赤泥磷酸浸出选择性脱硅

Selective Removal of Silica in Bauxite Residue by Leaching with Phosphoric Acid

赤泥是铝土矿生产氧化铝过程中产生的固体残渣,也是一种低品位含铝资源,但因其SiO_(2)含量高、铝硅比低,难以直接通过碱浸回收Al_(2)O_(3)。以赤泥钠化还原焙烧—磁选后所得非磁性物为原料,磷酸为浸出剂,实现了硅的选择性浸出及铝、硅之间的有效分离,为后续氧化铝的提取创造了有利条件。在磷酸浓度1 mol L、液固比15 mL g、浸出温度50℃、浸出时间60 min的条件下,SiO_(2)的浸出率达82%,浸出渣铝硅比为4.4,较非磁性物提高了2倍左右,实现了铝、硅之间的较好分离。磷酸浸出渣再碱浸,采取35%NaOH溶液,浸出温度260℃,Al_(2)O_(3)的浸出率从未脱硅前的69%增大至93%。磷酸选择性浸出非磁性物中硅的原因是铝硅酸盐矿物中含硅组分溶解在酸溶液中,而含铝组分与磷酸反应转变成了AlPO_(4)不溶性沉淀。

Bauxite residue is the solid waste generated in the alumina production process from bauxite ores,and it is also a low-grade alumina resource.Alumina is difficult to be directly extracted through alkali digestion process due to the high content of silica and low alumina-to-silica ratio.Phosphoric acid was introduced in this study to achieve the selective dissolution of silica and separation of alumina against silica in the non-magnetic material derived from reductive roasting and magnetic separation process of bauxite residue.Under the optimum conditions including phosphoric acid concentration of 1.0 mol L,liquid to solid ratio of 15 mL g,leaching temperature of 50℃,and leaching time of 60 min,the leaching rate of silica is approximately 82%,and the alumina-to-silica ratio of the leached residue is 4.4,enriched about 2 times compared with the non-magnetic material.Subsequently the acidic leached residue was further subject to alkali digestion process with NaOH solution at 35%at leaching temperature of 260℃.The leaching ratio of Al_(2)O_(3)is 93%,which is only 69%in the non-magnetic material before desiliconization.The selective separation of silica in non-magnetic material through phosphoric acid leaching process is owing to the dissolution of silica in aluminosilicate minerals in the acid solution whereas the aluminum-contained components is transformed into the insoluble AlPO_(4)precipitate after reacting with phosphoric acid.