The principle of the placer gold beneficiation process is to recover gold and its associated heavy minerals from the original ore to a large extent through gravity separation, and then separate the gold and various minerals through the combined operations of gravity separation, flotation, amalgamation, magnetic separation and electrostatic separation. The heavy minerals are separated from each other, so as to achieve the purpose of comprehensive recovery.
Placer gold ore separation is generally divided into crushing and screening, desliming and separation processes.
1. Crush and sieve
Many placer mines contain lumps of cemented mud, some of which are larger than 100mm in diameter. If the mud blocks do not break down, they will be removed along with the waste rock during the screening process, resulting in gold loss.
In addition, cement can also be cemented on gravel or pebbles. If it is not broken, it will cause gold loss during the screening process. The screening operation can remove 20-40% of the waste rock (gravel, pebbles), which is an indispensable operation for placer gold beneficiation.
On gold dredgers, crushing is done in a cylindrical screen together with the screening operation. The cylindrical screen is equipped with discontinuous spiral angle steel. During operation, the washing water pressure in the drum screen should not be lower than 35 kPa. In the fixed land concentrator, washing sediments for crushing and screening are set up. Use two water cannons of flat gauge 50 or flat gauge i-100, and repeatedly flush along the diagonal direction. The outlet pressure of the water gun shall not be less than 20 kPa.
Washing on the screen can not only improve the screening efficiency, but also further decompose the cement, so most of the screening operations in placer gold mines are water screens. The flushing amount of the water filter should be determined according to the washing requirements, and should meet the concentration requirements of the following segment selection operations as much as possible. In the case of chute roughing, the flushing amount should be 8-14 times the amount of sand ore.
Materials smaller than 0.1 mm in placer gold generally do not contain gold or contain very little gold. For example, the placer gold ore of the Hunchun Gold Mine is less than 0.1 mm, accounting for 0.18%, while the slime of the same grade accounts for 13.77% of the original ore. Gold smaller than 0.1 mm is often referred to as floating gold and is difficult to recover during separation, while sludge of the same particle size can interfere with separation processes, especially mechanical separation processes. Therefore, in placer gold concentrators, sludge smaller than 0.1 mm is always removed.
Practice has proved that gravity separation is an effective and economical method to deal with the 399001 mine. Due to the different particle size composition of placer gold mineral gold, the effective particle size limits of materials processed by various gravity separation equipment are also different, so a reasonable placer gold mineral separation process should be a combined operation of several gravity separation equipment.
The gold grade of the gold-bearing concentrate obtained in the roughing section is 100 g/ton, and most of the heavy sand minerals are above 1-2 kg/ton. At present, there are three methods for processing gold-containing coarse concentrate:
(1) after manually panning the gold particles with a gold pot, discard the heavy sand;
(2) use an amalgamation tank to carry out internal amalgamation to obtain amalgam and discard the heavy sand;
(3) After artificial panning or amalgamation to extract gold, the heavy sand is sent to the concentrate plant for processing, and various heavy sand minerals are recovered by magnetic separation and electric separation respectively.
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