(1) Solid mining
Solid deposits have a long history of dry mining and water harvesting. In recent years, some countries have gradually replaced the room-column method with the water-soluble method.
Dry mining is basically the same for all kinds of salt deposits. At present, the traditional house-column method developed by the shaft is widely used in foreign countries, and this method is also adopted in the Yunnan Kanye well potash mine. The shaft has strong adaptability to various salt deposits, and is especially suitable for ore bodies with high grade and buried depth of less than 1 000 m and mines with large production capacity. Most of the shafts mined are concrete-lined circular wells with a small number of rectangular wells. The circular well diameter is about 4.5-5.5 m, and the rectangular well section is generally 2 m × 4 m ~ 2 m × 6 m. Mines and pillars are generally rectangular and square. The mining width of the rectangular mining room is generally 15-20 m, the length is 100-200 m, the height is 6-10 m, and the well depth is several hundred meters to thousands of meters. Shaft production capacity, foreign single-well production capacity of several thousand tons / day, Yunnan single wild well single-well several hundred tons to more than 1,000 tons / day. The recovery rate is generally 40% to 60% in foreign countries, up to 75%, and the highest recovery rate of Yunnan Kanye well potassium mine is 35% to 40%.
Water extraction is divided into diverticulum water dissolution method and drilling water dissolution method. The diverticulum water-dissolving method is used in special cases where there are many sediments and low grades. For example, this method is adopted in the Kanye well potassium mine. Drilling water dissolution method is widely used in foreign countries. The drilling water-dissolving method can be divided into single well operation and multi-well operation. This method is to install a pipeline in a borehole with a depth of 2 000 m, communicate with the underground ore body, inject fresh water into the ground through a water injection pipe, and etch the ore body to create an artificial cavity for containing the dissolved salt solution. The obtained solution is piped to the ground, and then concentrated by manual or natural evaporation to separate the product by crystallization. The obtained mother liquor is adjusted by adding water and returned to the ground for repeated use. This method is widely used in Sichuan and Hubei to mine salt mines.
Compared with general room and pillar mining, the main advantages of drilling water-soluble mining are: deep mining deposits can be mined up to 1 000-2 000 m, and Sichuan water mining depth is 1 200 m; suitable for mining and mining thickness is small, Ore body with low grade; short construction time, low labor intensity, easy operation; no safety problems in underground operations; can eliminate mining and transportation processes. The main disadvantages of the water-soluble method are: large-scale ore body collapse will occur; thin-layer ore body drilling costs are high; pipeline corrosion is severe; recovery rate is lower than dry mining. The recovery rate of foreign housing column method is 40% to 50%, the borehole water dissolution method is 2% to 35%, and the single well convection method is 2%. China's single well convection method has a high recovery rate, generally 7% to 8%.
(ii) Underground brine mining
The underground brine is mined by the brine well to expose the brine layer, and the casing is cemented and then brine is collected. In some brine layers, brine can be sprayed out of the ground. This is self-spraying. Some brines cannot be sprayed out of the ground to maintain an equilibrium liquid level in the well. At this time, brine is extracted from the well by means of a brine extraction machine.
Common methods for mining underground brines include: gas lift mining method, pumping unit-deep well pump mining method, electric submerged halogen pump mining method and extraction and brine extraction method. These kinds of halogen extraction methods in Sichuan are used. The adaptability and economic indicators of the mechanical equipment to the conditions of the brine well are shown in Table 4.9.10.
Table 4.9.10 Comparison of technical and economic indicators for various underground brine extraction methods
(iii) Modern salt lake mining
The modern salt lake potassium deposits have more exposed surface, and the solid potassium salt ore bodies are buried shallowly, mostly using artificial mining and a few mechanized mining. The potassium salt mining method is similar to the stone salt mining method. Inner Mongolia Jilantai Salt Field and Qinghai Chaka Salt Field have achieved mechanized mining, and the output of each class can reach 80-250 tons.
The salt lake brine mining method is relatively simple: the brine is pumped into the salt field, and the sun is used to evaporate the beach, and the sodium chloride is concentrated to remove the potassium salt. The product can also be extracted directly from the brine. This method is used to extract potassium-containing intercrystalline brine in Chaerhan Salt Lake, Qinghai.
The mining of Chaerhan Salt Lake, the preferred location on the east bank of Lake Dabson, is 8 km wide from east to west, 12 km long from north to south, and covers an area of ​​96 km2. According to the change and dynamic law of intercrystalline brine, shallow brine is extracted by channel method. The brine extraction channel is excavated in the rock salt layer, and the channel has two north-south directions with a spacing of 3 km, which is collected at the water intake point A. At the water intake point, a solid ship pumping station is set up. From the southern end of the brine extraction channel, the brine pump is pumped into the salt field to enter the brine point B and then poured into the sodium salt pool. The continuous water walking mode is adopted in the beach, and the specific gravity of the brine in the pool is adjusted to about 1.28. At the same time, the intergranular brine is continuously discharged into the two hawstone pools of the east and the west, and the ore brine is produced by steaming in the salt field. The main technical and economic indicators for brine extraction in Chaerhan Salt Lake are shown in Table 4.9.11.
It can be seen from the old halogen emissions in the table that the salt lake is discharged into the South Hobson Lake by 10 million tons per year. The long time will inevitably cause pollution in the entire lake area. It is necessary to solve the problem of comprehensive utilization of old halogens while strengthening environmental protection.
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