Relatively little water used during mining and processing needs to be clean or potable, so mines can reduce both water consumption and treatment costs by understanding what water qualities are needed where.
According to Peter Shepherd, partner and principal hydrologist at SRK Consulting, the mining sector’s drive towards ambitious water conservation targets means recycling more – so that less fresh water needs to be procured. There is also a financial benefit to recycling, as having to treat water before use or discharge is an expensive exercise. Shepherd highlighted that treatment can be kept to a minimum if mines are clear about what level of water cleanliness is required by its different on-mine processes.
“Clearly, a mine does not want to be using potable water to mix with tailings for pumping to a tailings storage facility,” said Shepherd. “Most of a mine’s water will generally be used in the process plant, and these applications can usually manage with much lower water qualities.”
That said, there would be specific phases of the plant that require cleaner water – for the mixing of reagents and chemicals, for instance. There is also a need for water that is low in sediment particles for use in the gland seals of pumps.
Mines can therefore optimise the reuse and recycling of their water through developing a water quality ‘cascade’, explained Bjanka Korb, principal environmental engineer at SRK Consulting. This will detail the minimum water quality demanded by each process, so that water is not treated to higher levels of quality that needed at the point of use.
“This approach opens the door to increasing the volumes that can be reused and recycled,” said Korb. “The accumulation of water in the system and resultant discharge of low-quality water into the environment is thereby also minimised.”
An additional benefit is that the mine would be able to reduce its reliance on treated municipal water and therefore the operational cost to the mine could also be decreased. Where untreated dam water can be procured from a municipal source, the mine could use this directly in the plant – and only treat water to potable standards that is used in bathrooms, kitchens and drinking use.
Read the full article in the First Mining DRC-Zambia Newsletter
