易葵, 陈伟, 周康根, 吴业惠子, 邱在容. 锂钠冰晶石的沉淀‒溶解平衡[J]. 工程科学学报, 2024, 46(8): 1489-1497. DOI: 10.13374/j.issn2095-9389.2023.12.01.002
引用本文: 易葵, 陈伟, 周康根, 吴业惠子, 邱在容. 锂钠冰晶石的沉淀‒溶解平衡[J]. 工程科学学报, 2024, 46(8): 1489-1497. DOI: 10.13374/j.issn2095-9389.2023.12.01.002
YI Kui, CHEN Wei, ZHOU Kanggen, WU Yehuizi, QIU Zairong. Precipitation–dissolution equilibrium of lithium sodium cryolite[J]. Chinese Journal of Engineering, 2024, 46(8): 1489-1497. DOI: 10.13374/j.issn2095-9389.2023.12.01.002
Citation: YI Kui, CHEN Wei, ZHOU Kanggen, WU Yehuizi, QIU Zairong. Precipitation–dissolution equilibrium of lithium sodium cryolite[J]. Chinese Journal of Engineering, 2024, 46(8): 1489-1497. DOI: 10.13374/j.issn2095-9389.2023.12.01.002

锂钠冰晶石的沉淀‒溶解平衡

Precipitation–dissolution equilibrium of lithium sodium cryolite

  • 摘要: 新能源行业的迅猛发展,使废旧磷酸铁锂(LiFePO4)电池的高值回收再利用成为目前的研究热点. 但其正极粉料夹带残留的铝集流体,导致回收制备的磷酸铁(FePO4)中铝含量偏高,从而影响再生FePO4的电化学性能. 本文以硫酸铝、硫酸锂、硫酸钠和氟化铵为原料,通过调控氟铝配位合成锂钠冰晶石(Na3Li3Al2F12),研究其沉淀‒溶解平衡行为,为废旧 LiFePO4 粉料酸浸液氟化配位除Al提供依据. 系统考察了配位沉淀过程中F/Al摩尔比、Na/Al摩尔比、Li/Al摩尔比、反应初始pH、反应温度以及反应时间的影响. 得出优化的沉淀条件:F/Al摩尔比为7、Na/Al摩尔比为1.5、Li/Al摩尔比为2、反应温度70 ℃、反应pH为4.5以及反应时间3 h. 在最佳工艺条件下,氟化剂配位沉Al 后,滤液中各离子浓度趋于稳定,其中Al3+质量浓度为75.02 mg·L−1. 此外,探究了Na3Li3Al2F12在不同pH溶液中的溶解度. 在温度30 ℃,pH小于3时,酸度越大,Na3Li3Al2F12的溶解度越大,pH大于3时,pH值对Na3Li3Al2F12溶解度影响不大. 为验证其具有指导意义,在实际应用中,废旧LiFePO4正极材料酸浸液NaF配位沉Al后,Al3+沉淀率达99.4%,实现深度除Al.

     

    Abstract: A strong affinity is observed between fluorine and aluminum, which can both easily undergo sixth-level complexation to form \mathrmAlF_6^3- . Their coexistence with alkali metal ions (such as Li and Na) leads to the formation of a homogeneous solid solution, namely aluminum–sodium composite lithium salt, based on the stoichiometric ratio between the ions. The considerable affinity between fluorine–aluminum bonds and the insoluble nature of fluoroaluminate precipitation provide important guidance for the harmless treatment of fluorine-containing wastewater, aluminum removal from lithium battery positive electrode powder acid leaching solution, electrolytic aluminum smelting industry, and the geochemical and environmental chemical behavior research of aluminum and phosphorus in acidic fluorine-polluted soil. A current research hotspot focuses on the high-value recycling and reusing of iron and phosphorus components in waste lithium iron phosphate (LiFePO4) batteries due to the rapid development of the new energy industry. However, the residual aluminum collector fluid transported by the positive electrode powder had high aluminum content in the recovered iron phosphate (FePO4), thereby affecting the electrochemical performance of regenerated FePO4 and reducing economic benefits. In this study, the synthesis of lithium sodium cryolite (Na3Li3Al2F12) by regulating the coordination of fluorine and aluminum was conducted using aluminum sulfate, lithium sulfate, sodium sulfate, and ammonium fluoride as raw materials. A basis for the fluorination coordination and removal of Al from waste LiFePO4 powder acid leaching solutions is presented based on an investigation of the precipitation–dissolution equilibrium behavior of Na3Li3Al2F12. The effects of the F/Al, Na/Al, and Li/Al molar ratios, initial reaction pH, reaction temperature, and reaction time on the coordination precipitation process were also investigated. The following optimized precipitation conditions were obtained: F/Al molar ratio of 7, Na/Al molar ratio of 1.5, Li/Al molar ratio of 2, reaction temperature of 70 ℃, reaction pH of 4.5, and reaction time of 3 h. Under optimal process conditions, the concentrations of various ions in the filtrate tended to stabilize after coordination and precipitation of Al through the fluorinating agent, revealing an Al3+ concentration of 75.43 mg·L−1. The solubility of Na3Li3Al2F12 in solutions with different values of pH was also investigated. At a temperature of 30 ℃ and a pH of less than 3, high acidity led to the high solubility of Na3Li3Al2F12. The pH had a minimal effect on the solubility of Na3Li3Al2F12 when the pH exceeded 3. Considering its guiding significance in practical applications, Al3+ reached a precipitation rate of 99.4% after NaF coordination precipitation of waste LiFePO4 cathode material acid leaching solution, thereby realizing deep removal of Al.

     

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