MechChem Africa September-October 2024

A woman’s journey into extractive metallurgy In celebration of Women’s Month, Wilna Hoffmann, a business development manager for Multotec, talks to MechChem Africa about her love of extractive metallurgy and her journey from being “not the best of students” to loving every subsequent moment of her working life.

W ilna Hoffmann matriculated in 1990 from JJ du Preez high school in Cape Town. “In my matric year I had decided to study chemical engineering, which I believed offered a huge range of opportunities in the industrial field. After my first year studying chemical engineering in Cape Town, however, I was awarded a bursary from Anglo American to study extractive metallurgy, so I moved to Gauteng to study at the Vaal University of Technology (VUT),” she tells MCA. She graduated in 1995 with a National Higher Diploma in extractive metallurgy from VUT and was offered a job with De Beers focusing on diamond liberation at Finsch diamond mine. She was soon seconded to Namakwa Sands during commissioning of the smelter in 1996. “As soon as I started working, I became obsessed with extractive metallurgy, and I have loved every moment since!” she exclaims. “My first role in diamond mining was as a metallurgist for small plant improvement projects, while also managing the laboratory. I later managed and executed a project involv ing tailings cyclones for the infill slimes dam on the Finsch Diamond mine in the Northern Cape. This was new technology for improving the rate of rise and stability of the slimes dam: extremely exciting at the time. “In 2003, as the client representative for De Beers Marine, I was also involved in deliv ering the Atlantic Diamond Recovery Vessel Upgrade and, in 2008, I was the lead process engineer at Bateman responsible for design ing and executing the new Finsch Diamond Recovery plant,” she adds. Describing the basic principles of miner als extraction, Hoffmann says the process involves liberating the valuable minerals embedded in their ores from the surround ing waste rock. “Usually, the ore will first be crushed and/or ground to liberate the mineral being mined. Extraction metallurgy refers to the processes that need to be applied to separate, completely, the waste from the pure target mineral. “The processes you need to employ are mineralogy-specific, though. At De Beers, we were separating diamonds from rock, so after crushing, the ore was passed into a dense medium separation (DMS) plant. Because the density of the diamonds is generally heavier

than that of the waste rock particles, the diamonds sink in the medium, while the waste particles float. This allows diamonds to be recovered by a Dense Medium Separation Cyclone,” explains Hoffmann, adding that the medium used needs to be chosen and mixed to best match the exact composition and densi ties of the mineral ore “to ensure that as many of the diamonds as possible are recovered”. The process is followed by magnetic separation, x-ray and laser recovery of the diamonds. “I love the task of choosing the best separa tion techniques for a particular mineral with its unique mineralogy and challenges. When a mine needs to develop or fine-tune a minerals processing cycle, we will jointly try to arrive at a physical separation solution that optimises recovery, yield and grade. This is my current position at Multotec. As well as supplying equipment, including DMS cyclones and clas sification cyclones, we can aid in separation by designing screening media, sieve bends, static screens, tailor-made spirals and various other products. Daily, I get to meet clients mining different commodities from all over the world and my job is to understand their needs, and to understand both what they want to achieve, and the minerology of the ore being mined. Then, we can suggest the most

suitable separation solution for the delivery of maximum recovery at the minimum possible cost,” she informs MCA. She goes on to describe a bulk reduction technique that, when done early in a process flowsheet, can make the project much more cost effective. Copper extraction using ei ther a flotation or leaching process requires expensive reagents and is energy intensive and costly. By physically separating out as much of the unwanted waste rock as pos sible from the copper-containing minerals, we can remove up to 70% of the total weight from the flotation or leaching process, which significantly reduces the capital cost of both the downstream plant and reagent volumes. The downstream processes are therefore a lot smaller after spiral or DMS bulk reduction – and most end-stage downstream processes are usually much more expensive, so process

Multotec’s UX7 ultra-fine chrome spiral is designed to extract the ultra-fine fraction of chromium ores.

16 ¦ MechChem Africa • September-October 2024