Mining

MINING ENVIRONMENTAL MANAGEMENT: 

MINING ENVIRONMENTAL MANAGEMENT Worker safety and comfort and the underlying principles

Slide2: 

Fascinating Minerals

Slide3: 

Efforts to Mine Gold

Slide4: 

Relative Values of Metals, April 2007

Slide5: 

Gold Bullion

Slide6: 

Gold Producing Countries

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Open cast mining

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Excavation Equipment

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Excavation Equipment, cont’d

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Ore from Dead Bullock Soak is transported to The Granites using the largest road train in the world. Some 305 feet (93 meters) in length, the train carries an average payload of 275 ton Ore Transport

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Typical Location of Gold in S. Africa

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Underground Mining

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Metallurgical Processing

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Processing Plant Gold and silver are extracted from the ore at the processing plant. Ore processing consists of the following stages: crushing and grinding of the ore addition of process water (generally decanted from the tailings pond) to form a slurry addition of lime to the ore, and cyanide solution to the slurry, to leach the gold and silver into solution addition of carbon to adsorb dissolved metals and remove them from the slurry stripping the metals from the carbon by acid washing and circulation of a caustic cyanide solution precipitation of the gold and silver by electro-winning smelting of metal products into bars of doré bullion pumping of the barren slurry (tailings) to the tailings storage facility.

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Grinding and Sizing. Ore processing is a 24 hour operation. Ore is stockpiled (1) at the Processing Plant, and the process begins by feeding the ore into a hopper with a loader. The ore is conveyed, and lime is added (2) to raise the pH of the ore. Following crushing through a jaw crusher (3), the ore is fed into the semi autogenous grinding (SAG) mill (4) along with water and steel balls.The grinding process reduces the rock to a slurry. The SAG mill is a large revolving cylinder. Rock is ground by the turning action of the mill, and impact from the hardened steel balls and the rock itself. In order to ensure that the rock is ground finely enough the SAG mill has a trommel screen (5), which acts like a large sieve. The oversize rock (SCATS) is caught by the trommel, along with the worn hardened steel balls. This material is fed past a magnet (12) to separate out the steel balls. The oversize rock passes through the SCATS cone crusher (13), prior to passing once again into the SAG mill (4) for further grinding. The slurry that is fine enough passes through the trommel to a sump (6) and then to a primary hydrocyclone (7). This hydrocyclone classifies the ground rock particles according to size – using centrifugal and gravitational forces to split the fine particles from the coarse particles. The fine particles are pumped via a sump (8) to a secondary hydrocyclone (9), and the larger particles return to the SAG mill (4) for further grinding. The secondary hydrocyclone (9) further classifies the slurry, with the coarse particles being directed to the ball mill (14) and fine particles reporting to the trash screen (10). The ball mill is very similar to the SAG mill, except it has a larger proportion of steel balls to assist in the grinding process.

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Leaching and Adsorption. The slurry (1) of ground ore and lime moves into a series of six leach tanks (2) where a sodium cyanide solution is added. The tanks provide sufficient retention time to allow the gold and silver to be dissolved by the cyanide solution. Oxygen is added to assist in this process. The slurry then moves through a series of carbon adsorption tanks (3). While the leaching process continues in these tanks, the primary objective is to remove the gold and silver from the solution. To achieve this, carbon is fed through the tanks (4) and the gold and silver adsorbs (attaches) to the carbon granules. Carbon is heated to 600 degrees C and fed into the circuit countercurrently to the slurry flow, moving from the last adsorption tank to the first. By the time the slurry reaches the final adsorption tank, most of the precious metals have been removed. The barren slurry, now known as tailings, is pumped to the tailings storage facility (5). In contrast, by the time the carbon reaches the first adsorption tank it has recovered most of the gold and silver from solution. This 'loaded' carbon is then pumped to the elution circuit (6) where the gold and silver is washed off with superheated water. The washed solution, called pregnant eluate, is passed to the electrowinning circuit (7). The remaining barren carbon is reactivated by acid washing and kilning and returned to the adsorption tanks (8).

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The pregnant eluate (1) is passed through a series of electrowinning cells (2), containing cathodes in the form of stainless steel plates. The gold and silver migrates and attaches itself to the stainless steel cathodes. The cathodes are then rinsed, yielding a muddy sludge, and the cathodes are reused.The muddy sludge is dried (3), and the powder that remains is mixed with fluxes (4) and put into the furnace (5). The furnace attains a temperature of 1200 degrees C and after several hours the molten material is poured into a cascade of moulds (6) to produce doré bullion bars. The fluxes form a slag of impurities which is removed, leaving a bar which is a 99% pure melt of gold and silver. Each bar of doré bullion contains around 90% silver and 10% gold, and weighs approximately 20 kg. The bullion is sent to the Western Australian Mint in Perth, where it is further refined to separate the gold from the silver. After refining, the gold and silver is credited to the mint accounts of each of the joint venture companies, Normandy Mining and Otter Gold. From there, each Company makes its own decisions as to the selling of the precious metals. Precious Metals Recovery

Research at GoldFields SA: 

Research at GoldFields SA Finding a solution to excessive disinfectant requirements Finding the cause of high nitrite levels Finding bacterial inhibition mechanisms

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Underground Proved: 25.2Mt grading 10.5g/t gold Probable: 58.8Mt at 11.0g/t gold Total underground: 84.0Mt at 11.0g/t gold, containing 29.3Moz Surface Probable: 31.9Mt grading 0.6g/t gold, containing 0.6Moz Total: 115.9Mt grading 8.1g/t, containing 29.9Moz of gold

The effect of height (depth) on atmospheric pressure: 

The effect of height (depth) on atmospheric pressure Pressure changes by 1% per 88m elevation change Therefore, at 88m above sea level, air pressure = 0.99 atm At 176m above sea level: air pressure = 0.992 = 0.99176/88 At any height above sea level: air pressure = 0.99h/88 Generalized: P = P0 (0.99)h/88 Increase below sea level = P0 (1.01)h/88

Air pressure in a 4km deep mine: 

Air pressure in a 4km deep mine The pressure at this depth, 2500 m below sea level, mine being at 1500m above sea level, can be calculated as 101 kPa (1.01) 2500/88 = 134 kPa Ambient pressure at 1.5 km above sea level 101 kPa (0.99)1500/88 = 85 kPa

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Cooling in mines Air not suitable at great depths. Compression of air due to gravity creates more heat than what needs to be removed from the surroundings

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The need for water cooling

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Resistance to Potable Water Use

Possible Inhibitors: 

Possible Inhibitors High temperatures Heavy metals Disinfectant byproducts or residues

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Lab Simulation of Cooling System