以难处理广西高铁复合型铝土矿为研究对象，在明晰铝土矿中氧化铝的赋存形式基础上，第一步采用氢氧化钠溶液，对其中的氧化铝进行溶出。结果表明，该铝土矿的主要矿物成分是三水铝石、一水软铝石、铝针铁矿、赤铁矿以及锐钛矿、石英等。其中，氧化铁72.22wt%以铝针铁矿形式存在，27.78wt%以赤铁矿形式存在，在铝针铁矿中，铝对铁的取代率为24.5 mol/mol；氧化铝以三种形式存在，即三水铝石、一水软铝石和铝针铁矿，各占原矿的37.48wt%, 3.89wt%和42.46wt%。在低碱浓度(Na2O 100 g/L)、反应温度180℃、反应时间1 h条件下，高铁铝土矿中以三水铝石和一水软铝石形式存在的氧化铝可近完全溶出，但矿物中的铝针铁矿在此温和条件下难以转化，严重影响新工艺的经济性。为了解决铝针铁矿中铝铁分离问题，基于针铁矿在一定温度下可向赤铁矿转化的机理，采用低温焙烧的方法将铝针铁矿转化为赤铁矿和活性氧化铝，在450℃温度下将富铁相焙烧0.5 h。研究发现，在转化过程中，铝针铁矿中约57wt%的氧化铝被释放到赤铁矿晶格之外，实现了铝-铁的分离和相转化。第三步将转化之后的矿物再次在低碱浓度(Na2O 100 g/L)、反应温度220℃、反应时间1 h条件下溶出。被释放的氧化铝溶出后，三步法氧化铝的总溶出率可达到85.92%，且溶出后尾渣氧化铁含量达到83.06wt%以上，可用作炼铁原料。

Taking the unserviceable Guangxi high-iron composite bauxite as the research object, a new three-step process is developed based on clarifying the occurrence forms of alumina in bauxite, the results indicates that they are gibbsite, boehmite, Al-goethite, hematite, anatase, quartz and so on. Among these, iron oxides includes 72.22wt% exists in the form of Al-goethite and 27.78wt% exists in the form of hematite, and the substitution rate of aluminium for iron in Al-goethite is 24.5 mol/mol; Alumina in bauxite exists in three forms, namely gibbsite, boehmite and Al-goethite, each accounting for 37.48wt%, 3.89wt%, and 42.46wt% of the total alumina. Firstly, extract alumina in the forms of gibbsite and boehmite under conditions of Na2O 100 g/L, reaction temperature 180℃, and reaction time 1 hour, which can be easily and completely dissolved, while Al-goethite mineral is difficult to transform under this mild conditions, as seriously affects the economy of this new process. In order to solve the problem of alumina dissolution in Al-goethite, low-temperature roasting is adopted to transform Al-goethite into hematite and activated alumina in order to solve the problem of aluminium leaching from Al-goethite based on the thermal transformation mechanism from goethite to hematite at a certain temperature. By roasting this iron-rich phase for 0.5 h at a temperature of 450℃, about 57wt% of the alumina in Al-goethite is released outside the hematite lattice, thus aluminium-iron separation and phase transformation are achieved. In the third step, the transformed minerals are dissolved again under the conditions of low alkali concentration (Na2O 100 g/L), reaction temperature of 220℃, and reaction time of 1 h. Under these conditions, the activated alumina outside the hematite lattice is dissolved. The total dissolution rate of alumina in the three-step process reaches 85.92%, and the iron oxide in the mineral is greatly enriched in the tailings after dissolution, and its iron oxide content reaches 83.06wt%, which can be used as raw material for ironmaking.