铁酸锌还原磁化分解过程基础理论研究

Zinc ferrite, which is very difficult to be leached out with low concentration sulphuric acid, is widely distributed in zinc concentrate boiling calcine and steel mills dust. Thus, the processes of leaching materials under high temperature and high concentration acid have to be adopted in industry. Although this kind of process resulted in high leaching rate of zinc, iron also entered the solution together with zinc, which making it difficult to recover iron resources. Complex process also has to be used to remove Fe, and amount of slags which are prohibited to stockpile by the state is also produced. All of these restrict sustainable development of zinc industry. Zinc ferrite could be decomposed into ZnO and Fe3O4 with reduction-magnetizing roasting process, and other iron species are magnetized at the same time. Then using low concentration acid leaching on the above product, high leaching rate of zinc could be guaranteed and iron not be leached. Iron in leaching residue can be recovered by magnetic separation, and the accompanying valuable metals such as lead, silver and so on can be recovered from the tailings of magnetic separation. That is to say all the contents of resources could be utilized with this technology. The key of this technology is efficient decomposition of ZnFe2O4 and precise control of roasting product. Basic theoretical study on the decomposition of ZnFe2O4, would be carried out based on thermodynamics, kinetics, crystal structure of ZnFe2O4, molecular dynamics, technological conditions testing, process mineralogy and so on, in order to resolve several technical problems such as efficient decomposition of ZnFe2O4, redundant iron reduction inhibition, particle size growth of Fe3O4 and so on. This research will provide theoretic basis for magnetized roasting system and selection of magnetic separation process.

锌精矿沸腾焙砂和钢厂尘泥中含有大量铁酸锌，铁酸锌系低酸难浸出物种，工业上不得不采用高温高酸浸出高铁酸锌物料，在获得高锌浸出率的同时铁也大量进入溶液，导致铁资源无法回收，除铁过程工艺复杂，并产出国家禁止堆存的除铁渣，制约锌行业可持续发展。采用还原磁化焙烧可将铁酸锌分解为氧化锌和四氧化三铁，同时将物料中其他含铁物种一同磁化，采用低酸浸出即可保证高的锌浸出率且铁不被浸出，对浸出渣进行磁选可回收其中的铁，从磁选尾矿中回收伴生的铅银等有价金属，实现资源全量利用。该技术的关键是铁酸锌的高效分解及焙烧产物的精准调控，本研究从分解过程热力学、分解动力学和分解历程及机理、铁酸锌晶体结构及分解过程分子动力学、分解工艺条件和工艺矿物学等方面对铁酸锌分解基础理论作深入研究，解决铁酸锌高效分解、铁过还原抑制和焙烧产物四氧化三铁粒径长大等关键技术环节涉及的科学问题，为磁化焙烧工艺制度和磁选工艺方案选择提供理论指导。

本课题针对含铁酸锌冶炼物料处理难的问题，提出了“磁化焙烧-低酸浸出-磁选”或“磁化焙烧-磁选-低酸浸出”新技术路线，即将该类物料中的铁酸锌选择性的分解为氧化锌和四氧化三铁，再通过弱酸浸出和磁选工艺进行锌铁分离，实现铁、锌及其他有价金属的高效利用。重点研究了铁酸锌还原性磁化分解基础理论和铁锌高效分离关键技术问题。在热力学计算的基础上，首先采用TG/DTG技术研究了铁酸锌的分解行为，结果表明CO能将铁酸锌选择性转化为氧化锌和四氧化三铁，且铁酸锌的过还原较难控制；提高温度、增加CO分压或降低CO2分压，既有利于铁酸锌的分解，又能促进铁酸锌的过还原；还原气氛气中配入一定比例的CO2能有效抑制铁酸锌的过还原。然后采用XRD、XPS、SEM-EDS和激光粒度分析仪等技术，研究了铁酸锌微观结构演变规律、物相转化行为及四氧化三铁晶型调控机制，结果表明铁酸锌选择性还原反应表现为失氧过程，还原产生的Fe2+使铁酸锌分解产生氧化锌，氧化锌 含量与Fe2+含量线性相关。Fe2+向铁酸锌内部迁移替代Zn2+，Zn2+则向外部迁移并富集于表面，促使 氧化锌 在表面形成。铁酸锌逐步向磁铁矿转变，Fe2+的嵌入和锌的迁出使铁酸锌晶胞参数先增大后减小，还原产物为氧化锌和含锌的磁铁矿。尽管形成的四氧化三铁晶型较好，但是由于固态反应原子迁移速度慢的限制，导致四氧化三铁晶粒生长缓慢，形成的四氧化三铁单体粒度较小。最后系统的研究了高铁锌焙砂的磁化焙烧、低酸浸出及弱磁选工艺及相应过程矿物学特征变化，获得了最佳工艺参数和相应产物的矿物学特征。CO磁化焙烧的最佳条件为温度750℃、CO浓度8%、CO/(CO+CO2)为10~20%和焙烧时间60min。磁化焙砂再经一段中性浸出和一段低酸浸出工艺，可实现锌浸出率高达90%、铁浸出率小于5%的最佳指标。浸出渣经一粗一精弱磁选作业，可得铁品位为53.24%的铁精矿，同时铁回收率达84.34%。此外，试验结果表明工业煤气可以取代CO进行该磁化焙烧试验。