Underground Solution

of useful minerals, a method of extracting a useful mineral through wells by dissolving the mineral in water at the place of occurrence. The method is used to work deposits of rock and potash salts.

The method of obtaining rock-salt brines through wells has been known since the 12th century. Technology for the controlled underground solution of salts was proposed by E. N. Trap of the USA in 1933 and improved upon in the USSR by P. A. Kulle and P. S. Bobko. The underground solution of potash salts on an industrial scale was begun, in Sasketchewan, Canada, as late as 1964.

In underground solution, a salt deposit is opened by a well with concentric, independently operating columns that supply the water and remove the brine. The water, which acts as the solvent, enters the salt deposit under pressure through the radial clearance between the brine-collection and water-inlet columns.

Brines of industrial concentration (305–310 g/l) are obtained by working the productive stratum in chambers successively from bottom to top. A nonsolvent, such as petroleum, kerosine, or air, is introduced to the roof of the chamber to keep the ore block from being dissolved by the solvent. Because the solvent forced into the chamber is lighter than the brine, it floats to the upper part of the chamber and contacts the salt deposit; it gradually becomes saturated and settles to the mouth of the brine-collection column. The brine is removed in the brine-elevation column to the surface under residual pressure. It is transferred from the well through pipes past a distribution-control point to a reservoir of standard brine and then transported to users. Solutions obtained by underground solution serve as raw materials for the production of chlorine, soda, and table salt. In 1973, more than 20 million cu m of brine were produced in the USSR.

The development of underground solution is related to an acceleration of the process of congruent solution and the introduction of methods of selective dissolution. Methods of selective solution are based on the use of additives of heavy metals, the creation of a magnetic field, or the use of a heated solvent.

Underground solution is also used to create storage tanks for petroleum products and liquefied gases in salt deposits.