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By Marcello M. Veiga

Informal gold mining operations in the Amazon emit about 100 tonnes of mercury annually because of poor amalgamation practice. Lack of information and the complexity of mercury transformations hinder effective action to prevent such pollution and/or monitor its extent. In the past, mathematical equations have been formulated to deal with the correlation of natural variables and mercury in biota but often, the error range is too great to provide useful models. Projection of physico-chemical variations in an environment subjected to mercury emissions onto the extent of bioaccumulation is fraught with many uncertainties and unknowns such as internal correlations between variables and the site-specific nature of biota contamination. Often assumptions about closed systems are invalid when applied to natural environments. This work presents a heuristic approach to this problem in which amalgamation methods and natural variables are dealt with using an IF-THEN rule-based system that concludes about levels of emission and risk of bioaccumulation. The system is able to handle uncertain or vague data and yet still provide useful output. Belief in mercury oxidation or dangerous conditions are examined using Fuzzy Logic techniques and Inference Equations. These belief levels are derived from thermodynamic equilibrium data together with field observations of natural variables. This procedure can reduce the need for sophisticated analytical equipment and can provide information and diagnosis to non-technical people.

Jan 1, 1994

By H. Majima

In spite of the importance of the presence of pyrite in the flotation of sulphide ores, not many studies have been made from the electrochemical point of view. It is generally recognized that the oxidation of sulphide minerals is one of the most Important factors among those which affect the floatability of sulphide minerals. The concept that the presence of oxygen is essential to the flotation of sulphide minerals is supported by numerous experimental results (1). The presence of oxygen in sulphide minerals- aqueous solution systems would affect the electrochemical behaviour of sulphide minerals and subsequently lead to more complicated reactions on the surface of sulphides. Actually some of the phenomena observed in sulphide flotation are deemed to be more appropriately explained from the electrochemical point of view. The author and co-workers have studied extensively the electrode reactions of pyrite and its significance in sulphide flotation. The results have been partly published elsewhere (2-7). In this paper, the author discusses the electrochemical nature of pyrite, and the three different phenomena observed in pyrite flotation: (1) Xanthate¬dixanthogen system on pyrite, (2) Flotation of complex sulphide ores containing pyrite and (3) Depressive mechanisms of pyrite with cyanide. The phenomenon which has been known as an iron contamination effect due to steel grinding media on sulphide flotation is also explained from the electrochemical aspect. However, this problem is not directly concerned with pyrite, and it will be discussed elsewhere (8).

Jan 1, 1971

By N. Dashbold, E. Rudnik

"Waste electric and electronic equipment currently comprises the fastest-growing waste stream in the world, but at the same time it is seen as an important source of metals for the recycling industry. E-waste is usually treated pyrometallurgically, with hydrometallurgical methods used to a lesser extent. This paper reports the results of research on the selective recovery of copper from smelted low-value electronic waste. Pyrometallurgical pretreatment of the scrap allowed the removal of plastics and the increase of metal content in the material. The obtained alloy of copper, zinc, tin and silver was a multiphase solid consisting of two brass phases and inclusions rich in iron, lead and silver. Copper alloy was further anodically dissolved in ammoniacal chloride solution. It resulted in high degradation of the material and accumulation of the metals mainly in the slime. The slime was then leached in acid or ammoniacal chloride and sulfate solutions followed by selective copper electrowinning. Hydrochloric acid was the most efficient solvent for the slime, but ammoniacal solutions were more selective for copper. Copper could be leached with 96 to 100 percent and 87 percent efficiency from the slime by the chloride and sulfate solutions, respectively. Copper with 90 to 99 percent purity at current efficiency of 42 to 76 percent was obtained from the acid solutions, while copper with 98 to 99 percent purity at current efficiency of 60 to 86 percent was deposited from the ammoniacal baths. IntroductionObsolete electrical and electronic equipment makes up the fastest-growing waste stream in the world (Baldé et al., 2015), due not only to the introduction of wider ranges of new types and models of a variety of electronic products but also to the shortening of their life-spans, sometimes referred to as planned obsolescence by producers (Keeble, 2013). About 42 million tons of electronic waste, or e-waste, are estimated to have been generated globally in 2014 (Baldé et al., 2015), and it is expected that in the European Union alone the waste electrical and electronic equipment (WEEE) stream will reach more than 12 million tons by 2020 (European Commission, 2015). Accurate evaluation of e-waste generation (Wang et al., 2013) and its global transport (Breivik et al., 2014) is difficult, mainly due to a lack of high-quality data related to its market and socio-economic dynamics.Many countries introduced legislation to control e-waste flow, collection and recycling. For example, Directive 2012/19/EU on waste electrical and electronic equipment (European Parliament and the Council of the European Union, 2012) obliges all E.U. members from 2016 to maintain a minimum collection rate of 45 percent of the total weight of WEEE collected. From 2019, the minimum collection rate to be achieved annually shall be 65 percent of the average weight of electronics placed on the domestic market in the three preceding years, or alternatively 85 percent of WEEE generated in the territory of the particular member."

Jan 1, 2017

By Syd Peng, Gamal Rashed

"Bumps in coal mines have been recognized as a major hazard for many years. These sudden violent failures around mine openings have compromised safety, ventilation and access to mine workings. Previous studies showed that the violence of coal specimen failure depends on both the interface friction and width-to-height (W/H) ratio of a coal specimen. The mode of failure for a uniaxially loaded coal specimen or a coal pillar is a combination of both shear failure along the interface and compressive failure in the coal. Unstable interface failures provide a sudden de-confinement to coal rib, thus triggering uns and compressive failure in the sidewalls. The compressive failure of a coal specimen or a coal pillar can be controlled by changing its W/H ratio. As the W/H ratio increases, the ultimate strength increases. With a proper combination of interface friction and the width-to-height (W/H) ratio of pillar or coal specimen, the mode of failure will change from sudden violent failure, which is brittle failure to non-violent failure, which is ductile failure. The main objective of this paper is to determine at what W/H ratio and interface friction the mode of failure changes from violent to non-violent. In this research, coal specimens of width-to-height ratio ranging from 1 to 10 were uniaxially tested under two interface frictions of 0.10 and 0.25. The results are presented and discussed.INTRODUCTIONCoal mine bumps are sudden, violent bursts of coal from a pillar or pillars or a block of coal, resulting in a section, the whole pillar, or the solid block of coal being thrown into an open entry. These bursts are accompanied by very loud noises (Peng, 2008). Several case histories in mining have long described coal pillars or coal faces failing violently with an accompanying ejection of debris and broken material into the working areas of the mines (Campoli et al., 1987; Osterwald, 1962; Peperakis, 1958; Garvey et al., 2013). Because of the catastrophic nature of these sudden failures, understanding the causes of coal mine bumps is essential to create a safe underground working environment. This phenomenon has motivated many ground control researchers to conduct extensive field investigations throughout the past century. Rashed and Peng (2014) compared the mechanical properties of two kinds of coal, one from bump and the other from non-bump-prone mines. They found that coal itself does not play any significant role in coal bumps and recommended that future research should focus more on the local variation of geological conditions such as the interface friction between pillar and roof and between pillar and floor."

Jan 1, 2015

By C Hedemann, N Silveste, H Davis, C J. Moran

For nearly two decades water scientists have been debating the need to use appropriate models for the questions being asked and the data available. This paper puts forward a rationale for a hierarchical framework for water balance modelling as it applies to mine sites. The hierarchy is based on the complexity of models and their data requirements. Scientific models are the most complex and require the most data; next is engineering models, then systems models and the simplest representations are given by conceptual models. A position is put forward that systems models have a range of uses that the others do not provide. A systems model, called SiteMiser, is described and its calibration illustrated. The model is applied to seven coal mines from the Northern Bowen Basin in Central Queensland. Currently, there is little relationship between total water use and coal production. This relationship is not any stronger when fresh (raw) water is compared to reused water. Leading practice water use levels are simulated for all sites. The simulation results demonstrate that there is considerable opportunity to reduce water consumption and, in particular, to import less fresh (raw) water to the sites.

Jan 1, 2006

By Houyuan Liu

A new process was developed to recover nickel and cobalt by leaching laterite ore at atmospheric pressure and.95"-105" C. The nickel-containing goethite in limonite was first leached with sulphuric acid to liberate over 90% of nickel, cobalt and iron. The dissolved iron was then precipitated as Ni-free goethite by the additioil of saprolite. The acid released during iron precipitation as goethite was simultaneously used as lixiviant to leach saprolite to recover more nickel. With this process the limonite and saprolite were essentially converted into goethite-, gypsum- and silica- containing tailings. Twenty bench scale tests and two campaigns of pilot plant operation were carried out at BHP Billiton's Newcastle Technology Centre (NTC) from January to August 2002. The overall nickel and cobalt extractions were 81 to 90% and 91 to 100% respectively. The average plant availability was 99%. The advantages of this process over existing processes include high plant availability, high consistency, robustness and simplicity of the operation.

Jan 1, 2004

By M. E. Rossi, J. A. Bassan, J. B. Novillo

Sampling and geological models are the basis of recoverable resources models. They are pillars of mineral resources and reserves estimation, and what geostatistical methods for grade estimation should rely upon. The resource model is best estimated if geostatistical methods make good use of sound geologic models. Data collection from the original drill holes, including field procedures and the quality assurance and quality control (QA/QC) of those samples are pillar one of a resource model. The second pillar of the model is the good use of the logged geological information, resulting robust geological interpretations, and the corresponding three-dimensional models of those interpretations. These models are partly subjective and mostly conditioned by the quality of logging and the geologist’s experience. They are also conditioned by the quality of the three-dimensional models built, regardless of the modeling method employed, traditional or implicit. Grade estimation is more commonly done by applying some geostatistical method and using the two basic sources of information, data and geologic model. Multiple stages are involved in this process, and in all of them there are uncertainties and risks that have to be dealt with. Knowledge, understanding, interpretation, and management of the model’s fundamentals are critical, given that they directly affect its accuracy and predictive quality. The mitigation of related risks allows for the creation of opportunities, generating value and reducing the project’s uncertainty. This paper discusses some of the key variables, uncertainties, and risks involved in the resource modeling process, illustrating with specific examples; discusses possible risk mitigation alternatives, and proposes best practices to avoid or mitigate those uncertainties. Emphasis is placed on taking advantage of technological advances without ignoring fundamentals. INTRODUCTION In the area of mineral resource estimation, one alarming trend that these authors have observed in the past 20 years or so is that the care and diligence in checking the work as it progresses has generally diminished. This is, perhaps, an unintended consequence of the availability of new technologies and tools that attempt simplify and speed up the work involved. This has led to a more casual attitude towards checks and balances that have to be in place at any given stage of the process before proceeding to subsequent stages, as best practices dictate. To some extent, some of these aspects are covered in international standards for resource estimates reporting (JORC, 2012; CIM, 2010). But these are broad, and do not specifically recommend best practices to a level of detail that would have an impact on certain aspects of the process. There are numerous references in the geology and mining journals and conferences that discuss the consequences of poor recoverable resource models (Baker and Giacomo, 1998; Vaughan, 1997).

Jan 1, 2019

By C. G. Hunkin

In situ, or in-place leaching is concerned with the extraction of metals from natural mineral disseminations without removal from their geologic location which, in many cases, amounts to the reversal of the deposition process accompanied by a presumed increase in velocity of the processes, if the project is to be profitable. Solution mining processes involve removal of minerals such as sulfur, common salt, and potash, generally leaving cavernous voids, in contrast to in situ leaching which term is applied to the selective dissolution of a mineral from its gangue without sensible disturbance of the formation. Where such a process can be operated, the advantages are manifold and have been so recognized by miners from the earliest days of mining. Recent technological developments have encouraged a reassessment of the status of in situ leaching, and it now appears possible to extend the application of the method from a few isolated special situations to many uranium and copper deposits. Anaconda's interest in the techniques stems from long experience with vat and heap leaching, 'dump leaching, and natural leach activities associated with several established mines. Increasing activity through-out the industry has been noted, particularly in leaching low grade pillars and the peripheral zones of operating mines, often by the introduction of leach solutions via boreholes drilled from surface. Reactivation of dormant mines] using similar techniques has been successful. Over the long term, environmental improvement activity will lead to excess sulfuric acid production, even to a disposal problem. The cost of leach solutions and reagents must be reexamined in this light. The mineral industry now classifies as uneconomic deposits of readily soluole minerals whose potential value, on a per acre basis, may De several times that of many currently profitable oil field reser-

Jan 1, 1971

By David S. Holmes

An overview of existing biological technologies for the recovery of copper and uranium is presented. Engineering and biological challenges and opportunities in these areas. are discussed. New opportunities for the biooxidation of refractory gold ore are described. Techniques for the development of new strains of microorganisms. for commercial metal recovery applications are discussed with special reference to the genetic manipulation for bacterial strain improvement.

Jan 1, 1991

By P. K. Kaiser, C. D. Martin, F. Amann

"This article focuses on the uniaxial compressive strength (UCS) of homogeneous and heterogeneous rocks. Critical factors impacting the UCS of rocks are reviewed and then separate assessments of UCS data from homogeneous and heterogeneous rocks are presented. The variability (coefficient of variation) of UCS test results for homogeneous rocks is found to be generally <25% while for heterogeneous rocks the variability is >35%. Failure mode variation is found to be the cause of the variability of UCS test results in heterogeneous rocks. Empirical engineering design methods that use UCS as an input parameter are discussed and suggestions are provided for selecting appropriate UCS values.INTRODUCTIONThe UCS is one of the most commonly used rock engineering parameters whether for rock mass classification or for strength determination. The mean UCS and its variability are often assumed to represent a reliable rock material property. For the reasons discussed in this article, UCS is rarely representative of the intact rock UCS. The UCS test simply records the collapse load during uniaxial loading of a cylindrical specimen. As suggested by many, the UCS is an index rather than a unique engineering parameter. The UCS is thus a proxy for rock strength which depends on the loading rate (e.g., Bieniawski 1967), specimen geometry (e.g., Hudson et al., 1971), specimen size (e.g., Bieniawski 1968), and many other factors. Furthermore, the UCS is not the same as the Hoek-Brown strength criterion parameter sci.There are differences in opinion on what is commonly considered to be ‘intact rock’. When sampling ‘intact’ pieces of core from drillholes crossing blocks of rock bound by block forming discontinuities, samples will be ‘intact’ but some samples will be veined, others will be damaged, and others will be neither. According to Hoek (1983), intact rock pieces are “the unfractured blocks occurring between structural discontinuities in a typical rock mass” and the sci parameter for intact rock is determined using the fitting procedure proposed by Hoek and Brown (1997) based on the data requirements outlined by Hoek (1983). Studies (e.g., Bewick and Kaiser 2014; Kaiser and Kim 2014) have shown that independently determined UCS and sci values for the same rock type are not equivalent. Thus, UCS data cannot be used as a replacement for sci."

Jan 1, 2015

By E. Ghali, W. Zhang, G. Gabra, N. Sorour, G. Houlachi

The additives polyacrylamide, 1-Butyl-3-methylimidazolium chloride, Tetra-butylammonium bromide, Benzalkonium chloride and chitin are evaluated during zinc electrolysis from synthetic acidic sulphate electrolyte containing Mn2+ ions, in absence and in presence of 0.0055 mg dm-3 of Sb3+ ions. Galvanostatic polarization tests for 2 hours at 50 mA cm-2 and 38oC were carried out to determine the cathodic and anodic potentials, and current efficiency of the deposited zinc. Potentiodynamic polarization and cyclic voltammetry tests have also been employed to study the electrochemical behavior of each additive on the zinc deposit on aluminum electrode. Results showed that, in presence of Sb3+, adding 1 to 3 mg of 1-Butyl-3-methylimidazolium chloride increases the cell voltage by ˜0-7 mV. Current efficiency is increased by ˜4.90-6.40%; power consumption is reduced by ˜147-173 kWh t-1 by adding 1-3 mg, respectively. However, in absence of Sb3+, cell voltage is decreased by ˜7-28 mV, current efficiency is increased by ˜0.70-1.50%; power consumption is reduced by ˜41-47 kWh t-1 by adding 1-3 mg. The effect of the other additives on cell voltage, current efficiency, lead content and morphology of zinc deposit has also been examined. Surface morphology and crystallographic orientation of the deposit was studied using scanning electron microscopic (SEM) and X-ray diffraction (XRD), respectively. The content of lead in the deposit has also been measured using inductively coupled plasma spectroscopy (ICP).

Jan 1, 2015

By Guy Reed, Russell Frith

"The method of determining coal pillar strength equations from databases of stable and failed case histories is more than 50 years old and has been applied in different countries by different researchers in a range of mining situations. While common wisdom sensibly limits the use of the resultant pillar strength equations and methods to design scenarios that are consistent with the founding database, there are a number of examples where failures have occurred as a direct result of applying empirical design methods to coal pillar design problems that are inconsistent with the founding database.This paper explores the reasons why empirically derived coal pillar strength equations tend to be problem-specific and should be considered as providing no more than a pillar strength “index.” These include the non-consideration of overburden horizontal stress within the mine stability problem, an inadequate definition of super-critical overburden behaviour as it applies to standing coal pillars, and the non-consideration of overburden displacement and coal pillar strain limits. All of which combine to potentially complicate and confuse the back-analysis of coal pillar strength from failed cases.A modified coal pillar design representation and model are presented based on coal pillars acting to reinforce a horizontally stressed overburden, rather than suspend an otherwise unstable self-loaded overburden or section, the latter having been at the core of historical empirical studies into coal pillar strength and stability.INTRODUCTIONThe inspiration for this paper is founded in three statements from two eminent persons in the field of coal pillar strength research, Jim Galvin and Essie Esterhuizen, as follows:Both Salamon and Munro and [the University of New South Wales] based the derivation of their pillar strength formulae on a criteria that the diameter of a panel of pillars, W, had to at least equal the depth of mining, H. This was thought to result in full tributary loading. It is now known that there are some mining environments included in both the South African and Australian databases in which mining span must exceed depth by a considerable margin in order to achieve full deadweight loading. Hence, it is logical to conclude that these data points may have contributed to pillar strength being overestimated by Salamon and Munro and UNSW (underline added by authors). Normally, this should be of no consequence because it is reflected in the probability of design success associated with any given safety factor (Galvin, 2006)."

Jan 1, 2018

By G. X. Wang

The nonliving dried water hyacinth (E. crassipes (Mart.) Solms) roots were investigated for biosorption of cadmium and lead and other heavy metal ions in aqueous solutions. Dried water hyacinth roots, when suspended in solution, strongly and rapidly sorb several different metal ions. Factors such as reaction time, pH, initial concentration of metal ions, presence of other metal ions and biomass concentration were investigated. Metal ions, including Cd2+ and Pb2+, were bound to the root in a very pH-dependent manner, with the binding increasing after about pH 3. High levels of removal were obtained. The adsorption was shown to follow the generalized Langmuir adsorption equation. The relative affinity of the roots for lead is greater than for cadmium. The maximum sorptions of the roots were about 33 and 86 mg/g for cadmium and lead, respectively. Only 15-20 minutes were required for the process of uptake onto the biomass to occur. The batch sorption kinetics of the uptake of cadmium and lead can be described by an apparent first-order reversible reaction model. The roots could be regenerated after the metal ions were stripped. A solution of CaCl2 in acidic medium appeared to be the best eluant for desorbing the sequestered Cd and Pb completely at pH 3. The kinetics of the metal stripping process was quite rapid. Successful desorption of Cd and Pb from the biomass by acidic CaCl2 solutions revealed that the metal uptake phenomenon is reversible, implying physical sorption of Cd and Pb.

Jan 1, 1997

By D. McConchie

BauxsolTM, prepared by treating bauxite refinery residues with Mg2+ and Ca2+, has an excellent ability to remove arsenic from acidic waters. The addition of BauxsolTM to sulphidic waste rock at the Gilt Edge Mine, South Dakota, reduced As concentrations in leachate water from 35 mg/L to < 0.005 mg/L; the concentrations have remained below 0.005 mg/L for the five years since the treatment was initiated. However, ordinary BauxsolTM does not effectively remove As from near-neutral water and it needs to be acid-treated or blended with small amounts of reagents, such as jarosite or ferrous sulphate, to increase the proportion of positively charged binding sites on the particles. The use of a jarosite/BauxsolTM blend can effectively treat ponded water, and As(V) concentrations can easily be reduced from over 1 mg/L to < 0.001 mg/L; As(III) has to be oxidised to As(V) for effective removal. Metal contaminants in the jarosite are trapped by the BauxsolTM and only very small amounts of the As, or other elements bound during treatment, are liberated using a TCLP leaching test. The exhausted treatment reagents meet the criteria for classification as an inert solid and do not need to be disposed of in a secure repository.

Jan 1, 2006

By R. R. Wells

As a part of the strategic mineral program, examining engineers of the Bureau of Mines collected samples several manganese properties in Colorado. As all of the ores were too low-grade to be acceptable to manufacturers of ferromanganese, beneficiation studies were required .to determine the amenability of the ores to concentration. Manganese in the form of impregnations in sedimentary beds is found in the Denver plains area a few miles east of the Rocky Mountain front. Deposits are reported to occur intermittently over a distance of more than 200 miles. The manganese oxides occur in beds of conglomerate or arkosic sand, generally accompanied by limonite. The Manganese and iron oxides,, however, usually are found in separate layers. Three samples were submitted for beneficiation tests, two samples from Buckley Field bombing Yang, Arapahoe County, and one from near Franktown, Douglas County.

Jan 1, 1952

By D. H. Platt

Gypsum and gypsite, used in the manufacture of plaster and plaster products, have been mined from deposits near Acme, Hardeman County, Tex., for more than 30 years. The Certain-toed Products Corp., 120 East Lancaster St., Ardmore, Pa., operates the Acme, Tex., mine. Underground hauling was done with storage-battery and Diesel-electric-powered shuttle cars. Many mining companies and individuals have manifested interest in all types of equipment powered by Diesel or Diesel-electric units, as attested by the recent increase in use of Diesel-powered equipment in underground metal and nonmetal mines. The purpose of this paper is to describe the manner in which a storage battery-powered Joy Model 60D2 shuttle car was converted to Diesel-electric power. The conversion was made, at the instance of the operating company, by Stewart & Stevens on Services, 4801 Lemon Ave., Dallas, Tex. This is believed to be the only such converted shuttle car in use.

Jan 1, 1950

By Richard C. Neavel

Among the many compositional parameters used to judge the quality of a steam coal is the fouling factor of Attig and Duzy1 [% base in ash % acid in ash X % Na20] in ash. The higher the fouling factor, the more likely the heat transfer surfaces of the boiler will acquire a deleterious deposit of sintered ash. While examining the elemental composition of ash from various size and gravity fractions of coals from Illinois, we noticed that variations in the fouling factor were attributable mostly to variations in the sodium content. Further, sodium content was essentially the same in all sink-float fractions from a given coal. In other words, sodium was related neither to the ash nor to the organic material. We therefore concluded that the sodium was most likely in the pore water, which was approximately a constant proportion of all fractions. This led to the supposition that the sodium might be removable through water extraction. This supposition tended to confirm the observations of Daybell,2 Daybell and Gillham,3 and Gluskoter and Ruch4 that much of the sodium in coals existed as water soluble sodium ions. In passing, it should be noted that most sodium in Western U.S. coals (i.e., Wyoming, North Dakota, Montana) is not water soluble, but rather is fairly strongly held in association with the organic material (ion-exchanged).5 Because data reported in the literature were not very conclusive about the typical proportions of sodium that might be removed by water extraction, and because there were few data indicating extraction rates, and finally, because our calculations showed a favorable economic incentive to lower sodium contents, we initiated an experimental program to investigate water extraction of sodium from Illinois coals.

Jan 1, 1976

By D. B. Dreisinger, M. Mokmeli, B. Wassink

Dissemination of selenium and tellurium in sulphide minerals results in the contamination of pregnant leach solutions and electrolytes in the hydrometallurgical treatment of sulphide ores and residues. The selenium and tellurium content of the copper sulphate-sulfuric acid solution may be reduced into insoluble precipitates of copper selenides and tellurides using cuprous ion. This study presents the use of the thermodynamics and kinetics for the removal process of selenium and tellurium in real life application. Dominant species of selenium and tellurium in acidic copper sulfate solutions were identified and the reduction rates of species were compared. The findings were applied to industrial conditions by modeling the Vale’s CRED (Sudbury, Canada) plant’s selenium and tellurium purification circuit. Rate reducing factors on selenium and tellurium removal were identified and discussed.

Jan 1, 2014

Newcrest Mining Limited (NML) owns and manages the Ridgeway Gold Mine (RGM) located outside Orange in the state of New South Wales. RGM is a new underground sublevel caving (SLC) operation that is ramping up production to 4 Mtpa. The success of the SLC method at RGM is strongly influenced by production drill and blast practices. Distinguishing features of the Ridgeway SLC operation include choke blasting against broken rock, drawpoint brow preservation, loading of blastholes with different in-hole bulk emulsion densities, precharging of production rings and routine drawpoint fragmentation assessment. These areas are described in the context of RGMÆs required blasting objectives, production drilling and charging activities and innovative practices.

Jan 1, 2002

By A. De1

Because of the extremely low utilization of strain energy in the breakage of solid particles, the energy efficiency prevalent in comminution technology is extremely poor. Schoenert considered that single-particle comminution under slow compression is the most energy-efficient mode of comminution and that energy efficiency should be compared to that. The usual method for grinding minerals and cement has been the ball mill, in which the hit-and-miss aspect of loose-bed comminution severely reduces energy efficiency. The fine grinding of minerals is a particularly energy-intensive process. Schoenert showed that the energy consumed in the comminution of particles in confined beds is second only to that of single-particle comminution under slow compression and developed the method of conducting particle-bed comminution continuously in a high-pressure roll mill. Since its first industrial installation in 1985, the high-pressure roll mill has established itself as the comminution device of choice for significantly improving the productivity and energy efficiency of size reduction from coarse size feeds down to products finer than 20 microns. The first of several hundred installations were in cement plants. The preliminary design and optimization of the industrial operation of high-pressure grinding roll (HPGR) systems, owing to the continuous nature of the device, cannot be efficiently done through laboratory experiments and needs to be achieved through proper system modeling. While the energetics of size reduction in high-pressure grinding rolls has been modeled very well, no model exists for the macroscopic variables in HPGR comminution. In high-pressure roll mill grinding, size reduction results from confined particle-bed comminution under compressive stresses such that the daughter particles produced are highly fractured, stressed, or otherwise weakened. This paper attempts to relate the comminution / compaction behavior for confined particle-bed under compression in a piston-die press with the macroscopic variables in HPGR comminution. A model describing the pressure-densification relationship is presented and used to accurately simulate the macroscopic variables in high-pressure grinding rolls, utilizing experimental data for particle-bed comminution with the piston-die press. The accuracy of the predictive simulations strongly suggests that, starting with a few batch-mode laboratory-scale experiments, it should be possible not only to identify the optimal operating conditions for existing operations but also to successfully design new industrial high- pressure grinding roll systems.

Sep 1, 2012