低品位硼镁矿制备硼酸及回收硫酸镁的研究

采用硫酸法浸出低品位硼镁矿制备硼酸,并采用高温结晶的方法回收母液中的硫酸镁。结果表明:在适当搅拌条件下,硫酸用量为理论用量的85%,硫酸浓度控制在20%~25%之间、反应温度控制在95℃、酸浸时间为100min时,硼酸的浸出率较高,可达93.80%,硼酸收率达到71.06%。硫酸镁浓度控制在25%以上、结晶温度为180℃、结晶时间为4h,一水硫酸镁有较高的收率,可达到45.03%。析出一水硫酸镁后的二次母液含有少量的硼酸和硫酸镁,可代替水加入到矿粉中,整个过程形成闭合循环,无废液排放。

Preparation of Boric Acid from Low-grade Ascharite and Recovery of Magnesium Sulfate

Boric acid was prepared from low-grade ascharite by sulfuric acid method and monohydrate magnesium sulfate was recovered from mother liquor by high temperature crystallization method.The influence of amount of H2SO4,concentration of H2SO4,reaction temperature and reaction time on the leaching rate of boric acid were examined.The results show that under following conditions,namely,the amount of H2SO4 is 85% theoretical dosage,the concentration of H2SO4 is 20%～25%,reaction temperature is 95℃ and reaction time is 100minutes,the leaching rate of boric acid can reach 93.80%.Agitation is necessary to make the ascharite powder suspended.The recovery of boric acid reached to 71.06%.Monohydrate magnesium sulfate was obtained by high temperature crystallization method.The effects of mass fraction of magnesium sulfate,crystallization temperature and crystallization time on the recovery of monohydrate magnesium sulfate were investigated and the optimal crystallization conditions were established as follows:the mass fraction of magnesium sulfate is controlled at >25%,crystallization temperature is 180℃ and crystallization time is 4h.The recovery of monohydrate magnesium sulfate reached to 45.03%,the second mother liquor containing a little boric acid and magnesium sulfate was put into ascharite instead of water,the whole process is a closed circle without discharging waste liquid.