Solution mining

Early demand for chlorine centered on textile bleaching, and chlorine generated through the electrolytic decomposition of salt (NaCl) sufficed. Sodium hydroxide was produced by the lime—soda reaction, using sodium carbonate readily available from the Solvay process. Increased demand for chlorine for PVC manufacture led to the production of chlorine and sodium hydroxide as coproducts. Solution mining of salt and the avadabiHty of asbestos resulted in the dominance of the diaphragm process in North America, whereas soHd salt and mercury avadabiHty led to the dominance of the mercury process in Europe. Japan imported its salt in soHd form and, until the development of the membrane process, also favored the mercury ceU for production. 

Brine Preparation. Sodium chloride solutions are occasionally available naturally but they are more often obtained by solution mining of salt deposits. Raw, near-saturated brines containing low concentrations of impurities such as magnesium and calcium salts, are purified to prevent scaling of processing equipment and contamination of the product. Some brines also contain significant amounts of sulfates (see Chemicals FROMBRINe). Brine is usually purified by a lime—soda treatment where the magnesium is precipitated with milk of lime (Ca(OH)2) and the calcium precipitated with soda ash. After separation from the precipitated impurities, the brine is sent to the ammonia absorbers. 

Resources for Potash Fertilizers. Potassium is the seventh most abundant element in the earth s cmst. The raw materials from which postash fertilizer is derived are principally bedded marine evaporite deposits, but other sources include surface and subsurface brines. Both underground and solution mining are used to recover evaporite deposits, and fractional crystallization (qv) is used for the brines. The potassium salts of marine evaporite deposits occur in beds in intervals of haUte [14762-51-7] NaCl, which also contains bedded anhydrite [7778-18-9], CaSO, and clay or shale. The K O content of such deposits varies widely (see Potassium compounds). 

An assessment of world potash resources (108) is shown in Table 15. Of the 67 x 10 t of total estimated reserves and resources in Canada, nearly 5 X 10 t is recoverable by conventional mining methods and the remainder by solution mining. As of 1974, Canada had about half of the known world reserves and about 90% of known world resources of potassium. 

Because of these characteristics electromagnetic flow meters have been widely appHed to the measurement of difficult Hquids such as raw sewage and wastewater flows, paper pulp slurries, viscous polymer solutions, mining slurries, milk, and pharmaceuticals. They ate also used in less demanding apphcations such as the measurement of large domestic water volumes. 

Table 1 gives the average metal content of the earth s cmst, ore deposits, and concentrates. With the exceptions of the recovery of magnesium from seawater and alkaU metals from brines, and the solution mining and dump or heap leaching of some copper, gold, and uranium (see Uranium and uranium compounds), most ores are processed through mills. Concentrates are the raw materials for the extraction of primary metals. 

In Situ Leaching. Copper and uranium ores are sometimes leached ia place by circulatiag acidified mine water through the underground deposit. This process is known as solution mining. 

Sylvinite ore is relatively soft and easily broken. Thus, continuous miners of the boring- or rotating dmm-type can be used. These machines are modified continuous coal miners. This method is used in some of the mines in New Mexico, in all Canadian mines except the solution mines, and in many European mines. Ore is removed from the face by a number of methods, eg, with extensible belt conveyor ore-loading machines and shuttle cars to the main haulage line. To obtain maximum benefits from the continuous miners, the ore transport system must be as nearly continuous as possible. 

A fourth source of brine is obtained through solution mining. Potash is mined in Moab, Utah by solution mining. Much of the food-grade sodium chloride in the United States, Europe, and other parts of the world is solution mined. Large beds of potassium salts in Canada and trona beds in Wyoming and California are being solution mined. 

Solution Mining. Solution mining, also known as brining, is the recovery of sodium chloride or any soluble salt in an underground deposit by dissolving it in situ and forcing the resultant solution to the surface. 

Solution mining produced nearly 23 million metric tons of salt in 1989 representing more than half of the total U.S. salt production (14). Salt brine is made from bedded salt at more than 18 different locations and from 17 salt domes (15). Bedded salt of the salina formation is the most widely and intensively exploited by solution mining. Enormous reserves of salina salt are available. Cost of solution mining salt is usually less than the cost of salt produced by dry mining. The method is particularly good where salt deposits are deep and dry mining would not be feasible. 

Fig. 2. Typical solution mining operation in a salt dome (9).

An environmental risk in solution mining is surface subsidence. This risk is greatest with embedded salt. No cases of salt subsidence have been reported in mining domes that have been mined according to standard industry approved practice in the United States, but some have been seen in other countries. One side benefit of dome solution mining is use of the cavities later for storage of industrial fluids, chiefly petroleum and natural gas. 

Solution mining for sodium chloride is extensively used in Europe and the states of the former Soviet Union. 

Boron is found in two underground ores, ulexite and colemanite. Research and pilot-plant studies have been completed to solution mine these ores, but as yet it is not done commercially. Boron is found in many different evaporite deposits (17). 

Recovery Process. The Texas Gulf, Cane Creek potash operation (60) of Moab, Utah produces KCl by solution mining (61—64). Brine is pumped from underground to 1.6 x 10 (400 acres) of solar ponds where a mixture of KCl and NaCl is crystallized in a salt mass called sylvinite. 

In the mid-1980s FMC began solution mining trona beds at Green River, Wyoming to produce soda ash. NaTech is currently developing a solution mining process for sodium bicarbonate [144-55-8] in Colorado. 

Occurrence. About half of all the sodium chloride [7647-14-5J produced in the wodd is from brine. Approximately one hundred million tons pet year are produced from brines of the ocean, terminal lakes, subterranean aquifers, and solution mining (14). Sodium is found in large quantities in most areas of the world. Its quantity is so large that prices in some locations are only a few dollars per ton. Many areas have millions of tons but prices are so low that it is not economical to mine or process the salt. The largest exposed sodium chloride bed is at the Salat de Uyuni, Bohvia, but Bohvia is landlocked and very htde of the salt can be processed and sold at a profit. 

W. H. Husband, Application of Solution Mining to the Recovery of Potash, presented at the Annual Meeting of the AIME, New York, 1971. 

Fig. 10. Three types of solution mining mbblized (explosives or mining), hydrofracted, or chemically iaduced porosity, where A represents the oxidized B,...

Shikazono, N. (1972b) Solubility of sulfide minerals in hydrothermal solution. Mining Geology, 22, 403-412 (in Japanese). 

R. W. Bartett, Solution Mining Leaching and Fluid Recovery of Materials, Gordon and Breach, Philadelphia, 1992. 

Davis, K. and McDonald, L.K., Potential corrosion and microbiological mechanisms and detection techniques in solution mining and hydrocarbon storage wells, in Underground Injection Science and Technology, Tsang, C.F. and Apps, J.A., Eds., Elsevier, New York, 2007. 

Calandria evaporator, in sodium chloride solution mining, 22 804 Calcicard, molecular formula and structure, 5 97t, 118t Calciferols, 25 791-793 dietary sources of, 25 793 Calcination, 2 353, 403, 407—410 12 726-727... 

Forages, as ruminant feed, 10 863 Foraminifera, 17 690 Forastero cocoa beans, 6 353 Forced air cooling, of food, 21 560 Forced circulation crystallizer, 8 136 Forced-circulation evaporators, in sodium chloride solution mining, 22 803, 804 Forced convection, 13 245 Forced drainage experimental procedure, 12 12... 

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