二次铝灰硫酸铵焙烧提铝过程氟的迁移规律

Fluoride migration in the aluminum extraction process of roasting secondary aluminum dross with ammonium sulfate

采用硫酸铵焙烧-水浸法回收二次铝灰中的铝是实现其无害化与资源化最重要的途径之一。二次铝灰的无害化与资源化利用要求尾渣氟的浸出毒性满足国标要求(无机氟化物质量浓度低于100 mg/L)。二次铝灰中氟的浸出毒性远高于100 mg/L,故需深入研究二次铝灰硫酸铵焙烧-水浸提铝过程氟的迁移规律。借助复合氟离子电极、XRD、XPS、SEM和XRF研究了二次铝灰硫酸铵焙烧-水浸提铝过程氟的迁移转化行为。结果表明,延长焙烧时间、提高焙烧温度、增大硫酸铵配比可促进二次铝灰中的氟进入焙烧尾气;延长浸出时间、提高浸出温度、增大液固比有利于降低浸出渣中氟的含量和占比。在焙烧温度450℃、焙烧时间2 h、物料配比6:1、浸出温度85℃、浸出时间80 min、液固比6:1条件下,二次铝灰中43.85%的氟以气态形式进入尾气,23.92%的氟进入浸出液中,32.23%的氟以AlF_(3)和AlF_(3)·3H_(2)O形式残留在浸出渣中。焙烧尾气经脱氟、喷淋吸收,可转化为硫酸铵;浸出液脱氟后可制备聚合硫酸铝,用作水处理剂;浸出渣的浸出毒性符合国家标准,可用作建筑材料,从而实现二次铝灰的资源化与无害化处理。

Recovery of aluminum from secondary aluminum dross by roasting with ammonium sulfate and leaching with water is one of the most important methods to harmlessly utilizing secondary aluminum dross.However,fluoride leaching toxicity of the leaching residue should satisfy the national standard's prescription(the mass concentration of inorganic fluoride is less than 100 mg/L).Thus,it is necessary to study the F migration in the Al extraction process of roasting secondary aluminum dross with ammonium sulfate and leaching with water.In this work,the regularities about migration and transformation of F in the process of extracting Al from secondary aluminum dross via roasting with ammonium sulfate and leaching with water was investigated by fluoride ion electrode,XRD,XPS,SEM and XRF.The results showed that prolonging the roasting time,elevating the roasting temperature and increasing the mass ratio of ammonium sulfate to secondary aluminum dross could accelerate the migration of F from secondary aluminum dross to roasting offgas.Additionally,extending the leaching time,increasing the leaching temperature and increasing the liquid-to-solid ratio was beneficial to reduce the content and proportion of F in the leaching residue.About 43.85%of F released from secondary aluminum dross to roasting off-gas in the form of gas,23.92%of F went into the leaching solution as fluorine ion,and 32.23%of F remained in the leaching residue in the forms of AlF_(3) and AlF_(3)·3H_(2)O under the most suitable conditions with the roasting temperature of 450℃,the roasting time of 2 h,the mass ratio of ammonium sulfate to secondary aluminum dross of 6:1,the leaching temperature of 85℃,the leaching time of 80 min,and the liquid-to-solid ratio of 6:1.Ammonium sulfate could be recovered from roasting off-gas by spraying after defluorination.Moreover,polyaluminum sulfate as a water treatment agent could be prepared from the leaching solution with the removal of F.The leaching toxicity of the leaching residue was accorded with the national standard.