Gravity separation is one of the common methods of gold ore beneficiation. It uses different specific gravity of materials and different settling speeds in the medium for layer separation. Generally in placer gold mines, gold mostly exists in the form of single natural gold, which has a large density difference from gangue, and the effect of using gravity separation for gold is very good, and the economic benefit is relatively high.
There are various gravity separation methods, such as jigging gravity separation, shaking table gravity separation, spiral chute, spiral gravity separation, centrifugal gravity separation and wind gravity separation. In gold ore beneficiation, the commonly used methods of gravity separation gold selection are jigging gold selection, shaking table gold selection and spiral chute gold selection. Fodamon engineers’s explaination as below:
1. Gold selection by Jigging
The main equipment of jigging and gold separation is jigger. The process of jigging is to mix the mineral particles with different specific gravity. In the vertical movement of variable speed medium flow, the minerals with small specific gravity are located in the upper layer and the minerals with larger specific gravity are located in the lower layer. Then, the mechanical and water flow are used to discharge the layered materials respectively.
Jigging is suitable for the separation of coarse-grained mineral particles (mineral raw materials with any particle size except fine materials). The particle size range of metal minerals is 50mm-0.074mm. For placer gold, the lower limit particle size can reach 0.04mm on the premise that the specific gravity difference is ≥ 1.25 and the ore monomer is separated. The process is simple and the equipment processing capacity is large, so the application effect in coarse-grained gold separation is very good.
2. Gold selection by Shaking table
The main equipment of gold separation by shaking table is the shaking table, which is used to select other equipment in the horizontal medium flow. The driving mechanism is used to drive the bed surface to do longitudinal reciprocating motion, to do the flushing and bed surface differential motion. In the reciprocating motion, the ore particles are subject to the layering action perpendicular to the bed surface and the separation action parallel to the bed surface, so that the materials with different particle sizes are discharged from different sections of the bed surface to achieve separation.
According to the different particle size of ore, the ore can be divided into three types: coarse sand bed, fine sand bed and slime bed. The coarse sand bed is suitable for the separation of ore particles with the particle size of 2.0mm-0.5mm, the fine sand bed is suitable for the treatment of ore particles with the particle size of 0.5-0.074mm, and the slime bed is suitable for the treatment of ore particles with the particle size of 0.074-0.037mm.
The ore feeding granularity range of the shaking table gold dressing is generally 3mm-0.019mm, the gold dressing is stable and reliable, the ore belt distribution is clearly visible, the rich ore ratio is higher than other ore dressing methods, easy to manage, and the ore required can be separated at one time.
3. Gold selection by Spiral chute
The main equipment of the chute gold separation is the spiral chute, which uses the inclined water flow to separate the materials. With the help of the combined force of water flow, mineral gravity, friction between the ore particles and the bottom of the chute, the ore particles settle in different areas of the chute according to the specific gravity. The ore particles with small specific gravity are taken away by the water flow, leaving the ore particles with significant proportion, that is to say, the separation is completed.
The spiral chute is suitable for the treatment of fine particles with low mud content. The particle size range of the material is 0.6-0.03mm. It has simple structure, large treatment capacity and low comprehensive cost.
The above three gravity separation gold separation methods are only used for monomer dissociated gold mines (grit gold mines). For vein gold minerals, the gravity separation process is rarely used alone. Generally, it will form a joint process with other processes, such as the gravity separation-flotation combined gold extraction process, gravity separation to assist gold extraction, use of jigs, spiral chutes and shakers in the grinding and grading circuit, first recovery is easy to solve The separated coarse-grained gold creates better separation conditions for the subsequent flotation and cyanidation processes, which can effectively improve the gold ore index and the total gold recovery rate.
In gold ore beneficiation, the selection of gravity separation depends on the nature of the gold ore. It is recommended to conduct a beneficiation test before the process selection, analyze the properties of the gold ore, and determine whether it is suitable to select the gravity separation process through the test and obtain the ideal gold selection process.