There are many kinds of alluvial gold deposits. The gold is in a free state in the alluvial gold deposit and has the obvious specific gravity difference with sand, so the gravity separation process is an ideal and efficient method to extract gold from placer.
The alluvial gold mining process generally adopts the gravity separation process to extract the gold from the raw ore and those associated heavy minerals as much as possible (the lower limit of particle size limit is usually 0.01 mm), and then adopts the gravity separation, flotation, magnetic separation and electrostatic separation method to separate the gold and various heavy minerals, so as to achieve the comprehensive recovery.
In the production process, the common alluvial gold mining process mainly includes washing, screening, gravity separation and concentration.
The ore washing is an important procedure before the separation of alluvial gold, whose main purpose is to separate the gravel, sand and granular soil, wash the fine mud and the gold ore mixed in it. In general, the alluvial gold ore usually contains more weathered clay, the gold ore is wrapped in it, and form the cemented block or mud body together. If they are not broken up in advance, the cemented block or mud body will be discharged along with waste rock in the screening process, thus reducing the recovery rate of alluvial gold and causing the loss of gold.
In the ore washing operation, wash the ores with the water and then dissociate the ore sand wrapped in the cemented block or mud body through the plane vibrating screen, cylinder washing machine, cylinder screen, so as to separate the gravel, sand and clay, wash the clay and gold grains adhered to the gravel. This operation can improve the separation ability of alluvial gold ore and increase the recovery rate of alluvial gold ore.
In general, the main purpose of the screening is to screen the alluvial gold ore after washing, remove the large pieces of gravel without gold, so as to improve the efficiency of gold extraction. In general, the screening operation can remove 20-40% of waste rock (gravel, pebbles).
The screening of alluvial gold mining usually adopts the water screen to disintegrate the ore mud, which can improve the screening efficiency of alluvial gold mining. Usually, the size of the screen mesh used in the alluvial gold screening needs to be determined according to the composition parameters of the gold particle size in the original ore sand. At the present, the common screen mesh is generally 10-20mm.When adopting the fixed chute for the roughing, the size of screen mesh can be larger, but cannot exceed 60mm. The fixed concentrators often adopt the vibrating screen or grid screen as the screening equipment, and the gold dredger often adopts the cylinder screen.
The gravity separation process is mainly used in the alluvial gold mining. First, the alluvial gold ore has the large proportion and coarse particle size (generally 0.074~2mm). Second, the gravity separation has the advantages of low cost and simple process. The gravity separation is the key in the separation stage of alluvial gold mining. Adopting the jig, shaking table and spiral chute to discharge the most of waste rock, so as to obtain the coarse gold concentrate.
Jig
On the premise of specific gravity difference ≥1.25 and ore monomer disintegration, the lower limit particle size of jigging in the alluvial gold mining can reach 0.04mm. the jigging has the advantages of simple operation and large processing capacity, which is widely applied in the roughing.
Shaking table
The shaking table is suitable for processing the minerals with fine particle size, which is featured with is stable and reliable operation, clear ore belt distribution, higher rich ore ratio than other gold extraction methods, easy-to-manage, one-time ore separation. According to the different particle size of the ore, the shaking table can be divided into coarse sand shaking bed, fine sand shaking bed and mud shaking bed:
◆ Coarse sand shaking bed is suitable for processing the minerals size between 0.5mm and 2.0mm;
◆ Fine sand shaking bed is suitable for processing the minerals size between 0.074mm and 0.5mm;
◆ Mud shaking bed is suitable for processing the minerals size between 0.037mm and 0.074mm.
Spiral Chute
According to the particle size, the chute can be divided into coarse-grained chute and fine-grained chute. What’s more, the fine grain chute can be divided into ore sand chute and slime chute.
◆ Coarse-grained chute is mainly used for the separation of alluvial gold mining, whose upper limit of feeding particle size is up to 100-200mm and the lower limit of particle size is about 0.074mm.
◆ Fine-grained chute is often used for the roughing of coastal alluvial gold mining (the gold ore particle size is -2mm);
◆ The ore sand chute is suitable for the size between 2mm and 0.074mm
◆ The slime chute is used to for the size of -0.074mm.
According to the different types of alluvial gold ore, the concentration can adopt the gravity separation, magnetic separation, flotation, electric separation or combined separation methods to separate the gold from the various heavy minerals, so as to further improve the grade of gold. It is necessary to pay the special attention to the selection of concentration processing method and equipment for avoiding the loss of gold in the concentration process, and fully improving the recovery efficiency of gold and other heavy sand minerals, so as to achieve the purpose of comprehensive recovery.
In general, the dewatering operation is determined based on the process used in the concentration stage. The gravity separation, magnetic separation and flotation process can be carried out under the wet conditions, while the electric separation process requires the dry conditions. In general, the dewatering stage of alluvial gold mining adopts the concentration + filtration process.
In the actual production, the selection of alluvial gold mining process and equipment is related to the ore properties, plant condition, investment budget and other factors. The same alluvial gold mining process and equipment cannot be fully applicable to all the alluvial gold concentrator. Therefore, it is recommended to choose equipment manufacturers with mineral processing qualifications to customize the scientific and reasonable alluvial gold mining.
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