Heap leaching gold extraction process (1)

The heap leaching method is mainly suitable for dealing with low-grade ore that cannot be solved by conventional methods. This has a unique attraction for resource utilization with little gold reserves. Secondly, the construction period is short. In North America, some are built in only four months. Putting into production, this means that the capital turnover is fast; the third is the low production cost, which is about 40% of the conventional law. In particular, it can be applied to low-grade ore, and the gold content of some ore used by some manufacturers is even only 0.25g/t. It should be noted that conditions in some areas may not be applicable to heap leaching. First, the temperature should not be too low. When the leaching temperature is lower than 10 °C, the speed of immersion gold with cyanide is extremely low. For colder regions, the effective production period is necessarily shorter. Using solar energy or other energy sources to heat the leachate can make up for this. Insufficient; the second is dry, high temperature and water-deficient areas. The use of heap leaching will cause difficulty in water supply due to excessive evaporation of the immersion liquid. The relevant data indicates that the evaporation loss can reach 15% to 25%. In addition, the gangue will also take water away. The volume fraction is 25%~50%.
The heap leaching method has the advantages of simple process, less equipment, less investment, quick effect, low production cost, and adaptability of the nature, grade and quantity of the ore. Heap leaching is to mix fine ore particles with protective alkali (lime), pile it on the non-leakage floor (dip pad), and spray the cyanide solution on the heap, slowly passing through the solution from top to bottom. When the heap (diafiltration) occurs, the dissolution of gold occurs. The gold-containing solution (your liquid) flowing out from the bottom surface is sent to precipitate the precious metal. The cyanide solution (lean solution) after gold removal is returned to the spray heap. The size, height and shape of the heap are subject to the uniform and smooth penetration of the cyanide liquid. The production scale is also considered. Some piles are only tens of tons, some hundreds of tons or even 10,000 tons.
Heap leaching involves geology, mineralogy, civil engineering, water balance, environmental assessment and economic analysis. The whole process of heap leaching includes sampling, laboratory test, pilot test, field test, heap leaching site design and construction, production operation, and treatment of the heap after the end of production stoppage.
In addition to emphasizing fine crushing and granulation of ore, the heap leaching method also uses a process of continuous leaching and direct electrowinning of gold (i.e., leaching several heaps with a batch of leaching solution, and then from the rich gold liquid obtained) Gold accumulating) and oxygen leaching into the heap, as well as steaming in the cold area (or cold season) to enhance the leaching of gold.
1. Type of ore suitable for heap leaching
The gold leaching method is relatively thick, and the leaching rate of gold is relatively low. Therefore, in general, it is only suitable for treating low-grade gold ore, especially low-grade oxidized ore. Most of this part of the mine is a surface oxide ore.
The large number of industrial practice has proved that for heap leaching of oxide ores, ore occurrence of different types of gold, gold-bearing quartz veins have, BRECCIA, structural alteration, andesite, sandstone, porphyry, heat metamorphic fluid silicide mylonite secondary dozen auriferous iron cap, wherein a high degree of oxidation, occur in small fractures gangue minerals or gold particles easily understood and readily exposed gold heap leaching.
Gold ore having the above characteristics and suitable for heap leaching treatment mainly belongs to the following three types.
1 dip dyed oxidized ore;
2 sulphide ore in which gold is not symbiotic with sulphide minerals;
3 A vein gold or gold deposit containing a small gold particle or a gold particle with a large specific surface area.
Ore suitable for gold extraction by heap leaching shall have the following characteristics:
1 Gold grade is low, most of them are in the range of 1.0~3.0g/t, and the gold ore grade of only some deposits is greater than 3.0g/t;
2 gold inlaid fine grain size, or flat type, easy to cyanide leaching;
3 ore is loose and porous due to oxidation and weathering, and is permeable;
4 using the crushing method to expose the gold in the ore with few pores;
5 ore contains no or little acid, and contains no or little element which can react with cyanide;
The 6 ore contains no substances that adsorb or precipitate dissolved gold.
The table below lists the types and properties of gold ore that have proven to be suitable for gold extraction by heap leaching. [next]

Heap leaching ore type and nature

Serial number

Deposit or ore type

Gold particle size

Relationship between gold and carrier minerals

Harmful element content

Ore permeability

Ore appearance

1

Quartz vein oxidized ore

Medium grain, fine grain

Gold is mostly produced in limonite

Rarely

good

Gold-bearing sulphide ore is oxidized to limonite, weathering is severe, and crack development

2

Porphyry

Fine grain

Mainly in quartz, feldspar , limonite

Very few

good

The degree of oxidation is high, the weathering is serious, the cracks develop, and the secondary pores are densely packed.

3

Altered andesite

Fine grain

Natural gold 50% in mineral cracks

Rarely

good

Cracks and voids in the ore, good permeability

4

Carbonate type

Fine

Mainly in calcite , followed by quartz

Very few

good

The good ore is crushed and crushed, and the secondary pores are network-like and highly oxidizing.

5

Tectonic altered rock

Fine

Coexisting with limonite and cuttings

Very few

good

By squeezing, crushing, loose texture, fissure development, multi-hole

6

Gold-bearing iron cap

Fine grain

Gold is produced in limonite and quartz.

More copper

general

The degree of oxidation is deep, the cracks develop, and the ore is muddy.

7

Metamorphic hydrothermal type

Fine grain

Major quartz, followed by limonite

Silver higher

general

Strong weathering, serious muddy, dense secondary holes, high degree of oxidation

8

Silicified mylonite

Fine

In limonite, jarosite, quartz

Very few

general

Severe muddy, deep oxidation, secondary pores such as cobwebs

9

Sandstone type

Fine grain

Gold is produced in quartz sandstone

High copper

good

The degree of oxidation is general and the structure is dense

10

Hydrothermal filling type

Fine grain

Produced in limonite and peptizer

Lead Zinc High

general

Strong weathering, serious ore mud, cracks, and dense holes

11

Broken breccia

Fine

In quartz, limonite and peptizer

Slightly higher sulfur

good

The degree of oxidation is general, the pores are cracked, and there are many cemented materials.

12

Altered basalt

Fine

Gold particles are mostly in fine mud

Very few

general

The ore contains a high amount of mud, which requires a heap leaching of the ore.

13

Muddy siltstone

Very fine

Gold particles are often found in fine mud

Very few

general

The ore contains more than 30% of mud , such as agglomeration treatment, the leaching rate can reach 80%.

14

Silicified altered rock

Fine

Dip-like, distributed in altered rock

Very few

good

The ore is highly oxidized, the fractured pores are developed, and the leaching is easy.

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The three important physical properties of the heap leaching ore are: 1 fine fraction; 2 saturated water capacity; 3 loose density, ie bulk density.
The fine fraction content in the ore generally refers to a material of less than 74 μm or less than 149 μm, which has a great influence on the permeability of the ore heap leaching: high fine fraction and low permeability. Generally less than 74 μm, when the content exceeds 5%, granulation heap leaching is required.
The ore saturated water-capacity rate refers to the percentage of the ore's water content to the total mass of the ore after being saturated with water (dry mine weight plus water absorption) when the ore water reaches saturation state. It is another important factor affecting the permeability of ore. This value is not only related to the grain size of the ore, but also to the mineral composition of the ore. Kaolin, chlorite, sericite, etc. have a strong water-absorbing mineral ores contained. When a solution passes between the ore particles, these minerals absorb a large amount of water and swell, causing the original high-strength ore particles to be broken, even pulverized and muddy, thereby significantly deteriorating the permeability of the ore.
The loose density of ore, this value is directly related to the relationship between the volume of the ore and the quality of the ore. Therefore, it is also a more important parameter in heap leaching.
2. Heap leaching process characteristics The heap leaching method is not a new gold extraction technology. The heap leaching process is similar to the leaching leaching. It is only that the heap immersion is not in the tank, but is exposed to the air. Therefore, how to extract gold from the leachate is not necessarily limited to a certain method.
It can be seen that the key to the characteristics of the gold extraction process in the heap leaching method is the building method and the spraying technique, and the extraction of the precious metal from the collected gold-containing cyanide precious liquid can be carried out in various processes. Figure 1 shows the principle flow of the heap leaching gold extraction technology, which fully reflects the basic characteristics of the heap leaching process. Among them, scheme I is gold extraction by metal zinc replacement precipitation method; scheme B is gold extraction by activated carbon adsorption method; and scheme LQ is gold extraction by ion exchange resin adsorption method.

The process for recovering metal from the gold-containing precious liquid obtained by heap leaching includes: in addition to the above-mentioned activated carbon adsorption method, zinc wire (powder) replacement method, ion exchange resin method, solvent extraction method, direct electrolysis method, aluminum Replacement and sulfide replacement methods. Figure 2 to Figure 6 show the main processes of several methods for recovering gold. [next]

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