中国有色冶金

Driven by the dual demands for high energy density and high safety in power batteries, the allowable threshold for magnetic impurities (e.g., Fe, Ni, Cr, Zn) in battery-grade lithium carbonate continues to decrease amid the rapid development of the global new energy industry. The current non-ferrous metals industry standard “Battery Grade Lithium Carbonate” (YS/T 582—2023) specifies that the magnetic impurity content must be ≤300ppb (mass ratio, 10-9), while some companies require this threshold to be reduced to 100ppb. Although most domestic lithium salt producers can meet the current industry standard, issues such as significant fluctuations in magnetic impurity content and occasional non-compliant batches persist. To address this, based on the spodumene lithium extraction process via the sulfuric acid method, this study adopted a full-process quality tracking approach and identified the main sources of magnetic impurities in the lithium carbonate production system: raw and reagents, martensitic phase transformation induced by cold processing of stainless steel equipment, construction contaminants, and particles from environmental corrosion. It was found that solution treatment (quenching at 1050-1100℃) of austenitic stainless steel can effectively reverse martensitic phase transformation, restoring the relative magnetic permeability (μ_r) to approximately 1 and thereby suppressing the release of magnetic impurities from equipment. Based on comprehensive quality tracking and control, a “five-in-one” hierarchical control technology was proposed, encompassing raw material screening, equipment upgrading and demagnetization, process optimization, environmental purification, and staff standardization. Practical application demonstrates that implementing this control technology can stably maintain the magnetic impurity content in battery-grade lithium carbonate products at ≤50ppb, meeting the quality requirements for high-end lithium battery materials. The successful implementation of this technology promotes the green and high-quality upgrade of the sulfuric acid-based lithium extraction process and provides a technical paradigm for quality control of raw materials in the lithium battery industry.