Alkaline leaching is a hydrometallurgical process used to extract metals from ores or waste materials using alkaline solutions, primarily sodium hydroxide (NaOH) or ammonia. This method is particularly effective for extracting metals such as lead (Pb), zinc (Zn), and aluminum (Al).
In alkaline leaching, metals are dissolved in a basic solution, which enhances the solubility of certain metal compounds. For example, in a strong alkaline environment (pH > 12), lead can dissolve as lead hydroxide complexes such as Pb OH42− and zinc as Zn OH42-.
The dissolution typically involves the formation of soluble metal hydroxides, which can then be separated from the solid residue through filtration.
Alkaline leaching is widely used for recovering metals from various sources, including:
- Spent batteries: Metals like lithium and aluminum are extracted from spent lithium-ion batteries using NaOH solutions.
- Industrial waste: Alkaline leaching can recover valuable metals from electric arc furnace dust and other industrial byproducts.
- Mineral ores: It is also applied to ores containing zinc and lead, where it can selectively dissolve these metals while leaving other components intact.
The process is considered cost-effective and relatively simple to operate compared to other leaching methods, such as acidic leaching. It allows for the selective extraction of metals, minimizing the loss of valuable resources during processing.
The main challenge is that solid-liquid separation can be difficult in strong alkaline solutions, which may lead to residual metals in the waste. Otherwise, optimization of parameters such as leaching time, temperature, and concentration of NaOH is crucial for maximizing metal recovery.
Alkaline leaching is a valuable technique in metallurgical processes for recovering metals from various materials, leveraging the properties of alkaline solutions to enhance metal solubility and facilitate extraction.
