Search Documents

By Craig M. Sams

Phosphate mines in Florida are continuing to encounter higher dolomitic content host rock with the phosphate pebbles(1) necessitating a change in grinding conditions and/or circuits, One of these changes is to install hydrocyclones and close circuit the mill as opposed to the traditional open circuit grinding plant. Close circuiting of the grinding mill with hydrocyclones allows one to take advantage of reduced process mill power requirements by circulating the coarse mill discharge back into the mill for multiple chances of particle breakage. Additionally, as in this case, the hydrocyclones de-slime the pebbles, allowing for more efficient use of grinding power by reducing the amount of dolomitic material recycled to the mill.

Jan 1, 1986

By A. B. Phillips

The Randfontein Estates Gold Mining Company (Witwatersrand) Limited (REGM) operates three metallurgical complexes for the recovery of gold from the Witwatersrand Gold Reefs at the town of Randfontein, 40 kilometers west of Johannesburg. Mining operations in the. area commenced in March 1889 and ceased temporarily in 1965 when the viable ore reserves had been depleted. Exploratory drilling in the 1960's indicated viable deposits of gold in the Elsburg reefs, south of the Witpoortjie Horst Block, _which formed the Southern limit of the previously exploited areas. Three shaft complexes have been established to exploit this area, known as the Cooke secti'on. In 1983 the Doornkop shaft was sunk to the north of the Cooke section to mine Kimberley reef and the South reef.

Jan 1, 1992

By A. L. Mular

Introduction The cost of grinding may be divided into a fixed equipment cost portion and an operating cost portion. The fixed equipment cost is the amount of money required to purchase the grinding mill itself. This amount may be kept separate from the installation cost which, often, is taken as a percentage of the fixed equipment cost. A good average is 43%; therefore a $100,000 ball mill would cost approxi¬mately $143,000 installed. Operating costs are variable and paid per unit time for power, liner replacement, grinding charge replenishment, labor, and mainte¬nance including major parts replacement. Such costs depend on the geographical location and will vary with the cost of labor. Operating costs are difficult to estimate. Most mining companies consider such information proprietary. This section provides a means to obtain an estimate of the equip¬ment cost of a grinding mill with a rated accuracy of±l0%. Compara¬ble methods to determine operating costs are not available. Such costs are presented in table form with suggestions for updating them. Esti¬mating the cost of liners and steel replacement is possible as described in a later section. Capital Costs of Grinding Mills Grinding mill costs have been related,124 by means of equations and corresponding graphs, to the nominal horsepower requirements of mills. All graphs are based on a Marshall and Stevens cost index for Mining and Milling of 300, where a cost index is a ratio used to estimate current prices of equipment from obsolete prices. Where (Cost Index Now) Cost Now = (Cost Then) (Cost Index Then) (I) For example, the cost of an autogenous mill that requires a 3000¬hp motor is estimated as $500,000 (Fig. 95). This was the estimated price when the M&S (Marshall and Stevens, Mining and Milling) cost index had a value of 300. If the index is currently at 400, then the estimated current price of the autogenous mill is: Cost Now = ($500,000) (400) (300) = $667,000 Most professional journals will publish current values of cost indices at least once a month. In subsequent pages, each graph of grinding mill cost vs. mill horsepower has an associated graph of capacity vs. horsepower along with a table that relates mill size to horsepower. The associated graph and the table must be used with caution, since both apply to an average ore under average conditions. Example calculations showing how graphs should be used are shown in the following. It should be stressed that the cost data incorporated herein ex¬cludes the cost of pumps, motors, lines, and classifiers, unless other¬wise stated. Costs are not direct quotes; they are the averages of quotes supplied by manufacturers and analyzed by means of regression analysis. Example 1. Calculate the power required to grind 100 tons of dry solids per hour (in a closed circuit with a classifier) when the

Jan 1, 1985

By J. Lovering, H. Wilhelm, P. Siewert

Introduction The Afton property is located 290 km (180 miles) by air east-northeast from Vancouver and 14 km (8.7 miles) west of Kamloops, a city of 60,000 people, in south central British Columbia, Canada. The mine is adjacent to the Trans-Canada Highway at an elevation of 670 m (2198 ft) above sea level. The ore body is a porphyry copper deposit that has undergone supergene alteration. The major economic minerals in the supergene zone are native copper and chalcocite with chalcopyrite and bornite in the hypergene areas. The grade is 1% with an overall copper distribution - 70% native, 25% chalcocite, and 5% chalcopyrite with bornite and covellite. The ore also contains important but variable amounts of gold and silver. The mill was designed to treat 6350 t/d (7000 stpd). Semiautogenous grinding was selected to minimize capital cost and because of the expected high clay content of the ore, which would have caused problems in a conventional crushing and screening plant. Test work indicated that a recovery of 87% was possible in a circuit incorporating both flotation and gravity separation. Flowsheet Run-of-mine ore is crushed in a 1.06 x 1.65-m (3.5 x 5.4-ft) Allis Chalmers gyratory crusher set at 228.6 mm (9 in.), closed side setting. The surge pocket, below the crusher, is emptied by a Hydrastroke feeder onto number one conveyor, which discharges onto a 180,000-t (198,416-st) coarse ore stockpile. Six Hydrastroke feeders on two conveyors withdraw the crushed material from the bottom of the pile. These two conveyors, in turn, discharge onto the belt feeding the semiautogenous mill. The live storage in the stockpile is approximately 22,000 t (24,250 st), sufficient for three days' mill feed. Primary grinding is accomplished in an 8.5-m (28-ft) diam by 3.7-m (12-ft) long Koppers (Hardinge Cascade) mill (Fig. 1) containing a 10% ball charge and driven by a 4000-kW dc variable speed motor. The mill dis¬charge is pumped by a 10 x 12 G.I.W. pump to a 1.22 x 4.88-m (4 x 16-ft) stationary screen sloped at 20°. Screen oversize returns to the semiautogenous mill (SAM), and the undersize flows by gravity to the ball mill discharge pump box. Secondary grinding is performed in a 5-m (16.4-ft) diam by 8.84-m (29-ft) Koppers overflow ball mill driven by a 3430-kW synchronous motor through an air clutch. The mill is in closed circuit with a Krebs Cyclopac containing 10 635-mm (25-in.) cyclones and the cyclone overflow, at 35% solids and 65% to 70% -200 mesh, is flotation feed. In order to limit the buildup of native copper, circulating in the secondary grinding circuit, a portion of the underflow from the cyclones is processed in a circuit containing screens, cyclones, and shaking tables to produce a finished metallic copper concentrate. Primary mill variable speed drive The overall waste to ore ratio at Afton was 4.5:1. The mining was to be done with only three shovels, which meant that it was highly unlikely that more than one of them would be in ore at any one time. The resulting inability to blend the mill feed made it impossible to prevent wide swings in the grade and grindability. The variable speed do drive motor installed on the semiautogenous mill was selected because of the extreme variability of the Afton ore body. This variability has persisted throughout the lifetime of the mine. There are times, however, when due to ore conditions, the mill is operated at full speed (78% of critical) for extended periods of several shifts duration. There are other times when the mill speed may be changed several times in a 12-hour shift due to changing ore conditions. When ore is processed that contains a fairly large proportion of fine native copper, the primary mill speed and, consequently, the tonnage may be reduced to improve the secondary grind and to maintain an acceptable grind and recovery. High clay ores require less mill speed and more dilute grinding densities. In the latter case, the slower primary mill speed also helps to minimize damage to the mill liners. Approximately 57% of the time the mill operates between 90% and 100% of full speed or between 71% and 78% of critical. The variable speed is also used for inching during mill relines.

Jan 1, 1987

By John Lovering

The Afton property is located 180 air miles East-Northeast of Vancouver and nine miles West of Kamloops, a city of 60,000 people, in South Central British Columbia, Canada. The mine is adjacent to the Trans-Canada Highway at an elevation of 2,200 feet above sea level. The orebody is a porphyry, copper deposit that has undergone supergene alteration. The-major economic minerals in the supergene zone are native copper and chalcocite with chalcopyrite and bornite in the hypergene areas. The grade is one percent with an overall copper distribution: 70% native, 25% chalcocite and 5% chalcopyrite with bornite and covellite. The ore also contains important, but variable amounts of gold and silver.

Jan 1, 1985

By J. T. Winkelmann

The Mineral Park Mine is an open pit copper-molybdenum mine located in northwestern Arizona, approximately twenty miles northwest of Kingman, Arizona. The concentrating facility has been regarded, with the expansion in 2011, as a plant capable of treating fifty thousand short tons of feed per day for the mixture of supergene and hypogene ores available. The grinding circuit consists of two 32? x 14? SAG mills and four 20? x 28? ball mills. As ores became harder with greater depth in the adjacent pit areas, however, the SAG mills became severely throughput limited. The traditional treatment for similar properties is the installation of a recycle pebble crushing circuit. Because the cost of such an installation is quite elevated, and preliminary testing and research was inconclusive regarding the predicted throughput increases, management and technical personnel set out to find another solution to the problem. The result entailed a redesign of SAG lifters/liners and a nearly unique circuit change which was, at best, a difficult step that defied current grinding logic. This paper describes these changes, events leading up to them, and the results.

Feb 23, 2014

By M. D. Baker

Coal-water slurry preparation requires fine grinding and cleaning of coal by flotation. Finer grinding leads to increased ball wear and its effect on the surface properties of coal becomes of concern. Marked ball wear tests were performed to study the effects of oxygen, pH, the soluble species of coal and the addition of pyrrhotite on ball wear. The synergistic action of coal and oxygen greatly enhanced the corrosion of mild steel balls during grinding. Electrochemical measurements on a mild steel electrode in coal slurries and SEM observations of grinding ball surfaces were carried out to explore the corrosive wear mechanism.

Jan 1, 1989

By Vathsala Rajagopal, lwao lwasaki

The grinding media materials for the mining industry require corrosion and abrasion resistance properties not only to minimize the wear but also to improve the flotation recoveries of sulfide minerals. The media wear mechanisms and the factors influencing the grinding ball wear during grinding are discussed with respect to abrasion, corrosion and impact wear of grinding media materials. Interactions between the grinding media and sulfide minerals in a ball mill adversely affect the floatabilities of the ground minerals. The possible galvanic interactions between grinding medium-mineral and their effects on the flotation responses of sulfides are also reviewed. The selection criteria for alloy composition that reduces the overall wear along with adverse effects on flotation are brought out.

Jan 1, 1992

By D. C. Dahlin, W. K. O’Connor, G. E. Rush, C. A. Summers, S. J. Gerdemann

The Albany Research Center (ARC) conducted studies of mechanical activation by conventional and ultra-fine grinding techniques to enhance olivine reactivity in mineral carbonation reactions. Activated olivine is one of several solid feed materials used at ARC in reactions with carbon dioxide to form carbonate minerals. This paper compares grinding techniques via energy demand data and product characteristics, including particle size distributions, surface areas, full width at half maximum (FWHM) XRD analyses, and particle morphology by SEM analyses. Reactivity was gauged by percent conversion to carbonate in subsequent carbonation tests.

Jan 1, 2004

By S. McTavish

Since mechanically suitable grinding mills were available in 1908, mill operators have been searching for the best material and design with which to line the mills. These liner systems had to fulfill several criteria. First and foremost they had to last long enough in an operating mill to protect the mill structure from the abrasive wear of the ore and the grinding media. In addition they had to be able to efficiently transfer the energy from the mill to the mill charge in order to facilitate the grinding process. The liners also had to be easily attached to the mill when new and removed from the mill when worn out. The first liners used were generally made of cast white iron, Hadfield manganese, unalloyed high carbon steel and composites of steel and concrete or cemented in flint blocks or natural stone. 1

Jan 1, 1989

By N. Arbiter, C. C. Harris

The economic advantages of large diameter ball mills can be compromised by unexpected capacity limiting conditions. These arise because media rotational flow to ore axial flow ratios, and the number of mill revolutions that ore is subjected to during residence, are both inversely proportional to mill diameter. Because of this, mixing efficiency and grinding kinetics may decrease and become capacity limiting when mill diameters reach a critical range. There are two possible scale-up problems involved in the design and use of mineral processing machinery: • Selecting the size and operating conditions for available larger equipment, to insure that operating results will match those obtained with smaller units; or •Extending the size ranges of equipment beyond existing limits. Previous research at Columbia University into flotation machine hydrodynamics has demonstrated the importance in scale-up of internal flow relationships; these perform a similar role in grinding (Arbiter and Harris, 1980).

Jan 1, 1982

By D. W. Fuerstenau, G. S. Sudhir, P. C. Kapur

Quartz-limestone feed mixtures were ground in a laboratory-size, choke-fed, high- pressure roll mill. As compared to individually ground minerals, the harder component (quartz) in the product mixture is coarser, and the softer component (limestone) is finer. An energy split index is introduced for quantifying the disproportionate split of the mill energy between the feed constituents. This index is incorporated into a grinding kinetic model for simulation of the product size distributions of the mineral components as a function of energy input to the mill. The self-similar character of the size distributions is analyzed and an energy-size reduction relationship for the roll mill is highlighted.

Jan 1, 1992

By L. F. Moran

Rod Mill Grinding is an important and fundamental step of the concentrating process in Marcona Mining Company's plants at San Nicolas Bay, Peru. This Paper summarizes experience in regard to consumption and specifications of grinding rods based on twelve years operation of the grinding circuits. Marcona operates a Plant complex producing 10 million tons per year of beneficiated iron ore products including pellets, sinter feed concentrates, high grade concentrates as slurry and filter cake. Processing capacity is 15 million tons per crude ore per year of which 13 million are around in rod mills. A continuous testing program was carried out over the years. Initial studies of daily production operations gave indications of poor grinding rates in relation to mill size and power consumption, with a high rate of broken liners and rods. The broken nieces of rod were not automatically expelled and further interfered with grinding efficiency, while replacement of liners caused unwarranted do n tire. Objectives were to improve all phases of the Process by studying the effects of changes in rod diameter, length, alloy constituents, and volume and weight of rod charge.

Jan 1, 1975

By Norbert Patzelt, Johann Knecht

Future ore reserves of major gold producers in North America and elsewhere will consist of refractory gold ores. About 60 % of the current U.S. gold production is mined in Nevada. Several of the large gold operations in this state indicate that 40 to 90 % of their future ore feeds will contain refractory gold. To com­pound problems, average head grades for refractory U.S. gold ores had fallen from 8 - 9 g/mt to about 4 g/mt by 1991. In Latin America, 52 % of the gold operations will require milling for optimal recovery. Deeper reserves are, like in North America, refractory. Therefore a special treatment process is needed in order to allow for the gold ore to be leached downstream in a conven­tional cyanidation process for a high gold recovery. There are several options available for this oxidation process like treat­ment of the gold bearing ore in pressure oxidation, in a biooxi­dation or in a roasting plant depending on the reason for the refractoriness. If organic carbonaceous matters and sulfides are the prima­ry reasons for the refractoriness, whole ore roasting is a pre­ferred method for the treatment of this type of ore. Since dry ore is to feed to the roaster, a dry grinding mill is advantageous. For the dry grinding system, the moisture content and the ore char­acteristic is of importance. Those parameters decide the mode of the grinding system. For autoclave systems common wet grind­ing systems can be applied. This paper deals with technical aspects for dry grinding plants and gives an outlook on and pos­sibilities for new grinding systems.

Jan 1, 1996

By Dominic F. Howarth

Groove deepening (deepening of a groove in rock by successive passes of a rock cutting tool) is a potential operational feature associated with tunnel boring machines. Little research has been undertaken in this area which is of direct practical relevance to the design and application of tunnel boring machines. Laboratory experiments using single, double and triple disc arrays have revealed an important fundamental cycle of events associated with disc cutters when progressively deepening a groove. Furthermore, in contrast to pick cutters, groove deepening by discs is shown to be an efficient operation. This can be directly attributed to the increased interaction between disc cutters due to the increase in magnitude of lateral forces generated as a groove is deepened.

Jan 1, 1981

By Marc Carriere

Bright-orange couplings adorning piping systems are a common sight in just about every underground mine in North America. Grooved mechanical piping, the pipe-joining system that utilizes these couplings, is the preferred method for joining underground and plant piping systems in the mining industry, due to the ease and speed of installation and maintenance. However, the applications for such systems have traditionally excluded high-pressure systems. Most grooved mechanical couplings have a moderate working-pressure limitation, so high-pressure systems have required the use of alternative joining methods, typically heavy-duty flanges. However, the introduction of high-pressure couplings (up to 4,000 psi) has made the grooved joining method viable, and even preferable, for backfill, deep-mine chilled water and dewatering lines and other high-pressure piping applications. As engineers explore the use of high-pressure couplings, questions will undoubtedly arise about the joining method?s capabilities. This article will address the capabilities and specifications of high-pressure couplings, and compare flanged and grooved mechanical pipe joining in traditional as well as high-pressure underground mining applications.

Jan 1, 2011

By Alexander I. Feldman, Michael S. Kucker, Robert A. Robinson, Harvey W. Parker

An extensive geotechnical monitoring program was used to assess ground and liner behavior, provide input to a Disputes Review Board, and verify design assumptions during construction of the Mt. Baker Ridge Highway Tunnel along I-90 in Seattle, Washington. The stacked-drift tunnel liner was constructed with twenty-four 2.9 m diameter concrete-filled drifts forming a semi-flexible compression ring, followed by excavation of the 19.4 m diameter soil core. Instrumentation data was used for monitoring hillside stability, liner deflections and loads, impacts on adjacent highway tunnels, for back analyzing soil properties, and for helping to limit construction-induced settlements to about 6 cm.

Jan 1, 1987

By Michael S. Kucker, Robert A. Robinson, Harvey W. Parker

Ground deformations are of major concern during tunneling, especially in downtown environments, since they have a significant impact on the costs and practicality of tunneling. This case history describes soil and groundwater conditions and ground behavior during the construction of twin transit tunnels for the Downtown Seattle Transit Project (DSTP). The tunnels were excavated through complex glacial soils ranging from hard glaciomarine drift to flowing sand. The tunneling process was greatly facilitated by the prediction of soil layer positions to an accuracy of ±0.6 m (2 ft). Tunneling was complicated by the presence of over 500 temporary tiebacks and by disturbed ground overlying an operating railroad tunnel. A variety of ground improvement techniques were used to successfully minimize settlements, which ranged from 1 cm (0.4 in.) in glaciomarine drift to 6 cm (2.4 in.) in flowing sands. Ground improvement techniques included compaction grouting, chemical grouting, jet grouting, and eductor well systems.

Jan 1, 1991

By R. J. Pruett, P. I. Prescott

Ground calcium carbonate (GCC) is used in the paper, plastics, paint, rubber and caulks and sealants industries. The favorable properties of GCC include high whiteness and brightness, low hardness and outstanding rheology in water systems. The quality of calcitic GCC ores, which includes chalk, limestone and marble, is dependent on calcite purity and the nature and quantity of the impurity minerals. Wet and dry grinding are used in the processing of GCC. Ore processed by optical sorting, flotation and/or particle-size classification has higher brightness and lower abrasion characteristics. GCC markets are a function of the product's properties, purity and cost.

Jan 1, 1997

By P. I. Prescott

Ground calcium carbonate (GCC) is used in the paper, plastics, paint, rubber, caulks, and sealants industries. The favorable properties of GCC include high whiteness and brightness, low hardness, and outstanding rheology in water systems. The quality of calcitic GCC ores, which include chalk, limestone, and marble, is dependent on calcite purity and the nature and quantity of ancillary minerals. Wet and dry grinding is used in the manufacture of GCC. Ore processed by optical sorting, flotation, and/or particle size classification has higher brightness and lower abrasion. GCC markets are a function of the product's properties, purity, and cost.

Jan 1, 1995