With the development of the gold industry, the high-grade gold resource is less than before, and the development and usage of low-grade gold become the focus. Gold heap leaching process, as one of the gold processing technologies, is an effective way of low-grade gold extraction.
The gold heap leaching process is that, the gold-bearing ore broken to a certain size is piled up on a leak-proof base of asphalt, concrete or plastic. The ore is sprayed with cyanide solution from above to dissolve the gold, and then the gold is extracted in this way. With a low cost,The gold heap leaching process is short, easy to operate, and fast effective. It is widely used in the gold processing industry. However, the gold heap leaching processing is influenced by multiple factors. If the treatment is not good, easy to lead to production standards, process accidents and other problems, thereby affecting the plant efficiency. The following, we will sketch the four factors influencing the gold heap leaching process: the ore, leaching solution, spray, and heap leaching.
There are usually some other minerals in gold ores, such as iron, lead, antimony and so on. The metal minerals influence the cyanide leaching to a certain degree. It reduces or increases the speed of gold dissolution. If there is carbon in gold ore, the mineral particles encased in carbon may react with cyanide solutions, which blocks the dissolution of gold. Besides, the activated carbon may absorb the dissolved gold, which is also called the gold robbery. It reduces the gold leaching rate, recovery rate, and seriously influences the gold heap leaching process.
To reduce and eliminate the influence of other minerals on gold leaching process, the gold heap leaching process should be thoroughly sprayed with saturated alkaline solution before cyanide leaching. It precipitates and decomposes other harmful mineral components and maintain the PH value of the solution discharged from the ore heap above 9.54. The washing water is removed as well. At this time, the gold heap leaching process can be carried out.
In general, the smaller the ore grain size is, the shorter the leaching time is, the higher the leaching rate is. However, in practical terms, the heap leaching of ore grains that have been broken to 5~20 mm. If the amount of pulverized ore -200 mesh content is more than 35%, under the condition of conventional heap leaching method, the surface of the ore heap will be hardened to form groove flow and the leaching rate of gold will be reduced.
The gold dissolution speed is fast in the cyanide solution with cyanide concentration under 0.05%. Inversely, the gold dissolution speed is slow in the cyanide solution with cyanide concentration more than 0.15%. Therefore, according to the ore composition and different leaching stages, the cyanide solution concentration should arrange from 0.025%~0.1%.
The gold dissolution speed is proportional to the concentration of oxygen in the solution. The reduction of the oxide concentration is bound to lead to the reduction of gold dissolution speed. Therefore, it is necessary to ventilate the leaching solution with oxygen to ensure that the oxygen involved in the reaction is sufficient at any time.
When the spray intensity is high, the relative movement between the solution and the ore is strengthened, the diffusion is strengthened, and the leaching rate is increased. However, the spray strength should be controlled in 0.05~0.1L/t per minute.
The ore heap has good permeability, and the gold-containing solution can be timely discharged through the ore heap to accelerate the leaching reaction speed, shorten the cycle and improve the leaching rate. The size of leached ore and the content of clay in ore all affect the permeability of ore heap.
The ore with good permeability can be set higher. The ore with poor permeability should not be too high. Otherwise, it will reduce the permeability of ore heap and prolong the leaching time. Generally speaking, the mine stack height should be kept at 3~10 meters. The height of the mine stack can be determined by experiments.
Although the gold heap leaching process is short in schedule and fast ineffective, it also influenced by a lot of factors. To make sure the smooth carrying out of gold extraction, all kinds of influencing factors must be considered comprehensively and effective measures should be taken to analyze, study and control them.
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