In lithium extraction, the stability and acid resistance of chitosan composite microspheres, serving as the lithium extraction adsorbent, are crucial. While acid crosslinking can enhance the structural strength of chitosan, excessive crosslinking or improper treatment often leads to decreased adsorption performance or even damage to its original structure. To avoid the damage caused by acid crosslinking to the lithium extraction adsorbent, multiple aspects need to be addressed, including the selection of crosslinking agents, optimization of crosslinking conditions, introduction of template ions, composite material design, and improvement of regeneration processes.
The choice of crosslinking agent directly affects the acid resistance and adsorption performance of chitosan composite microspheres. Traditional aldehyde crosslinking agents, while forming stable structures, are prone to hydrolysis under acidic conditions, leading to the breakage of crosslinking bonds. Therefore, it is necessary to explore novel crosslinking agents, such as multifunctional compounds or natural polymeric crosslinking agents, which can remain stable in acidic environments while minimizing damage to the chitosan molecular chains. For example, certain natural polyphenols not only possess antioxidant properties but can also form stable covalent bonds with chitosan, improving the acid resistance of the composite microspheres.
Optimization of crosslinking conditions is key to avoiding damage. The parameters of the cross-linking reaction, such as temperature, time, pH, and cross-linking agent concentration, need to be precisely controlled. Excessively high temperatures or excessively long reaction times may exacerbate chitosan degradation, while inappropriate pH selection may affect the activity of the cross-linking agent. By designing experiments to determine the optimal cross-linking conditions, the damage to the chitosan structure can be minimized while ensuring the cross-linking effect. For example, using mild reaction conditions, such as low temperature, short reaction time, and suitable pH, can effectively reduce the negative impact of acid cross-linking on chitosan composite spheres.
The introduction of template ions provides a new approach to improving the acid resistance and selectivity of chitosan composite spheres. Through template polymerization, specific metal ions are used as templates to undergo adsorption reactions with chitosan, forming a polymeric adsorbent material with "memory" function. After cross-linking, the template ions are eluted, and the released active sites exhibit higher selectivity and adsorption capacity for target ions. This method not only enhances the stability of the composite spheres under acidic conditions but also improves their adsorption efficiency for lithium ions.
The design of composite materials is another important way to improve the performance of chitosan composite spheres. Combining chitosan with other polymeric or inorganic materials can form composite lithium extraction adsorbents with excellent properties. For example, combining it with polyacrylonitrile can produce composite spheres with a hierarchical porous structure, whose unique pore structure facilitates the rapid diffusion and adsorption of lithium ions. Simultaneously, the introduction of composite materials can enhance the acid resistance and mechanical strength of chitosan, improving its stability in harsh environments.
Improving the regeneration process is crucial for maintaining the long-term stability of chitosan composite spheres. During lithium extraction, the lithium extraction adsorbent undergoes multiple adsorption-desorption cycles. Traditional desorption methods, such as acid washing, while effectively removing adsorbed lithium ions, may also damage the chitosan structure. Therefore, it is necessary to explore gentler desorption methods, such as using low-concentration acids or neutral desorbents, to reduce damage to the composite spheres. Furthermore, optimizing desorption conditions, such as temperature, time, and desorbent concentration, can further improve desorption efficiency and regeneration performance.
