The carbon adsorption operation is carried out in an adsorption tower (tank) equipped with activated carbon. According to the solution are two ways: one is that the top-down solution containing gold cyanide permeation through the fixed activated carbon layer; two gold cyanide solution is applied by a pump pressure at a constant rate through a charcoal bottom The layer is placed in a "boiling" state, or the char is suspended in a solution. The choice of mode depends on the turbidity and mud content of the leachate. For a fixed carbon layer and a compacted carbon column, the maximum feed flow rate is 3.4 L / (m 2 · s), there must be no free fine material in the feed liquid, because the fixed carbon layer is like a sand filter, the slime will Will block the carbon layer and affect the passage of the solution.
Compared with the two liquid feeding methods, the first method has the advantage that less activated carbon is required, but the clarity of the solution is higher. The second method is often used in industrial production practice to adsorb un-refined heap leaching rich liquid containing a small amount of shale. In designing the second way to use the boiling layer adsorption scheme, the following four factors must also be considered:
The flow rate of the feed solution is determined based on the amount of enrichment discharged from the heap leaching operation per day.
2 The daily production of precious metals is determined according to the maximum gold content of each stack of discharge solutions in different operation periods.
3 activated carbon maximum loading capacity.
4 The particle size and type of activated carbon used.
If the adsorption capacity of activated carbon can be used to the maximum, the amount of carbon can be reduced and the scale of the adsorption and desorption equipment can be reduced. In industry, in general, it is suitable to adsorb 2 to 5 kg of gold (or gold and silver ) per ton of activated carbon.
The particle size of activated carbon used in foreign heap leaching is 1.0~3.35mm or 0.6~1.40mm. Generally speaking, the flow rate of the feed solution required to keep the activated carbon layer with particle size of 1.00~3.35mm in suspension is 17L/(m 2 · s). For activated carbon with a particle size of 0.6 to 1.4 mm, the required flow rate is 10 L/(m 2 ·s). Under the above conditions, the activated carbon will expand by 50%. At rest, the height of the activated carbon layer should not be more than three times the diameter of the adsorption tower; the height of the tower should be 2.5-3 times the height of the static carbon layer, which provides sufficient space for the expansion of the carbon layer and the flipping of the solution.
Using a fluidized adsorption system with 0.6 to 1.4 mm carbon particles, the amount of activated carbon required is 10 times the amount of desorbed carbon removed per day. If 1.00~3.35mm activated carbon is used, the amount of carbon required is a factor of the amount of carbon removed per day. This is because the latter has a high feed rate and a short contact time. Industrial production experience shows that for more successful and more efficient carbon adsorption systems, the same quality of activated carbon is divided into 4 to 5 carbon towers (tanks) in series.
Cyanide rich liquid At the beginning of the carbon countercurrent adsorption system, each adsorption tower may adsorb all of the precious metals. After a period of time, when the per ton of carbon in the first column is adsorbed to about 600 g of gold, the gold content of the solution flowing out of the first column will gradually increase and be adsorbed by the subsequent carbon layer. Always check the adsorption conditions, the solution from each charcoal tower should be sampled and analyzed at regular intervals. When the gold content of the lean liquid in the last tower is higher, or when the gold loading amount of the carbon in the first tower has reached the required value or the saturated value, a part of the gold charcoal can be taken out from the first tower for desorption, and then The same amount of charcoal was taken from the next tower, and the char in each tower was advanced in advance, and an equal amount of fresh charcoal was charged into the last tower. Activated carbon can also advance the entire tower, and the last tower is replaced with new charcoal. [next]
The figure below shows the distribution of gold extracted from the 5000t ore cyanide leachate. The solution contains gold 3.1g/t, and four carbon adsorption tanks are connected in series, and each tank is filled with charcoal for 1t.
Before the activated carbon is added to the adsorption tower, it is necessary to pre-screen the fine-grained carbon of less than 0.4 mm with a safety sieve to prevent the fine-grained carbon from being lost to the slag after adsorbing the gold.
In foreign heap leaching operations, coconut shell activated carbon with a particle size of 0.59~1.68mm is commonly used. It has the advantages of high strength, difficulty in crushing during use, and strong adsorption capacity. Apricot nuclear charcoal (GH16A) produced by Beijing Guanghua Timber Factory has a good effect.
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