The gold extraction by heap leaching method, because the ore particle size is quite coarse, and the effect with the leaching agent of jelly is weak, the leaching rate of gold is relatively low. And most of these mines are surface oxide ores. According to a large number of Fodamon engineers’ industrial practices, it is further proved that the types of rocks that gold can accumulate in heap-leaching oxidized ores are gold-bearing quartz veins, gold-bearing breccia, tectonic alteration rocks, andesite, sandstone, porphyry, thermal Liquid metamorphic rock, silicified mylonite, secondary gold-bearing iron cap type, etc., among them, the degree of oxidation is high, the gold present in gangue or mineral fissures, and the small and easily exposed gold is easy to heap leaching .
The ore suitable for heap leaching should have the following characteristics:
(1) The gold grade is low, most of them are in the range of 1.0-3.0g/t, only the gold ore grade of some deposits is higher than 3.0g/t;
(2) The inlay grain size of gold is fine or flat, which is easy to be leached by dense leaching;
(3) The ore is loose and porous due to oxidation and weathering, and has permeability;
(4) Gold in ores with few pores can be exposed by crushing;
(5) The ore contains no or less acidic substances or elements that can react with cyanide;
(6) The ore does not contain adsorbed or precipitated dissolved gold.
The gold ore suitable for heap leaching is mainly classified into the following three types.
(1) Disseminated oxidized ore;
(2) Sulfide ores that are not closely symbiotic with sulfide minerals;
(3) Vein or placer gold deposits containing tiny gold particles or gold particles with large specific surface area.
Three important physical properties of heap leaching ore are as follows:
(1) Fine grained content;
(2) Saturated water holding capacity;
(3) Loose density, that is, bulk density.
The fine-grained content in ore generally refers to the material less than 74fzm or 149ftm, which has a great influence on the permeability of heap leaching of ore: the fine-grained content is high, and the permeability is reduced. Generally, when the content of less than 74 fzm is more than 5%, it needs to be made into pellets and heap leaching.
The saturated water capacity of the ore refers to the percentage of the water content of the ore to the total weight of the ore saturated with water (dry ore plus water absorption) when the water absorption of the ore reaches saturation. It is another important factor affecting ore permeability. This value is not only related to the particle size of the ore, but also to the mineral composition of the ore. Kaolin, chlorite, sericite and other minerals contained in the ore are very absorbent. 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 break, even pulverize and sludge, thereby significantly deteriorating the permeability of the ore.
The loose density of ore is directly related to the relationship between ore heap volume and ore quality. Therefore, it is also an important parameter in heap leaching.