硼精矿加压碱解与结晶制备偏硼酸钠的动力学

对硼精矿在NaOH-H2O体系的分解制备偏硼酸钠的反应动力学进行了研究. 结果表明，实验条件下硼的溶出符合缩核模型，主要受表面化学反应控制，宏观动力学方程为1-(1-X)1/3=1.3712′102e-31640/(RT)t，活化能为31.64 kJ/mol. 升高温度或提高初始NaOH溶液浓度可强化硼的溶出. 经两级串联溶出的4次循环实验，在第一级温度140℃、初始NaOH浓度25%(w)、液固质量比4:1、时间2 h和搅拌速度500 r/min的条件下，第二级温度150℃、其他条件与第一级相同的条件下，各次溶出的硼转化率为86.84%~96.26%，第二级溶出液含硼达27.33~29.84 g/L，Si和Al等杂质维持低浓度. 90℃密闭保存陈化脱色的第二级溶出液自然降温至25℃，恒温搅拌结晶6 h (200 r/min)，2 h时基本达平衡，粗晶依次用无水乙醇和饱和偏硼酸钠溶液洗涤，40℃干燥12 h，制得截面呈平行四边形或六边形的NaB(OH)4，纯度约90%，结晶率大于70%.

Kinetics of Alkaline Leaching of Boron Concentrate and Crystallization of NaB(OH)4

Decomposition kinetics of boron concentrate in NaOH-H2O system was studied. The shrinking core model with surface chemical reaction control described the process reasonably well under the experimental conditions. Macrokinetic equation of leaching reaction of boron was 1-(1-X)1/3=1.3712′102e-31640/(RT)t with the activation energy of 31.64 kJ/mol. Increasing temperature or initial concentration of NaOH solution intensified the leaching of boron. The experimental results of two-stage leaching via four cycles indicated that under the conditions of 140℃, initial mass fraction of NaOH 25%, mass ratio of liquid to solid 4:1, reaction time 2 h and stirring speed 500 r/min in the first stage leaching while 150℃ in the second one with other conditions being the same as in the first stage, the conversion rate of boron reached 86.84%~96.26% in each leaching. The concentration of boron in the leachate from the second stage reached 27.33~29.84 g/L while the content of Si and Al kept low. The leachate from the second stage, hermetically preserved at 90℃ until faded, was naturally cooled to 25℃, crystallized isothermally for 6 h (stirring speed of 200 r/min) and nearly reached equilibrium after 2 h. Washed with anhydrous ethanol and saturated NaBO2 solution successively and dried for 12 h at 40℃, NaB(OH)4 was obtained, with the purity of almost 90%, crystallization rate of over 70% and sections of parallelogram or hexagon.