The natural generient infusion process is a new in-situ process developed on the basis of low acid leaching and weak alkali leaching. The process can effectively leach the uranium in the ore under the condition of minimally changing the groundwater environment. Therefore, the process has a complex sandstone uranium deposit with high salinity, low ore permeability and high calcium content. It has good leaching effect, and has the advantages of less reagent consumption, less impact on groundwater environment, less corrosiveness to equipment and materials, stable uranium concentration in leachate, and no damage to the natural permeability of ore. This process has been widely used in the country of Uzbekistan.
A uranium deposit (NO2) in Xinjiang is a newly discovered loose sandstone-type uranium deposit in recent years. Due to the high content of calcium carbonate in the ore, high salinity of groundwater, high content of Ca 2+ , Cl - and SO 4 2- in groundwater, etc., the deposit is immersed by conventional acid method and alkali method. During the uranium mining test, problems such as serious chemical blockage of the ore-bearing layer, decreased ability of the borehole pumping fluid, and low uranium concentration in the leachate occurred. Since the intrinsic leaching process of the natural generative agent has unique advantages compared with the conventional acid-base leaching, the deposit is expected to achieve a technical breakthrough by using the natural generient reagent leaching process.
This paper is part of the natural leaching reagent infiltration test for a uranium deposit in Xinjiang. The purpose of this paper is to evaluate the possibility of leaching uranium using natural genetic reagents by analyzing the geological and hydrogeological conditions of the uranium deposit. The sandstone uranium resources provide the basis and basis.
First, the principle of natural immersion reagents and applicable conditions
The natural genetic agent originally refers to groundwater containing chemical components such as oxygen and bicarbonate that are naturally present in the ore-bearing aquifer. Groundwater usually contains the chemical component of natural heavy calcium carbonate, magnesium carbonate, and oxygen, but low levels, reach the level of leaching of uranium ores and leaching of uranium concentration is very low. Therefore, the generalized natural genetic agent is based on the chemical components naturally present in the groundwater, in which compressed air (or oxygen) is injected into the ore-bearing aquifer, or a small amount of dilute sulfuric acid is added, or a small amount of CO 2 gas is added. An agent having a certain leaching strength is formed in the ore-bearing aquifer.
Uranium minerals in sandstone-type uranium deposits mainly exist in tetravalent form, do not directly interact with carbonates, and should be oxidized to hexavalent uranium before leaching. Air or oxygen is a good oxidant. The natural uranium entrapment process uses mainly air or oxygen, which is widely used in nature, as an oxidant.
The process of leaching uranium from natural generative reagents is similar to the process of bicarbonate leaching. The basic principle is: pressing human air into the borehole, oxidizing uranium ore with chlorine gas in the air, converting U + to U 6+ , and then using groundwater. The bicarbonate or carbonate in the leaching of uranium.
Hexavalent uranium reacts with bicarbonate present in groundwater to form uranyl carbonate ions, forming a leachate. The combined reaction of uranium is as follows:
When the ore contains carbonate, H + reacts with the carbonate to form bicarbonate ions, resulting in an increase in the concentration of bicarbonate ions. If the ore contains a small amount of sulfide, the sulfuric acid formed by the oxidation of the sulfide acts on the carbonate, and the generated CO 2 is more advantageous for leaching. The reaction formula is:
It can be seen from the above analysis that the natural causative reagent leaching process has strong adaptability to uranium deposits with high carbonate content and high sulfide content in the ore.
Since the concentration of the natural causative reagent in the groundwater is low and the leaching strength is weak, the uranium concentration of the leachate is low, so that the liquid leaching ability of the immersion drilling hole is required in the leaching process. In addition, in order to press the high-pressure air into the borehole to fully oxidize the ore layer, the process has high requirements for the hydrogeological conditions of the deposit and the immersion drilling structure. Therefore, the intrinsic leaching process of natural generative reagents is not suitable for all in-situ leachable sandstone-type uranium deposits, and has a certain scope of application:
(1) The ore contains a certain mass fraction of carbonate, generally required to be greater than 1% (calculated as CO 2 , the same below). When the mass fraction of carbonate in the ore is low, it can be directly immersed by acid method.
(2) The ore has good permeability, and the general requirement is greater than 0.5 m/d, which is determined by the characteristics of large amount of drilling fluid and low uranium concentration of the leachate in the uranium mining process of the natural genetic reagent.
(3) The ore-bearing aquifer has a good water-removing bottom plate to ensure that the air pressed into the ore layer can fully contact the ore.
(4) Due to the limitations of air compressor equipment, wellbore equipment and materials, the water head value of the ore-bearing aquifer is required to be less than 200m.
Second, the geological conditions of the deposit
The sandstone uranium deposit is controlled by the interlayer oxidation zone. The ore body is distributed in the east-west direction, with a length of 820m and a width of 26-400m. To form a plate-based ore, partially rolled for complex, occurrence consistent with the sand, and NNE general inclination is generally 30 ~ 80, ore depth is 81.6 ~ 174.9m. The thickness of the ore-bearing layer is 22.8-59.9m, with an average of 41.8m. The middle part contains 0.5~5.0m clay rock interlayer. The ore-bearing layer is divided into upper and lower sub-layers, the upper part is the No. I ore body, and the lower part is the No. II ore body. , in which the No. II ore body is the main ore body. The ore section usually contains 1 to 3 layers of dense calcareous sandstone and clay conglomerate interlayer with a thickness of 0.2-1.0 m. The ratio of thickness of the ore layer to the thickness of the ore-bearing layer is 0.38-0.49, with an average of 0.44. The main parameters of the uranium deposit are shown in Table 1.
Table 1 Hydrogeological parameters of test block
Mineral deposit | Length / m | Width / m | Thickness / m | Buried depth / m | Uranium grade /% | Umethane per m 2 / kg |
Upper mine layer I | 110～520 | 50~150 | 3.5 to 3.8 | 81～158 | 0.025 | 2.57 |
Lower mine layer II | 80～820 | 26~400 | 0.9 to 20.9 | 93～175 | 0.035 | 4.86 |
The natural type of ore is inter-layer oxidation zone sandstone type, mainly loose, sub-loose, gray, dark gray sand (gravel) rock ore, followed by mudstone ore and dense calcareous cemented sand (gravel) rock ore. The ore is mainly contact-bonded with a small amount of dissolved pore cement. The cement is mainly clay and contains a small amount of carbonate. The mass fraction of quartz in the ore mineral composition is 30% to 40%, and the mass fraction of feldspar is 10% to 25%. Clay minerals are montmorillonite and kaolinite,, a small amount of chlorite (see Table 2), in addition also contain minor amounts ore pyrite, carbonate minerals. The chemical composition of the ore is shown in Table 3. Compared with the mineral quality education of the NO1 deposit in Xinjiang and the Mengutuk deposit in Uzbekistan (divided by the degree of sulfuric acid solubility), the mineral composition of the sandstone uranium deposit is complex, and the carbonate mass fraction in the ore is >2%, which is not conducive to Acid dip (see Table 4).
Table 2 Mineral mass fraction of ore clay phase
Kaolinite | Montmorillonite | Chlorite | Illite | Erie-montmorillonite |
45.7 | 11.8 | 6.2 | 14.9 | 21.4 |
Table 3 Mass fraction and loss on ignition of each component of ore
U | SiO 2 | Al 2 O 3 | K 2 O | Na 2 O | CaO | MgO | Fe 2 O 3 | FeO | MnO | P 2 O 5 | CO 2 | Loss on ignition |
0.015 | 74.80 | 11.48 | 2.77 | 0.95 | 0.80 | 0.89 | 3.31 | 1.42 | 0.02 | 0.008 | 2.89 | 2.85 |
Table 4 Average mass fraction of each mineral in the mine
Degree of dissolution | mineral | Deposit | ||
Xinjiang NO1 | Monkutuk | Xinjiang NO2 | ||
insoluble | Quartz, siliceous rock debris | 79 | 81.4 | 67.3 |
By-mineral | 1 | <1 | <1 | |
total | 80 | 82.40 | 68.3 | |
Hard to dissolve | Feldspar | 13 | 10.2 | 13.9 |
Water mica | 1.1 | 1.37 | 2.85 | |
Kaolinite | 2.4 | 3.5 | 10.18 | |
Organic matter | 0.5 | 0.5 | 0.23 | |
total | 17 | 15.57 | 27.16 | |
Dissolve | Uranium mineral | 0.1 | 0.1 | 0.1 |
Chlorite | 1.2 | 0.9 | 0.26 | |
Carbonate | 0.2 | 0.27 | 2.48 | |
Limonite | 0.7 | 0.35 | 0.8 | |
Sulfide | 0.8 | 0.41 | 0.9 | |
total | 3.0 | 2.03 | 4.54 | |
3. Hydrogeological conditions of the deposit
There are 8 aquifer groups in the mining area, and the ore-bearing aquifer is located in the V-aquifer group. Groundwater seam pore water pressure, water depth of 39.95 ~ 42.62m; impermeable bottom roof area in a continuous and stable, large thickness, good water separation properties; lithology is mainly shale, sandstone and argillaceous coal layer. The porosity of the ore-bearing layer is 8.65%~39.84%, with an average of 26.75%. The permeability coefficient ratio of the ore-bearing rock to the non-mineralized layer is 1.24:1. The other hydrogeological parameters of the deposit are shown in Table 5. The groundwater chemical type is Cl·SO 4 -Na, the salinity is 8.46～13.16g/L, the pH is 6.9～7.5, the Eh is -64～-23mV, the water temperature is 18～21°C, and the chemical composition of groundwater is shown in Table 6.
Table 5 Hydrogeological parameters of the ore-bearing layer
Static water level /m | Head height /m | Permeability coefficient /m·d -1 | Unit water output /L·s -1 ·m -1 | Salinity g·L -1 | PH | Water temperature / °C |
39.95~42.62 | 87.69～93.45 | 0.2 to 0.3 | 0.076～0.0146 | 8.46~13.16 | 6.9 to 7.5 | 18~25 |
Table 6 Chemical composition of groundwater containing ore
U | K + | Na + | Ca 2+ | Mg 2+ | ∑ | λ | HCO 3 - | SiO 2 | SO 4 2- | Cl - |
2.2 | 21.17 | 2033.0 | 752 | 325 | <1 | 0.04 | 46 | 10 | 3150 | 3370 |
It can be seen from Table 6 that the mineralization of the groundwater is high and it is a high-salt groundwater. If the hardness of water is expressed by the amount of Ca + and Mg 2+ per L of water, the total hardness of groundwater calculated from Table 6 is about 130 mmol, indicating that the hardness is high.
According to the chemical composition of the groundwater in the deposit, chemical precipitation such as CaCO 3 , Ca(HC0 3 ) 2 , MgCO 3 , CaSO 4 may be formed during the leaching process of adding chemical agents, and various iron precipitates may be formed in the vicinity of the liquid. The formation of chemical precipitation is related to the solubility product of ions in groundwater and the ionic strength. The theoretical solubility product constants and solubility of the main precipitates and the calculated actual solubility products and solubility are shown in Table 7.
Table 7 Actual solubility product and solubility of main components of groundwater (20 ° C)
Precipitate | Solubility product | Solubility /g·L -1 | ||
Theoretical value | Calculated | Theoretical value | Calculated | |
CaCO 3 | 4.8×10 -9 | 5.8×10 -6 | 0.013 | 0.030 |
MgCO 3 | 3.5×10 -8 | 3.9×10 -6 | 0.22 | 0.025 |
Ca(HC0 3 ) 2 | 0.385 | 0.627 | ||
CaSO 4 | 6.1×10 -5 | 5.93×10 -4 | 2.02 | 2.625 |
Seen from Table 7, the solubility product and the actual composition of the deposit groundwater solubility greater than theory, groundwater may precipitate components have reached saturation; but not the causes chemical precipitation water is Cl - higher concentrations, salt The effect of the effect increases the solubility of the components, leaving the groundwater in a state of dynamic equilibrium.
Fourth, the evaluation of mineral deposit conditions
From the perspective of in-situ uranium mining, the geological and hydrogeological conditions of the deposit are divided into favorable factors and unfavorable factors. The favorable factors are: the ratio of the thickness of the ore body to the thickness of the ore-bearing aquifer, the location of the ore body relative to the ore-bearing aquifer, the depth of the burial of the ore layer, the continuity of the water-blocking top, the original water level of the ore-bearing aquifer, and the head. Height, etc.; poor permeability, but still meet the basic requirements for leaching uranium (≥0. m / d). The unfavorable factors are: the complex interaction between the permeable rock stratum and the non-permeable rock stratum (mud rock layer or calcareous layer), which tends to dilute and lose the solution; the ore content in the ore is too high, it is not suitable to use acid leaching; The groundwater is high salinity water, the chloride content in the groundwater is high, the calcium and magnesium ions have reached saturation, and chemical precipitation is easy.
When uranium is immersed in natural genetic reagents, the conditions for leaching uranium can be broadened, and the unfavorable factors such as high content of HCO 3- in the ore-bearing aquifer and high carbonate mass fraction in the ore become favorable factors, and can be avoided. The high degree of mineralization of groundwater, the high content of chloride in groundwater, and the high content of calcium and magnesium ions have an impact on the in-situ leaching process. Therefore, the leaching of uranium by natural generative reagents can be used to rationally mine the deposit.
V. Indoor test
(1) Stirring leaching test
1. Tap water or groundwater leaching
A number of finely ground samples and natural size samples were taken and placed in air for natural oxidation, and these samples were used for leaching tests using tap water or groundwater as a leaching agent. The test conditions and results are shown in Table 8.
Table 8 Leaching test conditions and results using tap water or groundwater as leaching agent
See from Table 8:
1 After natural oxidation, the leaching rate of the ore sample after leaching with groundwater is 35.4%, which is greater than the leaching rate of tap water using tap water, indicating that the carbonate in groundwater has leaching performance.
2 Whether leaching with tap water or leaching with groundwater, the leaching rate is low, indicating that the natural oxidation degree of the ore and the concentration of the leaching agent are low, and the leaching conditions must be strengthened.
2. O 2 +CO 2 leaching under pressure
Since the calcium and magnesium ions in the groundwater of the deposit are already supersaturated, the method of increasing the concentration of HCO 3 - by adding bicarbonate will destroy the chemical balance between various ions, forming a chemical precipitate and reducing the permeability of the ore. Therefore, a new equilibrium system must be established in the ore-bearing aquifer. In this new equilibrium system, the concentration of Ca 2+ and HCO 3 - plasma is higher than that of groundwater, but no precipitation of CaCO 3 and CaSO 4 occurs. Moreover, the uranium concentration and its leaching rate are also significantly improved. For this purpose, a pressure leaching test using O 2 +CO 2 + groundwater as a leaching agent was carried out.
The test was carried out in an autoclave. The sample was not naturally oxidized by 200 g, the uranium grade was 0.0283%, the leaching agent was O 2 +CO 2 + groundwater, the liquid solid product mass ratio was 10 L/kg, and the leaching time was 24 h. First pass C0 2 and then pass O 2 . The test results are shown in Table 9.
Table 9 CO 2 pressure leaching test results
PB/MPa | Leachate PB/(mg·L -1 ) | PH | EH/mV | Leach rate /% | |||||
CO 2 | O 2 | Ca 2+ | SO 4 2- | CO 3 2- | HCO 3 - | U | |||
0.05 | 0.4 | 862 | 3930 | <1 | 722 | 53.75 | 6.15 | 172 | 46.3 |
0.1 | 0.4 | 902 | <1 | 767 | 55.14 | 6.58 | 150 | 47.5 | |
0.2 | 0.4 | 882 | 3510 | <1 | 812 | 62.53 | 5.96 | 196 | 53.9 |
0.3 | 0.4 | 882 | 4080 | <1 | 812 | 56.32 | 5.90 | 196 | 48.5 |
It can be seen from Table 9 that uranium leaching rate of 46.3% to 53.9% can be obtained by leaching of groundwater injected with O 2 +CO 2 , and with the increase of CO 2 concentration, Ca 2+ , HCO 3 - and SO 4 2- There are different degrees of increase, and the pH value is continuously decreasing.
(2) Column immersion test
Two kinds of leaching agents were selected for the column leaching test, that is, the groundwater after removing Ca 2+ and Mg 2+ and the untreated groundwater. The specific test conditions are shown in Table 10. The test results are shown in Figure 1 and Figure 2.
Table 10 Natural Oxidized Ore Column Dipping Test Conditions
Column number | Leaching agent | Loading quality /g | grade/% | Sample height Degree / cm | Mineral body Product / cm 3 | Bulk density g·cm 3 | Porosity /% | the inside diameter of /mm |
ZR-1 | Calcium and magnesium groundwater | 600 | 0.0719 | 64.5 | 425.6 | 1.41 | 37.08 | 29 |
groundwater | 600 | 0.0716 | 62.5 | 441.5 | 1.36 | 36.28 | 30 |
1-ZR-1 column; 2-ZR-2 column
Fig.1 Variation of leaching rate with mass ratio of liquid solid product
1-ZR-1 column; 2-ZR-2 column
Fig. 2 Curve of the ratio of the leaching solution P(U) to the solid mass ratio of the liquid
It can be seen from Fig. 1 and Fig. 2 that when the groundwater is directly leached, the peak value of P(U) is higher, and the mass ratio of liquid solid content at the peak is about 1.0 L/kg; the leaching rates of the two leaching agents are about 40. %, the leaching rate is basically the same as the liquid solid mass ratio, but to obtain a higher leaching rate, it is necessary to add O 2 and CO 2 for enhanced leaching.
(III) Evaluation of indoor test results
Although the concentration of calcium and magnesium ions in the groundwater of the deposit is high and the carbonate content in the ore is high, in the indoor column leaching test, after the ore is naturally oxidized, the leaching of the groundwater by the ore layer has achieved good results. When the mass ratio of solid product is 4L/kg, the leaching rate of ore reaches more than 40%, which is not significantly different from the leaching of groundwater after calcium removal, indicating that the deposit may be immersed in natural genetic reagents.
Conclusion
The ore at the end of a uranium mine in Xinjiang is poorly permeable. The ore layer has a calcareous cementation interlayer or crystal, the ore has a high carbonate content, and the ore-bearing aquifer groundwater is a high salinity water, which is immersed by conventional acid and alkali methods. Uranium processes are difficult to apply in large-scale industrial production. However, the new process of leaching uranium using natural generative reagents can transform the unfavorable factors of the deposit into favorable factors, and at the same time, the burial depth of the ore deposit, the continuity of the water-blocking bottom, the burial depth of the original water level of the ore-bearing aquifer, etc. The hydrogeological conditions basically meet the requirements of the uranium enrichment process of natural genetic reagents.
After the natural oxidization of the uranium ore of this deposit, the leaching rate of about 40% was obtained by indoor leaching with natural reagent-mineral aquifer groundwater, which laid the foundation for further field test. The natural generient reagent leaching process is an in-situ process that requires continuous strengthening. Oxidizing ore with compressed air, or pressing O 2 +CO 2 is a commonly used method of enhanced leaching, which achieved nearly 60% leaching rate in laboratory tests.
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