High-Solids Slurry Washing & Desalting: Membrane Routes for Washing, Desalination and Concentration

Bottom line: For high-solids slurries (nano powders, lithium iron phosphate, titanium dioxide slurries, etc.), washing is shifting from repeated "press filter – re-slurry – press filter" dilution cycles to a one-step washing + desalting route built on cross-flow tubular membranes. The membrane retains the powder while letting soluble impurity ions pass through with the water, cutting wash-water ratios to ~50% of conventional processes and powder loss from 5–8% down to under 0.1%. The washing mother liquor is then integrated into UF/NF concentration-and-recovery steps that turn wastewater into sellable products such as metatitanic acid and ferrous sulfate. High solids content is not the problem — choosing the right membrane flow channel is.

1. Why is high-solids slurry washing so hard?

Conventional powder washing (diaphragm filter presses, vacuum leaf filters, centrifuges) follows an intermittent "dilute – press – re-dilute" route: the filter cake is re-slurried to dilute impurity-ion concentration, pressed dry, and repeated until salt content meets spec. This comes with three intrinsic drawbacks:

• Product loss: nano-scale powders (e.g. 10–50 nm ultrafine TiO₂) penetrate filter cloths — conventional diaphragm filter presses lose 5–8% of particles, i.e. the most valuable product itself;

• High water consumption: high wash-water ratios drive up both water cost and downstream wastewater treatment;

• Time and footprint: multiple re-slurry/press cycles mean long wash times and large equipment footprints, especially painful for retrofit projects.

2. Membrane washing: how to retain powder and let salt through in one step?

Jiuwu's tubular membrane system works on a cross-flow mechanism: under pressure, the high-solids slurry flows at high velocity along the inner surface of the membrane tube, soluble impurity ions pass vertically through the membrane wall with the water, while powder particles are retained on the membrane surface and recirculate with the concentrate. By continuously feeding desalinated water and drawing off wash water, soluble ions are steadily "displaced" out of the slurry — this is how membrane washing accomplishes washing and desalting simultaneously: solids stay, salts are washed away, and the powder never sits still, so no repeated re-slurrying is needed.

Measured performance for ultrafine TiO₂ washing (10–50 nm particles, strongly acidic high-ionic-strength slurry):

3. How do membranes handle high solids? Wide channels and backwashable structures

The first requirement for washing high-solids slurries is not "precision" but "no clogging". Jiuwu's sintered tubular membrane used for powder washing is purpose-designed:

• Ultra-high-molecular-weight PE particles are sintered into the support, with a coated PVDF high-precision separation layer — high mechanical strength, abrasion resistance, and tolerance of repeated chemical cleaning;

• Wide-channel, inside-out cross-flow design — wide flow channels tolerate high-solids feed without particle bridging or plugging;

• Unique membrane structure enables in-line backwashing — backwashing restores flux for long, stable operation;

• Compact layout + automatic control — for the lithium iron phosphate (LFP) washing case, O&M costs are 60% lower than conventional processes.

Lithium iron phosphate slurry (a cathode precursor for Li-ion batteries) is the representative duty for "high-solids tolerance + high-precision washing": high viscosity, high solids content, and strict limits on impurity ions (sodium, sulfate, etc.).

4. The concentration route: wash water is not waste — it is a "liquid mine"

The dilute mother liquor from washing (containing acid, salts, and traces of product fines) is the other half of the economics of powder washing. Jiuwu uses UF–NF membrane integration to "cascade-concentrate and split" the liquor into recoverable fractions. The benchmark is a Shanghai TiO₂ acidic wastewater resource-recovery project (BOT model, design capacity 2,500 m³/d × 340 d):

This process logic applies to every powder-washing scenario: membrane washing strips salts off the powder into the mother liquor, and membrane concentration then turns the salts and acid in that liquor into reusable or sellable resources — washing, desalting, and concentration form a closed loop in which the plant moves from "paying to treat wastewater" to "earning revenue from wastewater."

5. Selection guide: which route fits my slurry?

6. FAQ