In-Situ Leaching (ISL)
he advantages of this method include: a decreased danger for the personnel in an emergency situation, lower operating costs, major tailing dumps are not required.
Development of deposits using the ISL method as compared to conventional mining methods substantially reduces the harm caused to the environment and has its specific features.
Land and underground water reclamation in case of ISL method includes liquidation of process wells of the operating block, reclamation of contaminated soil and transfer of land for agricultural use. In general, reclamation of land after ISL operation has the following features:
- natural underground waters in the area of ore deposits in the majority of cases are not suitable for potable and technical water supply, since by their type of mineralization they belong to brackish waters (mineralization in excess of 2 g/l), they contain products of uranium radioactive decay in concentrations higher than the MAC (maximum allowable concentration) (first of all radium) and sulphurated hydrogen;
- in terms of hydrogeological conditions they are characterized by stagnant hydrodynamic mode (with the underground flow speed of fractions of centimeters per year) which does not foster spread of contaminated ground waters over significant distances;
- geological environment has protective properties due to neutralization and reductive capacity of rock and presence of bioactive sulfate-reducing and denitrifying bacteria.
ISL development of deposits through a system of boreholes has an incomparably lower adverse impact upon the ground surface. There is no sagging and disturbance of the ground surface, off-balance and waste ore dumps and tailing dumps. None of the development stages, including stripping and ore body preparation, produce dust. The scope of processing is much smaller due to the fact that the process flow does not include cumbersome operations of ore acceptance, ore preparation and leaching. With a view to preventing spills of process solutions before launching operations of a site a strip of fertile soil layer 4 — 5 m wide to the depth of 40 — 50 cm is removed along the entire row of operating boreholes. When development of reserves is finished the fertile soil layer is returned to its original place.
Thus, with relatively small labor input and expenditures within a short period of time (4 — 5 years) from the beginning of operations as the sites are developed land returns for agricultural use without deterioration of its fertility. Due to the fact that reserves of certain ISL sites are developed for only several years, there is no need to remove the whole deposit area from the land use for the entire period of development and this is a positive feature of the ISL method. As the reserves are exhausted the developed sites are transferred for agricultural use.
Borehole method of stripping and development of deposit entirely precludes existence of any sources of dust and decreases dozens of times emission of radioactive substances into the air.
Thus, the ISL method is the environmentally safest method among all known mining methods.