Modern Mining August 2020

is combined and fully integrated with RO to produce a high-recovery or Zero-Liquid-Discharge (ZLD) solution. “Remember that RO was designed to remove monovalent ions, while IX is more selective to larger divalent and trivalent ions. Hence, by combining the two technologies and allowing the IX to firstly remove the elements which scale up the RO mem- branes, you allow the RO plant to do what is was designed to do, which is to remove monovalent salts at significantly higher recoveries. Furthermore, we can potentially provide a ZLD system by recirculating the concentrated sodium brine stream to regenerate the resin in the ion exchange plant.” Proving capabilities In one of the flagship Minimum Liquid Discharge (MLD) systems, Multotec designed and supplied a complete system to a mining operation that is extremely sensitive to water usage and waste pro- duction in the desert of the Middle East. For this plant, Multotec needed to consider four respective brine streams that were all significantly different in nature. “As such we designed a plant comprising an HDS system for the specific removal of arsenic and antimony, although only two of the effluent streams needed to feed to this specific area,” he says. “The product water feeds the dual Continuous Counter Current IX system (known as DeSALx), which removes the scaling components, calcium, magne- sium and sulphates among other components from the water stream.” The softened stream is combined with two other effluent streams before being sent to an RO plant to produce potable water quality at >90% recovery. The only effluent streams that are produced is the gypsum by product from the IX, which was incor- porated in the onsite gypsum plant for profit and the minimal concentrated brine stream sent to an evaporation dam. The arsenic sludge from the HDS is dewatered by filter press while the solid cake is disposed of. Recovering residual precious metals Water treatment is often considered a so-called “sin tax”, as it comes at a relatively significant capital cost without any clear and obvious advantages to the mine owner. One of the major advantages of utilising ion exchange for the treatment of effluent and/or tail- ings streams, reasons Ridgard, is that in addition to being environmentally compliant, potentially increas- ing recoveries and reducing reagent consumption by providing a fit-for-purpose process water, ion exchange offers the possibility of recovering residual trace metals, which would have otherwise been lost to the mine owner. “Mining operations spend millions of dollars to lib- erate and recover their target elements, but despite

their best efforts, 100% recovery of these elements is simply not possible and large percentages end up in the tailings dams or is lost to the environment,” says Ridgard. “What the Clean-IX Continuous Counter Current Ion Exchange technology offers is the opportunity to recover what is lost from the processing plant and potentially provide an economic benefit which signif- icantly offsets the cost of the water treatment plant. Depending on the concentration of the valuable metal and the total flowrate that is being treated, a complete payback within a matter of months could be possible,” concludes Ridgard. 

The cost of effluent treatment is significant, hence a high recovery system is essential.

Key takeaways  One of the greatest challenges facing mining operations is the develop- ment and management of water resources  Water is arguably the second most valuable asset on a mine after the ore body itself  Multotec offers fit-for-purpose, niche technologies specifically suited to the treatment of divalent and trivalent containing mining waters  Multotec has partnered with Australian based Clean TeQ Water to provide the African mining market with a continuous counter current ion exchange technology  Multotec provides the mining 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

August 2020  MODERN MINING  33