CS199836B1 - Method for underground leaching,especially of uranium-zirconium ores difficult to leach - Google Patents

Description

The invention relates to a method for underground leaching of uranium-zirconium ores, which solves the increase in uranium recovery by utilizing heat.

Methods of underground hydrochemical mining of useful minerals, not requiring mining technology, usually associated with large investments, laboriousness and necessity of mining large volumes of ballasts, have been known in some cases for many years. In this way, for example, rock salt is mined, and Frasch's sulfur extraction process falls to some extent. A special case of these methods are the hydrochemical methods utilizing the desired mineral reagents for underground leaching.

In uranium mining, the first underground leaching experiments were associated with C.W.Livingaton (US Patent No. 2,818,240), the proposed leaching medium being a solution of sodium carbonate and bicarbonate. The method is suitable for ideally deposited ores, which contain single-bound uranium mainly in hexavalent form, so that they are well leachable. At the same time, however, suggestions appeared, including practical tests with underground acid leaching, mainly sulfuric acid, at concentrations of veam and not exceeding 50 g HgSO4 / l. This procedure is also not universal and is not suitable, for example, for bearings deposited in rocks showing a high acid consumption. The shortcomings of the prior art have been attempted to overcome US Patent No. 2, 896,930, proposing an alkali metal carbonate solution for underground leaching and the addition of an oxidant and a complexing agent, both without further specification. The injectable solution according to the first claim of the cited patent should be cold or corresponding

199 836

199 939 bearing temperature. U.S. Patent No. 2,954,218 discloses that uranium bound in rocks with an increased content of carbon or organic carbon compounds is very difficult to leach without treatment, and that a satisfactory increase in yield is achieved by roasting such an ore. It is therefore proposed to inject either gaseous or liquid hydrocarbons and oxygen or air into uranium deposits, to carry out underground combustion and subsequent leaching with a not very concentrated acidic or even alkaline solution. This method is practically unusable for bearings, characterized by low permeability of ore parts and pressurized water regime (hard or aubarthesis, but also with pressures of 1.5 MPa and more).

As the nature of uranium deposits varies considerably from case to case, some other procedures have been proposed for the underground leaching method as well. In industrial scale applications, however, practically exclusively the basic variant is used, which is characterized by the injection of leaching solutions through the nets of injection boreholes and pumping of leachate through the nets of extracting boreholes, with slightly acidic solutions (up to 50 g HgSO4 / l) preferred. the larger part is given by the bearing temperature and the average air temperature, which is most often in the annual average between 10 and 15 ° C. The disadvantages of the prior art processes are the relatively low yields achieved in deposits, characterized by the common occurrence of uranium and zirconium, which results in difficult leachability and low permeability of the ore layers, which hinder the penetration of solutions by uranium minerals and the return transport of the leached metal.

These drawbacks are overcome by the underground leaching of uranzirconium ores according to the invention, which consists in heating the ore deposit by injecting leach solutions containing sulfuric acid at a concentration of 1 to 200 g / l, heated to a temperature of 20 to 80 ° C. The warm solution gradually passes through the lined block of ore as it passes through the underground, creating better leaching conditions.

The process of the invention results in an increase in yield or shortening of leaching cycles; this can speed up the reclamation of large exploited areas. In addition to the economic benefits of bringing the invention and significant benefits of environmental protection. According to laboratory tests, the increase in yield with a temperature increase of 1 ° C, in the range of 15 to 60 ° C, depending on the type of ore, is 0.4 to 1.5% of the total uranium reserves. At the beginning of said temperature interval and the more difficult to leach ore, yield gains are usually higher and vice versa Since at the same time increasing the steepness of the yield curves in the first leaching flight, the major effect may be a substantial reduction in leaching time required to achieve the determined yield.

Three factors, which increase the yield per unit of time, apply here (to varying degrees to different types of ores).

The acceleration of the filtration processes in the growing ore due to the lower viscosity of the solution means a faster delivery of the reaction reagent to the less permeable layers and a faster transport of the precipitated metal from these layers.

Increasing the rate of diffusion processes is particularly important for very poorly soluble to impermeable layers, lenses and laminae, usually containing the utility component at a higher concentration than the diameter of the bearing.

Furthermore, the specific bonds of uranium and zirconium in the respective minerals are more intensively disrupted, and at the usual bearing temperatures they are very stable even against the effects of

199,838 commonly used acid leach solutions.

The necessary heat can be obtained from conventional combustion processes or from nuclear reactions. It is particularly advantageous to use the heat released in the processes associated with the production of sulfuric acid, which is also the main reagent for underground leaching of uranium, or other waste heat from technological processes. The heat exchange processes can be carried out using conventional postures and in conventional type equipment.

The heat loss calculations associated with the application of the process of the invention have shown that heat loss to the subsoil and overburden of the ore layers is acceptable. In the first two years it is around 25% of the heat supplied, later falling below 10%. Losses in boreholes and surface distributions can be solved by thermal insulation or by adjusting the drilling network, distribution system and injection mode.

Exemplary embodiment

The average thickness of the permeable horizon containing the ore body is 25 m, the average volume thermal capacity of the rock is 2.43 MJ.m ^-3 .K ** ¹ , the natural layer temperature is 15 ° C, the ore contains substantially zirconium and is highly resistant to The spent solution after uranium separation and acidification to a concentration of 50 g H 2 SO 4 / l passes through a heat exchanger where it is heated to 60 ° C. The heated solution is distributed through a pipeline to the injection wells and through them to the horizon of interest. Due to heat losses on the surface and in the wells, the average solution temperature at the inlet of the layer is 45 ° C. With a circulation intensity of 151. m “ ² . day ** ¹ the area is one hectare and the daily heat dose is 18.8 GJ. 18.2 TJ is needed to heat the entire horizon on the same surface by 30 ° C. Because the heat from the layer escapes to the subsoil and overburden and later to the leachate, it heats the ore body by 20 ° C in 3 years and in 8 to 10 years while the heat consumption is constantly decreasing due to 27 ° C increasing temperature of the pumped solution. With a 15-year mining cycle, yield increases by 18.6% ·

The invention can be used in all cases of underground leaching of mineral minerals, where the extraction cycle time is relatively long relative to the medium solution turnover time and the increase in yield in relation to the price of the product guarantees the profitability of the application.

Claims (1)

SUBJECT OF THE INVENTION A method of underground leaching, in particular of hardly leachable uranium-zirconium ores, characterized in that the ore deposit is heated by injecting leaching solutions containing sulfuric acid at a concentration of 1 to 200 g / l, heated to a temperature of 20 to 80 ° C.