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By L. Y. Feng

The percentage of leached zinc in massive zinc oxide ores (11.7% Zn, >2 mm) is up to 73.3 % in 120 days. Alternatively, crushed to -0.154 mm, mixed with cement 5% (wt), pelletized and solidified. The diameters of the pellets obtained are between 5 mm to 8 mm. When the pellet solidification periods are 3 days, 10 days and 45 days respectively, the alkaline leaching rates of zinc in the pellets are up to 95.8%, 89.1% and 76.4% respectively. Decreasing the solidification time can re-duce reaction time, increase dissolution of zinc in pellets and lower the effect of initial zinc concentration on leaching rate. The experiment results show that the minimum solidification time is three days, and the kinetic study indicates that alkaline leaching of the low grade zinc oxide pellets is controlled by the diffusion of the leach liquor through the gangue layer in the whole leach process, and the apparent rate constants are 3.33×10-2 day-1, 9.18×10-3 day-1, 5.82×10-3 day-1 respectively.

Jan 1, 2014

By U. S. Chattopadhyay

The estimated requirement of the nation by the year 2020 is approx. 80 Mt of steel and more than 0.2 million MW installed capacity of the electricity, thereby increasing the consumption of the coking and non-coking coal, which is expected to be in tune of about 75 Mt & 500 Mt respectively. One of the major deleterious factors in achieving the goal is the deteriorating quality of the feed coal used in both steel and power industries. Indian coking coals, in general, are typified by high ash, high inert (both organic and inorganic), low rank, low reactive macerals content, heterogeneous petrographic make-up, inferior coking properties and poor amenability to washing, thereby necessitating suitable washing measure. Coke-based steel industries in India require washed coking coal containing ash % varying between 17-19. The situation demands taking on immediate challenges to fill up the gap between the requirements and supply of coking coal. This paper reviews the R&D attempts in this laboratory and throws light on the key measures as long-term solution to the problem. Search for alternative source of coking coal, like LVC coal and their judicious preparation technology. The low volatile coking coal (LVCC) constitutes about 50% of the total coking coal reserves in India. These coals are characterized by high raw coal ash content (37 to 40%) and very difficult washability potential. If these coals are treated in the existing washeries, which are generally 2 or 3-product systems, the cost of clean coal is high as the byproduct sale value is low. It has been proposed to produce a new type of by product, which enjoys high demand and good coking properties.

Sep 1, 2012

Coal preparation plants usually operate with water in a closed circuit mode. In this practice, large quantities of water is continuously being recycled. To compensate the natural losses, only small quantity of fresh make up water is added into the circuit. As a result, a gradual build up of residual concentrations of flotation reagents (frothers, collectors, coagulates etc.) take place in the water and the concentration levels of the contaminants increase. Besides, the recycled water accumulates higher amounts of total dissolved components (1600 ppm) and hardness (740 ppm) than the fresh water. Nearly 80 ? 85% of the process water used in a coal preparation plant is utilized in treating the coal fines in flotation circuit. The presence of certain alkali earth metal ions (e.g., Ca++, Mg++) may adversely affect the flotation performance as they precipitate sparingly soluble hydroxyl complexes on the coal surface and change its surface charge. These studies showed that the use of recycled water in flotation has a significant effect on the selectivity and kinetics of the flotation process because, the dissolved compounds, both inorganic and organic, alter the chemistry radically. By treating the recycled water through a softening process, the concentrations of alkali earth metals and hardness were reduced significantly. The concentration of alkali earth metals and hardness were reduced to 10 ppm and 35 ppm respectively in the softened recycle water. From the selectivity studies, it has been observed that the flotation yield and recoveries increased by four to seven units by softening the recycled water. The kinetic studies indicated that the clean coal particles followed first-order kinetics. The kinetic parameters namely, flotation rate constant (k) and maximum recoveries (R8) of flotation, were found higher with softened recycle water than the recycled water. This reduces the residence time in the flotation cell and thereby, increases its productivity. Keywords: coal flotation, hardness of water, water chemistry, softening process, selectivity, kinetics, flotation rate constant and maximum recovery

Sep 1, 2012

By J. C. van Dyk

In a previous study by Van Dyk, et al., (2006) and Van Dyk et al. (2006), a FactSage model was developed to understand the chemistry and interpret mineral matter transformation during a fixed bed counter-current gasification process. It was concluded that the FactSage model developed, compared with HT-XRD experimental results and that the FactSage thermodynamic modeling sup-plies insight into specific mineral reactions and slag formation. The specific value for Sasol in using FactSage, in combination with HT-XRD is that it can be used to analyze equilibrium conditions for reactions occurring between inorganic and organic materials together, as well as to provide insight into mineral transformation and slag formation. The purpose of the present study was to improve the current FactSage modeling approach, by combining specific zones in the gasification process. This can improve and speed-up the interpretation of mineral matter transformations and flow properties of reacted mineral matter in coal and assist in identifying and quantifying slag formation in the gasifier operation at temperatures not reflected by normal AFT analyses. The updated and improved FactSage model compared favorably with the original model as well as with HT-XRD results and thus will be able to supply results in a faster and more convenient manner. In the new FactSage model, supported by HT-XRD experimental findings, it is indicated that feldspar formation (including anorthite) correlated with slag formation at temperatures around 1000°C and no slag formation in the base case coal was observed in the drying and devolitilization zone, as was to be expected. Feldspar is one is the mineral species which has the lowest AFT causing the most slag-liquid formation and forms probably as a product between the SiO2, Al2O3 and Ca-containing species. In the gasification zone it was clear that slag-liquid formed at a temperature of 1000°C, with a decrease in the feldspar content. Mullite formation was also observed in the base case sample in the temperature range 1000°C and 1100°C. The decrease in the amount of SiO2 at 1100°C is related to the formation of mullite, but also that the slag-liquid phase also contains an amount of SiO2 in the molten form.

Jan 1, 2014

By Z. F. Dai

The Thompson Nickel Belt, located in Northern Manitoba, Canada, contains more than 400 million tonnes of ultramafic low-grade nickel mineralization in 9 deposits. One of these, the Pipe deposit, was mined between 1971 and 1983 producing a Ni concentrate of 9% to 11% grade at 73% recovery. The operation was terminated because the poor recovery, low Ni grade and high MgO con-tent of the concentrate made processing this ore uneconomical at the metal prices prevailing at that time. Vale Inco is now re-evaluating these deposits with the intent of providing a new source of concentrate for its Thompson integrated processing facility. It is known that serpentine slimes coating on the sulphide surfaces are responsible for the poor metallurgy. Various desliming methods were tested including settling, elutriating, tabling and hydrocycloning. Hydrocycloning has proven to be the most effective means of desliming. With a feed assaying 0.70% Ni and 33% MgO, a rougher flotation concentrate assaying 22.7% Ni and 4.8% MgO was produced at a Ni recovery of 62.5% (relative to the feed to grinding), with no utilization of slimes dispersants. Another 16.6% Ni recovery was achieved in scavenger flotation resulting in a total Ni recovery of 79.1%. Batch flotation tests using various flowsheet configurations to optimize the grinding, desliming, reagentizing and flotation conditions are in progress.

Jan 1, 2014

By Chi Zhang, Junyi Wu

"With the increasing popularity of lithium cobalt oxide in lithium ion battery industry, which is driven by new energy vehicle and mobile device applications, the demand of cobalt is also growing rapidly in recent years. There is a significant trend of increasing investment on cobalt capacity in China, and the automation renovation is considered as an option of improving production efficiency. This study aimed at evaluating the practicability of stainless permanent cathode blank and automatic stripping process in cobalt electrowinning process. The purpose is to replace the old starter sheet process in cobalt electrowinning, which so far was used by most of cobalt refineries in China, but very labor intensive and exposed operators to serious aerosols that contained both cobalt and acid. In the old starter sheet process, the initial cobalt starter sheet is produced onto a plate made of titanium, while the titanium cathode blank and hanger bar fit the critical corrosive environment but is lack of mechanical strength for automatic production which has been mature in copper electrowinning process. To evaluate the proper materials instead of titanium, the coupon corrosion tests with different raw materials including 316L and other stainless steel grades were held for several months in production environment at a cobalt tank house in China. Following the comparison between titanium and other tested materials, a pilot production test in a cobalt tank house is also on-going.INTRODUCTION Cobalt has been known in early China and used in pottery glazes, and the ancient Greeks and Romans used its compounds to make colored glass since long time ago. The blue on the colored porcelain from the Tang Dynasty in China was also due to the presence of cobalt compounds. The word cobalt is known being derived from the German kobalt, from kobold meaning ""goblin"", because the cobalt-bearing blue ore, CoAsS, was called kobaltin in Europe in the Middle Ages, it may have been thought to be harmful to the health of the miners because of arsenic in the ores."

Jan 1, 2018

By J. J. Liu

In the Bayer process, control of alumina trihydrate particle size, oxalate stability and morphology and foaming is crucial for improving the yield and quality of alumina trihydrate. One way to economically achieve such control is to employ specifically developed chemical additives, termed, crystal growth modifiers (CGM?s). In this paper, the mechanism of action and practical application of CGM?s in the Bayer process are summarized. The application of CGM additives allows for both enhanced agglomeration and secondary nucleation control, and hence coarsening of the particles. Current research efforts have utilized the information gained from mechanistic studies to enhance the performance of CGM products. It was demonstrated in both laboratory tests and industrial operations that the newly developed CGM formulations have a range of properties with enhanced performance, compared to the current commercial products.

Jan 1, 2014

Vanadium-titanium magnetite from Panzhihua was crushed with open and closed circuit process by high pressure grinding roller (HPGR). The particle size characteristics of the crushed product were analyzed and the micro-cracks generated by HPGR during the crushing process were studied. The results showed that, in crushed products, the reduction ratio increases and the size distribution becomes more uniform with increasing of the pressure on roller?s surfaces. The fine fraction content of crushing products from -3.2 mm classification closed-circuit by HPGR increases obviously compared with that by Jaw Crusher and particle size distribution is more uniform. Large amount of intra-crystalline cracks and cleavage cracks are generated in vanadium-titanium magnetite crushed by HPGR, which makes the specific surface area larger and Bond grinding work index (objective particle size is 0.074 mm) decreased by 14.05% than that by Jaw Crusher. And the liberation degree of monomer of the product crushed by HPGR increased compared with that by Jaw Crusher with the similar fineness of grinding. Keywords: iron ore, high pressure grinding roller, micro-crack

Sep 1, 2012

Anglo American Platinum practices fine grinding in its processing plants to enhance the liberation of valuable minerals. If the fine particles of valuable minerals generated during fine grinding are not recovered during the flotation process, this could significantly contribute to the overall losses. This study examines the flotability of fine moncheite (PGE mineral) particles in a controlled environment (moncheite size distribution, concentration and liberation). A barren Norite ore ground to 40% and 80% passing 53µm was spiked, with four different size fractions of moncheite (-5, -10+5, -25+10 and -53+25µm) in order to evaluate the effect of particle size on flotation. The investigation also included the effect of energy input and collector dosage on the flotation of two moncheite size fractions, namely -5µm and -10+5µm. The results showed that the moncheite particle size has a significant impact on flotation. Coarse particles (-53+25µm) showed the highest Pt flotation kinetics and overall recoveries. The -5µm size fraction of moncheite could also be recovered by flotation, however, at a lower rate compared to the other size classes investigated. The increased collector dosage of 300g/t at the finer Norite grind of 80% passing 53µm enhanced the flotation rate of the -5µm size fraction of moncheite when compared to the lower collector dosage of 150g/t. The higher energy input during laboratory flotation, at an impeller speed of 1000rpm also increased the flotation rate of the -5µm size range, however, at a lower concentrate grade, when compared to the lower impeller speed of 700rpm. More favourable Pt flotation kinetics data was obtained for the -53 +25µm size fraction of moncheite at the fine Norite grind when compared to the coarse Norite grind. Keywords: flotation, moncheite, particle size, energy input and SIBX

Sep 1, 2012

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 V. K. Chandaliya

N-Methyl-2-pyrollidone (NMP) has already been proven a good solvent for extraction of coal. It is believed that organic components of coal are likely to be dissolved with the solvolytic power of NMP. During dissolution process, original coal also gets disintegrated and thus helps in further extraction. Coal extraction highly depends on temperature, coal to solvent ratio, N-Methyl-2-pyrollidone (NMP) to Ethylenediamine (EDA) ratio and the size of coal particles. The process has been established in the laboratory. There is no reference available beyond lab scale. In present study, we are running a bench scale plant with 40 kg/batch capacity. Design of experiment was done in such a way that the optimum zone of the process gets evaluated for clean coal having low ash with high yield. Bench scale plant trial was conducted based on optimum zone developed during design of experiments (DOE). From the DOE analysis it was observed that feed size and coal to solvent ratio are important parameters for this process. Total 27 experiments (four factors with 3 level of variation) were designed through Box-Behnken model. It was observed that -0.5 mm feed size of coal, 150 °C extraction temperature, 17:1 NMP to EDA ratio, 1:9 coal to solvent ratio was optimum conditions. The results obtained at optimum conditions are 50% clean coal yield with 5% ash.

Sep 1, 2012

By S. M. Mustakim

Red mud is the major waste material produced during digestion of bauxite ores with caustic soda in alumina production following the Bayer?s process. Its disposal remains a worldwide issue in terms of environmental concerns. A lot of research and developmental activities are going on throughout the world to find effective utilization of red mud, which involves various product developments. At present, building materials, industries are fast growing industrial sector where the need of various raw materials is enormous. The use of red mud in building material production is one of the options for conservation of natural resources and reduction of environmental pollution. A cost-effective and energy efficient mineral cementation process has been developed at CSIR-IMMT, Bhubaneswar for use of red mud in manufacture of building brick, block and aggregate. The red mud is an alkaline material, which contains both leachable and non-leachable soda along with different mineral constituents of alumina, iron and silica. The effort has been made to use the mineral constituents of red mud to develop cold setting building brick by mineral cementation process using a binder specially prepared from Portland Slag Cement, Lime, Gypsum and Alkali metal sulfates. The red mud has been used from 40 to 70% by weight along with fly ash and binder in development of cold setting building brick conforming to the specification of IS:12894:2002.

Sep 1, 2012

By Arun Appadurai

Pneumatic transport systems play a vital role in conveying discrete particles over a sizable distance with minimal energy consumption. However if such a system is not designed keeping particle physics in mind, it leads to intractable problems which could possibly assume dangerous proportions, including but not limited to expensive redesign of the entire system. This paper describes a novel method, which harnesses the powerful technique of Computational Fluid Dynamics (CFD) to investigate a problem occurring in rotary kilns using coal as a major fuel source. In some of the sites, a unique phenomenon of abnormally high CO emission was observed and owing to the highly random nature of occurrence, it was difficult to scientifically investigate the problem and its cause. Most of the published solutions for the high CO problem tend to concentrate on the incomplete combustion aspect of the kiln and resolve the situation by increasing the air supply thereby improving the stoichiometric ratio of combustion. This paper offers an alternate correlation that relates high CO emissions to the phenomenon of coal delivery fluctuations caused by the sub-standard operation of the coal transport system. A CFD model for the coal delivery pipe is validated by utilizing the actual process data sourced from the measurements taken from a functioning plant. The results of the model are used to derive correlative conditions that point to the unstable operating conditions of the coal delivery pipe prevalent in the industry. The conclusions are summarized into a series of recommendations for optimized design of coal delivery systems which are implemented in a pilot plant. The results irrevocably prove a statistically significant reduction in CO emissions without resorting to increased air supply and power consumption. Keywords:CFD, Pneumatic Conveying, Saltation Velocity, Particle Flow

Sep 1, 2012

By C. R. Mambote

Vanadium is an important metal that is used mainly in ferrous and non-ferrous alloys due to the high tensile strength, hardness, fatigue resistance and corrosion resistance. Vanadium consumption in the steel industry represents about 85% of the vanadium-bearing products produced worldwide. The primary sources of the metal are patronite, roscoelite, and mottramite. Vanadium has also been produced as a by-product of the uranium production program which uses carnotite ores as a source of uranium. Vanadiferous magnetite iron ores are used for producing vanadium as well. In addition, it is known that vanadium can be recovered from the ashes of crude oil and petroleum coke. The process for treating boiler residues, fly ash and petroleum coke is similar to the process used to treat spent catalysts and ores. However, some of these materials may contain high carbon that must be removed at specific stage of the operation. Several processes are available for obtaining vanadium from fly ash, such as roasting vanadium bearing materials in the presence of sodium salt. The salt roasted calcine is subsequently leached with an alkaline or acidic solution. To obtain a cal-cine from which the vanadium can subsequently be recovered, the carbon in the source materials has to be eliminated prior to the roasting process. Other processes use the conventional hydrometallurgical route, in which fly ash is leached with sulphuric acid to obtain an impure vanadium pentoxide. The impure vanadium pentoxide is then treated with a sodium carbonate solution under atmospheric conditions to subsequently precipitate vanadium as ammonium metavanadate. Actually, the salt roasting process is the only process used commercially. In the present study, the progress in the technology of vanadium extraction from secondary materials is reviewed. The perspectives and the challenges for new process development are discussed.

Jan 1, 2014

By G. F. Zhang

Yunnan mineral is a kind of containing Ta-Nb rare earth deposit, the most potential economic valuable element in it is Sc, and raw mineral has 17.0 g/t Sc. Take the character of Sc into account, the key problem in producing scandium chloride molten salt by adaptive technology is how to man-ufacturer anhydrous scandium chloride molten salt. During the course above, the key problem is that preventing Scandium chloride from being hy-drolyzed into ScOCl. The ScOCl content of molten salt not only affect purifying scandium but al-so do harm to the production of Mg-Al alloy. In order to restrain the creation of ScOCl, add ammo-nium chloride into molten salt. As long as ScOCl is created, it would be chloridized. Thus, during the course of dehydrating anhydrous chloride molten salt this method prevents scandium from hydrolyzing. Accordingly, the key phase of this producing course is eliminate ammonium chloride and the surplus crystal water, and the most crucial of it is restrain scandium chloride from being hydrolyzed into ScOCl. This research analyzed the theory that ammonium chloride is trend to be hydrolyzed into ammo-nium chloride, and propose the research scheme of restraining this process from creating ScOCl. The new process of restraining the generating of ScOCl and dehydration for crystal water rare earth chloride is adopted: Inert gas temperature increases rapidly to a certain degree to eliminate ammonium chloride and crystal water. The experimental research were done such as : the temperature of eliminating ammonium chloride and crystal water, amount of ammonium chloride, time, temperature growth speed, influence of inert gas flow toward to scandium percent hydrolysis, whereby, we conclude the optimal process condition in this period: Temperature: 400°C, proportion of oxidized scandium and ammonium chloride is 1:1.5(Proportion of oxidized scandium and additional salt is 1:5.4), time is 120minute, temperature growth speed is 10?/min inert gas flow is 5L/min.

Jan 1, 2014

By L. Rintala

The design of a hydrometallurgical process starts with the analysis of the raw materials to be treated, for example mineralogy, chemistry, deposit size are analysed. Based on this information suitable unit processes for pre-treatment, leaching, solution purification and product recovery are selected. Typically, process design for the new ore deposit relies on laboratory tests such as pre-treatment and leaching experiments. The experimental work is the most time consuming and expensive part of the process design. Reducing the number of experiments would shorten the time of designing a new flowsheet or development of new process technology. A large amount of information is available about the hydrometallurgical experiments and the amount is increasing continuously. For example, word search using ?hydrometallurgy? from Scopus database results in over 4 000 publications with the word in title, abstract or keywords. This number consists of 2 500 articles, 900 conference papers, and 90 reviews since 1972. The number of hydrometallurgical publications per year has increased from 13 in 1972 to 150-200 in the last few years. The objective of this study was to analyze how detailed data of experiments about the gold extraction is published and how that data could be exploited more effectively when designing hydrometallurgical processing for new ore. The leading idea is that similar ores should have the similar response in leaching. If the published information was used more efficiently, the amount of experiments would be reduced. More than 200 cases of experimental data of gold leaching have been analyzed for this study. There are over 30 factors that could be used in comparison when selecting process alternatives, but challenging fact is that not all these factors are documented in all publications. Results show that the usefulness of the published data in the development of hydrometallurgical flow sheet for gold using decision-support tools is not that straightforward. The quality of the published information about gold extraction varied between the publications and the descriptions of the raw materials, experimental arrangements and results were often missing details. Methods to normalize the data for description of the cases and a system to describe different features unambiguously are needed. Keywords: refractory gold, host mineral, leaching, data analysis, case-based reasoning

Sep 1, 2012

By U. M. J. Boin, E. V. Verhoef

Pyrometallurgical reactors constitute a key processing component in the total primary and industrial/recycling resource cycle, being involved both in primary smelting, converting and extraction, as well as the reprocessing of scrap, from aluminium cans to end-of-life automobiles. Therefore the pyrometallurgical reactor?s role in achieving sustainability is the central theme discussed in this paper since optimising their operation minimises waste, residue and offgas (NOx, dioxin, CO2) and maximises product quality and therefore efficiency. To effectively control the overall resource cycle, one needs to take a systems modelling approach of the whole cycle, seeking to also understand the dynamic process behaviour of the individual components of the cycle, and then especially the part that contributes most to the chemical conversion, namely the pyrometallurgical reactor. This paper highlights the role of pyrometallurgical thermodynamics in the whole resource cycle and specifically places equilibrium thermochemistry in the context of process dynamics where large, variable inventories are recycled or maintained within the system. This paper will therefore review the semi-empirical dynamic modelling tools, which are used to model complex systems with the specific goal of developing dynamic predictive models, which also include slag-alloy chemistry, towards controlling the recycling in a feed forward manner. To illustrate the primary production of metals, high carbon ferrochrome and Ni-Cu-matte smelting will be presented as a brief case study. Also fundamental studies in blast furnace and waste incineration kilns will be given. It also will show how the distributed nature of the chemistry of melts in the case of primary extraction, and industrial (recycling) materials such as recycled end-of-life vehicles, have a significant impact on the process outcomes and model predictions. It is therefore argued that the fundamental thermodynamics and kinetics in metallurgical reactors play a final crucial role in modelling the closed material cycle, but only when it is used in conjunction with process systems theory based on reconciled data for parameter estimation and model calibration. System models for aluminium and car recycling will be given as well as a dynamical system model that describes the interconnected material flows for Ag, Au, Bi, Cu, Fe, Ni, Pb, PGM, Sn and Zn for a study on lead-free solder.

Jan 1, 2003

By A. Shibayama

Soil contamination by organic compounds is one of the most concerned issues on polluted soil. It is well known that there are limited methods to remediate the contaminated soil on site. Especially, the in-situ method for contaminated soil is too difficult to de-contaminate the organic pollutant. In this study, the fundamental ability of soil remediation, which aimed to decrease oil concentration in, in-situ process, have been researched by using a high pressure gas generated from ?crush composition? on artificially oil contaminated soil. The n-hexadecane (n-C16H34) and other organic compounds were selected as soil oil contaminators, gravimetric analysis by soxhlet extraction and GC-MS were used as qualitative and quantitative analysing methods. For the experimental examination, the influences on the difference in the concentration of n-hexadecane (and other organics), the tamping amount, position and repetition of crush composition in soil, and scale (size) of experimental model were investigated. The n-hexadecane concentration reduced by the explosive effect of crush composition showed a reasonable decrease of about 30 wt%~60 wt% compared to the initial n-hexadecane. The removed amount of n-hexadecane and distance from explosion point of the crush composition was related in scale and model of contaminated soil.

Jan 1, 2014

By P. Condori

In spite of the importance of the slurry transport and discharge in autogenous and semiautogen-ous (AG/SAG) mills, it is evident that a more comprehensive and useful model is still required. Semi-empirical models used up to now have many limitations and cannot be used beyond the ranges in which they were developed. The breakage of particles as they are transported along a mill com-plicates the experimental analysis and the modelling of the transport process within the mill. The interaction of the grate discharge and the pulp lifters, with the added issue of backflow from the pulp chamber into the mill, makes the discharge modelling process difficult. In order to overcome these difficulties, a mechanistic approach has been applied. The general transport and discharge model was subdivided into four independent models: Flow through the charge, flow through the grate, flow in the pulp lifter, and flow-back. This paper gives an overall description of the modelling approach and discusses in particular the modelling of transport of fluids through the charge. In order to evaluate and calibrate the model, experimental work was carried out. To evaluate the gradient pressure under different conditions of charge packing and flow rate, a specialised experimental rig with a highly sensitive pressure gauge was used. Preliminary results identify the differences of the charge and grate on the restriction of flow. The existence of a dynamic voidage in our particular system was more evident and as a result, a semi-empirical correlation for the voidage was developed. In general, results show that the me-chanistic model derived from Ergun?s equation for flow through a packed bed can be satisfactorily adapted.

Jan 1, 2014

By M. M. Moghaddam

Charge motion is of prime importance in the efficiency of comminution in tumbling mills. Since direct observation of charge shape and its motion in industrial mill are not possible, a combination of analytical and physical studies was used to determine charge trajectory. Software packages, which predict charge motion such as the GMT (Grinding Media Trajectory) only consider the outermost layer of charge (single ball) and ignore the interactions of grinding elements. In this research, the measured charge trajectory in a 1m-diameter mill with the transparent end, called model mill, was compared with that of the GMT. Four types of polyurethane rings were accurately machined to scale down the liners arrangements at two industrial mills. To explore various charge shapes and trajectories, the model mill was operated at 55, 70 and 85% of critical speed for five levels of mill filling (10, 15, 20, 25 and 30% by volume). The angular displacement of the toe, toe departure, shoulder and charge impact point were determined from the photographs taken from the model mill. New relationships to predict charge shape and charge impact points were introduced to modify the GMT results. The relationships were validated by the model mill using the new liner of the Sarcheshmeh copper complex SAG mill. The relative error of prediction was found to be 1.1%. The results indicated that when the lifter face angle increased from 7 to 30º, the distance between the charge impact point and the toe decreased from 52 to 31º for 25% filling. This meant increasing the probability of charge impacting the toe not the liner which favoured more efficient comminution practice. After converting AG mills to SAG mills on account of liner profile change, 31% increase in throughput (from 419 to 548 t/h) in addition to 4% decrease in the product size (from 516 to 496 µm) were realized which was a significant contribution in the plant performance improvement.

Sep 1, 2012