The important role of re-election in primary gold ore beneficiation

Reselection method for recovering this old gold and other heavy mineral sands from the method, in recent decades due to the development of equipment and operation technologies, it has not only a sand deposits, but also for a large number of the pulp before flotation in place of Recovering monomer-dissociated coarse gold and fine gold before mercury cyanide or gold mud cyanide leaching. The former can eliminate mercury damage, the latter can shorten the cyanide time and increase the gold yield. Both can produce finished gold in advance and speed up the capital turnover of the plant.

In the early stages of mining, the South African gold mine mainly used re-election-alkali method to recover gold. After the introduction of cyanidation in South Africa in 1890, the re-election method was replaced in many mines. However, subsequent practice has proved that although the cyanidation process is highly efficient, there are many advantages to using the re-election method to recover as much gold as possible in the grinding cycle. I.e., (1) grinding of gold-bearing iron ore, mainly to ensure that the degree of unwrapping from gold, quartz to prevent excessive wear gangue minerals; (2) the grinding cycle of discharge from the mill outlet collector monomer Dissociation of gold, can avoid it re-entry into the mill, so that the accumulation of gold in the gap of the ball mill liner is greatly reduced; (3) cyanide slurry after pre-re-selection of gold (completely collected by coarse-grained monomer) The gold content can be reduced by 50%, which is beneficial to shorten the cyanide time, facilitate the cyanidation operation and increase the gold recovery rate; (4) Capture and recover part of the gold in advance, which can accelerate the output of finished gold and accelerate the turnover of funds; (5) many South African gold veins contained 0.002 ~ 0.02g / t ore fines osmium iridium, if not lost to the gravity separation occurs in the tailings. Especially when dealing with gold-rich ore, it is more advantageous to insert a re-election operation in the process. Therefore, the re-election method can be applied to any ore containing more than 10g∕t.

For the above reasons, nearly two-thirds of the South African gold mines today employ one or more re-election methods. Among these plants, the most widely used are modified Johnson cylinder concentrators , belt grate concentrators, flat bed concentrators, corduroy chutes, and jigs. This type of concentrator is used in South Africa's selection of coarse gold, and the recovery rate of gold is as high as 75% or more. In other countries, the application of the re-election method is also quite extensive. In the past 100 years, many re-election equipments have been introduced at home and abroad. Some of the new and improved equipments have achieved good levels in terms of the lower particle size recovery and recovery rate of gold, as well as the simplification of working conditions, and each has its own characteristics.

The Johnson cylinder concentrator is a 3.66m continuous rotating cylinder with an axial inclination of 10% and the cylinder is lined with corduroy. The improved cylindrical concentrator is axially inclined by 2.5° to 5°, and the cylinder is lined with a serrated rubber strip parallel to the axial direction (see Figure 1). The strip is 3mm deep, 3.5mm wide and 3mm apart. The simplified direction of rotation is opposite to the serrated tip of the rubber strip, and as the slurry flows along the axial direction of the cylinder, heavy minerals are deposited in the bars. When it is rotated to the apex, the water sprayed from the sprinkler pipe flushes the heavy minerals into the concentrate tank. This type of concentrator is used to treat the discharge from the hydrocyclone underflow or the secondary ball mill. It is simple to operate and low in power consumption, and a 1 kW motor is enough to rotate the cylinder. Table 1 shows the specifications and operating specifications of three cylinder concentrators in South Africa. The produced concentrate is enriched by a belt-type strip concentrator and then mixed with mercury.

Table 1 Specifications and operating specifications of the Johnson cylinder concentrator

Figure 1 Johnson cylinder concentrator

The belt type strip concentrator, also known as the mechanical chute, is connected by a corduroy rubber strip to an infinite strip, and a selective concentrator for the coarse concentrate. The glue has a bandwidth of 1.52m and the belt is inclined by 10° to 12° (Fig. 2). The belt moving speed is reduced from 0.1 to 0.36 m/min by the gear reducer. The bars are 3mm high and have a pitch of 5mm. The flow direction of the supplied slurry is opposite to the direction in which the belt moves. The concentrate is collected in the grid to the lower part of the bed, and is flushed by water spray to the concentrate tank. The tailings are discharged from the bed at the end of the belt. The specifications and operating specifications of the belt type slag concentrator used in South Africa for processing concentrates of cylindrical concentrators and flat bed concentrators are shown in Table 2.

Table 2 Specifications and operation index of belt type concentrator

Figure 2 belt type strip concentrator

The flat bed concentrator has a three-stage stepped shape, also known as a three-stage flat bed concentrator. Since the machine has no moving parts and is not actually repaired, it has been used by many South African plants to capture gold from secondary ball mills. Such concentrators are usually used in series of 2 to 3 units. The bed surface is made of steel or wooden, and the rubber strips are laid vertically on the stepped bed surface. Below the ladder there is a transverse narrow groove to collect the concentrate flowing down the grid. The pulp flowing faster above the grid passes downstream into the next stage. The produced concentrate is further enriched by a James shaker or a belt type concentrator, and the gold is recovered by amalgamation. The specifications of the flat bed concentrator for South Africa and the operating indicators for secondary grinding and ore discharge are listed in Table 3.

Table 3 Specifications and operation indicators of flat bed concentrator

The corduroy chute began to be used in South Africa in 1922 to replace the amalgam plate. Because of its good catch gold effect, but also save labor and water, silver, gold and mercury to prevent the theft of workers to eliminate salivation (mercury poisoning symptoms), it is still widely used in South Africa. The chute bed and the bracket are made of concrete. The groove surface is 2.74m long and 1.52m wide. The area is large. Usually, the corduroy cloth is replaced by 4~h, and no special person is required to take care of the operation. It is widely used in the classifier circuit to capture monomeric gold.

The Nelson Hydraulic Concentrator is a centrifugal cone concentrator that has been developed in the last three decades (Figure 3). The cone is frustoconical, with an inner diameter of 762mm (35"). It consists of two layers inside and outside. The number of rotations of the cone is 400r/min and the power is 5.6kW. The inner cone is 50mm × 50mm (2" × 2"). Open the 1.6mm (1/l6") hole, the static pressure water is fed from under the cone, and enter the inner cone through the hole to form a "water pad" to keep the concentrate in a loose state, so that the precipitation is not too tight. The ore size is less than 6mm, the treatment capacity is 20~23m ³ ∕h, and the water consumption is 1.8m ³ /min. The centrifugal strength of the machine is about 300 times that of gravity, which enables the light mineral floating well to overflow from the upper part of the cone. The recovery rate of monomer gold can reach 95% to 99%, including some -560 ~ +625 mesh fine gold particles. Each time you can work continuously for 8~10h, or when the concentrated concentrate is about 200kg in the cone, stop the plug and rinse it with water for about 5min to unload the concentrate. Due to its high efficiency and easy operation, this machine has been widely used to replace gold amalgamation plates to recover gold from the ball mill discharge.

Figure 3 Nelson Hydraulic Concentrator

The Wrightke Cone Concentrator was originally developed for the recovery of gold from sand mines in Australia and was also very successful when used in the re-election of vein gold mines. It is characterized by a wide range of particle sizes for processing raw materials, up to 0.038 mm (400 mesh), and high recovery.

The Dutch round jig has a zigzag motion curve and can recover fine gold. The gold recovery rate for sand gold deposits is up to 94% or more, and the ability to process raw materials is large, which has become the main re-election equipment on gold mining vessels.

In foreign countries, there are still quite a lot of old and new rebuilt equipments that are widely used today, and will not be introduced here.

The plastic felt is a plastic belt-drawing machine fabric. The products are available in a variety of colors and thicknesses. They were originally used to lay sports grounds or to decorate indoor and outdoor lawns, also known as artificial turf. Canada first put it on the Rotary chute instead of carpets to collect gold particles, the effect is very good. In 1984, Heilongjiang Province introduced green plastic felts with thicknesses of 6mm and 20mm for the production of gold in the Longjiang-1 type chute. The catch rate of gold was increased by about 20% compared with sacks and carpets. Liaoning Hejia Gold Mine is a small selection plant located in a densely populated area. It is not suitable to use mercury plates. Instead of using plastic felt chutes, it can capture 16.4% of gold from the pulp. And the felt is elastic, easy to use and durable.

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