FLOTATION TECHNOLOGY
Simplified flowsheet of an Eriez HydroFloat Coarse Gangue Rejection ( CGR ) application
HydroFloat is an adjunct to the conventional flowsheet . Rather than the underflow product of conventional flotation being regarded as a waste product that is typically being thickened and pumped to a storage facility , it reports to a classification step to enrich the coarse fraction of the tail before being fed to a HydroFloat . Often the coarsening step is already part of the operation for generating sand for building material or raising the dam . The business case for a tail scavenging application is primarily based on the additional recovery of lost coarse pay-metals , which is generally three to five percent of total plant production . A side benefit of implementing tail scavenging is that the mill circuit ’ s grinding target can be increased without losing recovery , enabling the mass throughput to be increased with existing assets .”
The next evolution in the use of the HydroFloat is now being commercialised at several sites which is a Coarse Gangue Rejection ( CGR ) application . “ Although more challenging to implement , the CGR application creates many additional benefits , the foremost being a significant reduction in the amount of grinding that is required in a flotation flowsheet .” A simplified CGR flowsheet is shown in the attached figure .
In this application , the HydroFloat is added into the mill circuit , as may occur with a centrifugal gravity concentrator or flash flotation unit in other existing circuits . Two stages of classification are used , here shown as cyclones , to produce three streams based on size . The fine stream reports back to conventional flotation , he middling stream reports as HydroFloat feed and the coarse stream returns to the mill . In this scheme , the HydroFloat generates a coarse barren tail , resulting in a significant reduction in the circulating load returning to the mill . The size of the coarse barren tail is usually about three times the size of the conventional tail .
Anglo American told IM earlier in 2020 that it is constructing a demonstration plant at the El Soldado copper mine in Chile , that will use a single 5 m diameter HydroFloat cell , the largest in the world , to treat 100 % of mill throughput , with the objective of proving the waste rejection process at full scale . The plant is expected to start up in Q1 2021 . Anglo ’ s
Processing Development Lead , Adrian McDonald commented : “ CPR [ Coarse Particle Recovery ] has the potential to be a breakthrough technology in the processing of sulphides . If we can prove the process at El Soldado , Anglo American will be the first company in the world to deploy CPR successfully to reject coarse gangue on a commercial scale . If that happens , it will change the way the mining industry approaches flotation . I hope that what we ’ re doing at El Soldado , as early adopters , will enable Anglo American to set new standards for base-metal concentrate processing and to become the industry leaders in dry stacking . That would give us significant competitive advantage .”
To quantify some of the benefits of each of these HydroFloat applications , Eriez Flotation and their coauthors from Capstone Mining , Fluor Canada , and Paterson and Cooke prepared a study looking at the effect of each option at a polymetallic mine in Mexico . This study was presented at the 59th Conference of Metallurgists in October 2020 . Wasmund shared a summary of some of the conclusions for this article . “ The study consisted of HydroFloat lab tests performed on samples from the current mine tailing and mill cyclone underflow to understand the applicability of HydroFloat on each of these streams . Two stages of screening were used so that the HydroFloat feed was between 160 and 700 microns . The tail sample yielded additional percent copper and silver recoveries in the high 80s , with zinc and lead in 70s to 60s . The cyclone underflow HydroFloat results were in the same range as the metallurgical recovery by conventional flotation , so that the HydroFloat could be considered like an ore sorter and the HydroFloat tail could be continuously removed from the mill circuit without further processing and without being returned to the mill circulating load .”
The effect of classifying the mill cyclone underflow , adding the HydroFloat and removing the HydroFloat tail was modelled to see the benefit of grinding reduction , relative proportions of fine and coarse tail and the size distribution of each tail .
The simulation of the CGR application indicated that the 80th percentile of the coarse barren tail was approximately 600 microns as compared with the conventional flotation tail which was approximately
230 microns . The coarse barren tail was approximately 30 % of the total mass of tail from the plant . The overall end-point of the grinding product from the mill circuit was approximately 380 microns versus 230 microns and the mill circulating load could be reduced by almost four times . This would result in an estimated reduction in mill power of 30 to 50 %. Acting as an ore-sorter and removing a coarse barren tail , the HydroFloat would reduce the capacity requirement for conventional flotation by 40 %.
In the tail scavenging application , the incremental global recovery of pay-metals could be increased by two to 11 %. “ As we have seen elsewhere , metals with lower recovery in the conventional plant will see bigger overall increases with the addition of coarse particle flotation on the tailing stream . Because the grinding is already done , there are no direct opportunities with tail scavenging to reduce grinding and increase tail size . However , some practitioners have reported that the HydroFloat adjunct does allow them to increase the grind size with a shift in concentrate production moving from conventional flotation to the HydroFloat .”
Wasmund adds : “ While both applications can have solid business cases and will enable more responsible and economic processing of the ore , the coarse gangue rejection application has the greatest benefit for reducing water consumption and tailing management safety . Coarse tail products have high hydraulic conductivity , meaning they can be easily and inexpensively de-watered and do not have to contribute to a wet tailing facility . If they are added to a wet facility , they drain quicker and are less likely to liquefy during rain or flooding . Some companies are also looking at ways to mix and co-deposit the coarse tail with fine tails since this has potential to reduce wet impoundments or make them safer .”
He concludes that coarse particle flotation is a tool that can increase the efficiency and responsibility of the mining industry to operate more efficiently and safely . “ The HydroFloat can be used in different ways with different results . The best placement of HydroFloats within flowsheets is a question that is being actively discussed by many and will always depend on a number of site-specific factors . As the adoption of the HydroFloat and HydroFloat flowsheets becomes more prevalent , Eriez and its partners strive to improve the safety and economics of the business .”
Maelgwyn – continued potash strength & future innovations
Wales , UK-based Maelgwyn Mineral Services ( MMS ) has had extensive experience in potash flotation over the last 20 years including for Belaruskali in Belarus working alongside NPO Passat ( 36 installations since
2005 ), K + S in Germany ( five installations since 2000 )
and FMC in Argentina ( 2011 ) for flotation of potash fines . Now the potash brine market is really taking off with MMS Imhoflot cells having been integrated with a cutting-edge K-UTEC potash flowsheet in the Kalium
28 International Mining | NOVEMBER / DECEMBER 2020