Search Documents

By Xiao Yang

Calcium oxide is one of the major fluxing agents used for steel refining. Because unreacted CaO remains in slag in most cases, discharged slag is difficult to be recycled smoothly. With the growth of environmental concerns, improving utilization efficiency of CaO is required to reduce the amount of discharged slag and energy consumption. The authors have reported a resource and energy-saving process by using multi-phase flux for dephosphorization. Reaction behavior of phosphorus in multi-phase CaO–FeOX–SiO2–P2O5 flux system was investigated. Formation mechanism of P2O5-rich phases was clarified at the interface between solid CaO or 2CaO, SiO2 and molten CaO–FeOx–SiO2–P2O5 slag. Phase relationship and thermodynamic properties of 2CaO, SiO2-3CaO, P2O5 solid solution were observed to confirm the condensation of P2O5 in solid phase. Based on these results, reduction of CaO consumption, discharged slag curtailment, and energy-saving effects in the novel refining process by using multi-phase flux were discussed.

By Patrick R. Taylor

The synthesis of high-purity ultra-fine barium strontium titanate powders (BST: BaO6Sro.4TiO3) has been performed in a non-transferred are D.C. thermal plasma reactor. Slurries of aqueous solutions of dissolved barium and strontium nitrates and solid titanium dioxide powders were used as precursors. Oxygen and argon were used as carrier gases, and pure argon and combinations of argon and nitrogen were used as plasma gases. The plasma torch power was varied, as well as the oxygen flow rate and the total molar concentration of the precursors. A graphite plate was designed to protect the torch electrode and lower the level of impurities in the product. A thermochemical analysis of the Ba(NO3)2-Sr(NO3)2-TiO2-H2O-O2 system was performed to predict the conditions for the formation of BST and the feasibility of the reaction, The powders collected from the different sections of the reactor were characterized using Transmission and Scanning Electron Microscopy, X-Ray Diffraction, and ICP chemical analysis. The powders produced showed high conversion to BST, ultra-fine particle size (< 30 rim) and high purity, which makes this a potential process to produce ceramic materials for electronic devices.

Jan 1, 2003

By A. G. Guézennec

Electric Arc Furnace (EAF) steelmaking co-produces amounts of dust (15 to 25 kg per ton of steel), which require to be collected and stored in specific landfills. The collection, handling, and possible beneficiation of EAF dust depend on its composition and morphology. We first studied theoretically the chemical evolution of dust particles along the fume extraction system, from the furnace down to the filters, using thermodynamic calculations of the Fe-Zn-O system. We show how it would be possible to favor zincite formation in dust and therefore increase further zinc recovery. Then, we developed a new morphological model, based on population balances, for predicting the granulometric evolution of dust particles as a result of agglomeration and sintering in the fume extraction ducts. The contribution of the various mechanisms (Brownian, turbulent, and sedimentary agglomeration; thermophoretic deposition; coalescence and sintering) is assessed. The influence of the exhausting conditions on dust granulometry is detailed. For the extraction system studied, intense agglomeration of the sub-micronic particles and complete coalescence take place inside the furnace; micronic particles then undergo little evolution from the elbow to the water-jacket, whereas big agglomerates are formed downstream. These results are in good agreement with dust particle observations.

Jan 1, 2006

By R. M. Moon

Neutron scattering has played a crucial role in advancing our understanding of rare-earth materials. It has provided a detailed description of the rich array of exotic magnetic structures; it has confirmed the accuracy of theoretical wave functions for the 4f electrons; and it has provided fundamental data on the collective magnetic excitations in these materials. The fundamental property of the neutron which has been exploited in this work is the magnetic interaction which exists between the magnetic moment of the neutron and atomic magnetic moments on individual rare-earth atoms. This interaction produces scattering of neutrons in a manner closely analogous to the scattering of X rays by atomic charge distributions. In a material exhibiting long-range magnetic order, Bragg diffraction peaks will appear at scattering angles determined by the periodicity of the magnetic structure. The Bragg intensities are determined by the magnitude and relative directions of the atomic moments. The rare-earth metals and alloys are characterized by sinusoidal modulation of magnetic moment components which can be combined in various ways to produce a variety of magnetic structures. The periodicity of these modulations is frequently not related simply to the underlying periodicity of the chemical structure. The major features of these structures are explained by the combined, and sometimes competing, exchange and crystal-field interactions. At a more fundamental level, neutron diffraction also gives information on the spatial distribution of a magnetic moment in a rare-earth atom. This moment comes from the 4f electron shell, and accurate measurements of the neutron scattering amplitudes have been used to check the accuracy of atomic wave function calculations for the 4f electrons. It was found that relativistic Dirac-Fock calculations are in excellent agreement with the experimental results. Collective excitations of ordered magnetic systems are described in terms of spin waves, which are sinusoidal modulations in space and time of the direction of the ordered moments. Inelastic neutron scattering is used to measure the energy and wave length of these collective excitations. Analysis of these data gives direct information on the interatomic interactions responsible for the magnetib properties of these materials.

Jan 1, 1992

By Zenjiro Asaki, Teruo Tanabe

"To clarify the formation of light rare earth (R =Ce, Pr, Nd or Sm) -Fe compounds in the reduction-diffusion (RD) process, two kinds of experiments were carried out: (a) RD experiment in which briquettes composed of R oxide powder, Fe (particles or wire) and CaH2 were reacted, and (b) immersion experiment, where an Fe plate was immersed into R-Fe melt having the composition of Fe-side liquidus line in Fe crucible. The compound formation was examined by using XRD, SEM and EPMA. The formation rates of RzFe17 measured by the RD experiment were compared with those obtained by the immersion experiment. The growth rates of compounds obtained in the RD experiment for Pr-Fe and Nd-Fe systems were much lower than those obtained in the immersion experiment. This result was explained by the difference of the reduction rates of R oxides by Ca. The parabolic rate constants for the formation of RzFe17 were separated in two groups of (a) Pr-Fe and Nd-Fe systems and (b) Ce-Fe and Sm-Fe systems. This was discussed in connection with the difference of their crystal structures and the driving force of diffusion. The parabolic rate constants for the formation of compounds in Ce-Fe and Sm-Fe systems decreased in the order of RFez, RFe3 and RzFe17.IntroductionTo understand reaction behaviors in the production of rare earth (R) -iron intermetallic compounds, which have excellent magnetic properties, is very important from engineering point of view. And the reduction-diffusion (RD) process<O has recently attracted attention as one of the promising processes to economically produce R-related materials. A few fundamental studies on the compounds formation in the RD process have previously been reported. Qi, Hino and Yazawa(2) observed the formation of R(Nd, Sm)-Fe and R-Co compounds in the process from various view points. Song and Ogawa(3) measured the growth rates of Nd-Fe and Sm-Fe compounds by using Nd or Sm vapor supplied from Nd-Ca or Sm-Ca melts. The authors have also carried out fundamental studies (4)-(8) to clarify the rate and mechanism in the production of R-Fe intermetallic compounds."

Jan 1, 1998

By L. N. Ertzeva

The process for thermal treatment of current pyrrhotite concentrate in reducing environment with the use of disperse metal iron as an iron-bearing additive (optimal volume 20-30%), with downstream magnetic separation of the calcine, has been studied. The reduction process has been performed in conditions emulating those of both tube and fluidize-bed furnaces.

Jan 1, 2006

By C. G. Bastos Andrade, V. F. Justo, F. R. Valenzuela-Diaz, M. G. S. Valenzuela, C. M. Matos, C. Volzone

For industrial use, the smectite clays are usually treated with inorganic acid of high concentration at temperatures under boiling point, which provide the bentonite´s bleaching power. In the present paper, a sample of brown smectite from Paraiba, Brazil, was submitted to treatment under moderate conditions (90°C, reaction times of 1, 6, 12, 18 and 24hours in close reactor, concentration of the aqueous solution of hydrochloric acid 1.5M, clay/acid solution ratio of 1g/10mL), aiming to reduce impurities, responsible for the color of the clay, without causing significant changes in their structure. The samples were characterized by scanning electron microscopy (SEM), energy dispersive X-ray detector (EDS), stereomicroscopy, Cation Exchange Capacity (CEC), Thermal Analysis (TG/DTA), and X-ray diffraction (XRD). It was observed a bleaching in samples with time of 12h to 18h. With the DRX was possible to monitor the peak intensity of the clay structure and the sample with 12 hours of treatment was not significantly altered its crystalline structure, maintaining the peak clay at d(001). The most pronounced changes in the bleaching occurred within the first 12 hours of acid treatment. Thus, clay can be used in products with high added value.

Jan 1, 2015

By F. Nava-Alonso, O. Alonso-González, A. Uribe-Salas, R. Pérez-Garibay

"Cyanidation is the most used method to recover gold and silver from their ores. In this process, other metals besides gold and silver may sometimes dissolve and interfere with the efficiency of extraction. Copper is one of those metals, reaching concentrations as high as 1000 mg/L in some cyanidation plants, making difficult the extraction and purification processes, and increasing the operating costs.This preliminary work was intended to study the feasibility of using amines to form a precipitate and to eliminate copper from a synthetic solution containing high copper and cyanide concentrations, as is the case of some cyanidation effluents. The solid formed is removed from the solution using conventional filtration techniques. Seven amines were evaluated at different pH values and amine additions. Up to 90% of copper present may be removed at the natural pH of the effluent (alkaline). The remaining copper would permit to recycle the solution back to the cyanidation process. IntroductionCopper is generally considered the most problematic metal in gold leaching due to the rapid formation of copper cyanide complexes when some readily-soluble minerals are processed (e.g., azurite, malaquite, cuprite, chalcocite and bornite). The copper solubilization as cuprous cyanide complexes leads to a significant economic penalty in terms of excessive cyanide consumption and high cost for cyanide elimination. When activated carbon is used to recover gold and silver, the copper-cyanide complexes decrease the efficiency of the process because of the competition of the cuprocyanides with the aurocyanide for the adsorptive sites on the activated carbon (Rees and Deventer, 1999).Several techniques have been developed to attempt to overcome the problems caused by the copper presence in cyanidation solutions, notably: acidification-volatilization-regeneration (AVR), ion exchange-electrolysis or solvent extraction-electrowinning (Lu et al., 2002). In this work the use of some amines is proposed to remove the copper-cyanide complexes by precipitation of a copper-cyanide-amine solid. The process was evaluated for different amine additions and pH values, using copper-cyanide synthetic solutions of composition similar to that presented by some cyanidation plants with high copper."

Jan 1, 2008

By V. Bhagavathy

This paper describes a method for the determination of traces of rare earths using energy dispersive x-ray fluorescence spectrometry (EDXRF) after preconcentration of their oxine complexes onto activated carbon. Various parameters that influence adsorptive preconcentration of rare earths onto activated carbon viz. pH, amounts of activated carbon and oxine, time of stirring and aqueous phase volume were systematically studied. A numerical method based on simple least square procedure using fifth order polynomial with 25 consecutive values was developed for smoothing and differentiation of EDXRF data which was previously digitized and averaged. First order derivative EDXRF in conjunction with adsorptive preconcentration on activated carbon enables to determine as low as 10 ppb of each of individual rare earth elements.

Jan 1, 1989

By H. Y. Cheng

A pulse column solvent extraction system was evaluated as an alternative to mixer-settlers for the separation and purification of rare earths. The column tested had an inside diameter of 44.5 mm and had 36 sieve plates with a free area of 25%. Pulsing was provided pneumatically using a solenoid valve controlled by a timer so that both pulse amplitude and frequency could be varied. Feed to the column was a mixed rare earth chloride solution containing 10 g RE L-1. The extractant was 5% Ionquest® 801 in Shellsol 2037 diluent. Hydraulic performance of the pulse column was excellent with no propensity towards stable emulsions or crud formation under normal operating conditions. The column was operated in organic-continuous mode with flow rates chosen so that yttrium and the heavy rare earths were extracted with high efficiency while the light rare earths were rejected. Yttrium extraction varied from 83 to 99.2%. Concentration profiles were measured in both the aqueous and organic phases, and, from this data, the height of a transfer unit (HTU), the mass transfer coefficient (Kxa) and the continuous-phase axial dispersion coefficient (Ey) were computed. The HTU ranged from 17-92 an which is within the range of values reported for other (non rare earth) pulse column systems.

Jan 1, 1992

By L. Trincado

Mantoverde is a heap leach-SX-EW plant that was commissioned in December 1995 at a production rate of 42,130 ton of copper per year and 5.4 million ton of ore per year. Copper production has steadily been increased to 57,290 ton in 2002. Forecast copper production for 2003 is 60,000 ton for an ore treatment rate of 8.5 million ton. Several improvements in the heap leach process have been implemented. The main process improvements are related to the optimization of heap height, particle size, irrigation rate and leach cycle, in addition to a better heap drainage design and a solution management system. A first dump leach operation was started in 1999 at a production rate of 1,922 ton of copper. A second dump leach operation was started in early 2002 at a production rate of 2,805 ton of copper. Dump leach production will be increased over time to as much as 24,000 ton of copper. The main heap leach process improvements, as compared to the original plant design, as well as the main dump leach operating parameters are discussed in this paper.

Jan 1, 2003

By Sylvie C. Bouffard

The need for a better understanding of the heap biooxidation pretreatment of pyritic refractory gold ores has prompted us to develop a rigorous mathematical model of the process. The hydrological structure of the model takes the form of lateral stagnant pores in contact with a uniformly distributed gas stream and connected to vertical plug flow channels, as suggested by the results of an independent study of column hydrology. A model of pyrite oxidation kinetics was derived based on electrochemical leaching theory and the results of potentiostatic stirred tank and column tests. The growth rates of attached and planktonic iron- and sulfur-oxidizing cells are modeled with separate Monod expressions over three separate temperature ranges corresponding to mesophiles, moderate thermophiles, and extreme thermophiles. Isothermal column tests validate the model simulations. Excellent fits of several leaching indicators (potential, extent of sulfide oxidation, iron concentration, cell numbers) reveal the rate-limiting step to shift from particle kinetics to oxygen gas/liquid mass transfer with increasing temperatures and pyrite head grades. Competition for oxygen between sulfur- and iron-oxidizing microorganisms lowers potentials and slows down pyrite oxidation. This modeling tool may assist engineers in the design and operation of heaps to give more complete gold liberation in a shorter time.

Jan 1, 2003

By T. I. Arbuzova

The present work presents the original data concerning using a high pressure torsion method and a shock wave loading technique to produce compact oxide nanomaterials and investigations of the effect of severe plastic deformation on a microstructure, crystal lattice and stability of these compounds. This allowed us to compare two ways of deformation action that can be characterized as quasi-static and dynamic effect, correspondingly. Particular attention was paid to a stoichiometry and surface composition changes upon severe plastic deformations. A procedure for studying chemistry of the oxide nanomaterials by means of nuclear microanalysis and Rutherford back scattering has been worked through. For surface studies the X-ray photoelectron spectroscopy has been used. It was shown that both distortion methods permit to produce massive nano-scale oxide materials from the coarse-grained powder during a single technological cycle. Bulk nanocrystalline materials based on LaMnO3, TiOy and ZrO2:Y2O3 were obtained by the quasi-static deformation technique. Nanoscaled ceramics of CuO, Mn3O4 and LaMnO3 were produced by the dynamic deformations. The density of the nanoceramics comes to 99%. Size effects and specific imperfection of the nanoceramics obtained lead to a set of particularities of physical properties.

Jan 1, 2006

By Kiichiro Hayashi

"Indonesia is one of the world leaders in palm oil production. Palm oil industry is an industry to be considered when it comes to environmental impacts. This paper utilizes three step approaches. First, a material flow analysis of palm oil related industry was conducted in Indonesia. Second, a factory visit survey was conducted for getting information on environmental impacts of plantation and CPO mills. Third, a LCA study was made for a model Indonesian CPO mill in several bio-waste treatment options. Main findings were that, first; over 70% of FFB was bio-wastes generated from CPO mills. Second, some mills introduced a zero emission bio-waste policy. However, untreated bio-wastes in the zero emission policy, such as, CH4 from POME ponds, may have potential to reduce more impacts on the environment. Introduction Indonesia is one of the world leaders in palm oil production with approximately 12.4 million tons of crude palm oil (CPO) production in 2005 and with the plantation area 5.6 million ha spreading out in 19 provinces [10]. The expansion of palm oil cultivation in Indonesia and its export oriented industry heavily relies on the strong world market demand for food. Currently, there are 320 CPO industries in Indonesia [10]. These include plantations and palm oil related factories. Among them, there are six biggest players in CPO business in Indonesia: PT. Perkebunan Nusantara (PTPN) consisting of 9 PTPN, Sinar Mas, Raja Garuda Mas, Astra Agro Lestari, Minamas Plantation and Indofood. They are managing more than 50% of plantation estate in Indonesia and are leading the Indonesian palm oil business.Palm oil industry is an industry to be considered when it comes to environmental impacts. Unfortunately, there is not so much available information related to the performance of each CPO on environmental impacts. There are reports which provide information on environmental impacts of CPO mills in South East Asian countries, but are limited to, for instance, Thailand’s cases [4 and 5] and Malaysia’s cases [1, 3, 6, 7, 9, 11 and 12]. On the other hand, similar studies on the Indonesian’s case are not well established in academic literatures. And also there is limitation on Indonesian palm oil industrial information from plantation to consumption and disposal in academic articles. There is no literature related to material flow analysis focusing on the whole Indonesian palm oil related industry. One way to describe and present the environmental impacts is through a life cycle assessment (LCA). The LCA could be used to estimate the impacts of CPO production including the stages of plantation, transportation and milling [5, 8 and 11]. However, studies on Indonesian CPO production process were not well established in academic articles. The purpose of this paper is thus to clarify environmental impacts of palm oil industry in Indonesia especially by focusing on plantation and CPO mills with consideration to various bio-waste treatments."

Jan 1, 2008

By Jeffrey F. Adams

Gypsum fouling is a common problem in the hydrometallurgical industry. It is a particular problem in free sulphuric acid neutralization, or iron removal operations where sulphates are removed from aqueous solutions by the addition of calcium-containing bases. Previous work revealed a strong correlation between the degree of gypsum supersaturation in the reactor and the rate of scale growth indicating that scale formation and growth are primarily controlled by chemical phenomena. However, the chemical behaviour of gypsum is variable and unpredictable with solution chemistry and temperature. Many of the "rules of thumb" that are used to predict its behaviour (and avoid fouling) are in fact based on gypsum solubility in water, rather than on real mixed metal sulphate systems. However, despite this unconventional solubility behaviour, we have been able to accurately model it in Ni, Mg, and Zn containing solutions over a wide range of temperature (25°C-90°C) and solution concentration (0-6 m) using the OLI simulation software. Furthermore, by studying fouling rates in a simulated continuous neutralization reactor, the relationship between process conditions and fouling rates were explained for the first time. This has led to an understanding of how techniques for minimizing gypsum fouling work.

Jan 1, 2003

By Bruce Cavender

Managers are frequently faced with the decision to perform a task or manufacture an object in-house or to hire an outside vendor to perform the function. Outsourcing decisions are usually driven by economics: work is outsourced if it can be completed at a lower cost or in a shorter time than it can in-house. A technique termed incremental analysis can be used to make this decision. Incremental analysis examines the financial impact of outsourcing decisions as a function of the firm&apos;s fixed and variable operating costs. To use this tool, individual components of production cost are identified as being either constant or varying with levels of production activity. The assignment of cost type can be made in several ways: though analysis of historical operating data, understanding of individual expense types, and so forth. Changes in fixed and variable costs resulting from each potential course of action are explicitly identified to project the financial outcome of each alternative. The alternative having the greatest positive impact on profit is selected for implementation. By using the fixed- and variable-cost framework, the analysis is conceptually straightforward and substantially simplified. Production managers can therefore use incremental analysis as a tool for fast economically beneficial decisions on a real-time basis.

Jan 1, 1999

By Rzyman Michal, Nakamura Takashi, Shibata Etsuro, Grabda Mariusz, Oleszek-Kudlak Sylwia

"Tetrabromobisphenol A (TBBPA) and many systems based on the synergistic effect of brominated organic compounds with Sb2O3 are extensively used as effective brominated flame retardants (BFRs) in many materials such as plastics and textiles. Thermal degradation of BFR containing plastics leads to the formation of hydrocarbons and gaseous compounds such as HBr and SbBr3. Our thermodynamic considerations indicate that these gases can act as bromination agents for metallic oxides such as ZnO, Cu2O, CuO, PbO and FeO. Moreover, these metallic oxides have the thermodynamic tendency to brominate easier than does Sb2O3. The aim of this study was to investigate experimentally the reactivity of ZnO with 1) HBr originating from the thermal decomposition of TBBPA and 2) SbBr3, which is formed during thermal degradation of brominated flame retardant plastics. The thermal treatments of the mixture of compounds of interest were investigated by thermogravimetry coupled with mass spectrometry.IntroductionTetrabromobisphenol A (TBBPA) and many systems based on the synergistic effect of brominated organic compounds with Sb2O3 are extensively used as effective brominated flame retardants (BFRs) in materials such as plastics and textiles. For instance, 4.5 million tons of flame retardant plastics containing BFRs are produced in Japan each year. Thus, in thermal treatments such as the incineration and melting of solid wastes, BFR containing plastics are intentionally or unintentionally included in the wastes. Thermal degradation of BFR-containing plastics leads to the formation of hydrocarbons and gaseous compounds such as HBr and SbBr3 [1-5]. Our thermodynamic considerations [6] indicate that heavy metal oxides such as ZnO, Cu2O, CuO, PbO and FeO should easily react with HBr prior to Sb2O3 and also with SbBr3, the main gaseous product in the thermal decomposition of TBBPA, forming low boiling point metallic bromides suitable for the volatile separation of heavy metals. The metal oxides are also expected to qualitatively and quantitatively affect debromination and decomposition of the flame retardant."

Jan 1, 2008

By Biserka Lucheva, Tzonio Tzonev

"Recycling of aluminum scrap and dross is significant in the economic and energy saving, as well as in the environmental protection. Recovery of metal aluminum depends on many factors. The aim of this work is to investigate experimentally the metal recovery under different conditions. The processing of aluminum dross was carried out in DC electric arc rotary furnace. The optimal technological parameters are determined. It is turned out that the presence of crushing refractory bodies during the processing of the aluminum dross in the rotary furnace increases the degree of aluminum recovery with about 10 %.IntroductionCompact and granular aluminum dross are used for the fulfillment of the experiments, which were obtained by salt free melting of aluminum scrap. The only preliminary preparation of the compact dross is crushing them into proper size, in compliance with the size of the opening for furnace charging and removing of fraction – 1 mm. The granular dross is subjected to sieving also with the purpose to remove the fraction – 1 mm. In these conditions the content of the metal phase in the compact dross is 72 %, and in the granular – 77 %. The processing of aluminum dross was carried out in DC electric arc rotary furnace (Figure 1).The purpose of this research is to investigate experimentally the metal recovery under different conditions and to establish the dominant factors, which need to be controlled."

Jan 1, 2008

By Cz. Mazanek

Specific biostimulating and anticancerous properties have been observed in peat, Ash Vacanta, and in an amorpous silica that is obtained as a by-product of alumina production from Turow clay in Poland. The anmphous silica was characterized and found to have a large specific surface area. This property may account for the beneficial characteristics of the material.

Jan 1, 1989

By Dieter Offenthaler

Catalysts used in petroleum industry often contain valuable amounts of PGMs. The typical recycling route for those materials is the pyrometallurgical one, but this treatment way offers limited flexibility with respect to small charge weights. A new process, combining a pyrometallurgical pre-treatment step of the ceramic carriers with a hydrometallurgical leaching procedure overcomes this disadvantage. It not only allows the economical treatment of even very small charge weights, but also gives the possibility to maximize the PGM yield by individually adapting the process to the different charge materials. Due to an ingenious process design, where all leaching agents and effluents are recycled in a closed loop and therefore no waste waters leave the process, process operation becomes very economical. However, the temperature-time-regime in the pyrometallurgical pre-treatment step is of major importance for the success of the whole process. Therefore various investigations have been done to identify how the different process variables in the pyrometallurgical pre-treatment influence the subsequent leaching procedure. It turned out, that the adjustment of the correct phase-modification in the ceramic carrier materials during the pyrometallurgical treatment is the key factor of this process step. Although it is a troublesome issue to exactly adjust the correct phase modifications, it is the prerequisite to take advantage of the benefits of this new process concept.

Jan 1, 2006