FLOTATION TECHNOLOGY
Froth fine tuning
Paul Moore takes an in-depth look at the key players , developments and technologies in the global flotation cell market which remains at the heart of most metals and minerals recovery operations
Taken together , FLSmidth and Metso Outotec
represent in excess of 90 % of the global flotation cell market so it makes sense to cover those companies first before looking at some of the other innovators and unique solutions that are available .
First up for the “ big two ” review , IM spoke to Dariusz Lelinski , Global Product Director , Flotation at FLSmidth to get an update on some of its key innovations announced in recent years including the mixedROW™ Flotation System that combines the benefits of its two key flotation machines – nextSTEP™ forced air and WEMCO ® self-aspirating technologies . The nextSTEP rotor is designed to produce ideal flow streams . It also produces optimised turbulence to enhance bubble-particle attachment . This improves recovery rates and concentration grades while lowering energy requirements .
The nextSTEP machines are placed at the beginning of the row , where it can recover easy floating and coarse material using the least amount of energy possible . Because of this positioning , the mixedROW lowers energy consumption by between 15-40 %, and increases recovery by up to 5 %. The WEMCO machines are placed at the end of the row , which increases both coarse and fine particle recovery , as it is capable of treating a wide range of particle sizes . The elevated rotor position within the machine also reduces particle detachment , as there is short distance from point of attachment to the froth zone .
Another recent introduction , offering substantial opportunity in the retrofit market , is a radial launder and froth crowder system . This system allows the for improved separation efficiency which maximises economic gains by shifting the grade recovery curve allowing either deeper froth or faster froth removal . Designed for greater flexibility and control , radial froth crowders reduce top-of-froth surface area and increase froth movement to the nearest radial launder . Bolt-on froth crowders require no cutting or welding and there are no permanent structural changes to the existing cell , which allows for retrofit during scheduled maintenance shutdown without additional downtime .
“ nextSTEP has been a huge success for us – to date we have sold about 250 units on new cells as well as retrofitting about 250 units on existing cells .
The retrofits have mainly been on our older Dorr- Oliver technology but also on competitor flotation cells . We are just starting dry commissioning at a plant in Mexico where the whole concentrator uses nextSTEP rotors mechanisms .” The plant is part of Fresnillo ' s Pyrites Plant Project that will produce 3.5 Moz / y of silver and 13,000 oz / y of gold and will be fully commissioned this year . The FLSmidth WEMCO nextSTEP 300 m 3 cells will help improve overall recoveries by processing historical and ongoing tailings from the Fresnillo and Saucito mines . The plant will float pyrite concentrates that will be leached in a 2,000 t / d dynamic leaching plant and Merrill Crowe plant to produce precipitates .
At another major gold operation in the Americas , FLSmidth will install two rows of 600 m 3 cells which represent its third plant with cells of this size using nextSTEP . Other upcoming new FLSmidth 600 m 3
Woodgrove Direct Flotation Reactors ( DFRs ) installed at Copper Mountain
cell installations will include Teck ’ s Quebrada Blanca 2 copper mine in Chile ( startup Q1 2021 ).
“ The nextSTEP rotor-stator combination is the most energy efficient on the market . In fact , we guarantee that we will be 15-40 % lower in power consumption than any other conventional flotation cell in the world , which is part of the FLSmidth Mission Zero initiatives . Also because of the design , working with our Krebs ® pump group in Tucson , we also guarantee that the mechanism will last 50 % longer before replacement . The wear is much lower as we are spreading the stream along the whole blade of the rotor and the whole blade of the stator . One of the most challenging applications is in Platreef platinum ore in South Africa where cells were retrofitted with nextSTEP with excellent results in wear rates .” The third aspect Lelinski mentioned was that the design also produces very good metallurgical results in recovery terms .
Looking then at mixedROW , this is being offered as a design for greenfield flotation plants as well as for existing plant expansions . A good example of this is at Southern Peru Copper ’ s ( part of Grupo Mexico ) Toquepala mine which has doubled its concentrator plant throughput from 60,000 t / d to 120,000 t / d . “ We designed a whole new mixedROW plant for this expansion – it has been operating since December 2019 and they have had outstanding results . The plant has two rows of 5 x nextSTEP and 2 x WEMCO cells , all 300 m 3 ; it has exceeded their expectations .” Lelinski summarised the mixedROW approach : “ So you start with nextSTEP and get the fast floating material using low power , basically getting everything you can with forced air which by the way includes very different froth recovery to WEMCO due to different hydrodynamics with different froth mobility and collection . You can also make the froth
Results shown above were obtained during testing of the FLSmidth 660 m 3 nextSTEP flotation cell as a rougher scavenger in Cu-Mo circuit . As it can be seen roughers recovered flotable material in the 20-150 microns range ( Cu feed distribution is shown as a blue curve ), nextSTEP recovered all fine and coarse material from the feed achieving up to 100 upgrade ratio
22 International Mining | NOVEMBER / DECEMBER 2020