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By Z. G. Tao, Y. Y. Peng, W. L. Gong, M. C. He

"This paper presents an overview of the major landslide hazards in open pit mines in China, the currently used landslide control and monitoring techniques, and development of a new slope control technique incorporating the reinforcement, sliding force monitoring, remote sensing and forecasting in one system in order to constrain the displacement of the sliding blocks in the landslide to minimized the influenced area and provide precise warnings timely for the imminent landslides. For implementation of the new technique, a novel rock cable with large deformation and high resistance (also known as HE cable) was developed, which can elongate as long as 2m. At the same time, the necessary and sufficient condition for initiating a landslide and energy balance equations are formulated. Based on the proposed mathematical models and Beidou satellite system, the software and data transmission hardware for remote sensing and forecasting were developed the new landslide control technique has been applied successfully in 245 landslide sites in 12 provinces across China. In this article, two practical application cases in the open pit mines are reported.INTRODUCTIONChina is one of the countries in the world with the most widely distributed landslides and suffering the heaviest damage. According to the incomplete statistics, landslide hazards have caused death of hundreds of people and direct economic losses of several hundred million RMB each year. The landslide hazards have a great impact on the life and property safety of the people, safety of the infrastructure, as well as the social stability. Thus development of new techniques for forecasting and prediction of the landslides is imperative and of great importance. In general, the forecasting and prediction of the landslides consists of three major aspects, i.e. sliding time forecasting, landslide activity intensity forecasting and landslide hazard degree forecasting. Since a considerable part of the landslide-suspected area are adjacent to the residential areas or important infrastructures, development of the advanced landslide control and monitoring techniques to cope with the sliding time forecasting problem is more important.Over the past one hundred years, the most widely used slope monitoring techniques are based on displacement monitoring (Xu, et al. 2007; Toshitaka, 1998). In the early days owing to the limitation of the technology and equipment, the ground surface displacement and underground water level change were inspected mainly by man power for inferring the possibility of a landslide. In recent several decades, more and more ground surface displacement monitoring devices were brought to the market, such as the automatic total station, theodolite, digital level, borehole inclinometer and GPS based instruments, etc. Based on these modern techniques, some advanced instruments have been developed and applied to the landslide monitoring, for example, the “landslides early warning monitoring system” (Leonardo, et al. 2002), the “In-SAR” technique (Reevea, et al. 2000), the GPS and satellite geodetic survey based technique (Reevea, et al. 2000), and real-time telemetry technology (Xu, et al. 2007). These monitoring approaches have made significant contributions to the landslide disaster monitoring and forecasting. The major limitations for the ground surface displacement monitoring techniques are lie in the inconsistence between the displacement in ground surface and that in the sliding surface for the sliding mass, resulting in low degree of forecasting accuracy."

Jan 1, 2015

By J. M. Mutmansky, R. A. Jankowski, M. A. K. Mohamed

"SYNOPSISKnown health hazards associated with the breathing of respirable dusts, particularly silica dust, during mining are becoming a great concern in many parts of the world. The search for effective and low cost dust control methods for underdeveloped countries will help in improving the productivity and keeping the mine environment safe. This article addresses the problem by providing suggestions concerning the easiest and most cost effective methods to control respirable dust in mining and mineral processing operations. INTRODUCTIONMedical BackgroundLung diseases caused by dust in mining operations have been recognized by mankind since the time of the Roman Empire. The writings of Pliny the Younger on natural history reported on maladies associated with dust in mining in the first century AD. However, no significant advances in controlling the lung diseases of miners came about for many centuries. The effects of mineral dusts were further described by Georgius Agricola in his sixteenth century book on mining (Agricola, 1556). After the appearance of Agricola""s book, lung diseases were more readily recognized, but the nature and severity of the ailments associated with mineral dusts could not be readily interpreted.In 1896, the discovery of x-rays by Roentgen advanced the diagnosis of lung diseases and the knowledge of what causes these diseases. In addition, the discovery allowed medical personnel some method of judging the extent and severity of the lung diseases in human beings. During the ensuing years, the term 'pneumoconiosis' became the common term to describe any of the diseases of the lung in which dust particles deposited in the lungs caused fibrous tissue and loss of some of the respiratory function. However, little in the way of social remedies for the diseases resulted until much later. Society was still not ready to act decisively to reduce the causes of lung disease due to the dusty conditions in the work place.Social action against lung diseases did not occur in the United States (US) until the 1930s. At that time, a tunnel driven through a sandstone mountain near Gauley Bridge. West Virginia, caused the death of several hundred workers due to acute silicosis, a severe form of pneumoconiosis caused by silica (Seaton, 1975). Dust conditions in this tunnel were quite bad, causing many of the workers to be subjected to extremely high silica dust concentrations. The severity of the disease in many of the workers became known to the public and prompted the US Congress and many of the states to enact laws to reduce the dust levels."

Jan 1, 1998

By Marcela Morvová, Mário Janda, Morva Imrich

"The possibilities of greenhouse gas mitigation using various methods are brought out. The special case of utilization of mixture of CO2 with other greenhouse gases in a synergetic way inside non-thermal plasma based system is described in detail.Measurements on pilot system comprising pyrolysis chamber as alternative energy system (production of hydrogen and liquid tar) were made for various biomass and waste as the input material. The exhaust from this system was treated with non-thermal plasma gap suitable for up to 650Nm3/hour of exhaust gas flow. Condensable portion of exhaust is liquefied in distillation unit; produced hydrogen is stored on-line inside nano sized carbon of our own production.The CO2 removal efficiency varies depending on exhaust composition between 45 to 98%. Other oxides as CO, NOx, SOx and several hydrocarbons and VOC are also removed. The main product connected with CO2 removal is a solid powder of proteinoid nature. There exist strong probability, that precursor of the origin of life on the Earth from primary atmosphere were formed in the similar way as it is present in the electric discharge system used. Our system is equipped with on-line as well as ex-post analysis of all forms of products. We have also developed a system for recuperation of all forms of produced heat. It is stored inside as latent heat of waxes.IntroductionNatural greenhouse effect on the Earth is caused mainly by water vapour with the average absolute concentration about 4%. Other gases able to absorb long-wave radiation and thus this causing greenhouse effect are CO2, CH4, N2O, halocarbons and as precursors ozone and NOX. Some of them we produce and introduce into atmosphere in large quantities during production of energy and in transport. This factor leads to permanent increase of average temperature of air, sea and oceans, so called global warming.Nowadays large amount of data exists showing that the temperature of Earth in the last 150 years has been continually increasing. It represents about 03°C per ten years and the most of climatologist believe, that the increased concentration of greenhouse gases in the atmosphere is responsible for this effect.The most important greenhouse gas is carbon dioxide CO2. Majority of CO2 emissions comes from electric power stations working with fossil fuels, cars and industry. Burning of fossil fuels contribute up to 80% to world wide anthropogenetic emissions of CO2."

Jan 1, 2010

By Alphonce Wikedzi, Mussa D. Budeba, Samwel V. Manyele, Sospeter P. Maganga

The present study provides an overview of the challenges and opportunities in processing complex gold-copper ores. The systematic literature review was conducted using Scopus database and seven-step methodological approach. The study indicates that the major challenges in processing complex gold-copper ores through the conventional cyanidation method include (1) increase in cyanide consumption; (2) increase in cyanide destruction cost; (3) low gold recovery; (4) decrease in adsorption efficiency; (5) decrease in electrowinning efficiency, and (6) difficulties in the measurement of free cyanide concentration in the leaching system. Moreover, the study indicates that several methods have been developed and some have been implemented in the mining industry for processing complex gold-copper ores. This includes ore segregation, pre-aeration, pre-treatment methods (e.g., ammonia), alternative lixiviants (e.g., thiosulfate, thiocyanate, glycine), cyanide destruction methods, and cyanide and copper recovery technologies. The study concluded that using lixiviant mixtures (e.g., cyanide-glycine), pre-treatment with environmentally friendly reagents (e.g., glycine) and the integrated membrane-based process (SuCy process) are new directions in processing complex gold-copper ores. However, more investigations are required to advance these processes to a commercial scale.

Sep 30, 2023

By M Akhtar, E Jak, M Shevchenko

This article presents an overview of the experimental phase equilibria studies of S-containing systems (Ni-Sn-S, Cu-Sb-S, and Cu-Sn-S) and As-containing systems (Fe-Sb-As and Fe-Sn-As). These systems improve the prediction capabilities of FactSage in a 20-component ‘Cu2O’-PbO-ZnOFeO- Fe2O3-CaO-SiO2-S-(Al2O3-MgO-CrO-Cr2O3-Na2O)-(As, Sn, Sb, Bi, Ag, Au, Ni, Co) system for complex pyrometallurgical operations during both refining and recycling. Experiments involved equilibration at predetermined temperatures (300–1200°C) with or without preheating, followed by rapid quenching in a brine. Quenched samples were then directly measured using an electron probe microanalyser. For the Ni-Sn-S system, liquid phases (NiS- and SnS-rich mattes and liquid metal) and solid phases (Ni1+xSn, SnS, Ni3Sn, FCC-Ni, Ni1-xS, NiS2, Ni3Sn4, SnS2, Sn2S3 and β-Ni3S2) were observed. A new Ni3Sn2S2 phase was found to melt incongruently. For the Cu-Sb-S system, liquid metal, matte, FCC-Cu, digenite, Sb, CuSbS2, Cu3SbS3 and Cu3SbS4 phases were observed. For the Cu-Sn-S system, liquid metal, matte, digenite, SnS and Cu3Sn phases were found at liquidus.

Jun 17, 2024

By J. J. Sammarco

Computer-aided control of a mining machine pl aces its operator in a safe, remote location, thus reducing health and safety risks, Sensing systems that provide machine position (xy coordinate) and heading (yaw), are extremely useful in aiding remote positioning of mining machines. The U. S. Bureau of Mines has developed two sensing systems for position and heading information: A scanning laser system based on the Lasernet sensor and a mechanical position and heading system based on linear-position transducers. The Bureau is also investigating a system from Honeywell, the modular azimuth and positioning system that employs ring-laser gyroscopes. This paper presents a brief background and status of these sensing systems as applied to the remote positioning tasks of a continuous mining machine. Included are field test results of each system operating in a room-and-pillar research section at a cooperating mine in West Virginia.

Jan 1, 1992

The emerging coal seam gas (CSG) industry has the potential to provide a large-scale energy province for Queensland. Aquifer impacts and management of associated by-product water, both in terms of quantity and quality, are pivotal considerations for the development of a sustainable CSG industry.Legislative changes have been introduced to ensure that the CSG industry manages potential groundwater impacts and beneficial reuse of the by-product water to a level acceptable to both government and the community.The relevant new pieces of legislation covering petroleum and coal seam gas activities include the Petroleum and Gas (Production and Safety) Act 2004 (P&G Act), Petroleum and Other Legislation Amendment Act 2004 (POLA Act), the Petroleum and Gas (Production and Safety) Regulation 2004 and the Petroleum Regulation 2004. Other relevant legislation includes the Petroleum Act 1923 (Petroleum Act) and Part 7AA of the Mineral Resources Act 1989 (Coal Seam Gas Regime). The P&G Act introduces a full regime for managing water rights. This includes provisions for monitoring and reporting on the effects that the taking of underground water under petroleum tenure has on other bores in the area. The P&G Act also imposes a æmake good obligationÆ on petroleum tenure holders, which requires the restoration of bores affected by the taking of water or the payment of compensation. These provisions represent a significant departure from the Petroleum Act, which says very little about water rights and does not specify restrictions on the taking of water under petroleum tenure. This paper attempts to outline the requirements and obligations of the P&G Act for the CSG industry in terms of underground water rights, development impact assessments, aquifer trigger thresholds, monitoring and reporting requirements, as well as the make good obligations.

Jan 1, 2006

By T. Ediz

Sarkuysan Electrolytic Copper holds three competitive technologies namely Outokumpu, Southwire (SCR®) and CONTIROD® under the same roof. After more then thirty years experience of Outokumpu Upcast ® in producing oxygen free wire- rod, and twenty years of SCR® experience, in 1999 it was decided to introduce the CONTIROD® process to the customers with a chance and advantage to test capabilities of each process in order to fulfil their requirements, expectations, and turn this know-how to their benefit. After reviewing the milestones of Sarkuysan's evolution in Turkey as global wire-rod producer, this paper will briefly present the modernization and expansion activities in the CONTIROD® plant consisting of the different phases following the first start-up, and the results of these activities. It will highlight the gains and improvements of some operational parameters within this period.

Jan 1, 2007

By Paul D. Klipfel

Introduction Mineral exploration interest, principally for gold, in the south-western Pacific has surged to new proportions. This is primarily due to the application of epithermal exploration concepts in the Australian-Oceana region. Other factors that have contributed to the high level of exploration interest include governmental policies supportive of mineral exploration, along with relative ease of tenure access and a relatively short bureaucratic process. This paper highlights exploration and development activities in the North Island of New Zealand, Fiji, Vanuatu, the Solomon Islands, and Papua New Guinea (Fig. 1). It provides a framework to understand the overall recent enthusiasm that has been brought to the south Pacific by explorationists. Through these recent developments, it is clear that the south Pacific region will become a significant gold producing area and thereby worthy of attention and study. Papua New Guinea alone is the free world's seventh largest producer (Table 1). And, with the addition of production from deposits presently being developed, this status is likely to be raised. History Gold was first noted on various Pacific islands in the late 1500s by Spanish explorers. They thought they had reached the legendary King Solomon mines. Since then, the history of prospecting in the southwest Pacific has coincided with the colonization of the region. Settlers in New Zealand extensively mined alluvial and lode gold deposits starting in the 1850s. The spread of European colonization to the more remote Pacific islands from 1880-1940 was accompanied by varying degrees of prospecting activity by planters, traders, and settlers. Some were successful, others may have been successful, but never returned due to hostile indigenous peoples or disease. In general, records of such prospecting activity are meager and exploration leads are, in some cases, gained through local village folk memory. Most early discoveries were alluvial finds. These led to placer operations, particularly in New Zealand, the Solomon Islands, and Papua New Guinea. Continued prospecting located lode deposits such as the Morobe Gold-field of Papua New Guinea, the Coromandel Peninsula of New Zealand, and the Emperor of Fiji. Some areas were prospected thoroughly. Yet others, such as Vanuatu, remained relatively unexplored until the present exploration surge began. During World War II, interest in minerals was diverted. It was renewed significantly until the middle 1960s and early 1970s when regional porphyry copper exploration was conducted.

Jan 10, 1987

By J. J. Talja

An investigation of oxidation of various nickel concentrates was carried out using differential scanning calorimetry (DSC). The aim of this study was to determine the ignition temperature and investigate other oxidation behavior of various sulfide-based nickel concentrates. Variables in the experiments were mineralogy, particle size and partial pressure of oxygen with temperature increasing linearly at 25 K/min from 323 to 1023 K (50-750 °C). The igni¬tion temperature was determined to represent the starting point of rapid oxidation. The reac¬tion enthalpies of the concentrates were determined and the amount of heat generated up to various time were used to calculate the extent of reaction. Mineralogical changes at various stages of oxidation were also investigated. For this purpose a second set of DSC-experiments were carried out in which each experiment was interrupted at a desired temperature between 673-873 K. From these tests the weight loss of samples were determined and changes in the individual constituent of sulfide minerals were analyzed. For pentlandite-based Ni-concentrates the ignition temperature was 705-710 K (approximately 435 °C). Pyrite was the first sulfide to oxidize. Reactivity of the violarite-based concentrate was greater than those of the pentlandite-based concentrates. The stoi-chiometry of pentlandite changed before ignition because of preferential oxidation of iron. Rapid oxidation of the pentlandite mineral occurred at about 823 K (550 °C). By 900 K about 90 % of the iron in pentlandite was converted to hematite, and NiS containing some iron was formed.

Jan 1, 1994

At the Orieco mine quartz veins carrying sulphides were localized in parts of an extensive fault zone in the Mathinna Beds during late Middle Palaeozoic mineralization.These deposits were subsequently exposed, and oxidation of the sulphides by percolating groundwaters resulted in the formation of gossans at the surface, and replacement close to the permanent water table of the more soluble sulphides by copper sulphides (chalcocite, coveIlite). A restricted zone containing copper oxides (cuprite, tenorite), copper carbonates (malachite, azurite), iron arsenates (scorodite, pharmacosiderite) and possibly rare copper sulphates occurred above the water table.The renewed oxidation of these deposits following mine development has been facilitated by the ready circulation of air and water combined with the formation of large free surfaces ideal for evaporation of aqueous solutions. Under these new conditions of high initial sulphate concentration, low pH, and relatively high Eh, the previously formed mineral assemblage is unstable and numerous Cu (Fe,Zn)-sulphates and Fe (Cu,Pb)-arsenates are presently forming in fractures in the fault zone and on the adit and stope surfaces for some considerable distance from the Sulphide-rich ore shoots. The observed spatial sequence of the major sulphates with respect to the sulphide-rich zones (Le. chalcanthite-antleritebrochantite and langite) is consistent with decreasing sulphate concentration and increasing pH away from the oxidizing sulphides.

Jan 1, 1970

By R. G. Reddy

The oxidation kinetics of A13Ti intermetallics have been studied at the temperature range of 850°C to 100O0C in pure dry oxygen. The oxygen diffusion rates were investigated using TGA method. Parabolic rate constants were calculated. The oxidation scales were analyzed using SEM, EDS and X-ray diffraction. A continuous A120, scales with a little TiO2(rutile) were formed on the intermetallic surface. The A13Ti intermetallic exhibited excellent oxidation resistance among the Ti-Al base intermetallics.

Jan 1, 1997

By Reynold Q. Shotts

Data are presented which show that fractions of varying densities-from the same coals are oxidized at different rates by nitric acid. From oxidation data, the approximate quantity of "bright" and "dull" components may be calculated. Definite relationships between oxidation rate and rank are shown for density fractions from at least two bituminous coals.

Jan 1, 1950

By S Ivanaj

Oxidation of chalcopyrite from a copper concentrate in an electrochemical cell having separate-anodic and cathodic compartments was studied by potentiodynamic, potentiostatic and galvanostatic experiments. Oxidation of chalcopyrite particles was mainly realized by in-situ electrogenerated FeIII and Cull ions. The use of an ion exchange membrane, in this experimental set, avoids the reduction of the ferric and cupric ions. The effects of particle size, current feeder potential, current intensity and pulp density were studied to optimize the oxidation parameters. Selective complete oxidation of chalcopyrite was achieved. Oxidation of pyrite was negligible. Mom than 85 % of sulfur was obtained in its elemental form. This may allow selective extraction- of copper from the chalcopyrite concentrate without sulfur dioxide emissions.

Jan 1, 1995

By Peter R. Sanford

Cyanides are present as a dilute constituent of streams from a variety of metallurgical and mineral-processing operations. In addition, a cyanide concentration in excess of approximately 100ppb is toxic to aquatic life, and consequently these operations require a waste-treatment process to reduce the already dilute cyanide species by several orders of magnitude. Furthermore, the waste streams may have flowrates in excess of a million gallons per day. The paper reports on research conducted with a laboratory?scale electrochemical porous (graphite felt) electrode (anode) flow-reactor, which was conducted in conjunction with a computer-aided simulation of a mathematical model describing the intrinsic rate-phenomena associate with the electrode processes. The laboratory-scale cell, of rectilinear geometry, was found to be capable of reducing a feed-stream anolyte (KCN-KOH and supporting electrolyte of a single salt ? K2SO4) with a cyanide concentration of 10ppm, to less than 100ppb, at current efficiencies in the neighborhood of 50%. The computer simulation of the cell performance based on the mathematical model (and constraints imposed for tractability) was found to provide only for qualitative agreement.

Jan 1, 1998

By David C. Lynch

FeCl3 particulate of 10 to 100 um in diameter was reacted with radicals produced in an oxygen plasma at pressures between 1 to 20 Torr. The particulate, in a fluidized bed, was positioned above the plasma to avoid over heating the oxide product which is known to lead to crust and clinker formation[ 1 ]. Reaction between the iron chloride and the gas phase occurred at temperatures between 66 and 226 °C. Oxygen radicals react with the surface material to a depth of approximately 2.5 4m. Surface material, analyzed with a x-ray technique, indicates that the maximum amount of FeCl3 reacted on a weight basis was found to be approximately 67%. More typically, 40 to 50 wt% of the chloride was reacted within 30 minutes to 1 hour.

Jan 1, 1996

By Hongqiang Wang, Qingliang Wang, Eming Hu, Zhiwu Lei, Fang Hu, Rui Zhang, Wei Hou

Pyrite, a mineral associated with uranium ore, is closely related to uranium leaching. In this study, Ozone micro-nano bubbles (OMNBs), as an environmentally friendly advanced oxidation technology, were used for the first time to oxidize pyrite under experimental conditions to improve the leaching rate of uranium. A laboratory-scale agitation leaching experiment of pyrite was carried out with a pH of 1.0–3.0, gas flow of 1–3 L/min, ozone generation rate of 0.55–2.22 mg/s, and pyrite concentration of 0.1–5.0 g/L for 1 h. By adding three different co-oxidant: Mn(II), Mn(IV), and Fe(III), it was found that only Mn(IV) increased the oxidation rate of pyrite by 21.7%. The results of the scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) show that the formation of Fe(III)-O film on the surface of the ore suppresses the oxidation rate of pyrite to a certain extent. Pyrite can be rapidly oxidized up to 57.6% by OMNBs, which is beneficial to uranium leaching. This method is expected to be used for in situ acid leaching of uranium with OMNBs injected into the ground.

Jan 3, 2022

The merging of flash smelting with spray converting in one single furnace is proposed as a continuous copper making process. The proposed process is expected to produce blister copper, clean slag and gas with high sulfur dioxide concentration. Some high grade matte is an intermediate product recycled within the proposed furnace, spray-atomized and converted. The thermodynamic equilibria of the simultaneous oxidations which take place during copper smelting and converting are discussed in order to establish the gradient of oxygen potential along the furnace required for smooth operation. The proposed process is a dynamic system designed to reach equilibrium only close to the slag skimming end of the furnace. The process feasibility is based on the predesigned significant difference between the rates of converting reactions in a finely dispersed system and the rates of deconverting reactions between immiscible liquid phases of restricted interface area. The converting of small stationary droplets of matte, in a silica saturated system, was studied in the laboratory for extremely short oxidation times (10 to 120 seconds). These experiments led to some interesting observations on reaction mechanisms and kinetic trends. The droplet size and the matte grade affected very strongly the oxidation rate and the proportion of the different products obtained.

Jan 1, 1976

By H. Soto, J. Jara, F. Nava

"A combination of oxidation and precipitation was used to eliminate cyanide from gold milling effluents. Preliminary laboratory work developed with both synthetic cyanide solutions and with industrial effluents indicated that ozone can easily destroy free cyanide and weakly complexed cyanide (i.e. copper and zinc cyanide). In this case the reaction is quite fast and seems to be controlled by the mass transfer of ozone to the solution. Experimental results indicate that free cyanide and weak-acid dissociable cyanide in mill effluents can be reduced to less than 1 ppm. However, the iron-cyanide complexes proved to be quite resilient to destruction with ozone and they remained in the solution even after most of the free and weakly complexed cyanide was destroyed with ozone. These results were confirmed in a pilot trial developed at the Sphinx plant in northern Quebec.To deal with the problem presented by the presence of the iron complexes two different approaches were studied: use of a combination ozone-ultraviolet light oxidation, and the precipitation of iron-ferrocyanide complexes in the residual solution after ozonation. This last method proved quite promising since reduced the total cyanide levels of industrial solutions assaying as much as 250 ppm to less than 1 ppm of total cyanide. Control of the · pH of the solution was the key to obtain the precipitation of the iron complexes. The use of iron to precipitate cyanide complexes has the advantage of being less expensive and less toxic than copper (used by the Inco process)."

Jan 1, 1992

By H. Soto, J. Jara, F. Nava, J. B. Hiskey, B. J. Scheiner

Laboratory tests showed that ozone can destroy free cyanide and weakly complexed cyanide (copper and zinc cyanides). The iron cyanide complexes were resilient to ozonation but they were effectively eliminated by precipitation with Fe (II) ions under controlled pH conditions. Tests carried out with effluents from a number of gold mills confirmed the results obtained previously in the laboratory. The industrial samples contained cyanide in the form of free cyanide and also complex copper, zinc and iron cyanides. Solutions that contained up to 184 mg/L total cyanide, after the ozone treatment analyzed only 2-3 mg/L dissociable cyanide and 50-90 mg/L CN(t) (accounted for by iron complexes). After precipitation with ferrous ions total cyanide was reduced below 1.5 mg/L. For most solutions ozone consumption ranges from 3 to 6 g per g of cyanide destroyed. However, certain impurities (such as SCN and S203 ), present in some effluents, increase ozone consumption and make it more difficult to reduce copper concentration to satisfactory levels.

Jan 1, 1993