Mineral Processing Engineering

Methods of Mining Metals

This report summarizes mining practices of a large number of metal mines in the United States and foreign countries. The adaptation of mining methods best suited to the various natural conditions in mines is discussed, and comparative costs are presented. The basic data—gathered in the field by Bureau of Mines engineers and consultants in cooperation with mine operators—have been published in a series of information circulars dealing with practices and costs at individual mines and ore-dressing plants. The data have been made comparable by adhering to a standard form of presentation in the individual reports.

The first circular was issued, 250 dealing with mining and milling of metallic ores had been published. Of this number, 164 deal with operations at individual mines and plants—94 with mining only, 59 with milling only, and 11 with mining and milling. Eleven circulars are summaries, each covering a particular mining method, and 53 are discussions of separate operations involved in mine operation or deal with special phases of mining. Seven of them treat special ore-dressing and allied subjects, and 15 arc a part of a mineral-industries survey by counties or districts, in which many individual properties are described and costs and other data are presented. Earlier

By David| 2017-04-17T11:24:59+00:00 March 17th, 2017|Categories: Methods|Comments Off

Grinding Mill Design & Ball Mill Manufacturer

All Grinding Mill & Ball Mill Manufacturers understand the object of the grinding process is a mechanical reduction in size of crushable material. Grinding can be undertaken in many ways. The most common way for high capacity industrial purposes is to use a tumbling charge of grinding media in a rotating cylinder or drum. The fragmentation of the material in that charge occurs through pressure, impact, and abrasion.

Grinding is converting energy: When the grinding charge is forced to tumble the motor energy is converted into new particle surface and heat.

An important point for the economy is that the size of the grinding media suits the material to be ground.

The choice of mill design depends on the particle size distribution in the feed and in the product wanted. Often the grinding is more economic when executed in a primary step, followed by a secondary step, giving a fine size product.

As experts in crushing and grinding – can offer a full range of grinding mill types and sizes. Our mills are identified by codes of letters:

C=central trunnion discharge
P=peripheral discharge
R=spherical roller trunnion bearing, feed end
H=hydrostatic shoe bearing, feed end
R=spherical roller trunnion bearing, discharge end
K=ring gear and pinion drive

CRRK

By David| 2017-04-28T00:08:53+00:00 February 20th, 2017|Categories: Crushing & Screening|Comments Off

CuSO4 Copper Sulfate Crystallization

CuSO4 Crystallization for Typically Acidic Extraction: A small body of acid-leachable copper ore or a small existing stream of copper-bearing acidic mine water is often unable to justify a plant to produce cathode copper. Electrowinning is capital intensive, and small reserves are generally considered higher risks for financing. Electrowinning is also intensive in electric power and labor, both of which are in short supply to

small operations in remote locations. The market for cathode is a large one, and small quantities may not bring the full market price. Many operators stay with the cementation process for these reasons, paying high prices for iron and getting low prices for cement copper, despite the feasibility and attractiveness of SX on a small scale.

Production of copper sulfate as an end product is an alternative. SX strip liquor is a good feed to crystallization, which may be accomplished in simple vats. Figure 3 and Table III describe this possibility. The flowsheet basis is 24 tons per day of copper sulfate pentahydrate. The SX stripping solution and strip liquor are appropriate for LIX 64N, or a somewhat stronger (more acidic) extractant if required.

By David| 2017-06-20T09:12:12+00:00 June 18th, 2017|Categories: Electrometallurgy|Comments Off

Waste Mine Tailings Characterisation

Any critical evaluation of the potential for contamination of groundwater by leachates from mining wastes must include consideration of the waste quantities and locations, the physical and chemical characteristics of the waste, and the waste disposal practices. The primary types of solid wastes generated by mining activities include overburden and waste rock from surface mining, waste rock from underground mining, bulk tailings from the milling of metal ores and non-metal minerals, and refuse from coal preparation-plant processes.

In the United States, more than 65 commodities, including coal, metal ores, and non-metal minerals, are presently mined.

In the remainder of this section, the amounts of wastes generated during the past 20 years are quantified on a regional and mineralogical that is, commodity) basis. Then, the character of these wastes is presented to describe the amounts of acid-forming or toxic-product-forming components they contain, finally, the waste disposal practices commonly employed in the mining industry are reviewed, with emphasis on the extent to which these practices favor or inhibit the formation of an acid or toxic leachate.

Quantities of Wastes Generated

Bases for Estimates

Waste-quantity estimates presented in this report were either taken directly from or estimated on the basis of data and information published in the Bureau

By David| 2017-06-16T15:24:04+00:00 June 16th, 2017|Categories: Environment & Tailings|Comments Off

Mine Tailings Disposal Methods

As discussed previously, the primary types of solid wastes generated by the mining industry are overburden and waste rock from surface mining, waste rock from underground mining, bulk tailings from metal-ore and non-metal mineral beneficiation and milling processes and refuse from coal preparation-plant processes. The methods commonly employed for disposal of these wastes in each of the industry segments (that is, coal mining and metal-ore and non-metal mineral mining) are described below.

Mining Coal Tailings Disposal

As has been pointed out earlier in this section, immense quantities of wastes are produced by coal mining activities. Many of the regulations governing these wastes have only recently been enacted, and the Surface Mining Control and Reclamation Act of 1977 (PL 9587) will be a major factor influencing coal mining waste management in the future. The discussion of coal mining waste disposal practices which follows is organized by waste type, since the practices commonly employed are a function of this factor.

Overburden

Overburden from surface coal mines consist of soils, gravels, shales, coaly shales, and other unconsolidated material and, occasionally, some bedrock which overlies the coal seam. Surface mining is conducted by two basic methods: contour strip mining and area mining. Contour strip mines are used in

By David| 2017-06-16T15:11:23+00:00 June 16th, 2017|Categories: Environment & Tailings|Comments Off

Mine Tailings Waste Leaching & Groundwater Contamination

Each year the mining industry generates tremendous quantities of solid wastes as a byproduct of the mining and concentration or preparation of valuable ores, minerals and coal. In addition, the quantities of these wastes generated on a yearly basis is increasing due to:

increased production resulting from rising demand,
the depletion of near surface high-grade ores which makes necessary the mining of lower grade ores at greater depths,
changing mining methods, and
the promulgation of strict emission standards which ultimately require more extensive cleaning of coal.

Inherent to the disposal of mining wastes on land is the potential for groundwater contamination due to the leaching of these wastes by rainwater.

It is evident that the crushing and grinding of mined material during extraction or preparation processes and subsequent disposal of process wastes in surface disposal areas creates conditions which are favorable to the rapid weathering of these wastes. These conditions are especially favorable to the accelerated oxidation of pyrite and subsequent production of acid. This, in turn, may accelerate the rate of leaching of trace metals contained in mining wastes. The rapid release of acid and metals from mining wastes by natural leaching processes, therefore, presents a great potential for the contamination

By David| 2017-06-16T15:28:17+00:00 June 16th, 2017|Categories: Environment & Tailings, Hydrometallurgy|Tags: 980|Comments Off

Shredded Automobile Scrap Recycling

The Bureau of Mines is involved in research directed toward the utilization of municipal solid waste. One of the primary objectives is the recycling of the magnetic fraction of municipal solid waste (raw refuse). This is consistent with one of the Bureau’s goals, which is to minimize the requirements for mineral commodities by maximizing metals recovery from secondary domestic resources.

In this investigation, cupola trials were made using combinations of refuse scrap with shredded automobile scrap under basic and acid slag practices. Furnace operating information and the behavior of alloying and tramp elements was obtained. The research showed that it is possible to utilize up to 60 percent refuse scrap in the cupola under basic practice and 30 percent under acid practice. Aluminum in refuse scrap, present in bimetallic cans, increased the recoveries of silicon and manganese charged to the cupola. Increased use of refuse scrap provided iron of lower sulfur. The alumina resulting from oxidation increased the slag volume. The aluminum and tin contents of the iron increased with increasing levels of refuse scrap in the charge. Lead was not a problem with respect to contamination of the iron, in basic practice, operation of the cupola was satisfactory since

By David| 2017-06-16T12:05:30+00:00 June 15th, 2017|Categories: Magnetic|Tags: 980|Comments Off

Hydrothermal Boehmite Precipitation

The currently proposed method for the recovery of alumina from nonbauxitic materials involves acid leaching (Figure 1). Primary emphasis is on kaolin clays. To date, leaching by nitric acid, hydrochloric acid, and sulfurous acid has been considered, and it appears that leaching with hydrochloric acid (25-27%) is the most practical process. The first step in the overall process (Figure 1) is to decompose the hydrated aluminum silicate ore to meta kaolin (silica and acid-soluble alumina) by calcination at 700° to 800°C. This calcined materials is then leached with HCl to extract aluminum as dissolved Al3+. The undissolved solids are separated from the process stream, and the solution is purified of iron by organic solvent extraction. The aluminum content of the fluid is then precipitated as AlCl3·6H2O by evaporation or by sparging the solution with HCl gas. Then the aluminum chloride hexahydrate is decomposed into alumina and HCl by calcining at high temperature. This process releases HCl, which is then recirculated for leaching of fresh ore and for crystallization.

The thermal decomposition of aluminum chloride hexahydrate is energy intensive. Hence, an alternative process in which aluminum hydroxide or oxides are precipitated from the aluminum chloride solution, if realizable, would be a technically

By David| 2017-06-15T14:23:11+00:00 June 15th, 2017|Categories: Pyrometallurgy|Tags: 980|Comments Off

Copper Nickel Flotation

The Bureau of Mines investigated the flotation responses of two copper nickel ore samples from the Duluth Complex with the objective of recovering bulk sulfide concentrates. One of the ores studied was taken from a test pit; the other was taken from a test shaft. The samples were quite similar except that the pit sample analyzed 0.35 pct Cu and 0.11 pct Ni and the shaft sample analyzed 0.69 pct Cu and 0.14 pct Ni. Flotation responses were studied in both laboratory and pilot plant tests.

Pilot plant flotation responses were similar for both samples resulting in grades of 12.2 pct Cu and 2.5 pct Ni for the pit sample and 12.2 pct Cu and 2.1 pct Ni for the shaft sample. Weight recoveries were 2.5 pct for the pit sample and 5.2 pct for the shaft sample. Copper and nickel recoveries for the pit sample were 87 and 62 pct, respectively, and 92 and 73 pct for the shaft sample. Both concentrates contained small but significant values of cobalt and precious metals. Cobalt recoveries were low—less than 40 pct for both concentrates. Precious metals contents of the concentrates were 1.59 oz/ton for the pit sample and 0.99 oz/ton for the

By David| 2017-06-15T14:15:49+00:00 June 15th, 2017|Categories: Flotation, Laboratory Procedures|Tags: 980|Comments Off

Clay Flocculant

Under its mission to effect pollution abatement, the Bureau of Mines began intensified research seeking means for economically disposing of the large amounts of Florida phosphatic clay wastes and reclaiming the mined land. The clays, which are discharged from the processing plants at about 3 to 5 pct solids , have colloidal characteristics and are difficult and slow to dewater by natural settling. The quantity of water retained and stored with them is so great that impoundment in above ground, dammed storage areas is required. Boyle has estimated that one processing plant produced 4 million tons of phosphatic clay wastes per year, and Vasan has estimated that about 2 billion tons of clay wastes are stored behind impoundment dams. The stored suspensions represent a serious potential danger for pollution to the land and aquatic environments of the area because of possible dam failure.

The Bureau of Mines is developing a method for dewatering the suspensions of clay wastes using polythylene oxide (PEO) as a flocculant. Polyethylene oxide can act as a bridge between colloidal particles causing agglomeration that results in rapid separation of clays from water. Once the water is released from the agglomerates, it is removed immediately by mechanical means.

By David| 2017-06-13T13:28:10+00:00 June 13th, 2017|Categories: Environment & Tailings, Reagents & Chemicals|Tags: 980|Comments Off

Cyanide Destruction in Gold Heap Leach

In the past 25 years there has been a wide expansion of the use of cyanide heap leaching by the mining industry. This process allows profitable recovery of gold and silver from low-grade ore. Heap leach pads are constructed on slight drainage grades and lined with an impervious clay and/or geotextile. Ore is stacked and leached in successive lifts or benches on the pad. Sprinkler systems set within and on the surface of the lift to be leached deliver a high pH sodium cyanide solution that, in its percolation through the ore, forms stable complexes with gold, silver, cobalt, iron, copper, nickel, zinc, and cadmium. This pregnant solution is collected as it drains from the pad for precious metal recovery.

After leaching, the heap still contains interstitial and adsorbed cyanide species, including free cyanide and metal-complexed cyanides. The metallo-cyanides are present as weak acid dissociable (WAD) complexes of cadmium, copper, nickel, and zinc, and extremely stable iron and cobalt cyanide complexes (Smith and Mudder 1991). These cyanides have the potential to degrade surface and ground water resources.

The Montana Water Quality Act directs the Montana Department of Health and Environmental Sciences (MDHES) to maintain standards for pollutants. The standards are referenced by

By David| 2017-06-13T07:44:19+00:00 June 13th, 2017|Categories: Environment & Tailings, Hydrometallurgy|Comments Off

Heap Leaching Agglomeration

We investigated a particle agglomeration technique for improving the flow of leaching solution through heaps of clayey or crushed, low-grade gold-silver ores, wastes, and tailings. This technology has been adopted on a broad scale by the precious-metals-processing industry. This report presents information on five commercial operations that have benefited from agglomeration technology and that represent a cross section of current heap leaching practice. The technology is cost effective because of decreased leach times and improved precious metal recoveries.

Exploration identified numerous low-grade precious metal deposits, mine waste materials, and tailings piles throughout the Western United States. The increase in precious metal prices during this period generated interest in processing these low-grade feed materials by low-cost heap leaching technology. Heap leaching with cyanide was applied to many of the materials; however, many conventional operations were unsuccessful because excessive amounts of clay in the feed or fines generated during crushing prevented a uniform flow of cyanide solution through the heaps.

As part of its research program to improve the recovery of gold and silver from low-grade domestic resources, the Bureau of Mines investigated agglomeration pretreatment to overcome the percolation problems associated with heap leaching. Agglomeration of the clays and fines before heap building permitted

By David| 2017-06-13T07:34:59+00:00 June 13th, 2017|Categories: Hydrometallurgy|Tags: Heap Leaching|Comments Off

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