CaF2强化红土镍矿自还原过程中金属相聚集长大行为

针对高镁高硅型中低品位红土镍矿,采用煤基自还原-细磨-磁选工艺制备镍铁粉,研究了内配碳比对红土镍矿中铁、镍氧化物自还原的影响,CaF_2对红土镍矿自还原过程中氧化物的还原、金属相的析出及聚集长大的影响规律。研究表明在CaF_2作用下通过降低内配碳比可抑制氧化铁的还原,从而获得镍品位较高的镍铁粉,但相应牺牲镍的回收率;CaF_2能与红土镍矿中高熔点的硅酸盐脉石通过固相反应生成低熔点的透闪石(Ca_2Mg_5(Si_4O_(11))_2F_2),使硅酸盐矿物结构由岛状转变为链状,提高硅酸盐矿物反应活性,促进镍、铁氧化物的还原;通过降低红土镍矿脉石相的熔化性温度,CaF_2能明显强化红土镍矿自还原过程中金属相的析出、聚集和长大,促进镍铁与脉石的有效分离,从而大幅度提高镍铁粉中镍和铁的品位及金属元素的回收率。

Promoting effects of CaF2 on the aggregation and growth of metal phases in self-reduction of laterite nickel ore

In view of low-grade laterite nickel ore including high magnesium and silicon, the process of coal-based self-reduction, grinding and magnetic separation is utilized to produce ferronickel powders. The effects of C/O atomic ratio on the self-reduction of iron oxides and nickel oxides are investigated, as well as the influences of CaF₂ on the reduction of oxides and the precipitation, aggregation and growth of metal phases in the self-reduction. The results show that under the action of CaF₂, the reduction of iron oxides can be suppressed by reducing the C/O atomic ratio to obtain ferronickel powders in high-grade nickel but the recovery rate of nickel will be decreased. The low melting point tremolite(Ca₂Mg₅(Si₄O₁₁)₂F₂) is generated from the solid-state reaction between CaF₂ and silicate gangue with high melting point, which can make the silicate minerals transform from island structure to chain structure, increase the reactivity of silicate minerals and then promote the reduction of nickel oxides and iron oxides. With the addition of CaF₂, the melting temperature of laterite nickel ore gangue can be decreased. In that case, the precipitation, aggregation and growth of metal phases can be strengthened in self-reduction and then the separation of metal and gangue can be promoted. Accordingly, the grade of nickel and iron in ferronickel powders and the recovery rate of metal elements are improved significantly.