Search Documents

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 Christopher Davey, Marian Mazurkiewicz, Yvonne Spooner, Dana Hankey, Peter Kanjorski

The concept of a high pressure liquid jet mill with highly unsteady flow, has been developed and recently patented by Cornerstone Technologies LLC (CsT), for the purpose of micron and sub-micron particle production. The mill accepts feed sizes up to 15mm for some materials and is capable of submicron production. Successful material range from precious metals such as silver and palladium to dielectric components and substrates such as Barium Titanate slips, zirconia, titania and silica. The process has also succeeded in adequately reducing the size of materials for both composite and coating uses such as anthracite coal, graphite, chrome metal, wollastonite and more than 100 others. A unique design approach has been taken to highly maximize the energy flux in the mill's chambers to create extremely high turbulence and destructive cavitation. This is assisted by shock waves, which cause particles to undergo ultra high frequency pressure pulsations, high frequency collisions and then abrasion, shattering, hydrowedging, and cleaving. Due to these extreme properties the processing occurs in just fractions of a second allowing throughputs up to 1000 kg/h on a machine that would fit inside a 60 cm box. The technical solution and technological advance, as well as the environmental and economic benefits indicate rapid and wide spread acceptance of high-pressure liquid jet milling in modern industry.

Jan 1, 2003

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 Rhulani F. Maluleke, Francis W. Petersen, John H. Marsh, Johann de T. Steyl, Allan Nesbitt

"Pressure leaching of chalcopyrite and nickeliferrous pyrrotite at temperatures between 105 and 200 ºC has been proposed as a potentially viable route for the extraction of mineral elements from sulphide concentrates. In general, these concentrates contain iron, and the economic success of the processes is partially dependent on the choice of the environmentally acceptable iron-removal technique. One of the most widely used methods for the removal of iron from sulphate liquors is precipitation as hematite, goethite, or jarosite. The nature of the iron precipitate formed, dictates downstream dewatering and residue treatment and disposal options. However, a better understanding of iron precipitation under the defined process conditions would consequently be of benefit in process design and optimization.This study investigated the precipitation of iron in the autoclave at temperatures between 105 and 200 ºC. The effects of temperature, acid concentration, iron concentration, and the presence of other metal cations on the nature and composition of the precipitates were determined."

Jan 1, 2003

By Stoyan N. Groudev, Ioannis Paspaliaris, Plamen S. Georgiev, Irena I. Spasova, Kostas Komnitsas

"The uranium deposit Curilo located in Western Bulgaria for a long period of time was a site of intensive mining activities including both the open-pit and underground mining techniques as well as in situ leaching of uranium. The ore was rich in pyrite and, apart from uranium, contained some non-ferrous metals. The mining operations in the deposit were ended in 1990 but since that time the deposit is a permanent source of acid drainage waters. The generation of these waters is connected mainly with the oxidation of pyrite and other sulphide minerals by the indigenous acidophilic chemolithotrophic bacteria.Laboratory and pilot-scale studies revealed that an efficient clean-up of the above-mentioned waters was achieved by means of passive systems of the wetland type. In 2001 a wetland was constructed in the deposit to treat a portion of the acid drainage waters which were discharged to a small ravine. This ravine reaches into the Teina, a small river that is a tributary of the upper reaches of the Iskar river.The wetland was constructed in the ravine and its bottom was located on intrusive rocks with a very low permeability. The rocks were covered by a 30 – 50 cm layer consisting of a mixture of soil, plant compost and crushed limestone. The wetland was characterized by an abundant water and emergent vegetation and a diverse microflora. Typha latifolia, Typha angustifolia and Phragmites australis were the prevalent plant species in the wetland but species of the genera Juncus, Eleocharis, Carex and Poa as well as different algae were also well present.The acid drainage waters treated by the wetland had a pH in the range of about 2.5 – 4.1 and contained uranium, radium, some heavy metals (iron, manganese, copper, zinc, cadmium, lead), arsenic and sulphates in concentrations much higher than the relevant permissible levels for waters intended for use in the agriculture and/or industry. The watercourse through the wetland covered a distance of about 0.2 – 1.0 l/s."

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

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 Francesco Montanari, Gianni Schena

"Recent improvements in X-ray computed tomography allow investigation of objects several tens of millimetres in dimension with spatial resolutions in the order of a few microns. These improvements are made possible by coupling the micro-focus technology adopted by some of the latest cone-beam X-ray sources with an increase in the efficiency of the detectors. The micro-focus technology allows the production of clearer images at high magnification by reducing the penumbra (fuzziness) associated with larger focal spot size.Even higher resolutions can be expected in the next few years with the commercialisation of nano-focus X-ray tubes. In practice one can inspect a system of fine composite particles and analyze the different mineralogical phases in each individual particle. Computed tomography allows accurate liberation studies, e.g. providing liberation spectra or washability data in tens of minutes. However, on-line application of micro-focus computed tomography is unlikely in the foreseeable future, despite rapid development.Dual-energy (DE) radiography is another X-ray technique, which allows retrieval of the volumetric content of valuable components in two-phase particles in a fraction of a second. A digital radiograph of a single two-phase particle produces a grey level image, where the luminosity of the pixels is determined by the sum of the attenuation levels of all the structures. Thus morphological and compositional effects concur to produce the radiographic image, which does not allow retrieval of the composition of the particle, as the 3D-structure of the particle is compressed into a 2D-image, with an obvious loss of information. Thus, in principle it is not possible to discriminate between thick, comparatively penetrable, and thin, comparatively impenetrable mineralogical components."

Jan 1, 2003

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 J. Tian

"BHP Billiton carried out a pre-feasibility study on the LanPing zinc deposit to evaluate the possibility to jointly develop the zinc deposit into a large-scale zinc project with their Chinese partner. The unique characteristics of the complex LanPing zinc orebody and ore are 1) smithsonite (ZnCO3) as one of major zinc bearing mineral besides sphalerite, 2) varying and irregular oxidation degree of zinc (0 ~ +90%) in the different zone and depth of the deposit, and 3) varying host gangue from limestone/calcite dominant to quartz dominant, which requires a robust and flexible flotation process to recovery zinc from both sulphide and oxide efficiently.The conventional mineral processing flowsheets have been tested on the LanPing samples taken from the various orebodies by various parties during the past 20 years that includes a sequential flotation flowsheet that was tested in a demonstration plant using the mixed ore. The results of the demonstration plant runs show that the conventional oxide flotation using Na2S and amine collectors could achieve 50 ~ 75% of oxide zinc recovery at very high sulphidiser consumption for the mixed ore but the highly oxidised ore did not satisfactorily respond to the flowsheet in terms of performance consistency and efficiency of oxide zinc recovery, which is very crucial to the overall economics of the project."

Jan 1, 2003

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

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

Jan 1, 2003

By 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 P. K. Sen, Mrinal K. Ghose

Tailing slurry is usually abrasive and possesses high viscosity. This paper examines the existing iron ore beneficiation process and focuses on some of the key environmental issues related to the disposal of tailings. It identifies that almost 32% of the iron ore extracted ends up as tailings and they are usually disposed in slurry form in tailing ponds. By the year 2000, 27 Mt of iron ore tailings were generated in India, which has become one of the biggest waste handling problems to the industry. Characteristics of the tailings vary widely. So the physical nature of tailings cannot be considered separately in isolation without considering the mill effluent from the beneficiation plant. In the present investigation, studies were carried out in three iron ore mines in India to evaluate the characteristics of tailings from the beneficiation plant. The tailing samples were collected from different locations during a time period of one year and analyzed. The results will be discussed and the characteristics of the tailings have been evaluated. The disposal system of tailings at the three mines was evaluated. The research on the settling characteristics of tailings indicates that the area provided in the existing tailing ponds in India is much more than that of the experimental results. This paper concludes that sedimentation tests are essential to design appropriate tailings pond with respect to size. In the proposed scheme it is suggested that an additional unit process, i.e. sedimentation tank be added to the process before the disposal of tailings to the tailing pond.

Jan 1, 2003

By Kauko T. Ingerttilä, Jouko O. Kallioinen, Jaakko O. Leppinen, Alexander V. Lashkul, Vladimir E. Nenno

"Separation in Froth (SIF) is a process for the separation of mineral particles during their descent downwards through a moving froth layer, generated on the surface of water or some other liquid media by means of a bubble generator and frother. Due to the special operation principles of SIF it is possible to separate mineral particles that are about 10 times coarser than the optimal particle size for conventional flotation. In this paper the performance of the SIF technique is presented in the separation of apatite, calcite and silicate minerals from various industrial sources, based on tests with laboratory and pilot plant-scale SIF machines. Basic laboratory test results of the flotation of pure diamonds are also presented.It was shown that calcite, apatite and diamonds with particle size up to about 3 mm can be successfully floated with SIF at high recovery and grade, provided that the degree of liberation is sufficiently high. Coarse calcite (+0.25-2.8 mm) was concentrated with reverse SIF in one flotation step at 87% recovery with better than 99% grade. Apatite particles coarser than 0.2 mm are not well floated in the conventional flotation circuit leading to high P2O5 content in the coarse size fractions of flotation tailings. On the contrary, SIF is capable of recovering such coarse particles at high recovery. However, P2O5 content of the SIF tailings starts to increase at about 0.7 mm due to insufficient liberation of apatite. At higher particle size the lack of hydrophobicity of apatite particles is also likely to lower the recovery.The pilot plant testwork showed that SIF can be successfully used at operating plants not only for preliminary upgrading of the feed of conventional flotation, but also for producing final grade calcite concentrate (>99.5%) from the screen overflow or from the cyclone underflow in a particle size range up to 1 mm. It was particularly promising that the separation took place in one SIF flotation step, instead of several stages of the conventional flotation circuit, with over 90% calcite recovery. The specific capacity determined with the 1 m2 pilot plant unit was approximately 30 t/m2h. Simultaneously the consumption of chemicals was significantly lower than for conventional flotation."

Jan 1, 2003

By Natalie J. Shackleton, Deryck de Vaux, Cyril T. O’Connor, Vratislav Malysiak

"The major losses of PGM and base metals in the beneficiation of platinum group deposits occur during the separation of gangue from the value minerals by selective flotation. A number of studies have shown that this negative impact on flotation is due to surface passivation, caused by various ions that may originate from the external water supply or, as is likely in the majority of cases, from the oxidation of the mineral surfaces and the grinding media. The objective of the study was to investigate the effect surface passivation and inadvertent activation have on flotation and how this can be managed so as to increase the separation of pentlandite and pyroxene. The aim was to minimise the percentage pyroxene reporting to the concentrate and simultaneously maximise the pentlandite recovery. The testwork incorporates the addition of an activator (copper sulphate), a complexing agent, such as DETA (diethylenetriamine) and a dispersant (polyphosphate) at pH 6 and pH 9 in an attempt to alleviate the surface passivation of pentlandite and inadvertent activation of pyroxene. Both synthetic minerals and plant ores were studied in order to determine the effect surface passivation and inadvertent activation have on mineral surface alteration and floatability. Zeta potential determinations, microflotation, ToF-SIMS (Time of Flight Secondary Ion Mass Spectrometry) analyses, laboratory batch flotation tests and continuous flotation testwork were used as tools to study the surface alteration and/or floatability.Zeta potential determinations and ToF-SIMS analyses showed that copper adsorption is non-selective. Both pentlandite and pyroxene become copper (II)-activated in the presence of copper sulphate and subsequently, in the presence of xanthate, adsorption of the collector will occur onto copper activated mineral surfaces. Zeta potential determinations also showed an alteration of the surface charge in the presence of polyphosphate, thereby inhibiting surface passivation of sulphides by slime coatings due to surface repulsion."

Jan 1, 2003

By Sun Chuanyao, Jia Muxin

Generally, if the bond valence (BV) between metal ion and oxygen of the mineral is greater than 0.8, only surface species –Me-O-H or –Me-O exposures on the mineral interface, if the BV is between 0.2-0.8, the metal ion exposures on the interface, and if the BV is less than 0.2 the metal ion dissolves into water. The PZCs of oxide minerals and island silicate minerals are determined by the bond valence of the bond in the mineral crystals, the higher the bond valence the lower the PZC of the mineral. So the PZC sequence of Al2SiO5 minerals is kyanite> andalusite> sillimanite. The general rule for framework silicate minerals is as: The higher the Al content, the lower the PZC of the mineral, when the ratio of Al to Si in the tetrahedron skeleton is below 1:3. The higher the Al content, the higher the PZC of the mineral, when the ratio of Al to Si in the skeleton is between 1:3 and 1:1. The general rule for layer silicate minerals is summarized as: the three-layer silicate minerals have much lower PZCs than that of the two-layer silicate minerals. The threelayer silicate mineral with the octahedron layer occupied by lower charged cations has lower PZC than that of the three-layer silicate mineral with the octahedron layer occupied by higher charged cations. The twolayer silicate mineral with the octahedron layer occupied by lower charged cations has higher PZC than that of the two-layer silicate mineral with the octahedron layer occupied by higher charged cations. The layer silicate mineral with Al substitution in the tetrahedron layer has lower PZC than that of the layer silicate mineral without Al substitution in the tetrahedron layer. Such pyroxene minerals whose M1 is occupied by a trivalence cation and the M2 is occupied by a monovalence cation has lower PZCs than those both M1 and M2 are all occupied by bivalence cations. Such hornblende minerals whose M2 is occupied by a trivalence cation and the M4 is occupied by a monovalence cation has lower PZCs than those both M2 and M4 are all occupied by bivalence cations. There is no Si4+ or 4 coordinated Al3+ exposures on the surface of framework silicate minerals, the metal ions of three layer or chain silicate minerals are compact between tetrahedron layersor chains, they hinder the metal ions to interact with oleate acid radical, the metal ion octahedron layer exposures on the surface of a two layer silicate mineral, but the the oleate acid radical can not attach to a metal ion by replacing a –OH- that connects three metal cations in the same time, So the floatability of such silicate mineral is bad. The metal octahedron chain style of an island silicate mineral affects it floatability, the mineral exposures octahedron chain metals with two dangling bonds in two directions floats better than the mineral exposures octahedron chain metals with two dangling bonds in one direction.

Jan 1, 2003

By Elzbieta Mielczarski, Jerzy Mielczarski, Jan Drzymala, Yann Duval

"The monoalkyl ethers of polyethylene glycols are universal flotation reagents because they can be used as collectors, frothers, surfactants, and depressants. Their collecting power was demonstrated for different minerals including coal and quartz.It was confirmed in this work that monoalkyl ethers of polyethylene glycols could be used as collector in flotation of quartz in a monobubble Hallimond cell. Since feldspar does not float in the same cell, it was also shown that selective separation of quartz and feldspar in the Hallimond tube is possible. However, a trail to use the monoalkyl ethers of polyethylene glycols compounds for separation of quartz and feldspar by flotation of mixture of these minerals in a Mechanobr laboratory flotation machine was futile, indicating that these reagents required special environment for flotation.Most probable parameter responsible for a decrease in quartz flotation in the flotation machine is the hydrodynamics of process, and different adsorption/desorption conditions. To prove this, another series of experiments was carried out to separate quartz and feldspar, in which a laboratory flotation column was utilized. The performance of the flotation column was in between that of in the Hallimond tube and flotation machine. These experiments confirmed that the hydrodynamics of flotation plays a vital role in flotation of quartz with monoalkyl ethers of polyethylene glycol compounds."

Jan 1, 2003

By Francesco Vegliò, Luigi Toro, Francesca Beolchini, Francesca Pagnanelli, Stefano Ubaldini

"Biosorption is an innovative technology used to remove heavy metals from aqueous solutions from mining waters and other industrial wastes. A wider application of this alternative process is strictly dependent on the understanding of the chemico-physical aspects involved, in order to optimize the operating conditions. Mechanistic models are the most useful tools used for understanding purposes, even if the empirical models are still widely applied for their simplicity.In this paper especially propagated biomasses of Sphaerotilus natans, calcium alginate and some waste materials were tested as adsorbents for single and binary solutions containing heavy metals at different pH. The equilibrium experimental results were fitted according to empirical and physical models with growing complexity outlining the inadequacy of the predictive models; in fact, the non-ideal interactions among metals require the insertion of additional correction parameters."

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 present study is devoted to improvement of the leaching efficiency during phosphorous removal from high phosphorous gravity-magnetic concentrate. Before leaching the concentrate has been subjected to roasting with the addition of either Ca(OH)2 or CaO. The oolitic iron ore is roasted at 900°C for one hour. This reflects in reaction between alkaline earth additive and quartz, aluminosilicates, phosphorus, and some other minor components of the gangue minerals. The application of leaching, physical separation, and wash out of salts has resulted in the decrease of phosphorus from 0.7 to 0.15 % and it is established that the major influencing factor is the concentration of acid and to a less extent duration of the leaching process. About two third of the phosphorus can be removed by roasting with 3 % CaO to hematite, coarse grinding to d50 0.3 mm, dry high intensity magnetic separation and leaching of the magnetic fraction with hydro-chloric or nitric acid.

Sep 1, 2012