由铬酸钾制备铬酸钠结晶分离过程研究

Preparation of sodium chromate from potassium chromate via crystallization process

以铬酸钾中间体为原料,系统地研究了采用结晶分离等常规手段制备铬酸钠产品的清洁制备方法。应用等温法分别测定了KNO3在Na2CrO4水溶液中和Na2CrO4在KNO3水溶液中的相平衡数据,绘制了溶解度曲线,确定采用先冷却结晶后蒸发结晶的方法制备铬酸钠晶体产品。考察了冷却结晶终点温度和物料配比,分析了分步蒸发结晶产品,确定了结晶最佳操作条件:K2CrO4与NaNO3的质量比在1∶(0.9～1.2),冷却结晶的终点温度控制在4℃。提出铬酸钾通过结晶方式转化为铬酸钠的整体工艺流程,并进行了全流程循环实验。采用重结晶法对铬酸钠产品进行精制,获得高纯度的铬酸钠晶体,质量分数由81.4%提高到92.2%,且粒径较大,粒度均匀。

To achieve the conversion of chromate products from potassium salts to sodium salts, the clean manufacturing process of sodium chromate was systematically investigated with potassium chromate as the raw materials. With isothermic method, the phase diagrams of potassium nitrate in aqueous sodium chromate solution and sodium chromate in aqueous potassium nitrate solution were plotted according to the experimental data. Through investigating the solubility of potassium nitrate and sodium chromate, the cooling crystallization and evaporating crystallization method of sodium chromate preparation was designed. The terminal temperature of cooling crystallization and material ratio were studied,and the sodium chromate crystals getting by stepwise evaporating crystallization were analyzed. The optimal operating conditions of crystallization process were determined, with the mass ratio of potassium chromate and sodium nitrate from 1 ： 0.9 to 1 ： 1.2, and the terminal temperature of cooling crystallization of 4℃. The integrated technology of the Na2CrO4 preparation from K2CrO4 through crystallization was proposed. The circulation process for Na2CrO4 preparation was studied. The good purity of sodium chromate products is obtained by recrystallization, which is increased from 81.4% to 92. 2%. The final sodium chromate crystal is uniform with larger size.