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The natural sedimentary cycle of the Salt Lake solid deposit is contaminated by aeolian sand. The ore produced is generally dissolved, purified, physically sorted and chemically processed. By utilizing the characteristics that salt minerals are easily soluble in water, it is obviously economically reasonable to use a dissolution method for mining deposits with complex conditions and low grades, which combines mining and processing.
   First, the dissolution mining practice
The salt lake solid deposits are exposed to the surface or shallowly buried. According to the cloth liquid and liquid collection methods and means, there are several ways of diffuse flow mining, liquid collection and drainage, drilling and jet perforation.
(1) Examples of surface drainage and liquid dissolution
The surface cloth is dissolved in liquid, and the solvent can be used for atmospheric precipitation, or near the salt lake or low-mineralized water at the bottom of the lake.
Example 1 The natural salt deposit of a layer of salt deposits in the salt lakes of the Jijiur Salt Lake in Inner Mongolia is directly mined due to the large amount of silt sand contaminated by wind sand. The salt quality is not edible. During the rainy season, direct atmospheric precipitation and grassland water are used to remit water into the salt lake. The surface layer dissolves the surface stone salt and recrystallizes by evaporation in the sun. A layer of white stone salt with a thickness of about 10 cm is deposited. First, it is loosened with a toothed loose miner, blamed by the machine, and then shoveled with a continuous shovel. The tractor tows the trailer and transports the salt out of the lake.
Example 2 There is a dry salt lake in the middle of Carmen Island, Mexico, with an area of ​​about 3km 2 , a salt layer thickness of 3m, and insoluble matter of 8% to 10%. The annual evaporation in this area is greater than 25000mm, and the evaporation conditions are good. The open channel is used to introduce seawater into the salt lake to dissolve the salt layer. After the solution is saturated, it is infiltrated into the salt well, pumped by the pump, and transported to the Yantian Sun through the pipeline to obtain high-purity stone salt products. The annual harvest of stone salt is 8-15 thousand tons.
(2) Examples of trench collection and solution mining
In the salt lake of Qijiaojing, Xinjiang, the upper salt layer is exposed to the surface, and the thickness is about 1-2 m. In addition to insoluble materials such as muddy sand, the salt layer also has mud and mud columns (Fig. 1). The length of the mud ridge is generally 2 to 10 m, the length is up to tens of meters, the width is generally less than 1 m, the thickness is generally 0.1 to 0.3 m, and the ridge spacing is 3 to 5 m. The mud column is lenticular or irregular.
Figure 1 Schematic diagram of irregular mud column
1- salt crust; 2- halite layer; 3- Thenardite layer; 4- mirabilite layer; 5- clay; 6- mud column
The salt layer was initially excavated with grooves. Wash the salt in the brine in the ditch. Due to the large amount of excavation trenches, natural evaporation, the brine level is down to the low plate, the solid salt cannot be directly collected, and the mine is changed to use the trench to dissolve and mine. Drilling the groundwater under the lake area into the lake through the ditch, into the ditch, the depth of irrigation is 0.2-0.3m, dissolve the bottom of the ditch and the salt layer on both sides. After the brine reaches saturation, it will evaporate and crystallize on the spot, and precipitate the white salt. Then use artificial mining, bagging and storing on the spot.
(III) Examples of hydrothermal jet perforation and dissolution
The area of ​​Lake Macedonia in Canada is 1.64km 2 , the thickness of the mirabilite mine is up to 9~17m, and the reserve of sodium sulfate is 3.5 milliont. The ore body contains 15% to 50% of a mixture of organic matter, clay and sand, and is sandwiched with mirabilite.
The lake mirabilite mine was originally used for seasonal surface layer dissolution and frozen precipitation of thenardite. Due to the low concentration of the solution. The amount of halogen and frozen juvenile nitrate can not meet the production ore. The ore body contains insoluble matter. After the mirabilite is dissolved, the residual mud sand covers the dissolved surface, hindering the continued dissolution, and the ore is changed to hydrothermal jet perforation and dissolution.
The hot melt mining process is shown in Figure 2. The brine is extracted from the lake and returned to the mother liquor by the processing plant. It is heated to 37.8 °C by the heater and transported to the sink in the lake area. The outlet is evenly arranged according to the need, and the hose with the nozzle is connected. The jet flushing and dissolving action are quickly inserted into the bottom of the ore layer to form a dissolved hole. Then gradually dissolve and expand from the bottom. In the mine with high ore content, it can be washed and dissolved 5m deep per hour. Since the dissolution is carried out from the bottom up, the muddy sand is deposited on the bottom plate, which overcomes the shortcomings of the surface cloth solution. The clean brine is extracted from the top.
Figure 2 Glauber's hot liquid perforating solution mining process
1- Glauber's salt, mud and sand interbed; 2-clay, sand bottom plate; 3-brine water; 4-residual mud sand;
5-pump; 6-heater; 7- to the processing plant pipeline
   2. Evaluation of dissolution mining of Yanhu deposit
First of all, from the perspective of technical difficulty and economic rationality, the water-filled ore deposit with large ore body thickness and deep burial is not only a large amount of engineering, but also difficult to directly mine. Technically and economically justified.
Mud ridges, mud-filled ore layers, and thin ore layers that are interbedded with mud and sand, can not be mined by general machinery, and can only be mined by dissolution.
Henhouse ore bodies shape, lenticular scattered, and low grade ore; or associated with other minerals, low-grade, large reserves, no direct mining value, such as solid potassium Salt Lake magnesium ore mainly exists halite layer forming From bottom to top, it is divided into seven levels of K 1 to K 7 , and has a thin thickness (0.5 to 1.5 m), a low grade (average KCl content of 2.47%), and a complex shape (like layered, lenticular, small). It is characterized by lenticular shape and large reserves (more than 100 million tons of KCl content of more than 2%). The potassium-containing minerals are mainly carnallite and a small amount of potassium salt. If high-sodium brine can be used to promote the conversion of solid carnallite to the liquid phase to supplement the consumption of KCl when mining intercrystalline brine, it can turn waste into treasure.
Secondly, there are many factors that contribute to the dissolution of the salt lake deposit:
(1) Salt lake minerals mostly have good solubility to varying degrees. First, the water-soluble salt, the concentration of the saturated solution at room temperature of greater than about 17%, such as rock salt, sylvite, carnallite, bischofite, Glauber's salt, trona and the like; followed by water soluble salt, significantly improved water solubility, such as trona, Glauber's salt, borax and the like; some acid, lye-soluble salts, such as gypsum, ulexite, column Borate, water shed square stone.
(2) Water is the basic "tool" for dissolved mining. The catchment area of ​​the closed basin in the salt lake is often tens to hundreds of times larger than the area of ​​the salt lake itself. The surrounding mountain snow and melt water provides sufficient water for the salt lake basin. Generally, low salinity water is present around the bottom and bottom of the salt lake, which provides the necessary conditions for dissolved mining.
(3) The salt lake is located in arid areas and has good evaporation and freezing conditions. It is economical to realize liquid-solid conversion and product processing through the full use of solar energy in salt fields.