溶析结晶法脱除钛白废酸中硫酸亚铁盐的研究

摘要

针对钛白粉工业的废酸,选用乙醇(EtOH)为溶析剂,研究了溶析结晶法脱除钛白废酸中硫酸亚铁盐的可行性.在5~30℃,采用激光检测法系统地测定了七水硫酸亚铁在水、硫酸溶液和醇酸混合水溶液中的溶解度,考察了溶析剂浓度、温度、硫酸浓度等因素对硫酸亚铁盐溶解度的影响.在此基础上,以钛白废酸(含硫酸20%(wt)、七水硫酸亚铁8%(wt)为对象,在搅拌结晶器中考察了溶析剂加入量、加入方式、搅拌速度、晶种和熟化时间等工艺操作条件对硫酸亚铁脱除率的影响.结果表明,以乙醇为溶析剂,可在常温下显著降低硫酸亚铁在硫酸溶液中的溶解度.在醇酸混合水溶液中,硫酸亚铁盐的溶解度主要受溶析剂浓度影响,与硫酸浓度无关.控制适宜的搅拌速度、溶析剂加入速度和熟化时间有助于提高硫酸亚铁的脱除率.适宜的溶析结晶条件为:温度为 5~10℃,溶析剂与废酸的质量比 1:1,溶析剂加料速度6 mL?min?1、熟化时间60 min.在此条件下,七水硫酸亚铁的脱除率可达到87% ~91%.%The removal of ferrous sulfate heptahydrate from waste acids of titanium dioxide industry was investigated by using solventing-out crystallization with ethanol(EtOH)as the anti-solvent.The solubility of ferrous sulfate heptahydratein in water, sulfuric acid aqueous solution and ethanol-acid-water mixture at 5~30℃ was measured using a laser detection method. Effects of temperature, ethanol concentration and H2SO4 concentration on the solubility of ferrous sulfate heptahydrate were studied. Operation conditions of solventing-out crystallization, such as volume and addition method of EtOH, stirring speed,crystal seed and aging time were also studied in a stirring crystallizer. The results show that the solubility of ferrous sulfate heptahydrate in sulfuric acid aqueous solution is substantially reduced by adding ethanol as the anti-solvent at 5~30℃. In the ethanol-acid-water mixture, the solubility of ferrous sulfate is significantly dependent on the concentration of ethanol, but independent on the concentration of sulfuric acid. Suitable stirring speed, ethanol adding speed and aging time can help to improve the removal rate of ferrous sulfate. For the waste acid from titanium dioxide industry which contains 20%(wt) H2SO4 and 8%(wt) FeSO4.7H2O, the appropriate conditions of solventing-out crystallization were determined as follows: mass ratio of ethnol to waste acid is 1:1, temperature 5~10℃, adding rate of ethnol 6 mL?min?1 and aging time 60 min. The removal rate of ferrous sulfate heptahydrate can reach to 87%~ 91%.