硅酸钠焙烧提取钙热还原稀土冶炼渣中稀土的研究

Extracting REEs from Smelter Slag of Calcium Thermal Reduction by Roasting with Sodium Metasilicate Nonahydrate

采用钙热还原法生产稀土金属时会产生大量的稀土冶炼渣,渣中稀土的存在形式包括稀土金属单质、稀土氧化物和稀土氟化物,其中的稀土金属和稀土氧化物易于被无机酸直接浸出,而氟化稀土则难被酸浸出,成为从钙热还原稀土冶炼渣中高效回收稀土的瓶颈。在工业生产氟化钠晶体方法的启发下,开发了九水硅酸钠焙烧-HCl浸出提取钙热还原稀土冶炼渣中稀土的方法,通过九水硅酸钠焙烧钙热还原稀土冶炼渣,将渣中稀土氟化物转型为易溶于酸的稀土氧化物,而氟元素则转型为Na F被水洗除去,实现了稀土和氟的高效分离。考察了焙烧温度、时间和HCl浓度等因素对稀土提取率的影响,结果表明:在焙烧温度为850℃,焙烧时间为2 h,九水硅酸钠与钙热还原渣质量比为1∶1,酸浸温度为60℃,酸浸时间为1. 5 h,HCl浓度为4 mol·L^(-1),液固比为11∶1的条件下,稀土提取率高达99. 06%。

Smelter slag was produced during thermal reduction of rare earth metals with calcium contains rare earth elements (REEs),in the form of rare earth metals,rare earth oxides,and rare earth fluoride.Rare earth fluoride cannot be leached efficiently from this slag by a direct acid leaching method,therefore it is difficult to leach and use the REEs in the slag fully.Being inspired by the process of the industrial production of sodium fluoride,a novel process that involves roasting smelter slag with sodium metasilicate nonahydrate followed by acid leaching was developed to improve the leaching efficiency and to recover REEs from the smelter slag.A total REE leaching efficiency of 99.05% can be achieved for a roasting temperature of 850℃,a smelter slag/sodium metasilicate nona-hydrate mass ratio of 1:1,a roasting time of 2h,4mol·L^-1 hydrochloric acid,an acid leaching temperature of 60℃,an acid leaching time of 1.5h,and a liquid/solid ratio of 11:1.The results indicated that the REEs in the smelting slag can be efficiently extracted by the proposed method.