In recent years, many scholars in China have conducted a lot of research on uranium mining, and people have done experiments in the aspects of in-situ leaching, heap leaching, column leaching, tank leaching, and percolation leaching. Heap leaching process in which its process is simple, less investment and quick, simple management, low extraction costs for low-grade uranium ore leaching, environmental pollution compared to conventional hydrometallurgical less, etc., by the majority of metallurgical workers extensive attention. In recent years, the heap leaching process has been widely used in many mines. One of the main factors affecting the leaching rate in the heap leaching process is the ore particle size. The size of the ore heap is small, the leaching period will be relatively shortened, and the leaching rate will be greatly improved, but at the same time, it will bring about high acid consumption, high cost, easy blockage, slab, muddy, etc., on the contrary, the leaching period is longer, leaching The rate is low. Therefore, selecting the appropriate particle size for heap leaching production is a key process parameter for heap leaching. According to the heap leaching process used in a uranium mine, the size of the middle and upper ore is too large, and the leaching rate is low. The column leaching test with different particle sizes is carried out to monitor the influence of particle size on the leaching effect, so as to find the best The ore particle size.

First, the experimental preparation

(1) Experimental samples

The ore sample used in this experiment is from a mine site mined in a mine. The ore sample of 1t is collected, and the ore quality of -10mm, -8mm, -6mm ore is 150kg, which is used for column leaching test. The natural types of ore at this site are classified into secondary oxidized ore types and primary ore types. It is a type containing secondary uranium ore and a type of bituminous uranium ore. The type of secondary uranium ore is affected by different degrees of oxidative leaching, the ore is loose, and the uranium mineral is mainly secondary uranium mineral. The main mineral quartz, hematite minor minerals such as calcium silicate uranium minerals uranium, copper, uranium mica, black uranium, uranium phosphate, tallow curite like; type containing pitchblende pitchblende containing erythro Iron ore silicified fractured rock type ore, the ore is less oxidized, and the uranium mineral is mainly asphalt uranium ore. The ore is dark red and pig liver color, which is dyed and short veined. Secondary uranium minerals are visible locally. The chemical composition analysis of the ore samples is shown in Table 1.

Table 1 Chemical composition of mineral sample /%

(2) Experimental device

The experiment was carried out in a PVC plastic tube having a diameter of 155 mm and a height of 1500 mm. The constant-flow peristaltic pump is used to transport the leaching agent, and the daily spray amount is controlled by adjusting the rotational speed of the peristaltic pump.

(3) Test conditions

The leaching test uses sulfuric acid solution as the leaching agent. The concentration of the leaching agent in the early stage of leaching is 20-25 g/L, the concentration in the late leaching is 5-10 g/L, and the pH of the leaching solution is controlled below 2.5. Spraying strength is 12-15L/(m ² ·h), continuous spraying is used in the early stage of spray leaching. When the uranium concentration of leaching solution is 100mg/L, intermittent spraying is adopted, and the spray-stop ratio is 1..1.

Second, the experimental results and discussion

(1) Column immersion test results

In the experiment, three different particle size (-10mm, -8mm, -6mm) spray leaching columns were sprayed in the same series (99 grade). The test conditions are shown in Table 2. The final leaching rates of the liquid gauges were 79.0%, 86.2%, and 90.5%, respectively, and the leaching rates of the slag meters were 78.9%, 85.5%, and 89.0%, respectively. The spray agent, sulfuric acid and leaching rate consumed by the three experimental columns have a certain relationship with the ore particle size of the upper column. The detailed column leaching results are shown in Table 3.

Table 2 Column immersion test conditions

Table 3 Column immersion test results

(II) Analysis of leaching results

It can be seen from Table 3 that the larger the ore particle size, the less the spray agent, the less sulfuric acid, and the lower the leaching rate; on the contrary, the ore particle size is small, the spray agent, sulfuric acid is consumed, and the leaching rate is high. The main reason is that the size of the upper ore ore is different. In the case of a certain quality ore, the ore with a small particle size has a large specific surface area, a relatively sufficient contact with the spray agent, and a high leaching rate; and many acid-consuming substances exposed on the surface of the ore, More sulfuric acid is consumed.

In the production process of the heap leaching process, under the same spray conditions, the smaller the particle size of the pile, the higher the leaching rate, and the shorter the leaching period when the same leaching rate is reached. It can be seen from Fig. 1 that when the leaching rate reaches 70%, the leaching grades of the ore with different grain sizes (-10 mm, -8 mm, -6 mm) are 54, 46, 41, respectively; when leaching the same number of days, the particle size The smaller the leaching rate, the better the -6 mm particle size from the experimental leaching efficiency. It has been found through experiments that when the spray intensity of each grade of ore is 12-15 L/(m ² ·h), no liquid accumulation is found at the top of the ore layer. When the slag of each column was discharged, it was found that there was a knot phenomenon in the lower layer of each column, and the ore slab phenomenon of -6 mm grain size was serious, which was not conducive to industrial production. Therefore, the optimum pile size is -8mm when performing process heap leaching.

Third, the conclusion

Considering the experimental leaching rate, the leaching period and the feasibility of the process parameters, the optimal pile size of the uranium ore heap leaching process suitable for the mine is -8mm.

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