Solvent Extraction Recycling of Ni-Cd Batteries Without Salt Waste

The patent replaces the thermal field system of pyrometallurgy with a chemical field system of hydrometallurgy. Sulfuric acid leaching dissolves metals into the solution, followed by solvent extraction using P204 and DZ272 extractants to selectively separate cadmium, cobalt, and nickel. This substitution eliminates high-temperature processing, dramatically reducing energy consumption while maintaining effective metal recovery through chemical reactions and phase separation.

The patent changes the operating parameters from high-temperature conditions in pyrometallurgy to ambient or moderate temperature conditions in hydrometallurgy. The leaching process occurs at controlled temperatures with sulfuric acid, and the extraction process occurs at room temperature with specific pH control. This parameter change transforms an energy-intensive thermal process into a low-energy chemical process while achieving comparable or superior metal recovery effectiveness.

The patent applies the discarding and recovering principle by treating the sodium sulfate solution generated during extraction not as waste to be discarded, but as a resource to be recovered. The sodium sulfate is evaporated and crystallized to produce industrial-grade salt products. This transforms the harmful waste stream into a valuable by-product, eliminating secondary pollution while maintaining the high metal separation purity achieved through the extraction process.

The patent converts the harmful factor of salt-containing wastewater into a beneficial outcome. The sodium sulfate solution, which would normally be treated as polluting waste requiring expensive treatment facilities, is instead evaporated and crystallized to produce marketable industrial salt. This converts an environmental liability into an economic asset, eliminating secondary pollution while preserving the high-purity metal separation achieved through the extraction process.

The patent applies preliminary action by heating the sodium sulfate solution before evaporation to prevent crystallization during the concentration process. By pre-heating the solution to maintain it above the crystallization temperature, the system prevents pipe blockages before they can occur. This preliminary thermal treatment ensures continuous operation while maintaining high extraction efficiency through the sodium hydroxide-based extraction process.

The patent changes the temperature parameter during the evaporation and crystallization process. By controlling the temperature to remain above the crystallization point of sodium sulfate during solution concentration, the system prevents premature crystallization that would cause pipe blockages. This parameter control allows the extraction process to proceed continuously with high efficiency while avoiding operational disruptions from crystallization blockages.

The patent applies discarding and recovering by directing the sodium sulfate solution to evaporation and crystallization to produce industrial salt products, rather than converting nickel soap. The nickel-containing organic phase is separately treated to recover nickel. This approach prevents nickel loss to wastewater while solving the pipe blockage issue through controlled evaporation with temperature management, achieving both process continuity and substance conservation.

The patent segments the treatment process into separate streams: the aqueous sodium sulfate solution is directed to evaporation for salt production, while the organic nickel-containing phase is directed to separate recovery processes. This segmentation allows each stream to be treated optimally - the salt solution without risk of nickel contamination, and the nickel phase without pipe blockage issues - thereby preventing nickel-containing wastewater generation while maintaining continuous operation.