氧化铝生产系统中有效碱的经济回收与利用研究

Study on Economic Recovery and Utilization of Effective Alkali in Alumina Production System

拜耳法生产氧化铝中,母液每次循环后,苛性碱损失,无效碱增多,导致蒸发排盐效率下降,能耗、碱耗增加。为了回收损失的苛性碱、减少无效碱,以国内高碳一水硬铝石氧化铝生产系统为例,设计蒸发排盐苛化、蒸发排盐苛化+赤泥脱碱及回收、蒸发排盐苛化+赤泥脱碱及回收+一洗液苛化三种工艺条件,研究生产工艺中Na_(2)O的流向,计算系统中有效碱的损失、转化和回收量。从技术及经济性方面,分析和对比了赤泥脱碱与一洗液苛化的特点。赤泥脱碱可脱除并回收赤泥钠硅渣中的Na_(2)O回到生产系统;一洗液苛化可将母液中的Na_(2)CO_(3)转化为NaOH,并降低系统碳碱含量。赤泥脱碱和一洗液苛化均可使氧化铝生产碱耗下降,节约生产成本。以某产能100_(t)/a的氧化铝厂为例,采用赤泥脱碱和一洗液苛化可使生产碱耗下降66~70_(k)g/t,节约氧化铝生产成本85~134元/t。

In the production of alumina by the Bayer process,after each cycle of the mother liquor,the caustic alkali is lost and the invalid alkali is increased,resulting in a decrease in the efficiency of evaporation and salt discharge,and an increase in energy consumption and alkali consumption.In order to recover the lost caustic alkali and reduce the invalid alkali,this paper took the domestic diaspore alumina production system with high carbon content as an example,and designed three process conditions:evaporation salt discharge causticization,evaporation salt discharge causticization+red mud dealkalization and recovery,evaporation salt discharge causticization+red mud dealkalization and recovery+first washing solution causticization.The flow direction of Na_(2O) in the production process was studied,and the loss,conversion and recovery of effective alkali in the system were calculated.From the technical and economic aspects,the characteristics of red mud alkali removal and causticization of primary lotion were analyzed and compared.The dealkalization of red mud can remove and recover the Na_(2O) in the sodium silicon slag of red mud and return it to the production system.The causticization of the first lotion can convert Na_2CO_(3) in the mother liquor into NaOH and reduce the carbon-alkali content of the system.Dealkalization of red mud and causticization of primary lotion can reduce the alkali consumption of alumina production and save production costs.Taking an alumina plant with a capacity of 100 t/a as an example,the alkali consumption of production can be reduced by 66~70 kg/t by using red mud alkali removal and causticization of primary washing liquid,and the production cost of alumina can be saved by 85~134 yuan/t.