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By A. L. Hinde

The steady-state and dynamic behaviour of semi-autogenous grinding (SAG) mills are arguably best described using a population model that caters for the breakage kinetics and the material trans-port of rock and pulp inside the mill. Breakage kinetics are usually expressed in terms of a specific breakage rate function and a separate primary breakage distribution function. Material transport usually invokes the concept of a specific discharge rate function. Unfortunately, the breakage rate and breakage distribution functions for SAG mills are very difficult to estimate uniquely from plant data alone. Simplifying assumptions must be made to over-come this problem, which leads to many unresolved dilemmas with regard to whether or not the de-rived functions are accurate, precise, and reflect reality. For example, it is sometimes assumed that the breakage distribution function for a SAG mill treating run-of-mine ore can be derived from laboratory dropweight and tumbling tests on small rocks in narrow size ranges. Such tests hardly reflect the environmental conditions likely to be encountered in a pilot or production SAG mill where there is a wide spectrum of particle sizes. It is shown that the dilemmas associated with standard population balance models (models that utilise separate breakage rate and breakage distribution functions) can be overcome by expressing breakage behaviour inside a SAG mill in terms of a single function. This function is an energy-based cumulative breakage rate function defined as the fractional rate at which particles and rocks coarser than a given size break to below that size per unit specific energy input. A model for SAG milling is formulated, which invokes the concept of a cumulative breakage rate function. Comparisons are made between the mathematical structure of this ?simple model? and standard population balance models. Perhaps the most attractive feature of the ?simple model? is that the cumulative breakage rate function can be uniquely estimated from measurements of size distributions and mass flows of the feed and discharge streams together with the size distribution and holdup mass of the mill charge. Such measurement can easily be made at pilot scale. It is concluded that this simplified approach to SAG milling may turn out to be the quickest way to fully describe and quantify the performance of these very complex mills.

Jan 1, 2014

By R. M. Zhao

The process conditions and mineral characters of cleaning separation stage in magnetite concentration plant are studied in the paper, and the affecting factors and the methods to increase the concentrate grade are analysed and given. The BKJ cleaning special drum magnetic separator is developed specially for the cleaning stage according to process conditions and mineral character. The separation mechanism, structure characters, separation process and excellent adaptability of BKJ special magnetic separator are described. The results in Zhangjiawa Concentration Plant show that the BKJ special drum magnetite separators play an important role in increasing the concentrate grade and improving the economic benefit.

Jan 1, 2014

By Robert van Hille, Alison Lewis

The precipitation of a selection of metals from both a synthetic and an actual metal-rich effluent was investigated. The experimental aspects of this study were carried out in a two-stage process consisting of a pre-treatment clarifier and a fluidised bed (pellet) reactor. Each unit operation in the two-stage process was investigated separately. The pre-treatment clarification stage at pH ˜ 5 resulted in a 99.9% removal of iron and 97.3% removal of aluminium. The pellet reactor was used to precipitate nickel as nickel carbonate from a pure stream and a removal efficiency of 99.6% was achieved. The high local supersaturation at the reagent inlet points caused the formation of a large amount of fines, but these agglomerated onto the pellets up the length of the bed. For copper precipitated as copper sulphide from a pure stream, a maximum removal efficiency of 92% was achieved. The high local supersaturation at the reagent inlets also caused the formation of a large amount of fines, but the extremely sparingly soluble nature of copper sulphide meant that the fines were not agglomerated up the length of the bed. For removal of cobalt as cobalt carbonate from an actual stream, a stable cobalt removal of only 60% was achieved. This was found to be due to the presence of magnesium, which reduced the cobalt precipitation efficiency through the formation of the magnesium bicarbonate ion.

Jan 1, 2003

By H. G. Hedlund

Tailings in Mining Industry can be handled in different ways. Today tailings disposal is in focus by projecting new plants as well as treating and handling of old Tailings dams.The trend today is to process minerals, detoxify the Tailings and place them as dry surface Deposition or Underground Backfill. This paper will briefly present five different Mining plants in North and Central America, where Tailings have to be dewatered for dry depositing. The Metso-Sala VPA is a filter especially developed for dewatering and drying of Mineral Concentrate and Mineral Tailings. Keywords: tailings disposal, dewatering, drying, mineral tailings

Sep 1, 2012

By X. Q. Cao

As the second largest phosphate resource in the world, Chinese phosphate ores generally grades with low of P2O5. The presentation of beneficiation test on the low grade of phosphate rock in this paper may be used for a reference for development and utilization of the similar reserves. The ore is a marine sedimentary phosphate rock containing low grade of P2O5 and high content of MgO and R2O3; The banded structure shows its suitability for heavy medium separation. The laboratory heavy liquid testing results indicate that as specific gravity of the heavy liquid is 2.85 g/cm3, a rougher concentrate assaying 28.71% P2O5 could be obtained while the rougher tailings contain only 4.47% P2O5. When the combined process with heavy liquid separation followed by direct & re-verse flotation is employed to treat the feed containing 21.15% P2O5, 3.79% MgO, 1.86% Fe2O3, 3.66% Al2O3, 23.75% A.I, and specific gravity of heavy liquid is 2.84 g/cm3, the optimum mesh of grind is 67.5% minus 200 mesh, a phosphate concentrate contained 32.51% P2O5, 0.48% MgO, 0.81% Fe2O3, 1.69% Al2O3 can be produced at a yield of 55.24%. The concentrate P2O5 recovery is 85% with which quality comply with the Class A specifications for production of phosphate fertilizer.

Jan 1, 2014

By V. Sheikhzadeh, M. Saghaeian, R. Hejazi, A. Abazarpoor

"The morphology of pellet feed is known to influence several properties of iron ore pellets, including drop number, compression strength and reduction properties. The effect of grinding method on the particle size, specific surface area and particle shape of an iron ore concentrate has been studied. Grinding methods considered were ball mill and high pressure grinding rolls (HPGR). 5 different samples (Blaine= 1800, 1900, 2000, 2100 and 2200 cm2g-1) were used to compare the size, shape and specific surface of particles for each grinding methods. Particle size was meticulously examined by sieve analysis, laser sizing and image analysis. In samples ground by ball mill, it has been observed that the fraction of particles <10µm increases from 39% to 46% as the Blaine number increases from 1800 to 2200 cm2g-1. For HPGR samples, corresponding figures are 41% and 49% respectively. It is evident that for samples ground by HPGR, the fraction of fine particles is higher than that of those ground in the ball mill. To measure the specific surface area of particles, Blaine and BET were used. A higher real surface area was observed from HPGR treatment in comparison to ball mill grinding, provided by a higher porosity, cracks, roughness and new surfaces. Shape factor of particles was determined using three descriptors: circularity, roughness, and aspect ratio. It was also observed that particles produced by HPGR were more elongated, less circular, and rougher than those processed by the ball mill. 1. INTRODUCTION Particle size and shape are important parameters that can significantly affect mineral processing plants and pelletizing plant performances (Brozek and Surowiak, 2007). It has also been proposed that green pellet quality is directly related to the amount of fine particles in a pelletizing plant (Dwarapudi et al., 2008; Umadevi et al., 2008; Gul et al, 2014; Van der Meer, 2015). Particle size distribution and specific surface area (SSA) are also key factors that can control the quality of green and fired pellets. Processing circuits generally reduce the fines fraction to lower than the required specific surface area (SSA). It is therefore necessary to regrind concentrates to produce suitable pellet feed for further treatment in the balling and firing steps [1, 2]. Two main methods are used for re-grinding of concentrate; high pressure grinding rolls (HPGR) and ball mill. Given the different forces used to reduce size in these methods, it is expected the shape of particles will be different (Pourghahramani and Forssberg, 2005)."

Jan 1, 2018

By J. Yianatos

The regrinding stage is necessary to achieve the particle size (liberation) for the final upgrade in the cleaning flotation process. At present, vertical mills (Vertimill) are employed at industrial scale, using small steel balls as grinding media. The regrinding process characterization requires mixing regime knowledge along with the mean residence time of the liquid and solid phases. The residence time distribution (RTD) and the actual mean residence time estimations from theoretical relationships are complex due to the presence of three components (solid mineral, balls and water), mass transport characteristics and segregation affecting solid holdup. Therefore, the experimental RTD determination is suitable for industrial mills. In this work, RTD measurements were performed in two different industrial flotation plants. Both plants operate with Vertimills of 1000-1500 HP in the regrinding process with different circuit arrangements according to the plant treatment capacity. The RTD was measured using the radioactive tracer technique. This technique allows for non-invasive tracer detection where the procedure consists of selecting a liquid (Br82 in aqueous solution) or solid (irradiated solid) tracer for RTD data acquisition in real time. The RTD was modelled by the Large and Small Tanks in Series (LSTS) model, which allowed the characterization of the different mixing regimes for both liquid and solids in the regrinding mills. Effective mean residence times in the range 2-11 min were obtained with RTD shapes similar to those obtained in tumbling ball mills. It was found that residence times of liquid and fine particles were similar, which is consistent with results observed in other mixing systems, e.g. mechanical flotation cells. Also, the mean residence times estimated from the RTD allowed the mass balance adjustment to be validated from metallurgical sampling data. RTD estimations are useful for better understanding the Vertimill behaviour and to identify the actual breakage rates. Keywords: vertical mill, residence time distribution, particle size, modeling

Sep 1, 2012

By M. V. S. Cavalcante

The quality of iron ore pellets, represented in terms of parameters such as cold compressive strength (CCS) and Tumble Index (TI), has a strongly influence on the productivity and energy of reduction furnaces like the blast furnace and on the quality of hot metal or liquid iron. The main objective of pelletization operations is to produce iron ore pellets of desirable specifications and ensure high levels of plant productivity and energy efficiency. Advanced process control of an industrial iron ore pellet induration process using a soft sensor for pellet quality and fuzzy-logic based control algorithm is described in this paper. The pellet quality soft sensor consists of a rigorous mathematical model of the induration process and a statistical model for the pellet quality parameters. The mathematical model is based on the fundamental principles of heat and mass transfer between gases and pellets, kinetics of drying and condensation of moisture, combustion of coke, calcination of limestone, and melting and solidification of pellets. The predictions of wind-box temperature profiles are in close agreement with the measured profiles. The time-temperature profiles of the pellets during induration, along with raw material characteristics and induration process operating conditions, are used as inputs to the quality model to predict cold compressive strength and the Tumble Index. The predictions of the quality soft sensor along with the rules based on fuzzy-logic derived from simulation results and operator experience are then utilized to control the induration process to achieve precise control of the quality parameters and to optimize the induration process in terms of fuel efficiency and productivity. The mathematical model is also utilized as a soft sensor for temperature, moisture and composition profiles of pellets and gases. Results of implementation of this model-based control strategy on an industrial scale induration process will be presented. Keywords: iron ore, pelletization, simulation, process control, optimisation

Sep 1, 2012

By Andries Van Wyk, Steven Bradshaw, Guven Akdogan, Jacques Eksteen, Cornelius Snyders, Cleophace Mpinga

"In order to exploit lower grade and complex platinum group metal resources, cheaper and more efficient alternatives to the conventional mill-float-smelt-refine route are being sought, particularly for resources’ in areas that are water-scarce and where electrification is costly and problematic. Leaching with cyanide is a promising process option and although recoveries are lower than in the conventional process routes, progress into the understanding of cyanide leaching of PGM containing ore and concentrate has been made. Research regarding the feasibility of upgrading the pregnant PGM leach solution using activated carbon has, however, been lacking and hence forms the focus of this paper. Bottle roll adsorption tests for dilute PGM solutions (0.15ppm Pt, 0.38 ppm Pd, 0.1 ppm Au) onto granular activated carbon showed high rates within the first 60 minutes (giving more than 90% recovery of precious metals). Comparison of the Pt isotherm to Au isotherms from literature indicated a similar loading capacity, while that of Pd was found to be significantly lower. The effects of solution pH, temperature, base metal concentration, free cyanide concentration, thiocyanate concentration, initial PGM concentration and activated carbon concentration were investigated and are discussed. Elution of the Pt and Pd, with the AARL elution process, was found to be effective with recoveries of 95% after 5 bed volumes of eluant at the optimum pre-treatment concentrations and a temperature of 80°C. Temperature, NaCN and NaOH pre-treatment concentration and the ionic strength of the eluant were found to be the most important factors affecting elution while base metals concentration, acid-pre-treatment, carbon loading and thiocyanate concentrations to a lesser extent. Simplified combined flow sheets are suggested and the corresponding mass balances are compared."

Jan 1, 2014

By D. W. Lui

Tangdan copper oxide deposit, the largest independent copper oxide deposit in China so far, is located in the northeast of Yunnan province, southwest of China. The ore from this deposit is characterized by: low grade, high oxidation ratio, and fine-grained disseminated, resulting in poor flotation recovery. The analysis of plant flotation data reveals that the loss of copper minerals into tailings is mainly with coarse size fraction due to insufficient liberation and fine size fractions, especially minus 10 microns fraction, which proved to be very difficult-to-float with conventional flotation. In order to improve the performances of plant flotation of this ore, laboratory flotation tests were conducted with the pure malachite, which was the principle copper oxide mineral in Tangdan copper ore deposit. The results obtained suggested that a finer grinding (up to -325 mesh or even -400 mesh) be needed to decrease the loss with coarse size fraction, and vacuum flotation is a promising way for the recovery of the fine malachite effectively.

Jan 1, 2014

By U. A. Peuker, A. Grohme

"The cost effective and sustainable production of high purity rare earth elements is still challenging. The most commonly used method, known as solvent extraction, is very complex, needs many steps to separate the rare earth ions in a high purity, and causes a lot of environmental problems. An alternative method is the utilization of a separation column filled with adsorbent material. Within the column the desired target substance can be selectively separated out of a multi component mixture in one step. To find out if an adsorption material is suitable for the separation with a column, a characterization of the adsorbent material is necessary. In this paper are described the usage of modified activated carbon (oxygen and phosphorous modification), Di-(2-ethylhexyl) phosphoric acid (D2EHPA) impregnated Amberlite® XAD 7 HP and Lewatit® VPOC 1026 as adsorption materials. Several adsorption isotherms and process conditions are determined to characterize the selectivity between the adsorption materials and different rare earth ions. With these isotherms the mass specific rare earth ion retention for the adsorbent materials can be calculated. In addition to the isotherms the best working parameters are investigated e.g. pH-value and the time for equilibration. Finally, the separation factors between two rare earth elements are determined. The separation factor shows how successful a two element system can be separated."

Jan 1, 2014

By Brian Hart, Rong Fan, Roger Smart, Andrea Gerson, Ning Xu

A complete strategy has been developed for identification of the reasons for losses in recovery and/or grade, due to changes or complications in mineralogy and in mineral surface conditioning, and their subsequent correction. The sequence of methods starts with comparison of mineral phases between QEMSCAN/MLA (compositional) and Rietveld XRD (crystalline diffraction) with bulk assay reconciliation. This methodology has recently led to identification of unrecognised amorphous content (12-40 wt.%), previously attributed to crystalline phases, in the fine fraction (<35 µm) of some problematic flotation feeds. Attached amorphous silica, talc- and chlorite-like fines have direct influence on the hydrophobic/ hydrophilic ratio on value mineral surfaces adversely affecting flotation. SEM/EDS is used in the backscattered imaging mode to determine possible problems with liberation (e.g. remnant local locking), not detected in standard liberation analysis, resulting in gangue flotation. EDTA extraction is used to assess bulk feed pre-oxidation and sequential oxidation product loading through the circuit. Changes in circuit solutions are assayed with speciation modelling of precipitates and potentially adsorbing species. ToF-SIMS with principal component analysis is then used to correlate surface species with specific minerals and can be used to assess the effectiveness of specific reagents particularly collectors. This approach identifies unwanted activating species and interference with value surfaces by adsorbed hydrophilic ions, precipitates and fine particles. When the interference or ineffective reagents are specifically identified, remedial action can be targeted. This method has identified residual talc-like layers (<10 nm thick) inducing gangue flotation of pyroxene and chromite in PGM flotation. Recent case studies of application of the full methodology to losses of molybdenite at KUCC and to sphalerite activation in the Cu/Pb circuit at Brunswick Mines with remedial action are discussed.

Jan 1, 2014

By Carsten Gerold

The paper is giving an overview about successful operating Loesche Vertical ? Roller ? Mills (VRM) installations and summarises the main benefits of the dry compressive Loesche grinding technologies in Airflow- and Overflow-Mode. Some of these benefits are optimised energy efficiency of the grinding - classifying - circuits, increased mineral recoveries and decreased OPEX costs, at a parallel simplification of the process route. Within this paper the process values of the Loesche VRM are compared to existing or planned conventional grinding ? classifying circuits. Further advantages discovered in pilot trials and examples for new more efficient process route alternatives are given. The paper reports about production and pilot trial experiences obtained by crushing and grinding Iron Ore, Iron Ore Concentrates, Copper Shale, Copper Matte, Copper Slag, Titanium Slag, Tin Slag, Steel and Stainless Steel Slag with Loesche VRM.

Sep 1, 2012

By Y. D. Gao

A new technique has been developed for comprehensively recovering tantalum niobium tungsten ore by adoption of stage grinding, stage separation, combination of flotation and gravity separation, gravity separation for coarse particles, flotation for fine ones, combination of ore-dressing and hydrometallurgy. The new type and high efficiency combinative collector mainly composed of benzyl hydroxamic acid is firstly used to treat tantalum niobium and tungsten slime, besides the new type equipment for gravitational separation ?YTF-C shaking table for fine particles is adopted to treat flotation rough concentrate, hence having notably enhanced both recovery and concentrate grade of fine tantalum niobium and tungsten minerals. The commercial test obtains the tantalum concentrate assaying Ta2O5 31.98% with recovery 43.44% and tungsten product assaying WO3 89.40% with recovery 76.02%. The developed technique provides a reliable approach and an effective way for comprehensive utilization of lean fine complex refractory tantalum niobium tungsten ore resource.

Jan 1, 2014

The ball level and pulp load play a key role in the operation of industrial scale ball mills. These two operating variables have a significant influence on the performance of the ball mill and any attempts to optimize these devices require manipulating either one or both of these variables. There are several models that can be employed to perform simulations to optimize the performance of industrial ball mills. However, most of these models require ball load and pulp load measurements as inputs to calibrate the model. The changes suggested by the simulator also provide operating regimes that involve moving either the ball level or pulp load and sometimes both of these variables. A ball mill model coded in JKSimMet was used in conjunction with the Sensomag to optimize the secondary ball mill at Waterval concentrator in South Africa. The results show that the perfect mixing ball mill model can be used in conjunction with the Sensomag to optimize the performance of the secondary ball mill.

Sep 1, 2012

By V. E. Vigdergauz

The work presented shows results of electrochemical study of pyrite hydrophobicity evaluated by air bubble induction time (IT) measurements. On the basis of measured IT?s an average thickness of the thin liquid film prior to its rupture has been evaluated, which confirms long-range character of the interactions between air bubbles and hydrophobic surfaces. Obtained data are discussed in the frame of recent studies of structures of solid-liquid interface based on molecular dynamics simulations and results of surface force measurements.

Jan 1, 2014

By Andrew Logan

Newcrest has a strong history of growth over the past 20 years, yielding value from previously marginal ore bodies. We have grown regionally in Asia Pacific through our operations in Australia, Indonesia and Papua New Guinea, and also established a beachhead in West Africa. The company has a reputation of realizing value from large, low-grade deposits adopting step change approaches. Newcrest is focused on an overall strategy of gold, low cost, long life and moderate growth. Capability step changes play a large delivery role. They transition from a business offline-to-online approach as opportunities mature. Newcrest believes in a) Knowing what ?good? looks like, b) An open innovation approach to actively working with others, c) The leap frogging leverage of making the ?old new again?, d)An adopt-adapt-develop methodology enabled by rapid prototyping/piloting, e) Getting our handsdirty with test work and plant analysis, and f) Staying focused on a few high business leverage areas. This paper describes Newcrest?s approach and our experiences in establishing renewed metallurgical processes, specifically aimed at increasing innovation adoption. Some of our step changes discussed include: 1) Early waste rejection to avoid high energy processing downstream, 2) Broader gold product channels to reduce site based processing needs, 3) Lower energy processing, and 4) Geo-Metallurgy approaches. Keywords: Newcrest, gold, step change, open innovation, adopt, adapt, develop, offline, online, prototyping, old new again, waste rejection, low energy, geo-metallurgy

Sep 1, 2012

By Kremena Dedelyanova, Tsvetan Damyanov, Nikolay Hristov, Evgeni Kostadinov, Lubomir Kuzev

"Spherical grinding media (balls) are the most widely used media for comminution of ores by grinding. One way to optimize the grinding process in a tumbling mill is associated with the development and testing of a new media shape. By modelling simulation study of the behaviour of two types of grinding media (balls and tetraballpebs) in the grinding process was conducted to determine the possible advantages of the new media shape. Tetraballpebs are in the shape of tetrahedrons with spherical convex walls. D305 mm and L305 mm Bond ball mill sizes were used in the experiment. They are modelled milling tetraballpebs bodies corresponding by weight to five ball sizes, namely ¾, 7/8, 1, 1¼ and 1½ inches which form the grinding media used in a Bond ball mill. They are cast steel grinding bodies. Studies carried out with both types of grinding media include equal number of milling bodies of the same weight and volume. Having thus ensured a uniform mass of the grinding media and the same number of milling bodies, all other conditions and process parameters being identical, conclusions can be drawn about the influence of the grinding media shape on the grinding process. Compared to steel balls, the tetraballpebs used in laboratory tests carried out in closed cycle by Bond ball mill and the study of the rate of grinding gave five to six per cent higher yield of a control size of minus 0.1 mm. Measurements of the Bond ball mill power consumption demonstrated that tetraballpebs grinding media achieved energy saving of 4.7 per cent for the production of one gram of the control size of minus 0.1 mm."

Jan 1, 2014

By B. Rezai

Impeller speed and air flow rate are two influence parameters on coarse particles flotation and collision and attachment angles. So, in this research recovery of quartz particles at four diameter classes carried out and collision and attachment angles investigated. It is found that maximum flotation response was observed at Impeller speed of 1100 rpm and 15 L/h air flow rate. For either more quiescent (Impeller speed<1100 rpm) or more turbulent conditions, flotation recovery decreased steadily. Furthermore, amount of attachment probabilities is calculated using suitable equation. According to this study, with decreasing particle size, air flow rate and impeller speed, probability of attachment increased and with increasing contact angle, probability of attachment increased. For various air flow rates, impeller speed and particle size, collision angle has been calculated. Maximum collision angle obtained at with 15 L/h air flow rate, particle size of 256 µm and impeller speed of 700 rpm and minimum collision angle obtained at with 45 L/h air flow rate, particle size of 545µm and impeller speed of 1300 rpm. In this study, maximum attachment angle, , was around 75 L/h air flow rate, particle size of 256 µm, contact angle of and impeller speed of 1300 rpm and minimum attachment angle was with 15 L/h air flow rate, particle size of 545 µm, contact angle of and impeller speed of 1300 rpm. ?82.72 ?64 cr??33.39 ?90 ?13.0 ?60

Jan 1, 2014

By Achilles Dutra, Everton Santos, José Oliveira

The beneficiation of phosphate ores by froth flotation is the most efficient process used to separate apatite from gangue minerals like calcite, dolomite and quartz. However, the similarity of surface properties between apatite and calcite generally lead to non-selective adsorption of reagents, rendering the selective separation of these minerals a worldwide problem. The phosphate deposit of Itataia, State of Ceará, Brazil, studied in the present work, presents a complex mineralogical composition having uranium associated with the apatite mineral. The main gangue minerals are calcite and quartz. The bulk flotation of apatite and calcite with anionic collectors in an alkaline medium followed by the selective flotation of calcite at pH 5.5 using phosphoric acid as well as citric acid as depressant have been suggested for this ore. This paper presents the results of contact angle measurements obtained using jojoba oil, a natural reagent composed mainly of gadoleic acid (C20:1) and long-chain fatty alcohols (eicosenol and docosenol), as an alternative collector for the selective separation of apatite and calcite minerals. The hydrophobicity studies were carried out using a computer controlled contact angle goniometer. Additionally, the collector adsorption was evaluated via electrophoretic mobility and FTIR measurements. The results indicated that a high selectivity can be obtained by using jojoba oil as collector in a slightly acid pH range, without the use of depressant. The best results were achieved with a jojoba oil concentration of 200 mg.L-1 at pH 6.5, where the apatite was fully hydrophilic and calcite showed a high hydrophobicity (? > 60 º).

Jan 1, 2014