Every used lead acid battery that arrives at a recycling plant is a bundle of different materials waiting to be sorted: sulfuric acid, a plastic or hard rubber casing, and two lead-bearing fractions that look alike but are chemically very different — the lead paste and the lead grids. Getting these two apart cleanly is one of the first jobs a recycling line has to do, because the paste and the grids take completely different routes downstream. This article walks through how lead acid battery recycling equipment separates lead paste from grids, step by step.
Why the paste and the grids must never be mixed
The lead grid is the metal skeleton of the battery plate. It is mostly metallic lead, alloyed with small amounts of antimony, calcium or tin to give the plate strength. Because it is already in metallic form, a clean grid can go almost straight to a refining kettle once it is free of paste.
The lead paste is the dark, damp active material pressed onto that grid. It is a mixture of lead sulfate (PbSO4), lead oxide (PbO), lead dioxide (PbO2) and a little metallic lead. The paste cannot be melted directly. The sulfur locked in the lead sulfate would turn into sulfur dioxide gas during smelting — a toxic, polluting emission — so the paste has to be desulfurized first and then smelted to reduce it back to metallic lead.
If the two fractions are mixed, the sulfur in the paste contaminates the grid stream, smelting becomes less efficient, and the final lead quality suffers. That is why a properly designed breaking and separation system treats the paste and the grids as two separate products from the very start.
Step 1 — Cut the battery and drain the acid
The line starts with a used lead battery cutter. A hydraulic cutter such as the HBC-045 slices the casing into four parts and drains the acid out first, so the electrolyte stays contained instead of spilling across the rest of the plant. Cutting the battery open before crushing keeps the acid under control and makes everything downstream easier to manage.
Step 2 — Break the battery and wash the paste off
The cut pieces are fed into the lead acid battery breaking and separation system, where a crusher reduces them to a manageable size. Water is added and the mixture is agitated. The paste is a fine powder that is only loosely bound to the grid, so it washes off easily and becomes suspended in the water as a slurry, while the hard grid metal stays solid.
Step 3 — Screen the slurry
The slurry is passed over vibrating screens. The mesh is sized so that the fine paste particles fall through with the water, while the grids — larger and heavier — stay on top and are carried off. The grids are rinsed again to make sure no paste is left clinging to them, and the wash water is recycled back into the process.
Step 4 — Remove the plastic and dewater the paste
The paste slurry still carries small pieces of plastic and hard rubber that broke off during crushing. Because lead compounds are far denser than plastic, the slurry is sent through a density separation stage, where the heavy lead paste settles out and the light plastic is carried away. The concentrated paste is then pumped to a filter press equipment, which squeezes out the water and leaves a solid paste cake ready for the next stage.
Step 5 — Two separate routes downstream
From here the two streams never meet again. The clean grids go to a lead refinery kettle, where they are melted and refined into high-purity lead. The paste cake goes to a de-sulfurization unit, where the lead sulfate is converted into lead carbonate, and then to a rotary furnace or blast furnace for paste reduction, where it is smelted into crude lead. Both streams end up as saleable lead, but each follows the route that suits its own chemistry.
Why separation quality matters to your bottom line
The quality of the paste/grid separation has a direct effect on the economics of the whole plant. If the paste is not fully washed off the grids, lead is lost into the grid stream at a lower value and the overall recovery rate drops. If plastic is not removed from the paste, it burns in the furnace and wastes energy. A well-built breaking and separation system recovers the paste and the grids as clean, separate products, which is why it sits at the heart of every used lead acid battery recycling plant.
Choosing the right equipment
Separating lead paste from grids is not something improvised machinery can do reliably. It needs a purpose-built breaking and separation system, matched with the right cutter, screens, density separators and filter press, and sized to the plant's throughput. San Lan Technologies has been building lead acid battery recycling equipment since 2007. Its breaking and separation plants are available from 1 to 10 tonnes per hour, and complete recycling lines have been supplied to customers in more than 20 countries. If you are planning a new plant or upgrading an existing line, getting the paste/grid separation right at the design stage is the single best way to protect your recovery rate and your lead quality.
