Modern Mining August 2020

WATER TREATMENT AND RECYCLING

Water management at mines – every drop counts Water plays an essential role in most mining and extractive

processes, and responsible water management is a critical business case for the mining sector at large. Managing mine impacted water often requires water treatment, but there is no one-size-fits-all approach when it comes to the design of water treatment plants, thus mines need to select a site-appropriate water treatment technology that meets their project specific needs. To this end, Multotec offers integrated fit-for-purpose water treatment systems that consider overall requirements of the site. By Munesu Shoko .

Vincent Ridgard, process engineer, Multotec.

O ne of the greatest challenges facing mining operations is the development and manage- ment of water resources. It is important that every operation prioritises the most effi- cient control and management of valuable water resources to maximise the efficient use and reuse of every drop of water that is involved with a mine site operation. This also minimises the long-term environmental liabilities that could result from the mismanagement of water resources. Reiterating the effect of mining practices on sur- rounding communities and the environment, Vincent Ridgard, process engineer at Multotec, quotes James Lyon, who, in an interview with the Mineral Policy Centre, said, “Water has been called mining’s most common casualty”. According to Ridgard, mining affects fresh water

through heavy use in processing ore, through pol- lution from discharged mine effluent and seepage from tailings and waste rock impoundments, com- monly known as acid mine drainage (AMD). He is of the view that water pollution from mine waste rock and tailings may need to be managed for decades, if not centuries, after closure, as the water sources continue to naturally produce sulphuric acid when sulphides in rocks are exposed to air and water. This results in oxidation and acidification pro- cesses, which continue to leach trace metals from the exposed rock face, and are discharged into the environment. “Furthermore, chemicals used in leaching or flota- tion process, such as cyanide or sulphuric acid, enter the process water that is being recirculated within an operation, and some of these solvents remain in

The arsenic sludge from the HDS is dewatered by filter press while the solid cake is disposed of.

that water and, as it migrates, the toxic solvents are carried into the agricultural soils and into the water source of downstream communi- ties,” explains Ridgard. Significance of water in mining Water, according to Ridgard, is arguably the second most valuable asset on a mine after the ore body itself. Strangely enough, he rea- sons, it is more often considered an “afterthought” for many design houses and mine owners. Mining uses water for mineral processing, including comminution practices, classification by screen- ing and hydrocyclones, dust suppression, slurry transport and employees’ needs, among others.

30  MODERN MINING  August 2020