Modern Mining August 2020

WATER TREATMENT AND RECYCLING

The utilisation of resin-based chemistry for the removal of target species has long been understood and respected globally in the industry, he says. It offers the selective extraction of contaminants by the exchanging of ionic functional groups, engi- neered on the resin beads, for target elements in the surrounding solution of like charge. The problem, however, has always been that there has not been a suitable technology to effectively facilitate the enor- mous advantages provided by the resin chemistry. “The Continuous Counter Current Ion Exchange technology, engineered by Clean TeQ and sup- plied to the African market by Multotec Process Equipment, is a game-changing, moving bed tech- nology,” he says. Contrary to the conventional fixed-bed systems, the use of resin transfer mechanisms allows the CIF (Continuous Ionic Filtration) to:  handle up to 150 ppm of solids (conventional systems need a 100% clean liquor), hence offer- ing simultaneous removal of TSS (total suspended solids) and TDS (total dissolved solids);  offer optimised resin inventory (resin is the most expensive part of the plant and hence it is critical to ensure the longevity is maximised and the volume is minimised);  provide very high water recoveries;  handle in column precipitation;  offer low power consumption (given the limited power availability on isolated mine sites in Africa, this is another major advantage); and  produce valuable by-products and/or trace metal recovery. Fit-for-purpose treatment systems When designing its plants, Multotec considers the overall requirements of the site before building a complete fit-for-purpose solution based on the vari- ous effluent feed streams and the desired product water quality. “There is no one-size-fits-all approach when it comes to the design of these plants,” says Ridgard. If a certain quality of process water is required, then a system which produces the required quali- ties is specifically engineered, to treat specific elements which could potentially affect the overall process efficiency – such a system could poten- tially comprise of a combined HDS (High Density Sludge) and Continuous Counter Current IX system. If environmentally compliant dischargeable water is required, then a simple HDS system is perhaps the ideal solution. “Even if the end goal is to change mine service water to potable drinking water, we design a high recovery system to meet these needs – this could potentially consist of an HDS, Continuous Counter Current IX and RO system,” explains Ridgard. Depending on the customer’s ultimate water quality requirements, Continuous Counter Current IX

“Utilising completely clean water, however, does have its disadvantages in that residual reagents which carry over back into the process have been removed, and your operational cost increases to supplement this. Thus, it is critical to implement a fit- for-purpose water treatment system which removes target contaminants while allowing other elements to make up the necessary process water composition,” adds Ridgard. High recovery water treatment systems The cost of effluent treatment is significant, hence a high recovery system is essential. One of the common ways of treating effluent water is Reverse Osmosis (RO). RO was initially designed for sea water desalination to remove monovalent salt mol- ecules (NaCI). Due to its success in this application, it has since been introduced to other sectors such as industrial and mining. “The problem is that sources of wastewaters also include a wide variety of other elements, such as divalent and trivalent elements which cause scaling of membranes. This means that when a standalone RO plant is utilised to treat these waters, it is oper- ated at lower recoveries to enhance the lifespan of the membranes. It results in large volumes of highly concentrated brine streams, which are either recir- culated within the system or require very expensive effluent treatment systems,” says Ridgard. Multotec offers fit-for-purpose, niche technolo- gies specifically suited to the treatment of divalent and trivalent containing mining waters. To this end, the company has partnered with Australian based Clean TeQ Water to provide the African mining mar- ket with a continuous counter current ion exchange technology. “The resin used in these systems is specifically manufactured to be more selective to the extraction of larger molecules and as a result provides the min- ing industry with a high recovery (>90%) system to provide fit-for-purpose process waters to be utilised within the water balance or discharged safely to the environment,” explains Ridgard.

Multotec offers fit-for-purpose, niche technologies specifically suited to the treatment of divalent and trivalent containing mining waters.

32  MODERN MINING  August 2020