contact time = 80 min using 9 g L⁻¹ of adsorbent dose for initial As(III) concentration of 10 mg L⁻¹. Using adsorbent dose of 10 g L⁻¹, the maximum removal percentage remains same with initial As(III) concentration of 25 mg L⁻¹ (or 50 mg L⁻¹). The maximum adsorption capacity of the material is found to be 182.6 mg g⁻¹. Subsequently, the experimental results are used for developing a valid model based on back propagation (BP) learning algorithm with artificial neural networking (BP-ANN) for prediction of removal efficiency. The adequacy of the model (BP-ANN) is checked by value of the absolute relative percentage error (0.293) and correlation coefficient (R² = 0.975). Comparison of experimental and predictive model results show that the model can predict the adsorption efficiency with acceptable accuracy.     

Numerical simulation and experimental study on metallographic structure characteristics of melting trace caused by overcurrent fault of copper wire

The microscopic characteristics of melting trace caused by copper wire fault are an important basis for the physical evidence identification of electrical fires. Metallography is an important method in electrical fire research, and computer-aided quantitative analysis on metallographic structure is common in materials aspect. In this study, the metallographic structure and phase composition characteristics of melting trace caused by overcurrent fault were explored with the aid of a metallographic microscope and an X-ray diffractometer (XRD). The results show that the grains are mainly slender dendritic and columnar crystals when the current is 128 A, while they are coarse dendritic and cellular crystals when the current is greater than 192 A; the average grain diameter of melting trace of copper wire grows with the increase in current. The main phases of melting trace caused by overcurrent fault of copper wire are α-Cu base and Cu₂O, and the new phases Cu₄Si and Cu₂Mg are formed when the current is higher than 160 A. In addition, the solidification process of metallographic structure of copper wire under different currents was simulated by the Procast software. It is found that the simulation results are basically in agreement with the experimental data, which suggests that this model can effectively predict the microstructure characteristics of melting trace of copper wire under different currents. The research results can provide a sound basis for the physical evidence identification of electrical fire and improve the accuracy and scientificity of electrical fire investigation.     

The electrocoagulation/flotation study: The removal of heavy metals from the waste fountain solution

The objective of this study was to investigate the possibility of heavy metals (copper, zinc and nickel) removal from the waste fountain solution by the electrocoagulation/flotation (ECF) treatment. After the printing process, the fountain solution changes its composition due to direct contact with different printing materials (plates, inks, etc.) and becomes enriched with metals. The effect of operational parameters, such as electrode materials and combinations, current density, interelectrode distance and operating time, was studied. Also, response surface methodology (RSM) was applied to evaluate the effect of main operational variables and to get a balanced removal efficiency of metals from waste fountain solution by ECF treatment. The iron/iron electrode combination yields a higher percentage of copper and zinc removal efficiency (>95% and >80%, respectively), while for nickel the aluminum/iron and iron/aluminum electrode combinations (>95 and >85%, respectively) proved to be more successful. The optimum interelectrode distance was 1.0 cm (for copper) and 1.5 cm (for zinc and nickel) for all current densities. Heavy metal removal efficiency increases with the increase of electrolysis time for all electrode combinations. Also, the increase of current density improves the ECF removal efficiency. Based on the results obtained through RSM, the optimized parameters for the ECF waste fountain solution treatment for metal removal were identified as: Fe(−)/Al(+) electrode with interelectrode distance of 1.5 cm, operating time of 60 min and current density of 8 mA cm⁻². Overall, the ECF treatment was proven very efficient in the removal of heavy metals from the waste fountain solution under optimum conditions.     

Synthesis and adsorption studies of NiO nanoparticles in the presence of H2acacen ligand,for removing Rhodamine B in wastewater treatment

Cost efficient NiO nanoparticles were synthesized by hydrothermal production of nano-scale Ni(OH)₂, using Ni(NO₃)₂·6H₂O and NaOH as precursors, in the presence of H₂acacen ligand, followed by calcinations of the produced Ni(OH)₂. Prepared samples were then characterized using X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), Fourier transform infrared (FT-IR) spectra, Brunauer–Emmet–Teller (BET) and transmission electron microscopy (TEM). BET analysis revealed high surface area for pure nano sized NiO, averaging 176.56 m²/g and confirming its application as an efficient adsorbent. Experimental studies for Rhodamine B (RB) removal from aqueous solutions in batch systems revealed that the adsorption equilibrium was best represented by Langmuir isotherm, with the maximum monolayer capacity of 111 mg/g for RB. The kinetic data was well described by a pseudo-second-order kinetic model, having intraparticle diffusion model as a rate limiting step.     

Synthesis of hydroxyapatite/clay and hydroxyapatite/pumice composites for tetracycline removal from aqueous solutions

Synthesized hydroxyapatite/clay (HA-C) and hydroxyapatite/pumice (HA-P) composites were used for tetracycline (TC) uptake studies from aqueous solution and their uptake capacities were compared. HA-C and HA-P composites were synthesized by precipitation method and the structures of the synthesized composites were characterized by XRD, SEM and BET analyses. Cation exchange capacities of HA-C and HA-P were found to be 84 meq/100 g and 33 meq/100 g, respectively. The TC adsorption using HA-C and HA-P was studied on batch mode. Various parameters such as contact time, solution pH, initial TC concentration, composite dosage, salinity and temperature were optimized. Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models were applied to the equilibrium data. The maximum adsorption capacity onto HA-C was found to be 76.02 mg/g and about four times larger than the adsorption capacity of the HA-P (17.87 mg/g). The results indicated that the TC uptake onto HA-C and HA-P composites is mainly by a surface complexation and ion-exchange mechanism which depend on the solution pH. The calculated values of thermodynamic parameters indicated that the TC adsorption is favorable, physicochemical in nature. The sorption process follows pseudo-second-order and intraparticle diffusion kinetic models. The TC adsorption mechanism by HA-C and HA-P has been proposed.     

6种生物滞留填料对磷的吸附特性研究

为筛选出除磷效果更好的生物滞留填料,通过等温吸附、解吸附和动力学实验,分析沸石、石英砂、麦饭石、陶粒、无烟煤、铝污泥6种填料对磷的吸附特性。结果显示,6种填料均表现出较好的磷吸附性能。铝污泥对磷的吸附效率接近90%,解吸附率仅为12.78%,表现最为突出,其后依次为无烟煤和陶粒。6种填料的等温吸附过程符合Freundlich吸附模型,并均可采用准二级动力学模型描述其吸附动力学过程。     

Isotherm and kinetic studies for the biosorption of cadmium from aqueous solution by Alhaji maurorum seed

Cadmium is an extremely toxic metal commonly found in industrial regions. Anthropogenic activity is the most important factor causing its interference to water, soil and air resources. The aim of many researches is to present remediation strategy or to remove cadmium from contaminated resources through an economical and efficient method. Cadmium adsorption from aqueous solution using Alhaji maurorum seed adsorbent has been investigated and optimized in this study. Moreover, isotherm and kinetics of adsorption process was studied. The seeds are washed by distilled water after separation from the plant, and then dried in room temperature for 48 h. They are powdered by grinder and passed through sieve no.18 as well. Adsorption process was optimized in 4 steps regarding pH, contact time, adsorption dose and initial concentration of cadmium effects. The cadmium concentration in solution was measured using ICP-OES method. The results of optimization tests showed that the optimum condition of cadmium adsorption (85.5% removal) occurs at pH of 6.5 with 20 g/L of adsorption dose for 45 min. In addition, the efficiency of adsorption process increases as the cadmium concentration reduces in the initial solution. Adsorption process follows the pseudo second-order kinetics and Freundlich isotherm with correlation coefficients of 0.999 and 0.99, respectively. According to the findings of this analysis, it was concluded that A. maurorum seed is a good biological adsorbent for adsorbing cadmium from aqueous solution.     

Removal of humic substances from landfill leachate by Fenton oxidation and coagulation

In this study, chemical oxygen demand (COD) was characterized as total organic constituents and the isolated humic substances (HS) were characterized as an individual organic contaminant in landfill leachate. It was found that the HS content of landfill leachate was 83.3%. The results of laboratory tests to determine the roles of HS in reducing the organic content of landfill leachate during Fenton process are presented. Furthermore, the performances of oxidation and coagulation of Fenton reaction on the removal of HS and COD from leachate were investigated. The change curves of HS removal were similar to those of COD. The HS removal was 30% higher than COD removal, which indicated that HS were mostly degraded into various intermediate organic compounds but not mineralized by Fenton reagent. The oxidation removal was greatly influenced by initial pH relative to the coagulation removal. The oxidation and coagulation removals were linear dependent with hydrogen peroxide and ferrous dosages, respectively. Ferrous dosage greatly influenced the coagulation removal of COD at low ratio ([H₂O₂]/[Fe²⁺] < 3.0), but not at extremely high ratio ([H₂O₂]/[Fe²⁺] > 6.0). The coagulation removal of HS was not affected obviously by oxidation due to both Fenton oxidation and coagulation remove high molecular weight organics preferentially. Higher temperature gave a positive effect on oxidation removal at low Fe²⁺ dosage, but this effect was not obvious at high Fe²⁺ dosage.