从钙热还原氟化稀土渣中提取稀土热力学分析

Thermodynamic Analysis on Extracting REEs from Smelter Slag of Calcium Thermal Reduction of Rare Earth Fluoride

在已有较优直接酸浸和碱处理(碱煮、焙烧)-酸浸工艺条件下,对钙热还原稀土渣(简称稀土渣)进行酸浸热力学理论分析,应用X射线多晶衍射仪(XRD)分析碱处理过程物相变化,应用扫描电镜型附带的能谱仪(SEM+EDS)对碱煮的样品进行线性扫描和元素分析。热力学理论计算和实验结果均表明:碱煮条件下,氟化稀土能转化为氢氧化稀土;碱性添加剂焙烧条件下,氟化稀土能转化为氧化稀土,但NaOH,Na_(2)CO_(3)焙烧-酸浸工艺稀土却不能完全浸出,原因是酸浸过程CaF_(2)对稀土浸出影响大。此外,碱煮-酸浸的稀土提取率低,原因是碱煮时新生成的氢氧化稀土"包裹"了氟化稀土,阻碍了氟化稀土进一步碱转。在与添加Na_(2)SiO_(3)焙烧方面,Na_(2)SiO_(3)焙烧处理能削减CaF_(2)对稀土浸出的影响,使稀土接近完全浸出,因为酸浸Na_(2)SiO_(3)焙烧产物将生成偏硅酸和SiF^(6-)络合物,[SiF_(6)]^(2-)络合物的生成结合了CaF_(2)中大量的F^(-),同时抑制了稀土离子对CaF_(2)的解离作用,促进了稀土的浸出。此时,溶液中CaF_(2)固体与Ca^(2+),[SiF_(6)]^(2-)和稀土离子共存达到新的平衡。

Thermodynamic analysis was carried on extraction of rare-earth by acid leaching smelting slag(rareearth residue for short)which produced by calcium thermal reduction with fluorinated rare-earth,under the optimum technological conditions of acid leaching in direct and alkali treatment(leaching or roasting)-acid leaching.X-ray diffraction(XRD)was used for the primary characterization of the phase changes in the alkali treatment process,and linear scanning and elemental analysis were carried out for alkali leached samples by scanning electronmicroscope and energy spectrometer(SEM+EDS).Both thermodynamic calculation and experimental results showed that rare-earth fluoride can be easily converted into rare-earth hydroxide under alkaline leaching condition.Rare-earth fluoride is easily converted into oxidized rare-earth under the condition of roasting with alkaline additives,but the rare-earth cannot be completely extracted.The reason is that CaF_(2) has a great influence on rare-earth leaching in the acid leaching process.In addition,the extraction rate of rare-earth from alkali leaching-acid leaching is lower,as the reason is that the newly formed rare-earth hydroxide wraps rare-earth fluoride around during alkali leaching,which prevents the conversion of rare-earth fluoride to rare-earth hydroxide.In terms of roasting with alkali additives,roasting with Na_(2)SiO_(3) can reduce the influence of CaF_(2) on rare-earth leaching,as the metasilicate and SiF_(6)^(2-) complex will be generated when acid leaching calcine by Na_(2)SiO_(3) roasting,and the formation of[SiF_(6)]^(2-) complex combines a large amount of F in CaF_(2),inhibits the dissociation of calcium fluoride by rare earth ions,and promotes the leaching of rare earth.In this solution system,the coexistence of CaF_(2) solids and Ca^(2+),SiF_(6)^(2-) with rare-earth ions reaches a new thermodynamic equilibrium.