Carbon extracting process - selection of activated carbon

Select the CIP gold extraction of activated carbon, the most important conditions One has a good absorption characteristics of gold, the second is the carbon particles must have a strong wear resistance. Carbon with good adsorption characteristics has good selectivity to gold and silver , and large adsorption capacity and recovery rate; carbon with strong wear resistance can minimize grinding loss and reduce the loss of gold-loaded charcoal with slurry loss. The loss of gold. This is due to the carbon used in the carbon slurry process. In the production process, it is generally formulated into a carbon suspension, which is sprayed or hydraulically conveyed, compressed air or mechanically stirred, sieved, and the like. In particular, the quality of each batch of charcoal cannot be uniform. Some of the carbon particles and all carbon particles have edges and edges (because they are not spherical particles), have low mechanical strength, are weak in abrasion resistance, and are most prone to wear. And they are the most active part of carbon, which has good adsorption performance and large adsorption capacity. Its wear will not only increase the loss of gold and silver, but also cause the whole batch of carbon adsorption performance to decline, causing fluctuations in operating indexes, and also increasing the amount of carbon input during the operation. To this end, for each batch of new charcoal in industrial production, the wood chips and sundries should be screened before use, and then stirred in a mechanical agitation tank together with the abrasive (the same gold-free waste rock as the ore). Grinding carbon particles and corners with weak mechanical strength, making the carbon particles approximately spherical, and sieving to remove the carbon powder for use. In the production, attention should be paid to the wear index of charcoal in the operation of carbon slurry and in the process of recycling. As far as possible, the brand of charcoal with good wear resistance should be selected.

In addition to the characteristics of the following table, D. MacArthur et al. proposed the following technical indicators:

1. Balanced adsorption in a gold-containing 1g/m 3 solution for 24h, the carbon loading capacity of the carbon should reach 25g∕kg;

Second, in the gold containing 10g ∕m 3 solution for adsorption for 1h, the adsorption rate of carbon to gold should reach 60%;

Third, put the charcoal in the bottle and roll it on the rock machine for 24h, the wear rate should be less than 2%.

Table Physical and chemical properties of typical gold-clad coconut shell activated carbon

classification

Technical characteristics

Numerical value

Physical properties

Particle density (determined by mercury replacement method) ∕g·mL - 1

0.8 to 0.85

Heap density ∕g·m - 1

0.48~0.54

Hole size ∕nm

1.0 to 2.0

Hole volume ∕mL·g - 1

0.7 to 0.8

Ball hardness (ASTM, the US test material standard) ∕%

97~99

Particle size 1 ∕mm(H)

1.16~2.36

(14~8)

Ash ∕%

2 to 4

Moisture %

1 to 4

Chemical adsorption

characteristic

Specific surface strip (N 2 , BET, ie Brenner-Emmett-Teller nitrogen determination)

∕m 2 ·g - 1

1050~1200

Iodine value / mg · g - 1

1000~1150

Carbon tetrachloride value ∕%

60~70

Benzene value%

36~40

In view of the specific surface area of pores of activated carbon of gold generally 900 ~ 1200m 2 / g (N 2, BET), when the adsorption capacity of the selected 6g Au / kg carbon, rather only 800m 2 than the surface area of a gold atom, an area occupied by Very few, the general commodity carbon is easy to meet the requirements of adsorption capacity. Therefore, the activated carbon selected for the carbon slurry method mainly considers its wear resistance, that is, the carbon is added to the finely ground slurry to be stirred and leached together, and the carbon product with good wear resistance is preferably selected from the comparison.

Despite the design of the modern charcoal process plant, the separation and transportation of charcoal has replaced the vibrating screen and steel pipe with fixed screens and plastic pipes, and some factories have also modified or coated rubber materials such as rubber on the tip of the mechanical stirring impeller. Great improvements have been made in preventing carbon wear. However, when choosing activated carbon, it should pay attention to its wear resistance and minimize the loss of gold due to carbon abrasion.

Since activated carbon adsorbs gold from cyanide liquid containing a large amount of heavy metals and other impurity ions, another important indicator of carbon is the selective adsorption property to gold and silver. Coco charcoal, which is widely used in the United States and South Africa, has good adsorption capacity and selectivity because of its large adsorption capacity and selectivity. In addition, the United States is also a trial to suppress charcoal wood, hay, peat and lignite, peat, South Africa also try to develop a pressed charcoal.

In addition to the use of imported coconut shell charcoal in some cyanide plants in China, most of them use domestic coconut shell charcoal and apricot kernel charcoal, and have also developed and tested a variety of core charcoal. The Sichuan Institute of Forestry has also developed a kind of wood charcoal, which is said to have a strength of 86% to 93.8%.

In the former Soviet Union, in addition to the focus on the use of ion exchange resins, the main development is the synthesis of synthetic and polymer synthetic carbon. The activated carbon developed by them is not as strong as the ion exchange resin, but it has good selectivity to gold and a large adsorption capacity. Since they can selectively adsorb gold from a solution containing a large amount of heavy metal ions, the desorption and regeneration method of the gold-loaded carbon is also simpler than that of the resin, and the color of the recovered gold is also high. Moreover, the activated carbon has a large specific surface area, and it is easy to strengthen the adsorption process. Б.Н. Laskolin (Ласкорин) reported the КАД-type activated carbon made from charcoal scrap, and compared it with the AM-2Б anion exchange resin commonly used in the resin slurry method. The results show that in the cyanide solution containing a large amount of copper , the gold capacity of КАД carbon decreased by only 30%, while the AM-2 resin decreased by 4 times. In the cyanide solution containing a large amount of zinc , the capacity of КАД carbon decreased by 60. %, while AM-2 resin decreased by 9 times. When the БАУ type activated carbon of birchwood is used for comparison test from multi-metal mixed cyanide liquid containing Au, Cu, Zn, Ni, Co and Fe, the adsorption saturation capacity of БАУ carbon is 2-8 times that of AM-2 Б resin. . Therefore, the former Soviet Union recovered by-product gold from the cyanide-containing beneficiation liquid containing gold and silver polymetallic ores, and adsorbed by КАД or БАУ-type activated carbon using equipment such as adsorption columns.

The literature describes a АУ-50 type activated carbon which is synthesized by phenolic resin and activated at a high temperature in a vacuum of 1000 ° C or a CO 2 gas stream. The carbon has a pure surface and excellent anion exchange in a medium containing air oxygen, and has extremely high reducing ability for heavy metal ions and simple gold and silver ions and complex ions, especially for adsorption of gold and silver. Excellent selectivity. When using АУ-50 charcoal to test the cyanide solution containing gold, silver and associated impurities such as copper, zinc, iron , nickel and diamond, gold, silver and copper have just entered the carbon. As the adsorption capacity increases, Impurities such as copper are gradually replaced by gold and silver, and the capacity of gold and silver in carbon is increasing. When the carbon finally reaches saturation, the distribution ratio of the total adsorption capacity is Au 80%, Ag 20%, and the gold + silver selection coefficient is equal to 1. When the AM-2 oxime resin was used for the comparative experiment under the same conditions, when the resin finally reached saturation, the adsorption capacity of gold was 5.2 mg ∕g, accounting for 19% of the total capacity, the selectivity coefficient was equal to 0.19, and the others were zinc. 75%, silver and nickel each account for 2% to 4%.

In addition to various chemical types and high molecular weight carbons, the former Soviet Union also tried a kind of wood charcoal made from pulp and spherical carbon sintered from bituminous coal.

The Canadian Yellowknife mining company uses the cyanidation process to treat the soot produced in the boiling roaster. The solids in the slurry are fine-grained mud with little wear on the charcoal. In order to improve the adsorption recovery index, the company chose a large-cavity large-capacity pine activated carbon with a slightly lower strength. According to reports, its total adsorption capacity can reach tens of kilograms / ton of carbon, and the recovery rate of gold is also 5.8% higher than zinc replacement.

Adsorption of gold from the proposed liquid separated from heap leaching, leaching leaching and other leaching operations using static adsorption equipment such as adsorption columns and filter tanks, whether using a fixed bed flowing from top to bottom or a solution The expanded bed flowing from the bottom to the top, the solid carbon does not undergo strong grinding, and the activated carbon with low specific surface area, large capacity and stable chemical properties can be selected. Although the carbon with large pores has poor adsorption selectivity, its capacity is also large, and it can also adsorb and recover non-ferrous metals such as silver and copper with larger ionic radii than gold, and improve the comprehensive recovery value. For factories that do not need to recycle, and burn saturated metal charcoal to smelt and recover metal, even cheap common brand activated carbon can be used.

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