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By R Atmuri, W Liang, R Prasad, Y Liu, E Wingate

Yellow phosphorus (YP) has been commercially produced since the 1920s. First in the USA by the Tennessee Valley Authority (TVA), next in Russian (Kazakhstan) in the 1950s, and finally in China in the late 1970s and early 1980s. There are operations in Vietnam and Sarawak on a smaller scale. YP has become very in vogue due to its use in the production of lithium iron phosphate battery cathode precursor materials by the Chinese and other western battery manufacturers. The YP is also used to produce purified phosphoric acid and higher grades of acid using a thermal oxidation process after smelting. This paper will look at the basics of the smelting including slag chemistry, alloy chemistry and offgas chemistry. The paper will look at the design of the furnaces used in the YP production process as well as the downstream recovery of phosphorus from the smelter off-gas stream to YP. The next part of the discussion will focus on the operations of a YP smelter with regards to control of the furnace to optimise phosphorus recovery to YP. Will discuss tapping cycles for alloy and slag with a view to optimal phosphorus recovery. The discussion will close out with a review of operational challenges in the smelter and a brief description of the downstream conversion of YP to high purity phosphoric acid.

Aug 21, 2024

By T Raynlyn, A Edenton, M Adam, R J. Holmes, J R. Manuel, N Ware, R Smyth

Due to ongoing demand and increasing depletion of high-grade iron ore resources from large deposits, Australian iron ore producers are developing smaller size deposits to maintain current export levels. The iron grade, mineralogy, chemical and physical characteristics of iron ore fines being mined from different deposits vary considerably. It is therefore imperative to develop long-term strategies to maintain the quality and consistency of iron ore fines while moving to a larger diversity of smaller deposits. Blending is a common practice in sinter plants as it is almost impossible to produce a high performance sinter mixture displaying the required characteristics from one single ore. Blending is also one of the most effective options being used by iron ore producers to ensure the long-term stability of their products while increasing production. When designing a blend, the blend components are selected to support each other to achieve the required overall balanced metallurgical performance of the final product at a relatively low cost. To do so, a fundamental understanding of the key characteristics of iron ore fines and their potential impacts on the iron ore sintering process and sinter quality are required. In this paper, the sintering process and sinter structure have been analysed and the key factors affecting the sintering performance of iron ore fines, including productivity and quality, identified. Under fixed sintering conditions, the granulation efficiency, nuclei stability and the volume and properties of the primary sinter melt are believed to have important impacts on both sintering productivity and sinter quality. Discussion is then focused on the effects of ore chemical, physical and mineralogical characteristics on the key factors identified and in turn the consequences for sintering productivity and sinter quality.

Jan 1, 2009

By J Webb

The mining industry is relatively niche and complex compared to other global industries in its safety and operating environment. Whilst some of the technology required to decarbonise the mining industry will emerge from the mass market (eg batteries, energy storage solutions and renewable power generation) where exogeneous external investment and innovation will drive supply, bespoke applications such as material movement will be constrained by industry limitations. Underground load and haul equipment burns the majority portion of underground mine diesel, and typically 25 per cent of scope one and two emissions. Transitioning away from incumbent diesel engines offers a considerable health benefit to all mine workers, as well as decarbonisation achievements, and through trials there is emerging evidence of more productive equipment and realistic expectations of lower operating costs of fleet. However, new equipment and material movement systems that support these industry goals are currently approached with caution due to the pivotal role they play in delivering productivity goals, and the lack of experiential data and certainty to mitigate the supplier development risk during this technology transition period, where all resources are required to meet a booming industry. A group of mining companies and suppliers have the aligned aim to accelerate the understanding and availability of heavy haulage mobile equipment through collaboratively piloting equipment and working with suppliers and each other to aggregate market demand, encourage investment and resolve the mine design and technology choices through their involvement in the Electric Mine Consortium (EMC). This paper will outline the major challenges the industry must overcome in sourcing and adopting a zero-diesel particulate and zero-emission mine, drawn from cases and insights across ten EMC mining company members.

Mar 29, 2023

By J St George

Much of AucklandÆs transport infrastructure has been developed on surface with little or no consideration of underground options. Current and planned transportation routes are now facing high costs due to land values and increasing environmental resistance to surface development. The option of utilising underground space becomes a feasible investment decision for these links as well as being the only option to develop the rail network within the inner city area. Transportation tunnels offer a quieter, more energy efficient means of getting around with minimal impacts on the surface environment. One of the major impediments to tunnelling is the high construction cost, which is partly related to the risks of encountering unexpected ground conditions and/or the possibility of causing surface ground deformations which could damage structures. The geology of Auckland has had substantial investigation through various studies and projects. The sediments of the East Coast Bays Formation (ECBF) underlie most of the Auckland urban area. It is classified as a soft rock and is a suitable material to tunnel through using either a tunnel boring machine or a roadheader. This paper reviews the limited amount of tunnelling completed in the urban Auckland area, together with the international advancements that have been made in the tunnelling industry. From the known features of the local geology and the problems encountered historically, the likely risks of tunnelling in Auckland are presented and ways in which those risks could be reduced and managed, are discussed. In addition, contractual arrangements between client and contractor are assessed with respect to complicated projects (such as tunnelling), so that the risks can be managed to create efficient infrastructure routes with reduced costs.

Jan 1, 2008

Mond gas-producer tar, and, in fact, all tars obtained from the retorting of coal where steam and air are admitted to the retort, are of entirely different chemical composition to the ordinary coal tar made in the gas or coke works. These tars contain none of, the aromatic hydrocarbons - benzene, toluene, naphthalene, and anthracene, sought after by the ordinary coal-tar refiner.The distillation of Mond tar shows it to consist of phenols of high molecular weight, unsaturated hydrocarbons of high gravity and low viscosity, paraffin wax, and resinous substances of whose composition little is known.The physical properties of Mond producer tar are also peculiar. It has a "short," granular texture when cold, which might be likened to candied honey. It "dries" (hardens) when exposed in thin layers to the air, and, for a coal tar, it cannot be considered sticky. This latterò property, combined with the short texture, prevents its being used successfully for road-making or macadamizing.The drying properties and the paraffin wax contained in: this tar cause it to hold up large percentages of water, probably in the form of emulsion. When containing as much as 10% to 15% moisture it appears to be quite dry.

Jan 1, 1918

By G Neely

COPING WITH COMPLEXITY In every industry, and mining is no exception, plant and processes increase in complexity over time and managers and operators need correspondingly more knowledge. The mine manager has to delegate details to operators, engineers, metallurgists, accountants, safety specialists, personnel officers and the rest. Is it reasonable then, to expect the Mines Inspector to be competent to judge the conduct of all these operations against the criterion of the regulations? Obviously not, but what are the alternatives? One is a superficial inspection where the inspector goes on a hazard hunt for broken steps and missing handrails. Another is one in which an army of specialist inspectors marches on a mine, sometimes outnumbering the staff. Each is competent to assess some part of the operation and if he or she can find an opposite number among the mine staff, they can discuss details. But what good does it achieve? The system acts to remedy present defects and to make recommendations which, if only they were followed, would prevent the same things happening again. Given that this process has been going on since the first Factory Act of about 1840, how is it that there are any more defects left to put right? The answer of course is that defects keep appearing, and new defects arise as fast as the old ones are found and corrected. Further progress can only be made by preventing defects at their source.

Jan 1, 1994

By B Zhou

Geophysical borehole logging, which measures various in situ petrophysical parameters, can be used not only for qualitative interpretation such as strata correlation, but also for geotechnical assessment through quantitative data analysis. It can play an important role for safe and productive mining operations. Here we provide various applications of geophysical logs such as the estimation of the strength of intact rock or unconfined (or uniaxial) compressive strength (UCS), automated lithological/geotechnical interpretation, geophysical strata rating and orebody delineation and grade estimation. These derived parameters could provide input to control of geological and geotechnical models. This could assist site geologists and planning and production geotechnical engineers to predict and manage mining conditions on an ongoing basis. Both conventional logs such as density, natural gamma and sonic, and less common logging data such as full waveform sonic and televiewer data are examined for different applications. Although the examples used here are mainly for coal mining applications, but they can be equally applied to hard rock metalliferous mining such as iron ore mining.

Nov 8, 2021

By D Lucato, B Haase, R Saha, S Limberger-Forte, J Lishman

Cadia East Mining operations have employed geometallurgical techniques to advance the understanding of the in situ rock hardness variability across existing Panel Caves (PC). Geometallurgy advances the understanding of variability across an orebody through the integration of geology, mineralogy and processing response and therefore enhances spatial mapping of comminution or separation properties. Spatially extensive geometallurgical measurements are necessary so that continuous rock properties can be generated and used for the development of comminution and processing domains using geostatistical modelling. Standard testing protocol across geological and mineralogical domains is vital to understand the variability in deposit wide comminution and separation properties. The high cost and large sample requirements associated with metallurgical test work typically results in insufficient data density and distribution, making it difficult to model and map deposit scale variability. Quantitative hardness proxy tools are useful to measure in situ rock hardness, however this data is typically either sparse or missing within advanced mining operations. In recent years, mineralogy and multi-element assay data has often been collected as part of the standard geological data set and is generally coincident with metallurgical test work. In this paper relationships between mineralogy and comminution parameters have been applied to multi-element assay data with coincident measured Bond Work Index (BWi) data to generate a predicted BWi using linear regression. The predicted BWi is intended to supplement existing measured BWi data to enable better extrapolation across the deposit. Geostatistical Conditional Simulation methods have then used the predicted and measured BWi data to produce a BWi variable as a new input to the resource model. The simulated BWi can be used as an input for specific energy models to predict required grinding energy consumption across a deposit.

Mar 22, 2022

By P Edmondson, S Narendranathan, S Setchell

The complexities of mining in current economic conditions, where ore extraction schedules are varied on a weekly basis so as to ensure constant supply to the process plant, can result in a number of scenarios that pose geotechnical challenges. This paper presents a case study where alterations in the mining schedule of a particular mine resulted in the necessity to mine under a large uncompacted embankment, ie integrated tailings and mine waste landform. To effectively ensure that ore recovery was maximised, a well-designed slope monitoring system to evaluate design performance and to provide timely warning of impending failures was imperative. In order for an appropriate slope monitoring strategy to be developed, a thorough understanding of the potential slope failure mechanisms, capabilities and limitations of available monitoring techniques is required. Communication of the monitoring results and response strategy to alarms generated by monitoring systems must also be carefully considered to maximise effectiveness. The results of preliminary stability modelling can be used to guide the design of a monitoring system, which in turn can then generate data which can be used to iteratively refine the geotechnical model. This paper illustrates the development and implementation of a slope monitoring system and associated communication system, using a case study developed at a large iron ore open pit mine in the Pilbara region of Western Australia.CITATION:Narendranathan, S, Lee, E C, Setchell, S and Edmondson, P, 2015. Modelling of an integrated waste storage facility, in Proceedings Tailings and Mine Waste Management for the 21st Century , pp 183–190 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015

By M McCurd, M Lynch, B H. Yin, S Mendoza, C W. Bumby, Y Iwasaki, B Rumsey

Iron and steel production is responsible for approximately 6.3 per cent of global anthropogenic CO2 emissions. Direct reduction of iron with hydrogen is a potential route for decarbonising the iron and steel industry. Extensive small-scale laboratory experiments have been performed to test the feasibility of hydrogen-direct reduction of iron ores sourced from diverse geographical locations. However, test results from the batch reduction of small-sample do not necessarily translate to continuous commercial-scale processes. Establishing a small-scale continuous test reactor for H2- DRI process is challenging, requiring substantial resources and investment. The limited availability of small-scale reactors that enable testing under relevant conditions has become a major obstacle for H2-DRI development, leaving a big gap between laboratory success and proof of commercial feasibility. Here, we report on the recent commissioning of a continuous counter-flow vertical shaft reactor, which has a processing capacity of 6 kg/hr iron ore pellets at up to 100 NL/min H2 flow. We believe this to currently be the largest H2-DRI facility in the Southern Hemisphere. In this talk, we will discuss the design and construction journey for this reactor, starting from the initial system design to the initial demonstration of H2 reduction of titanomagnetite ironsand pellets. This reactor now enables a range of research capacities, including the validation of laboratory results on a larger scale with practical operational variables, feasibility assessment of hydrogen direct reduction of different iron ores on a commercial scale; identification of scalability, sticking, and other potential issues before building a full-scale plant; and a viable solution for producing small-quantity DRIs for downstream melting investigations. Overall, this new research facility offers significant benefits for assisting the transformation of iron and steel production to a more sustainable and green industry.

Sep 18, 2023

By S Li, Y Lei, X Wu, C Ma, W Q. Zhang

The failure of roof of thin bedrock working face under loose aquifer in a coalmine can lead to water-sand inrush disaster. Based on the accident of water-sand inrush in 30108 working face of a mine in Shaanxi province, China, the mechanism of water-sand inrush is theoretically analysed. The process and critical conditions of water-sand inrush in working face are reproduced by numerical simulation where the bedrock thickness is 20 m, the clay layer thickness is 40 m and the mining height is 6.5 m. The study found that under the condition of thin bedrock and thick clay layer, the characteristics of the clay layer have a significant inhibitory effect on the development of the fractured zone, and the development of the water-conducting fractured zone is incomplete and insufficient. However, in the process of continuous mining of multiple adjacent working faces, the strength of the clay is gradually reduced by the influence of mining and the erosion of water, and the height of the fractured zone is gradually increased. In the subsequent mining process of the working face, the roof is more likely to be cut-off and lead to water-sand inrush. From the initial failure of the clay to the final crack directly through the surface, the shear strength of the clay is reduced by about 52 per cent. Further simulation found that in addition to the characteristics of the clay layer itself, the main factors affecting the water-sand inrush in the working face caused by overburden failure also include the difference in bedrock thickness and strength, and the difference in coal seam mining height. With the increase of bedrock thickness, the development height of the fractured zone increases gradually with increases of bedrock thickness when the cutting failure of overburden rock no longer occurs. With the increase of mining height, the height of water flowing fractured zone also increases, but the cracking ratio gradually decreases. Therefore, it’s of great practical significance to systematically study the mechanism and critical conditions of water and sand inrush in mines and the main influencing factors for preventing similar accidents in mines with similar conditions.

Nov 29, 2022

By K Nakashima, K Aya, T Sumita, N Saito

Electro slag remelting (ESR) is one of the methods used to produce high-cleanliness steel. In the ESR method, the product steel electrode is immersed in flux, and the electrode is melted by the Joule heat of the flux generated by high current. CaF2-based melts are mainly used as fluxes, but the electrical conductivity of CaF2-based melts varies widely among researchers and measurement methods. Therefore, this experiment aims to measure the electrical conductivity of CaF2-based melts based on the van der Pauw-Ohta method, which does not require the cell constant that is a fundamental error factor in electrical conductivity measurement at high temperatures. The measurement temperature was set at 1450–1600°C, and dehydrated Ar flowed through the furnace at 200 mL/min. Electrodes were fabricated by Pt-30mass per cent Rh alloy, and the electrodes were connected to an impedance analyser using a four-terminal probe. The electrodes were immersed in the melt, and the impedance and phase angle were measured by AC frequency sweep (50 Hz to 200 kHz). The electrical conductivity was then calculated by utilising the impedance’s real part values when the impedance’s imaginary component was zero. The electrical conductivity showed a positive temperature dependence. The electrical conductivity of 60(CaO⋅Al2O3)-40CaF2 melt increased with increasing temperature but was found to be roughly one-third of those of the previous studies. In the conductivity measurement of 60(CaO⋅Al2O3)-40CaF2 melt, the AC frequency with a phase angle of 0° was found to be different depending on the temperature and immersion depth. By sweeping the frequency, the impedance at the phase angle of 0° can be obtained, which enables us to measure the electrical conductivity more accurately.

Jun 19, 2024

Good morning and thank you for the opportunity to address this yearÆs New Zealand Minerals Conference.   As you have already heard from the Associate Minister of Energy, the Government believes that the minerals industry is an important part of our economy. In particular, our coal and lignite resources have the potential to play an important role in New ZealandÆs energy sector as both a primary fuel and as a means to produce electricity.   The Government has taken a keen interest in the primary fuel sector given the declining reserves of natural gas sector. The energy sector is a key driver of economic growth and it is therefore critical that we have a reliable supply of primary fuel as part of the energy mix.   In a global sense, New Zealand is like many other countries regarding the need to secure energy for the future. Natural gas will be a key bridging fuel in the transition from an energy market based on fossil fuels to one based on renewables over the next century.   However, natural gas as a solution to this energy transition has some pragmatic limitations for New Zealand. There is uncertainty as to when new domestic reserves of gas can be discovered and developed. And the alternative of imported LNG poses a number of costs and risks to the economy.   New ZealandÆs coal resources are vast-estimated to be enough to last hundreds of years at the current rate of extraction. The main question is can extraction be increased and sustained to meet the demand of domestic power producers and at the same time meet commitments to lucrative international markets?   At this point it is appropriate for me to place coal into context with Governments overarching policy objectives for energy. The Government has stated objectives for the energy sector emphasising energy efficiency and an increased focus of renewable energy, while still ensuring security of supply and certainty as to energy costs and risk. Coal certainly can make a contribution to these objectives going forward.

Jan 1, 2005

Hydraulic backfill is generally retained in stopes using permeable barricades. Mitchell et al (1975), Mitchell (1992) and Grice (1989) have shown that under normal drainage conditions, barricades experience low levels of loading. Cowling et al (1988) have also shown that barricades are susceptible to piping failures if excess water has ponded on the upper backfill surface and if leakage of backfill from the barricades has occurred. During 1997, six hydraulic backfill barricades failed in four different Australian mines. Fortunately, in each case, the quantity of backfill slurry released was small, and no injuries to personnel nor damage occurred. Detailed investigation of two of the incidents showed that the primary cause of failure could be attributed to the delivery of excess quantities of transport water from the low-density slurry. For each of the incidents investigated there was evidence of the development of piping failures, which resulted in hydrostatic loading conditions on the barricades from the ponded water on the upper backfill surface. The circular failure surfaces in the barricades were characteristic of the application of point loading conditions. This paper discusses the circumstances that led to these incidents and analyses the modes of failure. The standards for the safe operating of hydraulic backfill systems are reviewed along with requirements for ongoing management and control. The design requirements of barricade construction are analysed and some appropriate guidelines introduced.

Jan 1, 1998

By G McSpadden

At September 2001 the beneficiation plant at BHP Billiton Iron OreÆs Mt Whaleback mine is set to treat 9.5 million tonnes per annum (Mtpa) of iron ore, 40 per cent better than original design. This paper describes the steps, decision-making processes and innovations used to increase capacity at minimum cost. The plant was designed in 1979 to operate at 1133 t/h for 6000 hours per annum, treating 6.8 Mtpa. Sufficient suitable contact ore was unavailable and feed was finer than planned. The plant was designed with minimum surge capacity between multiple process units. It had never reached design capacity. In 1993 a study by Fluor Daniel to treat increased tonnage resulted in modifications to improve plant operations. Efforts to expand production by increasing reliability did not achieve the desired capacity. NJ Morrow (Pty) Ltd (NJM) conducted a technical audit in 1996 with process evaluation by Mineral Processors. Replacement of operator interface and PLC logic in 1997 made plant operation and diagnosis easier. Involving operators in logic development enhanced their plant knowledge. Fluor Daniel Simulation developed a simulation model of the process. Mineral Processors and NJM reviewed the model findings, recommended metallurgical improvements and developed preliminary designs and costs. BHP Engineering produced a detailed design with a cost estimate of $A34 million. After analysis and revision of the design, a $A10.4 million upgrade to 8.5 Mtpa was carried out. Detailed modifications to the process units, particularly the HM drum plant, allowed significantly higher capacities and improved metallurgical performance. The target capacity was achieved in June 2001. Further modifications are progressing to treat lower-grade ores.

Jan 1, 2002

The epithermal silver-gold Red Rock Deposit is hosted in the Late Permian inter- mediate to silicic composition Drake Volcanics of New England, N.S.W. This deposit represents one of the few low sulfur epithermal precious metal systems in eastern Australia, and differ! from epithermal models in that the hydrotherma: system which produced mineralization was active in a shallow water marine environment. The Red Rock Deposit has a resource of 180,000 tonnes of 66g/t Ag and 0.9 g/t Au, and a Ag:Au ratio of 70:1. Mineralization is largely associated with hydrothermal brecciation, and occurs as disseminations, vein stockworks, and struc- turally controlled lodes. Ore minerals comprise acanthite (argentite), electrum, native Ag, Ag- sulfosalts and base metal sulfides, Alteration minerals associated with ore are quartz, cal- cite, adularia, pyrite, illite, illite-mont- morillonite, chlorite and sphene (leucoxene). Illitic and propylitic alteration zones sur- round the hydrothermal breccia. Bulk rock analyses indicate that alteration is character- ized by the addition of Si, K, Fe, Mg and the loss of Na and Ca. Ore was deposited from a boiling fluid in a temperature range of 222- 295¦C, and of 0.5-7 wt. Z NaCl equivalent sal- inity. An upper hydrostatic depth limit of about 800 m is implied for the boiling fluid ii an open vein. Sulfur isotopes indicate a mag- matic sulfur source, and oxygen isotopes imply a predominantly marine ore fluid. Modern analogs of the submarine hydrothermal system that formed the Red Rock Deposit occur in the Taupo Zone, New Zealand, and southern Kyushu, Japan.

Jan 1, 1987

In essence, these statements concur, However, management predominantly controls the organisation's communication environment (5), Consequently, the participation by employees in safety is greatly influenced by the quality of upward communication, (See section on authority for discussion on two way communica-ò tionò) Emotional survival contributes to the communications and it is said to occur as follows: -- We. aU tend to move towaAA 6.itw tLon,s which aid the achievement oj5 owc goa o and way {y/wm ones which testh ict achievement." Consequently, although the work force are prepared to contribute, they will not make the effort for long if management does not respond in deed. The Robers report includes the following statement; "Satiety and heat h at wank is a matte o6 e66ic,ient management. But it .L not a management pn.enogative. Wank people muht be encouAagad to pattiaipate úu.Uy in the making and movutoni:ng ob a/vua.ngements ban .6aJety and heath, at their. pace ofj wonk.t'(3) Attitudes dominate within this region. Emotional surviv- al is paramount. Management is the catalyst. They dominate the communication channels. Participation does not exist without two way communications and positive responses by those involved, Fault Doctrine. Eliminate faulty human behaviour. This concept lives with us as the predominant prior- ity of many safety programs. The concept is a drain on limited resources., Remember, malaria. At one stage this disease was believed to be caused by the mat or bad air emanating from persons whose profaneness or impious behaviour incurred such reprisal. Today, such a concept of malaria seems so ridiculous, (9)

Jan 1, 1979

By S Grant, S Emeric, P Baker, E Jones, D Clark

As we strive for a sustainable and resilient future, repurposing assets has become a top priority. In Australia alone, we have a significant number of mineral projects in the pipeline, extensive existing operations, and over 50 000 legacy sites. Collectively, this presents a unique opportunity to be a world leader in mine rehabilitation. Complex stakeholder landscapes, inflexible policies, aged regulatory frameworks, technical uncertainties and increasing liabilities are all barriers hindering effective transition of legacy assets. The impetus for change is further catalysed by shifting consumer preferences, workforces in flux and regional Australians questioning what the transition means for their local community. We need innovative approaches to take a leading role in the industry and support global efforts more broadly. Co-designing an ambitious, shared vision spanning projects, operations and legacy assets with all key parties is a fundamental step to unlock and realise maximum societal, environmental, economic and reputational value. Serious play and gamification can further enhance this visioning process.

Aug 2, 2023

By J J. Jiang, B G. Bow

Atlas Iron Limited’s (Atlas) Abydos Mine has developed its Scarborough open pit proximal to a rock shelter that has been assessed as a significant Aboriginal heritage site by the Traditional Owners of the land. The rock shelter, named Yurlu Kankala, is located to the north-west of the pit with a stand-off distance of 35 m. Within Atlas’ Native Title Agreement with the Traditional Owners, and approvals from the Western Australian Department of Aboriginal Affairs, commitments have been made to conduct mining in a way that avoids or at least minimises disturbance and damage to the rock shelter. This complies with the Aboriginal Heritage Act 1972 (WA) and respects the heritage and culture of the Traditional Owners.CITATION:Bow, B G and Jiang, J J, 2018. Iron ore mining in proximity to a significant Aboriginal heritage rock shelter, Pilbara Region, Western Australia, in Proceedings Life-of-Mine 2018, pp 2–5 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 25, 2018

By B BussiFre, J Molson, M Aubertin, G W. Wils

Waste rock piles containing reactive sulfide minerals can serve as long-term sources of acid mine drainage (AMD). Within these piles, many physical, geochemical and biological processes can contribute to the production of AMD. The flow of water, for example, depends on internal pile structure, which depends on the dumping methods used to construct the pile. In this paper, the internal structure and grain size distribution of typical waste rock piles are first reviewed with respect to their effect on internal water flow. A numerical model is then applied to simulate unsaturated flow within a waste pile assuming two primary waste materials, different atmospheric conditions and several geometric configurations. The simulations suggest that water movement can be controlled by introducing fine-grained material layers within the coarser host material. However, these layers should not be horizontal because they can lead to localised high-saturation regions as well as preferential flow favouring the production of AMD. A shallow slope towards the pile boundary may be introduced to force drainage to the outside while maintaining low saturation within the interior, thus reducing the production of AMD.

Jan 1, 2003