铬酸钠溶液酸化过程研究

Acidification process of sodium chromate solution

基于离子平衡和溶液电中性原理,对Na2O-CrO42-/Cr2O72--SO42--H2O系中的铬酸钠溶液酸化过程进行理论计算。理论计算结果表明:铬酸钠转化率随溶液pH降低而呈"S"形增大,且增大铬酸钠浓度或降低溶液温度有利于铬酸钠的转化。在酸化纯铬酸钠溶液和工业铬酸钠溶液时,铬酸钠转化率的变化规律与理论计算结果一致,溶液pH从7.8降低至5.5时,转化率从大约10%显著增加至大约93%,此时加入的酸主要促进CrO42-转化为Cr2O72-,与红外光谱变化对应的是880cm-1处CrO42-的Cr=O弯曲振动的特征峰逐渐变小,在780 cm-1和930 cm-1处Cr2O72-对应的Cr=O弯曲振动的特征峰逐渐增强;转化率还随Na2SO4浓度的升高而增大,在pH≤2.5时,由于硫酸氢钠的大量生成,转化率测定结果大于100%。

The conversion rate of chromate in the system Na2O-CrO42？/Cr2O72？-SO42？-H2O was calculated theoretically based on the principle of ionic balance and electro-neutrality.The results show that the conversion rate increases in the form of ＂S＂ curve when the pH of the chromate solution decreases,and increasing the concentration of Na2CrO4 in the solution or decreasing the temperature of the solution favors the conversion rate of chromate.The experiment results indicate that the measured variation trend of the conversion rate is fairly in agreement with the calculation results in the acidifying pure or industrial sodium chromate solution.The conversion rate rises sharply from about 10% to about 93% with the solution pH decrease from 7.8 to 5.5 and CrO42？ transforms to Cr2O72？ in the acidification process,corresponding to the gradual decline in the strength of Cr=O blending vibration of CrO42？ at 880 cm？1 and the gradual increases in the strength of Cr=O blending vibration of Cr2O72？ at 780 cm？1 and 930 cm？1.In addition,the conversion rate rises along with the increase of concentrations of Na2SO4,and the formation of NaHSO4 at pH≤2.5 leads to the conversion rate higher than 100%.