碳酸稀土的沉淀与结晶过程

PRECIPITATION AND CRYSTALLIZATION PROCESS OF RARE EARTH CARBONATE

连续测定了碳酸稀土的形成过程及其结晶过程中平衡溶液的ｐＨ值，发现碳酸稀土的结晶过程与溶液ｐＨ的下降有对应关系，其下降幅度和速度与结晶物料量和结晶速度相关，表明可根据ｐＨ值变化来评价碳酸稀土的结晶化特征。提出了确定碳酸稀土结晶活性及结晶区域的实验方法，根据它们的结晶活性可将碳酸稀土分为易结晶、可结晶和难结晶三大类；结果表明铈和钇在常温下均为易结晶的，只是铈的结晶活性区域在低摩尔比区域（［ＮＨ４ＨＣＯ３］／［Ｃｅ３＋］＝１．４～２．８），而钇在高摩尔比区域（４．５～６．０）。同时，还对碳酸氢铵沉淀稀土的一般反应和结晶过程的反应机理进行了探讨，提出了相应的反应方程式。

The pH values of equilibrium solution in which the rare earth carbonate is formed with ammonium bicarbonate as precipitant and aged were determined continuously. It was found that the crystallization process of rare earth carbonate is always related to a descent of solution pH value which is associated with the amount of rare earth carbonate crystallized, and the time needed for crystallization is the reflection of crystalline rate. These relations can be used for the crystallization process studying. Some experimental methods for characterizing crystalline activity and crystalline district of different rare earth carbonates were established. Based on their crystalline activity, rare earth carbonates may be divided into three categories: easy to crystallize, capable to crystallize and difficult to crystallize. Although cerium and yttrium carbonate are all easy to crystallize at room temperature, their crystalline districts are particularly different, which expressed with molar ratio of NH 4HCO 3 to rare earth ion are 1.4～2.8 for cerium and 4.5～6 for yttrium. At the same time, the general precipitation reaction of rare earth with ammonium bicarbonate and the crystallization mechanism of rare earth carbonate were discussed and the corresponding reaction equations were proposed.