Heap leaching of uranium in uranium mining and metallurgy

Heap leaching is the abbreviation of heap leaching method, which is a leaching method by spraying diluted chemical solvent on the pre-piled ore heap to selectively dissolve (leach) the target components in the ore to form ions or complex ions, and then transfer them to the solution for further extraction or recovery. Heap leaching ore only needs coarse crushing, and the solution is in an unsaturated flow state in the heap. The research on heap leaching technology of uranium in China began in the 1960s. Through the continuous efforts of several generations of uranium mining and metallurgy scientists, breakthroughs have been made in many technical fields, and a large number of scientific research achievements have been successfully applied to the industrial production of heap leaching uranium, and remarkable economic benefits have been achieved. Heap leaching of uranium is one of the main processes of uranium metallurgy in China.

Heap leaching process of concentrated acid curing high iron leaching

The characteristics of this technology are as follows: firstly, the crushed ore is pretreated by concentrated acid ripening, so that the iron in the ore is oxidized to trivalent, and most uranium is converted into soluble salt, and then it is leached with clear water containing ferric sulfate. This process not only shortens the ore leaching cycle, but also improves the uranium concentration of the leaching qualified solution. After years of industrial application, it is shown that the leaching cycle of ore is only 60 ~ 100 d and the uranium concentration in qualified leaching solution can reach 7 ~ 9 g/L.

Pellet heap leaching technology of low permeability ore

Low permeability mud-bearing ore is chemically bonded for acid granulation. By participating in the chemical reaction, the binder can form a crystal structure network based on hydrate nuclei in the ore particles, thus greatly improving the permeability of the ore heap. Industrial production shows that the leaching rate of metal is over 95% after heap leaching after ore granulation pretreatment. Compared with direct heap leaching, the leaching period is shortened by 70%, and the uranium concentration of leaching solution is increased by 50%.

Heap leaching technology of fine ore

Through in-depth analysis and research on mass transfer mechanism and leaching process of heap leaching, the concept of heap leaching of fine ore is put forward, and it is considered that there should be an optimal economic particle size for heap leaching ore crushing. On the basis of full experiments, the calculation model of economic particle size of heap leaching ore crushing is deduced. At present, the research results have been applied in several heap leaching uranium mines.

Series heap leaching technology

In order to improve the uranium concentration of qualified ore heap leaching solution as much as possible and reduce the consumption of raw materials, a series of heap leaching experiments were systematically carried out on various uranium ores, and a mathematical model for calculating the operating parameters of each stage of ore heap leaching was developed. The application results of several heap leaching uranium mines show that the uranium concentration of qualified heap leaching solution can be increased by 2 ~ 3 times, and the material consumption of acid, oxidant and metal recovery process can be reduced by 20% ~ 30%.

Bacterial oxidation heap leaching technology

The research on heap leaching of uranium by bacterial oxidation in China began in 1960s. Thiobacillus ferrooxidans is mainly used to oxidize pyrite in ore or adsorb Fe2+ in tailings to convert Fe2+ into Fe3+, thus completing the oxidation leaching of low-valent uranium in ore. 4000 tons of industrial tests were carried out. The industrial test results show that compared with conventional oxidation heap leaching, sulfuric acid consumption can be reduced by 65438 02.5%, leaching time can be shortened by 32% ~ 45%, and uranium concentration in leaching solution can be increased by 88.2%.

Comprehensive heap leaching recovery technology of associated uranium ore

At present, there are a certain proportion of uranium deposits in the proven uranium resources. This kind of deposit often takes a long time to leach, and the leaching rate of molybdenum is low, so the separation effect of uranium and molybdenum in leaching solution is not ideal. The mixed acid aging activation leaching technology was used for heap leaching of ores, which shortened the leaching period of ores by more than half, and the leaching rates of uranium and molybdenum reached 90% and 70% respectively. A new type of ion exchange resin was used to adsorb uranium and molybdenum from the leaching solution at the same time. Through step-by-step leaching, the separation coefficient of uranium and molybdenum reached more than 2000.

Leaching uranium by percolation

For some complex uranium mines with high impurities such as iron, magnesium, calcium and aluminum, in the conventional heap leaching process, with the migration of the solution, the acidity of the solution in the heap will be continuously consumed, resulting in the continuous migration, accumulation and precipitation of iron, magnesium, calcium and aluminum in the heap, which will harden the heap and reduce the permeability of the heap. Osmotic leaching process changes the contact mode between solution and ore, which can keep the acidity of solution relatively stable and effectively avoid ore pile hardening. The industrial test shows that the leaching cycle of ore is shortened from more than 300 days to more than 60 days, and the uranium leaching rate is increased from about 60% to over 90% after the heap leaching process is replaced by percolation leaching process.