Search Documents

The introduction and subsequent ascendancy of autogenous and semi-autogenous milling for comminution circuits has undoubtedly lead to many economic advantages. From a process viewpoint, however, at least one downside has been the sensitivity of these machines to process input variations. Foremost among these is ore competence, though feed size comes a close second. This sensitivity is due to the reliance of ag/sag mills on the feed ore for their grinding media competence and size. Autogenous (ag) mills are the most sensitive in this respect with semi-autogenous (sag) mills being increasingly less so as the ball charge is increased. Increasingly designers and operators are recognising the importance of feed size and the benefits of manipulating it to improve performance. This has been achieved by installing additional crushing/screening capacity ahead of the ag/sag, better operation of the primary crusher, better control of segregation cased by stockpiles and bins and by changing blast design/practices to modify the ROM size distribution. This paper describes the influence of feed size distribution on ag/sag mill performance with reference to a range of plant data. It particularly concentrates on how changing blasting practice to modify ag/sag feed size can have a considerable overall benefit.

Jan 1, 2003

By M. T. Spyridopolous, S. J. Neethling

"There has been a significant research interest in the stability of single thin films, including prediction of their failure based on disjoining pressure and film thickness experiments and DLVO theory. It is, however, notoriously difficult to correlate information on the failure of a single thin film with measurements of foam stability. This is particularly true for the prediction of dynamic foam stability indicators, such as equilibrium froth height and surface bubble size.An alternative experimental approach to studying single thin film failure for predicting foam stability is to measure directly the coalescence probability between two approaching bubbles in a surfactant solution. These experiments can be performed under different chemical and physical conditions by using a micromanipulator that allows variation of bubble size, surfactant concentration, approach velocity and stationary position. The interface radius of curvature, the time to coalescence and the film area between the bubbles can be measured directly using image analysis.In a foam, the force exerted on the thin film separating two bubbles depends on the local radius of curvature of the Plateau borders and vertices, which depends in turn on the local liquid content. Results from different bubble sizes in the micromanipulator therefore translate into regions of different liquid content in the foam. Small bubbles, having a high radius of curvature correspond to the low-liquid content (Polyhederschaum) region higher in the foam, and large bubbles to the wetter (Kugelschaum) region closer to the liquid-foam interface. Experiments with different holding distances between the bubbles correspond to differences in bubble size in the foam, as the size of the film between the bubbles varies."

Jan 1, 2003

By Renato S. Costa, Afonso H. Martins, Flávia D. Mendes

"This paper presents some important aspects regarding the ion exchange treatment of an Ni and Co sulphate acidic liquor using chelating resins. Chelating resins possessing iminodiacetic or bis-picolylamine functional groups were compared in terms of nickel and cobalt recovery. The experimental resin with bispicolylamine functionalities (Dowex M4195) was evaluated with respect to Ni and Co uptake, and compared with Rohm &Haas commercial chelating iminodiacetate acid resin.The use of selective ion exchange to recover metals from sulphuric acid liquors has been studied for a long time. Companhia Vale do Rio Doce (CVRD) has been actively involved in hydrometallurgical applications of IX and has researched in selecting the optimum resin for nickel and cobalt selective removal and the design of a suitable IX circuit. When an IX operation is contemplated for a specific application, it is followed a screening process which generally involves consideration of the solution composition and pH, speciation of the metals in the liquor to be treated and other possible techniques that can be applied to achieve the desired specifications or recoveries. Once a decision has been made to use IX for a specific application, relevant testwork should be done to select the most cost-effective resin and design the IX circuit to achieve the desired criteria. The experimental part dealt with the working conditions, resin characteristics and the influence upon the resin maximum exchange capacity of the following factors: nickel concentration, temperature, pH and resin-to-solution ratio. Based on the experimental data obtained, it has been proposed a innovative technological treatment"

Jan 1, 2003

By Vladimir G. Kochnev

"Autogenous and semi-autogenous grinding (AG and SAG) have been considered a step forward in comparison to conventional grinding circuits with several stages of crushing and using ball (and/or rod) grinding mills. However, existing AG and SAG technologies still can be improved and have an immense potential from the viewpoint of economic benefits.Experience gained by the Technics & Technologies of Disintegration Ltd. (TTD) in the research of grinding processes shows that comminution in AG and SAG mills can be performed in a more effective way. The company’s approach comprises the following elements:- Novel mill design- New liners and lifters- Novel discharge grid design- Technique of treating material of critical particle sizeA novel mill of the cantilever type capable to operate in the AG and SAG mode has been developed. The cantilevertype mill has a high diameter to length ratio, which dramatically increases the throughput rate, and is characterised by high reliability, fast installation and low capital and operating costs.Tests of the new heel-shaped liners, originally aimed at improving the intact condition of diamond, indicated that they play an important role in the grinding process. Tests performed by TTD jointly with ALROSA, MINTEK and Anglo-American Corporation, demonstrated that the heelshaped liners provided the increase in the throughput rate varying from 30 to 80 % and the decrease in power consumption in the range 30-55 % for grinding of kimberlite and platinum-containing ores.Investigation of the influence of the main grid parameters on the efficiency of grinding led TTD to a special design of a mill discharge grid, with a radial location of openings, the slot width varying from the periphery to the centre and the grid surface provided with “heels”. The design allows one to control the particle size distribution of the ground product without affecting the grid throughput rate."

Jan 1, 2003

By Leon Lorenzen, Rodrick M. Lamya

"Leaching behaviour of nickel – copper matte in a CuSO4–H2SO4 solution during the repulping stage of a matte pressure leaching process has been studied. The base metal recovery process investigated in this study consists of a matte repulping stage prior to a series of pressure leach stages. The repulping stage is essentially an atmospheric leach stage in which the Ni-Cu matte, containing small amounts of cobalt and iron, is leached in copper spent electrolyte from the tankhouse, resulting in dissolution of the nickel with simultaneous precipitation of almost all the copper.Effects of various process parameters on the kinetics and extent of the leaching reactions, as well as on the cementation of copper from the solution have been quantified. The parameters investigated were temperature, particle size, pulp density, stirring speed, residence time, initial copper concentration and initial acid concentration.Leaching characteristics of the preleached matte during the subsequent pressure leach operation has also been studied. The effects of variations in the conditions in the repulping stage on the kinetics and degree of base metal dissolution during the pressure leach stage have been investigated. Any transformations that occur in the mineral phases of the matte during the leaching process have been studied, and a leaching mechanism proposed."

Jan 1, 2003

By Valentin V. Shatalov, Irina V. Pastukhova, Alexander V. Kurkov

"We have developed a technology to improve the quality of low-grade concentrates containing minerals of tantalum, niobium and tin on the basis of given conception by the way of improving selectivity and using certain reagents composition. The basic collector presents a traditional or complex-forming collector used together with organic diphilic reagents – the secondary reagents regarding the basic flotation regiment, capable of forming associates with the main collector on the surface of the mineral, thus altering the interaction energy. In the given process the main collector is the fraction of hydroxamic acids C7-C9, the reagent of the secondary action – sulphosuccinamate, which added in moderate concentrations range provides for a synergistic effect.We have determined the parameters of the process stability and necessary modifying reagents for a selective recovery of tantalum, niobium and tin minerals from refractory products. Variants have been studied where the main collector and the secondary action reagent were substituted with some more efficient flotation reagents. A possibility of a more flexible reagent compounding for the process has been shown. The flotation process is highly stable regards the saline composition of the liquid phase in the pulp. It can operate under conditions of the complete water recycling with the total salt content up to 12 kg/m3, iron up to 1.2 kg/m3.The given results consider the efficiency testing of the suggested technology for the gravitation products, which were obtained from ores of various genesis and contain large quantity of the most refractory minerals, such as topaz (80%), gamet (55%), tourmaline (30%). High selectivity of the process has been registered with the metal recovery about 92-98%, which appears to be similar to hydrometallurgical operations under certain conditions."

Jan 1, 2003

By Markus A. Reuter, Bernardete Castro, Antoinette van Schaik, Han Remmerswaal

This paper describes the inseparable relation between product design, liberation, and metallurgical recovery in the optimisation of the recycling of passenger vehicles. This is illustrated by the use of an optimisation model that uses among others a material combination matrix based on metallurgical process data, which depicts the consequences of the quality of intermediate recycling products on the metallurgical material recovery and final alloy metal quality. Various simulations will illustrate the effect of changes in product design and hence liberation on the recycling of end-of-life vehicles. Although this paper focuses on cars, the discussion is equally valid for any end-of-life product. Calibration of the model will be discussed with reference to experiments carried out in order to study the optimal recovery of aluminium applications used in passenger vehicles.

Jan 1, 2003

By Thomas Pretz, Alexandra Pehlken

Sampling of municipal solid waste is known to be difficult to sample if it has to be representative. When dealing with municipal solid waste, the usual method is to study separately waste material below 40 mm and particles bigger than 40 mm. The material < 40 mm cannot be sorted manual and is termed the “fine fraction”. The particles > 40 mm can be separated manually and are usually sorted into pre-defined groups of materials. These groups can be defined depending on the demand of quality assurance. But standardisation of procedures is not far progressed, even for the widely practised sorting methods.

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 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 Graeme Heyes, Warren J. Bruckard, Michael A. Somerville

"Over the past few years CSIRO Minerals has been conducting research aimed at developing a continuous copper converting process to replace the traditional two-stage batch process that is currently used to produce blister copper. Sirosmelt type reactors and calcium-ferrite (lime-based) slags have been used rather than the conventional iron silicate slags. The research work has now been extended to focus on the development of a single-stage continuous copper making process (so-called direct copper converting) in which copper concentrates are converted to low-sulfur blister copper in a single step, that is the smelting and converting steps occur in one continuous stage.One feature of the direct copper converting process is that copper losses to the slag phase can be high, meaning the slag produced needs to be treated to recover the copper value. The feasibility of the whole copper making process will most likely depend on the efficiency and cost effectiveness of the copper recovery stage. Flotation has been identified as the most economical option to recover the copper from direct copper converting slags where it has been estimated that a copper recovery from the slag of above 90% is required to make the overall single stage copper making process economically feasible.A limited series of laboratory batch flotation tests was conducted on a suite of calcium-ferrite-based slags made in laboratory smelting trials. Copper sulfide concentrates from MIM were used as feed-stocks. The objectives of this work were to develop a robust flotation process to maximise the copper recovery and iron rejection from slags made in the process, and to establish operating conditions for future continuous flotation pilot plant trials.The slags treated included a reduced low copper slag, an oxidised high copper slag composite, and a very reduced low copper self-pulverising slag. The copper content of the slags varied from 2.9% to 14% Cu and the CaO/Fe ratio varied between 0.30 and 0.54. In general, the higher the copper content the more oxidised the slag. The copper was present as metallic copper, oxide copper and copper-calcium ferrite phases with the phase mix related to smelting conditions. The slags were crushed, ground, wet-screened at 355 or 210 µm to remove coarse metallic particles of copper, and floated at natural pH (about pH 11) using reagents and conditions appropriate for the selective recovery of the copper phases. Reagent additions were typically 200 g/t KEX and 500 g/t Na2S.9H2O and the grind size was generally a P80 of about 40 µm."

Jan 1, 2003

By Pradip, Beena Rai

A molecular modeling study was carried out on an adsorbed oleate monolayer on the surfaces of three calcium minerals, fluorite, calcite and fluorapatite using Universal Force Field (UFF) potentials. The cleavage plane of calcite {104} was the best template for oleate monolayer adsorbed since the surface structure enabled all the calcium sites available on the surface to be occupied by oleate anions. The area occupied per chain of oleate in this well packed monolayer was computed to be 20.2 Å, which exactly matches the value calculated to be the parking area per oleate molecule for a fully packed monolayer based on strictly geometric calculations. On the other hand, the precentage of calcium sites occupied by oleate to achieve a fully packed monolayer in case of fluroite and and fluorapatite was found to be 67% and 75% respectively. The results of this theoretical study suggest that while all the three adsorption conformations, that is unidentate, bidentate and bridging type are equally likely on fluorite and fluorapatite, bridging is most likely on calcite. Interestingly, all the conformations are observed experimentally for calcite-oleate system also. The reasons for this discrepancy between the theoretical predictions and experimental observations are not clear. More work is required to resolve this discrepancy, in particular simulation studies in presence of solvent water molecules on the surface.

Jan 1, 2003

By Konstantin Fedotov, Victor Beloborodov, Anatoly Potyomkin

"There are areas in Russia, which cover huge territories and they are north, and Siberia. These difficult to access regions with cold climate are rich in a great number of distant deposits of valuable and rare metals, gold and platinum. The development of such deposits requires highly effective technologies of mineral processing which could be realized in modular and quick-built processing plants.The work presented includes the results of long term research in the development of new technologies of processing of zirconium (in the form of rare mineral Baddeleyite – natural zirconium dioxide) bearing ore of the Kovdor deposit which is located in the Polar region of the Kola peninsular and also in Siberia deposits of of ledge ores of gold."

Jan 1, 2003

By Renato S. Costa, Afonso H. Martins, Flávia D. Mendes

"This paper presents some important aspects regarding the ion exchange treatment of an Ni and Co sulphate acidic liquor using chelating resins. Chelating resins possessing iminodiacetic or bis-picolylamine functional groups were compared in terms of nickel and cobalt recovery. The experimental resin with bispicolylamine functionalities (Dowex M4195) was evaluated with respect to Ni and Co uptake, and compared with Rohm &Haas commercial chelating iminodiacetate acid resin. The Rohm & Haas chelating resin, Amberlite IRC 748, with its weakly acidic groups, did not work in acidic solution but exhibited good results at pH 4 and above. The resin that efficiently removed metals from high acidic solutions was the bis-picolylamine resin. Maximum nickel uptake values ranged between 85 g and 112 g Ni per Kg of resin.The experimental part dealt with the working conditions, resin characteristics and the influence upon the resin maximum exchange capacity of the following factors: nickel concentration, temperature, pH and resin-to- solution ratio. Based on the experimental data obtained, it has been proposed a innovative technological treatment."

Jan 1, 2003

By Yuexin Han, Zehong Wang, Fujia Yu, Wanzhong Yin, Xinchao Wei

Bauxite is the main raw material in alumina and refractory industries. China has plentiful bauxite resources, most of which belong to the diaspore type bauxite with characteristics of high aluminum content, high silicon content and low ratio of alumina and silica (A/S). The resources with A/S 4-7 account for more than 60% of the total resource reserves of bauxite. Therefore improving the A/S through bauxite desilication is the key task of bauxite concentration in China. Normally the grinding fineness of 80-90% - 0.074mm is required in the bauxite flotation process. Thus fine grinding of bauxite ores is necessary, which leads to the high energy consumption. In the meanwhile, bauxite ores are easy to produce slime during grinding processes. The large amount of slime produced in fine grinding greatly worsens the process environment of bauxite flotation, affects the separation performance and results in the loss of metal. Also, fine grinding makes the flotation concentrate difficult to dewater, while the water content in the flotation concentrate must be removed by distillation in the subsequent alumina dissolution process, causing the increase of energy consumption and cost in the production of alumina. In this study, the selective grinding behaviors were examined with Henan Bauxite as feed. Separation of alumina and silica at a coarser grinding fineness was achieved and new route was explored to enhance the desilication in bauxite concentration to improve the A/S of bauxite concentrate.

Jan 1, 2003

By B. Friedrich, A. Weyhe, H. Heegn

"Nickel-metal hydride batteries (Ni-MH) are storers of electrochemical energy, which have a higher specific storage capacity than lead or nickel-cadmium batteries. The demand for Nickel-metal hydride batteries is increasing rapidly since their market launch in the early 1990’s. Today there is no suitable and sustainable recycling process to recover nickel, cobalt and rare-earth metals. The discarded batteries are used today in the steel industry as alloy material because they contain nickel. Cobalt and rare-earth metals (RE) are lost; they are non-recycleable.In a German governmental funded research project, IME Aachen, ACCUREC Mühlheim and UVR-FIA Freiberg are cooperating in processing as well as in creating a feasibility study. The target of this project is the development of a new recycling process for metal recovery from Ni-MH-batteries. The proposed process described in this paper consists of a combination of mechanical, pyrometallurgical and hydrometallurgical processing steps. This process is capable of treating all types of Ni-MH-batteries. After comminution steel and organics are separated. The separated Ni-MH is smelted in an electric arc furnace. The products are a nickel-cobalt alloy and a slag phase enriched with rare-earth oxides for further treatment to ‘mischmetal’. Both the Nickel-Cobalt alloy and the ‘mischmetal’ will be directly used in battery production."

Jan 1, 2003

By Máximo Pérez, Julio C. Videla, Rosa Dzioba

"This paper reports the hydrometallurgical treatment of gravity concentrates of gold samples and outcrops associated with graphite ores obtained from:• flotation tailings of crystalline graphite minerals• outcrop samples of graphitic rock associated with auriferous minerals and free gold located in the Villa Union district and surrounding areas - La Rioja Province - Argentina.Previous studies of the flotation potential of crystalline graphite minerals failed to consider the presence of noble metals.The samples represent a mineralized zone of crystalline graphite which is distributed in different formations with a NE - SW trend in Maz, Punta Colorada and Las Ramaditas hills, covering an area of about 300 square kilometers."

Jan 1, 2003

By Chris J. Martin, Nichola A. McKay

"In mid-2001, North American Palladium commissioned a new 15,000 tonnes per day milling and flotation circuit at their Lac des Iles Mine (LDI), one of only two primary platinum group element (PGE) producers in North America. The mill treats an ore containing 2.3 g/t PGE producing a concentrate assaying 300 g/t PGE, at a recovery of roughly 75%.Top-size control crushing is conducted ahead of semi-autogenous milling. A portion of the SABC circuit feed is crushed to –25mm to increase mill throughput. Product from the SABC circuit is fed to flotation. Flotation consists of roughing and scavenging, with the rougher and scavenger concentrates each being reground using vertimills. Cleaner flotation uses two stages of cleaning using mechanical cells, and a third stage using flotation columns, the column tails being scavenged using a bank of mechanical cells. Rougher concentrate by-passes the first cleaner circuit. Reagents added include amyl xanthate collector, dithiophosphate promoter, MIBC frother and a carboxy methyl cellulose-based gangue depressant.SGS Lakefield Research, together with staff at LDI initiated a structured plant optimisation program comprising on-site testing, bench-scale flotation and mineralogical analysis using QemSCAN. The objectives of the mineralogical studies were 1) to identify feed PGM, their size distribution and mineral associations, 2) establish relationships between the PGM mineralogy and PGM floatability, and 3) characterize the culprit silicate minerals diluting the final concentrate.PGM flotation response at Lac des Iles is clearly bi-modal in nature, with about 60% of the PGM floating quickly, to a high value rougher concentrate. The mineralogical work was able to explain the causes of the bi-modal PGM floatability, which in turn created new opportunities for the metallurgists to optimise the circuit."

Jan 1, 2003

By S. Kelebek, A. Khan, J. Caceres, D. Beckett

"Pyrrhotite in nickel-copper sulphide ores is nickeliferrous and intimately associated with pentlandite. Due to its low nickel content, pyrrhotite rejection is an important step in processing of these ores. In our laboratory, various reagents were investigated for their effect on pyrrhotite depression. Among these, a combined use of triethylenetetramine and sodium metabisulphite was found highly promising.The work described in this paper has two parts. The firs part is a summary of results obtained on process samples from the pyrrhotite rejection circuit at Falconbridge’s Strathcona Mill. The second part involves simulation of the circuit performance based on the reagent conditions used in the experimental work and the concept of split factors.Two sets of reagent conditions were evaluated. The first one involved baseline conditions, simulating the current reagent performance. The second one simulated the impact these new reagents can have on the circuit performance.The simulation results obtained under baseline conditions indicated a good agreement with the current circuit performance (Figure 1). The simulation results suggest that at practically the same pentlandite recovery and tailing grades, the circuit concentrate nickel grade can be doubled through effective pyrrhotite rejection by these new reagents (Figure 2)."

Jan 1, 2003

By D. Whittles, S. Kingman, K. Jackson, S. Bradshaw, N. Miles

The influence of microwave energy at high electric field strength on ore strength has been investigated. Two ores of varying mineralogy were treated in both multimode and single mode microwave cavities. After treatment, any change in strength relative to untreated ore was established. It was shown that in the multimode cavity reduction in strength was related to the applied power level. Results of tests carried out in the single mode cavities showed that, for both ores, reductions in ore strength > 50% could be achieved in very short periods (<1 second). Thermal stress analysis showed that the mechanism of microwave induced failure was the development of tangential stresses at the grain boundaries. It was concluded that operation at 915 MHz with high power and short residence times gives feasible scale-up possibilities.

Jan 1, 2003