Modern Mining August 2021

contaminant removal via ion exchange,” explains Botha. Tolerating precipitation in the desorption column is a key feature of moving bed technology, allow- ing for cheaper reagents to be used and preventing blocking up. This is unique to Clean TeQ Water’s ion exchange technology and allows low-cost zero liquid discharge solutions and innovative flowsheets. “After the calcium and sulphates were removed, the final treatment step was reverse osmosis (RO) to deliver drinkable water. RO was initially designed for sea water desalination to remove monovalent salt molecules (NaCI). Due to its success in this applica- tion, it has since been introduced to other sectors such as industrial and mining. In this plant, the sys- tem was a Zero Liquid Effluent discharge. We also supplied the filter press, producing low moisture content sludge,” she adds. New solution The new solution entailed finding the best possible solution by using existing equipment. This proved to be a challenge as the contaminant levels had increased significantly and Multotec had to assist the client to get the most cost-effective solution. In the new plant, the limestone scrubber blow down with high calcium content, the acid quench blowdown, as well as the liquor and alkali blowdown are combined and enter a lime precipitator reac- tor, followed by a lime thickener and a settling tank. Here, the magnesium and calcium sulphate (from the Continuous Ionic Filtration (CIF) effluent stream) rich sludge is removed by a Multotec filter press. “The product water is sent to a feed buffering tank where oxidation occurs by means of hydrogen per- oxide before sending it to the three-stage arsenic/ antimony precipitation. The three-stage precipitation approach was selected due to the reduction of coag- ulant usage. The precipitation is then removed with a high-rate clarifier, sending the arsenic/antimony rich sludge to the second filter press in the plant,” explains Botha. Due to the high sodium content in the new efflu- ent steams, she adds, the original DeSALx

the upcoming RO can sufficiently treat the water,” explains Botha. The stream is then combined with the cooling water blowdown, sent through a multimedia filter and finally cleaned with RO, allowing the plant to deliver drinking quality water. The only waste produced is sludge that is further dewatered by Multotec filter presses. The water enters the system again to be cleaned. “The new plant includes an additional precipita- tion stage. Originally there was only an antimony/ arsenic precipitation stage, but with the change in feed and the increase in contaminants, an additional metal precipitation step was added, which called for the CIF solution,” explains Botha. True to its operating philosophy, Multotec has given the client continued support from 2017, and will continue doing so. “We provided support to the client from the beginning, offering solutions even when design parameters were still unclear. We have been there through the whole process, meeting daily to resolve all engineering issues to get this project done as quickly as possible. We are due for com- missioning this September. One of the challenges is that we might not be able to physically commission the plant. We have, however, set up an alternative remote assistance plan that will allow us to help the client to commission virtually,” con- cludes Botha. 

The only waste produced is sludge that is further dewatered by Multotec filter presses.

could not be used in this instance and was repurposed as a CIF. The tech- nology uses a moving bed of charged resin beads to attract and remove ionic species from water while filtering the water of sus- pended solids, ensuring optimum efficiency and continual high performance. A portion of the resin is cycled between columns

The Multotec plant is due for commissioning this September.

(usually hourly) using an air lift pump, allowing con- tinuous operation and regeneration of the system. “The CIF works similar to the DeSALx but removes only one targeted species instead of two. The tar- get species removed here is calcium to ensure that

August 2021  MODERN MINING  21