Titanium Dioxide Filter Cloth for Acid Dewatering
Sulfate-process titanium dioxide (TiO₂) production involves thermal hydrolysis of titanyl sulfate, producing colloidal metatitanic acid in hot 20% to 25% sulfuric acid. In published engineering practice, this aggressive duty utilizes acid-resistant polypropylene monofilament, thermal calendering for cake release, and application-evaluated corrosion-resistant seam assemblies.
Metatitanic acid dewatering in sulfate-process TiO₂
In sulfate-process titanium dioxide manufacturing, ilmenite or titaniferous slag is digested in concentrated sulfuric acid. Subsequent thermal hydrolysis precipitates colloidal hydrous titanium dioxide (metatitanic acid, TiO₂·nH₂O) in an acidic mother liquor containing 200 to 250 g/L free H₂SO₄ at 55°C to 75°C.
The filtration process must achieve two goals simultaneously: separate the metatitanic acid solid from the mother liquor, and perform thorough multi-stage counter-current displacement washing to remove entrained ferrous sulfate (FeSO₄) and residual acid before calcination. Residual acid or iron contamination impairs the brightness, opacity, and whiteness of the finished pigment.
Because the primary crystal size is submicron (0.2 to 0.4 µm) and the slurry is highly thixotropic, the cake forms a dense, compressible barrier. The filter cloth must mitigate colloidal blinding while maintaining high mechanical strength under continuous belt tension.
On a horizontal vacuum belt filter, it is an endless belt with a corrosion-resistant clipper seam and sealed edges. On a vertical pressure filter, it is a high-tensile zigzag cloth loop. Both typically employ polypropylene monofilament for chemical resistance against hot mineral acid liquors.
HVBF filter cloth specifications →Process flow, in words
- 01 Digestion & hydrolysis Ilmenite or titanium slag is digested with sulfuric acid; thermal hydrolysis precipitates metatitanic acid in an acid mother liquor.
- 02 Primary filtration Metatitanic acid cake is separated from the mother liquor containing 20% to 25% free sulfuric acid at 55°C to 75°C.
- 03 Counter-current wash Multi-stage displacement washing removes soluble ferrous sulfate and residual acid at 50°C to 65°C.
- 04 Final dewatering High vacuum pulls residual moisture out of the compressible cake to minimise subsequent calciner energy demand.
- 05 Scraper discharge Cake peels cleanly from the calendered fabric face at the discharge roll; high-pressure spray bars regenerate open area.
Operating parameters vary by plant: digestion concentration, hydrolysis temperature, wash stages, and target cake moisture. Specific parameters are verified against your process data during engineering review.
Filter equipment for titanium dioxide slurries
Metatitanic acid is primarily dewatered and washed on continuous horizontal vacuum belt filters (HVBF) and vertical pressure filters (tower presses). The machine dictates the cloth geometry, tensile requirements, and seam construction.
| Machine route | Operating duty in TiO2 processing | Cloth form | Specification requirements |
|---|---|---|---|
| Horizontal vacuum belt filter (HVBF) | Standard process route for metatitanic acid washing and dewatering in sulfate-process TiO2 plants. | Endless belt, clipper / PAD, edge seal | Brand + model + width + seam photo |
| Vertical pressure filter (tower press) | High-pressure membrane squeeze route for low final cake moisture prior to calcination. | Endless zigzag, low elongation | Plate size / area + old cloth |
Equipment brands and model references are used to define machine-family reference, dimensional specifications, and operating tension requirements.
What makes metatitanic acid demanding on filter cloth
The combination of aggressive mineral acidity, elevated operating temperature, submicron crystal size, and sticky cake rheology makes this one of the most chemically and mechanically demanding applications in liquid-solid separation.
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Hot sulfuric acid attack
The slurry contains 200 to 250 g/L free sulfuric acid (pH < 0.5) at temperatures up to 75°C. In published industrial literature, standard polyester (PET) hydrolyzes rapidly in hot mineral acid, losing tensile strength.
Cloth implication: 100% polypropylene monofilament is commonly selected in published practice for its high chemical resistance against sulfuric acid throughout continuous operation.
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Submicron colloidal fines and blinding
Primary metatitanic acid crystals measure 0.2 to 0.4 µm. Even with flocculation into 2 to 5 µm clusters, submicron fines penetrate open yarn structures and blind standard fabrics.
Cloth implication: Published literature indicates that thermal calendering establishes a surface barrier that mitigates particle lodging.
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Compressible, sticky cake rheology
Metatitanic acid cake exhibits thixotropic behavior and adheres stubbornly to uncalendered filament bundles, causing cake carry-over and return-roller fouling.
Cloth implication: High-pressure thermal calendering flattens warp and weft crowns into a smooth release plane for clean scraper discharge.
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Seam hook corrosion and fatigue
Standard stainless steel hooks (AISI 304 or 316) suffer rapid pitting corrosion in hot sulfuric acid and dissolved chlorides, leading to sudden mechanical seam failure.
Cloth implication: High-nickel candidate alloys (such as Hastelloy C-22 or 904L) with PEEK or coated pintles and protective flaps may be evaluated where chlorides and hot acid attack standard 316L joints. Final seam metallurgy is confirmed per order based on specific liquor chemistry and operating temperature.
Engineering Specification Structure for TiO₂ Dewatering
Specifications are divided into published process baselines, published material benchmarks, and order-specific engineering decisions.
Layer 1: Public Process Reference
Published metallurgical and chemical engineering references defining typical sulfate-process metatitanic acid conditions.
| Process Parameter | Published Reference Value | Benchmark Source |
|---|---|---|
| Free Acid Concentration | 200 to 250 g/L free H₂SO₄ (pH < 0.5) | Sulfate-process industry literature |
| Filtration Operating Temperature | 55°C to 75°C at filter deck | Published chemical process references |
| Primary Crystal Size | 0.2 to 0.4 µm (flocculated to 2–5 µm) | Metatitanic acid crystallisation studies |
| Filtration Route | HVBF (endless belt) / VPF (zigzag loop) | Industrial plant equipment surveys |
Layer 2: Public Material Reference
Published polymer and alloy performance envelopes cited from independent material science literature.
| Material Parameter | Published Reference Value | Benchmark Source |
|---|---|---|
| Polymer Chemical Stability | Polypropylene (PP) monofilament recommended in literature over PET/PA | Polymer mineral acid exposure benchmarks |
| Weave Geometry | Satin 4/1 or multi-layer DLW with calendered slurry face | Industrial fine-particle cake release benchmarks |
| Candidate Joint Metallurgy | AISI 316L, 904L, or Hastelloy C-22 candidate clipper hooks | Severe service corrosion engineering references |
Layer 3: Order-Specific Engineering Decision
| Engineering Parameter | Order Confirmation Protocol |
|---|---|
| Final Cloth Dimensions & Form | Confirmed from machine nameplate, OEM serial plate, or physical belt measurement |
| Target Air Permeability | Confirmed per slurry sample test or customer-specified air permeability target |
| Seam Metallurgy & Joint Flap | Confirmed per order based on verified plant chloride content, wash temperature, and cleaning regimen |
| Edge Reinforcement Width | Confirmed per machine tracking sensor layout (~35–50 mm reference) |
| Quality Inspection Documentation | Documented when agreed for that order; test method, ΔP, and reporting format confirmed in purchase contract |
What we can build for this duty
Our own values are not yet confirmed in writing, and we will not fill them in with industry averages. This section sets out the options this cloth is built from, what each one changes, and which piece of your data decides it. Nothing below is a specification — it is the shape of the decision.
Cloth form Metatitanic acid dewatering is operated on horizontal vacuum belt filters and vertical pressure filters. Both take continuous endless belts or zigzag loops, and the machine type establishes the geometry, tension, and joint structure before cloth specification begins.
Recommended material direction
Metatitanic acid slurry from thermal hydrolysis carries 20% to 25% free sulfuric acid (pH < 0.5) at 55°C to 75°C. Hot acid exposure makes polymer stability the critical gating decision for operational life.
This narrows the field; it does not pick. Which polymer goes on your machine is settled against your measured numbers and not on a web page — the same position the selection section above takes. What follows is the reasoning behind that position, not a departure from it.
- Polypropylene PP
Continuous reference up to ~90 °C — a published property of the polymer, not a value of ours
- Acid Excellent
- Alkali Excellent
- Hydrolysis Excellent
- Abrasion Good
Polypropylene offers high chemical resistance to sulfuric acid at standard process temperatures, making it the primary candidate polymer for metatitanic acid filtration.
- Polyvinylidene fluoride (PVDF) PVDF
Continuous reference ~120°C continuous / short excursions to ~140°C — a published property of the polymer, not a value of ours
- Acid Excellent
- Alkali Moderate
- Hydrolysis Excellent
- Abrasion Good
Fluoropolymer option for elevated temperatures or trace solvent exposures where polypropylene approaches its continuous thermal limit.
- PET Polyester suffers rapid acid hydrolysis in hot sulfuric acid; ester bonds break down under elevated temperatures, leading to severe cloth embrittlement and premature tearing.
- PA Polyamide degrades rapidly in mineral acids below pH 4.
What actually decides it Free sulfuric acid concentration and slurry temperature at the filter deck.
Everything in this block is reasoning from published polymer behaviour applied to the chemistry described further up this page. It is a direction, not a selection — and the selection is made against your measured numbers during the engineering review, then written into the quotation. The full polymer envelope is on the materials page.
Weave options
Metatitanic acid forms compressible, fine colloidal filter cakes with primary crystal sizes below 0.5 µm. Surface smoothness and cake release govern fabric selection.
- Satin Long floats, few crossing points. The smoothest surface of the three, so the best cake release and the easiest to wash back. Watch: Floats snag and abrade; retention is coarser at a given yarn count.
- Double layer / multi-layer Two or more interlaced fabric layers woven as one. A fine filtering face carried on a coarse structural back — high strength with fine retention, and drainage channels inside the fabric. Watch: Thicker and heavier; more expensive to weave. The usual answer on heavy belt duties.
- Twill The crossing point steps sideways each pick, giving a diagonal rib. More flexible and more permeable than plain at the same yarn count, with better cake release. Watch: Slightly less dimensionally stable than plain.
- Plain One over, one under. The most stable and the most rigid. Tight, uniform pores; lower permeability for a given yarn. Watch: Least forgiving of dimensional movement; can blind faster on fine solids.
Thermal calendering on the cake contact face creates a flattened, mirror-smooth plane to prevent submicron colloidal particles from lodging in yarn interstices.
Yarn form. Monofilament warp and weft constructions release sticky cake cleanly under scraper blades and wash back thoroughly during spray regeneration.
Yarn form, weave and surface finish are settled as one decision. Standard woven options are monofilament, multifilament and mono+multi combination; staple / spun yarn is evaluated under engineering review.
Permeability considerations
Air permeability is the figure everyone compares and the easiest one to quote meaninglessly. It is measured per ISO 9237 at a stated pressure drop — often 200 Pa — or per ASTM D737 (Frazier). A value with no stated pressure and no stated unit is not comparable to anything, including ours. The same applies to a pore or retention rating: on a woven cloth that is a nominal figure and not an absolute cut-off, because woven media do not have a single pore size and the cake quickly becomes the real filter.
Permeability balances fine solids retention against filtrate clarity; exact permeability is confirmed per order.
How each property is measured, and what to ask any supplier for alongside the number, is set out on the testing and inspection page. Naming the method is a fact about a public standard, not an assertion of completed mill testing.
Joint options
Clipper seams require corrosion-resistant metallurgy and sealed flaps to mitigate acid degradation and slurry bypass.
- Clipper (metal hook) Interlocking metal hooks crimped onto both cloth ends, joined by a pintle wire. Fitted and replaced on the machine without dismantling it. The fastest change-out. Watch: The joint is a discontinuity: it leaks vacuum as it passes the box, and it is where most belt failures start. Hook material has to suit the liquor.
- PAD / welded overlap The two ends are overlapped and thermally fused. A smoother, quieter joint that seals better than a clipper and carries load more evenly. Watch: Made off the machine or with a portable press; a change-out takes longer.
- Sewn overlap The ends are overlapped and stitched. Simple and repairable in the field. Watch: The stitch line is the weak point and a leak path. Least common on vacuum belts.
On acidic titanium dioxide duties, standard stainless steel hooks (304/316) risk chloride and acid pitting; candidate high-nickel alloy hooks (e.g. Hastelloy C-22 or 904L) with PEEK pintle wire and PTFE flaps provide high corrosion resistance and mitigate slurry bypass.
The four constructions drawn in cross-section: how joints fail and what each one costs you.
Edge treatment
- Cut and sealed The cut edge is thermally sealed against fraying. The baseline. Adequate where the machine edge seal is in good condition.
- Folded / hemmed The selvedge is folded back and secured. Adds thickness and stiffness at the edge where the seal rubs.
- Reinforced edge band A separate band is bonded along the selvedge. For machines that chew edges — the usual answer when a belt keeps failing at the edge while its body is sound.
- Coated / sealed band A polymer band is applied to the edge. Seals the edge against vacuum bypass as well as protecting it mechanically.
- Guide strip / tracking profile A profile bonded to the underside to run in the machine guide. Only where the machine is built for it. Fitting one to a machine that is not is a common and expensive mistake.
Ultrasonic hot-melt edge reinforcement seals polypropylene cut edges against fraying and lateral wear against tracking guides.
Edge constructions and finishing: specification options on technical filter fabrics.
Relevant equipment
Whatever cloth form this duty turns out to need, it is decided at the loom before it is decided anywhere else: what a weaving platform can hold — pick density, tension, width — sets what the finished cloth can be asked to do.
Delkor HVBF, Andritz Pannevis RT, FLSmidth Eimco, and Metso Larox PF filter equipment.
The eleven process stations from yarn to crate and the nine laboratory checks: manufacturing.
Factory capability for this duty
The rows below are the part of our capability envelope that this duty touches. The last group is the one that makes the rest of it worth reading — a supplier who can do everything has told you nothing.
Machine families
- Rubber-belt horizontal vacuum belt filter Confirmed per enquiry
Core family. Endless belt with clipper, PAD or spiral joint and a finished edge.
What decides it Brand and model, measured width and developed length, a photograph of the joint.
- Vertical / tower / stacked pressure filter Confirmed per enquiry
Core family. Endless low-elongation zigzag loop.
What decides it Plate dimensions or filtration area, plus the cloth you are replacing.
- Indexing / tray vacuum filters Not offered
Different cloth mechanics. We will tell you so rather than sell you a belt that does not fit.
What we do not do
- Quoting from an industry name alone Not offered
Two plants in the same industry run different slurries through different machines. We ask which.
The full envelope, including the machine families and services we decline: what we build to order and what we will not take on. Fifteen pages on how a specification like this is built and read: the filter cloth specification guide.
Common failure modes in titanium dioxide filtration
Premature belt failure on metatitanic acid is usually caused by polymer hydrolysis, fine particle blinding, or seam pitting rather than simple mechanical wear.
Acid embrittlement and tearing
Chemical hydrolysis of polyester fabrics in hot sulfuric acid. Shows up as general loss of tensile strength and edge tearing.
Diagnose this →Colloidal blinding and flow loss
Submicron fines lodging inside yarn bundles; vacuum rises, washing efficiency drops, and the cloth fails to recover after washing.
Diagnose this →Poor cake release and carry-over
Sticky metatitanic acid cake clinging to fabric crowns, building up on return rollers and accelerating mechanical wear.
Diagnose this →Seam hook snapping
Pitting corrosion and stress fatigue on 304 or 316 stainless steel clipper hooks exposed to hot sulfuric acid and trace chlorides.
Diagnose this →What we need from you to prepare a quotation
Gathering these seven operating parameters allows our engineering team to verify mechanical fit and chemical compatibility for your titanium dioxide circuit.
| Operating parameter | How to gather it |
|---|---|
| Machine family and model | Horizontal vacuum belt filter or vertical pressure filter; copy brand and model off the nameplate. |
| Dimensions of the cloth in use | Belt width and total length/circumference, or plate dimensions and loop layout. |
| Seam or joint type | Clipper hook metallurgy (stainless steel vs candidate high-nickel alloy) and flap construction. |
| Slurry acidity and temperature | Free sulfuric acid concentration (g/L H2SO4) and temperature at the filter deck. |
| Particle size distribution | Primary crystal size (0.2–0.4 µm) and agglomerated particle size from plant QC data. |
| Current cloth failure mode | Blinding, tearing, seam failure, or poor cake release; send photographs of the worn cloth. |
| Washing water regime | Temperature and pressure of the displacement wash and high-pressure cloth wash spray bars. |
Frequently asked questions
Why does polyester (PET) fail rapidly in titanium dioxide dewatering?
Sulfate-process metatitanic acid slurry contains 20% to 25% free sulfuric acid at 55°C to 75°C. At this temperature and acidity, polyester ester bonds undergo rapid acid hydrolysis. The fibers become brittle and lose tensile modulus, resulting in premature tearing. Polypropylene is chemically resistant under these conditions and maintains tensile stability.
When are high-nickel alloy clipper hooks considered over standard 316 stainless steel?
While 316 stainless steel is common in mild duties, hot sulfuric acid liquors containing trace chlorides accelerate pitting and crevice attack at mechanical hook joints. High-nickel alloys such as Hastelloy C-22 or 904L offer significantly higher pitting resistance in hot acidic and chloride-bearing environments. Selection is confirmed per order based on actual liquor assay and operating temperature.
Request an engineering quotation for TiO₂ filter cloth
Submit your machine model, cloth dimensions, and slurry conditions. Our technical team will verify mechanical compatibility, polymer selection, and seam specifications.
No online checkout.
Pre-shipment inspection and dimensional verification reports provided with each delivery when specified.
Where to go next
Technical Process Guide
Engineering specification guide for TiO₂ metatitanic acid dewatering on HVBF and VPF.
HVBF Filter Cloth
Continuous rubber-belt filter cloths for chemical and mineral processing.
Vertical Pressure Filter Cloth
Endless zigzag cloth loops for tower press filtration equipment.
Seam Failure
Corrosion resistance, hook selection, and pintle wire integrity.