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By L Cain, C Every, S Mirlatifi, J Ashley

This paper presents a geographic information system (GIS) based method for the prediction of ground movement and the associated impact on existing buildings and structures due to tunnelling in the North West Rail Link (NWRL) project. The NWRL is a priority rail infrastructure project for the New South Wales (NSW) Government and includes 15 km of twin tunnels between Bella Vista and Epping, which will be Australia’s longest rail tunnels. The NWRL tunnels will be constructed in an urban environment where the prediction of ground movements induced by tunnelling and the associated impacts to existing structures must be assessed in the early design stages of the project. An assessment process was developed using GIS able to respond to design changes.An iterative GIS analysis methodology was developed to generate ground settlement contours and identify impacted buildings and structures in response to multiple changes in tunnel alignment during design development stages. The GIS analysis undertook to rapidly provide detailed and accurate parameter information including tunnel depth from surface, tunnel separation, diameter and sample point proximity to the tunnel and assess ground movement contours along the project alignment. Determination of the ground surface settlements were based on empirical methods proposed by Peck (1969) and Mair (1993). The control parameters and the relationship between damage categories and risk classifications for impact assessment were based on Burland, Broms and de Mello (1977), Rankin (1988) and Boscardin and Cording (1989) methods.The GIS-based ground movement impact assessment approach adopted for the NWRL project demonstrates an efficient, iterative and robust approach and could provide an initial framework for other similar tunnelling projects where rapid design changes and early understanding of tunnelling impacts are required to bring greatest benefit to all stakeholders.CITATION:Mirlatifi, S, Cain, L, Ashley, J and Every, C, 2014. An iterative geographic information system based approach for the assessment of tunnelling impact to existing buildings and structures, in Proceedings 15th Australasian Tunnelling Conference 2014 , pp 647–652 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 17, 2014

By A Ross, B De Rivaz

The results of full-scale tests on precast segment made at University of Roma are presented. The segments were cast using fibre-reinforced concrete produced without any traditional reinforcement, by using fiber made in high-strength steel and a new type of anchorage.Bending tests were performed in order to check the bearing capacity of the segments under the flexural actions; these occur during de-moulding, handling, storage phases as well as in the in situ condition (due to asymmetric soil pressure). Furthermore, point load tests simulating the TBM thrust were performed, in order to study the construction phase (excavation).The results show that the segment response largely respects the material testing and design advice according to the Fib Model Code 2010. Providing engineers, precast operators and builders confidence in material strengths and design methodology.CITATION:De Rivaz, B and Ross, A, 2014. Full-scale tests on precast tunnel segments made in concrete reinforced with high-strength steel fibres, in Proceedings 15th Australasian Tunnelling Conference 2014 , pp 469–476 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 17, 2014

By A Hughes, S G. Rosin

This paper presents the design and construction approach adopted for the widening and stabilisation of the existing decline tunnel forming part of the Scenic Railway Upgrade project at Katoomba in the Blue Mountains of New South Wales (NSW), Australia. The overall upgrade project included new trains and track, rebuilding of the top and bottom station and installation of a new winch and control system. All the works were undertaken over an eight-month period between August 2012 and April 2013 as part of a $30 M upgrade of the railway.The railway is the steepest cable-driven line in the world at a maximum of 52° extending over 350 m and descending from the escarpment into the Jamison Valley. The track was built in the 1880s for coal haulage and is recognised as a remarkable engineering achievement for its time. The tunnel section extends for about 120 m at the start of the decline and is about 3.5 m wide and 3.5 m high. The tunnel was excavated principally within medium to high strength Banks Wall sandstone and given that the widening only involved about 200 mm of trimming of the crown and sidewall this aspect of the work was not a critical support issue, except at the upslope portal. The tunnel crown however is entirely intersected by a major near vertical shear zone which presented significant challenges for the tunnel stabilisation works.Three-dimensional laser survey scanning was used for definition of the tunnel clearance envelope for the widening, and also to subdivide the tunnel into various geotechnical sections to assist in support design. Specifically oriented rock bolts extending beyond the shear zone into stable rock were used together with mesh, shotcrete and extensive strip drains and flushing points for drainage of the shear zone.Unique aspects of this project were included into the specifications and work methods. This included construction of a mobile working platform for tunnel works, the use of dry shotcrete application, difficult access for rock bolting and limiting vibration during the tunnel trimming works due to the risks associated with crown instability. The works also took into consideration particular safety constraints/work exclusion areas to address the risk of detachment of rock which could mobilise downslope to the track area below. This was required because other works were in progress such as micro-piling and bottom platform works which were being undertaken concurrently with the tunnel work.CITATION:Rosin, S G and Hughes, A, 2014. Scenic Railway Tunnel upgrade in the Blue Mountains, New South Wales – an approach to design and construction, in Proceedings 15th Australasian Tunnelling Conference 2014 , pp 607–618 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 17, 2014

By N McKenzie, E Taylor, S V. L Barrett, H Lagger, A Purwodihardjo

This paper discusses the temporary support design methodology for the largest road caverns ever built in Australia—the Lutwyche Caverns—part of the Airport Link project in Brisbane, Australia. The Lutwyche Caverns with a maximum excavated span of 27 m form a key component of this major road project, allowing on and off ramps merging with the underground highway. In addition to the two large span caverns, a 15 m soft ground tunnel with 5 m cover above the caverns and two 24 m deep burial chambers for the 12.4 m tunnel boring machines (TBMs) had to be built in record time at Lutwyche.The temporary support design methodology involved the use of a range of analytical approaches, including empirical methods to provide a starting point for design development, key block models to determine the potential influence of discontinuities on excavation stability and 2/3D continuum and discontinuum models to determine the potential influence of adjacent excavations and the proposed construction staging on the design. In addition, probabilistic analysis of potential kinematic instability using a discrete fracture network (DFN) approach was also undertaken to establish the critical block loads for the temporary lining, while the continuum and discontinuum models were used to design the support for the 1.5 m diameter rock pillar at the north end of the northbound cavern.The numerical modelling was undertaken in close conjunction with the contractor to develop the optimal construction sequence, considering the available construction equipment on-site and the overall project program requirements. Part of the presentation will further show the applicability of the developed design during construction (deformations, monitoring field observations) and lessons learned for future cavern construction in Australia.CITATION:Lagger, H, Purwodihardjo, A, Barrett, S V L, McKenzie, N and Taylor, E, 2014. Temporary support design for the largest road caverns ever built in Australia – the Lutwyche Caverns, in Proceedings 15th Australasian Tunnelling Conference 2014 , pp 399–410 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 17, 2014

By G Harbort, D Clarke, D Morgan, C Sola

Northparkes Mines commenced production in 1994 and the mine has significant reserves to allow operation into the future. There are a number of potential future concentrator feed sources with variable sulfide mineralogy and grades.In February 2012 a comprehensive flotation survey was conducted to allow mass balancing and evaluate the operation of the flotation circuit. A rudimentary, copper element only, unsized flotation simulator was developed to evaluate high level potential for optimisation and improvement. In 2013 this flotation model was expanded to produce a mineral based, floatability component model to estimate the effect of future concentrator feed source on metallurgical performance. This revised model allows various circuit configurations to be simulated to provide a high level blueprint for the long-term planning to maximise performance.This paper provides a review of the process followed to develop the model, including an analysis into the mineral floatability component model and its calibration against plant operations. The effect of varying feed mineralogy and feed quality on future performance has allowed an internal review of potential circuit changes needed to accommodate the changing future feed.CITATION:Clarke, D, Harbort, G, Morgan, D and Sola, C, 2014. Northparkes Mines – flotation and planning for the future, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 203–208 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014

By P Holtham, K C. Runge, E Tabosa

Traditionally, comminution and flotation have been surveyed, analysed and optimised separately. This often results in less than optimal outcomes because of the complex interactions between the two processes. Flotation recovery is a strong function of the valuable mineral particle size distribution with lower recovery of ultra-fines due to poor flotation kinetics, optimum recovery for the intermediate sized particles and lower recovery for the coarser particles due to poorer liberation. Thus, to optimise flotation recovery and grade it is usually best to grind to a fine size. This requirement needs to be balanced by the cost of grinding finer and the revenue that results from an increase in grinding throughput, which often results in a coarsening of the flotation feed.This paper demonstrates a technique which can be used to predict the effect of a change in feed grind size on flotation performance. It can be used to determine the optimum grind size for a particular operation which optimises total circuit profitability. Analysis is relatively easy to perform, as a minimum, requiring only size by assay data of the feed and product streams of the process. Case studies will be presented that demonstrate the usefulness of this technique in feed grind applications. Potential use of the technique for regrind evaluation is discussed. The limitations associated with this technique in certain circuit scenarios will also be outlined.CITATION:Runge, K C, Tabosa, E and Holtham, P, 2014. Integrated optimisation of grinding and flotation circuits, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 77–84 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014

By W N. Qin, B Zhang, W Z. Huang, X S Mo

Mengzi Mining and Metallurgy Co, Ltd (MMMC) polymetallic ore contains recoverable amounts of tin, lead, zinc, pyrite and other valuable minerals. With the change in orebody, the run-of-mine (ROM) ore changed from lead zinc rich ore to tin rich ore, where the current ROM ore contains 0.45–1.25 per cent tin, 20–25 per cent sulfur, and 0.20–0.35 per cent copper. The previous processing flow sheet was designed to recover lead zinc rich ore and it is clearly not suitable for recovery of the current tin rich ore, where the tin was already overground and tin recovery was only 50.19 per cent. The Mengzi Mining Company has recently modified the concentrator circuit by incorporating rod mill and high efficient Derrick fine screen. As a result of the improved classification efficiency, the overgrinding of the tin ore was minimised and the recovery of tin was improved by 20.71 per cent, ie from 50.19–70.90 per cent. An additional $10 M revenue per annum can be achieved as a result of the modification.CITATION:Qin, W N, Huang, W Z, Mo, X S, Zhang, B and Wheeler, J, 2014. Application of high efficient fine screen to improve the recovery of tin concentrate, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 487–492 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014

By O Arafat, K M. Bartholomew

A voracious consumer of energy and grinding media, the modern ball milling circuit has a huge direct cost impact on a mineral processing operation. Through optimisation, grinding also has the potential to unlock great improvements in recovery and throughput, but how can the complex interactions between mills, classifiers, tonnage, ore-type and downstream recovery be measured, understood and managed in a systematic manner?Functional performance analysis provides the tools and insights needed to measure, understand and improve the two key process efficiencies in ball milling circuits: classification system efficiency (CSE) and mill grinding efficiency.CSE measures the composite performance of the classification system as a whole. In short, the purpose of the classification system is to ensure that grinding mill energy is used to grind coarse particles while minimising overgrinding. CSE is simple to measure in the plant and it provides immediate feedback to the plant metallurgist, mill superintendent and management about the performance of the classification system and the amount of wasted energy in the grinding plant.Mill grinding efficiency measures the capacity of the grinding mill to convert feed-sized material into product-sized material on a tonnes per kilowatt hour basis. It is normalised based upon the ore resistance to breakage, so it provides feedback about the ‘health’ of the milling process under varying operating conditions and ore types. Mill grinding efficiency is measured at the same time as CSE through circuit sampling.Functional performance analysis combines CSE and mill grinding efficiency to provide a measureable, manageable optimisation objective. It also provides a link to tonnage, ore type and recovery. As a result, systematic optimisation of a grinding circuit is a measureable and manageable process to meet business objectives.CITATION:Bartholomew, K M, McIvor, R E and Arafat, O, 2014. Functional performance of ball milling circuits – a plant metallurgist’s tool for process characterisation and optimisation, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 227–232 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014

By D Baas, D Bennett

This paper describes how Brisbane-based PanAust Limited develops process control strategies that are implemented at all operations and are used in functional descriptions for plant upgrades and new projects.The process control strategies are determined by operating management philosophies designed to maximise returns from the company’s assets.The approach is endorsed in the project planning and design phases to ensure facilities and equipment that form the major production assets are fit for purpose and capable of enabling the production managers and operators of the projects to maximise shareholder returns.PanAust’s process control approach has been to develop sets of process control standards which focus on two key areas. The first area covers hardware requirements and architecture, software objectives, control models and individual loop tuning methods. The second area defines control room layout, graphic standards and the alarm philosophy. The application of these standards in a new plant or upgrade decreases the time required to achieve design capacity and optimal performance.The PanAust process control strategy changes the operator’s role from one that controls a number of individual loops to one that sets the control objectives of the processing plant. To achieve optimal performance, all the process areas of the plant are analysed to identify opportunities to improve throughput, recovery and stability. Once a key opportunity is identified, a process control strategy is developed which defines the objective of the control, its functionality and how an operator will interact with it. After development of the control model the operators assist engineers to test and debug it. Once the model is robust, it can then be duplicated throughout the group and developed as a group process control standard.CITATION:Baas, D, Bennett, D and Walker, P, 2014. Developing process control standards for optimal plant performance at PanAust Limited, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 325–334 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014

By R Wynn, R A. Pax, S Mann, B Cornish

The semi-autogenous grinding (SAG) mill at the MMG Century operation has failing load cells that are essential to the control strategy used to stabilise the mill. Currently, mill-bearing pressure is used as a proxy for the load cells, but it has been found to be a noisy signal and lacking in useful sensitivity. It is also prone to variations and drift due to temperature. After consideration of a number of options, a non-contact acoustic array has been installed around the SAG mill to provide a more stable proxy load signal as well as other information about the internal operation of the?mill.The installation consists of 12 microphones to provide some detail into the operational differences that occur during normal operations at the MMG Century SAG mill. This acoustic approach acknowledges that operational grinding mills emit significant acoustic emissions that are a consequence of the dynamic environment prevailing inside them.Previous studies have attributed the acoustic noise to a range of events that occur inside these mills (Pax, 2011; 2012). Consequently, non-contact acoustic determinations of in-mill behaviour can provide powerful insights into the operation of the primary comminution tumbling mills. By measuring key microphone signal attributes at different positions around a mill, a holistic picture of mill internal operation can be developed.This paper will describe the installation of the 12 microphones and discuss the use of the acoustic load signals as a proxy for failing load cells. It will also present data from new observations of internal mill dynamics and the results of implementation of control using these acoustic signals. Key to the control approach has been the development of a logically coherent picture of the processes inside the mill.CITATION:Pax, R A, Wynn, R, Mann, S and Cornish, B, 2014. Implementation of acoustic arrays for semi-autogenous grinding mill?operation, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 273–282 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014

By D J. Hill

"Mining companies routinely invest in improvements to their processing operations, but often these enhancements do not work to full effect.Improvements can be ineffectual because underlying process problems are not identified or prioritised for correction or repair.This is frequently because ‘black box’ solutions deployed to implement process control improvements typically rely on instrumentation to provide data for algorithms to work effectively, and these solutions are often ineffective or disabled at mineral processing sites.There are three key reasons they can fail to deliver: vital instrumentation is not calibrated or functioning as required basic process control and loop tuning was not implemented correctly or is in need of tuning there is an inability to support the ‘black box’ solutions on-site.Many of these problems can be overcome by implementing operational analytics that identify where problems are occurring and prioritise where improvements need to be made.Incorporating operational analytics into process improvement is not a new methodology. It is more a back-to-basics approach to make more efficient use of capital and systems already deployed.Data collection systems, such as the OSIsoft PI System, provide real-time and historical process information for process control experts to analyse and identify areas for improvement. However, most systems are not used effectively. With some simple enabling, data collection systems can provide evidence for prioritising investments in improvements and determining an investment’s effectiveness.MIPAC advocates that the initial step, with analytical evidence, is that clients review the control strategies and implement small influential instrument repairs/calibrations and operator training. This can significantly boost process productivity without the need to spend large sums of money on new capital or employing expensive, difficult to maintain ‘black box’ solutions.A simple Stage-Gate®-style approach ensures that small investments in evidence-based process improvements deliver significant benefits to mining operations.CITATION:Hill, D J, 2014. How to prioritise process improvements, in Proceedings 12th AusIMM Mill Operators’ Conference 2014, pp 307–314 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Sep 1, 2014

By D van der Spuy, T Kewe, K Keet, N Moffatt, A P. Paine

The Blue Cube Mineral Quantifier Inline (MQi) instrument uses reflective light spectroscopy and advanced chemometrics to measure mineral or elemental grade in a slurry line. The instrument takes scans continuously and sends data to the DCS or PLC control system.Controlling the concentrate grades on a flotation circuit using low-frequency measurements can be difficult or impossible, especially on a circuit that has fast process dynamics. The ability to rapidly measure changes in grade makes it possible to continuously manipulate the flotation circuit operating parameters such as level, airflow and reagent addition set points to optimise plant performance throughout changing conditions.At Barrick’s Porgera mine in Papua New Guinea the flotation circuit feeds sulfide concentrate slurry to a pressure oxidation circuit. In order to maximise gold recovery in the flotation plant and increase performance in the pressure oxidation process, there is a stringent requirement to maintain a stable and optimum sulfur grade. The gold recovery is directly affected by the sulfur grade as most of the gold at Porgera is submicroscopic and associated with the sulfides (disseminated?pyrite).Porgera considered various points in the flotation circuit for installing Blue Cube analysers. This was part of a plant upgrade to improve process control. Due to budget constraints it was decided to initially only install one Blue Cube analyser on the final concentrate stream of the flotation circuit measuring sulfur, sulfides, gold and particle size. The accuracy of the calibration results were very good for all these properties. The sulfur measurement was used in an advanced control system to optimise and stabilise the grade. The paper presents comparisons between mineral grades determined using analytical laboratory analyses and the online Blue Cube data measurements, as well as benefits achieved by measuring grade online. An analysis of the plant data before and after installation of the Blue Cube and the advanced process control upgrade indicate that the flotation recovery increased by 1.98 per cent.CITATION:Kewe, T, Moffatt, N, Strobos, P, van der Spuy, D, Paine, A P and Keet, K, 2014. Evaluation of the Blue Cube MQi slurry analyser for application in an advanced control system for the optimisation of a gold sulfide flotation circuit, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 357–362 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014

By A McEwan, J Masters, C A. Jackson, A Catanzano, V Sharp, M Millen, S Rainey, S J. Spencer, G Roberts

A passive acoustic emission (AE) monitoring system has been developed and trialled on two M10000 IsaMillsTM. The analyser detects AE stress waves generated by grinding media impacts with the mill liner during mill operation. Locally propagating stress waves can be detected on the exterior liner surface using strategically mounted broadband accelerometers.The analyser has been developed into a robust commercial prototype system, and has been designed, installed and commissioned with Xstrata Technology at two mineral processing plants.A six-month field trial showed large-scale variation in AE power signature with process conditions. Analysis of the enveloped AE power output demonstrated a strong correlation with mill process conditions – more specifically grinding media relative loading, feed pulp density, feed volumetric flow rate and feed type.Placement of accelerometers along the length of the mill body provided key information on the grinding media relative deportment. The enveloped AE power detected by the mill body, discharge pipe and bearing housing sensors all captured information strongly correlated with mill operating parameters and process state.The prototype analyser demonstrates suitability as a long-term online tool for stirred mill performance monitoring, and potentially for optimisation and control, in beneficiation plants.CITATION:Jackson, C A, Spencer, S J, Masters, J, Sharp, V, McEwan, A, Rainey, S, Catanzano, A, Roberts, G and Millen, M, 2014. Monitoring of M10000 IsaMill™ process performance by passive acoustic emissions, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 241–254 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014

By D Morgan, D Sato, B Lumsden, S Senanayake

Laboratory flotation tests on fresh cyclone overflow samples are a useful tool to troubleshoot and indeed to improve plant performance; however, reproducibility between laboratory flotation test and plant performance is important for interpretation of the laboratory tests and hence their usefulness. Chemical reproducibility can be achieved with the addition of the required reagents; however, reproducing the physics of forces and energy in a 5 L cell compared to a 50 000 L plant cell or a 500 000 L plant cell is not generally studied or discussed. For some tests such as collector evaluation the physics of the flotation process may not be critical, but for some evaluations in the laboratory, it can be important.All flotation plants suffer from losses of valuable <20 µm mineral. Selective mineral aggregation has long been recommended to improve the poor flotation recovery of <20 µm sulfide minerals; however, successfully testing any type of selective sulfide mineral aggregation’s effect on flotation recovery in the laboratory on practical plant samples requires reproducing plant cell physics. The energy input per litre and the forces in a laboratory cell are vastly different to a plant cell. Reproducibility between laboratory and plant tests requires that these differences be minimised. The physics of the laboratory flotation cell is particularly important when fine mineral aggregation tests are carried out.This paper outlines a modified laboratory aggregation and flotation method that closely reproduces plant performance in a laboratory test.CITATION:Sato, D, Lumsden, B, Senanayake, S and Morgan, D, 2014. Development of a laboratory flotation method to test plant mineral aggregation, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 173–178 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014

By S Farrokhpay, C Akop

Copper-gold-pyrite ore types with an elevated pyrite head grade utilise a sequential flotation circuit to recover initially a copper-gold concentrate with a pyrite-gold concentrate being produced from the tailing of the initial circuit.A simpler flotation circuit with lower operating and capital costs for treatment of such copper-gold-pyrite ores with an elevated pyrite head assay was sought in the described work. After characterising the ore, the objective was to apply bulk rougher flotation of both the copper minerals and pyrite for the copper-gold-pyrite ore at natural pH. Hence, no lime or other pyrite depressants were required in bulk roughing. The bulk rougher concentrate was upgraded in a cleaner circuit to reject non-sulfide gangue and then the resulting sulfide concentrate was separated by depressing the pyrite to produce two products (copper and pyrite concentrates, both having significant gold assays). A standard test with a sequential circuit was applied to the same ore for comparison.The chalcopyrite and pyrite losses in the tailing from the rougher circuit were the same for both bulk and sequential roughing (less than six per cent). In cleaning (bulk circuit), the effective pH for pyrite depression was 11.8–11.9; copper recovery was 70–75 per cent (grade of 15–20 per cent copper) and the sulfur recovery (pyrite product) was 80–85 per cent (grade of 34–36 per cent sulfur).These results approached those for the sequential circuit where copper recovery was 80–85 per cent (grade of 15–20 per cent copper) and the sulfur recovery (pyrite product) was 83 per cent (grade of 38 per cent sulfur).The observed effects of feed sizing on the liberation of minerals in the rougher feed are discussed. Options for improving the bulk circuit results are also considered. Importantly, the implications of various aspects of these findings for the bulk circuit are discussed with an industrial focus.CITATION:Akop, C, Farrokhpay, S and Johnson, N W, 2014. An alternative circuit for chalcopyrite-pyrite ores with elevated pyrite content in Cu-Au ore treatment, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 407–416 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014

By D Engelhardt, G Lane

The Cadia mine has shifted from an open pit operation to the Cadia East underground panel cave. The resulting increase in milled tonnes, more competent ore and the decrease in fines production through shifting to panel caving were predicted to require an increase of over 25 per cent in installed power. This expansion was accomplished via the installation of secondary and high pressure grinding rolls (HPGR) crushing of the ore, with the semi-autogenous grinding (SAG) mill receiving a combination of primary, secondary and HPGR crushed feed. This design, criteria and rationale for selection was presented at the SAG Conference 2011. This paper reports on the initial impact of secondary and HPGR crushing on the circuit performance with the new panel cave feed.CITATION:Engelhardt, D, Lane, G and Powell, M S, 2014. Cadia expansion – the impact of installing high pressure grinding rolls prior to a semi-autogenous grinding mill, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 233–240 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014

By I Ametov, S Harmer, R Alford

A process that allows selective flotation separation of low Cu/S ratio minerals (chalcopyrite and pyrite) from high Cu/S ratio minerals (bornite and chalcocite) from a mixed copper mineral concentrate under controlled oxidative-reductive potential conditions has been developed. The process has been extensively tested on samples with varying mineralogy using laboratory batch flotation tests and mini pilot plant trials.In this process, the mixed final copper mineral concentrate is purged with nitrogen, and then treated with sodium dithionite to achieve a slurry Eh in the -200 to -100 mV standard hydrogen electrode (SHE) range. Flotation was then carried out using nitrogen gas. As a result, a low Cu/S ratio concentrate (<1.3) and a high Cu/S ratio (>1.6) tailing stream were produced. QEMSCAN analysis of the flotation products showed that more than 85 per cent of the chalcopyrite and 95 per cent of the pyrite reported to the froth concentrate. Chalcocite and bornite were almost evenly distributed between the concentrate and tailing streams.Surface analysis studies, focused on the mechanism of separation, showed that at a negative redox potential xanthate and possibly dixanthogen are the dominant hydrophobic species on the surface of chalcopyrite and pyrite. As a result, the flotation of these minerals remained unaffected. In contrast, a much lower concentration of xanthate species on the surface of chalcocite and bornite particles was observed. Therefore, it is likely that at low Eh the copper xanthate complex desorbs from the chalcocite and bornite surfaces, causing a decrease in surface hydrophobicity and the diminished floatability of chalcocite and bornite.CITATION:Ametov, I, Harmer, S, Grano, S and Alford, R, 2014. Selective flotation of chalcopyrite and pyrite from a mixed copper mineral concentrate under controlled redox potential conditions, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 131–140 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014

By M Schaffer, T Kewe, N Moffatt

Porgera mine is 95 per cent owned by Barrick Gold Corporation. It is located at an altitude of 2200–2700 m above sea level in the Enga province of Papua New Guinea and produces approximately 460 000 oz per annum with a proven and probable reserve of 6.2 Moz. The refractory ore is ground in a conventional semi-autogenous grinding and ball mill circuit. After the gravity gold is recovered, the slurry is floated, oxidised in the autoclaves and then leached. This paper will focus on the flotation circuit and the recent upgrade of the control system. The five interdependent flotation circuits were challenging for operations to control as they dealt with variable grade, throughput and circulating loads, as well as the physical limitations of the equipment. With the installation of 18 Portage Froth Characterization® (PFC) cameras, the plant’s operation has been converted from a level-control based strategy that was focused on individual cells to one that targets grade and recovery control across the entire circuit. Variability in feed and the corresponding launder issues were addressed with a unique site initiative of deflector plates to indicate filling level. Non-linear closed loop control was implemented directly in the DeltaV Distributed Control System (DCS) using Portage Advantage Regulatory Control (PARC) algorithms and optimised with AwaRE advanced controllers. The most noticeable benefits achieved with the upgrade include improved flotation gold recovery, consistent flotation sulfur grade and autoclave performance. Correspondingly, there was a significant drop in boiler diesel fuel usage and launder overflow conditions.CITATION:Kewe, T, Moffatt, N and Schaffer, M, 2014. Porgera flotation circuit upgrade and expert system installation, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 345–356 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014

By P Holtham, J Meng, E Tabosa, W Xie

Turbulence and its distribution are of great importance in flotation, and have received considerable attention recently. However, there is no mature technique to measure turbulence in three-phase (liquid-solid-gas) industrial flotation cells due to the opaque, highly aggressive and abrasive nature of the slurry involved. Previous research has shown that the piezoelectric vibration sensor (PVS) is a promising tool for turbulence measurement in industrial flotation cells. The PVS is a robust device that converts mechanical vibration to electrical signal, from which turbulence information can be extracted. An improved calibration method has allowed development of a frequency model to calculate the force applied to the sensor. Experimental results and comparison with laser doppler anemometry (LDA) have shown that the PVS can measure fluid kinetic energy, which is related to turbulent kinetic energy, a parameter used in the literature to represent turbulence in flotation. Laboratory measurement in a two-phase (water and air) 60 L cell and with slurry in a 3.5 L cell gave good stable results and mostly consistent trends between the measured turbulence profile and cell operation. When applied in a 300 m3 industrial cell filled with water, the addition of air or slurry to the cell resulted in a shift in the turbulence profile. This is expected because a change in fluid density will change the force applied to the sensor. It is therefore concluded that the piezoelectric sensor is an easy-to-use and robust technique that is fully capable of measuring turbulence in industrial flotation environments.CITATION:Meng, J, Tabosa, E, Xie, W, Runge, K C and Holtham, P, 2014. Development and application of a piezoelectric sensor for turbulence measurement in industrial flotation cells, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 457–470 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014

By F Burns, G Peachey

The Hidden Valley process plant has recently undertaken a program to relieve process flow bottlenecks and improve process automation. An environment of cost reduction and restrained capital necessitated solutions that primarily utilised existing equipment and internal resources. Removing bottlenecks relieved pressure from a strained circuit that was unable to maintain consistent performance. Improved process automation firstly stabilised the process, then allowed the circuit to sustainably operate at the expanded capacity limits. These allowed implementation of an operating approach that focused process operators towards identifying and resolving process disturbances in advance. Plant recovery and throughput have markedly improved as a result.CITATION:Burns, F and Peachey, G, 2014. Recent process improvements at Hidden Valley gold mine, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 43–54 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014