Ore Breakage Research Articles

Analysis of different-type mechanical effects on selectivity of mineral dissociation

The authors have tested effect of mechanical impact type and energy on selectivity of spodumene ore breakage in a disintegrator and in vibratory and ball mills in terms of pegmatite with lithium content of 0.1%. It is shown that the highest efficiency of mineral dissociation is achieved in disintegration by free impact. Analysis of grain-size distribution and chemical composition and the X-ray study also reveal advantage of the disintegration process, which allows higher content and recovery of lithium in concentrate at reduced sliming.

Ore particle breakage behaviour in a pilot scale high voltage pulse machine

SELFRAG AG has developed a flexible pilot scale Pre-Weakening Testing Station (PWTS) using high voltage pulses (HVP). This provides a unique opportunity to investigate the machine setting conditions on ore breakage behaviour. A joint campaign was undertaken by the Julius Kruttschnitt Mineral Research Centre and SELFRAG AG to investigate the breakage behaviour of two copper–gold ores and one iron ore in the PWTS. The effects of specific energy, pulse voltage, cumulative discharges, feed particle size and ore particle breakage pattern (body breakage or surface breakage) were investigated. The investigation revealed that the mass-specific energy of HVP was the most significant factor affecting the breakage behaviour in the PWTS. This effect was compounded with the effects of ore properties and particle size. Comparison between the PWTS and a laboratory HVP machine indicates that there is considerable scope for optimisation of HVP performance based on processing zone design.

A t10-based method for evaluation of ore pre-weakening and energy reduction

Currently the effect of the pre-weakening of ore particles by high voltage pulses is evaluated by the percentage change of A∗b values between pulse-treated and untreated ore particles. The values of A∗b, widely used as an ore breakage competence indicator in the mineral industry, are determined from the parameters of the JKMRC breakage models. In this study a t10-based method was developed to predict the degree of size reduction, t10, of pulse-treated particles from that of untreated particles broken at the same size/energy level. This method incorporates one parameter, CAb, which is equivalent to the percentage change of A∗b values.The t10-based method was validated using nine sets of comparative JK Rotary Breakage Tester data on pulse-treated and untreated ore samples over a wide range of impact specific energies and particle sizes. The t10-based method can be used to calculate the energy reduction due to the pre-weakening effect in the downstream comminution process. It indicates that the energy reduction by pre-weakening increases with an increase in the target product fineness and the degree of pre-weakening, and with the decrease in feed particle size.

Investigation on pre-weakening and crushing of phosphate ore using high voltage electric pulses

Mechanical size reduction processes in the mineral processing industry are energy intensive. In this study, a novel High Voltage Electric Pulses Crusher (HVEPC) was designed and developed to pre-weaken and crush a phosphate ore. To compare the effectiveness of the new HVEPC in crushing with the conventional crushers, several rock samples of a phosphate ore were used and the effect of the capacitor, the voltage level and voltage rise time on the phosphate ore breakage was investigated. Comparing the particle size distribution of the crushed samples using both the HVEPC and the conventional crushers revealed the difference between their breakage mechanisms. The final results showed that applying the high voltage pulses at specific energy of 3–5kWh/t could significantly increase and extend the cracks and microcrakcs inside the rocks and consequently lead to decline in the Bond crushability and Abrasion indices of the crushed samples by 10.6% and 28.1%, respectively.

Rapid ore breakage parameter estimation from a laboratory crushing test

Drop weight testers have been widely and successfully used to characterize ore breakage parameters for simulation of crushers and mills. In some cases, limitations of time, sample availability, and even cost, can prevent the conduction of these tests when preparing samples for chemical analysis and/or grindability and flotation/concentration testing. The present work demonstrates how a laboratory cone crusher equipped with a power meter, in conjunction with Whiten–Awachie crusher model, has been used to quickly estimate the A*b breakage parameters. With an average absolute error of 36% when applied to a variety of materials, it is demonstrated that the method is not a priori restricted to the particular crusher used, neither to the crushing conditions employed. It is discussed that the method, when part of a variability study, can be used as a convenient tool for geometallurgical mapping of ore deposits regarding ore breakage response.

Characterisation of pre-weakening effect on ores by high voltage electrical pulses based on single-particle tests

A method based on single-particle tests has been developed to characterise the pre-weakening effect of high voltage pulses on ores. A pre-weakening index, PWI, defined as the percentage change in ore breakage resistance indicator (A*b) per unit of specific energy, is used to evaluate the energy efficiency of an electrical comminution machine, and to assess an ore’s amenability to pre-weakening by high voltage pulses. A reduced JKRBT (JK Rotary Breakage Tester) testing procedure using five tests (instead of the standard 12 tests per sample) to determine the ore breakage parameters, makes characterisation by high voltage pulse pre-weakening more practical.A gold–copper ore sample treated by high voltage pulses, based on single-particle tests with a specific energy of 1.6kWh/t, achieved an A*b change from 31 to 84 at a nominal particle size of 30mm, representing a 171% pre-weakening result. X-ray tomography images show the induced cracks/microcracks in the pulses-treated rocks. The pre-weakening effect was found more pronounced for larger fragments, suggesting that the use of high voltage pulses to pre-weaken AG/SAG mill feed may result in more significant benefits in terms of energy savings or increased throughput than pre-weakening ball mill feed.

Assessing the stirred mill design space

In the context of the mining industry, smaller grain size and other mineralogical characteristics have motivated the need to grind finer. In order to address this need, the interest in fine grinding technologies has grown over the last 20years as is illustrated by a growing body of knowledge on stirred milling. Emphasis in recent years has been on the use of computationally intensive modeling and simulation methods such as the discrete element method (DEM) and computational fluid dynamics (CFDs). However, due to the computational requirements of these two methods, initiating a study that spans the stirred mill design space would take a lot of computational effort and time. Therefore the goal of this paper is to propose and apply a simplified stirred mill model that will then be used to assess configurations in the stirred mill design space.To this end, a stirred mill model was proposed based on the assumption that the main if not only mechanism of ore breakage is shear. As the basis of this model is the fluid mechanics definition of shear stress, the stirred mill power model became a function of viscosity, mill speed and a new parameter called shear volume. An initial validation using published data indicated the shear based power model correlated well with measured power.Establishing a morphological chart to delimit the stirred mill design space indicated that 24 design and operating conditions can be assess using the established shear volume measure. The results indicated for the mill configurations tested that a change in stirred mill liner design can potentially increase shear volume and power from 14% to 290% as compared to smooth chamber liners.

The effect of microwave pretreatment on impact breakage of copper ore

It has been shown that very short exposures to a high level of microwave power lead to reductions in ore strength. In this paper, the influence of modulated microwave power on copper ore breakage has been investigated. This approach to power delivery is applied to ascertain whether the strength of porphyry copper ore can be reduced with lower average modulated power levels than using continuous power. Changes in resistance to breakage of the treated and untreated ore were quantified by comparative drop weight tests. Mineralogical investigation for the ore was carried out with the Mineral Liberation Analyser (MLA) for surface identification of minerals and X-ray tomography for volumetric analysis. The comparative drop weight tests showed that material treated for 5 s at 5 kW of modulated power was weaker than untreated material. However, for this particular low grade ore, the degree of breakage which was achieved could be achieved with substantially less mechanical energy. It is possible that by using much higher level of microwave power, better liberation might be achieved than using conventional methods.

Combined study of wear and abrasive fragmentation using Steel Wheel Abrasion Test

Scores of abrasive wear problems particularly those in the harsh environments involve remarkable breakage of the abrasive. One notable case is the ore breakage and the media wear in the comminution devices such as tumbling mills, where the abrasive breakage is indeed the objective of the process. While there are standard test methods for wear or breakage characterization of the materials individually, there is a need for standard test methods enabling us to conduct a combined study of the wear and breakage to create an environment similar to the actual applications. Steel Wheel Abrasion Test is one of the candidates providing us with such an environment to study wear, abrasive fragmentation and their inter-relation in one single apparatus because of its high-stress nature of abrasion. Moreover, there is a need for more precise tools of describing the quantity and quality of the abrasive breakage, and surface wear. In this research, breakage has been characterized through size distribution of the abrasive before and after the test, and estimation of the created surface area in abrasive based on the size distribution. Wear particles are collected from the used abrasive after the test using an electromagnet, precisely analyzed with laser scattering machine and their surface area density is calculated using the gas adsorption method. Characterization of the wear debris along with precise quantifying of the abrasive fragmentation provided powerful tools in studying the abrasive wear. Experimental results extracted from the Steel Wheel Abrasion Test indicate a strong correlation between the abrasive breakage and the wear which newly introduced tools were successfully capable of predicting. Additionally, the combined study of the wear and breakage enabled us to give explanation for some anomalous wear trends which were not justifiable in the past.

Influência da função distribuição de quebra na modelagem e simulação do circuito de moagem de Carajás - Parte 1 - ajuste de modelos

O modelo de misturador perfeito (PMM) leva em conta, tanto as características do equipamento, como as do minério. As características do minério são representadas pela função distribuição de quebra. Tal função pode ser determinada através de um método laboratorial proposto pelo JKMRC ou de funções padronizadas. O presente trabalho descreve o processo de modelagem matemática do circuito de moagem de Carajás, utilizando o software JKSimMet. Como resultado, foi possível avaliar a qualidade do ajuste do modelo em dois cenários: 1) utilizando a função distribuição de quebra-padrão do programa; 2) utilizando a função distribuição de quebra determinada para a alimentação do circuito de moagem. A partir desta análise, determinou-se, no ajuste do PMM e, em particular, na função taxa de quebra ou cinética de fragmentação, a influencia da função distribuição.

The steel wheel abrasion test (SWAT): A tool to study wear, friction and ore breakage in the mining industry

Developed from the rubber wheel abrasion standard test, the steel wheel abrasion test (SWAT) illustrates a simple highly controllable testing environment that produces repeatable results for studies of material wear, friction in wear and ore breakage during wear. The wear and friction results can be tied to equipment models such as those of mill charge motion to predict wear of both steel media and liner. The ore breakage results have the potential to be correlated to typical ore breakage tests such as the lab tumbling mill or the drop weight test. In this paper, the methodology used to avoid “highly anomalous results due to differential friction” is presented. It is shown that the proposed methodology leads to repeatable results for sample wear, friction and ore breakage. Wear, friction and breakage results from a selection of ore and steel media tests are presented. Further, steel media wear estimates are presented and compared with industrial mill reality.

Development of a rapid particle breakage characterisation device – The JKRBT

Ore breakage characterisation plays an essential role in the design and optimization of comminution circuits. Recently, the JKMRC comminution research team has developed a Rotary Breakage Tester (JKRBT) for rapid particle breakage characterisation tests. The JKRBT uses a rotor–stator impacting system, in which particles gain a controlled kinetic energy while they are spun in the rotor and are then ejected and impacted against the stator, causing particle breakage. The first industrialised JKRBT was installed at Anglo Research in Johannesburg in March 2007, and six more JKRBTs were deployed in 2008 around the world. This paper discusses the major design and calibration issues encountered in the JKRBT development and findings from detailed experimental studies.

Applying DEM outputs to the unified comminution model

The concept of a unified comminution model (UCM) was formulated with the vision of bringing all comminution models onto a common base. The structure of the model relies on knowledge of the mechanical environment in the comminution devices – the discrete element method (DEM) has been used as the tool to simulate this. The model structure tackles the fundamental causes of rock breakage, considering them to be independent of the comminution equipment. The equipment is considered to be the mechanism that applies a given comminution environment to the ore particles. Thus, once an understanding of the processes of ore breakage is gained, the mechanical environment from any type of equipment can be overlaid to provide a model that predicts the production of broken material.

Using DEM to model ore breakage within a pilot scale SAG mill

Using DEM to model ore breakage within a pilot scale SAG mill

Using DEM to model ore breakage within a pilot scale SAG mill

The best accepted method for design of autogenous and semi-autogenous (AG/SAG) mills is to carry out pilot scale test work using a 1.8 m diameter by 0.6 m long pilot scale test mill. The load in such a mill typically contains 250,000–450,000 particles larger than 6 mm, allowing correct representation of more than 90% of the charge in Discrete Element Method (DEM) simulations. Most AG/SAG mills use discharge grate slots which are 15 mm or more in width. The mass in each size fraction usually decreases rapidly below grate size. This scale of DEM model is now within the possible range of standard workstations running an efficient DEM code. This paper describes various ways of extracting collision data from the DEM model and translating it into breakage estimates. Account is taken of the different breakage mechanisms (impact and abrasion) and of the specific impact histories of the particles in order to assess the breakage rates for various size fractions in the mills. At some future time, the integration of smoothed particle hydrodynamics with DEM will allow for the inclusion of slurry within the pilot mill simulation.

An investigation into the influence of microwave treatment on mineral ore comminution

The influence of microwave pre-treatment on mineral ore breakage has been investigated. Samples of lead–zinc ore were microwave pre-treated prior to strength testing and change in strength with microwave exposure time determined. Comparisons of change in strength were made between microwave-treated and -untreated material. Using a multimode microwave cavity, it was found that strength could be significantly reduced in 0.5 s when using 15 kW of microwave power. Lower powers in this type of cavity were found to be less effective. Drop weight tests were used to quantify the change in strength in terms of reduction in required comminution energy. Reductions of up to 40% were achieved for particles of mean size 14.53 mm. Preliminary tests in a single-mode microwave cavity gave strength reductions of 50% at 10 kW of microwave power with a residence time of only 0.1 s, indicating that high electric field strength is important in the failure of ore. A preliminary energy balance indicating the benefits of single-mode heating is presented.

A portable load cell for in-situ ore impact breakage testing

This paper discusses the design and characterisation of a short, and hence portable impact load cell for in-situ quantification of ore breakage properties under impact loading conditions. Much literature has been published in the past two decades about impact load cells for ore breakage testing. It has been conclusively shown that such machines yield significant quantitative energy-fragmentation information about industrial ores. However, documented load cells are all laboratory systems that are not adapted for in-situ testing due to their dimensions and operating requirements. The authors report on a new portable impact load cell designed specifically for in-situ testing. The load cell is 1.5 m in height and weighs 30 kg. Its physical and operating characteristics are detailed in the paper. This includes physical dimensions, calibration and signal deconvolution. Emphasis is placed on the deconvolution issue, which is significant for such a short load cell. Finally, it is conclusively shown that the short load cell is quantitatively as accurate as its larger laboratory analogues.

Modelling the new LKAB Kiruna concentrator with USIM PAC©

LKAB has started the construction of a new concentrator at Kiruna, with a capacity of 5 Mtpy. The flowsheet of the new grinding circuit is technically innovative and critical because it entirely relies on ore breakage properties. It includes primary fully autogenous closed circuit grinding and secondary pebble milling. A critical size class of the magnetite ore is extracted from the autogenous mill and used as pebbles. In 1992, LKAB decided to adapt and use a simulator of the new concentrator. USIM PAC© was selected as the support software package, and a modelling team was set up, including both specialists of process modelling and simulation and specialists of the process itself. Specific model development included development of a phenomenological population balance pebble mill model, and adaptation of an existing Control International autogenous mill model. Model parameters were derived from extensive large scale pilot plant tests, and specific laboratory tests were performed to determine pebble mill breakage and selection functions for various types of pebbles and of ores. The simulator was used by the project team for comparing alternative flowsheets (one or two lines, various refinements), for predicting the influence of changes in throughput and plant feed grade, and for evaluating several options for equipment sizes. Additionally, the simulator helped understanding the process in depth and the way the unit operations interact in this particular case.

Applications of a new model-based method of ball mill simulation and design

The multi-segment ball mill model developed by Whiten and Kavetsky has been used together with an extensive range of data from operating mills to establish the parameters of a new ball mill model suitable for simulation and design of coarse grinding ball mills (i.e. mills containing some plus 2mm particles in the mill discharge). The model incorporates an ore-specific breakage function varying with mill diameter, and specific rates of breakage in each size fraction varying with mill diameter, percentage of critical speed and top ball size. The model obtained in this way is capable of simulating the performance of a coarse grinding ball mill of a given diameter, ball size and mill speed, operating on a given ore. The only additional information required for a simulation is the ore breakage characteristics determined by a laboratory pendulum breakage test on a sample of the ore particles. These characteristics may also be estimated from the Bond Work Index of the ore.

Design of an Adaptive Filter for a Laboratory Grinding Circuit

A phenomenological dynamic model was developped for a laboratory grinding circuit involving a grate-discharge ball mill (40 x 40 cm) and a rotating screen. The closed circuit model is then simplified and linearized for a formulation in the time-discrete state-space. A Kalman filter, based on the measurement of the fine product size distribution and of the recycled flowrate, is designed to reconstruct the whole mill particle-size distribution. To compensate for the ore breakage characteristics and the operating conditions variations, the filter paramaters are continuously updated. The simulation of the circuit under large sensors disturbances shows that the proposed adaptive filter is stable and accurate.