There are two common methods for recycling spent lead-acid batteries: pyrometallurgy and hydrometallurgy. Below, we will explore these two methods for extracting and refining the heavy metal lead.
Pyrometallurgy
Pyrometallurgy is the science and technology of extracting and refining metals from ores, concentrates, or other materials at high temperatures.
a) Emission Control and Utilization
When using pyrometallurgical processes to recover lead, the exhaust gases must be purified to meet emission standards. The sulfur dioxide (SO₂) generated during the smelting process can be collected and utilized.
b) Sealed Smelting Equipment
The smelting process should employ sealed equipment. The amounts of smelting and reducing agents must be strictly controlled to ensure the removal of all sulfur and other impurities, as well as the complete reduction of lead oxides.
c) Negative Pressure Operation
The smelting process for recycling spent lead-acid batteries should be conducted under negative pressure to prevent the escape of harmful gases and dust. The collected gases must be treated to meet environmental standards before being released.
Hydrometallurgy
Hydrometallurgy involves dissolving certain metal components from ores, concentrates, calcines, or other materials in aqueous solutions and then extracting the metals.
a) Pre-desulfurization and Electrolytic Deposition
For the pre-desulfurization and electrolytic deposition process, it is advisable to desulfurize the lead sulfate in the spent lead paste and convert lead dioxide (PbO₂) into lead oxide (PbO). The lead can then be transferred to a lead-rich electrolyte, where it is recovered through electrolytic deposition.
b) Solid-State Electrolytic Reduction
In the solid-state electrolytic reduction process, the reduced lead paste should be packed into cathode frames. During electrolysis, the solid lead in the paste is directly reduced to metallic lead.
c) Collection and Processing of Electrolytic Deposits
The crystalline or spongy lead deposits obtained from electrolysis should be collected and pressed into high-purity lead cakes. These cakes can then be sent to a furnace for casting into ingots or directly melted and cast into ingots.
d)Emission Control
When using hydrometallurgical processes for recycling spent lead-acid batteries, the emitted gases should undergo dust and acid mist purification to meet environmental standards before being released.
Both pyrometallurgy and hydrometallurgy offer effective methods for recycling spent lead-acid batteries. Pyrometallurgy is characterized by its high-temperature processes and the use of sealed equipment to control emissions, while hydrometallurgy focuses on aqueous solutions and electrolytic techniques to extract and purify lead. Each method has its own advantages and is chosen based on specific operational requirements and environmental considerations.
