Modern Mining August 2021

WATER TREATMENT

Dealing with multiple streams of effluent in antimony roastery plant

Having initially provided a water treatment plant to deal with various waste streams for a client producing antinomy metal, antimony trioxide and antimony-gold concentrates in the Arabian Peninsula, Multotec will this September commission an upgraded plant to deal with the change in feed and the increase in contaminants, process manager Anke Botha tells Modern Mining’s Munesu Shoko.

L everaging its experience in water treatment solutions for the mining industry, Multotec in 2017 designed and supplied a complete system to a mining operation that is extremely sensitive to water usage and waste production in the Arabian Peninsula. For this plant, Multotec needed to con- sider various waste streams. When the plant was first constructed in 2017, explains Botha, it had various waste streams to deal with, including limestone scrubber blowdown with high levels of calcium; caustic scrubber blowdown with high levels of sodium sulphite; cooling water blowdown; acid quench blowdown with high levels

of arsenic and antimony, as well as some spillages. During the first order, Multotec did extensive test work to ensure that these various streams could be treated. Additionally, the company also did test work on its filter presses to ensure that it removed as much moisture as possible. “The initial plant worked well, but had to be upgraded due to the change in feed and increased contaminants. As a result, the client had to resort to trucking some of the waste water to an off-site waste treatment facility that would treat the water for them. The exercise was cumbersome and costly,” she says. There were several changes to the client’s waste streams between 2017 and 2020, explains Botha, which necessitated for the upgrade. Firstly, it was the increase in flow from the acid quench blowdown. Secondly, there was a total increase in plant feed from 5,44 m³/hour to 10,5 m³/hour. There was also a significant increase in contaminant levels in the acid quench blowdown, with total arsenic, antimony and selenium. The client approached Multotec for an upgrade of the plant to deal with increased contaminants in its effluent. From the onset, the upgrade project was under a lot of pressure. “Our biggest challenges were to provide the client with a new water treat- ment plant using old infrastructure and taking the scope without having sufficient design details due to some logistical challenges. We, however, walked the road with the client to get to a feasible solution,” explains Botha. Initial solution The original solution included two separate pre- cipitators, followed by the DeSALx Ion exchange, a unique continuous counter current ion exchange technology from Australian-based Clean TeQ Water, offered locally by Multotec. This was used to remove calcium and sulphates. “The benefit is that the moving bed ion exchange technology overcomes a number of limitations faced by conventional fixed bed ion exchange systems. It can act as a sand filter if required, simultane- ously removing suspended solids while targeting

Anke Botha, process manager at Multotec.

Multotec did extensive test work to ensure that various streams could be treated.

20  MODERN MINING  August 2021