How to use a filter press to collect the paste of ULAB in battery recycling?

Why the Filter Press Matters in ULAB Recycling

When a used lead acid battery is broken down, it yields four main components: plastic casings, lead grids, sulfuric acid, and lead paste. The paste is a thick mixture of lead oxides and residual acid. It contains valuable lead that can be smelted and reused, but it is also highly corrosive and difficult to handle in its raw form. A filter press to collect the paste of ULAB solves this problem by squeezing out liquids under high pressure, leaving behind a dry, manageable cake that is ready for downstream processing.

San Lan Technologies designs filter presses specifically for this application. With filter plate dimensions of 800 x 800 mm, 60 filter plates, and a total filtration area of 60 square meters, the system handles large volumes efficiently. The unit weighs 3,440 kg and is built to withstand the abrasive and acidic nature of lead paste slurry.

Preparing the Slurry Before Filtration

Before the filter press can do its job, the lead paste must be mixed with water to create a pumpable slurry. This step usually happens immediately after the breaking and separation stage. A typical lead acid battery breaking and separating plant processes 1 to 10 metric tons per hour, feeding a steady stream of paste into a slurry tank.

Operators should monitor the slurry concentration closely. If the mixture is too thick, it will clog the pump and reduce flow rates. If it is too thin, the filter press will take longer to form a solid cake. A concentration of 20 to 30 percent solids by weight is generally ideal for lead paste filtration. The slurry should also be screened to remove large plastic fragments or lead grid pieces that could damage the filter cloth.

Step-by-Step Operation of the Filter Press

Step 1: Inspect and Assemble the Press

Start by counting and inspecting all filter plates. Each plate must be flat, intact, and arranged in the correct sequence. Check that filter cloths are installed without wrinkles, tears, or slack. The sealing edges must sit tightly against the plate face to prevent leakage. Confirm that the hydraulic oil level is within the safe range and that the pressure gauge reads stable values when idle.

Step 2: Close the Plate Pack

Use the hydraulic system to clamp the plates together. The closing pressure must reach the manufacturer-recommended value before feeding begins. Insufficient pressure will cause slurry to bypass the filter cloths and leak from the plate edges. For lead paste applications, corrosion-resistant plates and heavy-duty hydraulic cylinders are essential because the acidic slurry can accelerate wear on standard components.

Step 3: Feed the Slurry

Open the feed valve and start the slurry pump. Begin with low pressure to avoid sudden impact on the filter cloths. As the chambers fill, liquid passes through the cloth while solids accumulate on the cloth surface. Gradually increase the feed pressure as the cake begins to form. Monitor the filtrate outlet; when the liquid runs clear, the chambers are nearly full.

Step 4: Squeeze and Dewater

Once the chambers are full, apply the final squeeze pressure. Some filter presses use diaphragm membranes that inflate with air or water to press the cake further, reducing moisture content to as low as 15 percent. Lower moisture means less energy is required during smelting, and the risk of acid fumes is significantly reduced. This step is especially important when the cake will be fed directly into a rotary furnace or blast furnace.

Step 5: Open and Discharge the Cake

Release the hydraulic pressure and separate the plates. The dry lead paste cake should ｄｒｏｐ cleanly into a collection bin or conveyor. If any cake sticks to the cloth, use a plastic scraper to remove it gently. Avoid metal tools that could tear the cloth. After discharge, rinse the cloths with clean water to remove residual particles and prepare the press for the next cycle.

Best Practices for Long-Term Performance

• ｒｅｐｌａｃｅ filter cloths on schedule. Depending on throughput, cloths typically last 6 to 12 months in lead paste service. Worn cloths cause leakage and reduce filtration efficiency.
• Use corrosion-resistant materials. Lead paste contains sulfuric acid. Plates, frames, and hydraulic components should be made from stainless steel or coated with acid-resistant finishes.
• Maintain consistent slurry quality. Variations in paste composition from different battery sources can affect filtration speed. Blend incoming material to keep particle size and acid concentration uniform.
• Monitor hydraulic oil cleanliness. Contaminated oil damages seals and pumps. Change the oil every 3 to 6 months and inspect the tank for sediment quarterly.
• Integrate with effluent treatment. The liquid filtrate still contains diluted acid and trace metals. Route it to a water treatment plant for neutralization before discharge or reuse.

Integrating the Filter Press into Your Recycling Line

A filter press should never work in isolation. In a complete lead acid battery recycling equipment line, it sits between the breaking and separation stage and the smelting stage. Upstream, the battery cutter and breaking system deliver paste, plastic, and grids. Downstream, the filtered cake moves to a rotary furnace or blast furnace for lead reduction, while the treated liquid returns to the slurry mixing tank or is discharged safely.

San Lan Technologies offers turnkey integration support, helping operators synchronize the filter press cycle time with the upstream breaking capacity and downstream furnace batch schedule. When all components work in harmony, the plant achieves higher lead recovery rates, lower operating costs, and full compliance with environmental regulations.