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.
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Multotec’s UX7 ultra-fine chrome spiral is designed to extract the ultra-fine fraction of chromium ores.
Wilna 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 involving 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 delivering the Atlantic Diamond Recovery Vessel Upgrade and, in 2008, I was the lead process engineer at Bateman responsible for designing and executing the new Finsch Diamond Recovery plant,” she adds.
Describing the basic principles of minerals extraction, Hoffmann says the process involves liberating the valuable minerals embedded in their ores from the surrounding 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 densities 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 separation 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 classification 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 either 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 possible 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 processing and energy costs are significantly reduced and smaller, less expensive total solutions can be used. This makes bulk reduction a very cost-effective addition,” Hoffmann tells MCA.
“In some cases, the concentrated mineral from a physical separation stage can be a sellable product. In these cases, we focus on the specification of the off-take agreement to produce an optimal yield final product that is in specification.
“At Multotec, I find out from clients what they best need to feed into their downstream pipeline; I try to determine what the separation opportunities are; and the best technology to use to deliver on this need. Because we have various technical solutions, we can identify a very wide variety of separation solutions to suit almost any ore body and requirement. Once done, I can hand a concept to our process engineers to do the sizing and throughput calculations before recommending a holistic solution to the client,” she explains.
While Hoffmann says that new Greenfield’s projects in South Africa are currently scarce, Brownfield expansion projects and efficiency initiatives to improve the yield from existing operations or to reprocess previously discarded fines, are on the rise. “Over the years, we have been making steady incremental improvements to our processing equipment. Combined, these offer substantial gain opportunities on older plants seeking improved recoveries,” she notes.
“We are involved in using spiral-based reprocessing of tailings, because it is a low-cost option. The expensive mining and milling are already done, so extracting the remaining percentages of value from historical tailings proves to be very cost effective.
And latest-generation spiral technology can be used to concentrate and reprocess chrome, gold and many other minerals’ tailings,” she says.
She notes, in particular, the recent development of the new Multotec UX7 ultra-fine chrome spirals, which have been purpose designed to improve the recovery efficiency in the fraction between -75 and -38 µm.
“With traditional spirals, the recovery efficiency falls drastically for the fraction smaller than 75 µm. Adding a UX7 spiral to recover this ultra-fine chromium from old tailings is proving to be a simple and cost-effective way of adding a value stream to an operating mine,” she explains, before reinforcing the need to fully understand the minerology of the tailings for best results.
“We always strive to de-risk projects as soon as they come in, not just for the client but also for us, no matter how familiar we might think we are with the scenario. After looking into the size fraction, the composition of the tailings and the volumes, we will size and model equipment, and do efficiency and yield calculations. Then we will often do full scale verification tests based on the plant’s typical or best practices,” she adds.
Another Multotec innovation currently attracting attention is the Decanter Centrifuge for the dry disposal of tailings. “Due to environmental concerns and/or critical water shortages, some mine sites cannot get a license to build slimes dams to dewater their tailings. Now these plants have a dewatered tailings disposal option. Our tailings decanter centrifuge enables these tailings to be continuously dewatered to allow for safe stacking,” Hoffmann reveals.
At the heart of what Wilna Hoffmann does is help mining clients to enhance the efficiency of their extraction processes. She has been doing this for most of her 28-year career to date, with nearly half of that time with Multotec. “I continue to find this work inspirational and fulfilling, every day,” she passionately adds.
Wilna's philosophy of life is that discipline is the bridge between dreams and accomplishments. She advises other women leaders in South Africa to focus on hard work and self-care, emphasising the importance of perseverance and having a positive outlook. Her management style focuses on leading and mentoring engineers to achieve high standards while enhancing overall team output. She values dedication, hard work and integrity, while striving to lead by example.
Her work in a traditionally male-dominated field has been both challenging and rewarding. Starting as a bursar in 1992, she was the first female student to work in a plant position at her assigned mine. Experiences such as these have shaped her perspective and resilience, and she is encouraged by the positive changes in the workplace over the years.
Advocating for more young women to take up technical careers, she says that the mining engineering, minerals processing and extractive metallurgy fields are now far more comfortable places for women to work and are more accepted as the norm. “Dedication and tenacity are important in these sometimes difficult but often unbelievably exciting fields. But women can really do it and become extremely successful,” she advises.
