红土镍矿磷酸常压清洁提取新工艺的基础研究

Nickeliferous laterite is the main raw material to extract the nickel and cobalt. Atmospheric acid leaching is one of the promising approach, but it suffers low nickel recovery and low leaching selectivity of nickel/cobalt over iron and excessive Fe-containing waste generation. This project proposes the concept of intensifying selective leaching of nickel and cobalt, as well as production of iron phosphate from low-grade limonitic laterite using atmospheric leaching process with phosphoric acid. In view of the mineralogical characters of limonitic laterite ore, the thermodynamic and dynamic behaviors of various components in laterite during phosphoric acid leaching are investigated by using multi-disciplinary of principles and methods, including mineral processing, extractive metallurgy and material preparation, etc.. The mechanism for selective leaching with phosphoric acid is revealed, and the effects of leaching conditions on leaching and precipitation of valuable metals are investigated. Furthermore, the selective extraction behaviors of metals ions in lixivium is explored and the conditions for separation and purification of nickel and cobalt from phosphoric acid lixivium are optimized. Lastly, by exploring the optimum process and conditions of impurities removal from leaching residue, the principle flowsheet of battery grade iron phosphate production from the leaching residue is established. Based on above, the technology prototype of the cleaner processing of low-grade laterite via atmospheric phosphoric acid leaching is founded. Developing technology provides an efficient and cleaner method to process laterite, and it will contribute to healthy and sustainable development of nickel and cobalt industries.

红土镍矿是提取镍钴的主要矿物原料。红土镍矿常压酸浸工艺是一种极具应用前景的湿法冶金技术，但在处理低品位红土镍矿时存在镍浸出率低、镍/钴与铁浸出选择性差及酸性含铁尾渣产量大等问题。本项目以低品位褐铁矿型红土镍矿为研究对象，在深入分析红土镍矿矿物学特征基础上，提出基于磷酸常压选择性浸出提取镍、钴并同步制备磷酸铁的技术思想。项目综合运用矿物加工、提取冶金和材料制备等学科的原理与方法，研究红土镍矿中主要组分磷酸浸出过程的溶液化学基础和动力学行为，明确磷酸选择性浸出机制，揭示浸出制度对有价金属浸出及沉淀的影响规律；研究磷酸浸出液中金属离子的选择性萃取行为，揭示浸出液中镍、钴高效分离与提取条件；研究磷酸浸出渣中主要组分的溶解及分步沉淀行为规律，确立浸出渣制备电池级磷酸铁的原则流程。在此基础上，构建红土镍矿磷酸常压清洁提取技术原型，实现红土镍矿高效增值利用，为我国镍钴工业健康可持续发展做出贡献。

近年来国家大力推动新能源产业发展，动力电池行业的磷酸铁和氢氧化镍钴需求量均急剧增加。红土镍矿是提取镍钴的主要矿物原料，工业生产普遍采用高压硫酸浸出处理褐铁矿型红土镍矿。为实现镍/钴与铁选择性浸出，反应条件苛刻，浸出过程中产出大量酸性含铁废渣，污染环境。. 本项目依据磷酸根与不同金属离子间所形成的磷酸盐溶度积差异的特性，提出了红土镍矿磷酸浸出选择性提取镍钴并联产磷酸铁的技术思想。通过磷酸电离的H+与红土镍矿中金属氧化物的发生反应而使其溶出，H+实时浓度降低，促进磷酸电离；随着浸出不断进行，磷酸电离的PO43-及溶解的Fe3+浓度不断增加，促使Fe3+和PO43-反应生成磷酸铁沉淀，实现铁与镍/钴的选择性浸出；随着磷酸盐沉淀的生成，浸出液中实时PO43-、Fe3+浓度降低，又促进了磷酸电离和含铁矿物的溶解反应，从而实现红土镍矿中有价组分的高效浸出。. 采用预焙烧-磷酸常压浸出工艺，在400oC焙烧1h后，在磷酸浓度3mol/L，浸出温度90℃，浸出时间180min，液固比10mL/g，镍、钴浸出率分别为99.3%和90.9%，铁浸出率仅为3.3%；采用加压磷酸浸出工艺，在初始磷酸浓度3mol/L，浸出温度130℃，浸出时间2 h，液固比10ml/g的条件下，镍、钴浸出率分别为99.2%和81.8%，铁浸出率仅为0.5%，同步得到片层状铝掺杂磷酸铁产品，其纯度超过99%，(铁+铝)/磷摩尔比为1.0。. 对于所得磷酸浸出液，通过调节pH沉淀-P204萃取两段除杂后，采用P507从萃余液中分离镍钴，在优化条件下经三级萃取后钴的萃取率达到96.6%，镍萃取率仅12.3%。对于所得的铝掺杂磷酸铁，分别通过苛性碱溶解磷-除铝、盐酸溶解铁再通过均相沉淀法和水热法即可制备高纯磷酸铁产品。