Upgrading the thickeners at one of Australia’s largest gold producers not only boosted the mine’s bottom line but also realised important sustainability benefits, as the FLSmidth team behind the project explains.
Thickeners are a ubiquitous feature at mineral processing facilities and have been for many decades. And in an industry where the lifetime of major equipment is often measured in decades, they are particularly long-lived.
FLSmidth – whose association with thickeners goes back more than a century via the Dorr-Oliver and EIMCO brands that it acquired in 2007 – has many systems still operating at Australian mines that were installed in the 1960s, while a couple date back as far as the 1930s and 1940s.
In addition to its role in the production of target minerals, thickeners play an important part in mine water management and recycling: areas of focus in today’s mining industry where sustainability is becoming an ever more pressing day-to-day concern.
This is particularly true of mines in regions of high water stress, which is how the World Resources Institute categorises most of Australia.
With thickeners infrequently replaced, improving the performance of existing installations is key to meeting the industry’s changing sustainability and performance goals, according to FLSmidth Australia’s head of mining David Williams.
“Thickener technology is constantly evolving. Refurbishing and retrofitting therefore helps to ensure the ongoing integrity, reliability and productivity of existing machinery with the latest advances in thickener technology,” Williams said.
“At FLSmidth, we combine years of engineering expertise to offer a complete service package – from equipment and process evaluation to tailored upgrades, including complete new mechanisms, feed systems and new drives.”
FLSmidth’s experience and technology range is comprehensive, including the world’s largest and highest-capacity bridge and column-mounted thickeners.
Not keen to rest on its laurels, however, the company is always looking forward. Its research and development model integrates the evaluation of new technologies and concepts with continuous review and update of existing products.
“Our efforts focus on the development of solutions that combine high performance, reliability and availability with minimal environmental impact, in line with our MissionZero goal to reduce the water use and footprint of mining operations,” Williams said.
Among the latest developments in thickener technology offered by FLSmidth are its E-Volute feedwell and E-DUC and P-DUC feed dilution systems.
“The E-Volute feedwell is the result of many years of development work, including CFD modelling, at the laboratory and pilot scale,” FLSmidth global product line manager for thickening Fred Schoenbrunn said.
“The result is an involute design with sloped tapering shelf and sloped inner shelf, which promote superior energy dissipation in the feed stream, optimal mixing and improved shear profiles to ensure thickener performance and efficiency.”
According to Schoenbrunn, this provides a range of benefits including:
- increased retention time in the feedwell
- maximised solids throughput
- reduced shear rates and minimised flocculant consumption
- increased flocculation efficiency
- even distribution of feed slurry/solids
- enhanced settling rates and increased equipment capacity
- optimised underflow solids
- minimised short-circuiting
- reduced overflow solids.
Supporting the work of the E-Volute feedwell are the E-DUC and P-DUC feed dilution systems, both of which are designed to ensure even distribution of flocculated solids in the feed before it reaches the E-Volute feedwell.
“The E-DUC system is appropriate for applications that require consistently large volumes of feed dilution, whereas the P-DUC system incorporates a variable speed drive that allows for variable dilution flowrates in applications where large variations in feed flow or density are expected,” Schoenbrunn said.
Case study: Feed system retrofit at an Australian gold operation
FLSmidth has supported thickener performance upgrade at one of Australia’s largest gold mines for several years.
When the mine first approached the engineering company, it was operating third-party 34m diameter leach feed and 44m diameter tailings thickeners, and nameplate capacity was 700 tonnes per hour (tph).
“We initially upgraded the leach feed thickener, installing an E-DUC dilution system and E-Volute feedwell,” FLSmidth regional product line manager for dewatering Anson Gilbert said.
“This increased leach feed thickener underflow density from 48 per cent to 54 per cent solids at 850tph of feed solids, resulting in significant savings in both lime and cyanide consumption, as well as increasing carbon in leach (CIL) residence times.
Flocculant consumption also fell by 34 per cent on a gram/tonne basis.
Return on investment was achieved in less than six months.”
The mine successfully operated with this upgraded set-up for several years. Over time, however, the thickener started to bottleneck the process and the mine again approached FLSmidth to help.
“The mine’s proposal was to swap the duties of the 34m leach feed thickener and 44m tailings thickener,” Gilbert said.
“When we were called in, we set about analysing the idea with a comprehensive program of onsite test work, process evaluation and structural analysis of both thickener bridges.”
Through this work, the FLSmidth team observed continuous plumbing in the leach feed thickener in proximity to the overflow launders – with solid particles in the overflow visible at elevated throughputs – while faster settling rates and compaction times were seen in the tailings thickener.
“We were, therefore, able to prove the viability of swapping thickener duties to unlock additional thickener capacity,” Gilbert said.
“The faster settling tailings material could be treated in the smaller thickener, meaning the additional unit area required for the leach feed application could be obtained by using the larger thickener.”
FLSmidth recommended installing P-DUC mechanisms on both thickeners and an E-Volute feedwell on the 44m thickener.
The engineering team also recommended a larger feed box to allow for increased throughput and improved deaeration of the feed.
As a result of the upgrade, thickener throughput has increased from 1060tph to 1160 tph, without any increase in flocculant consumption on a gram/tonne basis.
There is also now no visible plumbing or particle carryover in either of the thickeners overflow.
“Thickeners are no longer the bottleneck to performance,” Gilbert said. “By increasing throughput and maintaining the same fixed costs, we also enhanced profitability, and payback has been achieved in under 12 months.”
The value of thickener upgrades
“The retrofit demonstrates the potential improvements that a thickener upgrade can bring to an operation,” David Williams said.
“In both units, we achieved a large improvement in solid–liquid separation, which facilitated a further flowsheet change and removed a customer pain point.”
Overall, the upgrade resulted in a 9 per cent increase in plant capacity allowing for reduced fixed cost per ounce.
This project also demonstrates the mutual benefits thickener upgrades can bring to a mine’s profitability and environmental performance.
There were multiple specific sustainability wins.
Increasing the underflow density from the leach feed thickener allowed for additional residence time in the CIL circuit, improving recovery at a given throughput.
This increased the production of gold without increasing the amount of ore mined.
The underflow water ratio in the tailings thickener dropped from 0.85 tonnes water to 0.75 tonnes water per tonne of solids processed – an 11 per cent reduction in water going to the tailings dam (even with the higher tonnage).
“These benefits align with our MissionZero sustainability program to drive sustainable productivity in mining – and demonstrate the complementary value this sort of project can bring to a mine’s productivity and environmental performance,” Williams said.
“As sustainability becomes an ever-important element in the performance of mineral processing operations, we believe the value of such projects will become increasingly important as mining companies seek to meet both financial and environmental goals.
“We are committed to supporting the industry on this journey.
“And, through our MissionZero program, we are working with our customers and other partners to build a truly sustainable mining industry.”
This article also appears in the April edition of Australian Mining.