Treating effluent on mines often makes use of reverse osmosis (RO) technology, but low recoveries can raise costs substantially; continuous counter current ion exchange can provide a fit-for-purpose solution.

This is according to Vincent Ridgard, process engineer at Multotec Process Equipment, who notes that RO was initially designed to remove monovalent salt molecules from sea water.

“However, wastewater on mines also includes divalent and trivalent elements, which cause scaling of membranes in RO systems,” Ridgard says. “This means that when a standalone RO plant is utilised to treat these waters, it is operated at lower recoveries to enhance the lifespan of the membranes.”

This results in large volumes of highly concentrated brine streams, he says, which are either recirculated within the system or require very expensive effluent treatment systems. To address these challenges, Multotec offers niche technologies that are suited to treat divalent and trivalent elements in water on mines.

“Through our close partnership with Clean TeQ Water in Australia, we offer mines across Africa a continuous counter current ion exchange technology,” he says. “This uses resin which is more selective to extracting larger molecules.”

As a result, these systems achieve high recoveries of over 90%, so that process water can be re-used within the mine’s process circuits or discharged safely to the environment. The resin-based chemistry removes target species, selectively extracting contaminants through exchanging ionic functional groups that are engineered on the resin beads.

Ridgard notes that, while these scientific principles are well accepted, there has previously not been a suitable technology to truly unlock the significant potential of resin chemistry. Clean TeQ’s ‘moving bed’ solution – supplied to the African market by Multotec – is therefore a game changer.

In contrast to the conventional fixed-bed systems, the use of resin transfer mechanisms allows the continuous ionic filtration (CIF) to handle up to 150 ppm of solids, whereas conventional systems need a 100% clean liquor. Total suspended solids (TSS) and total dissolved solids (TDS) can therefore be simultaneously removed.

It also optimises the inventory of resin, a significant cost contributor to the overall plant, and provides high water recoveries. Other benefits include its low power consumption and its ability to recover valuable trace metals as a by-product.