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By J. Brendan Mclaughlin, Casimir J. Koshinski, Michael V. Rose, Wolfgang Baum

Mercury contamination is a worldwide problem in the mining, smelting, and refining of gold, silver, and copper. In these areas, mercury may be found as a naturally-occurring material in ores and concentrates, and/or in secondary feedstocks such as leach residues, pyrometallurgical treatment residues, refinery by­products, electrowinning electrodes, autoclave discharge solids, and waste water and acid plant sludges. The United States Environmental Protection Agency (EPA) has designated mercury one of the most harmful heavy metal contaminant in the environment and has implemented regulations that prohibit land disposal of characteristically hazardous wastes containing greater than 0.20 mg/1 TCLP mercury without prior treatment, thus increasing the cost of managing these materials. The presence of mercury in mine, smelter, and refinery by­products and wastes severely decreases, and in some cases eliminates, the ability to recover residual metal values from the contaminated material. The lost revenue associated with this disposal, combined with the increased direct cost of waste treatment, and/or disposal and protecting workers and the environment, can adversely affect overall profitability. The safe, efficient, and economical removal of mercury from gold, silver, and copper mining by-products requires a treatment process that is capable of liberating the mercury from the wide variety of compounds and matrices in which it may be contained, reducing the mercury content in the matrix to desired levels, and recovering the mercury in pure saleable form, without producing any secondary solid, liquid, or gaseous wastes. This paper reviews results from commercial operations and pilot scale tests using a thermal process owned and operated by Mercury Recovery Services, Inc. (MRS) to remove and recover mercury from copper acid plant blowdown sludge, Merrill­Crowe precipitate from gold/silver mining operations, and Cottrell and salt slag dusts from a precious metals refinery.

Jan 1, 1997

By E. J. Rogans, W. N. Cartner

Carbon technology has largely superseded filtration plants as the more acceptable gold recovery technology. This has, over the last two decades, provided a tremendous driving force for the development of new equipment. One of the main focus areas of this technological development is the development of effi­cient interstage screening systems. Several variations of exter­nal and internal screens are available, with the more recent shift away from air cleaned units to mechanically swept units. This paper discusses the development of one such mechanically swept interstage screen and how the development led to the suc­cessful implementation of a carousel type of CIP operation. The first generation Pump-cell emerged as a consequence of the success achieved with the mechanically swept NKM screen, The idea was to modify the screen to incorporate the functions of pumping, screening and agitation in a single drive unit, the screen generating sufficient lift for interstage slurry flow so that all contactors would be at the same level. This sys­tem was further incorporated as a high intensity modular CIP contactor, i.e. low slurry residence times combined with high carbon concentrations. A discussion on the kinetic gold adsorp­tion theory and its manipulation in the design of the pump-cell concept is discussed in a paper published in a previous Randol Conference< 1), Testwork carried out at Vaal Reefs proved the concept of the Pump-cell on a pilot plant scale<2), which resulted in the building in 1990 of the first large Pump-cell plant at West Witwatersrand Gold Mine designed to treat 340m3 of pulp per hour and , even though the plant operated successfully with respect to gold recovery performance, a few problems were experienced with the basic engineering design(3),

Jan 1, 1996

By Steven Hart, Graeme Hill

Boddington Gold Mine is situated 130km South-east of Perth, WA. The operation is managed by Worsley Alumina Pty Ltd. The Direct Leach plant was commissioned in mid 1986 at a rate of 3 million tonnes per annum. The plant was upgraded to 4.5 mtpa in 1988 and almost immediately to 6mtpa in 1989. Subsequent debottlenecking resulted in further increases in throughput up to 7mtpa by 1991. The SupergenelBasement Plant was constructed in 1990 and commissioned in early 1991. It was designed to process both copper-gold-silver anomalies within the laterite gold orebody and future hard rock ores. The Supergene plant incorporated control potential s­ulphidisation (CPS) and flotation ahead of CIL to remove a host of copper minerals. It operated in that configuration for 2 years at rates up to 350,000 tpa and average grades of 6.0 git gold and 1.2% copper. Gold recovery averaged 90.7% and copper recovery averaged 80.0% before the flotation circuit was decommissioned in March 1993. Quartz hosted high grade, free milling oxide and basement ores were discovered at the northern end of the orebody in 1990 and now comprise the major feed source to the basement plant. Oxide ores are currently milled at a rate of 550,000 tpa, while basement ores are milled at a 420,000 tpa rate. Metallurgical testwork during the feasibility stages indicated that up to 30% of gold in plant feed could be recovered by gravity separation methods. It was also highlighted that signifi­cant improvements in overall plant recovery and reduced operating costs would be achieved by maximising gravity gold recovery ahead of cyanidation. To achieve this, rec;iesign and upgrade of the gravity circuit was necessary.

Jan 1, 1995

By T. E. Walsh

Introduction I will address two important alternative energy resources, solar and geothermal, with emphasis on their potential application in electric power generation. As a result of this presentation, I hope to leave you with a realistic view of the principal technology options that are being developed or that are available. Solar Types of Collection In terrestrial solar applications, the biggest challenge is to find ways of collecting the sun’s relatively low intensity energy so it can be converted economically to useful thermal or electric energy. Fig. 1 shows that there are both natural and technological ways of collecting solar energy. In nature we find that solar energy aids in the production of biological growth, rainfall, and wind, all of which can, in one form or another, be put to use in the production of heat or electric power. The sun’s rays also are collected and stored naturally in the form of heat in the upper layers of the ocean which can be put to use in the production of electric energy by means of ocean thermal energy conversion (OTEC) approaches. On the technological side, the sun’s rays can be intercepted by materials that directly absorb and convert its energy to low-grade heat, or by mirrors or lenses that focus the rays onto a material to produce high-temperature heat. The higher temperature systems can be used to drive efficient heat engines in the production of electricityy. The sun’s rays also can be collected on photosensitive materials, in either a direct or concentrated form to generate DC electricity directly. The systems I will discuss employ all of these means of collection and conversion, excluding biological and hydroelectric. The former is too ex

Jan 1, 1980

By J. Hoover

Real growth in the economy, increasing demand for electricity, and consumer stockpiling for a possible United Mineworkers of America (UMW) strike in October made 1984 a banner year for coal. Production and consumption climbed to record heights. Precautionary purchases brought inventories close to the peak levels of early 1981 when coal miners walked out for 72 days. Production slowed in the fourth quarter after labor and management concluded negotiations without a walkout. But output in every major coal producing state showed significant gains during the year US coal production totaled 807 Mt (890 million st) in 1984. This is a 13.8% increase over 1983 output. Lower production rates, principally in Appalachia, and sustained demand in the final quarter put downward pressure on coal stocks by the end of the year. Demand All market sectors experienced greater requirements for coal in 1984. Electric utility coal consumption increased 6.3%; exports climbed 4.8%; coke plants consumed 18.9% more coal; coal requirements in the other industrial sector expanded by 11.8%; and consumption in the residential/commercial sector rose 8.1%. Domestic consumption of coal reached a record 718 Mt (791 million st) in 1984. This is a 7.4% gain over the previous consumption high of 668 Mt (737 million st) in 1983. Electric Utilities The 4.6% increase in electric power generation in 1984 was coupled with expanding coal use relative to other energy sources. This resulted in a 6.3% rise in coal consumption, totaling 603 Mt (664 million st) for the year. Thirty-eight of 45 states where coal-fired electric power plants were operating shared in the 36-Mt (39 million-st) increase in electric utility coal consumption

Jan 5, 1985

By Yu. A. Polozov, V. A. Lagunov, O. Yu. Lushinkova, Yu. I. Svirskiy, Eh. Ya. Kipko, Roy A. Williams

1.1 GENERALIZED METHODS OF SUPPRESSING THE INFLOW OF GROUND WATER DURING THE CONSTRUCTION OF SHAFTS, DRIFTS AND TUNNELS Various methods are used to prevent or minimize the inflow of ground water into underground workings during their excavation. The two most common methods include freezing the saturated rock and grouting using cement, sodium silicate, polyurethane and/or other chemicals. Each of these technologies for combatting the inflow of ground water is effective only under specific hydrogeological conditions. For example, although the freezing of saturated ground is among the more universally adopted methods, it is designed to provide only temporary protection during construction. Before the saturated rock thaws it is necessary to emplace a waterproof liner which is labor intensive, time consuming, and expensive. Consequently, freezing is used only in exceptionally complex hydrogeological conditions, namely in those cases where the water-bearing strata consist of unstable rock or the ground water has an anomalous hydrochemistry. The classical grouting of saturated rock, carried out from the surface or from the face of the underground workings for the purpose of limiting the inflow of ground water during excavation, utilizes both cement and a variety of chemical grouts. Cement grouting has been regarded as the main method of combatting the inflow of ground water in fractured rock throughout the world. In such countries as the Federal Republic of Germany (FRG), Canada, the Republic of South Africa and Great Britain, cement grouting is the main method of reducing the inflow of ground water during the excavation of mine openings. In Great Britain and the FRG, cement grouting has been used in 80% of all shaft excavations. In the Republic of South Africa cement grouting has been used in almost 100% of all the shafts that have been constructed. The installation of grout curtains into permeable water- bearing strata significantly reduces their permeability and increases the rock strength. Grouting has the greatest effect in fractured sandstones, certain well indurated shales, fractured granites, fractured quartzites, and karstic limestones or dolomites. The following principal factors must be considered when assessing the expediency of grouting rock with cement: the geometry of the network of fracture openings, the saturated hydraulic conductivity of the fractured rock, the hydraulic head acting on the water in the rock, and the chemical composition of the ground water. On the basis of the geometry of the fractures and the thickness of each hydrostratigraphic unit, the characteristics of the cement grout are selected. As a rule, the cementing of large fractured zones with high ground water velocities is carried out using inert fillers (sand, mill slag, loam, loess, crushed limestone), special types of cement, setting accelerators, and high cement concentrations in water. Calcium chloride, soda ash, sodium silicate, sodium nitrate, amino alcohols, tin bichloride, trisulphate nitrate, and lumnite are used extensively as the setting accelerators for cement grouts. In the FRG and Poland, special cement injection compounds that embody a mixture of cement and active cement metal salts, water additives and binding substances are being used for the cementing of saturated zones with rapid ground water velocities. These reagents accelerate the rate of structure-forming reactions. In spite of the wide variety of additives used for cement grouts, the effectiveness of the method in large fractures below the water table is either poor or it leads to a very large consumption of cement due to the erosion of the grout through the cracks before it hardens. At the present time, a large number of cement types and brands are being produced by various countries. These variations permit cementing to be employed in a variety of geological conditions. However, both pure cement grout and grouts with fillers constitute unstable systems with a high water loss rate. Therefore during the grouting of finely fractured rock the cement grout&apos;s premature loss of a large amount of free water causes its consistency to increase, whereupon the grout solidifies. Consequently, it inadequately penetrates into the fine fractures of the stratum. In addition the high water loss rate in the cement grout causes unreacted cement particles to remain, which greatly reduces the grout hardness and the resulting rock strength characteristics are weakened. As a result, the binding properties of the cement are utilized perhaps up to 60%. The remaining portion is left in the grout as a filler. All these conditions significantly decrease the efficiency of the isolation effort both with respect to strength and cost. In order to expand the cement grouting method, re- search is being conducted to improve the quality of cement grout, to increase its range of application with respect to permeability control, to reduce its water loss rate and to increase its capacity to withstand the erosive and corrosive effects of poor quality ground water. For example, mixtures of bentonitic clay, carboxymethyl cellulose, aerated sodium sulfide, sulphated alcohol distillery waste, nitrolignin, gip-

Jan 1, 1993

By Aurel Goodwin

Remarks of Aurel Goodwin, Chief, Division of Health, Metal and Nonmetal Mine Safety and Health, Mine Safety and fEealth Administration, U. S. Department of Labor, before the Society of Mining Engineers of the AIME, Littleton, Colorado, on October 18, 1979. I appreciate this opportunity to speak before the Society of Mining Engineers of the AIME. The topic of my presentation is the Mine Safety and Health Administrations&apos;s (MSHA) concern and obligations with regard to asbestiform minerals. Asbestiform minerals - the magical group of hydrated, silicate minerals which possess a fiber like structure capable of being woven, like and into cloth. Their unique combination of properties, such as resistance to heat and chemical attack, high tensile strength, and flexibility was recognized centuries before Christ. Pausanias, the early Greek geographer, speaks of golden lamps made about 430 B.C. with incombustible wicks of "Carpathian flax." The Romans used asbestos as cremation clothes to conserve the ashes of deceased persons of rank. Charlemagne had an asbestos table cloth that he used to pass through fire to clean (1). Early recognition of the health hazards associated with exposure to asbestos was documented in the first century by Pliny the Elder, a Roman naturalist, and Strabo, a Greek geographer. Bath wrote of slaves with sickness of the lungs, whose occupation was that of weaving asbestos into cloth. This concern for the health of asbestos workers disappeared over the ages.

Jan 1, 1979

By E. L. Bohnet

The purpose of this paper is to translate a mining company&apos;s "Corporate Objectives" into usable and practical guidelines for long term mine design and production scheduling. These guidelines are required to ensure that both operating and development properties are designed and economically ranked on the same basis, and with the "current" Corporate Objectives in mind. Secondly, if both management and mining engineers have a better understanding of the cause and effect of corporate policies, then penalties and risks associated with various Corporate Objectives can be put into better perspective for management. Corporate Objectives, relative to usable guidelines for either short and/or long term mine planning, could be defined as one or more of the following four objectives: 1) Maximize the recovery of the economic portion of the defined geologic resources, and hence, maximize total non-discounted project cash flows and profits (most common approach in mine design), 2) Maximize the Net Present Value (NPV) of the after-tax cash flows from each existing or proposed project, either on an individual basis or in concert with other projects, including downstream processing facilities (primary method used to judge relative investment merit of a proposed development or operating concept), 3) Limit short and long term capital expenditures to a defined ceiling, 4) Maximize product output for the existing facilities in the short term, or conversely, keep commodity production at a constant level for a series of years.

Jan 1, 1994

By William H. Engelleitner

Agglomeration by balling in cylindrical or shallow pan devices dates back to the early part of this century. The first sintering tests conducted by Dwight-Lloyd on nonferrous ores included a mixing step for ore, flux and fuel carried out in a deep pan device similar to the balling pans, or discs, presently in use. Further work directed mainly toward sintering of ferrous and nonferrous ores always included a preparatory step, usually referred to as mixing, agglomerating or green-balling of the ingredients. In the late forties and early fifties two methods of particle preparation prior to firing were in general use. In Europe the balling pan was used predominantly, both as a mixer and as a pelletizer. In the United States many pilot plants and semi¬commercial plants used balling drums. When the first iron ore pelletizing plants were built in this country, the most frequently used device for green-balling was the cylindrical drum. At the same time, the pan device was used both in Europe and the United States for many other materials such as fertilizer, cement, flyash, alumina and copper concentrates, as well as to mix the feed for sinter machines. The difference between these two balling devices - -the drum and the disc - has been the subject of much discussion and is well covered by several papers included in the 1962 publication "Agglomeration&apos; issued by AIMS, based on their 1961 International Symposium held in Philadelphia. (1)

Jan 1, 1965

By H. Y. Yang, L. L. Tong

For gold recovery, a Chinese refractory, high-sulfur gold concentrate was subjected to biooxidation with high pulp density in a single stirred-tank reactor. The flotation concentrate contained 36.9 percent sulfur (S) and 33.9 percent iron (Fe). Different experimental regimes for biooxidation were applied. With a mixed culture and by controlling the amount of addition of the gold ores and the pH of the biooxidation system, maximum iron oxidation of 82.6 percent and sulfur oxidation of 79.3 percent were achieved. The experimental results indicate that the pH control was beneficial to the biooxidation of this concentrate. Approximately 28.4 percent of elemental sulfur (S8) was found in the oxidizing slags. Two dissolution mechanisms of elemental sulfur are proposed: (1) FeS2 → S80 → S2O32− → SO42− and (2) FeS2 → S80 → SO42−. The high pH had a positive effect on the reduction of the S8. The results of thermodynamic analysis indicate that as an oxidant the dissolved oxygen can effectively reduce the Gibbs free energy of the pyrite oxidation process and, compared with the reaction of ferric iron as the single oxidant, the oxidation of pyrite is easier. The efficiency of the gold recovery was related to the iron oxidation as well as the sulfur oxidation. Gold and silver recoveries of 92.4 percent and 66.4 percent, respectively, were achieved.

By Regis F. Kopac

With the growing dependence on coal as an energy source, finding a means to prevent or reduce the freezing of coal during winter shipment has become increasingly important. Several chemical companies focused on this problem and applied chemical technology to develop suitable solutions. As a result, a number of freeze conditioning agents have been introduced in the past few years, several of which have been highly effective in controlling frozen coal. The efficacy of these chemicals has been well established, however many users have found that only a well defined program will produce acceptable results at a reasonable cost. Positive program results yielding recognizable benefits have caused many power generating and coking plants to consider freeze conditioning agents. A freeze conditioning agent (or FCA) has been defined as a multi-component organic liquid designed to be sprayed on coal particles at bulk shipping points to assure that receiving locations will be able to unload, store and use the treated coal with minimum delay or inconvenience. The chemicals are generally applied at rates of 1 to 2 pints (0.473 to 0.946 liters) per ton and normally function by changing the crystalline structure of water left on the coal during processing. The bond strength of the ice that may subsequently form is markedly reduced. Instead of freezing into solid, unmanageable masses, the coal can be easily unloaded by rotary dumping or the opening of hopper car doors.

Jan 1, 1980

By Isabel F. Barton, Eytan Bos Orent, Mark D. Barton

A new examination of tabular uranium (U)-vanadium (V) deposits within the La Sal district places mineralization in the context of the complex fluid flow history that has occurred in the Paradox Basin and Colorado Plateau. As the only currently producing district of this deposit type in the region, the La Sal district provides excellent opportunities to study deposit- and district-scale features that can serve as exploration guides where exposure is limited. The absence of major structures along a narrow and elongate mineral trend that runs E-W across the southern part of the Utah-Colorado border indicates a regional lithologic control. The trend was likely influenced by Jurassic drainage patterns, as indicated by paleocurrent directions shown in Fig. 1. Fluvial sandstone host rocks in the Jurassic Morrison Formation contain significant evidence of multiple superimposed fluid systems that have progressively changed local mineralogy. Apart from the presence of ore minerals, remnants of fluid systems are preserved as cements including quartz overgrowths, compositionally distinct carbonates, and sheet silicates. New geochronology methods provide constraints on the timing of initial mineralization and later remobilization. U-Pb ages of calcite associated with ore minerals provide evidence for Early Cretaceous mineralization, whereas textures and K-Ar ages show that early-formed V-minerals were replaced at the expense of V-bearing micas and clays during the Eocene. The paragenesis of minerals in U(-V) deposits of the La Sal district reflects the complexity of a sedimentary

Feb 1, 2025

By A. S. Speirs

Over the last few years, the never-ending search for mineral wealth has taken the exploration efforts of Canadian mining companies further and further into the High Arctic and isolated locations where regularly scheduled transportation and communication facilities are nonexistent. Names such as Black Angel, Nanisivik, Asbestos Hill, New Quebec Raglan, Rabbit Lake, and Arvik are today frequently mentioned in mining publications. Twenty years ago, mining in these locations was unheard of, mainly due to logistic problems. However, improvements in the design and use of helicopters, STOL aircraft, and icebreakers in northern areas have helped to overcome these problems, making these locations more attractive to mining companies. Since 1969, when Redpath completed its first Arctic project at Texas Gulf&apos;s Scrathcona Sound property on the northern tip of Baffin Island, Redpath has been actively involved in contracting and engineering projects in three general areas: the High Arctic, Ungava and Greenland. A map showing some of these projects is shown in Figure 1. In these areas, permafrost conditions exist from a depth of 274 metres in Ungava to a depth of approximately 610 metres in the Little Cornwallis Island area, with rock temperatures ranging from -5°C to -13°C. Outside temperatures range from a low of -50°C in the winter to a high of 21°C in the summer. High winds in the winter result in wind chill factors lower than -73°C

Jan 1, 1980

By Duk-Won Park

A new gage for monitoring fractures in underground openings was successfully developed utilizing the reflection photo-elastic technique. The gage may be used to detect crack initiation in mine openings or tunnels so that remedial action may be taken to prevent further deterioration. Fringes concentrated around the cracks were spread by the use of rubber backing. Crack growth as little as 0.003 inch up to as much as 0.1 inch width were detected in this study. Variation of gage materials will provide alternative ranges. The feasibility of the method was tested and calibration was made in the laboratory study. Field study successfully demonstrated the capability of applications in detecting mine roof crack development.

Jan 1, 1982

By Kelly F. Bailey

The issue of regulating non-asbestiform varieties of the amphiboles actinolite, tremo1ite, and anthophyllite to the same degree as asbestos has been studied in detail by the National Stone Association. The ramifications of such a regulation, and the over simplistic regulatory definition of a fiber, are enormous not only for the aggregate industry and its users, but also for the nation. Evaluation of the health, geological, mineralogical, technical, economic and legal issues do not support an "asbestos-like" regulation of non-asbestiform minerals. The adverse consequences of regulating non-asbestiform varieties of actinolite, tremolite and anthophyllite like asbestos would be magnified many times if a similar standard for generic mineral fibers were promulgated.

Jan 1, 1988

By Jonathan K. Hrica, CASSANDRA L. HOEBBEL, Jennica L. Bellanca

Accidents involving powered haulage and mobile equipment like haul trucks are a major safety concern in the U.S. mining industry. They account for more than 50 percent of surface mine fatalities each year [1]. A recent National Institute for Occupational Safety and Health (NIOSH) analysis of 91 fatal incidents identified loss of vehicle control and situational awareness as key contributors [2]. However, the first-hand perspectives of operators are often missing, emphasizing the need for deeper insights into operators’ decisionmaking, lessons learned, sensory cues and mental strategies used during near-miss events. The findings in this analysis will help inform the development of training and safety solutions to prevent or reduce haul truck accidents.

May 1, 2025

By V 9. 0 / 300 dpi

Papua New Guinea (PNG) stretches from the equator to Latitude 12° South and from Indonesia&apos;s Irian Jaya Province in the west to the Solomon Islands in the east (Figure 1). The population totals 3.5 million people who are mostly concentrated in highland valleys on the main island and around the coast. This paper outlines the history of mining, describes the natural, cultural and regulatory setting of mineral discoveries and highlights, by example, some of the more idiosyncratic environ-mental aspects of mining developments in PNG. It concludes with remarks on the progress made in the fifteen years since environmental matters entered the agenda for the establishment of a new mine in PNG.

Jan 1, 1988

By W. E. L. Minter

The most important witwatersrand gold placers occur on extensive unconformity paleosurfaces that were produced during protracted periods of fluvial degradation. The erosional etches on what was generally unlithified substrate indicate that low sinuosity erosion patterns prevailed. The transport systems were dominantly braided fluvial with a minor debris-flow component. The placer sediments were non-cohesive sands and gravels which were evidently transported by fluctuating, yet perennial, discharges across extensive, low relief, bra1dplains, not far from littoral environments. Progress made in understanding heavy-mineral transport processes now emphasizes the importance that selective entrainment probably had in producing concentrations. Cognizance that these characteristics are not unique to the Witwatersrand should be taken into account when designing exploration models.

Jan 1, 1988

By W. H. Reck

he need in the mineral industry to treat increasingly larger tonnages has caused a demand for larger installations. In order to limit the size of these installations, it was necessary to build machines with larger capacities or production output. With this aim in mind, WEMCO Division developed the No. 120 WEMCO-Fagergren Flotation Cell in 1967. These large cells have been compared to conventional smaller cells from the standpoint of metallurgical performance, investment costs, power requirements and maintenance requirements in many plants throughout the world. Figure 1 illustrates the size difference of the No. 120 when compared with the No. 66. All results to date indicate the large No. 120 cell surpasses the smaller machines in all categories.

Jan 1, 1969

By John P. Norton

Microcystaline silica has been mined in Illinois from the Clear Creek formation since the turn of the century, especially in the area around Tamms in Alexander County, in the southernmost part of the state. Production of this silica, consumed mainly by the abrasives and coatings industries but also sought after for many filler/extender uses, has grown with the economy with several new applications overshadowing traditional markets in recent years. Such an important commodity was given the early attention of the Illinois State Geological Survey and a very complete report was issued in 1953 (Report of Investigations No. 166), authored by J. E. Lamar. The mining and processing of the silica ore has changed very little since the first reported production in 1906, although emphasis has been placed on the production of the finer sized grades to meet newer market requirements. Industrial Mineral Notes 40, published by the Illinois State Geological Survey in June 1970, describes a method by which a less than 1-micron fraction could be commercially produced from the readily available finest commercial grade presently being marketed (99% minus 10 microns). The finer grades exhibit to a lesser degree the reinforcement, high flatting efficiency, thickening and dry brightness properties associated with the synthetically produced silicas. It is expected that the extremely fine grades of microcrystaline silica will become accepted in the markets that now use a combination of precipitated silica and less expensive extender/filler minerals such as kaolin or calcium carbonate.

Jan 1, 1976