THICKENERS AND FILTERS
FLSmidth argues that thickening and filtration should be seen together as the dewatering part of the flowsheet and not as individual unit operations
Dewatering duo
Thickeners and filters have a crucial role to play in filtered tailings - Paul Moore looks at this and other related developments
To get a good insight into both thickener and filtration trends , IM caught up first with one of the handful of full flowsheet providers in the form of FLSmidth and its Product Group Manager - Thickening and Filtration , Steve Ware . Starting with thickeners he pointed out that it is important to remember that there is technology involved in thickener tanks , especially with regard to floor slope and sidewall depth , which both contribute to residence time and mud flow . " It is all built into the process requirements , and that ’ s where it ties back in to testing , which helps give us a guide if at all possible – we want to select the right mud residence time to achieve to the right underflow density ." On thickener evolution , the original thickeners the industry now refers to as ' conventional ' were those where flocculant was not added . " Then you have what we would call today a high-rate thickener which are reliant on optimal feed dilution and flocculation for settlement & thickening – these are the most common in mining today ."
He adds : " But you still have a lot of variations – is it an on-ground tank or an in-ground tank with concrete floor and wall or anchor channel steel wall , or an elevated steel tank ? Is it a welded or bolted design ?" Some of these decisions are based on the plant layout and available space and some based on the position of the rest of the plant as the thickeners will generally rely on gravity feed . A welded design tank takes less time to fabricate but has much more time consumed for erection on site , whereas the opposite is true for the bolted design . Seismic requirements can also have a role to play .
The next progression in thickener type for increased underflow density is a high-density thickener with increased floor slope , deeper side wall , and higher torque capability . " It is probably the least mature in the market but definitely has become increasingly popular and adopted and has a role to play in many projects ." Beyond that you have deep cone thickeners with even steeper floor slopes , deeper side walls , and even higher torque capability for paste thickening which has its roots in the alumina industry . " Paste can be a great solution for some projects depending on water requirements and terrain , but paste
technology is also more expensive and comes with higher complexity downstream material handling issues as well as potentially expensive pumping solutions ."
And then the link between thickeners and filtration – such as filtered tailings projects – which represent the majority in consideration and in build today . High profile TSF failures , water scarcity , and environmental management of course have played a major role in this trend – and these projects absolutely require thickeners . " Whether you are talking about tailings or concentrate , you are going to thicken it before filtering it – because thickener capex and opex is less than that for filtration . If you send all that water to the filtration plant , you will need more filters relatively speaking , so you want to do as much thickening as possible upstream . So you really need to look at thickening and filtration together as the dewatering part of the flowsheet and not as individual unit operations ." There are also digitalisation opportunities to integrate thickening and filtration operations thus optimising performance , throughput , and opex .
Ware also emphasised the importance of thickener retrofitting . " Thickeners have been around for a long time . We see system upgrades
with our E-DUC or P-DUC feed dilution technology making a huge difference ,
but also mechanism upgrades , as raking technology has also advanced over the years . In combination with more advanced feed systems , it can drastically improve the % solids underflow result and reduce required torque ." Retrofits in tailings thickeners can allow TSF life to be extended or at least delay the requirement for a new TSF lift . In deep cone thickeners , FLSmidth is applying its latest spiral rake blade designs for increased raking capacity , reduced ratholing and improved mud bed residence time .
On filtration Ware said vacuum filtration and Pneumapress ( tower filters ) have a role to play alongside filter presses , especially in particular market niches in industrial minerals , backfill projects etc . In Brazilian iron ore , for example , large numbers of disc filters are used to filter iron ore concentrate and tailings – of which FLSmidth holds a large market share . Vacuum filters typically offer lower capex and opex while providing continuous versus batch operation for applications when the process allows , such as coarse PSD material , or low clay content etc
On filter presses , FLSmidth ’ s main product line for mining is the AFP – its 2 m by 4 m format Colossal AFP filter was one of the first large format filters in the industry and led to the development of a larger model AFP5000 design in partnership with Goldcorp . In the meantime , the AFP2500 filter was developed with the largest volume and plate surface area known in the market for this format size . This filter was designed to minimise opex and provide ease of maintenance , while focusing on process efficiency , resulting Ware says in the industry ' s lowest kW-hr per metric tonne dewatered .
FLSmidth has also invested heavily in the digitisation of the dewatering process with the development of a proprietary automatic moisture analyser . This is the key to advanced process control allowing the filters to automatically adapt
The Micronics Engineered Filtration Group , a global industrial filtration leader , has been a long-standing strategic partner of Ishigaki . Micronics markets Ishigaki LASTA MC Filter Presses for high-capacity mining applications both in North and South America
18 International Mining | OCTOBER 2022