A team of researchers led by Prof. WAN Yinhua from the Chinese Academy of Sciences has uncovered a groundbreaking mechanism that redefines ion transport in nanofiltration (NF) membranes. Published in Nature Communications on July 1, this study challenges long-held theories and offers a promising path to improve lithium recovery from high-magnesium brines, a critical resource for clean energy technologies.
For decades, scientists assumed that positively charged NF membranes would outperform negatively charged ones in separating lithium (Li⁺) and magnesium (Mg²⁺) ions, based on established principles like co-ion competition. However, real-world observations showed the opposite—negatively charged membranes often achieved better selectivity.
To solve this puzzle, the researchers combined molecular dynamics simulations with experiments. They discovered that highly negatively charged membranes with small pores could reject over 90% of Mg²⁺ ions while allowing an unusual negative rejection (–53.2%) of Li⁺ ions. This unexpected behavior was explained by a newly proposed “counter-ion competition mechanism.”
Under this mechanism, strongly hydrated Mg²⁺ ions gather near the membrane surface due to charge attraction. This process forces weakly hydrated Li⁺ ions to shed their water molecules at the pore entrance, making them smaller and enhancing their transport through the membrane.
Prof. LUO Jianquan, the study’s corresponding author, emphasized the implications: “Our findings provide a mechanistic foundation for designing next-generation NF membranes with tailored ion selectivity. This advances both the theory of nanofiltration and practical applications like lithium extraction from brines.”
This research not only overturns conventional wisdom about ion transport but also paves the way for more efficient lithium recovery methods. By leveraging this new mechanism, scientists can develop advanced membranes to meet the growing demand for lithium, a key component in batteries for electric vehicles and renewable energy storage.
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