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By E. De Souza

Two comprehensive surveys, which focus upon backfill practices and the economics of backfilling in underground mines in Canada, have been conducted. The two surveys were designed to assess operational practices and costs associated with the wide scope of filling operations that must be met by individual mines, ranging from raw material feed to the preparation plant, through underground backfill transportation, to in-stope product placement. This paper presents the current state of backfill usage in Canada, identifies trends in minefill practices and provides mine operators with an updated database of information upon which they might compare their own practices and costs with present trends throughout the industry.

May 1, 2003

By Ish Grewal

"Batch centrifugal gravity concentrators, which produce very high ratios of concentration, have become common place for recovering free gold within milling circuits. Their effectiveness has proven to be especially useful in recovering finer gold particles. The knowledge related to testing, modeling and scale-up of these systems has been well established over the recent decade mostly due to the efforts of the late Dr. Andre Laplante.Gravity separation technologies such as jigs, spirals and shaking tables can provide the increased mass yields required for minerals that occur at higher concentrations than gold, however their effectiveness tends to diminish at finer particle sizes. The development of high mass yield centrifugal concentrators has provided the opportunity to be able to recover a wide range of minerals at finer particle size classes when compared to the more traditional gravity concentration devices. These concentrators also provide additional benefits such as smaller unit footprint and automated operation.This paper discusses the background, current practices and future applications for high mass yield centrifugal concentrators in base metals, sulfides and industrial minerals. Bench scale, pilot scale and plant practice examples are also presented.INTRODUCTIONGravity concentration, one of the oldest mineral beneficiation processes, has evolved over the decades and continues to play an important role in modern mineral processing operations. The development and growth of froth flotation in the early part of the twentieth century led to a decline in the importance of gravity concentration. However, gravity concentration continued to be used for ores that are difficult to beneficiate using froth flotation; such as tin, tungsten, niobium/tantalum, iron, industrial minerals and oxidized coal. In recent decades, many operations have begun to employ a combination of both gravity concentration and froth flotation Since flotation relies on surface chemistry and gravity concentration relies on specific gravity differences, putting these techniques in series provides today’s metallurgist with unprecedented opportunities to maximize grade and recovery of many of these minerals."

Jan 1, 2009

"Placer Dome Inc.'s Dome Mine is located in South Porcupine, Ontario and has been in production since 1910. In the past, the mill leach circuit was preceded by preaeration and primary filtration circuits. These circuits were operated to overcome the effects of pyrrhotite in the ore which reacts with cyanide to form cyanates and thiocyanates and also consumes oxygen.In early 1989, primary filters were by-passed for an extended period. Actual plant results showed no affect on gold recovery or cyanide consumption so the circuit was left off-line permanently with significant cost savings.In 1990 it was determined that considerable savings could be realized underground if backfill storage facilities were located in the mill. It was decided to convert the preaeration pachucas to backfill storage tanks on a trial basis. The trial proved successful with no effect on recovery or significant increase in reagent consumption occurring due to the elimination of the preaeration circuit. The converted pachucas worked well as backfill storage tanks.Modifications such as these have helped to keep the Dome's millings costs among the lowest of Canadian gold producers."

Jan 1, 1992

By A. F. Banks

"Potash processing has much in common in terms of unit operations and plant operating strategy with other mineral processing plants. As it is a rather large topic the processes will be broad brushed to give you some background and then I will go into a little detail on the things we do in the Cominco plant that may be of interest to the group as a whole. In particular the centrallized computer control system and associated instrumentation and the operator training programs will be covered as well as the mill fire, something that could happen in any plant. THE ORE AND PRODUCTSThere are differences in potash ores as you would expect. It is my intention to deal with the ores processed in the Saskatoon area. These are mined from the beds in the Patience Lake Member and have a mineralogical description as follows:Sylvite (Potassium Chloride) 40%Halite (Sodium Chloride) 55%Insolubles (Slimes) 5%A number of products are made from this ore. It is characteristic of a potash plant that you put as much effort into grading and converting the sylvite to meet market requirements as you do in recovering it."

Jan 1, 1976

By Julie Culverhouse, Dennis Grimm, Kieran Harding, Jean-Francois Boulanger

"Agrium’s Canadian Phosphate Business (CPB) is comprised of Kapuskasing Phosphate Operations (KPO) in Northern Ontario, Canada’s only operating phosphate mine, and Redwater Phosphate Operations (RPO) in Alberta, which manufactures the fertilizer from KPO’s concentrate.Production from KPO’s South Pit commenced in 2009 and introduced contaminant problems: high aluminium from crandallite and kaolinite clays. These issues caused a drastic decrease in P2O5 recovery and throughput in both plants. KPO attempted to reduce Al clays by means of aggressive desliming. Meanwhile RPO experienced high amounts of dissolved metals in their feed that are detrimental to fertilizer production.This paper covers the mineralogy of the problem, its impact on contaminant separation at KPO, on RPO’s process and on Agrium’s Canadian Phosphate Business as a whole.Potential solutions to the problem are discussed and analysed, including a process change to deslime high aluminium streams more aggressively and high grade ore flotation, which is atypical at KPO. The latter is a demonstration of the value of communication between the concentrator and the client, as KPO accepted a recovery loss and increased production costs in order to increase overall CPB profits. General lessons learned are discussed, followed by a section on ore blending.INTRODUCTIONAlthough the existence of the Kapuskasing phosphate deposit has been known since the 1970s, it’s only since 1999 that Agrium has been operating the Kapuskasing Phosphate Operations (KPO). The mine consists of three major pits (Center, North and South) from which a mining contractor hauls the apatite ore to the Agrium concentrator. The beneficiation plant processes the ore, separating contaminants such as Fe, Mg and Al which are detrimental to its client, Agrium’s Redwater Phosphate Operations (RPO). The KPO concentrate is finally thickened, filtered and dried before being shipped by rail to RPO.At the Redwater plant, the KPO concentrate is added to a sulfuric acid solution in an attack tank, to create a phosphoric acid solution and gypsum:"

Jan 1, 2011

By Christoph Mueller

Mining operations are characterized by cost pressure and cycling product prices. A high potential for enhancing efficiency is the integration of all single steps of the mining working chain into a production process structure to make advantage of an optimized flow of material and information through the ?moving ore factory?. As modern mining machinery today is controlled electronically and even already operated autonomously, a smooth and cost efficient flow of data in the mining process will be crucial for cost efficient future mine operations. Therefor, the International Rock Excavation Data Exchange Standard (IREDES) was launched by major players in the industry. The task of this initiative is to define a ?common electronic language? for easy and standardized data exchange between mining machines and central computer systems. As in other industries, this standard is expected to have significant impact on the use of automated equipment. It shall provide easy ways of using multi vendor machine installations in data controlled mining processes. At the same time it reduces cost for individual development of interfaces for all parties involved. Standardized data exchange is also a crucial precondition to integrate the mining process into enterprise level modeling, cost analysis and decision finding systems. The standard?s technical architecture is open and flexible for future applications. It uses modern XML technology enabling easy data exchange with commercial databases as well as open on line networking. The IREDES work is carried out by the initiative members working jointly together in the technical work groups. Prototyping implementations of the Drill rigs profile are currently going on. Further profiles under development cover LHD?s/Loaders/Trucks and Explosives Chargers. The first official release covering the Drill Rigs profile is planned for the end of 2002.

May 1, 2002

By Lauri Gregg

Key Message Energy focused Change Management Process that engages operations managers is the missing tool needed to build capacity for energy/GHG management

May 1, 2007

By G. C. McKerrow

"Mr. G.C. McKerrow, Assistant Manager of Noranda Mines and formerly Smelter Superintendent attended the meeting to answer questions as to why smelters imposed penalties for too much zinc in a copper concentrate or too much copper in a zinc concentrate, etc.D.W. Bridges -Mattagami Lake MinesWhat limits do you set on zinc and lead in a copper concentrate?G.C. McKerrow - At Noranda, we allow 5% zinc free and charge 25 cents for every unit above that. For lead, it is 1% free and 25 cents per unit above that. Lead is a much more harmful impurity than zinc because it tends to recycle more in the smelter circuit and creates a greater health hazard in the plant.E. Thornton - Sullivan GroupWHat harm does fluorine do in the smelting process?G.C. McKerrow - Fluorine usually does not occur in harmful concentrations in non-ferrous smelters. Fluorides are present in exhaust gases in the aluminum and phosphate industries. If these fumes escape into the atmosphere, they may settle out on forage grasses in concentrations that are harmful to livestock.Thorton - Sullivan GroupI have asked this question other places and have been told that it is hard on brick linings and causes gold and silver to be lost up the stack.G.C. McKerrow - Almost any volatile constituent in a smelter charge will aid in carrying other metal values. To this extent it may be harmful.E. Thornton - Sullivan GroupMr. Tait mentioned before a smelter where they have a copper-tin ore and they pay for copper, tin, bismuth and silver but object strongly to indium in the concentrate. Why would this be?G.G. McKerrow - 1 can't see why indium would be a serious impurity. It does tend to concentrate in flu dusts and if you get enough of it you can recover it and sell it but I have never heard of anyone putting a penalty on it.Question - I once ran into a small copper mine in Peru that had cadmium in the copper concentrate but no zinc. The copper smelter charged a penalty for the cadmium. Why would this be?"

Jan 1, 1971

By Christoph Miller

About 80 years ago the mining industry saw an advertisement of a machine manufacturer: ?One man ? one machine?, meaning the productivity gain by using a pneumatic rock drill instead of manual tools. Mechanization in mining had started. In the 1950's and 1960's when mechanization progressed the word could be transformed into the meaning of ?one man ? one drill rig?. During the 80's automatic functions were added to the machines. Automation started. In the 90's, the first autonomous machines were seen, transforming the advertisement from the 1920's into ?one man ? multiple machines? operated from a remote control room. Soon, the productivity gain achieved by pure automation will also be flating out meaning that the margin cost of further productivity gain will be inefficiently high. What next? In mining operations there is still a high potential of unused productivity lost by ?trivial? things like organization, logistics and operational management. Changing the focus from mechanization and automation towards optimizing the overall mining process will unleash another big potential for cost cuttings and for enhancing efficiency of production. Optimizing an overall process is a task of much higher total complexity compared to an isolated machine automation focus. And a successful process integration requires the collaboration of machine vendors, infrastructure suppliers, IT services and the mine itself. It requires a number of of important preconditions to be fulfilled: ? Integrated IT systems with seamless interfaces between all components and peripherals involved ? Real time information access in all locations ? Real time overview of all operational aspects A crucial aspect for all of these issues is a seamless communication both above and also under ground and IT interfaces which are easy and price efficient to implement. This paper highlights ways to achieve productivity gains by process optimization. It also discusses needs for industry wide activities in order to enable cost efficient performance of mine process optimization projects.

Oct 1, 2009

By O. Matwijenko

"The Kidd Creek concentrator is located twenty-six kilometres east of Timmins, Ontario, within a metallurgical complex including a 109,000 MTPY zinc plant and a new 59,000 MTPY copper smelter and refinery. A complement of 159 persons is employed in the operation of the concentrator.Ore from the Kidd Creek Mine is crushed underground to minus 15. 0 cm, then transported twenty-seven kilometres by rail 1:0 the concentrator. After being crushed to minus 1. 6 cm, the ore is further processed by grinding and flotation.The concentrator commenced operations in November of 1966 at a designed capacity of 8,200 MTPD. Two parallel flotation and grinding circuits treated copper-zinc ore (2.28% Cu, 5.63% Zn) and a third treated silver-copper-lead-zinc ore (230 g/MT Ag; 0.57% Cu, 0.88% Pb, 7.89% Zn).By 1975, the concentrator was treating 9,100 MTPD of ore. Seven concentrates were being produced, namely, high silve1: copper, low silver copper, lead, low silver zinc, high silver zinc, pyrite and tin.Planned minesite expansion to a second underground mine required increased concentrator throughput. Expansion of the concentrator enabling a thirty-three percent increase in copper-zinc ore throughput occurred during the period 1975 through 1978. This expansion included increased load-in capacity, major redesign in the crusher house, the addition of a fourth grinding and flotation circuit, the building of a fourth dryer, and numerous expansions of services."

Jan 1, 1980

By P. H. Oliver

"The current theory of how explosives fracture rock offers no explanation for the improvements in fragmentation and the reduction of fly rock and back break which occurs when an adequate inter-row delay time is used. Nor does it explain why fragmentation improves with rectangular drill patterns where the hole spacing may be as much as four times the hole burden.A new theory of rock fragmentation is proposed which builds on the existing theory. It offers rational explanations for the many blast effects which the current theory does not address and the need for adequate timing delays between rows. It improves on the design of inter-row delay timing by defining the length of free-blasted face needed in front of a hole *Retired from Inco Ltd., Sudbury, Ontario when selecting the delay element which will provide an adequate inter-row delay time."

Jan 1, 2003

By P. H. Oliver

The current theory of how explosives fracture rock offers no explanation for the improvements in fragmentation and the reduction of fly rock and back break which occurs when an adequate inter-row delay time is used. Nor does it explain why fragmentation improves with rectangular drill patterns where the hole spacing may be as much as four times the hole burden. A new theory of rock fragmentation is proposed which builds on the existing theory. It offers rational explanations for the many blast effects which the current theory does not address and the need for adequate timing delays between rows. It improves on the design of inter-row delay timing by defining the length of free-blasted face needed in front of a hole when selecting the delay element which will provide an adequate inter-row delay time.

May 1, 2003

By J. W. Austin

"Introduction The Brenda dust collection system was originally designed to handle air at the 5000 ft. elevation with less than 1 grain of dust per cubic feet of air handled. The temperature variation is from 32°C in the summer to -20°C in the winter.DUST COLLECTIONOriginal Equipment 1. Primary Crusher 2 compartment baghouse, shaker type design capacity - 17,000 cfm2. Primary Screening 3 compartment baghouse, shaker type design capacity - 30,000 cfm3. Secondary Crusher 4 compartment baghouse, shaker type design capacity - 45,000 cfm4. Secondary Screening 4 compartment baghouse, shaker typedesign capacity - 60,000 cfmThe original dust collecting equipment was designed using a napped terylene fabric at an air to cloth ratio of 5:1. The ducting was designed to handle the dust laden air at 3200 ft. per minute with all elbows and blast gate sections rubber lined. The hoods and the pickup velocities were designed to handle the anticipated low dust counts."

Jan 1, 1976

By R. A. Bergman

"Process descriptions are provided for the following ten plants that treat high-magnesia lateritic nickel ores (saprolite) by pyrometallurgical means: PT Aneka Tambang; Cerro Matoso S.A.; Falconbridge Dominicana C. por A.; Hyuga Smelting Company Ltd.; Larco (Societé Minière & Métallurgique de Larymna); Loma de Niquel; Le Nickel, SLN-Eramet; Nippon Yakin Kogyo Company Ltd.; Pacific Metals Company Ltd.; and PT Inco Indonesia.Flowsheets, equipment information,chemistry and production data have been compiledfor plants based on both information providedby the companies and on calculated massand energy balances.IntroductionNickel is of vital importance to modern society. Without it, we would not be able to enjoy many of the things that we take for granted, such as computers, airplanes and stainless steel appliances in our homes and workplaces, to mention a few.Nickel occurs in nature both as sulphide and oxide ores. Approximately 36% of the nickel reserves in the Western World occur as sulphide and 64% as oxide ores. Sulphide ores respond to concentration processes, whereas, oxide ores do not. Sulphide ores mined at 1% nickel can be readily concentrated to 10% nickel, whereas, oxide ores cannot be concentrated and therefore have to be processed as mined.Laterite ores are normally classified intotwo groups:1. The high-magnesia ores, saprolites or serpentines, are, as a rule, processed by smelting. The main reason for this is that the nickel replaces magnesium in the magnesium-silicate lattice. To be able to recover nickel, the lattice has to be destroyed. This can be achieved by smelting under reducing conditions.Acid leaching is also possible, but in this case, large amounts of MgSO4 or MgCl2 will be produced making it costly to regenerate the acid.2. The high-iron, low-magnesia ores are known as limonite. The nickel is relatively loosely bonded to goethite and hence can be recovered by selective reduction followed by ammonium-ammonium carbonate leaching. In recently developed processes, these ores are also being extracted by acid pressure leaching, with high Ni and Co recoveries.This paper focusses on the production of ferronickel and nickel matte from the highmagnesia ores."

Jan 1, 2003

By J. E. Udd

"In early 2000, CANMET-MMSL was engaged by the Ontario Ministry of Labour (OMOL) to conduct an international study of the practices, in several key mining jurisdictions, of determining the criteria that are used to decide when the wire ropes used in mine hoisting are to be retired from service. Subsequently, the author visited key officials and institutions in Canada, the United States, the Republic of South Africa, the United Kingdom, Germany, and Poland. Material from the Australian province of New South Wales and Hungary was also included.The report that resulted included, among other sections: (1) the history of wire ropes and trends in manufacturing technology; (2) a review of mine hoisting practices; (3) the requirements regarding safety factors; (4) a review of the various operations and their potential future development; (5) the criteria for rope replacement; (6) potential future developments that could take place in both hoisting and rope inspection practices in Canada; and (7) recommendations.Subsequently, the report was issued by OMOL, and as a CD-ROM by CANMETMMSL. In this paper the author presents the key findings and the recommendations made in the study."

Jan 1, 2004

By R. E. Michelutti

"The Sudbury area environment became drastically altered commencing in 1871 with lumbering, repeated fires and early open roasting operations from 1887 to 1929. These combined factors had such a pronounced effect that approximately 24 square miles were totally denuded of any vegetation and 87 square miles were semi-barren to somewhat stressed.The two nickel producing companies in the area have reduced the sulphur dioxide emissions considerably over the years. Falconbridge Limited, alone, reduced sulphur dioxide emissions by 77% from 1971 to 1984.These reductions have resulted in improvements to the air, soil, lake and vegetation quality in the Sudbury area.INTRODUCTIONThe Sudbury area environment became drastically altered commencing in the 1870's with lumbering, repeated fires and early open roasting operations from 1888 to 1929. These combined factors had such a pronounced effect on the Sudbury environment that approximately 24 square miles (64 sq. km.) were totally denuded of any vegetation and 87 square miles (225 sq. km.) were semi-barren.Over the years, the Sudbury area environment has improved considerably. This has been due to emission cutbacks by both Inco Metals and Falconbridge Limited, coupled with industry, government and community reclamation programs. Before the improvements are discussed, a better understanding of the historical degradation is required."

Jan 1, 1986

By Paul Staples, Fred Woodcock, Robert Grant, Mike Cooper

"Noranda's Brunswick Mining Division, near Bathurst, New Brunswick, processes 10,500 TPD of complex Cu-Pb-Zn bearing ore. Brunswick uses conventional rod and ball milling techniques to achieve a flotation feed size of 75% passing 400 mesh. Over a two year period, testwork was performed using a Marcy pilot plant ball mill to assess the impact of several key variables on secondary grinding efficiency. Four graded mill charges were used to compare balls and slugs at 25 and 29 mm sizes. Data was evaluated by determining grinding rates using a commercially available steady state simulator. Results were critical in Brunswick's efforts to achieve finer grinds while minimizing cost per tonne.IntroductionBackgroundThe Brunswick orebody is an extremely fined grained volcanogenic massive lead, zinc, copper, silver, iron sulphide body between two metamorphosed sedimentary and felsic volcanic rock units. Pyrite content is about 60% with 20% non-sulphide minerals, mainly silica and chlorite.Size reduction at Brunswick is performed by three separate parallel lines consisting of rod mills, primary and secondary ball mill circuits, all in series. The line 3 grinding circuit is presented in Figure 1."

Jan 1, 1997

By Johnna Muinonen

"The Thompson Mill processes ores from the Thompson and Birchtree Mines. While the Thompson ore has very little magnesium containing gangue, the Birchtree orebody consists of veins of massive sulphide in a rock matrix that contains a high proportion of magnesium silicate minerals. A significant fraction of the magnesium is floatable, which lead to MgO levels varying from 3-11 wt% in the Birchtree concentrate. The magnesium in the concentrate causes a higher operating temperature in the smelter, reducing furnace life.Birchtree ore represented 20-30% of the mill ore receipts prior to October 2003. Since then the fraction of Birchtree ore has increased to 50%. A reduction of the MgO in concentrate to less than 3% in the total mill concentrate was required to allow safe and economic smelter operation.In October of 2002 a miniplant was set up to simulate the Birchtree plant circuit. Several flow sheet modifications were tested that led to a proposal for a circuit having increased cleaning capacity for the scavenger concentrate and a recleaner on this concentrate. Addition of CMC in rougher cleaner feed was also found to be required. The solution was confirmed through pilot plant testing in the mill in December of 2002. A full-scale installation was designed, engineered, and installed between February and September of 2003 with commissioning in September and October of 2003. Target metallurgy was achieved one week after start-up on slurry to coincide with the Birchtree Mine tonnage increase. This paper highlights the development, design and commissioning stages of the project.The new MgO rejection circuit has successfully allowed the processing of Birchtree ores producing concentrate consistently below 3% MgO. In addition, the new circuit increased overall nickel recovery in the mill.INTRODUCTIONThe Thompson Nickel Belt located approximately 700km north of Winnipeg was discovered in the early 1950’s. Inco first produced nickel from the area in 1960. Over the years the mill has processed several ores from different ore bodies in the area. Currently the Thompson Mill processes two significantly different ores from two mines, Thompson and Birchtree. The Thompson ore is a massive sulphide orebody hosted in schist, containing feldspars, quartz and biotite. Thompson Ore is characterized by high nickel recoveries and clean, low MgO containing concentrates (<2.5% MgO). The Birchtree ore is ultramafic and contains a high percentage of Mg-silicates such as serpentine, chlorite, biotite, amphiboles and talc. Some of these Mg-silicates report to the nickel concentrate and prior to commissioning of the MgO rejection circuit the Birchtree nickel concentrate typically contained 5-8% MgO"

Jan 1, 2006

By Mohamed Ourriban, Yongjun Peng, Qi Liu, Denis Cotnoir

"In the flotation of fine particles, there are two difficulties in general: low recovery of valuable minerals and high recovery of gangue minerals. The low recovery of fine valuable minerals is attributed to low bubble-particle collision and attachment efficiencies, while high recovery of fine gangue minerals is attributed to mechanical entrainment through water films between gas bubbles. Over the last five years COREM has been actively developing fine particle flotation techniques with the objective of improving fine particle flotation separation efficiencies.The fine particle flotation techniques with both generation of micro bubbles and enlargement of sizes of fine particles have been developed to increase bubble-particle collision efficiency. For oxidized fine sulphide minerals, both physical and chemical techniques have been developed to modify the hydrophilic surfaces and therefore increase bubble-particle attachment efficiency. To reduce mechanical entrainment of fine gangue minerals, a new approach, polymeric depression and flocculation, has been developed. By selecting the high molecular weight polymeric depressants to make fine gangue minerals hydrophilic and also enlarge their sizes, entrainment can be minimized. By combining these techniques, we are able to improve both flotation recovery and selectivity in some fine ore flotation systems.INTRODUCTIONWith depleting mineral resources and their declining grades, ores leaving grinding circuit for froth flotation are becoming increasingly finer to achieve mineral liberation. Together with the increasing demand for minerals, ever-increasing tonnages of fines are being produced. Therefore, flotation of fine particles is an immense challenge to be tackled by researchers all over the world today."

Jan 1, 2006

By P. D. R. Maltby

"1. INTRODUCTIONMy talk today will discuss a new development in the thickening of slurries and clarification of waste water - the Enviro-Clear thickener. Several industrial installations of the thickener have been made in North America in the following applications:1.,water clarification in sugar beet processing plants.2.,separation of pregnant liquors from solid wastes following acid leaching in uranium mills3.,clarification of waste water from coal treatment plants as described in a paper in the June 1975 transactions of the SME entitled ""Application and Utilization of the Enviro Clear Thickener in a U.S. Steel Coal Preparation Plant"" by A.A. Terchnik, D.T. King and J.S. Anderson.2. HISTORYThe application of the Enviro-Clear thickener can be traced back to the filing of U.S. Patent 3523889 in 1970 by the inventor F. Eis. The claims of this patent are shown in Slide 1.The new concept was developed for sugar beet processing by the Spreckels Division of Amstar Corporation, and several such thickeners have subsequently been installed in various sugar beet plants. The Enviro-Clear Co. or New York took over the world-wide manufacturing and marketing of the thickener. Experience in the sugar beet industry indicated that the Enviro-Clear thickener volume requirements could be reduced to as low as one tenth that of a conventional type thickener. Various coal samples were supplied by U.S. Steel Research Laboratories for testing. The tests indicated that feed rate loadings of 3 gpm/ft.2 could be obtained by the Enviro-Clear thickener. Such results led to several industrial applications in the coal industry. Subsequently other branches of the mineral processing industry have come to learn of the possibilities of using this thickener. Slide 2 shows a list of commercial Enviro-Clear installations at the end of 1975."

Jan 1, 1976