THICKENERS
FLSmidth thickeners at Escondida which are among the largest in the world
variability of material , so how do you maintain the same thickness of underflow ? There are also issues with all thickeners at the larger end of the scale where you have tailings material coming out of the concentrator in a large pipe , say 48 in diameter pipe in an 80 m thickener , for example , you have to try to distribute the material evenly . All the vendors have a solution for this – we have our Evolute™ feedwell . Its unique full shelf width entry allows for maximum residence time within the feedwell , increasing gentle mixing and aggregate growth as well as reducing unagglomerated fines and un-absorbed flocculant . The involute shape of the Evolute feedwell promotes even distribution of agglomerated solids into the thickener , minimising the risk of point loading of the raking mechanism , and maximising settling capacity of the thickener , whilst reducing internal dilution within the feedwell , negating any benefits of closed bottom feedwells .”
Once inside the thickener there can be issues with formation of channels in the mud bed – referred to as ratholing – “ we are doing a lot of work now with CFD models to better understand how we can change the rake designs and internals of the thickener to eliminate or reduce this problem and achieve a better and more consistent performance .”
Market wise overall in terms of numbers of units , the concentrate thickener market is also significant . As these mostly follow flotation plants , there FLSmidth is working on reducing the amount of froth inside the thickener . Wisdom added that in commodity demand it is also worth mentioning potash and phosphate projects in terms of larger non-tailings thickeners , where you could be dealing with 50:50 product and tailings ( versus a few % copper head grade ), where you could argue the unit is acting as a product thickener not a concentrate thickener . “ But in terms of dollar value , tailings thickeners dominate the market due to their sheer size and the volumes of
material they are having to deal with . For filtered tailings projects where there is currently a lot of interest , we wouldn ’ t specify a paste thickener as the material is too thick to flow into the filters , instead this market is what is driving significant interest in high density thickeners where you are still maximising the water removed with the thickener as they are cheaper to operate than any type of filter .”
Finally on reducing flocculant cost , Evolute feedwells can use either a P-Duc™ , a low pressure pumping system to pump supernatant liquid into the feed channel and mix it with the incoming tailings slurry , or an E-Duc ® system where the amount of water that is pulled from the clear water section depends on the feed flowrate . “ We have been able to demonstrate these technologies through retrofits at several mines such as at Carpentaria Gold in Australia , where an upgrade to the Evolute feedwell incorporating E-Duc feed dilution technology on the 22 m tailings thickener brought about immediate improvements in thickener operation . There are a lot of mines with existing thickeners out there that want better performance but of course you can ’ t convert a high rate thickener into a paste thickener due to the different floor slope required .”
Upgrading two thickeners at Collahuasi
The retrofit market also includes going back to much older thickeners and upgrading the technology to today ’ s standards , and in many cases this has included OEMs upgrading their own thickener installations .
Collahuasi mine is a large copper mine located at a high altitude of 4,000 m in the north of Chile in the Tarapacá Region and represents one of the largest copper reserves in Chile and in the world , having estimated reserves of 3.93 billion tonnes of ore grading 0.66 % copper . The processing area consists of both oxide and sulphide plants . Oxide and mixed ores are treated by heap-leaching , solvent-extraction , and electro-winning ( SX-EW ). Sulphide ore is crushed , ground and treated by flotation .
Outotec ( now Metso Outotec ) was approached to conduct a survey on the thickener to optimise feed conditions to optimise thickening performance . During 2017-2018 , the company worked alongside the customer with the aim of upgrading two Outotec conventional thickeners sold in the 1990s that were outdated and performing poorly . The business case and development were successfully completed , and Outotec received an order to upgrade the thickeners .
The solution included the latest available technology and developments , including the Outotec Vane Feedwell™ which incorporates a total of seven global patents into its design . One of the main design features is the interconnected upper and lower zone . The upper zone , into which
Back in 2017 , Outotec ( now Metso Outotec ) retrofitted seven radial thickeners at Norilsk Nickel ' s Talnakh concentrator with Outotec High Rate Thickener technology
56 International Mining | OCTOBER 2020