Example of heap leaching gold extraction in Yangu gold mine near Yuanshan, Nevada, USA

Tobacco Valley near the Nevada Round Mountain (Smoky Valley) gold mine, located 96km north of Tonopah Nigeria County. The total investment of the plant infrastructure is 18 million US dollars. It was completed in 1977 and put into production in 1977. The annual production of gold was 1.152t. The factory has 140 employees and is expected to produce 1.71 tons of gold and 0.98 tons of silver in 1979.

The ore has a ore reserve of 12 million tons fixed at a gold-containing cut-off grade of 0.68 g∕t, and the ore contains an average of 1.93 g/t of gold and 2.18 g of silver. With a cyanide liquid heap leaching, the recovery rate of gold is 86%.

The mine is open-pit mining. The ore produced is crushed to 178mm by a 1066×1651mm cone crusher . It is fed by a 914mm wide belt conveyor to a 2.1m Siemens (Symons) standard crusher and then broken to -50mm, then by two 2.1 m Siemens short-head crusher is broken to -9.5mm for heap leaching.

The entire heap leaching site is a rectangular section with a length of 640m and a width of 86m. The cushion of the site is 178 mm thick, and a 50 mm thick water-repellent layer composed of rubber sheets and asphalt is laid underneath, and asphalt is applied thereon. The transportation road made of powder ore is 660mm higher than the asphalt ground, and the site is divided into five pile immersion fields. Each site is tilted to one side and one end so that the leachate concentrates into the pool. Each pile leaching field can be piled up with 45,000 tons of ore, 4 piles for leaching, 1 pile for washing, slag and loading and quenching. It takes about 5 days to slag and pile up.

The leachate contained 0.045% NaCN and 0.04% CaO. The immersion liquid is supplied to each leaching pile through four plastic pipes through the main pipe. A set of Baghdad swinging ejector is installed on the plastic pipe every 12m. The ejector is made of a medical hose with a length of 228 mm and a diameter of 6.35 mm and a spray radius of 9 m. Each leaching pile has about 84 nozzles, the liquid supply speed is 2.7 ~ 3.4mL ∕ (m 2 · s), the spraying area is 116m 2 , and the spray per hour is about 1500L. The leaching period is 27d. During the heap leaching process, the leaching solution discharged from each leaching pile was sampled every day. When the leaching amount of gold was lower than the specified index, the leaching solution was closed and washed with water for two days.

The leached waste rock was transported to the waste rock site by two ore loading machines and five 45t trucks. Since the waste rock site is adjacent to the leaching site, it can be transported in 28 hours. In order to protect the asphalt pavement of the heap immersion field from damage, a layer of waste stone of 200-250 mm thick is left at the bottom of the pile. In order to check whether the leachate will penetrate into the ground through the leaching site, open a deep well in the lower part of the dip field and periodically sample and test.

The leached gold-containing liquid is pumped to the adsorption-desorption-activation plant by a turbo pump. The gold-containing liquid passes through five activated carbon adsorption tanks connected in series at a rate of 6056 L∕min, and after adsorption, a gold-bearing amount of about 7.775 kg∕t is produced. The leachate and the carbon particles are reversely operated, and the gold-loaded charcoal is taken out from the No. 1 tank every day for 1 t to be desorbed, and the activated carbon is added to the No. 5 tank for 1 t. The adsorbed lean liquid is discharged from the No. 5 tank, adjusted with sodium cyanide and lime, and returned to the leaching process for recycling.

The gold-loaded charcoal was eluted in a desorption tank at 88 ° C in hot NaOH and NaCN. The desorbed carbon particles are recycled to the recycled irotech kiln for recycling. The gold and silver-rich eluate accumulates in three electrolytic cells and recovers gold at the steel wool cathode.

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