Julius Kruttschnitt Mineral Research Centre Research Articles

On-line analysis of froth surface in coal and mineral flotation using JKFrothCam

The personal computer revolution has resulted in the widespread availability of low-cost image analysis hardware. At the same time, new graphic file formats have made it possible to handle and display images at resolutions beyond the capability of the human eye. Consequently, there has been a significant research effort in recent years aimed at making use of these hardware and software technologies for flotation plant monitoring. Computer-based vision technology is now moving out of the research laboratory and into the plant to become a useful means of monitoring and controlling flotation performance at the cell level. This paper discusses the metallurgical parameters that influence surface froth appearance and examines the progress that has been made in image analysis of flotation froths. The texture spectrum and pixel tracing techniques developed at the Julius Kruttschnitt Mineral Research Centre are described in detail. The commercial implementation, JKFrothCam, is one of a number of froth image analysis systems now reaching maturity. In plants where it is installed, JKFrothCam has shown a number of performance benefits. Flotation runs more consistently, meeting product specifications while maintaining high recoveries. The system has also shown secondary benefits in that reagent costs have been significantly reduced as a result of improved flotation control.

A Load-Interactive Model for Predicting the Performance of Autogenous and Semi-Autogenous Mills

The Julius Kruttschnitt Mineral Research Centre (JKMRC) has been involved in the study and modelling of industrial autogenous (AG) and semi-autogenous (SAG) mills for over 25 years. Recent research at the JKMRC has developed a new AG/SAG mill model which is based on charge dynamics. The model relates charge motion and composition to power draw and size reduction. Size reduction is described by considering impact and attrition/abrasion as separate processes. These are linked to energy available in the mill, the charge size distribution and the relative motion of the grinding media. Ore specific energy-breakage are described using laboratory data which are obtained from breakage tests over a wide range of energies and particle sizes. Slurry transport is described using the JKMRC’s latest model which incorporates the effect of grate design. This paper describes the overall structure of the model together with its main sub-processes.

Modelling cement grinding circuits

Modelling and simulation studies were carried out at 26 cement clinker grinding circuits including tube mills, air separators and high pressure grinding rolls in 8 plants. The results reported earlier have shown that tube mills can be modelled as several mills in series, and the internal partition in tube mills can be modelled as a screen which must retain coarse particles in the first compartment but not impede the flow of drying air. In this work the modelling has been extended to show that the Tromp curve which describes separator (classifier) performance can be modelled in terms of d 50(corr), by-pass, the “fish hook”, and the sharpness of the curve. Also the high pressure grinding rolls model developed at the Julius Kruttschnitt Mineral Research Centre gives satisfactory predictions using a breakage function derived from impact and compressed bed tests. Simulation studies of a full plant incorporating a tube mill, HPGR and separators showed that the models could successfully predict the performance of the another mill working under different conditions. The simulation capability can therefore be used for process optimization and design.

Modeling of the Mount Isa rougher-scavenger copper flotation circuit using size-by-liberation data

A flotation model developed at the Julius Kruttschnitt Mineral Research Centre was used to predict the performance of copper rougher and scavenger circuits at the copper concentrator at Mount Isa Mines. The model describes the kinetic response of an ore in a flotation cell in terms of ore floatability, cell characteristics and froth recovery. The float-ability parameters of the rougher feed ore were obtained directly from a detailed plant survey. Flotation analysis was carried out for twenty different size-by-liberation classes to account for the effects of particle size and liberation on flotation. This paper investigates the capability of the model to predict the flotation behavior of 20 different size-by-liberation classes in the rougher and the scavenger banks.

Application of baby deck initiation to reduce coal damage during cast blasting

ABSTRACT The extra explosive energy used in cast blasting reduces the amount of overburden to be handled by the machinery but increases the risk of damage to the underlying coal. This damage will lead to reduced coal recovery and may negate much of the benefit sought from cast blasting. The Julius Kruttschnitt Mineral Research Centre in close association with the Australian open cut coal mining industry has conducted a blast monitoring program to understand and quantify the role of cast blasting in coal damage and loss. This paper attempts to explain the mechanisms of coal damage and the influence of toe confinement on coal damage during cast blasting.

A study of the influence of buffering on coal edge loss and dilution from cast blasting

Abstract Cast blasting is commonly used in Australian dragline strip mines to minimise the amount of material handled by draglines. Cast blasts are designed with relatively high powder factors to 'cast' or displace a significant proportion of the overburden into its final dump location in the previous strip. Each additional cubic metre of material cast by explosive energy saves the cost of it being excavated and transported by the dragline. However, the extra explosive energy used increases the risk of damaging the underlying coal seam. Such damage will lead to reduced coal recovery and may negate the economic benefit derived from casting. The Julius Kruttschnitt Mineral Research Centre has undertaken a project to understand and quantify the role of cast blasting in coal damage. As a part of this project a blast monitoring program was undertaken at the Mount Thorley mine in New South Wales. Experiments were undertaken to quantify the effect of stand-off (the distance that the explosive is kept above the coal seam) and the use of an overburden buffer or buttress placed against the exposed edge of the coal to prevent its lateral movement during blasting. A 2D dynamic finite difference numerical model was used to study the impact of different blast designs on coal movement, damage and loss. A careful survey of coal recovery was conducted in the test areas and an economic analysis was prepared in conjunction with mine staff. The results indicate that appropriate design and careful implementation of blasting operations can have a very significant impact on the overall economics of the mine.

Comparison of comminution circuit energy efficiency using simulation

Simulation models were developed at the Julius kruttschnitt Mineral Research Centre to provide accurate estimates of power consumption for a wide range of equipment. With the models, a range of circuits and operating conditions can be compared by simulation for a particular ore type. Accurate models of classification allow for the interaction between classifier efficiency and target product size (e.g., P or percent passing 150 μm) to be considered. This paper considers a range of circuit types and overall energy efficiency in the context of case studies where different circuit types were treating similar ore types.

The applications of rock mechanics parameters to the prediction of comminution behaviour

A wide range of test methods are available to the rock mechanics engineer in order to assess rock strength. The application of these test techniques to the prediction of comminution behaviour is investigated. Previously test methods that rely on inducing tensile failure have been found to correlate well with power consumption and product grading from crushing machinery. Building on this previous work the point load, fracture toughness and Hopkinson Pressure Bar core based tests are examined in relation to breakage. The application of these testing techniques to the prediction of comminution behaviour has tremendous potential if the rock strength parameters can be linked to a measure of breakage. The measure of breakage used in this study is the drop weight apparatus developed at the Julius Kruttschnitt Mineral Research Centre. The A, b and t10 parameters provided by the drop weight test describe the ore-specific rock breakage in the context of comminution. This approach has been successfully used in the simulation and optimisation of numerous crushing and grinding circuits. As such this paper seeks to investigate the relationship between the parameters of tensile based tests and those of the drop weight test. Given the expense of obtaining drill core samples it is essential that the samples yield the maximum amount of information. Early indications suggest that this technique will enable data required for comminution plant design to be obtained from core samples.

Application of Magstream in Mineral Sands Separation

The Magstream separation process, developed by Intermagnetics General corporation, offers an alternative method for both laboratory and plant mineral separations. It is based on the concept of using a fluid whose effective density is magnetically derived. The separator can be applied to both purely gravimetric separation of non–magnetic materials and magnetic–gravimetric separation of paramagnetic material.The separation density can be easily adjusted by changing the speed of rotation or process fluid concentration. A separation band can be drawn on a plot of particle density and magnetic susceptibility to illustrate the separation of particles that would be achieved. The process fluid is a non–toxic, water–based bio–degradable magnetic fluid, and relatively inexpensive compared to heavy liquids and sodium polytungstates.The Model 100 separator available at the Julius Kruttschnitt Mineral Research Centre is portable and suitable for analysing small batch samples. The separator selectivity is at best ± 0.1 SG units, which may cause a lower grade of products in separations of materials with a small SG differential.The separator has been evaluated for mineral sands applications. Several good applications of Magstream have been identified. Particularly effective separations were quartz/heavy mineral concentrate, kyanite/zircon, monazite/zircon and rutile/zircon (multiple passes required).This paper describes the Magstream process, operation, the mathematical model of separation, and presents the results of the separation case studies in detail.

Automatic Flotation Control using On-Stream Ash Analysis

An on-stream coal slurry analyser for both ash and % solids has been developed cooperatively by the Julius Kruttschnitt Mineral Research Centre and the Utah Development Company Limited. An industrial prototype of this unit has been operating successfully at the Peak Downs coal preparation plant since April, 1984 and has been used for automatic control of a bank of coarse flotation cells since January, 1985. This paper will include a brief description of the ASHSCAN coal slurry analyser together with details of its accuracy. An analysis of the limitations of present manual control will precede a discussion of computer control of flotation utilising the ASHSCAN signals to control cell level and reagent addition. The aim of the control is to use the ash and % solids assays from the feed, concentrate and tailings streams to maintain the concentrate ash at a specified ash while maximising recovery.

Advances in in-stream analysis instrumentation for the mineral processing industry

In-Stream Analysis (ISA) systems have been installed in many mineral processing plants world-wide and Amdel systems have been operating successfully for more than 18 years. This paper discusses recent developments in ISA technology with emphasis on diversification into new applications including the dynamic environment of pilot plant operations. The modular design and ease of rapid calibration, typically within 48 hours of start-up, makes the system suited for pilot plant operations. The development by the CSIRO (Commonwealth Scientific and Industrial Research Organisation) of a voidage ISA probe, which basically measures the aeration of slurries, means that the system can be used to monitor accurately the % ash and % solids content of coal slurries. The Coal Slurry Analysis (CSA) system provides the means of controlling the process in coal preparation plants. Recently development has been completed of an instrument for on-line elemental analysis in mineral sands dry plants by using Amdel ISA instrumentation, together with a sample presentation system developed by the Julius Kruttschnitt Mineral Research Centre (JKMRC) located in Queensland. Units have been successfully tested in zircon and rutile product streams, and further applications for on-line analysis of dry concentrates and other fine materials are expected.

Optimization of complex coal preparation flowsheets

A simulation package was developed to model the size reduction and separation process commonly used in Chinese coal preparation plants. the data for the simulation package was collected in coal preparation plants in China, and supplemented by data collected at the Julius Kruttschnitt Mineral Research Centre, during studies of dense medium separators. The new or improved models developed are: (1) a roll crusher model; (2) a rotary breaker model; (3) an empirical model to predict the ash content of coal fractions after breakage; and (4) partition curve models for jigs and dense medium separators. These models were used in conjunction with existing process models to develop a simulation package for five size reduction and fourteen gravity separation flowsheets. These flowsheets can be combined to simulate the commonly used Chinese coal preparation circuits. The simulation program includes an optimization package to optimize: (1) screen apertures; (2) the separation densities for gravity separation devices; and (3) flotation time, so as to maximize the plant clean coal yield at a specified ash content. The Rosenbrock search technique was found to be the most suitable optimization method.

The status of comminution simulation in Australia

The modelling of the processes of mineral comminution and the associated processes of classification is a stimulating intellectual challenge, and as a scientific activity has produced more than its fair share of publications in learned journals and conferences such as this one. However it has no practical value whatsoever, unless the models can be put to use in an industrial context. Australian research groups, in particular the Julius Kruttschnitt Mineral Research Centre and the CSIRO Division of Mineral and Process Engineering, have for 25 years been leaders in the development of comminution models and their application in simulation. Steady state simulation is now a routine tool in process design and optimization. Application of these techniques has been made easier and more effective with the introduction of the JKMRC's interactive graphics based Simulator, JKSimMet, which is now in widespread use in Australia and overseas, and the CSIRO's package MINDRES. Simulation has come of age. An important criterion for the maturity of the methodology is that it is now being routinely used by practising engineers other than those involved in its development. There are many case studies which attest to its value in assisting engineers in producing cost-effective plant designs and in modifying existing circuits to increase performance or adapt to changing feed conditions. This experience has shown that the effectiveness of simulation methodology is very dependent on the way in which it is interfaced with the problem in hand. This paper reviews the technical and commercial implementation of the technology of simulation, and describes its recent use in Australia.

On-line coal slurry analysis for flotation control.

An on-stream coal slurry analyser for both ash and % solids has been developed co-operatively by the Julius Kruttschnitt Mineral Research Centre and the Utah Development Company Limited. An industrial prototype of this unit has been operating successfully at the Peak Downs coal preparation plant since April 1984, and has been used for automatic control of a bank of coarse flotation since January 1985.This paper will include a brief description of the ASHSCAN coal slurry analyser together with details of its accuracy. An analysis of the limitations of present manual control will precede a discussion of computer control of flotation utilizing the ASHSCAN signals to control cell level and reagent addition. The aim of the control is to use the ash and % solids assays from the feed, concentrate and tailings streams to maintain the concentrate ash at specification ash while maximizing recovery.

The Use of Density Tracers for the Determination of Dense Medium Cyclone Partition Characteristics

The density tracer technique has for some years been utilised for determination of the separation efficiencies of density separators in the diamond and iron ore industries. At the Julius Kruttschnitt Mineral Research Centre (JKMRC), the technique has been adapted for studies of coal separation, and refined to a point where a Tromp or partition curve for a dense medium cyclone module can be determined quickly and accurately. Test programs using 33 mm tracers in seven Australian coal washeries are reported, and the effects of selected operating variables on separator performances are examined. The density tracer technique is shown to have substantial potential in improvement of day to day washery operation and the detection of unusual operating conditions, and in coal preparation research.

Instrumentation in a Program of Blast Design Optimisation

One of the major problems associated with blasting research on a production scale is the availability of instrumentation. The Julius Kruttschnitt Mineral Research Centre is pursuing a large program of blasting research which relies heavily on dedicated instrumentation, some of which have been obtained commercially and some of which has been designed and constructed by the JKMRC to meet the specific needs of the research program. Considerable development has been required in the use of existing techniques of data collection and interpretation. The three broad areas of study are - i)in-situ rock, condition assessmentii)blast monitoring, andiii)blast effectiveness evaluation.In-situ rock condition assessment utilises a cross-hole ultrasonic technique. This system incorporates a repetitive, highly reproducible source, high sensitivity, high frequency detectors and a digital signal averaging, storage and analysis system. Blast monitoring includes vibration analysis requiring multichannel (8 channels minimum) digital recording with extended memory (64k x 8 bit words per channel minimum) capabilities. Of major importance also is the ability to record electronically the moment of initiation of each deck, blast hole or row in a normal production firing. Blast effectiveness is assessed in terms of extent of blast damage (using the cross-hole seismic technique in pre-and post-blast experiments) and also through the degree of fragmentation achieved. The latter technique requires extensive image analysis, in terms of particle size distribution, of the broken rock during extraction, or alternatively the automatic monitoring and logging of excavation equipment.

Ultrasonic characteristics of a rock mass

A programme aimed at the in-situ assessment of rock properties and rock condition has been undertaken at the Julius Kruttschnitt Mineral Research Centre of the University of Queensland. The project aims to quantify rock mass parameters and to use them in a model of blasting to predict and control fragmentation. A technique for characterization of a rock mass utilizing acoustic data obtained from test or production boreholes was investigated as part of the programme. The system is a cross-hole acoustic system which uses wave propagation velocities and the attenuation parameter, Q (as estimated from a measurement of the change in pulse shape during propagation) to asses the rock mass condition. This system is a modification of the ultrasonic stress monitoring device (USMD) developed by Gladwin [5] in which a magnetostrictive transducer, mechanically clamped in an NX borehole is used to produced ultrasonic pulses of approximately 37.5 kHz. Pulse transmission times to detectors clamped at measured depths are used to produce a velocity profile for distances of up to 15 m from the source hole. The viability of the technique and the required instrument specifications, have been studied in a series of field experiments, which indicate good agreement between structural core log data and pulse rise time. Characterization of the state of fracture of a rock mass is being carried out at several sites with markedly different geological environments. These sites include a high grade open cut hematite mine, an open cut coal mine, an underground dolomitic copper ore body, and an underground lead-zinc ore body. The ultrasonic technique is being supplemented by studies in the sonic frequency range using small explosive charges as a acoustic sources. A comparison between the two sets of data will be made for both velocity and Q measurements for the preliminary field experimentation.

The design and operational characteristics of a portable multi-stream on-line analyser

A portable multi-stream on-line analyser (PMSOLA) was commissioned at the Julius Kruttschnitt Mineral Research Centre, Brisbane, Australia. Its design and operational characteristics are outlined. The analyser is also compared with the systems currently being used by the industry.