Search Documents

By M. Evertsson, K. Bhadani, E. Hulthén, M. Bengtsson

"Modelling and simulations for mineral processing plants have been successful in replicating and predicting predefined scenarios of an operating plant. However, there is a need to explore and increase the potential of such simulations to make them attractive for users. One of the tools to increase the attractiveness of the simulations is through applying optimization schemes. Optimization schemes, applied on mineral processing simulations, can identify non-intuitive solutions for a given problem. The problem definition itself is subjective in nature and is dependent on the purpose of the operating plant. The scope of this paper is to demonstrate two optimization schemes: Multi-Objective Optimization (MOO) using a Genetic Algorithm (GA) and Multi-Disciplinary Optimization (MDO) using an Individual Discipline Feasible (IDF) approach. A two stage coarse comminution plant is used as a case plant to demonstrate the applicability of the two optimization schemes. The two schemes are compared based on the problem formulations, types of result and computation time. Results show that the two optimization schemes are suitable in generating solutions to a defined problem and both schemes can be used together to produce complementary results. INTRODUCTION The comminution process for a mineral processing plant consists of multiple crushing and classification stages and aims to produce fine material to liberate ore from the minerals. The modelling and simulation of such processes are well established using static process models (King, 2001; Napier-Munn et al., 1996). A recent development in the dynamic modelling for such processes has shown further increase in fidelity compared to the static process models (Asbjörnsson, 2015). The developed simulations can be utilized to design, operate and control mineral processing plants based on the requirements of users (Bhadani et al., 2017). Typically, the requirements in the operation of the comminution process are conflicting in nature, as for instance, reduction of power draw by process units, maximization of production of fine materials, and increasing utilization of the process units. These conflicting requirements leads to a Multi-Objective Optimization (MOO) problem to operate a mineral processing plant. The MOO problems are normally referred to as non-linear problems and its fundamental understanding with respect to process behaviour is difficult to achieve."

Jan 1, 2018

By I. H. Mukhametshin, E. N. Baranova, I. B. Fadina, E. A. Ashirbaeva

The purpose of the research is the development of a complex of solutions for the maximum extraction of non-ferrous and precious metals from persistent mineral raw materials by heap bioleaching from spent heap leaching (HL) stacks. Methodical recommendations for assessing the suitability of primary and technogenic refractory mineral raw materials for heap bioleaching are developed. Active associations of microorganisms have been created for the conversion from various types of ores to the solution of S, Fe, As, Sb, Cu, Zn, Mn, Ni, Mg, P and other elements, as well as methodologies for their storage, immobilization and preparation of bioreagents in industrial conditions. On a pilot scale, tests were carried out on samples weighing 15-17 thousand tons of refractory gold-sulphide ores (more than 50% of gold is associated with sphalerite), gold-quartz ores with colloidal gold (74% associated with quartz and pyrite) and gold-silver ores with elevated copper and zinc content (1.5 and 3,5%, respectively), as well as man-caused material lying for 4-5 years of spent quarry material of oxidized gold-silver ores. In the pilot-industrial tests of heap bioleaching of gold-sulfide ores, gold recovery of 84-85% and silver was achieved to 89-90%, the possibility of obtaining high-yield solutions of copper and zinc, suitable for hydrometallurgical processing, from gold-silver ores, and the possibility of obtaining waste with a dump content of valuable components, suitable for deep disposal in the construction industry. When comparing two technologies for processing refractory ores after biooxidation under HL conditions, when 1000 tons of ore processed by the bioreagent were re-milled from a size of 40 mm to 0.1 mm and cyanated under the conditions of the factory process, the same results were obtained for gold recovery (85%) and silver (90%), as with the heap version. The copyrights of the development are protected by a patent.

Jan 1, 2018

By J. Seo, W. Kim, I. Bae

"Microcrystalline silica impurities such as quartz and opal-CT commonly associated in bentonite should be controlled and removed as far as possible when bentonite is used as biocompatible raw material because they show sufficient evidence of carcinogenicity. Since opal-CT contained in bentonite in trace amounts cannot be well separated by conventional sedimentation method, in this work, the ultrasound-assisted removal of the impurity was attempted. Irradiating ultrasound into bentonite-water suspension promoted the production of fine montmorillonite particles in the suspension and the production markedly increased when montmorillonite was activated by Na2CO3. Subsequent centrifugation of the suspension made it possible to recover pure montmorillonite particles as an overflow product. Only 16.2 mass % of total solids was recovered as an overflow from the non-activated suspension, whereas 63.5 mass % was recovered from the activated suspension at centrifuging speed of 10000 rpm. Increasing sonicating time enhanced the yield of overflow, however, excessive sonication up to 10 min hindered the purification of montmorillonite. It was observed that the peak reflection of (101) plane of opal-CT in overflow increased as sonicating time increased during prolonged sonication. INTRODUCTION Bentonite consisting predominantly of mineral montmorillonite is clay-rich soft rock generated frequently from the alteration of volcanic ash. Depending on the nature of its genesis, bentonite contains a variety of accessory minerals, which may include mainly quartz, feldspar, opal cristobalite/tridymite (opal-CT), calcite, illite and mica. The presence of these accessory minerals can impact the industrial value of the deposit, reducing its commercial value depending on its applications. Therefore, bentonite is often purified by removing these impurity minerals for special applications where specific properties and characteristics are required (Murray, 1999). Among the special applications, bentonite is often used in the cosmetic and pharmaceutical industry as both excipient and active ingredient in the forms of liquid (suspensions, emulsions), semi-solid (creams, ointments) and solid (powder, capsules and tablets). The basic requirements for bentonite to be used as raw material are pure, microbiological and mineralogical inertness. Physical properties such as swelling volume and gel formation are also important. Particularly, microcrystalline silica polymorphs such as quartz, cristobalite and opal-CT should be controlled and removed as far as possible because they show sufficient evidence of carcinogenicity in humans."

Jan 1, 2018

By Liang Dianyin

In this paper, the molybdenite flotation tailing of cleaner-scavenger bank which has a mass of very fine particles has been taken as raw ore to be processed by flotation with/without ultrasonic. The effect of ultrasonic frequency, intensity, processing time and uploading location on molybdenite flotation efficiency is investigated by four-factor three-level orthogonal experiment, and the effect significances of these ultrasonic variables to molybdenite flotation efficiency have also been evaluated. Single-factor analysis of variance is conducted to investigate whether the effect of ultrasonic on molybdenum ore flotation efficiency is significant or not. The samples extracted from different ore species in different time have been mixed to analyze the particle size. The results show that the particle size of +38µm in concentrate obviously increases while the particle size of -25µmobviouslydecreaseswith ultrasonic, which means that ultrasonic is good for flotation due to sludge removing effect. Keywords: ultrasonic, flotation efficiency, sulfide ore, tailing, grade, sludge removing

Sep 1, 2012

By M. Pelser, Lorenzen L.

"The presence of calcium and magnesium in the hydrometallurgical processing of base metals, results in a number of process difficulties. These problems range from the contamination of the final product (where the final product is a precipitate) to high energy consumptions and large bleed streams during electrowinning. Calcium poses an additional problem in sulphate solutions owing to the low solubility of its sulphate salts. This can easily lead to a process stream that is supersaturated with calcium sulphate, resulting in unwanted solids formation within the process equipment.A review of literature has proven that there is no conventional method for the control of calcium and or magnesium, although a number of potential processes have been identified. The technologies investigated included precipitation, ion exchange and solvent extraction, for which at least one method was found under each. To make the reader aware of these processes a short description was provided of each within the text.Of these processes, fluoride precipitation was selected for experimental investigation based on the low solubility of calcium and magnesium compared to the base metals. This process involves the addition of a soluble fluoride to precipitate CaF2 and MgF2. The experiments were designed to investigate the equilibrium of the system at varying parameters of which the level of fluoride addition, the ratio of calcium to magnesium, and the identity of the soluble fluoride was reported. In all of the instances the process showed high selectivity towards calcium and magnesium over the base metals. The experiments proofed the process to have a higher affinity towards the removal of magnesium at compositions where the molar ratio of calcium to magnesium was higher than 1:3. It is often the case that the calcium to magnesium ratio is in the region of 1: 10. From this it follows that the fluoride addition has to be stoichiometric or greater for calcium and magnesium combined, if the calcium is to be precipitated. This was demonstrated as well. On the identity of the soluble fluoride hydrogen fluoride was compared to ammonium fluoride, of which the latter was found to be preferred."

Jan 1, 2003

By Tom Liu

This paper is a fundamental study of bubble-particle collision efficiency in turbulent flows. A CFD-based microscale scheme for the prediction of turbulent bubble-particle collision efficiency in a 3D isotropic turbulent flow is developed, and in this way, turbulence effects on particle-bubble collision efficiency are taken into account for the first time. By comparing the computed results with experimental data from the literature, the CFD simulation is shown to correctly predict the bubble-particle collision efficiency in a quiescent environment. The CFD method was then applied to the investigation of bubble-particle collision efficiency in a turbulent flow, and the simulation results are shown to be qualitatively consistent with the real observations. The predicted collision efficiency can be used in a multiscale modelling scheme, which would account for all control variables in a flotation cell, such as impeller structure and tip speed, air nozzle structure and air flow rate This study indicates how microscale simulations of bubble and particle behaviours, coupled to macroscale CFD simulations of flotation cells, can provide a powerful tool predicting the flotation rate in a real flotation cell.

Jan 1, 2014

By S. S. Yu

In this paper, the producing process of using V2O3 as raw material to obtain vanadium nitride was analyzed through the means of thermodynamic. The analysis shows that conversion follows the principle of reduction step by step in the conversion process of V2O3. The temperature of the reaction system has prominent influence on the nitrogen content of products, and the reaction is very sensitive to temperature. As raising temperature, the fine grain structure of the nitrides is more evident, and the grain size of nitrides increases. At 1703K, the nitrogen content of the products tended to be constant after soaking over 3 hours.

Jan 1, 2014

With the ambitious target of adding another 2,00,000 MW of power generation by the year 2017 in India the demand for coal is bound to grow. The non-coking coal deposits in India are characterized as high ash and difficult-to-wash coals. Quality improvement by beneficiation is almost mandatory due to MoEF notification to use <34% ash coal for all power plants except those located at pithead. Most of the coal washeries in India are based on wet process, where the coal fines are allowed to settle in thickeners. The coarser particles settle faster leaving the fine particles suspended for longer period. The dispersed fine coal particles contain some surface charge, which leads to the development of electrical repulsion between the particles, and as a result of this, the suspension becomes more stable. In order to destabilize the colloidal suspension, flocculants are usually added, so that the settling rate of the fine particles also increases. These flocculants are of cationic, anionic and non-anionic depending upon the type of charge released when dispersed in water. The flocculants may act partly for charge neutralization and partly for inter particle bridging and electrostatic patch formation. The effectiveness of any type of flocculants depends upon the molecular weight and charge density of the polymer. The paper discusses the settling behavior of non-coking coal fines suspension by using different flocculants. Keywords: floculent, coal fines, sedimentation rate, effluent

Sep 1, 2012

By G. W. Zhang

Ultra-fine Stirred Mill is a kind of high energy efficient equipment for ultra-fine grinding, and has been the mainstream equipment in the submicron powder and slurry industry. This paper mainly describes flow-field numerical simulation of the three popular ultra-fine grinding mills: (respective-ly as) Disc Stirred Mill, Pin Stirred Mill and Spiral Stirred Mill, by means of the software Computational Fluid Dynamics (CFD). In the flow-field numerical simulation, the velocity gradient, shear rate dispersion of the flow-field, the viscosity dissipation rate were analyzed with CFD. It is discovered that Pin Stirred Mill has the highest velocity gradient in circular directions and the most homogeneous distribution of shear rate among the three. Flow-field numerical simulation provides a new way (and means to) for the parameter optimization design and project enlargement of Ultra-fine Stirred Mill. The experiments were also carried out, the results are consistent with the results of the simulation analysis. For example, in GCC grinding experiments under the same conditions, the specific energy consumption of Pin Stirred Mill with 3600L in volume is 15%~17% less, and its processing capability is 13%~15% better than Disc Stirred Mill. Now with its optimized structure and excellent performances, more than ten sets Pin Stirred Mill with 3600L in volume have been used in industrial production in Shandong, Guangdong and Hunan province.

Jan 1, 2014

By Xubo Chen, Zhiqiang Hu, Zhijian Sun, Gaoyun Zhou

"The research aimed at developing an efficient and environmental frother,which was applied in the flotation of sulfide ores. The flotation properties of an efficient frother and pine oil have been studied relatively by flotation tests of lead and zinc sulfide ores. At the same time, the biodegradability of two kinds of frother has been studied by the method of biological respiratory curve. The test results show that the flotation properties of new frother are superior to pine oil such as flotation rate, dosage etc. and its biodegradability is superior to pine oil. INTRODUCTION Frother is a kind of important agent in flotation reagents.In practice, the criterion of the foaming performance of the frother is what is high and low according to flotation indexes. The difference of different minerals and flotation technologies has great influence on the foaming performance of frother, and it is very important to choose the corresponding frother. The type, dosage and selectivity of frother in flotation process must be considered carefully. In today's society, environmental protection and ecological protection are becoming more and more important, and the environmental and ecological damage from mine development has aroused increasingly more attention. The use of mine agents has promoted the development of mineral resources, greatly improves the recovering utilization of mineral resources, at the same time, the production and use of mine reagents also inevitably bring about pollution, and result some influence or damage in the ecological environment.The frother is a common kind of reagent in the flotation process of the concentrator. In many cases, the waste water in the concentrator can not be let out in the natural water because the higher content of the frother in the waste water results in higher index of COD.This will inevitably increase the cost of waste water treatment in the mine.Therefore, the choice of frother should not only consider its influence on the flotation index, but also consider its influence on environmental protection. Waste water treatment is a way to solve the waste water pollution, but it needs to cost a lot of fund, manpower and material resources.And the development of high efficiency pollution-free reagent is a good way to reduce the production cost of mining enterprises and reduce the environmental pollution."

Jan 1, 2018

By Luis G. Bergh

Today, large size mechanical flotation cells of 100 to 300 m3 are used in rougher operation in different flotation industrial plants, in Chile and worldwide. However, in spite of the advances in fundamental research and the notable growing in equipment size, with more complete instrumentation systems, there are still a lack of reliable data for industrial flotation modeling and simulation to advance in better control systems design. In this work, a model of a rougher flotation circuit, based on operating variables and parameters fitted from industrial data, obtained in some previous work, is used to develop a set of logic rules in order to aid operating decisions. The simulator was first used to sensitize the effect of changing the froth depth profile on target variables, and then to find out the best profile to reject common disturbances coming into the plant. The flotation circuit simulator was redesigned to incorporate an expert system following the proposed control algorithm. Several tests were performed to evaluate the control responses to different correlated series of input variables, such as feed grade, tonnage, particle size distribution, and solid percentage. Control alternatives are discussed based on the circuit simulator. Keywords: modeling, industrial data, flotation control, mineral processing.

Sep 1, 2012

By Rasool Hejazi

The feed to Chadurmalu iron ore concentrator plant is a mixture of magnetite and haematite iron ore with a Fe/FeO ratio of about 8. The feed to plant, after grinding via wet SAG mill, is pre-separated by wet low intensity magnetic separator. Magnetic product is conducted to magnetite processing circuit for producing magnetite concentrate, and nonmagnetic product is directed to haematite processing circuit. Due to surface oxidization of magnetite particles and a decrease in magnetic attraction properties, significant amount of these particles are misled to tailing which results in decreasing the efficiency of haematite processing circuit. This problem can be remedied by using magnetic drum separator with more magnetic intensity and/or gradient. In this paper, the replacement of LIMS separators with wet medium intensity magnetic separators with a field intensity of 3800 gauss on drum surface (MIMS) have been suggested and considered as the most suitable solution to prevent the loss of magnetite particles. The results of carried out investigations with replacement of drum separators in industrial scale, showed that utilizing MIMS in magnetite processing circuit resulted in increasing final concentrate weight recovery on average by 2.59%, without any adverse effect on the concentrate quality; decreasing the magnetite content in the feed to high gradient magnetic separator (HGMS) by about 3.5%; decreasing the feed to floatation part by about 7% and consequently decreasing consumption of chemical reagents; increasing Fe/FeO ratio of the feed to plant. Keywords: iron ore, medium intensity magnetic separator, haematite, Chadurmalu

Sep 1, 2012

By Y. S. Sun, P. Gao, Y. F. Li, J. W. Yu

"Oolitic hematite ore is one of the most refractory iron ores in the world. It is not feasible to separate iron minerals from raw ore by conventional mineral processing methods. In recent years, a new technology called coal-based reduction followed by magnetic separation has been employed to produce metallic iron powder from oolitic hematite ore effectively. In order to find the nucleation mechanism, a thermodynamic analysis of the carbothermic reduction of oolitic hematite ore was conducted by the HSC 6.0 thermochemical software. The phase transition and microstructure changes during the coal-based reduction were also investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that the iron oxides in the oolitic ore were reduced to metallic iron following the route of Fe2O3–Fe3O4–FeO–Fe in reduction process. The reduction reactions preferentially occur in the high activity regions to form a higher concentration of Fe elements, and then more supersaturated Fe separated out to form new phase nuclei. Under the action of homo-aggregation and principle of minimum free energy, the iron cores continuously absorbed migratory Fe around and grew into quasi-spherical iron particles embedded in slag phase. INTRODUCTION With the rapid increase of steel industry, premium grade iron ore in China has been gradually exhausted, and its supply has become bottleneck for the development of iron and steel industry (Guo et al., 2015). Therefore, it is urgent to exploit the refractory iron ores, such as oolitic hematite ore. Oolitic hematite ore is widely distributes in France, Germany, America, Canada, Pakistan, China, and among other countries (Maynard and Van Houten, 2004; Li et al., 2011). In China, the explored reserve of oolitic hematite ore is 3.72 billion tons, which accounts for approximately 1/9 of total iron ore resources of China (Gao et al, 2016). Oolitic hematite ore possesses complex composition,"

Jan 1, 2018

By Marianella Perez, Williams Calderón, Gonzalo Montes-Atenas

The lack of fresh water sources, particularly in the Northern part of Chile, has driven the mine sites to search for new and sustainable paths to obtain water resources to run minerals processing operations. Among them, the use of seawater in concentrators appears as an interesting solution to this problem. However, the presence of seawater will have an impact onto the operation, not only because it will enhance corrosion reactions in the equipment installed in a plant, but also because it may affect how particles will effectively be processed across the numerous unit operations existing in the mine site. Among such unit operations, the grinding stage is a highly regarded as it defines the success of the separation of valuable minerals from gangue material in the froth flotation operation. Then, one important aspect to be addressed is to understand how the presence of seawater will affect the different mechanisms acting during the operation of a ball mill. The aim of this research work is to assess the effect of changing the aqueous matrix from process water to seawater in ball mills onto the mill performance. The methodology considered the use of Fluent® software and its capabilities to run numerical simulations with heterogeneous media. On one hand, from the data analysis, it is possible to infer that breakability mechanisms should not be significantly affected. On the other hand, the high ionic strength of the matrix should impact importantly particle transport mechanisms within the mill. Particularly, when transporting finer particles. Rheology results were in agreement with previous published research studies suggesting the suspensions to behave as Newtonian, Dilatant o Pseudo-plastic fluid depending on the amount of fine particles present in the grinding media. The latter will result in changes in the residence time of particles in the mill producing overgrinding or an excess in the circulating loads.

Jan 1, 2014

By M. Vasudevan

In sulfide mineral flotation, the efficiency of separation is severely affected by the presence of non-sulfide gangue minerals, such as altered silicates and serpentines. Although this is an acknowledged fact, most studies in mineral processing have focused on value minerals, and studies on gangue minerals affecting flotation performance are quite rare, and even those that do are limited in scope. This paper is an attempt to highlight the use of grade-recovery curves in studying the effects of gangue minerals. Specifically, we present the flotation response of problematic Ni and Cu ores which show highly uncharacteristic but similar grade-recovery characteristics despite the very different mineralogy and try to understand this behavior and the underlying mechanism. Finally, we propose chemical modifiers as solutions to overcome the detrimental effects of these gangue minerals and improve efficiency of flotation performance. Keywords: Non-sulfide gangue, grade-recovery, sulfide minerals, serpentines, talc, shale, slimes, spiking, modifiers

Sep 1, 2012

The ever increasing demand for energy and the progressive depletion of crude oil resources, have renewed interest in oil shale as an alternative fuel resource. Weathered oil shale samples were assembled from El-Nakheil phosphate mine in Quseir area, Eastern desert, Egypt. The oil shale samples were prepared and analyzed by XRD (X-ray diffraction), XRF (X-ray fluorescence spectrometry), and optical microscopic techniques. Rock-Eval pyrolysis and total organic carbon were used to study shale hydrocarbon potential. A leaching procedure using inorganic and organic acids was used to selectively dissolve the oil shale associated ash forming minerals. XRD results showed that calcite is the dominant carbonate mineral, whereas primary silicate minerals are quartz and montmorillonite. SEM (Scanning Electron Microscopy) observations indicated that the organic matter is dispersed throughout the rock matrix. The acid soluble fraction upon leaching was determined to be 37.59 and 42.74 wt% by using 5% HCl and 10% HCl, respectively. The TOC was increased from 20.78 to 29.88 and 34.09 wt% by using 5% HCl and 10% HCl, respectively. Keywords: el nakheil oil shale, characterization, xrd, xrf, sem, elemental analysis, proximate analysis, ultimate analysis, thin section, rock eval pyrolysis, acid leaching

Sep 1, 2012

By Y. B. Zhang

China is rich in iron ore resources, but most of these ores are low-grade, polymetallic and refrac-tory ones. Furthermore, with the rapid development of chinese iron & steel industry, the comprehen-sive recovery of these ores is becoming more and more important. The tin, zinc-containing complex iron ores are typical polymetallic and intractable ones, and great reserves of them are found in China. At present, they have not been efficiently utilized. In this paper, based on the investigation of basic physicochemical properties of the tin, zinc-bearing iron concentrates, taken from a mineral processing plant, the mineralogy reason that these concentrates are so intractable and refractory is found out, using advanced microscopic testing methods, such as optical microscope (OM), Scanning Electronic Microscope (SEM), X-ray diffrac-tion (XRD), etc. It is found that the symbiotic relationship of iron, tin and zinc metallic minerals are very complicated, and magnetite in the concentrate is closely symbiotic or enwrapped by fine cassi-terite and sphalerite. So it is difficult to separate tin and zinc completely from the iron concentrates by simple regrinding and physical separation method. This investigation provides theoretical guid-ance for developing new approaches for utilizing these concentrates.

Jan 1, 2014

With shortage of sulfide nickel ores, laterite ore was paid more attention by scientists. Because its grade is commonly lower than sulfide nickel ores, laterite ore can not be utilized effectively be-coming the bottleneck of study. Leaching laterite ores from Yuanjing, Yunnan province, organic ac-ids show better selective than sulfide acid in nickel and cobalt recovery. Organic acid has low de-pendent on pH, keeping leaching capability even higher than 3. On the other side, when pH up to 2, sulfide acid can not leach laterite ores any more. After four kinds of organic acid leaching laterite ores, besides citrate, malate and succinate have good leaching and effectively selective capability. Especially, succinate has the best selective leaching capability of nickel and cobalt in four kinds of organic acids for latter anion purification and separation. Isolated from waste water with sugar, Aspergillus niger (zs1) has great capability to produce organic acids and vigorous growth. Laterite ores have been respectively processed by direct-leaching and indirect-leaching. Indirect-leaching gives a better result than direct-leaching. Extraction of nick-el by indirect-leaching reaches 44.3%, far more than that of direct-leaching. Moreover extraction of nickel at pulp density of 5% is higher than that at pulp density of 10%, reaching 63% in 11 days and extraction of cobalt also is 48.1% in the same period. Compared with nickel and cobalt, iron gives low extraction in solution, containing organic acids produced by Aspergillus niger .

Jan 1, 2014

By Walter W. Focke, Zola Kwela, Willem van der Merwe, Arao Manhique

"The advantages of the de Wet zirconium process for the manufacture of AZST from zircon sand include: Fewer processing steps; removal of radioactivity by leaching rather than by precipitation; alkali reagent recovery in the form of a sodium silicate solution that is essentially free of radioactivity; fewer waste streams and less waste to discard.Here we report on our efforts at maximizing the alkali recovery in the sodium silicate product stream: Milled zircon, d50 ˜ 9 µm, was fused with caustic soda pearls in open reaction vessels at temperatures between 650°C and 850°C. Fusion times of 1, 2, 4, 24 and 336 hours (with intermittent milling) were investigated.For prolonged fusion times the fusion products approached equilibrium compositions. However, the phases Na2ZrSiO5 and Na4Zr2Si3O12 observed at 850°C did not form at 650°C. Since they do not hydrolyse in water they limit the recovery of alkali. For 2-hour fusions a broad spectrum of non-equilibrium reaction-products, that are rich in sodium silicates, is formed. Optimum process conditions, with respect to NaOH recovery, correspond to a 2:1 stoichiometry and fusing for 2-hour at 850°C. At these conditions the alkali recovery is ca. 78% and the zirconia yield is ca. 57%."

Jan 1, 2003

By Juan B. Yianatos

"After almost 100 years, since the first commercial application began in Australia, flotation has shown an extraordinary growth and nearly 2 billion tons of ore per year are presently treated by flotation processes. During this time flotation has promoted a wide scope of research activities ranging from fundamental chemistry and hydrodynamic studies to studies of industrial operations. In general, fundamental studies have been mainly related to ideal situations. In recent years, however, large efforts have been focusing on achieving a better insight into the actual sub-processes provided by the development of new and more sophisticated instrumentation. Since the massive incorporation of flotation columns, around 15 years ago, a renewed interest in flotation fundamental studies, process modelling and new cell designs have been observed worldwide. The key role of the froth has been recognized as an independent and sometimes rate limiting process step. Thus, separation of pulp and froth process stages seems the most appropriate in terms of process modelling, diagnostic, design and scale-up purposes.In relation to flotation equipment development, until the middle of the 1970’s, only the sub-aeration mechanical cells were dominant. Since the 1980’s, the use of pneumatic cells and forced air mechanical cells has emerged strongly. Also, in the last decade, flotation equipment has shown a dramatic increase in size, reaching values of 200m3 in unitary mechanical cells and more than 300m3 in columns. The general feeling, however, is that, despite the great advance observed in terms of process knowledge, the mechanisms and principles of industrial flotation cells design and scale-up are still not fully understood.Advances in process instrumentation and control now in use allow for more efficient operations, both in metallurgical performance and savings in operating costs."

Jan 1, 2003