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By I. M. Marshall

SOME years ago the writer had the opportunity to plumb a number of mine-shafts, each of which presented various conditions and difficulties. This afforded the chance to compare several methods of shaft plumbing in the light of ease and rapidity. This comparison led to the development of an adaption of the Weisbach, or approximate alignment, method, to three wires in a single shaft. Professor Weisbach, some time prior to 1850, introduced his method of shaft plumbing by triangulation on but two wires, and was the first to show that a triangle of very narrow shape is the best for this purpose. THE WEISBACH METHOD The two-wire method, using a Weisbach triangle, is described in several .English text-books on mine surveying and is used frequently in various parts of the world, but in Canada it is almost unknown. The writer has described an example of this two-wire method (1), but a brief resumé here may clarify the explanation of its application to three wires. In this two-wire method, instead of endeavouring accurately to align the instrument with the wires, it is set only in approximate alignment, and the small angle formed at the instrument is measured. This is expressed graphically in Figure l, where C represents the position of the instrument and A and B the positions of the wires. The sides of the triangle are measured as well as the angle ACB, and the angles at B and A are found by applying the Sine Rule or the formula

Jan 1, 1938

By Randolph R. Dreher, Michael L. Schreder

"In recent years, FFE Minerals has designed, installed and commissioned several large grinding mill circuits. This paper discusses the issues related to the erection and commissioning of large grinding mill circuits. The three circuits discussed are Collahuasi in Chile, Minera Los Pelambres in Chile, and Century Zinc in Australia. These circuits include large SAG and ball mills with both gear and gearless drive arrangements, as well as, both trunnion and shell supported mills. Aspects of these features are discussed with respect to their impact on installation and commissioning. While the normal challenges of mill erection and start-up were experienced, there were also a few unexpected challenges encountered partly due to the large scale of the equipment. An overview of the equipment and design ratings of these circuits is also provided.COLLAHUASIOverviewThe Collahuasi mills were started-up in November of 1998. The site is located in the Andes Mountains at an elevation of 4300 meters. The grinding circuit includes two lines featuring one SAG mill and one ball mill for each line. The circuit features a recycle conveyor around the SAG mills with provision for adding a pebble crusher in the future. The design tonnage of the grinding plant is 60,000 MTPD with an ore BWI of 10.5 kWh/MT.The SAG mills are 32’ x 15’ (1 3’ EGL) with 10,800 HP drives. The drive arrangements are dual pinion through pneumatic clutches. The mills are driven by low speed synchronous motors with CCV variable speed drives. The SAG mills are trunnion supported and use hydrostatic lubrication. Feed to the SAG mills is via a rock-box type feed chute on a cart. The mills discharge on to trommel screens with a bucket wheel to remove the oversize.The ball mills are 22’ x 36.5’ (36’ EGL) with 12,500 HP drives. The drive arrangements are dual pinion through pneumatic clutches. The fixed speed mills are driven by low speed synchronous motors with GE Quadramatic load sharing drives. The ball mills are shell-supported and feature multi-pad bearings with hydrodynamic lubrication. The mills are fed via a rubber lined sump box with feed spout on a cart. The ball mills also discharge on to trommel screens. Twenty-six inch (26”) diameter hydrocyclones are in closed circuit with the ball mills."

Jan 1, 2001

By X. Cao, J. J. Jonas, Wanjara. P., J. Gholipour, E. Dalgaard

The linear friction welding (LFW) behaviour of near-ß titanium alloy Ti-5Al-5V-5Mo-3Cr (Ti- 5553) was investigated. Microhardness measurements were performed in order to evaluate the mechanical properties of the welded material. The linear friction welded (LFWed) Ti-5553 was examined with optical microscopy and scanning electron microscopy (SEM) to evaluate the microstructure’s response to the thermomechanical conditions. Characterization of the welds included analysis of the microstructural features of the weld region and thermomechanically affected zone (TMAZ) in relation to the parent material.

Jan 1, 2010

By Robert J. Maron, Mark Fernald, Alex Van der Spek, O’Keefe. Christian, Tim Bailey

"Sonar array-based non-invasive flow measurement technology is becoming an accepted and many times a preferred method of measuring challenging single and multi-phase flows in the mineral processing industry. This fundamental sensor and measurement technology has been extended to two developments that provide new measurement capabilities useful for monitoring and managing slurry flows and pipes.The first development is the non-invasive measurement of real-time velocity profile of slurry flow in horizontal pipes. Multiple non-invasive passive sensors measure localized velocities and are combined to provide a velocity profile measurement. This information can be used to determine the approach and onset of solid deposition on the bottom of the pipe. Having this information in real time can enable operation at lower velocities and/or higher solids concentration while avoiding solids deposition or plugging and its associated operational costs.The second development is the non-invasive measurement of pipe wear on slurry lines. Presently, such measurements are made by hand-held portable ultrasonic thickness gages. The numerous shortfalls associated with the manual method are overcome with a set of permanently or semi-permanently installed transducers clamped onto the outside of the pipe. This ring of sensors contains a series of conformable ultrasonic transducers spaced around the circumference, which are used to measure the thickness of the pipe under their respective locations. Compared to manual methods, this system and approach results in better repeatability and accuracy. It also decreases inspection labor costs and pipe access requirements. The minimal accuracy variations in the presence of varying environmental temperatures will be shown. Trending of pipe wall thicknesses in high wear pipelines will be illustrated. The benefits of significantly improved pipe wear monitoring in hydrotransport lines with abrasive solids, and associated improvement in the ability to insure safe operation and avoidance of costly environmental damage due to leaks caused by pipe wear will be discussed."

Jan 1, 2009

By G. G. Bowser

PERUSAL of a list of present-day commercial explosives perhaps does not convey a full realization that there has been a great deal of improvement since the original dynamite was discovered nor that, in recent years, great developments have taken place in specialized explosives. This is true particularly of high-explosives for use in metalliferous mining or what is more commonly termed 'hard-rock' mining. Not many decades ago, only two or three types of explosive were avail-'able for commercial use. One was black blasting powder. Another was ordinary nitro-glycerin dynamite in various strengths. Black blasting powder remains with but very little change. Despite its ancient lineage, it is still with us as perhaps the sole explosive in use today which is almost identical in appearance, physical properties, and working ability or execution co the original. Which dynamite the story is different. Its evolution may be likened to that of the dog, nitro-glycerin as first discovered being the counterpart of the wild dog and, like it, dangerous and hard to control. The original dynamite as made by Nobel might then be considered as representing the first domesticaced species. This original dynamite, however, has been 'crossed with other bloods' until one sees now many distinct 'breeds' in the list. Present-day explosives still have the 'bark' and the 'bite', but with control and research have come many improvements; and types have been created which are specially adapted for particular kinds of work. We still have the direct descendant of Nobel's dynamite in the form of an improved nitro-glycerin dynamite. This C-I-L explosive, Polar Dynamite, is no longer the best type to use in the hunt for gold, silver, iron, and other metals. There have been developed other explosives more suitable for chat work. In Canada, such explosives are accomplishing this work effectively, not only where climatic conditions are moderate but through the rigours of our northern winters, with their sub-zero temperatures.

Jan 1, 1938

By Peter A. Eshun

This paper studies two methods that account for risks associated with gold mining projects such as mineral risks and country risks. The first method is sensitivity analysis, which investigates the effects of a change in any economic parameter such as operating cost, capital investment, gold price or taxes on the viability of the project. The second method is Monte Carlo Simulation technique, which takes into consideration the simultaneous random variation of the economic parameters on the project's viability. An automated simulation cash flow model has been developed as part of this paper. Sensitivity analysis and the simulation model have been used to investigate the economic viability of the Dokrupe Gold Project (DGP) serving as a test case. It is concluded that, the Monte Carlo Simulation technique gives a more realistic judgement of the economic viability of gold mining projects.

May 1, 2004

By K. Chotruangprasert

This paper explores Global Reporting Initiative (GRI) reporting practices within the mining industry. Specifically, this paper investigates how and why a mining company makes voluntary reporting decisions to include the GRI indicators that may be considered ?negative? to the company?s reputation. Due to the voluntary nature of the GRI Guidelines, a GRI adopter is not legally obligated to report every GRI indicator. Not surprisingly, empirical studies that evaluated the extent to which companies? sustainability reports meet the GRI requirements (Guenther, Hoppe, & Poser, 2006; Morhardt, Baird, & Freeman, 2002; Samy, Odemilin, & Bampton, 2010; Skouloudis, Evangelinos, & Kourmousis, 2009) have found that reporting practices of the companies under their studies are well below the standards reflected in the GRI Guidelines. An influential study by Clarkson et al (2008) uses economic-based and socio-political theories to explain variation in companies? environmental disclosure. They have found that, as predicted by economic-based theory, superior environmental performers disclosed more ?hard? (i.e. verifiable) environmental information. Inferior environmental performers are found to disclose more ?soft? (i.e., not easily verifiable) claims, which is consistent with socio-political theories (Clarkson, Li, Richardson, & Vasvari, 2008). However, this study and the existing literature do not adequately explain why a company may act in a way that cannot be explained by economic-based and socio-political theories, for example, why it would report some negative soft data that it is not required to report. This paper intends to address this literature gap. GRI reporting by a Canadian mining company, which I would like to call ?Company C?, is used as a case study for this paper. Company C was selected for this research because in addition to ?positive? information, its GRI-based sustainability report also includes both hard and soft ?negative? information such as grievances. Research methods include interviewing Company C?s employees who are involved in preparing GRI reports and reviewing documents prepared both by the company and by external parties. I find that integrative social contracts theory (ISCT) offers a valuable explanation to Company C?s reporting practices. From the ISCT perspective, Company C?s management appears to feel that the company is obligated under social contracts to be transparent. Therefore, Company C disclosed both positive and negative social and environmental information to the public because the management appeared to think that it is the right thing to do. At the same time, being transparent about the bad news gave the company an opportunity to conclude that it had done something to avoid future occurrence of the negative incidents. Therefore, I propose that, in addition to the economic and socio-political theories that are more often used in literature, insights from ISCT are instrumental in improving our understanding of the corporate non-financial reporting practices phenomenon.

Aug 1, 2013

By H. W. Kasaini, E. Bourricaudy, T. Larochelle

Rare Element Resources Inc., a U.S. based company, has developed a three-stage process for producing a +98% mixed REO powder from hard rock feedstock (-48 mesh, 2.9-4.8% REO) consisting of bastnaesite and ancylite minerals. Firstly, the whole ore is digested in chloride media at low temperature in counter-current flow mode. Secondly, the rare earths (REEs) are selectively precipitated as oxalates directly from an impure pregnant leach solution (PLS). Finally, significant amounts of free acid and water are recovered from the REE-depleted filtrate and subsequently recycled within the process. Excess heat from the oxalate calcination process is captured and reused in the plant. Due to the low leach temperature (45 ºC) and moderate acid dosage (240-297 kg/t, HCl), rare earth oxides (REOs) are preferentially leached out of fine solids leaving most of the base metals (Ba, Fe, and Al ) in the residue. Selective recovery of REEs from the PLS is achieved by mixing dilute oxalic acid (33% H2C2O4) and PLS at elevated temperature (85-95 ºC). The REEs plus thorium are precipitated as oxalates (REE2 (C2O4).xH2O) while the base metals are left behind in the barren filtrate. Multiple batch and pilot test results have confirmed that 50-80% of the oxalic acid can be recovered from the REE-depleted PLS through low-temperature crystallization (10-15 ºC). Typical leach efficiencies of critical rare earths at 45 ºC range from 85-99% (average 93%) while oxalate precipitation at high temperature increases the crystal size of RE oxalates (>450 microns, d80) thereby improving filtration. The economic benefits of this process include elimination of flotation and magnetic separation Capex and driving hydrometallurgical Opex down to $6- 7/kg, REO produced. As part of a comprehensive risk mitigation strategy, Rare Element Resources Inc has operated multiple pilot plants at SGS in Lakefield, Ontario, Canada to optimize counter-current leaching (CCL), REE oxalate precipitation (OXP), and thorium removal circuits. This paper presents pilot testing data from CCL and REE OXP circuits.

Jan 1, 2016

By Sibabrata Patnayak

A major problem during shovel excavation in oil sand mining is the variability of material diggability resulting in varying mechanical energy input, cycle time, energy consumption, wear, and stress loading of shovel dipper-andtooth assembly. This variability greatly influences the mining equipment performance. Different approaches such as empirical ground classification systems, analytical methods, and performance monitoring that are used to determine diggability of groundmass are reviewed. It is concluded that the existing empirical diggability classification systems are site specific and mostly based on rock and therefore, cannot be used for shovel excavation in oil sands. The O&K wedge test is a simple and useful index test for establishing correlations between cutting resistance and geotechnical properties of coal and other soft rock overburden material. But this test, when performed on small size unconfined oil sand samples, may not give reliable indication of diggability because of the boundary conditions on the specimens. Digging predictions made using analytical and laboratory digging models need to be verified with performance monitoring data to better understand the digging effort in oil sands.

Apr 1, 2005

By Yi-Chun Lin

Mechanical/Electrical/Piping (MEP) systems, due to their complexity and diversity, are the most intricate part of building construction. This being the case, Combined Services Drawings (CSD) and Structure, Electric and Mechanic(SEM) drawings can ensure that all coordination issues are resolved prior to construction. Construction companies attempt to apply Building Information Modeling (BIM) to manage and integrate engineering information and solutions efficiently into the CSD and SEM processes to enhance the accuracy of design and the efficiency of review. There are several powerful commercial tools, such as Bentley Navigator, Autodesk Navisworks, and Tekla BIMsight, that can review the integrated BIM model and detect conflicts in systems, and allow planners to correct the conflict issues one at a time. However, for increasing numbers of conflicts, this may be inefficient, and requires them to be arranged in a list according to impact and seriousness before solving them. For this reason, this research implements a module for conflict impact assessment based on rule-based reasoning to classify and weigh conflict impact and seriousness, and highlight the conflicted objects in the BIM system in different colors depending on their conflict type and seriousness during the analysis. This system not only detects and lists possible conflicts and errors, but also sorts them according to the severity of impact and conflict type. Planners can effectively modify the BIM models according to these conflicts as they are listed and visualized in the BIM system. If these conflicts, such as pipeline interference and problems of insufficient space, can be avoided in the early stages of planning, it facilitates the achievement of project objectives in quality, scheduling, and cost.

Aug 1, 2013

By M. Côté, H. Pépin, Y. Richer, C. Gingras

Rolls-Royce Canada has been nominated as a Rolls-Royce Center of Excellence for repair of fan blades in 2003. One of the challenges of the Rolls-Royce Canada Component Repair Center of Excellence team is to reduce cost and time of inspection while ensuring trace ability and quality of the inspection performed on the fan blades. In the context of the dimensional control process optimization, and following the positive conclusions of initial trials carried out in 2003, the technical authorities at RRC have selected the SPG data 3D(TM) technology as a development base for dimensional control programs. The main goal of this development initiative is to develop and support an inspection system to perform the dimensional control and inspection of different components at the Montreal Fan Blade Repair Center of Excellence. The final objective of the program is to build a server platform capable to support different inspection sites within the Montreal facility for the future. This paper presents the certification process of the technology according to the VDI-VDE 2633 certification standards and some results of the fan blade inspection program of the BR 710, BR 715 and TAY according to the JES 195 engineering standards specification.

Jan 1, 2006

By W. B. Evans, D. P. Taylor

"ANFO has two major disadvantages as an explosive low density and no water resistance. ANFO can be blended with more dense, water-resistant explosives to form ""Heavy ANFO"". The use of emulsion or slurry explosives as a matrix is an attempt to correct deficiencies on the basic ANFO while maintaining cost effectiveness.This paper will deal with four main topics.1. Product description, general properties, strengths and weaknesses.2. Technology of ""Heavy ANFO"" , the emulsion matrix concept and the range of products.3. Relative performance and economics in various rock types.4: Current status in Canada and worldwide, and the expectations for future use.IntroductionANFO has been in use for roughly three decades and remains the explosive of choice where conditions are suitable. ANFO has not become the universal explosive - despite its undoubted superiority in cost effectiveness - because it has serious flaws as an explosive. The most serious of these flaws are the low density and absence of water resistance in ANFO. Low density implies a low concentration of explosive energy in a borehole. The amount of energy available can be increased by. adding an energetic material, generally aluminum, or by drilling more holes. Both solutions add considerably to the over-all costs. The absence of water resistance in ANFO is inherent and can only be overcome by changing the fundamental nature of the product. The history of research in the explosives industry since the advent of ANFO is mainly the story of the various attempts to overcome one or both of ANFO's shortcomings.Many technologies and products have been developed to compete against ANFO, among them slurries, emulsion s and the so-called Dense ANFOs (ANFO with an extra nitroalkane liquid sensitizer). None of them was cost-competitive with ANFO so their market penetration has been limited to wet holes or specialized applications. The exception to this result is Heavy ANFO. The aim here was to have the best of both worlds, the high density and water resistance of emulsions or slurries plus the low cost of ANFO. The concept is very simple. ANFO is about 50 % air, roughly 30% in the prills and 700,10 between the prills . The air in the prills provides the necessary sensitivity but the air between them is waste volume. If one fills this volume with a high density, waterproof product, the resultant mix will be denser and more water resistant than ANFO and with very little added cost. This basic concept was invented by B. Clay in the 1970s and is covered by Canadian Patent No. 1 115 959. The water resistance and/or density of the mix can be tailored by changing the emulsion level. Because Heavy ANFO is relatively inexpensive while providing good in-hole densities and water resistance, it can compete successfully against all other bulk products. It competes against ANFO and Al / ANFO by allowing pattern expansion and reducing over-all costs while it competes against emulsions and slurries on price."

Jan 1, 1987

By G. Stokreef, B. R. Davis, M. Kadiyski, Alvear Montenegro, H-P. Loock, V. Montenegro

An optical probe for burner monitoring in copper flash smelting, first developed at the University of Concepcion, is being industrially tested in a collaboration between Kingston Process Metallurgy, Aurubis AG, and Queen’s University. The sensor uses fibre-optics and optical emission spectroscopy to analyze the light emitted from combusting particles in the furnace reaction shaft. Information that can be extracted from the emission spectrum includes the temperature and brightness of the flame, as well as emission lines or bands from excited atomic and/or molecular species. Laboratory proof of concept testing of the sensor was first completed in a continuously fed drop tube reactor using O2/S stoichiometric ratios between 0.8–4.0. These O2/S stoichiometries capture the industrial operating condition, which is typically less than 1. The results from lab testing justified a plant trial of the optical probe, which was done in the Aurubis Hamburg flash furnace in September 2018. From this trial, approximately 31 hours of spectral data were collected and synchronized with furnace operating data. The results from both drop tower test work and the plant trial are discussed with implications for process monitoring in the commercial furnace. INTRODUCTION Flash furnace smelting is a continuous feed, batch tap, pyrometallurgical process. It is used to treat copper sulphide concentrates and small amounts of secondary materials, such as dust generated by the process. O2 enriched air and the concentrate blend are fed into the furnace reaction shaft through the concentrate burner. As the particles fall through the reaction shaft, they heat up and ignite, causing rapid, exothermic reactions that oxidize the iron sulphide, some copper sulphide and impurities in the feed. Reacted particles fall into the settler of the furnace, melt and separate into a matte and slag, while the SO2 enriched off-gas is carried out of the furnace for heat recovery and H2SO4 production. Operation of the furnace is achieved by adjusting a limited number of control variables. The main variables are the blast feed rate, blast oxygen enrichment, SiO2 flux feed rate and CH4 combustion rate (CH4 is used when the chemical energy of the concentrate is low) all measured relative to a set feed throughput. (Davenport & Partelpoeg, 1987; Davenport, King, Schlesinger & Biswas, 2002) The batch tapping nature of flash furnaces makes operation difficult because these control variables impact each other, and product quality can only be measured when matte and slag are tapped from the furnace. This means that operation of a furnace is based on feedback control from matte and slag assays. Because of the time-delay associated with understanding product quality, there is interest in using technology to monitor the combustion reactions that happen in the furnace reaction shaft.

Jan 1, 2019

By R. A. Wyman

A comparison of the amount of minus-28-mesh product produced by a standard grinding test procedure is provided for 45 non-metallic materials. The percentage of product, the weight of product per unit of energy used and the weight of product per mill revolution are shown. The results exhibited excellent reproducibility and demonstrated an accurate comparison of grindability for non-metallic materials.

Jan 1, 1977

By R. Loney, M. Militzer

There is a significant demand for new high strength steels with fine grain sizes for structural applications. One approach in this regard is to develop hot-rolled HSLA steels where refining the microstructure leads to increased strength levels, e.g. 700 MPa yield strength, that can be attained by suitable modifications of chemistry and processing. Here, an HSLA steel is investigated that contains 0.05wt%C-1.65wt%Mn-0.20wt%Mo¬0.07wt%Nb-0.02wt%Ti and approaches the above strength class. The ability to control and predict the mechanical properties of hot rolled steel depends strongly on the thermomechanical processes, which the steel undergoes. The final microstructure and, thus, the properties of the hot-rolled steel are a function of the austenite decomposition obtained during accelerated cooling on the run-out table and precipitation during coiling. The austenite-to-ferrite phase transformation under run-out table conditions has been investigated using a Gleeble 3500 thermomechanical simulator equipped with a dilatometer. The effects of cooling rate and initial austenite microstructure including the degree of work hardening on austenite decomposition kinetics and ferrite grain refinement have been quantified. Results show that grain refinement can be optimized by the presence of work hardened austenite and accelerated cooling. Based on the experimental results, a model is proposed to predict the transformation start temperature and the resulting ferrite grain size for run-out table cooling conditions.

Jan 1, 2004

By Robert D. Brown, Robert B. Parsons

"The mining industry may have survived the October 28 federal budget relatively unscathed, but the same certainly cannot be said of the petroleum sector-and many mining men are left wondering if their industry will be the next one to be singled out for special attention, as federal and provincial governments seek additional revenues and pursue nationalistic or provincial policies.Higher taxes, higher prices, a potpourri of ""incentives"", and a -""Canadianization"" policy mark the principal features of the new National Energy Program released by the government along with Finance Minister MacEachen's budget address.This month, Tax Notes examines the federal budget. with appropriate emphasis on the National Energy Program and its possible future implications forthe Canadian resource industries.IntroductionMost of the Canadian mining industry (tar sands miners excepted) heaved a sigh of relief on the evening of October 28, 1980, as Finance Minister MacEachen confounded the prophets in his budget address by not raising personal or corporation taxes and by making only relatively modest changes in the general tax system. Instead, he concentrated on a sweeping new energy policy. Unfortunately for that important sector of Canada's mining industry which is involved in mining the country's vast tar sands reserves, either now or in the future, the National Energy Program that was introduced along with the budget 'has serious implications."

Jan 1, 1981

By Wei Sun, Jaewon Choung, Zhenghe Xu, Zhangming Cui

"High intensity conditioning has been demonstrated in a number of cases to enhance fine particle flotation. The improvement could be attributed to the enhanced formation of particle aggregates. However, the understanding of aggregation mechanisms remains rather limited. Recently, an enhanced particle aggregation was observed by the formation of small air bubbles resulting from high intensity agitations (HIA). In this study, a novel visualization system is designed and constructed for characterizing the fine bubbles formed in an HIA cell. The new design allows determination of gas evolution and bubble size distribution. With this system, the effect of dissolved air on fine bubble generation by HIA is investigated. The results show that HIA creates a favorable environment for the formation of gas nuclei and small size bubbles due to hydrodynamic cavitation.INTRODUCTIONFlotation is a dominant separation technique employed by mineral industry to recover the valuable mineral particles. However, in general, particles finer than approximately 10 µm are not effectively recovered by conventional froth flotation technique due to their low inertia and high specific surface area (Fuerstenau, 1988). Therefore, the fine particle flotation has been considered as the central challenge of flotation research. Substantial advances have been made for fine particle flotation from both a theoretical and technological point of view (Fuerstenau et al., 1979; Song and Lu, 1990; Subrahmanyam and Forssberg, 1990; Sivamohan, 1990; Sedat and Barry, 1991; Matis, 1995). High intensity agitation (HIA), for example, has found some success to improve fine particle flotation kinetics in laboratory tests (Chen et al., 1999a and 1999b; Valderrama and Rubio, 1998; Rubio and De Brum, 1994).The effect of mechanical agitation on flotation kinetics has been recognized for many years. In mid-1970s, Warren (1975) reported that increasing the shear rate of the pulp could improve the efficiency of ultra fine particle flotation. He attributed this improvement in flotation to the formation of aggregates. This concept of aggregation has been extended by Rubio (1978), and Bulatovic and Salter (1989), who employed high intensity agitation (HIA) method to promote aggregation. They found that HIA with the addition of collectors, frothers and suitable modifiers significantly improved both the flotation recovery and selectivity of ultra fine sulphide minerals. The improvement was explained by warren’s shear flocculation theory. Till now, many studies (Chen et al., 1999a and 1999b; Valderrama and Rubio, 1998) have been undertaken to improve fine particle flotation by HIA. However, most of these studies were focused on the relation between energy input and flotation efficiency. Less information was available for describing how the aggregate formed during HIA process."

Jan 1, 2006

By K. S. Raja, B. McNall, B. Pesic

"High-level radioactive wastes are stored in large underground storage tanks made of low-carbon steel. The wastes consist of concentrated solutions of sodium nitrate (NaNO3) and sodium hydroxide (NaOH), and the radionuclides 137Cs, 99Tc, and 90Sr. The corroding steel microenvironment may produce localized reducing or oxidizing conditions that affect the solubilities of the species such as Tc(VII) and Tc(IV), which in turn modifies the kinetics of corrosion of the storage tank. To understand the influence of technetate ions on the corrosion of steel, electrochemical polarization studies of A 537 steel samples were carried out in 1 M NaNO3 + 0 .05 M S r(NO3)2 + 0.1 M NaOH with and without addition of HReO4 at different temperatures (24 – 85 °C). The concentration of HReO4 was varied from 0.014 – 0.04 M.INTRODUCTIONAqueous processing of spent nuclear materials generates a large amount of high-level radioactive wastes. The wastes are primarily salt solutions of sodium hydroxide and sodium nitrate which also contain fission products such as 137Cs, 99Tc, and 90Sr. Among the high level radioactive fission products, Tc-99 is of great importance because of its high concentration, long half-life (2.1 x 105 years), high solubility in geologic waters as technetate, and rapid diffusivity through the geologic systems. The solubility of technetate ions varies depending on the oxidizing conditions prevailing in the storage containers. High level radioactive wastes are stored in single shell or double shell tanks made of low carbon steels such as ASTM type A15, A516-70 and A537. Most of the available literature on corrosion of steel in simulated radio active waste environments pertains to nitrate induced stress corrosion cracking (Subramanian & Mickalonis, 2005). The corroding steel microenvironment may produce localized reducing or oxidizing conditions that affect the solubilities of the species such as Tc(VII) and Tc(IV). Corrosion of steel and formation of Fe(II) and Fe(III) will affect adsorption and reduction of Tc species. The radioactive species can irreversibly be sorbed on the steel surface by oxidation of Fe(II) to more stable Fe(III) and fixed as less soluble Tc(IV)/Fe(III). The solubility of Tc species is also affected by other factors such as dissolved oxygen, local pH, temperature etc. How the corrosion behavior of steel will be affected in the presence of Tc species is not clearly understood.Cartledge (Cartledge, 1960) demonstrated that passivation of iron can be achieved in the presence of oxygen along with suitable inhibitor ions/molecules of the general formula XO4 n-, such as pertechnetate (TcO4 -). The pertechnetate ion is univalent. Since it is derived from a strong acid, no buffering action can be expected from this ion. The redox potential of the reaction (1) is 0.738 VSHE (Pourbaix, 1974)."

Jan 1, 2012

By A. K. Debnath

The water resource is key to survival of the mankind and this resource is now becoming critical in many parts of globe including India. As per an assessment of Central Ground Water Board (CGWB) of India, a huge shortfall of about 58 billion m3 of water is anticipated by the year 2050. In order to counter this shortfall, there is thrust from Government of India to adopt water conservation measures. National Environment Policy, 2006 of Government of India also stresses upon the need to take up water conservation measures for water security of the country. The coal mines in India provide an excellent opportunity to take up water conservations measures therein. The mine water is not acidic unlike western countries and it conforms to the prescribed regulatory standards. This nature?s gift is utilized in Coal India Limited by allowing mine voids to get filled with mine water. The net recharge potential of the opencast mining area is found to be about 5% in comparison to 2% in non-mining area offering good prospects for ground water recharge. The seasonal rainwater is also diverted into mine voids left at the end of mining operations which act as huge reservoirs/ pit lakes for storage of the water. They also serve as surface water bodies for recharging of water table in the surrounding areas. The area and space left from where coal has been extracted completely in underground mines and will not be entered by any man or machinery after the extraction, called goaf, are also potential source of water conservation. These additional water resources created are being utilized for meeting the industrial, domestic, irrigation and other requirements of the projects and local communities eliminating the need to tap other fresh water resources including ground water. Presently, 75% of the water demand of the coal mining project is being met from the water stored in the mine pits. In future, CIL is likely to create about 3.3 billion m3 of water resource, on an average, in its opencast mines alone. In the mine closure plan of opencast mines, the last cut is proposed to be developed into water body for recharge of ground water and creating additional water resources. A clean potential source of potable water is thus developed after mine closure. This will ensure water security of the country.

Aug 1, 2013

By V. G. Papangelakis, A. Dani

"Alkaline pressure oxidation, particularly in the presence of trona as additive, can be used to oxidize high carbonate refractory gold ores as it prevents the formation of CO2 in the autoclave. However, the presence of silica in the ore can lead to the encapsulation of pyrite due to the solubility of silica in alkaline solutions and its subsequent reprecipitation on the reacting pyrite surface, leading to the formation of a passive layer. This fundamental study investigates the chemical composition and thickness of the passive layer on a rotating pyrite disk using XPS and SEM, as a function of process conditions at 230°C, in an aqueous slurry containing silica sand, sodium carbonate and calcium carbonate under 100 psi of oxygen overpressure.INTRODUCTIONAlkaline pressure oxidation (POX) has been used successfully to treat high carbonate refractory gold ores, which contain carbonates in addition to sulphides, most notably at Mercur and Goldstrike mines operated by Barrick Gold. There are several advantages to using alkaline POX over its acid counterpart, especially due to high carbonate content. First, it eliminates the production of CO2 in the autoclave without resorting to pre-acidification, which allows for high oxygen utilization. Second, alkaline POX suppresses the formation of elemental sulphur and intermediate sulphur oxyanions (such as thiosulphates and dithionates), which reduce gold recovery. Third, the use of sodium hydroxide or salts prevents the formation of anhydrite scale by forming soluble sodium sulphate. Other advantages are the use of cheaper materials of construction and the formation of non-acidic residue that do not require further treatment prior to cyanidation (Thomas, 2005).Sodium carbonate in particular is a promising reagent for alkaline POX because it was shown to significantly accelerate the kinetics of pyrite oxidation by molecular oxygen, when compared to other reagents such as sodium hydroxide, sodium borate and calcium hydroxide. This has been attributed to the following factors: a) the faster oxidation kinetics of Fe2+-CO3 complexes compared to Fe2+ oxidation, b) the buffering effect of carbonate ions on the acidic pyrite surface, and c) the increased solubility of oxidizing Fe(III) species due to carbonate complexation (Caldeira, 2010)."

Jan 1, 2012