BOKELA GmbH Hall 8 / A45

The reliable separation of interfering coarse particles from dispersions or absolute filtrate clarity is of great importance in many processes. Dynamic filtration and screening with the BoCross filter enables efficient solutions for both classification and clear filtration tasks where state-of-the-art processes such as wedge wire screens, cartridge and backwash filters, vibrating screens, centrifuges, cyclones or membrane filtration reach their limits.

In particular, the sieving of suspensions with a high particle concentration is not possible or not recommendable with the above-mentioned devices, or at least the suspension must be diluted before sieving. Depending on the task at hand, the Bo-Cross filter can be used to implement various processes tailored to the product and objective. Accordingly, a base layer on the separation medium can be reliably prevented or deliberately adjusted. The article explains the possible operating modes with a focus on screen filtration for separating unwanted coarse particles from highly concentrated suspensions. The aim is to achieve a continuous filtrate throughput with a high concentration of fine particles that is still capable of flowing.

Options are explained using two application examples: It is shown how the BoCross filter is used to continuously sieve off interfering coarse particles from a highly concentrated, viscous dispersion with a defined separation cut in a tightly sealed apparatus. The proportion of coarse material retained in the retentate is very low in relation to the filtrate throughput. Another example shows the separation of interfering mineral particles. The materials used here are used for coating electrodes. Even one particle protruding from the coating can lead to production rejects and must therefore be reliably removed.

The world is moving into a new era where energy is no longer produced on the basis of fossil fuels such as oil, coal and natural gas. The energy in the upcoming decades will be increasingly produced on the basis of wind and sun as well as nuclear power with more and more electric drives in vehicles, trains, ships and machinery in our households requiring a battery if used in areas that have no permanent connection to the grid. The metals and minerals required for electric motors are mainly copper for the winding, aluminium for the casing and iron-cobalt-nickel, neodym-iron-bor or samarium-cobalt for the permanent magnets. And the metals required for the batteries are mainly lithium, nickel, manganese, cobalt (NMC with high energy density) or lithium, iron, phosphate (LFP with lower energy density). And the demand of these elements will rapidly increase with...

Especially, elements like lithium, cobalt, neodym, samarium or other elements of the rare earth fraction appear in very low concentration in minerals and require an intense hydro metallurgical processing. This processing requires several steps of solids liquid separation steps with challenges such as extreme pH-values (<2 or >12), temperatures > 100 °C, intense wash of solids, low moisture, continuous operation, etc. Especially intense wash of solids quite often ends up in two or three steps of filtration with intermediate solids reslurry. However, this pushes CAPEX for filtration equipment to the high end and puts the realization of projects at risk.

Modern pressure drum filters such as the BOKELA BoHiBar Drum XL 18 or XL 26 are able to perform a three-stage counter current cake wash with a slurry that is fed to the filter with a temperature of up to 200 °C and solids with a d₅₀ of down to almost 1 micron...

The design of the filter with

- A high number of individual filter segments

- A quick drainage of the liquid into the piping system to the control head

- A sharp separation of the wash liquids in the control head

- An operation with back pressure on the filtrate separators

result in reaching the target figures with only one filter unit while other filter types like plate and frame filter presses require two filters with intermediate reslurry. Or the material of construction does not allow for temperatures in the range of 100-200 °C...