Run Of Mine Research Articles

Microbial succession during a heap bioleaching cycle of low grade copper sulfides: Does this knowledge mean a real input for industrial process design and control?

The paper Bacterial succession in bioheap leaching ( Brierley, 2001) showed the search for methods to analyze the microbial dynamics in bioleaching industrial processes as a key challenge for advancing commercial bioheap applications. “Chemical and physical conditions within bioheaps change radically from the time the bioheap is stacked and inoculated until bioleaching is completed.” The results from a comprehensive monitoring program by culturing and molecular techniques in an industrial bioleaching process for run-of-mine (ROM) low grade copper sulfide ore in Chile is summarized. The analysis of the compiled information permits an understanding of changes in microbial substrates availability, chemical and physical conditions. A data mining technique, called decision trees was used to analyze the information and to establish rules that represent patterns in the data. The bacterial succession in bioheap leaching solutions allowed the leaching cycle stages to be described as: i) Acid conditioning and soluble copper releasing, ii) Chalcocite Bacterial leaching (ferrous oxidation); iii) Chalcocite Bacterial leaching (ferrous and reduced sulfur compounds — RISC oxidation); iv) Bacterial leaching of sulfide minerals with higher rest potentials (pyrite and covellite), and v) Bacterial oxidation of remnant sulfide minerals and RISC. The impact of other factors on microbiology, such as the solvent-extraction process, aspects of the industrial design and operation are also discussed.

Numerical modelling of out-of-seam dilution in longwall retreat mining

Longwall mining is a common mining method in Iran that is often affected by out-of-seam dilution (OSD). The field investigations performed in Tabas coal mine show that OSD often occurs due to roof falls in front of the face area before support setting and also removing some floor material. The increase in unsupported roof span above the shearer may cause difficulty in controlling the roof and consequently increases dilution of the run of mine (ROM) coal. The paper presents the results of a study on some dominant factors causing OSD in prop-free front of the face in longwall retreat mining method. A series of two-dimensional numerical models are developed and analyzed to examine the effects of mining depth, in-situ stress, unsupported roof geometry above the shearer as well as roof and floor strata quality and dip of coal seam on OSD. Two criteria were established, one considers the roof falls, defined as low stress level or plasticity zones under yield tension which roof material unravels and other is about removing floor, defined as depth of support and shearer sinking into the floor. The equivalent linear relaxation depth (ELRD) and depth of removing floor (DRF) concepts were used to quantify OSD. The methodology presented in this study is useful since it can be applied to develop mine-specific design tools for the prediction of OSD.

A Holistic Approach to Control and Optimization of an Industrial R Ball Milling Circuit

Anglo Platinum's control schema for a Run-of-Mine (ROM) ball milling comminution circuit follows a layered approach that involves basic control (regulatory, interlock and sequence control), fuzzy logic rule-based and model predictive control. This allows for a robust approach to optimization. This paper reviews the above control schema for a ROM ball milling circuit and discusses the benefits that have been achieved from implementing optimization using Mode Predictive Control (MPC) to cater for a wide range of feed conditions.

Pilot-Scale Baum Jig Washing for Beneficiation of a High-Ash Indian Noncoking Coal

Coal will continue to play an important role in overall energy scenario in India. Despite its high-ash content, the run-of-mine (ROM) Indian coals are used directly for thermal power generation. There is an urgent need to improve quality of coal by reducing ash so that a consistent supply of quality coal can be supplied to the power plants. Pilot-scale studies were conducted on beneficiation of High Ash Indian Non Coking Coal obtained from the Samleshwari mines using a 20-t/h Baum Jig Washer. The results of the pilot-scale studies revealed that the ROM coal, containing 50% ash content, could be cleaned with the Baum jig providing a clean coal containing 36% ash at a yield of 52%.

Predicting lump and fines finished product grades and lump percentage from head grade

Cliffs Natural Resources Pty Ltd operates iron ore mines in the Koolyanobbing region of Western Australia. Ore is mined from three locations, separated by many kilometres. The ore is stockpiled at these locations, according to an in-house ore classification system (based on grade and source), and then trucked to the crushing and screening plant at Koolyanobbing. Lump and fines products are railed to Esperance for ship loading and export to Asian customers. Cliffs Natural Resources Pty Ltd prides itself on the relatively low intershipment grade variability of the products. The Koolyanobbing crusher is fed using a daily blend plan, generated to maintain lump and fines product grades within acceptable tolerance ranges around targets. Achieving low variability requires predicting lump and fines grades as accurately as practical from the estimated head grades of the Run of Mine (ROM) ores potentially going into the blend. The grade prediction model may be either a direct prediction of crushed lump and fines grades and lump percentage, or be split into two stages: the bias between blast hole estimated head grade and crusher head grade, and then the lump–fines algorithm for splitting the head grade between lump and fines products. The lump–fines algorithm comprises the percentage of lump, and the difference between the lump and fines grades. The authors describe a weighted least squares regression model for predicting crusher grades and lump proportion from the estimated head grade for Fe, P, SiO2, Al2O3, Mn and S. The method is applied to Cliffs Natural Resources Pty Ltd production data, where the regression model explains ∼60% of the variance in the crushed ore grade, for both lump and fines. A further small but significant improvement in prediction can be achieved by including the ore classification data in the model. The regression errors exhibit strong positive serial correlation, indicating trends in grade error across multiple blend records. To compensate for the longer term error, an exponentially smoothed model was developed and applied to the daily grade blend errors. This gave an increase in the longer term variance explained and therefore an improvement in grade prediction.

Microbial Succession during a Heap Bioleaching Cycle of Low Grade Copper Sulphides. Does this Knowledge Mean a Real Input for Industrial Process Design and Control?

The paper “Bacterial succession in bioheap leaching” [1] initiated the search for methods to analyze the microbial dynamics in bioleaching industrial processes as a key to advancing commercial bioheap applications. “Chemical and physical conditions within bioheaps change radically from the time the bioheap is stacked and inoculated until bioleaching is completed.” The results from a comprehensive monitoring program by culturing and molecular techniques in an industrial bioleaching process for Run-of-mine (ROM) low grade copper sulfide ore in Chile will be summarized. The analysis of the compiled information permits an understanding of changes in microbial substrates availability, chemical and physical conditions. The impact of other aspects on microbiology, such as the mining programme and the industrial design are also considered. The bacterial succession in bioheap leaching solutions allowed the leaching cycle stages to be describe as: i) Acid conditioning and soluble copper releasing, ii) Chalcocite Bacterial leaching (ferrous oxidation); iii) Chalcocite Bacterial leaching (ferrous and reduced sulfur compounds –RSC- oxidation); iv) Bacterial leaching of sulphide minerals with higher rest potentials (pyrite and covellite ), v) Bacterial oxidation of remnant sulfide minerals and RSC.

RNMPC Applied to a Nonlinear Model of a ROM Ore Milling Circuit

Abstract This paper presents simulation results of applying robust nonlinear model predictive control (RNMPC) to a nonlinear model of a run-of-mine (ROM) ore milling circuit. The model consists of nonlinear modules for the individual process units of the milling circuit, which allow arbitrary milling circuit configurations to be modelled. This study aims to cast a complex problem of a run-of-mine ore milling circuit into a robust nonlinear model predictive control framework without losing the flexibility of the modularised nonlinear model and implement the robust nonlinear model predictive controller using open-source software modules.

Preliminary investigations on recovery of zircon from alluvial pebbles

Owing to high demand of zircon, the exploitation of the sand deposits and recovery of zircon from such alternate sources is a priority at present. In this context, investigations were carried out on the recovery of zircon from river pebbles by gravity spirals and tables. The study revealed that the Run of Mine (ROM) sample contains 0.35% by weight Total Heavy Minerals (THMs) with 0.03% ZrO2. The sample ground to d80 (passing size of 1000 µm) was subjected to six-stage spirals followed by tables. The end-product obtained in this process contains 44.1% ZrO2 with 74% recovery.

Devolatilization of coals of North-Eastern India under fluidized bed conditions in oxygen-enriched air

Oxygen-enriched air can increase the combustion efficiency, boiler efficiency, and sulfur absorption efficiency of atmospheric fluidized bed combustion (AFBC) boilers which use high-sulfur coal, and other combustion systems that use coal. Devolatilization is the first step in the gasification or combustion of coal. In this work, devolatilization characteristics of five run-of-mine (ROM) coals of North-Eastern India having particle-size between 4 mm and 9 mm are reported. The experiments were performed under fluidized bed conditions at 1123 K in enriched air containing 30% oxygen. The devolatilization time was correlated with the particle diameter by a power law correlation. The variation of mass with time was correlated by an exponential correlation. It was observed that the average ratio of yield of volatile matter to the proximate volatile matter decreased with the increase in volatile-content of the coals. A shrinking-core model was used to determine the role of film-diffusion, ash-diffusion and chemical reaction. The experimental results indicate the likelihood of film-diffusion to be the rate-controlling mechanism in presence of oxygen-enriched air. A cost-analysis was carried out to study the economy of the process.

Looking for an Ideal Particle Size for Apatite Flotation

Today, the phosphate rock processed in the world represents around some 20 billion dollars per year. Some exploitable deposits are characterizing by low grade phosphate rocks, composed of the apatite group in association with a wide assortment of accessory minerals. Usually a combination of beneficiation techniques is used to process a phosphate rock since run of mine, and then a flotation is applied to recovery apatite. This work proposes an evaluation of particle size for apatite recovery by column flotation in bench-scale. The variables collector dosage and depressant dosage were investigated experimentally applying a factorial design. According to the experimental results, the particle size range between 37&m and 105&m is an optimum size used to obtain simultaneously a product with the industry demand grade (at least 33%) and phosphorus recovery, upper than 60%.

Coal-Fine Beneficiation Studies of a Bench-Scale Water-Only Cyclone Using Artificial Neural Network

Coal fines generated in Indian coal preparation plants account for 25%–30% of run-of-mine (ROM) coal. Coal cleaning is receiving increasingly greater attention of process engineers in view of the increase in amounts to be handled as well as the difficult washability characteristics of high-ash-content Indian coals. Froth flotation is usually practiced in Indian coal washeries for washing the coals to bring down their ash content to acceptable limits. Because of the supply of feed coal from multiple sources, their different characteristics and composition, viz., varying mineralogy and ash content, presence of microfines, and their varying oxidation levels, the fine coal circuits, more often than not, fail to deliver consistent product quality and desired yields. Water-only cyclones have been used in most of the western countries for treating coal and mineral fines below 3 mm. However, the industrial use of these cyclones in India has not yet been put to practice in the coal-washing industry; the primary reason for this being that their design is unsuitable for high-ash content coals and therefore needs to be suitably modified according to the feed material characteristics. Highlighted in the present paper are the results of a case study of beneficiation of high-ash fine coal, using a water-only cyclone. The influence of two of the critical design variables, viz., cyclone length and solid concentration, on which the cyclone performance and the process yield (%) depend to a great extent, is described. Further, based on the experimental data of a water-only cyclone of varying lengths used for below a 3 mm coal beneficiation study, an attempt has also been made to develop a three-layer feed-forward artificial neural network (ANN) model, which is inherently trained using an error-back propagation algorithm. The results evince that the predictions from the ANN model are in good qualitative and quantitative agreement with the experimental observations, thereby validating the applicability and accuracy of the developed ANN model.

Chemical and petrographical characterization of feed coal, fly ash and bottom ash from the Figueira Power Plant, Paraná, Brazil

Abstract The aim of the present study is the petrographic and chemical characterization of the coal at the Figueira Power Plant, Parana, Brazil, prior and after the beneficiation process and the chemical characterization of fly and bottom ashes generated in the combustion process. Petrographic characterization was carried out through maceral analysis and vitrinite reflectance measurements. Chemical characterization included proximate analysis, determination of calorific value and sulphur content, ultimate analysis, X-ray diffraction, X-ray fluorescence, Inductively Coupled Plasma — Mass Spectrometry (ICP-MS) and Inductively Coupled Plasma — Atomic Emission Spectrometry (ICP-AES) analysis, and determination of Total Organic Carbon (TOC) content. Vitrinite reflectance analyses indicate a high volatile B/C bituminous coal (0.61 to 0.73% Rrandom). Maceral analyses show predominance of the vitrinite maceral group (51.6 to 70.9 vol.%, m.m.f). Except of the Run of mine (ROM) coal sample, the average calorific value of the coals is 5205 kcal/kg and ash yields range from 21.4 to 38.1 wt.%. The mineralogical composition (X-ray diffraction) of coals includes kaolinite, quartz, plagioclase and pyrite, whereas fly and bottom ashes are composed by mullite, ettringite, quartz, magnetite, and hematite. Analyses of major elements from coal, fly and bottom ashes indicate a high SiO 2 , Al 2 O 3 , and Fe 2 O 3 content. Trace elements analysis of in-situ and ROM coals by ICP-MS and ICP-AES show highest concentration in Zn and As. Most of the toxic elements such as As, Cd, Cr, Mo, Ni, Pb, and Zn are significantly reduced by coal beneficiation. Considering the spatial distribution of trace elements in the beneficiated coal samples, which were collected over a period of three months, there appears to be little variation in Cd and Zn concentrations, whereas trace elements such as As, Mo, and Pb show a larger variation. In the fly and bottom ashes, the highest concentrations of trace elements were determined for Zn and As. When compared with trace element concentrations in the feed coal, fly ashes show a significant enrichment in most trace elements (As, B, Be, Cd, Co, Cr, Cu, Li, Mn, Mo, Ni, Pb, Sb, Tl, and Zn), suggesting a predominantly volatile nature for these elements. In contrast, Sn is distributed evenly within the different ash types, whereas U shows depleted concentration in both bottom and fly ash samples. According to the International Classification of in-seam coals the Cambui coals are of para/ortho bituminous rank of low grade (except for the ROM sample), and are characterized by the predominance of vitrinite macerals.

Multi-element analysis of iron ore pellets by Laser-induced Breakdown Spectroscopy and Principal Components Regression

Laser-induced Breakdown Spectroscopy (LIBS) in combination with Principal Components Regression (PCR) has been applied to determine the elemental composition of a series of run-of-mine (ROM) iron ore samples. The samples were presented for measurement both as compressed pellets and as loose chipped material. The present paper details the results of the measurements of the compressed pellets. Results from ore chips will be reported separately. LIBS spectral data was recorded in three separate spectral regions to measure major, minor and trace components of the iron ore sample pellets. Background stripping, normalization and spectral cleaning were applied to minimize the relative standard deviations of the LIBS data. PCR analysis was then applied to produce calibration models for iron, aluminum, silicon, manganese, potassium and phosphorous. These calibration models were then validated using independent LIBS measurements. Robust calibration models were determined for iron, aluminum, silicon and potassium, whilst the results for manganese were encouraging. Phosphorous, present at low levels in the ores measured, remained the most difficult element to determine accurately. The combination of LIBS and PCR shows potential for in-situ on-line determination of ore composition.

Correcting for dilution of rakes processed sequentially from multiple mines at BHP Billiton Iron Ore Newman Joint Venture operations

At BHP Billiton Iron Ore operations, run of mine ore from the several Newman Joint Venture (NJV) mines is railed in 12 kt rakes to Port Hedland. Rakes are processed sequentially, with the lump and fines components from each rake sampled after crushing and screening. The grade of ore from the individual mines varies around consistently different means. Although a discrete sample is attributed to each rake, the sample contains some material from the following and/or the preceding rakes due to dilution by ore from the neighbouring rakes during the dumping, screening and crushing processes. Individual rake grades at the port are therefore biased according to the mine sources of adjacently processed rakes. Dilution does not affect the grade of the overall NJV product or the accuracy of port stockpile grades, however it does limit the ability to use port rake grades to review the quality performance of individual mines and provide meaningful lump–fines algorithms and port–mine biases for individual mines, information that is useful when scheduling ore for mining. A non-linear regression model has been used to estimate the average dilution from the preceding and following rakes. It has been shown that the lump and fines samples for 12 kt rakes are each diluted within the Port process with about 8˙3% of the sample coming from the preceding rake and ∼3˙6% from the following rake. This can, bias the reported rake grade by up to 1% iron. The results of this analysis have been incorporated into the daily grade scheduling system to provide more accurate individual mine grade data and consequently better decision making.

Cleaning Potential of Samleshwari Noncoking Coal by Washability Investigation

Indian coals, which are of Gondwana origin, contain high ash wherein the extraneous material was intimately mixed in the coal matrix during the formation stage, causing a high level of impurities in the run-of-mine (ROM) material. These coals possess difficult to very difficult washability characteristics. Beneficiation of high-ash noncoking coals of India has become the prerequisite for improving the overall economics and efficiency of power generation. This article describes the washability characteristics of a typical noncoking coal from the Ib Valley Coalfields aiming at 34% ash level in the clean coal as per the stipulations laid by environmental gazette notification of the Government of India. Conventional float-and-sink testing was used to determine the yield of clean coal of 58% at 34% ash content.

English

A ten-year acid rock drainage (ARD) mitigation program conducted by PT Freeport Indonesia at the Grasberg Mine, Papua Province, Indonesia has developed strategies to maximise the beneficial use of the mined limestone for ARD mitigation. Laboratory columns and field test pad investigations have examined limestone blends, layers and covers. Full-scale trial dumps comprising truck blends, conveyor/stacker blends and truck placed limestone covers have been constructed and monitored. Construction of an operational blended stacker built dump commenced in 2004 and is operated in accordance with blending specifications developed from the 10-year trial. Trials have demonstrated that run-of mine truck constructed blended dumps are unlikely to be effective because the finer size fractions do not received adequate limestone. Stacker-built dumps can be effective provided the blend ratio is based on achieving adequate acid neutralising capacity within the finer fractions. Operational experience with the large stacker-built dump indicates that there is no discernable segregation of sulfur or acid neutralising capacity down the slope. The scheduling of potentially acid forming waste and limestone to the in-pit crushers is determining the spatial variability within the dump rather than segregation of sulfur or acid neutralising capacity during the dumping process.

Comparison of some physico–chemical properties of Victorian lignite dewatered under non-evaporative conditions

A Victorian lignite, designated Loy Yang low ash, run of mine (LYLA (R)) has been dewatered using mechanical thermal expression (MTE) at 150–200 °C and 6–25 MPa and by hydrothermal dewatering (HTD) at 200–300 °C and the products compared. Total acidity values for all samples as measured by a pyrolysis thermogravimetric Fourier transform infrared (TG–FTIR) method were similar to those measured by barium ion exchange. Stronger (carboxylic) acid values determined by pyrolysis TG–FTIR tended to be lower than ion exchange values, except for the 300 °C HTD sample, for which both methods gave similar values although these were much lower than at all of the other treatment temperatures. Equilibrium moisture contents (EMC) for the MTE products and the 200 °C HTD product were similar to those of the original lignite at relative vapour pressure (RVP) ⩽ 52%, but lower at RVP 92%. EMC values for 300 °C HTD products were all lower than for the original lignite, indicating that processing temperature was the most important factor in determining these properties. CO 2 adsorption surface area was also mainly a function of processing temperature, decreasing with increasing temperature. However, the pore volume as determined by mercury porosimetry was influenced by whether dewatering was effected by MTE or HTD, the mechanical pressure applied in the MTE process resulting in a lower porosity.

Molecular characterization of microbial populations in a low-grade copper ore bioleaching test heap

A culture-independent approach based on PCR amplification and denaturing gradient gel electrophoresis (DGGE) and sequencing of 16S rRNA gene fragments from both Bacteria and Archaea were used to analyze the microbial community inhabiting a low-grade copper sulfide run-of-mine (ROM) test heap of a project in Chile. In this paper, we summarize results of a 1-year monitoring study. Phylogenetic analyses of 16S rRNA fragments revealed that the retrieved sequences clustered together with Acidithiobacillus ferrooxidans, Leptospirillum ferriphilum, Ferroplasma acidiphilum and environmental clones related to them. In addition, some sequences were distantly related (< 95% similarity in the 16S rRNA gene fragment analyzed) to cultured microorganisms from the Sulfurisphaera and Sulfobacillus genera. Thus, the prokaryotic assemblage might be mainly composed of sulfur- and iron-oxidizing microorganisms. The remaining sequences were related to uncultured chrenarchaeota clones or had only partial homology with known microorganisms. Attempts were made to estimate the dynamic of phylogenetic microbial groups in different stages of the leaching cycle and to correlate them with chemical and physical parameters in the heap. The temporal distribution of microbial 16S rRNA gene sequences could be divided in three periods. In the bioleaching cycle, first stage A. ferrooxidans and Sulfurisphaera-like archaea were dominant within each respective phylogenetic domain. In the second stage (from days 255 to 338), Leptospirillum and Ferroplasma groups were mainly detected, respectively. Finally (the third period from operation days 598 to 749), Sulfobacillus-like microorganisms became predominant, while Ferroplasma was the only Archaea detected. These data are now being used to obtain more detailed and quantitative information on prokaryotic community structure over time and to explore the nature of the community metabolic pathways. These results extend our knowledge on microbial dynamics in bioheaps, a key issue required to improve commercial applications.

Forecasting fluctuations in coal quality delivered to a power plant via stochastic simulation

The new generation of coal-fired power plants in Brazil are expected to use run-of-mine (ROM) coal as fuel; however, variations in the quality of the coal are likely to be transferred from the mine to the final user. Contracts frequently establish maximum/minimum limits for geological and technological parameters, allowing for rejection or imposition of penalties when the quality of the lots is outside the agreed limits. The high costs associated with such penalties necessitate quality control of the final product (ROM). Geostatistical methods can be used to predict in situ ore quality and variability. Geostatistical methods employ a block model with grades assigned to each block. The block model obtained through the use of ordinary kriging is inappropriate in accessing the uncertainty associated with the geological or technological parameters being modelled. Consequently, this procedure fails to predict grade fluctuations correctly. Contrary to kriging, simulation methods aim at reproducing in situ grade variability and spatial continuity. Once one produces a block model, with each grade uncertainty evaluated, quality fluctuation can be predicted for any given mining route. Also the fluctuations associated with the size of a lot to be delivered to the customer can be predicted. Different mining routes and sizes of ore lots are tested until the desired level of grade oscillation is achieved. Results from a case study at a Brazilian coal mine prove the adequacy and functionality of the method and that geostatistical simulation adequately predicts quality fluctuations.

Application of a Life Cycle Impact Assessment framework to evaluate and compare environmental performances with economic values of supplied coal products

The South African economy is strongly based on coal as a mined resource, and various grades of coal are supplied to local and international customers. However, the environmental impacts associated with the preparation and production of different coal grades from Run of Mine (RoM) or raw coal are variable; specifically, the different mining methods used for coal extraction – opencast or underground mining – have different environmental impacts. The entire life cycles of the grades of coal must therefore be evaluated in order to compare environmental performances with supplied economic values. In this paper, a Life Cycle Impact Assessment (LCIA) methodology, based on the ISO 14040 standard, is applied for this purpose. Four cases are considered in South Africa: typical high-grade and low-grade coals from opencast and underground mines.