【作者】 王禄；

【导师】 孟长功； 马伟；

【作者基本信息】 大连理工大学 ， 物理化学， 2009， 博士

【摘要】 尖晶石型锰氧化物（Spinel-type Manganese Oxide,SMO）对溶液中的锂离子显示出特有的选择性,可选择性的从溶液中提取锂离子,因此被称为“锂离子筛”,用于卤水、浓海水等溶液中锂的提取及锂电池等含锂资源的锂回收。SMO型锂离子筛具有选择性高、吸附容量大等优点,是最有前景的锂吸附剂之一。但由于锰具有多种氧化态,如何控制反应条件制各具有结构稳定、提锂性能优良的离子筛,仍是锂离子筛制备方面面临的主要问题;其次研究各种吸附条件对离子筛提锂性能的影响,研究不同条件下的锂离子提取动力学、热力学行为,从而提供离子筛提锂操作过程的工艺参数,描述离子筛脱/嵌锂过程的机理,将对离子筛提锂的工业应用与开发提供实际及理论指导意义。本文以SMO型锂离子筛为研究对象,以锰盐和锂盐为主要原料,在采用固相法探讨离子筛前驱体制备条件与离子筛提锂性能关系的基础上,分别采用水热法、共沉淀法为主要合成方法,成功制备了具有高提锂容量、选择性好及结构稳定的两种锂离子筛材料,并研究了合成条件对材料制备及提锂性能的影响。利用制备的两种离子筛对比研究了溶液pH值、锂离子浓度、温度、吸附时间、离子强度等因素对锂离子提取性能的影响,及不同条件下的锂离子提取平衡、动力学和热力学过程,采用不同模型对提锂平衡及动力学进行了拟合,详细研究了在弱碱性缓冲体系下的提锂行为。结合仪器分析和实验现象,对离子筛的脱/嵌锂机制首次提出了“空位效应”作用,并对脱/嵌锂过程中存在的疑问进行了有益的解释。主要研究结果如下:随原料锂锰摩尔比在0.5～1之间增加,由固相法制备得到的离子筛前驱体中的锂锰摩尔比也增加,酸洗脱锂后得到的离子筛提锂容量也表现出随之增高的趋势。以LiOH为锂源比以Li₂CO₃为锂源制备的离子筛具有更高的提锂容量。离子筛产物晶粒长大和Mn₂O₃等杂质形成可能是造成离子筛提锂能力下降的主要原因。以水热法为主要合成方法,可以制备得到高选择性的锂离子筛MnO₂·0.5H₂O,采用共沉淀法也可以得到相似的产物,但共沉淀法制备的离子筛颗粒小（纳米级）、比表面积大、脱锂产物含H量高,尽管结晶度稍差,但其显示了更高的提锂容量及循环提锂性能。两种离子筛的提锂容量都在34 mg·g^-1以上,显示出较高的提锂能力,且在脱/嵌锂过程中,两种离子筛的溶损率都＜5%,显示了较高的结构稳定性。非缓冲体系下的溶液pH下降现象证实了Li⁺-H⁺离子交换在当前制备的尖晶石型锰氧化物锂离子筛提锂过程中起主要作用,由于提锂过程中溶液pH逐渐下降致使锂提取不完全,对于通常具有弱碱性或中性缓冲能力的实际溶液中锂资源,研究离子筛在弱碱性缓冲体系下的提锂行为显得尤为必要。pH 8.0缓冲体系下的锂离子提取过程研究表明,锂离子的提取平衡可以用Langmuir模型较好的描述,且当前制备的SMO离子筛的锂离子提取为一自发、熵增的吸热过程,提取平衡可在24h内达到,提锂动力学遵从拟二级动力学模型。离子强度对当前离子筛的提锂行为影响较小,扩散研究结果表明边界层扩散与粒内扩散联合控制离子筛的提锂过程,而两种扩散对限速步的控制程度与离子筛的晶体结构有主要关系。最后分别从离子筛本体结构、脱/嵌锂前后结构及Li⁺-H⁺离子交换过程的讨论出发,综合现有文献及本文实验结果,主要通过对离子筛结构中可交换H的讨论,及脱/嵌锂前后离子筛结构的变化,首次提出了“空位效应”作用,并据此描述SMO离子筛的锂离子脱出/嵌入过程。更多还原

【Abstract】 The spinel-type manganese oxides（SMO） show the high selectivity to lithium ions in solution and can recover lithium selectively from solutions,so it is named as "Lithium Ion Sieve（LIS）" which can be used in lithium uptake or reclamation from brine,sweater and waste lithium batteries.The SMO-type lithium ion sieve is one of the most promising lithium adsorbents due to its high selectivity and adsorption capacity to Li⁺.An element of manganese has several oxidation states,therefore,how to control the reaction conditions to prepare lithium ion sieve with stable structure and good uptake performance is still the main problem of LIS synthesis.Secondly,investigation of the effect of various adsorption conditions on performance of lithium uptake by LIS and study of kinetics and thermodynamics of lithium uptake can provide the process parameters of lithium recovery and the theoretical description of Li⁺ extraction/insertion of LIS.It can provide useful information to guide the application in the field and promote the development of lithium recovery by LIS in industry.In this paper,the SMO-type lithium ion sieve was the main research object,the manganates and lithium salts were taken as the main raw materials.Two LISs with high uptake capacity,better selectivity and stable structure were successfully prepared by hydrothermal method and coprecipitation method based on the discussion of correlation between Li⁺ uptake performance and the preparation conditions of LIS precursors.The effects of preparation conditions on Li⁺ uptake were also investigated.Furthermore,the uptake performance with the prepared ion sieves were studied in depth,including the influences of solution pH,effect of lithium ion concentration,temperature,adsorption time and ionic strength on Li⁺ uptake.The Li⁺ uptake equilibrium,kinetics and thermodynamics were studied under different conditions,with the buffer system and without buffer system,and models were used to describe the experimental isotherms and kinetics.At last,the "Vacancy Effect" was presented to illuminate the lithium extraction/insertion mechanism of LIS,and some problems that exist in the process of lithium extraction/insertion were given helpful explanation basing on the analysis of XRD,XPS and calculated results.The main results were summarized as follows:First,the Li/Mn mole ratio of LIS precursor prepared with solid state method increased with the increase of Li/Mn mole ratio of raw material between 0.5～1,and all the Li-extracted materials also showed an ascending trend of lithium uptake with the increase of Li/Mn mole ration of reagent.The LIS synthesized with LiOH usually have higher Li⁺ uptake capacity than the one with Li₂CO₃.The LIS particles grow larger and the Mn₂O₃ impurities could be the primary reason for the decrease of Li⁺ uptake.The MnO₂·0.5H₂O LIS with higher uptake capacity can be prepared by hydrothermal technique.Similar material can also be obtained by coprecipitation technique,and it has smaller LIS particle size（nano-scale）,larger specific surface area and higher H content,so it show the higher Li⁺ uptake capacity and better recycle performance even if the sample crystallinity is slightly inferior to LIS prepared by hydrothermal method.The Li⁺ uptake capacities of both ion sieves reached 34 mg·g^-1 which showed the excellent uptake performance,and the dissolving rates of both ion sieves were all less than 5%,which showed the good structure stability.Second,the results of solution pH decreasing in non-buffer system proved that the Li⁺-H⁺ ion-exchange played a major role in Li⁺ uptake by present SMO-type lithium ion sieves.Due to the decrease of solution pH,Li⁺ uptake cannot proceed completely.Moreover, it should be noted that the practical liquid lithium resources usually had weak basic or neutral buffer capacity,so it was very important to study Li⁺ uptake by ion sieve in weak basic buffer system.The results of Li⁺ uptake in pH 8.0 buffer solution revealed that the equilibrium can be reached in 24 hours and the equilibrium process can be well described by the Langmuir model.The processes of Li⁺ uptake by present SMO-type ion sieve were spontaneous,entropy increase and endothermic.The kinetic process obeyed pseudo-second-order kinetics model. The ionic strength only had a slight influence on Li⁺ uptake.The results of diffusion study indicated that both boundary layer and intraparticle diffusion may together control the uptake process,while the extent of the rate-controlled step was closely related with the crystal structure of ion sieves.At last,the results were integrated based on the discussions about the structure of LIS, precursor,relithiated LIS and the process of Li⁺-H⁺ exchange,respectively.Especially, through the discussion of the exchangeable H in LIS structure and the structure change of LIS in Li⁺ extraction/insertion,the "vacancy effect" was firstly proposed to interpret the process of Li⁺ extraction or insertion in SMO-type ion sieves.更多还原