Removal Of Metal Impurities Research Articles

Exploring the Potential of Acid Treated Bentonite Clay for Various Catalytic Applications

Clays are widely used as catalysts and catalyst supports for a broad range of chemical processes due to their unique layered structure and low cost. Potential of Bentonite clay from Gujarat region (India) as a catalyst is evaluated in this work. Beneficial properties such as high cation exchange capacity, high absorption capacity, stickiness, expandable layer etc. makes Bentonite clay suitable for a wide range of catalytic applications in chemical process industries. Treatment of Bentonite clay with 5 - 10M sulphuric acid (H2SO4) followed by calcination at 600 0C showed removal of metallic impurities which increased porosity. The physical and chemical characteristics of modified clay were checked by WET process analysis and FTIR. Results showed that increase in acid strength led to better removal of Al3+ ion and other metal oxides thereby increasing silica-alumina ratio. Better surface characteristics indicate that Gujarat Bentonite clay is suitable for use as catalysts and catalyst supports.

Phosphorus separation from metallurgical-grade silicon by magnesium alloying and acid leaching

In this paper, the separation of phosphorus from metallurgical-grade silicon was investigated based on an Mg alloying and HCl leaching approach. Experimental results show that P concentration was reduced from initial 15.1 ppmw to 0.2 ppmw with also large extent removal of metallic impurities by two times Mg alloying-leaching purification. The mechanism of enhanced P separation is clarified owing to the strong affinity between Mg and P, which is validated by SIMS elemental mapping. A two-parameter analytical model was developed to predict the P removal degree based on the variables of alloying metal concentration and interaction coefficient between alloying metal and P. The model is validated with experimental results and the interaction coefficient εMginSiP was obtained as −10.8. This approach can be applied to model the removal of impurity which follows Gulliver-Scheil solidification from other binary alloying systems. Furthermore, in order to study the effect of applied alloying-leaching operation times, a model was proposed which establishes the mathematical relationships among key processing variables like initial and target P concentrations, the amount of the alloying metal, and the process operation times.

Solvent versus thermal treatment for glass recovery from end of life photovoltaic panels: Environmental and economic assessment

End of life photovoltaic panels of different technologies (poly crystalline Si, amorphous Si, and CdTe) were treated mechanically in pilot scale by single shaft shredder minimizing the production of fine fractions below 0.4 mm (<18% weight). Grounded material was sieved giving: an intermediate fraction (0.4–1 mm) of directly recoverable glass (18% weight); a coarse fraction (which should be further treated for encapsulant removal), and fine fractions of low-value glass (18%), which can be treated by leaching for the removal of metal impurities. Encapsulant removal from coarse fraction was successfully performed by solvent treatment using cyclohexane at 50 °C for 1 h giving high-grade glass (52% weight), which can be reused for panel production. Experimental results of solvent treatment were compared with those from thermal treatment by economic analysis and Life Cycle Assessment, denoting in both cases the advantages of solvent treatment in recovering high-value glass.

Efficient gas-phase purification using chloroform for metal-free multi-walled carbon nanotubes

Gas-phase treatments using chloroform (CHCl3) and water vapor were used to remove metal impurities (MIs) from as-prepared multi-walled carbon nanotubes (AP-MWCNTs), which is a non-destructive way to produce highly pure CNTs with extremely low MI content and with retention of CNT properties. After purification using CHCl3, the MIs in the AP-MWCNTs had significantly decreased to 12 ppm, representing a purification efficiency of 99.8%. This purification method, applicable to various AP-MWCNTs with high contents and different compositions of MIs, is more effective than liquid-phase purification using acids and does not damage the CNT structure and morphology. This moderate purification is due to a combination of factors. Chlorine radicals and hydrochloric acid from the thermal decomposition of CHCl3 react with MIs encased by graphitic carbon layers to form metal chlorides that sublime at high temperature. Hydrogen, oxygen, and water vapor generated during the formation of the metal chlorides etch graphitic carbon layers and lead to the formation of new pores and cracks, which provide fast reaction and diffusion paths. During metal purification, the MWCNT surface becomes lightly coated with chlorine or chlorinated carbon, which are eliminated from the surface post-treatment using water vapor.

Production of Metal-Free Diamond Nanoparticles.

In this paper, the controlled production of high-quality metal-free diamond nanoparticles is demonstrated. Milling with tempered steel is shown to leave behind iron oxide contamination which is difficult to remove. Milling with SiN alleviates this issue but generates more nondiamond carbon. Thus, the choice of milling materials is critically determined by the acceptable contaminants in the ultimate application. The removal of metal impurities, present in all commercially available nanoparticles, will open new possibilities toward the production of customized diamond nanoparticles, covering the most demanding quantum applications.

Leaching characteristics and kinetics of the metal impurities present in rice husk during pretreatment for the production of nanosilica particles

Fundamental studies on the removal of metal impurities are essential for the production of nanosilica by combustion. This study reports the leaching characteristics, leaching kinetics and occurrence form of the metal impurities present in rice husk based on acid pretreatment. Acid pretreatment removes most of the metal impurities present in rice husk. In particular, 98 wt% removal of potassium can be reached. The acid concentration, leaching time and reagent type have significant effects on the leaching of metal impurities, and optimal conditions exist for the acid pretreatment process. Furthermore, the leaching of metal impurities occurs through two stages, and parts of the metal impurities exist in organic-bound form, which can be leached through ion exchange. The results show that the pseudo-second-order model is suitable for describing the leaching kinetics of the metal impurities present in rice husk, and empirical formulas for predicting the metal contents leached from rice husk during acid pretreatment at ambient temperature are also obtained. Additionally, the different occurrence form and quantities of metal impurities in rice husk lead to different leaching effects, which strongly influences the chemical properties and quality of the obtained silica particles.

Removal of Metallic Impurities from Off-Grade Copper Concentrate in Alkaline Solution

The removal of metallic impurities from off-grade copper concentrate was investigated in alkaline solution with H2O2. The analysis results of XRD and SEM-EDS revealed the oxidative mechanisms of all sulfides. The influence of various parameters of alkaline leaching were investigated including concentrations of sodium hydroxide and hydrogen peroxide, liquid to solid ratio, leaching time and temperature. The results showed that the removal rate of Mo, As and Zn were increased with increasing leaching time and H2O2 concentration, and that the removal rate of Mo, As and Zn were firstly increased and then slightly decreased with increasing liquid to solid ratio, temperature and NaOH concentration, respectively. More than 95% Mo, 94% As, and 94 % Zn are removed from the off-grade concentrate under the optimum conditions, while only 1.7% Cu is dissolved. These optimum conditions were sodium hydroxide 1.5 mol/L, hydrogen peroxide 1.0 mol/L, temperature 50°C, liquid to solid ratio 5/1 mL/g and leaching time 5 h.

Technical Features and Research Progress of Separating Impurities in Producing Tantalum (Niobium) Oxide by Traditional Technology

In order to meet the demand for high purity tantalum and niobium products and to adapt to the complexity of tantalum niobium ore and waste in smelting, it was necessary to prepare high pure tantalum (niobium) oxide by traditional technology. In this paper, the process features, principles and functions of the decomposition, extraction, neutralization, washing and calcination in the traditional technology were described in detail, and the key factors which affect the separation of impurities in each process and the influences of various factors on the process and product quality were analyzed. Extraction was the key process to remove metal impurities in products. The main factors affecting the extraction separation are acidity, grade efficiency, temperature, extractant, concentration of tantalum/niobium, mass ratio of tantalum to niobium and volume ratio. In the process of precipitation and calcination the reagent purity, the equipment material, and the environmental cleanliness must be concerned to avoid the inclusion of impurity elements. The research and progress of impurity removal technology in tantalum (niobium) oxide production process were reviewed. The innovation of the traditional technology can meet special low requirement of one or several elements in the product, such as fluorine, tungsten, antimony, etc. For the future the basic research on the existence state and transformation behavior of tantalum and niobium and other elements in each process of traditional technology should be strengthened.

Enhanced thermal conductivity and mechanical properties of polyurethane composites with the introduction of thermally annealed carbon nanotubes

Here we report a significant enhancement in the physical properties of polyurethane composites by incorporating thermally annealed carbon nanotubes. The highly pure and crystalline carbon nanotubes were prepared by thermally annealing the catalytically grown thin multi-walled carbon nanotubes (t- MWNTs) at 2,300 °C using a graphite furnace in argon. The results of thermally annealing the catalytically as-grown carbon nanotubes in argon at high temperature were the effective removal of metallic impurities, the decrease in both the interlayer spacing and R-value, and the development of straight, crystalline layers. Moreover, the observation of the strong optical signal from the thermally annealed carbon indicates the possibility of growing small diameter innermost tubes below 1 nm within the hollow core of t-MWNTs. Finally, the introduction of the thermally annealed carbon nanotubes allowed us to make more mechanically strong and more thermally conductive polyurethane nanocomposites.

The Growth of Carbon Nanotubes via Chemical Vapor Deposition Method; its Purification and Functionalization

Objectives: The main motive behind proposed work is to enhance the solubility of CNTs in aqueous medium and in various other solvents. Purification and functionalization helped in accomplishing aforementioned task. Methods/Statistical Analysis: Initially, CNTs were grown by Chemical Vapor Deposition method. Nickel metal catalyst solution was prepared and loaded onto SiO2 wafer, which is kept in vacuum assisted quartz tube. Acetylene was used as a hydrocarbon source and at 750 oC it decomposes at nickel metal surface resulting in growth of Carbon Nanotubes. Several characterizations such as SEM, EDX, XRD and FTIR were performed for confirmation of CVD grown CNTs. SEM confirms the formation of tubular structure i.e. carbon nanotube and EDX illustrates the presence of carbon and metal catalytic impurities. Findings: Such impurities restrict their use in physical, chemical, biological and environmental systems, thus purification is required. Among all purification methods, acid treatment suits best for removal of metallic impurities. An acid mixture of H2SO4 and HNO3 in ratio of 3:1 was utilized to remove the impurities present. These acid purified CNTs now contain carboxylic acid groups attached over defects, sidewalls and at ends. However another major shortcoming of CNTs is their insolubility in various liquids and polymers. Improvements: Therefore, to improve the solubility and to allow bonding with polymer matrix, amide functionalization was carried out. By the effect of thionyl chloride, the -OH bond was replaced by –Cl group, which was further replaced by -NH moiety. Characterizations were carried out at each step of CNT processing. Moreover, these functionalized CNTs encourages us to extend the present work to quantify the effect of as grown and f-CNT on the average static and dynamic mechanical properties of CNT/epoxy nanocomposites in future.

Removal of free carbon and crystal structure change of amorphous silica fume by calcination

The calcination process was used to remove free carbon and to change the structure of amorphous microsilica powder. The results show that the carbon content in amorphous silica powder strongly depends on the calcination temperature. When the calcination temperature is higher than 900[Formula: see text]C, the free carbon content, SiO2 content and weight loss of microsilica powder tend to be stable, with values of 0.05%, 83.8% and 4.8%, respectively. The crystalline structure, particle size and morphology start changing at a calcination temperature of 850[Formula: see text]C. When the calcination temperature is higher than 900[Formula: see text]C, the amorphous microsilica powder is fully crystallized. The morphology of the silica fume kept its original spherical shape under 850[Formula: see text]C, while above 850[Formula: see text]C the microsilica powder recrystallizes. These results provide a basis for chemical removal of metal impurities in the preparation of high-purity silica powder.

Removal of metal impurities in metallurgical grade silicon by cold crucible continuous melting and directional solidification

Abstract Cold crucible continuous melting and directional solidification (CCDS) was used to refine metallurgical grade silicon (MG-Si). The metal impurities concentrations, their spatial distributions and the purification effect were investigated and the removal mechanisms of these impurities were discussed. The results indicate that, along the ingot growth direction, metal impurities are mainly accumulated in the ingot top, and the accumulative degree is much higher for nickel (Ni) and relatively lower for calcium (Ca) and aluminum (Al). Along horizontal direction, in accordance with the microstructure, the metal impurities concentrations in the outer area are lower than that in the inner area. In the ingot bottom part, the removal ratios of all the metal impurities reach above 95%. Besides segregation, element evaporation and diffusion also affect the metal impurities redistribution behaviors. CCDS has shown to be a novel process to refine MG-Si with low crucible contamination and consumption, high metal impurity removal ratio, high production yield and purification efficiency.

The removal of metal impurities from the surface of Czochralski wafers using a porous silicon-based gettering under a gas flow HCl/O2 dry

In this paper, the gettering of Czochralski silicon (CZ) with a porous silicon layer (PSL) oxidized in the presence of hydrochloric acid (HCl) gas was well discussed. The porous silicon damage reduces the activity of the contaminants in silicon and seems to be more effective when used in combination with HCl treatments. This process combined both mechanical and chemical parts to enhance the impurity removal. The getter was evaluated by means of the Hall Effect device to measure the carrier mobility. An enhancement of a minority carrier lifetime was evaluated by the QSSPC technique. The C–V characteristics indicated a decrease of the bulk dopants concentration. In the dark I–V characteristics, we observed a reduction of the leakage current density (JL) which goes back to the important decrease of the majority carriers. However, this new process can getter unwanted impurities deep-levels and enhanced the photovoltaic properties of solar cells.

Removal of metal impurities in rice husk and characterization of rice husk ash under simplified acid pretreatment process

Acid pretreatment plays an important role in the preparation of amorphous silica with high activity and high specific surface area before combustion process. However, some limitations and problems exist in the pretreatment process of previous literatures. On the basis of this, this work is aimed at simplifying the acid pretreatment process and combustion condition, which could present a more advantageous process for practical industrial applications. Then the removal percentage and behavior of metal impurities in rice husk is studied by ICP‐OES, and effects of acid pretreatment on properties of rice husk ash (RHA) at various combustion temperatures are comprehensively investigated in comparison with previous results by scanning electron microscope (SEM), X‐ray fluorescence (XRF), X‐ray diffractometer (XRD), and surface analyzer. The results suggest that the removal degree of each metal is various due to each chemical form in rice husk, of which removal percentage of K is especially remarkable. The contributions of simplified acid pretreatment to the properties of RHA are equally prominent: smaller nanoscale particles, higher purity, and specific surface area of above 200 m2/g. In addition, the pretreatment can also eliminate the crystallization and keep the high activity of RHA in combustion temperature range of 600–900°C. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 830–837, 2017

Density Functional Theory Study on Formation Energy and Diffusion Path of Metal Atom near Dopant in Si Crystals

There is an increasing demand for “metal gettering” technology for removing metal impurities from the LSI active region. First principles calculation based on the density functional theory (DFT) is an effective tool for studying the gettering of the metals in Si crystals. In most cases, the calculated binding energy (Eb) of the gettering site (Gs) and a metal atom is used for the evaluation of the gettering. In order to understand the gettering mechanism at an atomic scale, the stability and the diffusion path of a metal atom in the vicinity of Gs should be clarified. In this study, we used the “Hakoniwa” approach, which is based on the statistical thermodynamics and DFT proposed by Kamiyama et al. [Materials Science in Semiconductor Processing, 43, 209 (2016)], to understand the gettering mechanism by dopant (B and P) atoms. The existence probability of metal atoms (Fe, Ti, Ni, and Hf) at the 1st–8th tetrahedral (T)-sites in the vicinity of the dopant was obtained by using a Si 64-atoms supercell. The average Eb of Fe-B and Ni-B are close to the experimental values. The thermal equilibrium concentrations of metal atoms near B atoms were evaluated. Useful data of thermal equilibrium concentrations of metal atoms in B doped p/p+ epitaxial wafers are also provided. Finally, the possible diffusion paths of a metal atom to a B atom are clarified by using the Linear Synchronous Transit-Quadratic Synchronous Transit method. The favorable diffusion path to a B atom depends on the metal atom. The results obtained in the present work should be useful for understanding the gettering mechanism at an atomic scale and also for improving the computer simulation of metal gettering based on the continuum model.

Optimization of operating conditions in the purification of graphite oxide dispersions

In the graphite oxide (GO) suspension purification process, some metallic impurities in GO cannot be separated. The residual metallic impurities dominate graphite oxide properties and have a negative influence on applications. Therefore, the removal of metallic impurities from graphite oxide has been brought into focus now. Single factor experiments and orthogonal experiments are used to get the optimal purification condition. The results show that purification agent, temperature, stirring intensity and contact time affect the purification degree, and the purification agent is the most important element for the purification efficiency. The optimal purification condition is 10% hydrochloric acid (H10), 20 °C, 0 rpm and 60 min. Besides, the theoretical stage is calculated by the mass conservation equation and distribution balance equation and the minimum stage is 3 under the optimal purification condition.

Removal of metal impurities by controlling columnar grain growth during directional solidification process

Silicon ingots with columnar grains and irregular grains as raw material for solar cells were obtained by directional solidification. The relationship between crystal morphology and concentration of metal impurities was studied. The result shows that columnar grains can improve the ratio of the high-purity area, where the concentration of metal impurities is less than 10ppmw and more consistent with the calculated value by the Scheil’s equation. Meanwhile, the metal silicide precipitates at the irregular grain boundaries. Large temperature gradient at the solid-liquid interface dedicated to the stability of solid-liquid interface, which is conductive to the growth of the columnar grains. High concentration of metal impurities introduces a large constitutional supercooling to reduce the stability of solid-liquid interface, then further form a mushy zone in front of the solid-liquid interface, which leads to the growth of irregular grains.

Effect of alternating magnetic field on the removal of metal impurities in silicon ingot by directional solidification

Multicrystalline silicon ingots without and with alternating magnetic field during directional solidification process under industrial system were obtained from metallurgical grade silicon (MG-Si). The concentrations and normalized concentrations of metal impurities in the two silicon ingots were studied. The result shows that the concentrations and normalized concentrations in high-purity area of the silicon with alternating magnetic field are lower than those of the ingot without alternating magnetic field. The transport mechanism for metal atoms in the diffusion layer area has been changed due to the alternating magnetic field. Alternating magnetic field introduces a convection to reduce the thickness of diffusion layer in the molten silicon, which results in a decreased effective segregation coefficients. Enhancing transport driving force of metal atoms in molten silicon is the effective way to improve the removal rate of metal impurities.

Cobalt products from real waste fractions of end of life lithium ion batteries

An innovative process was optimized to recover Co from portable Lithium Ion Batteries (LIB). Pilot scale physical pretreatment was performed to recover electrodic powder from LIB. Co was extracted from electrodic powder by a hydrometallurgical process including the following main stages: leaching (by acid reducing conditions), primary purification (by precipitation of metal impurities), solvent extraction with D2EPHA (for removal of metal impurities), solvent extraction with Cyanex 272 (for separation of cobalt from nickel), cobalt recovery (by precipitation of cobalt carbonate). Tests were separately performed to identify the optimal operating conditions for precipitation (pH 3.8 or 4.8), solvent extraction with D2EHPA (pH 3.8; Mn/D2EHPA=4; 10% TBP; two sequential extractive steps) and solvent extraction with Cyanex 272 (pH 3.8; Cyanex/Cobalt=4, 10% TBP, one extractive step). The sequence of optimized process stages was finally performed to obtain cobalt carbonate. Products with different degree of purity were obtained depending on the performed purification steps (precipitation with or without solvent extraction). 95% purity was achieved by implementation of the process including the solvent extraction stages with D2EHPA and Cyanex 272 and final washing for sodium removal.

Purification of terbium by means of argon and hydrogen plasma arc melting

The refining of terbium (Tb) by plasma arc melting using pure Ar and Ar + H2 mixture was examined, respectively. The temperature distribution and gas flow of the plasma arc during the melting process were simulated. The residual metallic impurities were examined by inductively coupled plasma-atomic emission spectrometer. Experimental results show that both methods of argon plasma arc melting (APAM) and hydrogen-argon plasma arc melting (HAPAM) can lead to a good removal of metallic impurities despite of high initial concentrations. HAPAM displays a better refining effect of Tb metal. Activated hydrogen atoms dissociated in high temperature plasma arc, bringing on special chemical interactions, are supposed to be the cause for the wonderful refining effect. The detailed behaviors of impurities and hydrogen atoms are discussed systematically in this study.