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By V. K. Kuppusamy, M. Holuszko

"Lamps and lighting products are the most commonly used electrical products around the globe. With the improvement in lamp technologies, lighting products have grown complex and hence require an improved recycling process. The LED lamps consist of various valuable metals such as iron, copper, aluminum, chromium, silver, and gold, as well as non-metals such as glass, plastics, and fibers. In addition, there are also traces of hazardous substances such as lead, arsenic, and mercury. A major step in the recovery process is size reduction, and researchers have suggested that up to 40% of the total valuable material is lost during the shredding and grinding processes. SELFRAG is a high voltage selective fragmentation comminution technology that uses high voltage pulses in a water medium to efficiently separate the metals at a coarser size without generating many fine particles. It has been proposed that during the fragmentation process of electronic waste (e-waste), the metals can be separated without fine grinding. This research considers the applicability of high voltage pulse fragmentation for LED lamps. Eight different types of LED lamps were processed through the SELFRAG unit at varying pulses to study metal liberation. The product obtained was characterized for metal liberation, metal grades, and liberation analysis. The specific energy consumption for this size reduction process was also monitored. INTRODUCTION Lamps and bulbs are the most commonly used electrical products in homes, offices, industrial operations, and streets. According to Energy Star research (2006), an average US household has more than 40 sockets for light bulbs and consumes approximately 2100kWh every year for lighting. The development in lamp technology has pushed the boundary for newer products. The LED lamps have been taking over the market from the incandescent bulbs and compact fluorescent lamps (CFL). According to the US Department of Energy (2012) and myLEDlight.com (2007), LED lamps have several benefits over other lamps. LEDs produce light hemi-spherically, which increases their efficiency in directional light emission. It has higher breakage resistance from vibration or transportation. LED lamps use up to 90% less power than incandescent bulbs thus making them highly energy efficient; They have a longer lifespan, lasting 10 times longer than a CFL and 133 times longer than the traditional incandescent bulb. Because of all the benefits, Smallwood (2014) suggested that the market of LED lamps will grow to $12.2 billion by 2018."

Jan 1, 2018

By Takashi Furuyama, Sukeyuki Mori, Takafumi Okuma, Norio Hashiguchi

"In order to achieve a high recovery of particles finer than 10µm, three types of dry Tower Mill (VD-1, KD-1, KD-2 and KD-3) have been developed. These mills differ from each other in the size of the comminuting part, the inside diameter and shape of the classifying part and the system involved in the collecting process. The last version (KD-3) of tower mills in which the comminuting and classifying operations has been separated, can produce particles finer than 10µm from a limestone ore sizing from 420 to 3360µm. In this tower mill, products in comminuting section are blown up and transported into the classifying column, made of an inverted cone on top of a cylinder, before they agglomerate and settle down. Fine particles are deported and recovered in a cyclone with a central spiral ribbon.Previous studies on the grinding efficiency of the tower mill KD-3 have shown how the maximum size of collected products increased with the airflow velocity, disturbing in the same way a smooth regulation of the grinding operation with the tower mill KD-3. A complete knowledge of factors that influence the maximum size of collected products is needed, therefore, to increase the efficiency of the grindingclassifying operation and ensure a better control over the collected products. The present study deals with this issue and, assuming that the structure of the classifying column could be one of these factors, its internal structure was modified (insertion of vertical plates, cone or horizontal nets) before carrying out comminution tests that would establish a relationship between the inward shape of the column and the maximum size of collected products. It was found that the weight of products collected in the cyclone decreases when a cone or some horizontal nets are inserted inside the column. At the same time, the weight of products collected in the column increases. This is due to the fact that coarse particles blown up from the comminution section collide with the base of the cone or the nets and settle down the bottom of the classifying column. Therefore, the cone and some horizontal nets inserted inside a classifying column, have the particularity to stabilize the maximum size of particles (15.1-17.5µm and 8.4-11.3µm) in the cyclone even when the airflow velocity in duct increased. These tools could of great help in the production of particles of definite size to fit for instance the paper industries requirements (production of limestone material sizing - 10µm as paper filler)."

Jan 1, 2003

By Yuhua Wang, Huilan Yang, Yanqing Jiang, Dongfang Lu

"Generally, the concentration of bauxite flotation tailings is around 10%, a large amount of water in tailings needed to be recycled in the flotation process. Sedimentation and dewatering properties of tailings were investigated under different conditions. Surface high negative charges on mineral particles are the key factor to destroy the settlement of tailings when the pulp pH is around 8.9. Hence, the modification of pulp pH around 7 is necessary to the diminution of the repulsive force between mineral particles and then the acceleration of sedimentation of tailings. Anionic polyacrylamine with molecular weight of 14 million is the best flocculant for the settlement of tailings in all tested polyacrylamines. P-toluene sulfonic acid shows better properties than hydrochloric acid for pulp pH adjustment when anionic polyacrylamine with molecular weight of 14 million is used as flocculant. Although the flotation of diaspore is depressed in the presence of polyacrylamine using sodium oleate as collector, but the recycling water traded by the combination of ployacrylamine and p-touenesulfonic acid does not show the depression effects on the flotation of bauxite ore. The lower residual content of polyacrylamine in recycling water treated by the combination of ployacrylamine and p-touene sulfonic acid plays an important role. INTRODUCTION Generally, the waste water generated from mineral processing plant is usually treated by sedimentation, oxidization, electrodialysis, ions exchange, active carbon adsorption and flotation technology, and the treated water is also used again in the industrial process. Flotation was adopted widely to improve the quality of bauxite from low grade diasporic bauxite in China. For flotation, the grinding fineness of bauxite is over 90% -0.074 mm, sodium carbonate and sodium hexametaphosphate were used as regulators, so the tailings pulp is very difficult to settle and be dewatered (Y. Wang et al., 2004; Y. H. Wang et al., 2007; Wang Yu-hua et al., 2008; Wang Yuhua et al., 2011). The water recycling of bauxite tailings are becoming the highlight for the industrial application of the flotation process for bauxite ore. Researchers in China shift their attentions onto this topic."

Jan 1, 2018

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 S. Banisi, A. Ghasemi, S. Zare, F. Ghorbani, E. Nematollahi

"Comminution is the most energy intensive operation which constitutes the major portion of operating and capital costs of the mineral processing plants. Working at the maximum operating capacity of comminution equipment plays a significant role in the efficiency of the circuit. Appropriate design of cone crusher feed box could result in the choked crushing which is known as a vital factor in achieving target performance. In this research, the non-uniform cone crusher feeding at the Sarcheshmeh copper complex was studied and appropriate measures were taken to solve the problem. The problem resulted in non-uniform and high wear rate of crusher liners and high fluctuations of power draw. In recent decades, the discrete element method (DEM) has been applied successfully to study the effect of different factors on the behavior of particles flow. In this work, various designs for feed box were tested using an in-house developed DEM software called KMPCDEM©. The best feed box design obtained from the simulations was selected, constructed and installed in of the cone crushers. The new feed box design resulted in more uniform feed distribution on the distributor plate of crusher indicated by a reduction of the standard deviation of power draw measurements from 13 to 3 kWh. The better control of the crusher, 49% increase in the crusher throughput and finer and narrower product size distribution were the main outcomes of the installation of the new feed box. Furthermore, the wear rate on mantle and liners of crusher not only decreased but it also became uniform.INTRODUCTION Comminution is the most energy intensive operation which constitutes the major portion of operating and capital costs of the mineral processing plants. Reaching the maximum operating capacity in comminution equipment is a key sign of approaching the nominal productivity of the process. Due to the effect of crusher efficiency on the downstream circuit performance, optimization of the crushing circuits has received considerable attention (Herbst, & Potapov, 2004; Quist, & Evertsson, 2010; Li, Huiqi, McDowell, Glenn R, Lowndes and Ian, 2014; Cleary, Sinnott, Morrison, Cummins, & Delaney, 2017). Improving the performance of crushing circuits not only decreases the capital and operating costs but also increases the efficiency of downstream grinding circuits (Jacobson, Janssen, & Urbinatti, 2010). In cone crushers particles can be subjected to two different modes of compressive breakage; single particle breakage (free feeding) and inter-particle breakage (choked feeding). The maximum efficiency of the cone crusher directly depends on the type of feeding arrangement (Operation Manual, 1977). An appropriate feeding must lead to choked feeding the cone crusher. If the rate and method of feeding the crushers are correctly be executed, the maximum efficiency of the crushers could be available (Jacobson et al., 2010)."

Jan 1, 2018

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 S. K. Kawatra, S. J. Ripke, T. C. Eisele

"An estimated 600,000 tons of bentonite clay are used annually in the U. S. as binder for production of iron ore concentrate pellets. Since this is a significant cost item for the plants, and the addition of bentonite to the pellets contributes undesirable silica into the finished pellets, there is considerable incentive for finding methods to reduce bentonite use. One way to reduce bentonite levels is to selectively use those bentonites that are most effective in this application, so that a lower dosage will still produce a sufficiently strong pellet. Unfortunately, there are no satisfactory methods available for accurately predicting which bentonites are actually most effective, short of using them to actually make pellets. One of the popular methods for attempting to evaluate bentonites is the “Plate Water Absorption” (PWA) test. While some plant operators accept the PWA results as indicating the relative quality of bentonites, others disagree and claim that, over a fairly broad range of values, PWA does not correlate with bentonite performance.Since both Ca+2 and Mg+2 ions are known to reduce the swelling and water absorption capacity of bentonite, it was believed that the presence of these ions in plant recycle water could be changing the bentonite performance. Since the standard PWA test uses only distilled water for its measurements, it could not detect these effects. Experiments were therefore carried out on a number of different bentonites using a modified PWA tests, with plant recycle water replacing the distilled water. These experiments showed little effect of the plant water on the PWA value, and chemical analysis of the water showed that the levels of dissolved salts were quite low.Water and accompanying salts were then extracted from a magnetite concentrate filter cake by rinsing with distilled water. Analysis of this water showed an extremely high level of dissolved salts, particularly salts of calcium and magnesium. When concentrations were compared with the recycle water from the plant filters, it was determined that levels of Ca+2 and Mg+2 retained in the filter cake were over 500 times higher than levels in the recycle water. This extreme elevation of soluble salts in the filter cake is believed to be due to adsorption of these ions into the electrical double layer of the magnetite particles."

Jan 1, 2003

"The Merensky Reef is a platinum group minerals (PGM) bearing reef in the Bushveld Igneous Complex in South Africa. The reef has been treated by bulk PGM and sulphide flotation with the aim of maximisingthe valuable minerals recovery and gangue minerals rejection.Synthetic water with a calcium concentration of 80 ppm and 500 ppm was prepared and the flotation results obtained were compared to a simple electrolyte in order to determine the effect water quality has on pentlandite and pyroxene surface alteration and, ultimately, floatability. During the study, the possible effect of interactions between the minerals investigated and Ca2+ ions in the presence of sodium isobutyl xanthate was studied at pH 6 and pH 9 by means of zeta potential determinations, microflotation tests and ToF-SIMS analysis.The results obtained on 1:1 pentlandite-pyroxene mixtures showed that the quality of process water plays an important role in flotation. The flotation recoveries of pentlandite and pyroxene were lower in synthetic process water compared to those obtained in a simple electrolyte solution."

Jan 1, 2003

By I. N. Gridasov, T. V. Ignatova, E. V. Shelepov

"Mikhailovskoye Deposit is comprised of oxidized ferruginous quartzites among other minerals with the former widely spread across the ore field and mined along with unoxidized ferruginous quartzites. PJSC Mikhailovsky GOK strategic development is aimed at iron ore product output expansion. The most critical item of the strategic development road map is process design for separation and concentration of hematite contained in oxidized ferruginous quartzites mined as the by-product in the open pit. Laboratory and semi-industrial tests run to design cost-effective, reliable and environmentally friendly process for Mikhailovskoye deposit oxide quartzites processing included the following processes: - pilot tests of reverse anionic flotation which produced concentrate with Fe60.1-62.9% total iron content and 66-69%Fe recovery rate; - combined magnetic separation and flotation (Marubeni Company, 1982) including slime removal, reverse anionic and cationic flotation and high gradient magnetic separation resulting in 48.9% yield, Fe55-57.5%, up to Fe60.5% hematite concentration ( Fe64.1% being the best result achieved),76.2% recovery. - magnetic separation and flotation, including separation in low gradient (1400 Oe) and high gradient (up to 17000-18000 Oe) magnetic field. The results of these pilots tests were the following: 57-59%Fe concentrate, 70%Fe recovery (Mekhanobrchermet, MGOK, 1982-1988): - magnetic roasting in pilot plant of TSGOK (Krivoy Rog) which produced 61.1%Fe concentrate with 81.5% recovery. Major disadvantage of the method is high generation of dust equal to 20% of the initial feed. Based on third-party studies flotation of oxidized ferruginous quartzites process embracing best processing methods was designed by Metalloinvest Management Company LLC and PJSC Mikhailovsky GOK engineers. This paper discusses analysis of studies aimed at intensification of separation processes with application of mechanical slurry agitation (MSA), addition of alkali (NaOH) and elutriation of initial feed. The paper also provides a design solution to implement a lab-scale MSA plant. It includes feasibility evaluation of MSA inclusion in flotation of oxidized ferruginous quartzites process to enable higher yield and hematite recovery in resultant concentrate. Outcomes of the discussed work have significant value for prospective engineering of OFQ concentration process."

Jan 1, 2018

By Briony C. Ruse, David V. Boger, Fiona Sofra1

"The sustainability of the mining industry must be addressed through improving tailings management. The use of thickened tailings and pastes stems from a paradigm shift towards designing tailings disposal sites to suit their surrounding environment, rather than manipulating the environment to accommodate the tailings. Thickened tailings and pastes usually exhibit non-Newtonian behaviour, so a thorough understanding of the rheological characteristics of the material is required in order to determine the disposal plant operating conditions.As environmental factors translate into economic issues, minimising waste production using dry disposal methods is gaining popularity. The use of rheological information is of high importance in evaluating the spreading characteristics, the transportation and the dewatering of thickened mineral tailings. The principles outlined may be applied to many industries encompassing a wide range of waste materials. The main obstacle to the widespread implementation of dry disposal methods has been the high initial capital cost of the methods due to the dewatering step, and the high cost of pumping thick suspensions across any great distance. Proper and thorough costing of tailings disposal activities combined with an accounting approach that shows closure and post-closure care costs on a per tonne basis of tailings disposed throughout the life of the tailings facility will show that dry disposal methods are more favourable than they might seem on initial appraisal."

Jan 1, 2003

By Matti Kongas, Kari Saloheimo, Antti Remes

"The paper studies the control performance of the flotation process as a function of the measurement accuracy and sampling frequency of an on-stream XRF analyzer, using a simple dynamic model. An additional aim is to assess how the economical result of a mineral flotation process depends on the quality of process control based on the on-line elemental assays.An on-stream XRF analyzer measures the concentrations of slurry lines in a continuous cycle from several process points. The control performance depends on the analytical accuracy and sampling frequency of the concentration measurement. With a long cycle time, the state of the process changes before a new measurement becomes available. With short measurement times the statistical variance of the counted Xray pulses increases, increasing the random error in the analysis. In addition, the measurement accuracy depends on the concentration of the component to be measured from the slurry.To quantify the effect of analysis error and frequency to process control, a simple dynamic process model is created in the Matlab environment. Data from a copper flotation circuit is used as a test case. The process model comprises a first order reaction equation and the grade-recovery -relationship estimated from process data. The control was modeled using the control strategies implemented into a rule based advanced control system. The economical performance of the control was studied by calculating the overall net smelter return at various analyzer parameter combinations."

Jan 1, 2003

By P. Harris

"Comparison of the two most commonly used classes of depressant in the South African platinum industry is complicated by the fact that these polymers induce different effects on the surfaces onto which they adsorb. The use of carboxymethyl cellulose (CMC), which is ionically charged in solution, can lead to increased particle dispersion in addition to the effect of reduced surface hydrophobicity (depression). Guar is typically only slightly charged in solution. Comparison of these two depressants is complicated since it is uncertain whether differences in their action is a result of either depression of dispersion effects.This work investigates the role of dispersion independently to that of depression in the batch flotation of a platinum bearing ore. An inorganic dispersant, sodium hexametaphosphate (NaHMP) was added in parallel to the uncharged guar depressant to simulate the action of depressants with varying degrees of dispersion. By distinguishing between the material recovered by entrainment and the floatable gangue and by including the effects of froth stability it was possible to decouple the effects of dispersion and depression.The results show that both dispersion and depression led to increased grade of the sulphide minerals. Depression leads to a decreased recovery of floatable gangue minerals. Dispersion leads to an increased recovery rate of these minerals and an accompanying decrease in froth stability."

Jan 1, 2003

By Jim Petrie, Mary Stewart, Damien Giurco

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

Jan 1, 2003

By Ponisseril Somasundaran, H-L. Chen, University of Athens, D. R. Nagaraj, Zhonghua Pan, Jing Wang

Gums are often used as depressants for talceous gangue minerals in the flotation of nickel and platinum bearing ores. However, the mechanisms of gum adsorption on talc are not clearly established. In this work, adsorption of guar gum at the talc-solution interface is investigated using spectroscopic and allied techniques. Guar gum adsorption on talc is not affected significantly by changes in solution conditions such as pH and ionic strength. Electrokinetic studies showed that guar gum decreased the negative zeta potential of talc but did not reverse the charge. Fluorescence spectroscopy studies conducted to investigate the role of hydrophobic bonding using pyrene and dansyl probes showed no evidence of the formation of hydrophobic domains at talc-aqueous interface. Urea, a hydrogen bond breaker, reduced the adsorption of guar on talc to the same extent as that for guar/alumina system, in which hydrogen bond plays an important role. All of the above results suggest that one of the main driving forces for guar adsorption on talc is hydrogen bonding rather than electrostatic or hydrophobic force.

Jan 1, 2003

By T. V. Chnyrenkova, J. Troncoso, V. A. Luganov, G. P. Kluev

"Arsenic-gold bearing ores are used as flux in smelting or are leached out with extraction of gold. For decreasing arsenic content in processed materials and for breaking up the lattice and opening up of gold the raw materials are roasted. Some regularity was established for sulfidizing of arsenic bearing compounds in a presence of pyrite and for oxidation of ores and concentrates in the presence of soda.This article analyses the results of laboratory and pilot testing of dissociating and oxidizing roasting of gold-arsenic bearing concentrates. During the dissociation roasting under vacuum arsenic is sublimated into elemental and sulfide forms. This process allows minimizing the negative influence on the environment but requires costly engineering solutions. Roasting in a limited quantity of oxygen in the gaseous phase makes it possible to sublimate arsenic in the form of oxides and sulfides and may be carried out in fluid bed furnaces."

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

By John O. Marsden

"Technology development and innovation has played a crucial role in the copper industry throughout history. The effective development and implementation of new technologies allows mankind to produce copper at progressively lower cost of production at a given feed grade and mineral type. This progress serves to counteract cost inflation/escalation over time and, depending on the magnitude of the cost benefit, allows ore cut off grades to be reduced thereby improving the availability, accessibility and utilization of resources. Two broad categories of technology development and innovation play a key role in this process: (i) incremental improvements and optimization of existing technology provide benefits in the near- to medium-term, and (ii) step change technologies provide value over the longer term. A key issue for potential developers and implementers of new step change technology is how to justify resource allocation and expenditures for such initiatives. This paper examines this issue with reference to specific case studies in the copper industry. INTRODUCTION AND BACKGROUND Technology development and innovation has played a crucial role in the commodity minerals industry throughout history, and none more important than the copper industry. As new, cost-efficient technologies are commercialized, the cost of production in real terms at a given ore feed grade and mineral type decreases. This progress enables ore cut off grades to be reduced allowing lower grade material to be processed economically, which in turn increases the availability and supply of the metal or mineral of interest. Cost inflation/escalation works in the opposite direction, squeezing margins for operations utilizing incumbent technology to process material from a given ore deposit. A prior review by the author considered the issue of technology development and sustainable competitive advantage. This review concluded that first movers and fast followers can achieve competitive advantage for periods of 10-15 years through effective deployment of new technologies (Marsden, 2004). A new, more comprehensive study and evaluation was completed in 2014. This paper presents a portion of the results from the 2014 study."

Jan 1, 2018

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 Carin Laubscher, Francis W. Petersen, Jaap P. Smit

"Waste streams, such as acid mine drainage, are often characterised by low pH values and high concentrations of heavy metals, dissolved solids, calcium and sulphates. Although lime remediation effectively removes most of the heavy metals as hydroxides, it is less effective at lowering levels of sulphates. Various methods of removing sulphates from effluents exist, such as precipitation with lime, precipitation with barium salts, co-precipitation with calcium carbonate, reverse osmosis, and ion exchange. Mintek developed a chemical precipitation (SAVMIN) process to treat acid mine drainage, which entails the addition of lime to precipitate the metal hydroxides, and the subsequent formation (precipitation) of calcium sulphoaluminate or ettringite. The key to the viability of the new technology lies in the correct use, regeneration and recycling of Al(OH)3 used to precipitate the ettringite. The water produced by this process is suitable for disposal to watercourses or for agricultural, domestic or industrial consumption. No brines are produced as the salts are converted to solid hydroxides, gypsum and calcium carbonate.The SAVMIN process has been tested successfully during several laboratory scale operations, and during two pilot plant operations at Stilfontein Goldmine for Anglogold and Navigation Plant, Witbank for Anglocoal. During the pilot plant campaign at Navigation Plant, metal and mineral precipitation was achieved with lime addition. The sulphate concentration in the water was reduced from 2136 mg/L to an average value of 102 mg/L and the calcium concentration was reduced from 727 mg/L to an average value of 70mg/L.The SAVMIN process generates a number of different waste streams including metal hydroxide sludge from neutralisation, gypsum sludge from the gypsum crystallisation steps, and calcite sludge from carbonation. The metal hydroxide sludge is composed of Mg, Ca, Mn and Fe hydroxide, and could be disposed of on a slimes dam. Gypsum sludge was greater than 99% CaSO4.2H2O. This gypsum could be used for dump or road capping, underground backfilling, production of wallboard and cement. The calcite sludge is pure CaCO3, which is recycled back to the neutralisation stage."

Jan 1, 2003

By P. N. Mohan Das, K. Harikrishna Bhat

"The major ilmenite reserves are located in India at Chavara (CH), Manavalakurichi ( MK) and Chatrapur, Orissa (OR). India stands first in terms of ilmenite reserves, which are estimated to be 278 million tonnes out of which, 142 million tonnes are processable. Mineralo-chemical analysis showed that Chavara ilmenite is the most weathered one with about 60% TiO2 while Chatrapur is the least weathered with about 50% TiO2. XRD and SEM studies of different magnetic fractions of these three mineral deposits established the co-existence of ilmenite with pseudorutile, rutile and haematite phases in substantially varying amounts. It is observed that the tropical weathering rather than the source rock difference has apparently played an important role in imparting major compositional and structural dissimilarities among the ilmenites in different places. Further, the chemical analysis, XRD and SEM characterisation of differently weathered samples of MK ilmenite separated by the magnetic fractionation showed that the degree of alteration was invariably associated with the decrease in magnetism, increase in the rutile phase and the change in Fe2+/Fe3+ ratio of ilmenite grains. Magnetically separated fractions when subjected to metallisation with carbonaceous reductant such as coke showed that the degree of reduction increases with the degree of alteration and with the decrease in the Fe2+/Fe3+ ratio.In the processing of ilmenite through the Becher process, aeration rusting of pre - reduced ilmenite is found to be the rate-limiting step thus, affecting the productivity and economy of the process. Investigations have proved that the addition of some organic compounds such as glyoxal, sucrose etc., to the system accelerates the reaction to such an extent that the rusting time has been reduced to less than half. The formation of acids by the these organic compounds during the rusting reaction was proved responsible for maintaining the pH of the solution in the range 3-4 at which iron hydroxide do not precipitate and block the pores in the reacting surface of the grain."

Jan 1, 2003