Hand selection concept and equipment

In the crushing workshop, the operation of separating the ore from the waste rock by manual means is called a hand selection. There are hand-selected two meanings: First, from the waste rock containing small amounts of gold in the ore sorting out; the second is excised from hand-selected ore waste rock. The latter is widely used in gold mines.

In most cases, mining causes waste rock mixing and ore depletion. Before grinding, try to use the hand to remove the waste rock in the ore to improve the ore grade. Meanwhile, when the ore contains clay in difficult shattering, clay in hand-selected may be discarded; hand-selected from ore without removing debris mixed waste, such as wood, iron wire, scrap metal, broken drill pipe, in order to avoid these heteroatoms Damage and accidents are caused by crushing, sieving and grading operations.

The hand selection process is simple, no special equipment is required, and it is only required on a simple hand-selected belt and a hand-selected table. Hand-selected belts must use flat belt conveyors, belt speed should not be too fast, generally 20 meters / minute or so; the surface is slightly concave, the ore is evenly distributed on the belt surface, so that the waste rock can be exposed; the belt width is generally not greater than 1200 mm . The hand selection station determines the area according to the number of participants, and the area of ​​the hand selection platform for 4 people is approximately 3.2 meters ² . The hand selection is arranged next to the large ore conveyor.

For most types of ore, gold-bearing ores and gangues are easily identifiable. Mainly white quartz waste rock, schist gray quartz, hornblende schist shale and black, but there are certain types of ore, gold ore which is indistinguishable from the waste rock. In this case, the hand selection must be very careful and carefully identified.

Adequate lighting is important for effective hand selection. After testing, the most satisfactory is to use a cold cathode fluorescent lamp. Fluorescent lights should be properly covered and hung below the line of sight to eliminate glare and shadows. In individual cases, the rubber belt of the conveyor is also coated with water red, yellow or green to distinguish the waste rock from the ore.

The hand selection of mud ore requires pre-selection washing and rinsing the slime adhered to the surface of the ore to expose the cleaned ore surface for easy visual identification. Hand-selected suitable particle size range is 75 ~ 250 mm .