Lithium Carbonate and Hydroxide Filter Cloth for Vertical Pressure Filters
Lithium carbonate and lithium hydroxide are crystallised, filtered and washed on the refinery side of a lithium plant. That duty is often taken on vertical pressure (tower press) filters, and the cloth is a single endless zigzag loop in a low-elongation construction, fabricated to your plate pack rather than bought off a shelf.
Two salts, one separation step, and where the cloth sits
The refinery side of a lithium plant makes two commercial products. Lithium carbonate is precipitated from a purified lithium-bearing solution; lithium hydroxide is produced either by converting carbonate or directly from a leach route, and it crystallises as the monohydrate. Whichever product the plant sells, the same three things have to happen at the end: the crystals are separated from the mother liquor, they are washed, and they are dried.
That middle step is where the cloth lives, and it is the step that decides the assay. A battery-grade salt is specified by its impurity limits — sodium, potassium, calcium, magnesium, sulphate, chloride — and those impurities are dissolved in the mother liquor, not in the crystals. Liquor left in the cake is impurity delivered to the customer. So on this duty the cloth is not only a filtration medium; it is the surface across which the wash has to displace evenly.
Lithium carbonate also has an awkward property the wash stage has to respect: unlike most salts, it becomes less soluble as the liquor gets hotter. That is why carbonation and washing on this product are normally run hot — cold wash water dissolves the product you are trying to keep.
The cloth itself is a consumable. On a tower press it is one endless zigzag loop threaded through the whole chamber stack, built to your plate dimensions and cloth path, and replaced on a cycle set by your duty rather than by a catalogue.
Lithium appears twice in a flowsheet and they are not the same duty. This page is the refinery side: carbonate and hydroxide crystals, tower presses, product purity. The concentrator side — spodumene and lepidolite concentrates, tailings and process residues — runs a mixed machine population: rubber-belt vacuum filters, vertical tower presses, indexing vacuum filters and centrifuges all appear there. Even where the machine is the same, the cloth form, the failure set and the product are not.
The cycle the cloth goes through
- 01 Fill Crystalliser slurry is pumped into the stacked chambers; every chamber in the pack fills in the same cycle.
- 02 Pressure filtration Pressure forces mother liquor through the cloth and the salt cake builds inside each chamber.
- 03 Cake wash Wash liquid is displaced through the cake to push residual mother liquor — and the impurities dissolved in it — out of the crystals.
- 04 Press / squeeze Where the machine has membrane plates, the cake is squeezed before drying to even out thickness and moisture.
- 05 Air drying Compressed air is blown through the cake to take out the residual free moisture.
- 06 Index and discharge The pack opens, the cloth indexes forward, cake drops off both faces, and the cloth is washed before the pack closes again.
A tower press is a batch machine: every chamber does all six steps together, then the cloth moves. Operating values for each step — liquor temperature, solids, crystal size distribution, wash ratio, cycle time, cake moisture — are plant-specific. We do not publish typical figures for them; they go on the confirmation list below instead.
What makes this duty hard on a cloth
Most filtration duties are judged on how dry the cake is and how fast the cycle runs. This one is judged on an assay as well, which changes what a “good” cloth means: even wash displacement across the whole chamber counts for as much as free area.
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Wash quality decides product grade
A battery-grade salt is defined by what is not in it — sodium, potassium, calcium, magnesium, sulphate, chloride. Those impurities travel in the mother liquor, so any liquor left in the cake is carried into the product.
Cloth implication: The cloth has to let wash liquid pass evenly across the whole chamber. A patch of blinded fabric does not just filter slowly — it washes badly, and that shows up in the assay rather than in the cycle time.
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One cloth, the whole machine
A tower press runs a single endless loop threaded through every chamber. A hole, a blinded band or a failed joint anywhere on that loop takes the machine out, not one chamber.
Cloth implication: Fabrication consistency along the full loop length matters more here than on a machine where cloths are per-plate and replaceable one at a time.
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Elongation, not breaking strength
The cloth is pulled through the pack on every cycle. If it stretches, the zigzag path lengthens, the cloth runs off its guides and the discharge stops landing where it should.
Cloth implication: Low-elongation construction and a joint that does not creep are specification items, not shop details.
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Alkaline duty on the hydroxide side
Lithium hydroxide liquor is strongly alkaline. Hot alkaline conditions hydrolyse polyester — the ester linkage is the weak point — which is why alkali resistance is a polymer question before it is a weave question.
Cloth implication: Polymer is chosen against the actual liquor chemistry and working temperature of your circuit, and the limits are written into the quotation rather than published here.
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Blinding by fine crystals and scale
Fines and scale lodge in the fabric and close the free area. On a pressure filter that shows up as a longer cycle, a wetter cake, and wash water finding a channel instead of displacing liquor.
Cloth implication: Weave geometry, surface finish and how well the cloth wash stage recovers the fabric each cycle are what decide how fast it closes.
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Anything the cloth sheds is a contamination path
The cake is the saleable product, not a waste stream. Fibre debris, joint material and wear particles all end up on the product side of the process.
Cloth implication: Construction and joint method are assessed with product purity in mind, not only with filtration performance in mind.
These are the difficulties common to vertical pressure filter duty on a high-purity salt. How severe each one is on your machine depends on numbers we do not have yet — which is what the confirmation list is for.
The machines this duty actually runs on
Vertical tower presses are a common route for refined lithium salts. The three families below are the ones observed in this machine class; the evidence level is stated as we found it, not upgraded, and company-reported figures are labelled as such.
| OEM family | Machine class | Duties observed | Evidence level | Next step |
|---|---|---|---|---|
| Metso Larox PF | 1.6–168 m² class | Mining conc., chemicals, food | Company + OBSERVED 3rd party | Send brand + model |
| Roxia TP | TP60 60–168 m² tables | Mining, chemicals | OBSERVED pages | Send brand + model |
| Pneumapress | UNKNOWN | Chemicals, minerals | OBSERVED compat pages | Send brand + model |
Cloth form for this machine family: Endless zigzag, low elongation. What a quotation needs from you: Plate size / area + old cloth.
Centrifuges and other filter types appear on lithium carbonate and hydroxide in real flowsheets, and the choice varies by plant and by product. If your salt comes off a centrifuge, this page does not describe your machine — tell us what you run and we will say honestly whether it is a duty we can quote.
Indexing vacuum — do not mix with Larox PF or RB. If the nameplate says RT or Pannevis, the cloth on this page is the wrong cloth, and we would rather say so now than after you have paid freight.
OEM names above are used only to identify the machine a cloth has to fit.
How the cloth is specified for this duty
Selection runs backwards from the liquor. Chemistry and working temperature narrow the polymer — and on the hydroxide side that is the binding constraint, because hot alkaline liquor hydrolyses polyester while polypropylene resists alkali but carries a lower temperature ceiling. Crystal size distribution and the wash requirement then narrow the weave and the surface finish: a tight surface holds fines back and washes evenly but closes faster, an open one runs longer between cloth changes but lets more fines through to the filtrate. Finally the machine narrows the fabricated dimensions, the cloth path, the joint and the elongation class.
We are not going to tell you on a web page which construction your lithium cloth should be. That decision belongs to your liquor, your wash configuration and your plate pack — and taking it from a published table instead of from your data is how a plant ends up with a cloth that filters well and washes badly, which on a battery-grade product is the expensive way to be wrong.
Specification status
Our factory specification package has not been confirmed in writing yet, so every parameter reads UNKNOWN. Each one is fixed against your machine and liquor during the engineering review, and it is stated in the quotation — not inferred from this page.
| Parameter | Value | Unit | How it is fixed |
|---|---|---|---|
| Polymer | UNKNOWN | — | Confirmed against liquor chemistry and working temperature |
| Weave / construction | UNKNOWN | — | Confirmed against crystal size and wash requirement |
| Air permeability | UNKNOWN | L/dm²/min | Test method and test pressure will be stated with the value, once the mill confirms them in writing |
| Fabric weight | UNKNOWN | g/m² | Reported with the value, once confirmed in writing |
| Elongation under working load | UNKNOWN | % | Confirmed per construction — the parameter this machine family lives on |
| Joint type for the endless loop | UNKNOWN | — | Confirmed against machine and a photo of the existing joint |
| Cloth path length (zigzag, endless) | UNKNOWN | mm | Confirmed against your measured cloth or machine drawing |
| Plate size / filtration area we can cover | UNKNOWN | m² | Confirmed against your plate pack |
| Continuous temperature limit | UNKNOWN | °C | Confirmed per polymer and finish |
| Chemical limit (alkali / hydroxide liquor) | UNKNOWN | — | Confirmed per polymer and finish |
Industry reference — not our specification
The machine classes and evidence levels in the equipment table above are published figures for third-party machines, not what our mill can cover. Our own area and cloth path limits are on the UNKNOWN list above until the factory confirms them. The cloth family in full →
What we can build for this duty
The parameter table above reads UNKNOWN because our own values are not confirmed in writing yet, and we will not fill that table with industry averages. This section is the other half of the answer: the options this cloth is actually 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 An endless low-elongation zigzag loop built to your plate dimensions — not a belt. The cloth form follows the machine family before anything else is discussed.
Recommended material direction
On the hydroxide side this duty is the textbook case for the single most consequential polymer property in filtration. Polyester is an ester polymer: hot alkali hydrolyses its ester bonds and the fabric loses strength from the surface inwards. The failure is chemical and it does not look like wear, which is why it is diagnosed late. The carbonate side is a separate question and this page does not assume it has the same answer.
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
Alkali resistance is where polypropylene is strongest, and on a hot hydroxide liquor that is the property that decides. Two constraints come with it: the reference continuous temperature above, and creep under sustained load — which on a low-elongation loop is exactly what the machine cannot tolerate.
- Polyphenylene sulfide (PPS) PPS
Continuous reference up to ~190 °C — a published property of the polymer, not a value of ours
- Acid Excellent
- Alkali Excellent
- Hydrolysis Excellent
- Abrasion Good
Excellent in both acid and alkali, with the highest reference temperature of the realistic candidates. This is the direction where the duty is genuinely both hot and alkaline and the cheaper polymers are ruled out on one or the other. The cost step is large.
- Polyester (PET) PET
Continuous reference up to ~150 °C — a published property of the polymer, not a value of ours
- Acid Good
- Alkali Limited
- Hydrolysis Limited
- Abrasion Excellent
The reference polymer everywhere else and the one to be most careful with here. On a hot hydroxide liquor its published weakness is the governing property, not a footnote.
- PTFE The best chemical resistance available and the worst mechanical fit for a tensioned endless loop — low tensile modulus and high creep, at a cost in a different bracket.
What actually decides it Whether the loop runs hydroxide or carbonate, the measured free alkalinity, and the working temperature at the filter. Then the machine take-up range, because elongation control is the other half of this specification.
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
Low-elongation construction is a defining requirement on a tower press, and heat setting is what holds it — an unset cloth changes length on the machine. That constraint sits above the retention question rather than beside it.
- 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.
- 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.
- 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.
Plain weave is the most dimensionally stable of the structures and the least forgiving of movement, which is the trade this machine family is built around.
Yarn form. Staple and spun yarns are seen more on pressure filtration than on vacuum belt duty, because the finer retention is worth the harder wash-back when the cake is formed under pressure.
Yarn form, weave and surface finish are settled as one decision. The four yarn forms available are monofilament, multifilament, mono + multi combination and staple / spun.
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.
On a pressure filter the cloth also has to release a cake formed under pressure and survive the discharge motion, so the as-new permeability is one of several numbers and not the headline. Ask for the method and the pressure with it regardless.
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 a claim about our laboratory.
Joint options
The four constructions below are described in vacuum belt terms, because that is where the vocabulary comes from — a tower press has no vacuum box. On this machine the same joints are judged on whether they hold their length under sustained tension and whether they pass cleanly through the plate pack.
- 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.
- 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.
- 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 an endless loop that has to hold its length, a joint that creeps is a specification failure and not a wear problem. The machine dictates what it is set up for; send a photograph of the joint you run now, both faces.
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.
These edge treatments are named in their belt-filter form because that is where the vocabulary comes from. On a tower-press loop the equivalent decision is how the selvedge is finished against the plate and the seal, and it is settled with the machine rather than from a list.
Relevant equipment
A pressure-filter loop 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. Our weaving runs on DORNIER (Germany) and Sulzer (Switzerland) platforms, machines built for technical textiles rather than for apparel.
Elongation control is decided at the loom and locked at the heat-setting frame. A loop that stretches into the take-up range on site was never going to hold it.
Model designations, working widths and installed quantities are being confirmed against the machine nameplates and are not published until they are. A weaving platform is easy to name and hard to fake, and we would rather you were able to check.
The full platform description, 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
- Vertical / tower / stacked pressure filter Built to your spec
Core family. Endless low-elongation zigzag loop.
What decides it Plate dimensions or filtration area, plus the cloth you are replacing.
- Drum, disc, leaf or chamber press Engineering review
Not our default family. We ask what machine you run before saying anything about cloth.
What decides it The machine family, confirmed first.
Dimensions
- Filtration area, pressure filters Built to your spec
Built to your plate dimensions.
What decides it Plate size and chamber count, or the machine model.
Fabrication
- Clipper, PAD / welded and spiral joints Built to your spec
Matched to the construction your machine is already set up for.
What decides it A close-up photograph of the existing joint, both faces.
What we do not do
- OEM spare parts Not offered
Replacement cloth fabricated to your machine dimensions. Not an OEM spare part.
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.
How tower press cloths come off the machine
A failed cloth is usually three-way: something in the cloth, something in the machine, and something in the process. Diagnosing it as purely a cloth problem is the fastest way to buy the same failure twice — and on a single-loop machine you buy it for the whole filter, not for one chamber.
Blinding and lost throughput
Process-side (fines, scaling, cloth-wash effectiveness) interacting with weave choice. The cycle gets longer before anything looks broken.
Diagnose this →Wash-through / off-spec assay
Cloth-side and process-side together: uneven permeability across the cloth, or a wash stage that no longer displaces liquor properly.
Diagnose this →Elongation and path drift
Cloth-side (construction, joint creep) and machine-side (guide condition, tension setting). Both get checked, not one.
Diagnose this →Joint failure on the loop
Fabrication-side and machine-side: joint type, squareness, and what the joint passes through on every cycle.
Diagnose this →Cake not releasing at discharge
Cloth surface and discharge geometry together; on a sticky salt this is rarely one or the other alone.
Diagnose this →Chemical attack on the polymer
Cloth-side against process-side: hot alkaline hydroxide liquor hydrolyses polyester, so the fabric loses strength before anything visible happens to the weave.
Diagnose this →Cloth life on a vertical pressure filter is duty-specific and is counted in cycles rather than in months, because the cloth indexes and is washed on every cycle. Published cycle-life figures for this machine family are the machine builders' own claims for their own cloth, not a number we can carry over to your duty, and we do not quote a life figure before seeing what you filter. Anyone who promises you a cycle count without asking what your liquor does to a polymer is selling, not engineering.
Measuring the old cloth and photographing where it failed is the first step in telling the three causes apart. How to measure your old cloth →
What we need from you to quote
This list is the engineering RFQ in plain form — what you gather here is exactly what the form asks for. Nothing on it is optional because we like paperwork; each item removes a guess from the specification.
| What to confirm | How to get it |
|---|---|
| Which salt, and which grade | Lithium carbonate or lithium hydroxide, and whether the cake is going to a battery-grade specification or to an intermediate. |
| Machine brand and model | Copy it off the machine nameplate. “Unknown” is an acceptable answer. |
| Plate size or filtration area | From the machine plate or the OEM data sheet — this replaces the width-and-length question used on belt machines. |
| Cloth path length | Measure the endless loop, or send the machine drawing showing the zigzag path. |
| The old cloth, or photos of it | Face and back, the joint, the guide edges, and wherever it failed. This is the single most useful thing you can send. |
| Joint type in use now | Photograph the joint close up before it goes in the skip. |
| What failed | Cycle time, wash result, elongation, joint, or cake release. Compare against the failure modes above. |
| Liquor temperature and chemistry | From the process sheet or a recent analysis — pH or free alkalinity matters most on the hydroxide side. |
| Wash configuration | What you wash with, how many displacements, and whether the wash result is what changed. |
Before you enquire
What information do you need to quote a lithium salt tower press cloth?
Machine brand and model, plate size or filtration area, the cloth path length, the joint type you run now, photographs of the old cloth including the joint and the guide edges, which salt and which grade you are making, what failed, and the liquor temperature and chemistry. If you have all of that, a quotation is straightforward. If you have only some of it, send what you have — we will tell you which missing item actually blocks the quote and which one we can work around.
Can one cloth cover our lithium tailings filter as well?
No, and we will not quote it that way. The concentrator side runs a mixed machine population — rubber-belt vacuum filters, vertical tower presses, indexing vacuum filters and centrifuges all appear there — and even where the machine is the same, with a different cloth form, a different failure set and a mineral concentrate or a tailings stream instead of a battery-grade salt as the product. The two duties are kept on separate pages and separate specifications for that reason. If you run both, send both machines through the engineering review and you will get two answers.
Get an engineering quote for lithium salt duty
Three steps after you submit: an engineer checks what you sent against the machine, we come back for anything missing, and you get a quotation or a sample plan.
Every cloth is fabricated to your machine dimensions — we quote per RFQ. No online checkout.
Samples available — freight terms confirmed per request.
Where to go next
Vertical Pressure Filter Cloth
The cloth family this duty uses: zigzag loop, elongation class, joint and area options.
Metso Larox PF Machines
How the tower press threads one cloth through the stack, and what we need per machine.
Tower Press Compatibility
OEM families in this machine class, what we can fit, and what each machine needs.
Measure Your Old Cloth
What to measure and photograph before the old cloth goes in the skip.