铜渣/红土镍矿共还原过程Fe-Ni-Cu三元合金形成及晶粒生长机制研究

Due to the rapid development of the oceaneering, hydraulic engineering and rail transit, the demand of Cu-bearing steels are rigidly increasing. On the other hand, it is important to the comprehensively utilization of copper slag and laterite for the release of Fe, Ni and Cu. Hence, in this study, on the basis of our relevant research, an innovative technique was proposed to co-reduction of copper slag and nickel laterite to produce to Fe-Ni-Cu alloy replacing electrolytic copper and nickel. However, nickel laterite is characterized by high SiO2 and MgO and complex dissemination, resulting in the difficulty in formation of liquid phase and migration of alloy particle in reduction process. To address these concerns, a new process named co-reduction of copper slag and nickel laterite was proposed. Owing to good fusion performance of copper slag, it also bears the potential for acting as “flux” that may lead to a decrease of melting point of slag system, promote generation of liquid phase when co-reduction with nickel laterite and improve the alloy particle size. Meanwhile, the Fe-Ni-Cu ternary alloy concentrates was obtained as the feed for producing Cu-bearing steel. Focusing on the key points of the new process, phase transformation and formation rule of liquid phase will be systemically investigated, and internal connection between directional migration of valuable elements，effective regulation of particle size and formation of liquid phase will be expounded to reveal the mechanism of strengthening migration and beneficiation of valuable elements by co-reduction of copper slag and nickel laterite according to metallurgical chemistry, mineralogy and morphology of crystal growth. This research can provide new ideas and scientific support to the high-efficient utilization of copper slag and nickel laterite to preparation of Fe-Ni-Cu alloy powder.

含铜特殊钢在海洋工程、大型水利、轨道交通等领域需求迅猛增加。另一方面，大量铜渣和红土镍矿的高值化利用对缓解铜、镍资源短缺、应对日益增加的环保压力具有重大意义。为此，申请者在前期研究基础上，创造性地提出了以铜渣、红土镍矿为原料生产Fe-Ni-Cu合金粉替代电解铜、电解镍冶炼含铜特殊钢的思路。针对红土镍矿镁含量高且矿物嵌布微细，直接还原过程不易生成液相，镍铁晶粒难以长大，导致金属回收率低，而铜渣直接还原极易生成液相导致还原难度加大的问题，提出了铜渣/红土镍矿共还原-磁选新工艺，利用铜渣良好的高温还原熔融特性改善红土镍矿液相生成能力，重点研究：还原过程物相转变行为及表界面作用下微区液相的形成规律；Fe、Ni、Cu有价组元定向迁移、合金相形成及合金晶粒生长有效调控机制，以期为铜渣与红土镍矿高效利用提供新的理论依据，最终形成以铜渣、红土镍矿为原料生产Fe-Ni-Cu三元合金粉的技术原型。

高效利用低品位复杂铜、镍资源制备低成本含铜、镍铁合金料，对在一定程度上缓解我国铜、镍资源严重短缺的难题，降低特钢生产成本具有重要意义。本项目针对红土镍矿镁含量高且矿物嵌布微细，直接还原过程镍铁晶粒难以长大，导致金属回收率低，而铜渣直接还原极易生成液相导致还原难度加大的问题，提出了铜渣/红土镍矿共还原-磁选新思路，通过两者交互作用，调控体系液相形成，促进传质过程和晶粒生长。本项目重点研究铜渣/红土镍矿共还原过程液相形成机制，揭示了还原过程有价组元物相转变规律及迁移行为，阐明了三元合金晶粒生长特性，建立合金晶粒生长动力学模型。项目取得的主要研究进展及重要结果如下：（1）铜渣中FeO含量高，可与红土镍矿中高熔点镁橄榄石共同作用形成低熔点的钙铁辉石相，从而降低体系熔点，提高还原体系液相量。随着铜渣的增加，体系的软熔温度下降，液相量增加。（2）铜渣与红土镍矿共还原过程中，镍氧化物与铜矿物较铁氧化物更易还原，为制备出高镍、铜的三元合金粉，则需要控制还原气氛，实现选择性还原。铁氧化物、铜矿物和镍矿物的直接还原过程动力学机理均为随机成核和随后生长模型，反应活化能分别为91.49kJ/mol、69.40kJ/mol和51.55kJ/mol。（3）添加铜渣有利于体系液相的加速形成，改善原子传质过程，促进了三元合金晶粒的生长、聚集。含40%的铜渣共还原时，合金晶粒平均尺寸明显增加。在还原温度1100℃~1250℃，还原时间5min~100min，较单一红土镍矿还原，含40%铜渣的共还原球团合金晶粒生长常数提高10%左右，合金晶粒生长表观活化能降低40%左右。（4）建立了基于液相传质的Ni、Cu迁移动力学模型，传质扩散常数分别为4.02×10-11m2/s和1.06×10-9m2/s，活化能分别为120.37 kJ/mol和156.52 kJ/mol。项目共发表SCI论文9篇，获得国家发明专利授权5项，培养研究生5名。