JPS6161843B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a method for collecting rare elements with a low Clark number that exists deep underground, and its purpose is to provide a method for collecting rare elements that is simple and effective, and is inexpensive. The goal is to provide a collection method. Conventionally, in order to extract useful elements from underground, except for a very small number of open-pit mines, most of the methods involve excavating tunnels with a total length of several hundred meters to several thousand meters underground, and mining them manually or mechanically. After being transported to the ground and undergoing physical beneficiation such as crushing and pulverization, useful elements are extracted through various hydrometallurgical processes starting with leaching. However, although the above-mentioned method is suitable for extracting elements with a high content in ores, the rare elements with a low Clark number have a trace amount of content, which is accompanied by economic and technical difficulties in separating and collecting them. There are some drawbacks. The present inventor conducted research on the hot water collected in conjunction with geothermal steam extraction used for geothermal power generation, and found that rare elements can be easily and We were able to find a method that allows for effective collection. That is, in a hydrothermal geothermal well in which geothermal steam is accompanied by hot water, the present invention mixes a solvent that selectively dissolves rare elements with the hot water returned from the reinjection well, and uses the hot water in the production well. This is a rare element collection method that is characterized by circulating the rare elements through a recirculation well and a reinjection well to concentrate the rare elements and then separating and recovering them. In hydrothermal-associated (or hydrothermal-dominated) geothermal wells, a large amount of hot water is extracted along with geothermal steam, but in such hydrothermal wells, the hot water is separated from the geothermal steam. After that, the water is returned deep underground through a reinjection well. The hot water that is returned to the deep underground by the slag flows back into the geothermal steam storage area and is collected again along with the geothermal steam. In the present invention, we focused on the behavior of hot water as described above, and by injecting a solution or a solvent that selectively dissolves rare elements underground, we were able to recover rare elements in a solution state. Although the drawings show one embodiment of the present invention, the present invention will be explained below based on the illustrated example. A hydrothermal-associated geothermal steam well is equipped with a production well 1 and a return well 2. A two-phase fluid of steam and hot water is collected from the production well 1, and the separator 3 separates the steam and heat. The steam is separated from water and sent to a turbine (not shown) through a pipe 4. On the other hand, the hot water separated from the steam by the separator 3 is sent to the reinjection well 2 and is returned underground. However, in the present invention, an appropriate solvent is added to the hot water reduced from the reinjection well 2 from the solvent addition device 5. Add and reduce.
The solvent used in the potting process is one that can selectively dissolve rare elements found underground. Table 1 shows the content of rare elements in hot water collected from hydrothermal geothermal wells.

[Table] That is, it is recognized that the hot water contains many rare elements. Therefore, for example, Li, Rb, Cs,
When collecting Sr, use NaCl as a solvent,
NaNO ₃ or the like can be used, and by using a solvent such as ethanol or acetylacetone in combination with the above solvent, an even higher concentration can be extracted. However, the amount of rare elements in these underground minerals may vary slightly depending on their compounds, crystalline state, etc., but even in such cases, they can be extracted by selecting an appropriate solvent. Further, the solvent used in the fixing may be in the form of a powder, or the solvent may be dissolved in water and added in the form of an aqueous solution.
Further, the solvent does not necessarily have to be selected for only one of the rare elements, but may be one that can dissolve two or more of the rare elements at the same time. In this case, the rare element can be dissolved more effectively. It is advantageous in that it can be collected. As mentioned above, the hot water to which an appropriate solvent has been added is returned underground from the reinjection well 2, heated by geothermal heat, and is used to generate underground mineral veins 7 existing above the fault (unconformity) 6.
After penetrating into the interior and selectively dissolving and extracting rare elements in underground veins 7, they are ejected from production wells 1 through cracks 8 and collected together with geothermal steam. In this case, the behavior and flow rate of hot water underground can be known by, for example, a gushing test using a tracer such as a radioactive substance, and thereby the positions of the production well 1 and the reinjection well 2 can be determined. Additionally, in general, when a hydrothermal-associated geothermal well continues to operate for several years, the hot water injected from the reinjection well 2 forms a hydrothermal flow path (permeable layer) in the underground mineral 7; It has been confirmed that it becomes easier for hot water to reach production well 1 by expanding the production well 1, and the hot water recovered in production well 1 is returned to the return well 2 and this operation is recycled. This method recovers and concentrates rare elements in hot water. When circulating the hot water, if a solvent is appropriately added to the hot water recovered from the production well 1 and the hot water is circulated, the amount of rare elements recovered can be increased. As mentioned above, hot water with added solvent was added to production well 1.
Rare elements in the hot water recovered by circulating between the hot water and the reinjection well 2 are separated from steam in a separator 3, and then separated and collected in an element separation device 9. In this case, the element separation device 9 precipitates rare element compounds from the solution using a conventional method, and easily separates the compounds by decantation, precipitation separation, ion separation membrane method, or the like. As described above, the present invention utilizes hot water collected from a production well and reduced in a reinjection well in a hydrothermal geothermal well, mixes a solvent that dissolves rare elements with this, and returns the hot water to the production well. By circulating between the well and
Since rare elements underground are recovered and concentrated in hot water, it is easy to recover rare elements, and there is no need for any special equipment other than adding a solvent and separating and recovering rare elements, reducing the collection cost. can be drastically reduced. Further, the original functions of the production well and the reinjection well are not impaired at all, and geothermal steam can be stably secured. Example: The following second sample collected from a hydrothermal geothermal production well
Hot water containing rare elements as shown in the table (flow rate 100t/
For H), 10% by weight of salt water and acetylacetone are mixed, and the hot water is returned underground from the reinjection well, the hot water is circulated between the production well and the reinjection well, and after 3 days it is collected from the production well and placed in a separator. The analysis of the hot water (flow rate 230t/h) separated from the steam was as shown in Table 3.

【table】

[Table] Comparison with Tables 2 and 3 shows that Li in the hot water is almost twice as concentrated as it was initially, and is therefore separated and recovered as LiCl using amyl alcohol in an elemental separation device.

[Brief explanation of the drawing]

The drawings are explanatory diagrams of one embodiment of the present invention. 1: Production well, 2: Reduction well, 3: Separator,
4: Pipe, 5: Solvent addition device, 6: Fault, 7:
Underground vein, 8: Crack, 9: Element separation device.

Claims (1)

[Claims] 1. In hydrothermal geothermal wells where hot water accompanies geothermal steam, a solvent that selectively dissolves rare elements is mixed with the hot water returned from the reinjection well, and the hot water is transferred between the production well and the reinjection well. A method for collecting rare elements, which is characterized by recycling and concentrating rare elements, and then separating and recovering them.