锂离子筛从高镁锂比卤水提锂过程中容量循环衰减机制与结构优化

A large number of salt lakes in China are characterized by a high ratio of Mg/Li, leading to great difficulty in lithium extraction. Lithium ion-sieve MnO2•0.5H2O, economical, selective, high adsorption capacity is praised as the most prospective adsorbent.However, industrial experiments shows that sharp adsorption capacity attenuation and serious manganese dissolution are encountered after many cycles. A route that attenuation mechanism of lithium ion-sieve directs the structure optimization is put forward. Lithium ion-sieve MnO2•0.5H2O is synthesized using hydrothermal process. Different constituents of brine as raw material, microstructure change during recycling adsorption or desorption is investigated using structural analysis. Electrochemical measurement combined with XPS and BET are applied to study Lithium diffusion behavior, manganese valency change, interface reaction behavior between Lithium ion-sieve and brine. Attenuation mechanism of adsorption cpacity and its decisive factors are made clear,dissolution mechanism of manganese are revealed and inhibition method is put forward.These results guide structure optimization and relationship establishment between recycling adsorption property and structure. Lithium ion-sieve with high adsorption capacity and long life will be successfully prepared. Theory and technical support for efficient extraction of lithium from salt lake brine with a high Mg/Li ration will be provided.

我国盐湖众多、锂资源丰富、但多呈高镁锂比特征，锂提取困难。锰系锂离子筛经济、环保、吸附容量高、选择性强，被誉为最有应用前景的盐湖提锂吸附剂。但工业试验发现，锂离子筛在卤水中循环使用多次后，吸附容量急剧衰减，锰溶损严重，制约了工业应用。本课题提出以锂离子筛容量循环衰减机制指导结构优化的新思路。采用水热法制备锰系锂离子筛MnO2•0.5H2O，以高镁锂比卤水为对象，用结构分析法研究锂离子筛在循环吸/脱附过程中结构演变规律；用电化学测试技术结合XPS、BET等方法研究锂离子扩散行为、锰价态变化和锂离子筛/卤水的界面反应行为，查明容量循环衰减机制及决定性影响因素，揭示锰溶损机理并提出抑制方法。以此为基础，优化离子筛结构和洗脱工艺，建立锂离子筛结构与吸附、循环性能的调控理论，实现高吸附容量、长使用寿命锰系锂离子筛的可控制备，为高镁锂比盐湖卤水锂资源的高效提取提供技术支撑和理论指导。

我国盐湖众多、锂资源丰富、但多呈高镁锂比特征，提取困难。锰系锂离子筛MnO2•0.5H2O被誉为最有应用前景的盐湖提锂吸附剂。但工业试验发现，锂离子筛在卤水中循环使用多次后，吸附容量急剧衰减，锰溶损严重，制约了工业应用。本课题以锂离子筛容量循环衰减机制指导结构优化。分别以电解MnO2和硫酸锰为锰源，采用水热法制备锰系锂离子筛MnO2•0.5H2O，以电解MnO2为锰源制得的锂离子筛在盐湖卤水中首次吸附容量达到了30.8mg/g，前驱体首次锰溶损率为3.14%，在盐湖卤水中循环10次后吸附容量为23.4mg/g，锰溶损率为0.48%。以硫酸锰和高锰酸钾为锰源的锂离子筛在新疆罗布泊盐湖卤水中的首次吸附容量达到了42.87mg/g，锰溶损率为2.26%。在盐湖卤水中循环10次后锂吸附容量为37.2mg/g，锰溶损率为0.26%，100次循环后锂吸附容量为36.0mg/g，容量保持率为83.9%，锰溶损率为0.15%。采用XRD，化合价和组成分析对合成的锂离子筛进行表征，发现锂离子筛在循环过程中晶胞参数变小，结构收缩，导致循环过程中锂吸附容量下降，采用电化学的方法测试锂离子筛在不同的溶液中锰溶损机制，在稀HCl中，初始锰溶损主要反应为2H2O+2Mn3+→Mn2++MnO2+4H+,稳态锰溶损主要为锂离子筛本身溶解，盐湖卤水中Cl-和SO42-加速锰溶损。以此为基础，对锂离子筛分别进行了表面包覆ZrO2改性和体相掺杂铬、掺杂铝和掺杂镓。包覆和掺杂均改善了循环稳定性，其中体相掺杂铝的效果最好，搀杂铝的锂离子筛前驱体首次锰溶损率为1.89%，锂吸附容量为42.0mg·g-1，循环10次容量保持率为90.1%，锰溶损率为0.2%，循环100次后容量保持率为87.6%，锰溶损率为0.1%。该研究成果为锂离子筛的工业化提供了基础数据，促进盐湖卤水大规模吸附提锂技术的工业化应用。