The membrane filter press (also called diaphragm filter press) is the highest-performance design for cake dewatering. By adding a second, “squeeze” step after filtration, membrane presses drive cake moisture below 18% — enabling dry-stack tailings, direct cement-kiln feeding, and 40-60% lower thermal drying energy downstream.
How the Membrane Squeeze Works
Every second plate in a membrane filter press is a “diaphragm plate” — a hollow plate with a flexible rubber or elastomer membrane covering its filtration face. During the filtration step, the membrane sits flat and the plate behaves like a normal chamber plate. After filtration, the press injects compressed air or water at 12-20 bar behind the membrane, which pushes the membrane outward against the cake. The cake is mechanically compacted from both sides, expelling additional liquid.
A typical squeeze step lasts 5-15 minutes and removes another 30-50% of the moisture that remained after filtration. Combined with the prior filtration, cake dryness improves from 22-28% (chamber-only) to 14-18% (membrane).
When the Investment Pays Off
Membrane presses cost roughly 25-40% more than equivalent chamber presses. The investment pays back when one of these matters: (1) you need to dry stack tailings instead of impound them; (2) you have a downstream thermal dryer and want to reduce its energy bill; (3) you ship cake long distances and pay per-tonne freight; (4) regulatory landfill leachate limits demand low-moisture cake.
For simple solid-liquid separation where 22-28% moisture is fine, a standard chamber filter press remains the better economic choice.
Common Applications
- Mining concentrate dewatering — copper, lead-zinc, iron ore at port shipping spec
- Dry-stack tailings — replacing wet impoundments
- Power plant FGD sludge — gypsum byproduct dewatering to cement-grade
- Hazardous waste solidification — minimizing landfill leachate
- Lithium battery slurry — separation of valuable lithium from solvent
- Pharmaceutical filter cake — direct-discharge oven-ready cake
Specifications & Customization Options
- Plate size: 800 / 1000 / 1250 / 1500 / 1800 / 2000 mm
- Filter area: 30 – 2,000 m²
- Squeeze pressure: 12, 16, 20, 25 bar options
- Membrane material: EPDM (standard), Viton (solvents), NBR (oils), TPE (food grade)
- Squeeze medium: Compressed air or water
- Cycle automation: PLC controlled — filtration, squeeze, discharge auto-sequenced
- Plate construction: Reinforced polypropylene (standard), stainless 304/316L for food/pharma
FAQs
How much extra moisture does the squeeze remove? Typically 30-50% reduction in residual moisture. Example: a chamber press giving 70% cake moisture (30% DS) becomes 42% moisture (58% DS) — a major improvement at the boundary between sludge-like and stackable solid.
Air or water squeeze — which is better? Water squeeze is more energy-efficient (a water pump consumes less than an air compressor for the same pressure) and gives more even compression. Air squeeze is faster, simpler, and avoids the wash-cycle that water systems require. Mining operations typically pick water; chemical and food operations often pick air.
How long do the membranes last? 3-7 years in normal duty. EPDM membranes degrade from solvent attack; check chemistry compatibility before specifying. Replacement membranes cost roughly $300-800 per plate.
Evaluating membrane press payback for your plant? Send Senjie your current cake moisture, downstream drying or transport costs, and slurry chemistry — we’ll model the payback on a membrane press upgrade.