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By O. Güven

In recent years, there is an increasing demand on manganese consumption which stems from the important role of manganese in carbon steel production. And the growing need for manganese ores makes the beneficiation of low-grade manganese ores more economical. In this study, the characterization and beneficiation studies were carried out to propose a flow sheet for typical low-grade Turkish manganese ores. For this aim, different gravity separation methods were applied. According to the mineralogical analysis, the major mineral phases are pyrolusite (MnO2) and psilomelane (MnO2) while the major gangue mineral is radiolarite. Gravity separation tests were accomplished by using jigs, shaking table, MGS (Multi Gravity Separator) and in order to obtain products with high Mn ratio, high intensity magnetic separation was also performed. As a result, different combinations of flow sheets were utilized and a concentrate assaying 56.5% Mn with 85 % recovery was obtained.

Sep 1, 2012

By Mary Stewart, Jim G. Petrie, Geoff Brent

"Life Cycle Assessment (LCA) is gaining increasing acceptance as a decision-support tool by which to evaluate the environmental performance of a product, process or service. This is evidenced by its inclusion in international policy documents (for example in the European Union’s Integrated Product Policy) and in environmental management standards (the ISO 14 040 series of environmental management codes relate to LCA). In response to this, the minerals industry has conducted a number of commodity-specific LCAs. These include studies for global production of a number of commodities including copper, nickel, aluminium and steel. In addition, a number of minerals companies profess to use LCA as part of their suite of project and technology assessment tools. Often, this collected use represents more a situation of “we do this because we’re told it’s good for business” rather than from any demonstrable evidence of this fact. This has led to a situation of much confusion and disillusionment within the industry, exacerbated by the obvious current limitations of LCA to accurately reflect the environmental performance of minerals and metals.Our point of departure here is that LCA, conforming as it does to the tenets of environmental systems analysis, is a valuable starting point, and that there is merit in exploring to what extent the methodology can be enhanced to better reflect the environmental performance of minerals and metals. Specifically, we explore here the further development of LCA to address the following:• Land Use issues• Consumption of Abiotic Resources including metallic and non-metallic minerals, water and soil)• Human and Eco-toxicity issues relating to mobility and bio-availability of metals• Salinityand address these through selected experimental and simulation case studies relating to energy- and base minerals production. Advances resulting from the United Nations Environment Programme/Society for Environmental Toxicology and Chemistry Life Cycle Initiative are presented in that they directly affect the application of LCA to mining, minerals and metals. Comments are offered on how best the mining and minerals industry might interface with future developments resulting from this Initiative in order that the Initiative can deliver outcomes which render LCA a useful tool for decision making in mining and minerals processing."

Jan 1, 2003

By Montaser S. EL Salmawy, Takahide Wakamatsu, Eishi Kusaka

"In conventional flotation, fluoride ions selectively would react with the aluminum site on the microcline surface and produce negative charged sites for amine to be adsorbed (Smith, 1976). According to this view, aluminum site is considered as a key feature in feldspar flotation. Generally, fluoride ion has been widely used as a modifying agent in silicate flotation. Since O'Meara's patent appeared on HF -amine reagent system to selectively float feldspar from quartz in 1942, relatively few contributions have been devoted in this issue. The reason might be that the process works very well, and accordingly there is no initiative to investigate in this area. However, due to the awareness of international community to restrict using of hazardous reagents like HF, sound engineering practice to search for alternative methods, not utilizing HF, has been launched. Inspection of literature, one can find several works dealing with this issue.In this contribution, the effect of ethoxylation of long chain alcohols on the quartz and feldspar flotation behaviors was investigated for surfactants of the octylphenol polyoxyethylene family. The tests were carried out with an average of 7.5 (Triton X 114), 9.5 (Triton X 100), 30 (Triton X305), 40 (Triton X 405) and 70 (TritonX 705) oxyethylene units. Electrokinetic and flotation studies on quartz have shown that at low pH values, quartz could be floated with polyoxyethylene octytlphenols. The possible mode of adsorption of these nonionic surfactants may be suggested to be due to hydrogen bonding between the oxygen of ether and hydrogen in the free hydroxyl groups on quartz surface. It was anticipated that the selectivity between quartz and microcline would decrease as oxyethylenic chain length increases."

Jan 1, 2003

By Jim Petrie, Mary Stewart, Damien Giurco

This paper describes a generic approach to analysing the environmental and economic performance of a generic global mineral/metal value chain, with the express view of improving the quality of prospective decision-making within the industry in order to ensure more sustainable outcomes. As a point of departure we propose that it is not possible to place metals in the context of the sustainable development of society without paying due regard to the entire metals value chain. Thus, the starting point for this analysis is the development of a global stocks flows and transformations model, for the metal of interest. Any aspect of the value chain, e.g. “metals refining, “goods manufacture”, “use and disposal”, can be assessed, either relative to other stages in the value chain, or in more detail by focusing on the technologies used within that stage. The use of this model as a decision support tool is explored here for the case of copper. Both primary and secondary production routes are enumerated, covering a range of processes, for seven distinct geographic regions around the globe. The value of the modelling approach is explored for different energy mixes. In particular, the case study examines the impact of increased recycling on the (re) distribution of global and regional environmental impacts for technologies-in-place in these different regions. The aim of these case studies is to highlight to the minerals processing and metals refining industries their potential role in a more sustainable global society.

Jan 1, 2003

By M. Barsky, A. Govorov, E. Barsky

A study was conducted to determine the structure and lifting capacity of a two-phase stream in a vertical pipe at different distances from the point of introduction of the material into the instrument. Stream velocity was set at 2.8, 4.0, 4.8, 5.6 and 6.25 m/sec to ensure separation regimes. It was found that the llifting capacity of the two-phase stream exceeded that of pure air by a factor of three or more, and that in a turbulent regime the velocity curve displayed marked deformation, becoming more rounded and tending towards a parabola. The following formula was obtained for entrainment of a given size fraction under turbulent, laminar and transitional particle flow regimes:

Jan 1, 2003

By Francesco Vegliò, Luigi Toro, Francesca Pagnanelli

"Different hydrometallurgical processes have been studied in order to recover manganese(II) from oxidised minerals such as MnO2 (Vegliò and Toro, 1994). An innovative acid reductive leaching carried out in soft experimental conditions was here considered using agro-industrial wastes containing carbohydrates as reducing agents (Vegliò et al., 1998).The leaching process was investigated from a kinetic and equilibrium point of view in order to optimize the experimental conditions and obtain high purity and concentrated MnSO4 solutions.The overall leaching process (not considering the complex network of intermediate oxidation reactions of the carbohydrates in hot sulphuric acid medium (Vegliò and Toro, 1994)) can be described by the following reaction:24 MnO2 + C12H22O11 + 48 H 24 Mn2+ + 12 CO2 + 35 H2O (1)A Shrinking Core Model (SCM) was modified by a variable activation energy term to take into account both the variable reagent concentrations and the reaction rate change with respect to the manganese dioxide conversion. The influence of the particle size in the kinetic model is discussed with the support of SEM analysis and BET surface measurements before and after leaching.Manganese extraction yield was maximised (170-190 g/L) using appropriate carbohydrates and acid excesses, while impurity concentrations were kept low (Fe<10ppm and Ca<300ppm) pre-treating the ores, using hydroalcoholic leaching medium and different combinations of down-stream processes. In particular precipitation, solvent extraction and adsorption onto active carbon were tested to eliminate Fe and Ca from MnSO4 solutions."

Jan 1, 2003

By A. C. Maffei, M. V. Lins Gonçalves

Ore concentration processes are a function of the respective particle size distribution; however, most of them do not use an efficient operational method to determine it. From a practical point of view, the surface area can be calculated for any size analysis. The physical principles for determining the size distribution in each method are different, for the results will not be compared directly. During the development of the research project of the sulfide ore flotation method using inert gas, different methods for calculating the specific surface area have been used, such as sieving, sedimentation/X-ray, laser diffraction and BET, i.e. specific techniques to determine the specific surface area of copper and gold ore concentrates. The statistical method of minimum squares was used to achieve practical correlation equations among them. Regarding these two ores, if one knows a specific surface area value using one of the methods above, one can predict the result of the others. Diminution of the reagent consumption was so controlled and it could be even decreased by using inert gas.

Jan 1, 2003

By A. F. Raschenko, Y. A. Golodcov, V. V. Elshin

"The autoclave noble metal desorption in apparatuses with a dense stationary sorbent layer is perspective for the technology of sorption gold and silver extraction from solutions and pulps by carbon sorbents. The study of the mechanism and optimization of the autoclave desorption process involve some difficulties. To overcome them it is necessary to use mathematical and quantum-chemical modelling. The given paper deals with a mathematical model for the dynamics of gold and silver desorption from active carbons by alkali solutions based on the physical-chemical notions of the process. The kinetics and the mechanism of the process were investigated using the mathematical model for gold and silver desorption.The calculation of the efficient mass-transfer coefficient (ße) for various initial and intermediate noble metal concentrations in carbon (Cy) made it possible to find that the dependence of ße on Cy in case of gold desoprtion shows a clear extreme character. The value of the initial metal concentration in carbon therewith does not influence the character of the curve the inflection point of which is changed essentially at elevated process temperatures only. The revealed characteristic property, in the author's opinion can only be indicative of the change in the mechanism of gold desorption under autoclave desorption conditions. The assumed [Au(CN)(OH)]- type intermediate that has a higher diffusion coefficient in comparison with the adsorbed complex [Au(CN)2]- can be considered as an intermediate compound in the process of gold desorption."

Jan 1, 2003

By M. Salas, L. Rolf, H. Z. Kuyumcu

"Industrial use of abrasive stress takes place in the area of fine grinding and in order to clean surface contaminated soil particles. Also, at many mechanical operations abrasion emerge as an unintended side effect. At the Institute for Raw and Waste Material Processing at the Technical University of Berlin systematic investigations are carried out, to further the knowledge regarding the dependence of abrasion process on material properties and stress mechanisms as a basis for design and optimisation of the process or for its avoidance. Aim was the mathematical description of the abrasion process running with a single particle stress. For the purpose of investigations an agitation cell was used. Limestone served as material.In the presented work the influence of particle diameter, particle shape and collision energy on the mass and particle size distribution of abrasion debris was studied. The surface geometry of the particle was characterised by the particle shape factor ?x and the particle diameter dp. The particle shape factor ?x stays in direct relation with the abrasion degree x, and can be substituted by a mathematical function of x.Physically the particle shape factor ?x can be interpreted as a proportion of abrasive stresses splitting up complete crystals and crystal fragments. These two different mechanisms depend on different ratios of curvature of the surface of the stressed particle. The abrasive stress of strongly curved surface areas leads to separation of complete crystals. The abrasive stress of weakly curved surface areas leads to separation of crystals fragments. Accordingly the mass of wear mAb and median diameter of the abrasion debris d50 are different. The derived mathematical relations consider this behaviour by the particle shape factor ?x , which represents the ratio of the mixture of both stress mechanisms. The dependence of the particle shape factor ?x on the abrasion degree x with an exponent approximately to 2/3 points out that the particle shape factor ?x represents a surface area relation."

Jan 1, 2003

By Peter N. Holtham, Mary M. Ng

"Resistivity measurements of minerals in the laboratory are commonly made with a low DC voltage source. Common test voltages specified in the ASTM Standard D257 are 100, 250, 500, 1000, 2500, 5000, 10000 and 15000 V, however 100 and 500 V are the most frequently used. Resistivity results obtained in the laboratory have been used to infer the electrical behaviour of minerals undergoing electrostatic separation. However because the voltages employed in electrostatic separation in the plant are of the order of thousands of volts, typically greater than 15000 V, whether the laboratory results are applicable as a predictor of plant performance is a critical question. It is unclear whether resistivity values taken at a low voltage are characteristic of those seen in electrostatic separation, in which the minerals are exposed to a much higher voltage. No definitive answer could be found in the literature.In this work, the resistivities of zircon, rutile and ilmenite were measured in a corona field for the first time. The measurement principle was based on a technique developed to measure fly ash resistivity in electrostatic precipitators, however the test apparatus and findings are novel.Resistivities of rutile and zircon were found to be easy to measure. The values measured in a corona field were several orders of magnitude less than those obtained with a dc voltage of 100 V. Evidence of back corona was observed with zircon. When the voltage drop was greater than the sample layer could withstand a localised electrical stress developed, resulting in a voltage breakdown, at which point a sudden surge of corona current (back corona) was detected in the sample layer. Rutile, on the other hand, exposed to the same conditions as that of zircon (i.e. same temperature and applied voltage) did not exhibit any sign of back corona. Its resistivity across the range of test voltages (14 to 33 kV) remained fairly constant."

Jan 1, 2003

By Hamid-Reza Manouchehri

"The triboelectric charge attributes of some silicate minerals (i.e., feldspar, quartz and wollastonite) after contacting different triboecharging medium made of different materials were studied. The charge acquisitions by different size fractions of minerals were monitored and accordingly the energetic work function values, i.e., the main parameter determining the entity of triboelectric charges acquired by mineral grains, of the examined minerals were estimated. Moreover the separation behavior of different size fractions of these minerals through the electric field of a laboratory free-falling separator when the mineral grains are charged by different tribochargers were observed and considered as the electrical separation potential of the examined minerals.Furthermore, the role of adsorption of different chemical species on triboelectric charge characteristics and charge acquisition of mineral samples were described from theoretical point of view and the effects of some chemical reagents on triboelectric charge acquisition of the examined minerals were studied. In addition the separation behavior of chemically conditioned quartz, feldspar and wollastonite minerals, using different anionic and cationic reagents, through the electric field of a free-fall electrostatic separator before and after chemical conditioning were monitored.Finally an attempt was made to translate the findings from single mineral systems to a complex silicate ore, containing mainly of feldspars, quartz, and wollastonite. Different separation tests under various conditions were conducted to this complex silicate ore. Before passing through the separation device, the ore sample was conditioned by different cationic and anionic reagents and then was triboelectricaly charged by different tribocharging medium in order to find the effective reagent and tribocharging medium for separating silicates. Besides the role of temperature and humidity of the surrounding ambient in separation behavior were considered."

Jan 1, 2003

By Kal Sastry, Anshuman Prasad

"Agglomeration of fine iron ore concentrates is carried out in two steps:Balling, which refers to the production of green pellets by tumbling moist fines powders in drums, discs, or cones, and Induration, which refers to the subsequent thermal treatment of the green pellets in straight grate or grate-kiln systems.This paper addresses computer simulation of balling or green pelletization step. The process of agglomeration from a mechanistic point of view can be described as the transformation of moist feed to well-formed species or pellets. The moist feed is composed of fines of infinitesimal size while well-formed species are of finite size and number. These well-formed species undergo changes in their size and number through different mechanisms of agglomerate formation and growth. Nucleation, coalescence and layering are the three main mechanisms that describe the formation and growth of granules during an agglomeration process. A population balance equation enables quantitative description of the evolution of agglomerate size distribution due to the occurrence of each of the mechanisms.A numerical solution for the population balance model is necessary and is obtained by the use of a sizediscretization approach. The numerical solutions provide a suitable basis for the analysis of the agglomeration process. Also a coalescence kernel has been introduced that is capable of describing the simultaneous occurrence of nucleation, coalescence and layering mechanisms. The effect of feed moisture has been described using a moisture factor with an exponential functional dependence on the moisture content. The effect of the feed to seed ratio is modelled by the introduction of a crowding factor. It was assumed that only the feed particles which are much more in number experience a crowding or restricted in space interactions effect. A computer simulation program has been developed with MATLAB as the simulation language."

Jan 1, 2003

By M. S. Prithvi

Over the decades, mine and mineral processing plant operations for the most part, have been found to have had adverse impacts on the environment. At the same time, mineral processing and mining operations produce mineral products that are indispensable to modern society. Thus, the sector has desirable and undesirable attributes simultaneously. The situation presents itself as a contradiction (i.e.) the mineral processing and mining operations are wanted by society, and at the same time unwanted by society. The existing methods of addressing the issues raised above have evidently not been very successful in reducing the opposition to new projects and to the related activities such as land acquisition. This paper attempts to show the relevance and applicability of TRIZ for addressing the issue. TRIZ, or Teoriya Rezheniya Isobretatelski Zadach, is a Russian acronym meaning Theory of Inventive Problem Solving. TRIZ is a powerful tool that can be usefully applied to resolve such contradictions, using resources usually available within the system of interest. Accordingly, this paper introduces the issue background, followed by an introduction to some key concepts of TRIZ such as the 40 principles, separation principles and directed evolution. The paper goes on to apply the 40 principles to two case studies. The results show that TRIZ could be a useful tool to generate potentially innovative and sustainable approaches. Its most appropriate position would be as a supplement to current decision-making procedures, and as a validation tool to review existing solutions for possible improvements. Keywords: minerals, environment, TRIZ, contradiction, resources

Sep 1, 2012

By Takashi Furuyama, Sukeyuki Mori, Ltd. Kyushu Metal Industry Co., Abel Bissombolo, Yoshitsugu Koga, Masamichi Hata

"Actually, the recovery of valuable metals such as iron, aluminium and copper is a nowadays practice in factories dealing with the processing of scrapped automobiles (Harder (WERG); Koga et al., 1997). This process has reach a recycling rate of about 75%, and generates a huge volume of waste (including cottons, sponge, plastics, rubber, etc…), locally known as “shredder dust”, which is commonly dumped on landfills; its recycling is either unsatisfactorily or not yet performed (Keller and Schebdat, 2000).The saturation and depletion of valuable disposal sites in the not-so-distant future, as well as the social and environmental problems related to the accumulation of these residues disposals are a major challenge for the automobile shredding industry.To promote an alternative way for the management of these disposals, the authors have initiated and developed a system for their processing, on the basis that more than 90% of these residues are combustible materials that could be used as refuses derived fuel. The developed processing system points out the mechanical/physical separation of a calibrated (–80+5mm) shredded automobiles residues into two streams by means of an ascending airflow passing through a vertical zigzag separator and, the compaction of the light-weight materials (that is about 60% of auto shredder residue recovered as float products and mainly composed of cotton, sponges and light plastics) to form a refuse derived fuel (RDF), the density, calorific value and ignition loss of which are 1.19 g/cm3, 4470 kcal/kg and 60.7%, respectively. A sedimentation tank is used to recover the light-weight materials deported in the heavy fraction stream."

Jan 1, 2003

By Ronald Smeink, Ton de Gouw

"Reagents are an important cost-factor in the flotation of minerals. The mechanism of collectors and frothers has been studied extensively, but on depressants – probably the biggest cost-factor in the reagent suite – very little is actually known. Theories are frequently faced with the bare facts, pointing in another direction. Fundamental research is complicated by the fact that the amount of possible interactions in the flotation cell is almost unlimited and makes “change-one-parameter-at-a-time” experiments questionable and at least difficult to interpret. Also, the adsorption of depressants on the ore is very strong and desorption merely impossible. Detection methods therefore tend to be indirect and – therefore - non-specific about the location of the depressant on the ore.Depressants are supposed to adsorb selectively on gangue minerals; not on the valuable minerals in the froth. In order to be able to develop better and ‘’smarter’’ depressants, an analytical method is therefore required that will enable to detect which (=qualitatively) depressant, in which concentration (=quantitatively) sits where exactly (= selectively) on the mineral surface. (Answering the question: ‘’ Which minerals is located direct under the depressant?’’)And also: does the depressant compete with other reagents for that location? (like collectors) This analytical method is under development. The actual status of the method is promising and the results will be shown."

Jan 1, 2003

By Jochen Petersen, Harro von Blottnitz

"The landfill disposal of slags is common practice in the metallurgical industry. Chromium may be a minor constituent in many cases. It is present mostly in the form of chromites, which are considered environmentally benign and hence safe for disposal. Wastewaters from metal finishing operations are most commonly treated by reduction and precipitation of dissolved metals, including chromium, by lime addition, and subsequent landfill disposal of the resulting sludge. The metals contained in such sludges are mostly in the form of hydroxides, and as such considered environmentally stable.Thermodynamically, trivalent chromium, which is the predominant form in these waste materials, can be oxidised to the hexavalent form by atmospheric oxygen. Detailed research work on both slags and sludges has shown that a gradual emergence of hexavalent chromium can indeed be observed. The mechanism is governed by close physical contact between chromium oxide (or hydroxide) phases on the one side and calcium oxide (or hydroxide), which is present as flux in slags and residual lime in sludges, on the other. If oxygen can migrate to the points of contact, gradual formation of calcium chromate ensues.Hexavalent chromium is associated with high environmental toxicity, and hence undesirable in landfilled materials. Moisture migrating through landfill deposits can mobilise the highly soluble chromates and thus potentially transport them into natural waterways. Such gradual release from stainless steel and ferrochromium slag deposits has been demonstrated in a column experiment."

Jan 1, 2003

By G. Weingrill, H. Flachberger, J. Neubacher

The so called Bublon®-process is an innovative process for the controlled expansion of volcanic glasses such as Perlite and for thermal treatment of other minerals. In this manner, functional light fillers with astonishingly altered physical properties can be manufactured. In contrast to conventional Perlite expanding processes no fossil fuels are burned in order to achieve the expansion. Instead, the feed material is heated electrically mainly by radiation based on heat transfer from heating elements. The main advantage is the better controllability of the production process. Therefore, the heating elements are segmented along the flow of the particles, hence in direction of the ongoing expansion. Overheating of the particles, which ultimately leads to the destruction of the particle surfaces and consequently decreasing the quality of the expansion product, can be reduced significantly. Due to flow characteristics and settling behaviors of fines the lower particle size limit of the feed in this process is restricted to not less than 100 µm. Otherwise process instabilities are to be expected. Manufacturing industry demands light and fine hollow microspheres. Therefore, a proven cooperation between Montanuniversität Leoben and Bublon GmbH was formed to develop a new process called ‘Bublite’. This issue was addressed by changing the conveying principle into a pneumatically conveying system transporting particles from the bottom to the top of the kiln by the means of a drag flow. This approach makes it possible to handle the difficult flow patterns in the kiln and to control the retention time of the particles in the heat transfer zone. As a result, it is now possible to expand very fine Perlite particles into a high quality functional lightweight filler with a glazed-closed surface. The dependence of the polymer industry on importing this kind of fillers from overseas can be reduced by producing it close to sites of demand. Also the Perlite mining and processing companies benefit from this technology because the mine lifespan and the output of the processing plant can be increased.

Jan 1, 2018

By Gökçe Törenli, Okay Tutar

"Predicting the performance of plant-scale comminution circuits is essential to monitor the energy use and product size distribution, allowing us to control and optimize the whole process. In the light of this issue, with the assist of recent technologies, simulation techniques utilize the chance of putting the theory into practice in the most accurate way. For this purpose, this study aims to evaluate and optimize the efficiency of a plant-scale ball mill circuit by using perfect-mixing ball mill model on a simulation environment. The comminution circuit is selected from a specific copper-ore processing plant in Turkey. The essential parameters which are required for this study such as fresh feed Bond work index, size distribution etc. are determined by laboratory experiments. The forecasted data which are calculated by third-party software will be compared by the industrial operating data, in order to determine the performance of comminution circuit. In addition to that, this methodology provides a greater ability to analyse, optimize and understand the comminution circuit of ore treatment plant. The authors believe this work will provide supplementary data for further studies on simulation and subsequent optimization of comminution circuits.INTRODUCTION By the assist of mathematical models of the grinding mills and classifiers, simulation of the grinding circuits become more common in comminution because it is relatively economical and able to consider many variables simultaneously. It’s proceeds depends on the accuracy of the models and capability of reflect real operations. Computer-based simulation studies would provide the quantified information about the effects of the proposed changes on the comminution circuit performance in terms of size distribution, mass flow rates, equipment efficiency etc. Then the mentioned data used in order to check the suitability of the current equipment to the modified conditions, and for equipment selection. The outputs of circuit could also be used to estimate downstream flotation circuit performance because the general aim in this study is to The aim of the study is to investigate optimum operating variables and achieve p(80) size of 57 µm and 64 % of -36 µm particle in hydrocyclone overflow stream, which is optimum for that porphyritic copper ore for best concentrate recovery after flotation process in specific copper ore comminution circuit by using modelling and simulation techniques. Sampling survey was carried on the fine ore bin in order to perform Bond work index test and determine work index value (Wi). Thereafter mass balancing, using the size distribution data and tonnages, models for ball mills and hydrocyclone were developed. Finally, the circuit performance were investigated by computer simulations via JKSimMet software."

Jan 1, 2018

By Seoul National University, Ki-Ho Kim, Jong-Pyo Kim, Sung-Min Joo, Hee-Chan Cho, Hyung-Seok Kim

Aragonite was synthesized in addition of Mg2+ ion and SrCO3 seed by carbonation process, and the best condition and mechanism of the synthesis was studied by analysis of continuous pH change, ICP, XRD, and SEM. As MgCl2•6H2O addition increased, aragonite phase increased at condition of CO2 flow rate of 100 mL/min and stirring rate of 250 rpm. It was the dissolution of Mg(OH)2 that determined overall reaction time. As SrCO3 seed addition increased at 0.2 mole MgCl2•6H2O, the amount of aragonite increased and the aspect ratio was from 5 to 9. And it was thought that Mg2+ ion prohibited calcitetransformation of aragonite formed by SrCO3.

Jan 1, 2003

By Johann Botha, Niel de Clerk, Tony B. Lange

"PROCESS COMPLEXITYDespite many years of research and development, mineral and metallurgical processes are in general highly complex and still difficult to understand and control. One of the biggest factors contributing to this complexity is the highly non-linear, multivariate, chaotic nature of such processes.This complexity is magnified in production environments where business optimisation rather than beneficiation is the primary objective. Return on investment, sustainability, and social issues such as Aids and the environment all form part of the goal hierarchy of industrial concerns. In addition, international competition and price volatility all have a huge impact on these processes in terms of operational constraints.Therefore the optimisation and control of beneficiation processes must take into account many factors other than pure process variables such as flow rates and levels. For example, commodity prices and client requirements all need to be added to the control problem, which together with incomplete process knowledge and non-linearities etc., make automation and optimisation extremely difficult.The ideal solution is to have a controller which in addition to performing full non-linear constrained optimal control can at the same time take into account other non-process factors such as price and client satisfaction."

Jan 1, 2003