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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 Mikhail I. Khersonskaya, Mark I. Mantsevich, Andrey V. Tarasov

"Due to depletion of the existing ore deposits the content of non-ferrous metals in produced ores has an inevitable tendency to decrease. Processing of low-grade ores is associated with production of low-grade selective concentrates and poses serious problems for the non-ferrous industry relating to increasing losses and expenses for waste treatment and disposal.The main component contaminating selective concentrates is iron sulphides.Copper-nickel, copper-zinc and polymetallic ores have been discussed as most important types of ores requiring removal of iron sulphides.One of the promising directions for development of selective flotation technology is the use of lowmolecular organic depressors. An advantage of organic compounds is in the possibility of multi-variant structure of organic molecules, which permits selection of a most efficient reagent for the given conditions. Another way for improving the grades of concentrates is concentration of valuable constituents associated with iron sulphides in an intermediate product and upgrading of the latter by chemical and metallurgical techniques.In order to remove iron from nickel concentrates, specific process conditions have been developed for selective flotation of pentlandite with the use of an organic depressor for pyrrhotite. The use of a depressor for flotation of high-grade copper-nickel ores ensures an increase in the nickel content up to 14% in the nickel concentrate produced as compared with 7% when using conventional process conditions, along with a nickel recovery improved by 2-3%."

Jan 1, 2003

By K. A. Natarajan

Interaction with microorganisms results in significant surface chemical changes on minerals. For example, chemolithotrophs such as Thiobacillus ferrooxidans and Thiobacillus thiooxidans significantly alter the surface chemistry of several sulfide minerals such as pyrite, chalcopyrite, sphalerite and galena. Heterotrophic bacteria such as Bacillus sp. could alter the electrokinetic properties of oxide minerals such as hematite, alumina, silica, kaolinite and calcite. Microbe-mineral interactions could thus be beneficially utilised in mineral beneficiation as different from bioleaching. Microbially induced mineral beneficiation unlike bioleaching deals with interfacial phenomena at mineral-solution-bacteria interfaces and surface chemical changes are brought about at very rapid rates amounting to a few minutes resulting in mineral separations in an aqueous medium.

Jan 1, 2003

By Sarah K. DeBono, Alan J. Monaghan, Emmanuel V. Manlapig, Gregory J. Harbort

"The Jameson Cell is a type of flotation machine in which air and pulp are brought together in a vertical tube called a downcomer. Within the downcomer the air and pulp are dispersed into a dense foam of fine bubbles, which creates a favourable environment for bubble-particle collision and subsequent collection of hydrophobic particles. The intense collection zone within the downcomer can be considered similar to the zone between the rotor and stator in mechanical flotation cells.Research into the bubble-particle collision and fluid dynamics of mechanical cells rotor-stator zone has been limited by the difficulty of achieving accurate measurements in production sized machines. With the Jameson Cell the downcomer is largely external and separated from the flotation tank, allowing ready access to the primary contacting zone for measurement and analysis.An investigation has been undertaken into the operating characteristics of the downcomer relating to bubble-particle collision. An effective mapping of the downcomer has been made through measurements of void fraction and bubble size taken across cross sections of the downcomer. Analysis of these measurements has provided an interpretation of the variations in the air and fluid dynamics, bubble size and distribution throughout the downcomer chamber."

Jan 1, 2003

By H. U. R. Kattentidt, W. L. Dalmijn, T. P. R. de Jong

"Research at Delft University aims to develop systems for automatic inspection and sorting of bulk solids which can be applied in the mineral processing and recycling industry. A recent development includes an automatic sorter based on airport X-ray inspection technology. It is designed for continuous inspection and sorting of 5 – 150 mm solids and has as objective a cost effective and high capacity on-line inspection and sorting.Dual energy X-ray transmission imaging provides instantaneous data about particle dimensions and the atomic number distribution. The system provides particle thickness and average atomic number on a pixel level at scanning speeds between 250 and 500 lines / second. With existing X-ray components inspection speeds between 0.5 and 2 m/s at approximately 1-meter inspection width and between 1.5*1.5 and 5*5 mm2 sensor resolution can be achieved.Imaging algorithms that were developed by Delft University for applications in recycling, waste cleaning and other applications acquire shape, size distribution and composition data. Currently on-line processing of a product at a rate of around 200 particles per second is possible using a standard PC. Experiments with a demonstration X-ray unit indicated good potential for various applications in solids processing. They include continuous inspection of organic content, sulphur, chlorine, ash, and metal distribution. It is applicable for coal cleaning, ore sorting, industrial minerals, and various applications within waste cleaning and recycling. Dual energy X-ray transmission fundamentals and recent progress in system development and applications are presented."

Jan 1, 2003

By Ralph J. Holmes, Victor Sharp, Steven J. Spencer, CSIRO Minerals, Kevin J. Davey, Jonathan J. Campbell, Peter L. Phillips

"Improved measurement tools for monitoring and control of AG/SAG mill performance have a high level of interest in industry. Historically, acoustic emission monitoring has been widely used on SAG/AG/ball mills and hydrocyclones to provide new information on the conditions inside these devices affecting their performance. The current work was focused on a new technique using surface vibration monitoring of a number of pilot-scale and production-scale AG/SAG mills to yield insights into the events occurring in the mills. The development of relationships between signal analysis outputs and mill operating conditions can be used for soft-sensor measurement of mill process variables. The technique used an array of accelerometers mounted on the mill lifter bolts linked to a fast data acquisition system which monitored the surface waves generated during operation. Details of the system are presented. Mill operating variables were adjusted systematically to provide a wide range of operating conditions for surface vibration signal collection. The experimental approach is discussed.The signals acquired during the experiments were analysed using a range of techniques. The results show that strong relationships exist between measured vibration power (both total power and within certain frequency bands) and mill load level/power and mill speed. A new method for extraction of power spectral density and band power information on features of interest in a mill rotation cycle is also presented."

Jan 1, 2003

By M. Barsky, E. Barsky

A study was conducted to elucidate the relationship between the hovering velocity and the particle settling velocity. The experiments were carried out in a water medium on five materials ranging in density from 1.070 to 4.000 kg/m3. Analysis of the results with allowance for the distribution of stream velocities over the cross section of the pipe revealed that the final settling velocity of the particles was equal to their local hovering velocity (on the stream axis), and not to the average velocity of vertical flow as is generally believed. It therefore follows that the kinetic structure of the stream must be taken into account when constructing theoretical models of the process for purposes of computation. In addition, the optimal stream velocity is not always equal to the hovering velocity and in fact is governed by other factors as well. Illustration is provided by the results of a study conducted in a vertical cascade classifier comprising eleven identical stages. The feed material was introduced at each stage successively beginning with the topmost (i* = 1 ) and ending with the lowermost (i* = 11). First, the stream velocity that yields optimum separation conditions at each stage of the cascade (i.e. k=50%, k being the yield of a given size class in the fines for a single stage) was sought. Subsequently the conditions of optimal separation for the instrument as a whole were determined (i.e. F(x) = 50%, F(x) being the yield of a given size class for the entire instrument). The results of the study are presented in the table.

Jan 1, 2003

By Scott C. Brown, Ivan U. Vakarelski

The particles commonly encountered in mineral benefication schemes have irregularites that are expressed at many different length scales. In part, this originates from preceding processes (e.g. makedown, comminution, handling and storage), which are known to chemically and physically modify the bulk particle and its surface. Interparticle tribology, dissolution and reprecipitation events along with large-scale mechanical stresses are just a handful of the interactions encountered during processing of particles prior to separation. It is feasible to imagine that each one of these events may impose a fingerprint of characteristic nanoscale, microscale, and macroscale morphological changes that can modify the overall interaction of these particles within a system. Suprisingly there are just a few works on how these resulting features can alter the performance of benefication schemes, and especially flotation.

Jan 1, 2003

By Xie Jiyuan, Hu Yuehua, Yang Songrong, Zhu Zhansheng, Qiu Guanzhou

"By the end of 2000, the first bio-oxidation plant in China that designed by ENFI come successfully into commercial operation in Yantai Gold Smeltery. Its capacity is 50t/d of refractory gold ore concentrate. After the extension, the capacity of bio-oxidation plant reached 80t/d of refractory gold ore concentrate at end of 2001.The refractory gold ore concentrate treated is from different gold mines. After proportionate feeding, the feed typically consists of Au (52.7g/t), S (24.42%), As (3.58%).The bacterial culture used in the bio-oxidation circuit is taken from a mine in south of China, and has been grown over 20 years on a variety of sulfide concentrates in a laboratory of mineral processing, and has shown to be adaptive to growth in a high concentrations of arsenic. It is a mixture of mesophilic microorganisms. The nutrients used in the bio-oxidation process are (NH4)2SO4, KH2PO4, KOH.Before feeding to bio-oxidation circuit, the concentrate would be milled to minus 43µm. The biooxidation product is fed to solid/liquid separation system that consists of a thickener and two press filters, solid from the system is fed to CCD circuit, liquid from the system is fed to neutralization area. The neutralized product is fed to another solid/liquid separation system, and the solid from the system is disposed of on a wasted quarry pit, the liquid from the system is returned to bio-oxidation circuit for reusing."

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 Patrick A. Turner, Timothy J. Olson, Abraham J. Schutte, Roman van Ommen

"The use of classifying devices in grinding circuits dates back to the early 1900’s when classifiers were installed to close ball mills. The search for ways to further improve grinding circuits led to the use of hydrocyclones in place of mechanical classifiers in South Africa in the early 1950’s. Today Hydrocyclones are considered as the best classifying devices to close grinding circuits. After 50 years of development the hydrocyclone has changed significantly when compared to the designs of the early days, but the focus to circuit optimization must be expanded to an understanding of the integral system consisting of mill, cyclone feed pump and cyclone.The key to good cyclone circuit design and operation in primary grinding circuits will be discussed including individual cyclone design features such as cone angle or materials of construction, as well as orientation and manifold configuration.Cyclone performance issues as well as maintenance considerations will be detailed in an effort to achieve consistent cyclone operation with minimal coarse solids in the overflow. “The importance of constant cyclone feed conditions is unquestioned today. The challenge of Cyclone sizing is a large number of not fully known variables prior to startup. The most significant unknown variable is slurry viscosity. Because of this, engineers often specify a conservative cyclone system that produces a finer than required separation. However, this approach often leads to higher circulating loads and a higher overflow density in order to produce the required separation. The higher cyclone overflow density results in a less efficient cyclone separation. The average concentrator can pick up 2-4% finer overall grind by having a more aggressive cyclone operation.”"

Jan 1, 2003

By Sami Makni, Ahmed Bouajila

"To remain competitive in an open market, mining companies are more and more requested to optimise their complex and highly multivariate processes. The increasing amount of process data, brought about by intensive use of instrumentation and the progress in computer data acquisition, enhances the need for more and more powerful and robust tools for the analysis and modelling of the process data. Now, with the emergence of multivariate data analysis (MDA) techniques, on-line clustering of mineral process behaviour is possible and could help in the extraction of valuable process operation indicators. MDA can be used in different mineral processes such as flotation, grinding, smelting etc. In this paper, the focus will be on grinding process as it is the one of the most costly node in the mineral processing scheme (i.e. power consuming) and it is a highly multivariable process. Particularly for primary grinding mills (SAG/AG), more instrumentation outputs and more powerful and significant process indicators are needed for efficient control and optimisation.MDA is a novel approach suitable for understanding mineral process behaviour compared to the traditionally approaches based on empirical and phenomenological modelling. Multivariate techniques can be used for several purposes. In this paper, the following objectives will be addressed:operation diagnosis: Shift differentiation and operation test differentiation can be showed by using MDA tools such as principle component analysis and factorial discriminant analysis.operation performance monitoring: operation regimes can be evaluated by clustering based on an economic criterion performance such as costs, tonnage, product quality, profit, etcIdentification of operation behaviour (monitoring) and selection of drift correction trajectories (control):MDA can be used to identify periods of unusual or abnormal process behaviour and to diagnose, if it is possible, causes for such behavior."

Jan 1, 2003

By B. C. Qi

"In water treatment, flocculation or coagulation with aluminium or ferric salts has been widely used for many years to remove natural organic matter (NOM), including humic acids. However, the adsorption of NOM to aluminium hydroxide flocs during conventional coagulation/flocculation processes is very complex, with the flocculation of aluminium hydroxide particles and the adsorption of NOM molecules on flocs occurring simultaneously. Any effect on the surface characteristics and micro-structures of the humic acids and aluminium hydroxides could affect the adsorption efficiency.It has been widely observed that if a reaction system (liquid-liquid or liquid-solid) is exposed to an ultrasound field, under appropriate conditions, a variety of physical (emulsification, aggregation/flocculation) or chemical (the production of radical and exited species; single electrotransfer) actions may be activated. Though the ultrasound effects have been used in biological and chemical decontamination in many conventional environmental protection practices, the idea to explore the ultrasound effects in the removal of humic acids by preformed aluminium hydroxide flocs is relatively new. In this paper, the effect of an in-situ ultrasonication on removal of the humic acids extracted from the acidification fermentation of lignocellulosic residues, by a preformed aluminium hydroxide, was evaluated; the effect of ultrasonication on the surface complexation of the humic acids with the preformed aluminium hydroxides was investigated."

Jan 1, 2003

By Jian Zhang, Yongfu Yu, Fuguang Zhang, Liping Che

There is one large-scaled iron ore deposit in Inner Mongolia of China, but it is very complex which includes about 170 types of minerals and 71 elements. The hematite, magnetite are mainly iron ores. It is difficult that the iron mineral can be separated efficiently by common dressing methods due to the complexity, and the iron concentrates in the mineral processing factory contains many foreign substance such as K, Na and Si so that the process in iron mill is influenced because of the foreign substance, so it is vital reducing the foreign substance.

Jan 1, 2003

By A. V. Nozhkina

"Transformation of diamond into graphite was investigated in the region of diamond metastability under the action of media chemically active relative to carbon in the temperature range from 770 K up to 2200 K and pressure range from 10-3 Pa up to 3 GPa/IV VIII group metals of periodic system and oxygen were used as media chemically active relative to diamond.Methods of electron diffraction, chemical analyses, emission spectroscopy and X-ray phase analyses were used for determination of the reaction products.It was found that in the region of diamond metastability the stage of catalytic phase transformation of diamond into graphite took place during the interaction between diamond and metal. Metal reduce activation energy for transition of diamond into graphite from 109,4 kcal/mole to 77,4 kcal/mole.Kinetic of phase transformation of diamond into graphite was investigated.Pressure does not considerably influence on the rate of phase transformation of diamond into graphite in the presence of transition metals."

Jan 1, 2003

By Wang Xiaotie, Yu Yongfu, Che Liping, Zhang Fuguang

The flotation process of native Rare Earth minerals such as bastnasite, monazite, mixed minerals of bastnasite and monazite, using the new effective collector Dh was studied in this paper, respectively, and the flotation properties are described. The good qualities of the new collector Dh were revealed through comparing with other collector of Rare Earth minerals. The test results of different ore samples show that at moderate pulp pH (8.5-9.5), Rare earth minerals can be effectively separated from barium, calcium and silicon bearing intergrowth minerals (barite, calcite and silicate minerals) and high quality Rare Earth concentrates can be obtained successfully by the new collector Dh, acid silica gel, turpentine and reagents fitting together rationally. In order to determine optimum technical conditions, the effect of pulp pH, pulp temperature, pulp density and the effect of dosage of reagents (Dh and acid silica gel) on the flotation were investigated in the test.

Jan 1, 2003

By Kazimierz St. Sztaba

"Mineral processing – the first technological stage of utilization of mineral – has a very long history. In particular, it revealed and reveals the continuous development and perfection of technological operations and process organization, comprising not only new design solutions and exploitation procedures but also, for example, perfected systems of control and automation as well as methods of process description and result evaluation. During the recent decades the attitude to mineral raw materials was clearly changed, both to the primary ones, i.e. minerals, and to the secondary ones, such as side products and waste, formerly considered useless and at present more commonly used. This results both from the appearance and growth of demand for more and more numerous components of mineral raw materials and also from the necessity of protection of natural resources, constituting the integral part of the system of sustained development of society.These circumstances, and especially the requirements concerning gaining some components which cannot be separated by means of “classical” (used for many years) technological processing operations and aiming at increasing the technological procedures, evoked the necessity of using new technological solutions, applying other basic operations, also the ones characteristic so far for other processing technologies, i.e. chemical, biotechnological and others.These development tendencies, in general commonly perceived, allow us to formulate an opinion that the former state of tasks and processes of mineral processing is being transformed into a qualitatively new form. It can be assumed that this process was signaled by a situation in which, due to the growing role of technological operations based on physicochemical phenomena (flotation and others), magnetic and electrical ones, etc., one should have observed that the former term of “mechanical processing” became inadequate for the real content of the notion determining the discussed stage of mineral utilization, so the adjective “mechanical” disappeared in most languages."

Jan 1, 2003

By Rebecca Hope, Derick Moolman, Frikkie Malan

"Despite the lip service that has been paid to pro-active plant maintenance processes over recent years, a significant portion of maintenance in industry is still reactive. The business driving force to prevent expensive production opportunity costs arising from “break-down maintenance” is obvious. Various benefits can be derived from successfully deploying remote equipment diagnosis technology and associated business processes.From an end-client’s viewpoint these include the ability to predict and take actions to prevent equipment breakdowns, increasing the lifetime of equipment by responding to appropriate operating instructions and therefore improving the return on capital expenditure. Better planning and scheduling of maintenance priorities and resources with performance measures like an Equipment Health Index are also possible. The knowledge that a qualified supplier engineer is constantly in touch with the operating conditions of their equipment, albeit remotely, is more than a comfort, and can be translated into quantifiable cost savings and improved supplier service levels."

Jan 1, 2003

By Johan C. van Dyk, Johan W. van Zyl, Martin J. Keyser

"Coal is a crucial feedstock for South Africa’s unique synfuels and petrochemicals from coal industry and it is used as the main feedstock to produce synthesis gas (CO and H2) via the Sasol-Lurgi Fixed Bed Dry Bottom gasification process. Detailed coal characteristics are essential to predict gasification behaviour when a specific coal source is to be gasified.The principle aim of this paper is to highlight and discuss those specific coal characteristics, which affect gasification behaviour and stability.In order to determine the suitability of a coal source for gasification purposes, the coal is characterized and the results compared with historical data. Benchmark data, where it was possible to operate the gasifier with ease and relatively high stability, is used as a reference.Coal sources with extreme properties (i.e. low reactivity, ash content <10% as is used by Dakota Gasification Company, or “brown coal” with moisture >30%) can probably be gasified in a Sasol-Lurgi Fixed Bed Dry Bottom gasifier provided that certain operational changes are implemented. Other properties, like high caking and extreme ash content for example, require blending to acceptable levels."

Jan 1, 2003

By Liping Yu Che, Xiaotie Wang, Mingli Cao, Jizu Yongfu Yuan

"It is difficult separating fluorite from Ca, Ba, Si intergrowth minerals than simple from Si, using common reagents such as combination of oleic acid or paraffin soap and water glass, but the finest quality fluorite concentrate whose grade is over 96%F must be required in chemical plant.This paper studies the flotation process of native fluorite from calcite, barite and silicate minerals whose flotation properties is similar to fluorite, using new effective collector H602 and new depressor S602 that is cheaper in cost, and describes the flotation properties. In order to determine optimum flotation separation condition, the effect of pulp pH, pulp temperature, pulp density and the effect of dosage of reagents on flotation were investigated and the flotation result was provided by oleic acid collector and the results of collector H602 were compared with those of collector oleic acid in the test. The test result of ore samples shows that at moderate pulp pH values (10.5-11.5) and other moderate technical conditions, the fluorite mineral can be obtained by new reagents and the rational reagents combination. The conclusion is 98%F of fluorite concentrate can be obtained, using the combination of H602 and S602 and only 5 steps in techniques. The paper discusses the mechanism of the flotation separation of fluorite mineral from intergrowth minerals."

Jan 1, 2003