A mine generates large amounts of highly concentrated wastewater due to contact between water and various types of minerals. The origin of these effluents can be found in the distinct processes undertaken in mining, in addition to drainage from rainfall.
Mining effluents can be caused by:
- Wash waters.
- Flow Process acids.
- Water leaching, flotation and concentration.
- Effluents from refining and gas scrubbers.
Meanwhile, rain that infiltrates the tailings of the mine can also cause oxidation, hydrolysis, washing, etc. producing a highly contaminated wastewater.
The contact between minerals and water, by process or rain, can produce distinct reactions. The effluents produced are of diverse compositions, depending upon the nature of each mineral, since there are those more or less soluble, hydrolysable and non-hydrolysable, as well as sorbents and non-sorbents. Thus, the discharge of such wastewater can provoke serious consequences in mining and its environment by completely altering water chemistry.
Traditionally, physico-chemical or biological methods have been used to treat these effluents. Presently, zero discharge has proven to be the smartest choice. It ensures the protection of the ecosystem and provides for water reuse in places where access to water is limited. In addition, zero discharge is most economical long-term alternative once installation costs have been recuperated.
The only present day technologies that can guarantee zero liquid discharge are vacuum evaporation and crystallization, combined or not, depending on the composition of the effluent, with other membrane technologies or pretreatment processes. Thanks to the installation of these wastewater treatment plants, we can achieve a 95% rate for distilled water ready to be reused. Moreover, solids rejected in the process can to be sent to waste management.