As with agitation leaching, in order to accelerate the rate of chemical reactions, oxidants are also required in heap leaching. It is known from the chemical principle of heap leaching that, in the absence of oxygen, the cyanidation reaction of gold cannot be carried out. UO 2 in the ore, if no oxidant is present, is also difficult to dissolve in dilute sulfuric acid (unless high acid is used).
The oxidant in the heap leaching relies mainly on air, or on other high-priced ions (such as Fe 3 + ) produced during the heap leaching process, and rarely adds other oxidizing agents.
The heap is impregnated with an unsaturated stream. The air and the leaching solution alternately enter the pores of the ore and the ore. The oxygen in the air continuously contacts the minerals in the ore, causing the mineral to be gradually oxidized. This process is similar to the weathering process of certain rock minerals in nature. But the process is much faster than the usual weathering process. The so-called "self-breathing" process in heap leaching is also good, and the "chimney effect" is also good. Both of them refer to the phenomenon that the ore heap in the heap leaching process can continuously absorb the oxygen in the fresh air and promote the oxidative decomposition of the mineral. Many of the ore heaps are completed after leaching. When the unloading is carried out, the size of the ore is reduced, and some even become powdery. For example, the heap is immersed in the Sharbrak gold mine in Xinjiang. The size of the ore is -40mm. When leaching, when unloading, it is basically -15mm.
In addition, some minerals are not oxidized by oxygen in the air at all, and additional means must be used. For example, arsenopyrite (arsenic pyrite) is difficult to be oxidized by air and the fine particles of gold are often wrapped arsenopyrite. Bacteria are often used to pre-oxidize arsenopyrite, exposing the packaged gold, dissociating it, and then leaching. Bacterial leaching of uranium ore is essentially a bacterial oxidation of pyrite , which makes iron at a high price. Fe 3 + oxidizes UO 2 to U 6 + , and U 6 + reacts with sulfuric acid to achieve leaching.
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