Taming tailings to protect the environment
23 Nov 2018
Mine tailings are, potentially, the most environmentally hazardous part of any mining operation. GEA has developed diverse technologies that can significantly reduce the impact of tailings on the environment and help minimize water usage, while isolating and extracting valuable minerals which can become an additional revenue source.
Mine tailings are the ore waste from mining operations mixed with process water as well as any reagents used during processing. These can be toxic and therefore need to be kept isolated from the environment. Traditionally, mine tailings, in the form of a slurry containing fine mineral particles, have been contained in large, man-made lakes where the solids are allowed to settle out and then the cleaned water skimmed off the surface. However, this process is less than ideal.
Settling takes a long time which means tailings ponds can become quite large. When it comes in contact with air and water, the waste material can generate acid mine drainage (AMD) or acid rock drainage (ARD) which pollutes the environment. Because these ponds frequently take up part of the natural topography and are retained by large dams, it can have a dramatic effect on the local environment. Breaches causing serious environmental damage, although rare, do happen: there were at least two major breaches of dams in 2015, 2016 and 2017 and four in 2014. In February 2018, there was a major breach at a bauxite mine in Brazil following heavy rain. Likewise, wildlife often mistake these ponds for safe habitats. These are major challenges to operators who strive to limit the effect of their operations as much as possible.
GEA tailings management solutions: better for the environment, better for the bottom line
GEA decanter technology is well established for dewatering a wide range of sludge materials. In recent years decanter capacity has improved now making it effective for use in mining operations. For example, GEA machines can handle up to 100 tons of slurry an hour – making them much more practical for this application.
A GEA Dewatering Decanter crudMaster, for example, is used to dewater the pre-thickened slurry, rotating at application based centrifugal forces. Because the machine is lined to protect against the abrasive nature of the feed, it is very robust – ensuring operational excellence. Anionic flocculants are added to the process to further agglomerate fine particles causing them to drop out of solution. As a result of the additional high-speed centrifugal treatment – the cleaned water – up to 90% – is returned to the process – or if meeting the right standards, returned to the environment. The solid matter, approximately 80% dry solids, is then discharged onto a conveyor, ultimately producing a dry cake for easy disposal or reprocessing.
– Tore Hartmann, senior product sales manager for chemicals and minerals, GEA
For applications where the cleanest possible water is required, the integration of a GEA nozzle disc stack centrifuge is an excellent solution. This centrifuge separates the process water from the fine particles and reduces, and can even eliminate, the need for further storing the slurry. Superior separation efficiency, at high throughput capacities in continuous operation are the key product benefits. During this process, customers also have the opportunity to extract valuable elements – such as gold, silver, copper, lead and zinc – which can be sold to generate extra revenue. And because the process takes place in a closed environment, the risk of chemicals or other hazardous materials leaking into the environment is restricted. “Being able to demonstrate responsible environmental stewardship can make the difference between receiving or retaining and environmental license an being refused or stripped of one by the presiding authorities,” says Hartmann.
