Sulphide minerals
Some of the most significant environmental problems and challenges with mining operations revolve around sulphide minerals. Due to their chemical composition, sulphide minerals can lead to the formation of acidic, metal-bearing waters that can contaminate surface and groundwater if such water is not handled properly.
Sulphide minerals are a group of minerals consisting of a compound between sulphur and one or more metals, such as pyrite, an iron sulphide which is a compound consisting of sulphur and iron. These minerals are formed in reducing (oxygen-poor) environments and remain stable as long as the conditions remain so; however sulphide easily become unstable in contact with oxygen or other oxidising substances. When pyrite comes into contact with oxygen, the mineral is destabilised and oxidises. This means that the bond between the sulphur and iron is broken, and the iron can go into an aqueous solution. The reaction also releases hydrogen ions, which lowers the pH and makes the water acidic. In some cases, lower levels of pH can speed up the weathering of minerals, and the pollution of the environment increases. This process is quite natural and occurs all the time in nature, however mining brings a large quantity of sulphur-bearing rocks to the surface and these rocks are crushed, which means large mineral grains surface is exposed to oxygen, which increase exponentially the oxidation process. The discharge of acidic, metal-bearing leachate is one of the primary environmental problems with mines where sulphide minerals are present.
Low pH values in water can be harmful to several different organisms. Often there are provisions and rules for how acidic the water that the is released by a mine can be, and how acidic the water in recipients (watercourses, groundwater and lakes) can be. The discharge of metals are also governed by these regulations.
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Due to problems with the weathering and oxidation of sulphide minerals, mining waste containing sulphide minerals is often covered with dense layers of soil or water, for the purpose of limiting the availability of oxygen. More intensive or extensive measures are often required to treat mining waste with a certain amount of sulphide mineral compared to other waste.
Last reviewed 2022-06-17