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By A Kuras

Segmental tunnel linings are becoming more common in Australia. One current project employing a segmental lining is the City West Cable Tunnel (CWCT) in Sydney. The project has been commissioned by Energy Australia and is currently being constructed by Thiess Pty Ltd. The project includes 1.6 km of tunnel boring machine (TBM) driven, segmentally lined tunnel. The majority of the CWCT will be excavated through Hawkesbury Sandstone. The tunnel is required to carry a 132 kV electrical circuit under SydneyÆs central business district (CBD), between Haymarket and Energy AustraliaÆs City North Substation on Sussex Street. The segmental lining has been designed as a 3.2 m internal diameter, 200 mm thick universal ring with six trapezoidal segments. The design and detailing of this segmental lining presents some noteworthy challenges, including exposure to saline groundwater, and the exclusive use of steel fibres for flexural and tensile concrete reinforcement. This paper describes some of the key elements of the segmental lining design. These include:the case for choosing segmental linings over other forms of tunnel construction;the major design checks required of a segmental lining including ground loading, hydrostatic loading, joint bearing, joint rotation, ram loading and the early strength lifting case;the benefits of using steel fibres over conventional steel reinforcement;the design approach used for steel fibre reinforced concrete;the application of 3D computer modelling in the design;the provision for components including connector dowels and gaskets;the design for passive fire resistance; andthe design for durability of steel fibre reinforced concrete in a saline environment. Segmental lining design requires the application of specialist design approaches. Input is required by the construction team, as the methods of demoulding, handling, transportation and installation impact on the lining design. As the segmental lining is functioning as immediate ground support and also a permanent lining, high standards of manufacture and construction quality control are required to ensure that the 100-year design life is met. The requirement for a watertight tunnel means that detailing and installation of the EPDM gaskets is of importance.

Jan 1, 2008

By B P. Wrench, N R. Steward, C Wu

A gold mine in southern China has transitioned from an open pit operation to a fully underground mine. An overhand mining method is used which requires the mined stopes to be filled with backfill having an unconfined compressive strength of at least 0.35MPa. Tailings from the process plant is deposited into separate flotation and Carbon in Leach (CIL) tailings storage facilities. The tailings has a high fines content and the thickener on site could only produce a dilute flotation tailings at a solids content of about 30 wt%. This resulted in two undesirable outcomes: the density of flotation tailings in the Tailings Storage Facility (TSF) was significantly lower than planned so that the TSF could not store the life of mine tailings and that the backfill product had to include a high percentage of manufactured aggregate and increased cement content to achieve the required strength. This paper presents results of a tailings study which identified that the flotation TSF would be capable of storing the remaining life of mine tailings if an amended backfill product made up of 100% of flotation tailings could be introduced. A 100% tailings backfill with the addition of 8% cement was developed by classifying the tailings and using the coarser fraction in the backfill. This backfill allowed 60% of the flotation tailings to be placed underground and only the remaining 40% in the flotation TSF. A new thickener was designed and installed to thicken the tailings and rheological testing of the tailings, using a closed loop pilot plant, provided parameters to upgrade the underground reticulation system to deliver cemented backfill to stopes throughout the mine and to deliver thickened tailings to the TSF. The revised design was implemented and has resulted in considerable cost savings. CITATION:Steward, N R, Wrench, B P and Wu, C, 2018. Optimisation of surface tailings storage and tailings backfill – a case study, in Proceedings Mine Waste and Tailings Stewardship Conference 2018, pp 454–464 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 23, 2018

Although most N.S.W. coal mines contain large amounts of combustible materials such as coal and timber, the introduction of mechanisation has extended the range of combustible materials now found underground. The role of combustible material in a fire is not clearly understood and as a result the assessment of these materials for flammability by small and large scale tests is doubtful. Extensive research has been carried out on the toxic and irritating gases evolved during the combustion of plastics. However, most autopsies report death due to carbon monoxide inhalation because the combined toxicity of smoke and fire gases is unknown.

Jan 1, 1981

By B Lumsden, R Smiles

Independence Group’s Jaguar Mine treats a polymetallic ore producing a copper concentrate and zinc concentrate. Effective separation of the sulfides requires relatively fine grinding with flotation feed P80 of about 75µm. Zn losses to final tails are greater than 60 per cent and <32 µm. When magnetic conditioning was first installed in 2010 it showed about an 8 per cent reduction of zinc in final tail and on some ores a similar benefit for silver as well. Current testwork is showing about a 12 per cent reduction in zinc and silver in final tail, consistent with the original testwork. Sizing of the final tail during the tests showed that the reduction of zinc and silver losses were only in the <32 µm fraction, as would be expected from an aggregation process. However, the most surprising result was about a 4 per cent reduction in zinc and silver in the plant feed with a >99 per cent statistical certainty. The reduction in zinc and silver in the feed is also only in the <32 µm fraction. Therefore, because the magnetic conditioning of Zn flotation feed cannot impact plant ore feed grade the hypothesis is that the magnetic conditioning is reducing the fine mineral from downstream processes, like filtering and thickening, returning to the plant feed in the recycled process water. This hypothesis is consistent with plant observation of dirty concentrate thickener overflow and measurements of solids in the overflow, as well as the average % Zn grade in cyclone overflow that correlates with the magnetic conditioning ON and OFF days. This paper presents these plant test results.CITATION:Smiles, R and Lumsden, B, 2018. Improving fine sulfide mineral recovery in Independence Group’s Jaguar Mine zinc circuit, in Proceedings 14th AusIMM Mill Operators' Conference 2018, pp 433–440 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 29, 2018

By D A. Shushkov

Analcime-bearing rocks are one of the varieties of raw zeolite material, although the characteristics of analcime are not as good as other kinds of zeolites such as clinoptilolite or mordenite. However, some fields of application of analcime-bearing rock have been found, eg a method of water purification has been developed and patented. Analcime-bearing rocks are rather widespread in the Timan region of the Komi Republic of the Russian Federation. They are represented by Upper Permian siltstones and mudstones. The analcime-bearing rocks have the following mineral composition (per cent): clay minerals (50 - 70 per cent), quartz (ten to 30 per cent), analcime (one to 30 per cent), feldspars (two to ten per cent), carbonates (two to five per cent) and pyroclastic material. Analcime aggregates encrust cavities and infill microfissures in rock. Both microcrystalline (crystals <0.01 mm in size) and medium-crystalline (~0.5 mm) aggregates are observed. The mechanical, gravitational, magnetic, sorption and ion-exchange properties of analcime-bearing rocks have been studied. They are characterised by a high index of grindability and a low index of abradability and crush resistance, low values of the benzol-based pore volume and toluene-based specific surface area, and a medium porosity value. The magnesium based ion-exchange capacity (IEC) ranges from 28.7 to 196 mg+equiv/100 g. Analcime-bearing rocks of the Timan region are characterised by low beneficiation potential. Preliminary ultrasonic treatment of the analcime- bearing rocks is efficient for the destruction of intergrowths along their boundaries and production of free analcime aggregates. The proposed beneficiation procedure yields 95 per cent analcime concentrate. In the Komi Republic, analcime-bearing rocks are utilised in agriculture. They are also used for domestic needs (eg as biotoilets for domestic animals) and the solution of ecological problems (regeneration of soil polluted by oil). We have completed experiments on the purification of potable and industrial water using analcime-bearing rock subjected to thermal treatment. The experiments demonstrated that it was possible to decrease water colouration by 20 per cent, turbidity by 79 per cent, permanganate oxidation by 30 per cent and total iron content by 70 per cent.

Jan 1, 2008

An on-stream iron ore analyser has been developed in collaboration with Hamersley Iron Pty. Limited for determining the iron content of both lump (- 30 + 6 mm particle size) and fines (- 6 mm particle size) on conveyor belts. The analyser, which is called IRONSCAN, is based on pair production, and is now commercially available from Mineral Con- trol Instrumentation Limited (MCI) in Adelaide. It can be mounted under existing conveyor belts with minimal modifications to the conveyor struc- ture, and the presence of steel cables in the belt does not interfere once the analyser has been correctly calibrated. The analyser has been exten- sively tested on both lump and fines on the shiploading conveyor at Damp- ier, and typically the root mean square (r.m.s.) deviation between single IRONSCAN measurements and conventional chemical analyses is better than 0.5% Fe. It is currently being evaluated on - 150 mm ore from the primary crusher at Mount Tom Price, and initial results are encourag- ing. The principal advantage of IRONSCAN is that it provides rapid infor- mation on ore grades. But perhaps its greatest potential is at the primary crusher where conventional sampling and analysis is very expensive to Implement. at the University of Melbourne, and those of us who were his students had learnt of the application of physical chemistry to pyrometallurgical processing, pioneered by Chipman in the USA, Wagner in Germany, and Richardson in the UK. It was possible, by applying this theoretical insight to the equilibria between metal, speiss or Legierung, matte and slag phases, to find a practical and effective way to recover metal values in some residues which had been accumulating for many years at the NA, but which had defied all attempts to treat them to that date. There was also an opportunity to study the batch lead refining methods still in use at all lead refineries apart from Port Pirie, and to devise optimis- ing techniques which greatly improved the operations and effected considerable savings. Next the writer spent some six years alternating between the BHAS, Port Pirie, and Imperial Smelting at Avonmouth in the UK, concerned with lead or lead-zinc smelting, and the develop- ment of several further continuous lead refining processes, before returning to Australia as Section Leader, Process Development in the CSIRO Division of Chemical Engineering, Fisherman's Bend, Victoria. Metallurgical opportunities which arose during this last period included the problem of tin smelting which had developed over about a decade: the world's tin smelters had been accustomed to treating fairly high grade tin concentrates, con- sisting of almost pure cassiterite, with very little impurity-mostly quartz, limestone, iron oxides, and sundry other silicates. Most such concentrates had been produced from alluvial deposits, where nature had already done some of difficult part of the mineral processor's work-at who knows what recovery-so that he could now produce high grade concentrates at high recovery. The smelters were not really set up for the treatment of lower grade concentrates, such as could be made with reasonably high recoveries from rock mining. Thus they imposed such penalties on impurities and lower than desired tin grades, that whenever a mineral processor improved tin recovery at the expense of lower- ing grade, such an improvement entailed a lower financial return to the miner. There was clearly a need for improved understand- ing of tin smelting, (at that time shrouded in secrecy) and develop- ment of techniques better suited to the treatment of lower grade concentrates. As well as the practical development, a start was made with the computer modelling of the smelting process, with the obiect of optimising the process parameters.

Jan 1, 1988

The Mineral Resources Act 1989-90 came into force on 1 Septem- ber 1990 and the Second Schedule of this Act set out the Savings, Transitional and Validation Clauses to this legislation. The Second Schedule gave rise to a number of interesting situa- tions however due to the fact that the time set aside to attend to these matters (the prescribed period) has now expired, with the exception of the points raised below, most of these situations are now history and are of no relevance. The Transitional provisions of the Second Schedule provided for a three month "prescribed period" in which certain actions were required to be undertaken to ensure tenements granted or applied for under the repealed legislation transitioned into the framework provided by the Mineral Resources Act. This Second Schedule of the Mineral Resources Act highlighted a number of anomalies which are still worthy of mention and are listed below.

Jan 1, 1991

Claiming the Green Revolution - Protecting Investment in Green Mineral Processing

Sep 13, 2010

By C D. Pocock

Maintaining catch berm capacity in open pit mines through controlled blasting prevents production delays associated with managing risks associated with wall instability. A method has been developed to quantify the drill hole deviation of presplit holes at Century Mine. Different controlled blasting techniques are used to control wall quality and decrease the risk. The performance of presplit drilling, in terms of deviation from design has been investigated. A methodology has been developed to quantify the drill hole deviation in three dimensions. This methodology was converted into a series of algorithms capable of handling an extensive range of data. The methodology was applied to a case study at Century Mine to evaluate the performance of drilling on two presplit blasts. Overall, 67 drill holes were investigated in the case study. The drill hole deviation was quantified in terms of three parameters: skewness, linearity and drill hole deviation parameter. Methods for quantifying each parameter were developed. Skewness, a measure of the amount of curvature and linearity, was defined as the measure of the consistency of the gradient of the drill hole. Drill hole deviation parameter is defined as the average measured deviation of the surveyed drill hole position from the design position. Acceptable drill hole deviation tolerances for each of the defined parameters were developed by analysing drill hole deviation parameters with respect to implications to catch berm capacity. Verification of the methodology was confirmed through the comparing of the completed drill hole deviation results using both visual inspection and cross analysis for each of the three methods. Holes with an R squared value of less than 0.97 for skewed deviation were classified as having skewed deviation, while holes with a difference in gradient of 3.5 were classified as having linear deviation. The results show that 76 per cent of the drill holes had deviation. Of this, 19 per cent were skewed, 57 per cent had linearity and 12 per cent contained both skewed and linearity deviation.

Nov 8, 2011

Laboratory studies of batch and continuous screening of ferrous sinter mixtures (4-0.5 mm) are described. The results are analysed by an equation derived from the first-order rate law for the condition of decreasing screen residue.The results of the studies show that the two screening operations are comparable in all respects if deck length in continuous screening and time in batch screening are interchanged.It is shown that the general screening process is determined by the numerical values of the screening rate constants of each of the particle sizes in the feed mixture and that the relationship between these constants and the particle size/screen aperture ratios is related to the appropriate probability function of the same ratios.It is also shown that the screening rates decrease exponentially with the amount of near-mesh material present in the feed and that oversize particles can increase these screening rates for some screen motions and decrease them for others.

Jan 1, 1985

A large scale distributed process con-trol system has been successfully applied to the automatic control of aluminium reduction cells at Boyne Smelters. A three stage hierarchy of minicomputers and microcomputers is used to continuously monitor and control conditions in each cell and to manage the data generated during the process.The automation hardware was purchased on the basis of low cost, high reliability, prior use in the aluminium industry and a high level of backup under failure conditions. The hardware has met performance criteria to date.The process control strategies have continually been updated to minimise the energy and raw material consumptions in each cell. A major change to systems software has recently been made to decrease the development time for-future changes. Various low energy potline retrofit alterations are currently being investigated requiring significant changes to the process control strategies.

Jan 1, 1985

By Lawson F

Chrome chemicals are commercially produced by the alkali roasting of chromite ores with sodium carbonate. Results of tests conducted in a laboratory furnace indicated that the sodium carbonate reacted rapidly with part of the gangue material to form a metastable intermediate that later reacted further with the chromite. For the conditions used, the recovery of water-soluble sodium chromate was able to be described empirically as yield % = a tn with a = 0.24 T - 241.3; n = 3.90 - 3.12 × 10-3 T and t is the reaction time in hours.The major rate limiting step in the overall reaction sequence appears to be the rate at which oxygen can get to the reaction sites across the liquid film coating the solid reactants.Sodium sulfate alone was found to be an unsatisfactory source of alkali for reaction with chromite. However when limestone also was added in quantities sufficient to allow the reaction CaCO3 + Na2SO4 + H20 ? Ca SO4 + 2NaOH + CO2 to take place, the results obtained were comparable to those found when sodium car-bonate was used.For chromite particles in the size range -124 + 105 µm, the use of stoichiometric excess of sodium carbonate did not appear to increase the yield or the reaction rate significantly. However, with smaller sized particles, - 53 µm, increased yields of water-soluble chromate were obtained when roasted with more than the theoretical quantity of sodium carbonate.

Jan 1, 1984

By Canterford JH

Current and future methods of data acquisition in hydrometallurgy are reviewed. Hydrometallurgical operations involve a wide range of chemical and physical processes for the recovery of metals and other products from ores and concentrates. Control of such operations requires information on the different liquid/solid and liquid/liquid mixtures being processed. Continuous. data acqui-sition for the liquid phases uses procedures already commercially exploited in other types of chemical plant. The major problem is the lack of robustness of measuring probes. Continuous analysis of the solid phases is much more difficult to-achieve because of the sampling and analytical techniques involved.

Jan 1, 1985

By Cunningham CG

Many epithermal gold-silver deposits areknown to occur in the Neogene-Quaternary volcanic complex of the central Andean region of southern Peru, northern Chile, western Bolivia, and north-western Argentina, an area of about 300,000 km2 where these volcanic rocks constitute the dominant cover. Some of the gold-silver deposits were mined during Spanish colonial times, as early as the 16th century,- whereas others were not discovered until the 19th and 20th centuries. The extraordinary gold-silver potential of this young volcanic complex, however, was not recognized until the 1970's when the phenomenal increase in gold and silver prices stimulated new exploration. New discoveries were made, chiefly in southern Peru and northern Chile, of high-grade ores in old mining districts and large low-grade ore bodies, both in old districts and in new areas having no history of mining activity. Many additional gold and silver deposits remain to be discovered within and beneath the young volcanic complex of this region.

Jan 1, 1990

By A N. Parry, G van Wyk

"Sensor based automatic ore sorting technologies are used in the minerals industries to efficiently remove waste and submarginal grade material from crushed and screened run-of-mine (ROM) ore, producing a coarse (typically >10 mm) upgraded preconcentrate at an early stage in the mineral processing circuit. This avoids additional energy intensive downstream processing of this rejected component of the ROM feed, leading to lower unit operating costs and reduced tailings disposal volumes.Test work on bulk low-grade gold ore stockpile samples from Central Norseman Gold Proprietary Limited has been conducted, indicating high gold recoveries as well as high material rejection rates. A financial model, based on these results, evaluates grade sensitivity and identifies a minimum stockpile grade for adequate financial returns. The base case modelling estimates that the ex-stockpile grade (including the fines bypassed fraction) can be more than doubled through ore sorting and that the project will be highly viable with strong cash flow generation at stockpile grades as low as 0.7 g/t gold. The modelling will enable the company to benchmark ore sorting options against stockpile reclaim and screening operations currently employed. Citation:Parry, A N and van Wyk, G, 2016. Upgrading Low-grade Gold Ore Stockpiles by Preconcentration Using Ore Sorting - an Assessment of the Economic Impact and Viability, in Proceedings 13th AusIMM Mill Operators’ Conference 2016, pp 179–190 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Oct 10, 2016

By D Miller, M Dowling, R Domotor

"This paper is focused on blasting activities undertaken as part of the Pacific Highway Upgrade – Tintenbar to Ewingsdale – project (T2E). This is a ‘priority 1’ Pacific Highway road construction project in New South Wales (NSW), to be completed by mid-2015 (weather permitting). T2E will provide approximately 17 km of dual carriageway road starting at the northern end of the Ballina bypass and extending to the Ewingsdale interchange, and will complete the existing dual carriageway road between Ballina and the NSW/Queensland border.Roads and Maritime Services (RMS) (formerly the Roads and Traffic Authority) is delivering the project on behalf of the NSW state and federal governments. In October 2011, RMS awarded a contract to Baulderstone Pty Ltd (now Lend Lease Engineering Pty Ltd – Lend Lease) to design and construct T2E. One of the key elements in this project is the St Helena Tunnel.In order to avoid the steep grades of St Helena Hill, eliminate a well-known accident black spot and maintain the aesthetics of the Byron hinterland escarpment, RMS and Lend Lease prepared designs to construct a 434 m long dual carriageway tunnel, 46 m below the ridge line of St Helena Hill. Lend Lease elected, where geotechnical conditions permitted, to use drill and blast methods to excavate the full tunnel profile, instead of traditional mechanical excavation techniques.Since all blasting locations (both inside and outside the tunnel) were in close proximity to nearby residents, the NSW Department of Planning and Infrastructure imposed strict air blast overpressure (airblast), ground vibration (vibration) limits and limited working hours. Both RMS and Lend Lease recognised that these restrictions meant that nearby residents may be exposed to blasting activities for longer than was necessary. As a result, after close consultation and agreement with the nearby residents, RMS applied successfully to the NSW Department of Planning to increase the airblast and vibration limits, as well as the working hours.Working under these new conditions, Lend Lease employed a range of best practice drill and blast technologies provided by both Orica Australia Pty Ltd and Atlas Copco Mining and Rock Excavation to improve the safety and efficiency of blasting activities and to minimise the potential negative impacts of the blasting works on affected residents. These technologies included: the use of a continuous environmental monitoring system to record the results of the blast events and provide quick and easy reporting to key stakeholders to address RMS specification requirements electronic detonators to enable accurate hole detonation timing for vibration compliance and to give project engineers the flexibility and precision to alter each design to suit the geological profile of each face the use of two software programs and advanced drill rigs to enable the efficient design of blasts, electronic transfer of designs to the drill rigs, as well as in-hole monitoring and recording of drilling performance the use of a specialised bulk emulsion system to deliver fully coupled bulk explosives into face blastholes to maximise fragmentation, and decoupled bulk explosives into perimeter blastholes, to reduce overbreak and deliver a cleaner profile.By taking a progressive approach towards the environmental restrictions and the work hours imposed, as well as utilising best practice blasting techniques, RMS and Lend Lease were able to blast with confidence and achieve their production deadlines and reduce the total cost of the project.Most importantly, RMS and Lend Lease were able to meet their environmental obligations and work constructively with the nearby residents to ensure that the blasting was undertaken as safely and efficiently as possible without delay or negative impact.CITATION:Dowling, M, Domotor, R and Miller, D, 2014. Improving excavation efficiency at the St Helena Tunnel using best practice drill and blast techniques, in Proceedings 15"

Sep 17, 2014

By V Yadi

Geostatistics has been widely used for more than four decades as a powerful tool in ore resource/reserve estimates and grade control. This method has gradually replaced the conventional method such as polygon and cross-section for grade estimation by more mathematical techniques such as kriging. The advances in geostatistical understanding and the availability of appropriate software packages have given much more contribution in speed and high accuracy during production. However, in many cases, these techniques are sometime applied without support with a good thorough understanding of the geological controls on metal distribution. To produce the result close to actual, the geological control in interpretation and appropriate geostatistical task is a must. Geological logging was described in the core must be consistent with the level plan produced by commercial modelling software used as a guide for grade control during production. Experience gained through evaluation of the Central I deposit resulted that the most effective systems continue to be based on geostatistical methods of resource estimation. Computer applications modelling software packages are necessarily as the core of an efficient in undertaking these assignments. They contribute to make a valued to data management and are becoming increasingly effective during processing. The latter role is particularly important to check the actual versus estimated values where will significantly to improve personnel to have a confident with their knowledge combined with experience and complete their jobs satisfy.

Aug 22, 2011

By T Blenkinsop, A Jenkins, H Moore, L Fisher, N Oliver, J Cleverley, M Nugus, J McLellan, J Hill, N Brunacci

The 2 Moz Vogue mineral resource is a recent discovery at the Sunrise Dam gold mine (SDGM), lying approximately 600 m vertically below the Sunrise Dam open pit. Unlike most other lodes, which are dominated either by steep vein sets or shallow high-strain (shear) zones, it lies broadly in the hinge of a folded felsic porphyry body, where it cuts intermediate volcanic lavas and volcaniclastic rocks and is not specifically concentrated at a lithofacies contact. The mineralisation is controlled by a complex interplay of moderate to shallow, west-dipping high-strain zones that are transected by irregular and discontinuous high-grade, north-west-, north–south- and east–west-trending breccia sheets that initially caused problems with attempts to model broad domains. However, by combining the structural controls and styles with the distribution of gold, arsenic, sulfur and antimony, we have improved opportunities for scheduling, extracting and processing the most appropriate material considering the current mining and processing constraints.The early delineation process for the Vogue lode revealed a significant mineral resource for the SDGM, coupled with the recognition of some potentially difficult downstream implications for mining and processing. The ultimate success of mining at Vogue will be a consequence of combining standardised data collection and geological modelling techniques with the results of the novel innovative techniques applied at an early stage of the project.Innovation (in the truest sense) drives change and application to deliver efficient and effective outcomes. Initial data generation and interpretation in lodes above Vogue provided a sound geological model based on strong structural foundations, leading to ideas that could be tested and validated by stress inversion analysis and modelling simulations. Geomechanical modelling simulations, based on the structural analysis, then provided an insight into both the structural and fluid evolution of the system and highlighted target areas. This promoted support for deeper drilling and sampling, which lead to the discovery of Vogue.With additional data, the structural model for Vogue was re-engineered through combination with geochemical and hyperspectral analysis and detailed geological and geostatistical domaining. Initial poor results from metallurgical tests from a small batch sample refocused efforts to undertake mineral and chemical characterisation and profiling (geometallurgy) and combine this data with the composite geological-structural-geochemical model. The result is a conditional probability model for differentiating mineralised or waste domains, with direct outcomes for planning, drilling and mining.CITATION:Nugus, M, Oliver, N, Blenkinsop, T, Hill, J, McLellan, J, Cleverley, J, Fisher, L, Brunacci, N, Moore, H and Jenkins, A, 2014. Exploration and innovation – the discovery and evolution of the 2 Moz Vogue Gold Resource, Sunrise Dam Gold Mine, Western Australia, in Proceedings Ninth International Mining Geology Conference 2014 , pp 323–340 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 18, 2014

By C Smith, J Cilliers, K Hadler

Unstable flotation froths, that burst before they overflow, produce no concentrate. Increasing the froth stability to improve recovery is therefore an obvious control strategy. Froth stability can be measured readily as the fraction of air entering the flotation cell that overflows as froth, rather than bursting on the surface; the ‘air recovery.’ Air rate is one of the most significant variables affecting froth stability. It is interesting that froth stability (air recovery) is maximised at a specific air rate, above or below which it decreases. It is important for metallurgists to realise that this maximum froth stability also produces the maximum mineral recovery, without compromising concentrate grade. Flotation cells must be operated at the air rate that produces the highest air recovery. The peak air recovery (PAR) to maximum mineral recovery relationship was first demonstrated by Hadler and Cilliers in 2009. Since then, the relationship between PAR and flotation performance has been widely explored; varying air rate, froth depth and particle size. Industrially, reducing the flotation bank air rate to achieve PAR yielded better mineral recoveries than other down-the-bank air rate profiles. In this paper, we present an overview of these key developments and findings in flotation optimisation based on PAR. Furthermore, using new industrial data, we show that PAR is not just applicable to rougher-scavenger cells, but also to flotation columns. Finally, we consider the future application of such an optimising control concept. CITATION:Smith, C, Hadler, K and Cilliers, J, 2018. Flotation control using froth stability: past, present and future, in Proceedings 14th AusIMM Mill Operators' Conference 2018, pp 441–454 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 29, 2018

By F A. Roddick, C Swaminathan

As remaining gold deposits tend to become more refractory, some form of oxidative pre-treatment involving hydro or pyrometallurgy is necessary to maintain high metal recoveries. These pre-treatments include pressure oxidation, bio-leaching or roasting. In the past, the primary criterion for selection of oxidative pre-treatment relied mainly on the extent of gold recovery and relative economics. In this study, a different approach has been adopted, ie the quantitative determination of environmental performance of the oxidative pre-treatment processes bio-leaching, roasting and pressure oxidation to assess which had the least impact on the environment. By establishing the environmental performance of processes, waste minimisation can be addressed early in process selection. Using mass balances, the environmental theme method was applied to determine the performance, on the basis of gold treated, of the oxidative pre-treatment processes of selected plants. No clear trend was observed in the overall impacts of each of seven plants, with all but one of the environmental evaluation indices being of the same order of magnitude; this was probably due to masking effects arising from the large variations in feed composition, tonnage, and gold levels. Within each type of pre-oxidation plant however, certain trends were detectable. For instance, irrespective of plant size, ore composition or mineralogy, for the bio-leaching and pressure oxidation units, the general order of environmental impact from greatest to least was sequentially toxicity, acidification potential, depletion of resources, solid waste generation and greenhouse enhancement. For the roasters the acidification potential was the most significant. Determination of the environmental performance of the oxidative pre-treatment of a hypothetical ore in a plant of fixed tonnage was undertaken to remove the possible masking effects of variables associated with feeds of different mineralogy, gold tenor and tonnage. The bio-leaching process gave a marginally better performance than pressure oxidation, the roasting process the worst, although there was not a great difference between them. The decreasing order of contribution to the environmental index was acidification potential, toxicity, resource depletion, solid waste generation and greenhouse enhancement for bio-leaching and pressure oxidation; whereas it was acidification potential, solid waste generation, toxicity, resource depletion and greenhouse enhancement for roasting. Since the major contributor to the environmental index was the acidification potential, the environmental performance of treatment processes for the acidic effluents was calculated. After neutralisation of the net acid resulting from bio-oxidation and pressure oxidation, and the application of various scrubbing and product formation processes for the sulphur dioxide from the roasting process, it was shown that pressure oxidation gave a marginally better performance than bio-leaching, ahead of roasting. This study demonstrated the potential for the development of a predictive tool which could be used in determining the environmental performance, and thus the selection, optimisation, and improvement of pre-oxidation processes for least impact on the environment. These would allow operation of these processes within defined environmental performance limits and decisions regarding the desirability of processing various parts of a heterogeneous orebody to be made on environmental grounds.

Jan 1, 2000