Evaluation of the efficiency and environmental impact (on subsoil and groundwater) of underground block leaching (UBL) of metals from ores

Abstract

One of the most problematic aspects of underground block leaching (UBL) of metals from ores is the possibility of pollution of water and air in the affected zone. Therefore, proving the possibility of mitigating environmental impact of metal leaching from ores by managing production processes with the implementation of nature- and resource-saving technologies is an important objective. The purpose of this study is to justify underground development effectiveness of ore deposits by traditional and integrated methods with leaching of metals from substandard and off-balance ores. This will allow the raw material base for extraction of metals from off-balance ores to be expanded and the environmental impact on subsoil and groundwater (hydrogeological systems) to be mitigated. A distinctive feature of a UBL (underground site for leaching of metals from shrunk ores) is that leaching solutions are supplied from sorption column placed in mining workings of the leaching level in the immediate vicinity of the extracting block. The pregnant solutions in the form of resin are discharged from the sorption column, placed in the leaching level mine workings, then winded in mine cars and further supplied to hydrometallurgical plant in tanks. A still rare attempt to justify the efficiency and environmental safety of underground metal leaching (UBL) from off-balance and substandard rock ores in installations mounted in mine workings, on the basis of monitoring and evaluation of subsoil and groundwater conditions was investigated. The average value of uranium concentration by level was established: 210 m – 3.6 mg/L; 225 m – 3.58 mg/L; 280 m – 0.91 mg/L. At the same time no contamination of underground mine waters was detected. Levels of sulfuric acid aerosols and radon decomposition products did not exceed the maximum allowable concentration (MAC) values. It is recommended that the hydrogeological environment be protected through silting the bottom of the stope for collection of pregnant solutions with clay mud and construct semi-active water-permeable chemically active barriers. The mentioned BIL process was implemented during the development of pilot block 5-86 and recommended for blocks 5-84-86 and 5-88-90 of Michurinskoye deposit of SE VostGOK, Ukraine, as well as during for development of ore deposits in Russia, Kazakhstan, and other developed mining countries.