What Is In-Situ Leaching?

In-situ leaching is referred to as in-situ leaching. Under the natural production conditions of ore, the leaching solution is injected into the ore layer through the injection hole. The leaching solution selectively leaches useful components in the ore. The soluble compounds generated enter the leaching liquid stream and are lifted to the surface through the extraction hole for processing. A mining technology that processes the extraction of metals.

A mining method that uses a leaching solution to selectively extract useful components from heterogeneous ores under natural burial conditions and extracts the compounds produced by the reaction is called in-situ leaching mining, referred to as in-situ leaching ^[1]

In situ leaching has been applied to mining

Compared with conventional mining and smelting methods, the main advantages of in-situ leaching:

1. Because there are no expensive and heavy wells or stripping projects, and no rock drilling and blasting, ore transportation and crushing procedures, the infrastructure investment is small, the construction period is short, and the production cost is low.

2. Good environmental protection, basically does not damage farmland and mountain forests, and does not pollute the environment.

3. The labor and health care conditions of production personnel have been fundamentally improved.

4, can make heavy and harsh mining work "chemical", "factory" and fully automated.

5. Can make full use of resources, for example, for some poor mines, buried isolated ore bodies, dispersed small ore bodies, and deposits with complex hydrogeological engineering conditions, mining with conventional methods is often inexperienced, and even technically not feasible, and the land is used. How fast and easy is the immersion method ^[3]

The main disadvantages of in-situ leaching mining methods:

1. Only applicable to ore deposits with certain conditions, the scope of application is limited.

2. If the mineralization is uneven, the cementation degree and permeability of the ore in each part of the ore layer are not uniform; or if some useful components in the ore are difficult to be leached, the total recovery rate of the resource is relatively low.

3. If ammonium carbonate and ammonium bicarbonate are used, or cyanide is used, it is difficult to purify groundwater in the mine.

clay west In-situ leaching of clay west

The mine is the first large-scale commercial in-situ uranium mining mine in the United States. It was put into production in April 1975. Pumping is jointly operated by USSteel and Niagara. Its annual production capacity of U ₃ O ₈ was 112.5t at the beginning and increased to 450t afterwards.

(1) Geographical location

The Cleves uranium mine is located 16km southwest of George West, Texas.

(II) Geological and hydrogeological conditions

The uranium ore body is present in tongue-shaped in the Miocene Oakville sandstone. The ore-bearing layer has an average buried depth of 116-150m and an average thickness of 10m. Ore-bearing sandstone with loose structure and permeability of 2000 millidarcies. The average ore grade is 0.1%. The main uranium minerals are pitch uranium ore and hydrosilicon uranium ore. Symbiotic minerals include selenium and molybdenum.

(Three) drilling arrangements

The total number of boreholes reached more than 2,000, with a total of four mining areas. Each mining area has an average of 550 boreholes, of which 250 are injection holes, 150 are pumping holes, and 150 are monitoring holes. Each group of drill holes is generally arranged in a 5-point pattern. The length of the square side is 16.67m, the liquid suction hole is in the center, and the four corners are liquid injection holes. The distance between the liquid suction hole and the liquid injection hole is 11.78m. The boreholes are also arranged in square shapes with side lengths ranging from 22.33 to 33.33m.

(Four) drilling structure

The structures of pumping, injecting and monitoring holes are basically the same. The drilling depth is slightly beyond the floor of the ore body. A polyvinyl chloride plastic sleeve with an inner diameter of 100 mm is installed in the injection and monitoring holes. Inside the pumping hole is a 150mm inner diameter PVC plastic sleeve; a filter tube is installed at the ore layer. Cementing the well between the hole wall and the casing wall, in order to prevent cement slurry from entering the filter pipe and the mineral layer during cementing, a joint with a gypsum plug is installed above the filter pipe; the cement slurry enters the casing through the drainage hole above the gypsum plug The outer gap and the gasket under the drainage hole can prevent the cement slurry from leaking. In order to protect the filter tube, the sleeve is provided with 3 to 4 centralizers to centralize the position of the sleeve and the filter tube in the hole.

(5) Preparation of leaching solution

Preparation of leaching solution, the initial use of ammonium carbonate, ammonium bicarbonate and hydrogen peroxide, and then replaced with sodium carbonate, sodium bicarbonate and oxygen. The content of oxygen in the leaching solution is 300-400 mg / L. The pH of the leaching solution is about 9.

(VI) Pumping equipment and pumping solution

The corrosion-resistant horizontal pump is used to inject the leaching solution at an injection pressure of about 1.5 MPa. The solution is drawn from the pumping hole, and a stainless steel submersible pump of 2.24 to 5.6 kW is used. The diameter of the stainless steel tube or fiberglass tube connected to the pump is 50. ~ 60mm. Due to the high permeability of the ore layer and the large amount of pumped liquid in the borehole, the content of U ₃ O ₈ in the pumped liquid is only 20-30 mg / L.

(VII) Hydrometallurgical processing of product solutions

Ion exchange resin was used to adsorb uranium in the product solution. NaCl (with Na ₂ CO ₂ ) was used as the eluent. The uranium was rinsed from the resin, and NH ₃ was used to extract the uranium-containing solution from the eluted solution. Precipitated uranium (ammonium diuranate), the final product is a powdery yellow cake. Waste fluid is injected into deep formations through drilling ^[4] .

In-situ leaching of the Chenjiashan uranium deposit

The Chenjiashan Mine is the first in-situ leaching mining site in China.

(I) Geological and Hydrogeological Conditions

The main industrial uranium deposits are gravel-bearing sandstone and glutenite, and the base is granite. The ore material composition is mainly quartz and feldspar, followed by biotite, hydromica and chlorite, as well as pyrite, argillaceous, carbonaceous and organic matter. Uranium exists in the form of pitch uranium ore and uranium black, and is adsorbed in cements such as carbonaceous, organic and muddy.

The ore permeability coefficient is greater than 0.72m / d, and the burial depth of the ore body ranges from tens of meters to one or two hundred meters.

(Two) drilling arrangements

The drill holes are arranged in triangles and rectangles, and the distance between the pumping hole and the injection hole is about 15m.

(Three) drilling structure

The structure of the pumping hole and the injection hole is basically the same. The hole depth is tens of meters, the hole diameter is 130mm, and the hole diameter in the ore body is 300-400mm.

(IV) Preparation of leaching solution

The leaching solution is prepared with groundwater, sulfuric acid and hydrogen peroxide.

(E) Extraction fluid equipment and extraction fluid

Stainless steel horizontal pump for liquid injection, air lift pump and stainless steel submersible pump for liquid injection. The uranium content in the extracted liquid is 50 to 150 mg / L.

(6) Hydrometallurgical processing of product solutions

Ion exchange resin was used to adsorb uranium in the product solution, NaCl (addition of H ₂ SO ₄ ) was used as the eluent, and NaOH was used as the precipitation solution. The final product is a pasty yellow cake ^[4] .