不锈钢渣老化和资源化过程中铬形态转化机理

It is clear that the leaching toxicity and valorization of stainless steel slag has been a hot issue for researcheres. At present, kinetic study on the solid phase oxydation of Cr(III) and carbonation of minerals in stainless steel slag at ambient temperature and pressure conditions is very little. No report is available about the effect of aging process on speciation transformation of chromoium in stainless steel slag. Whilst researcheres have a great dispute how the solidification of cementious slag affect on the leaching toxicity of chromium in it. In previous sequential leaching experments of stainless steel slag done by our research group, there is a certain amount of Cr(VI) with greater toxicity in the leachates. In this research, AOD and EAF slag were selected as the research objects. Correlation researches should be carried out with the method of thermodynamic simulation and lab experments, accoring to the process of natural aging, acidic rain leaching and preparation of construction materials as piling up and valorization of the stainless steel slag. The main objectives of this study are: 1) to explore the coupling effect of oxydization, carbonation and hydrolysis on the mineralogical compositon and speciation of chromium, 2) to illustrate the controlling mechanism of second-phase formation, dissolution, displacement and competitive adsorption on leaching concentration of chromium, 3) to reveal the internal impact of hydration, cementious reaction and physical sequestration on chromium leaching toxicity during waste valorization of the stainless steel slag. The research achievements not only enrich the intension with regard to metallurgical, minerallogical, electrochemical, and materialogical science about the stainless steel slag, but provide theoretical supports for valorizaiton of the stainless steel slag with typical toxic elements, which is of important academic signifance.

不锈钢渣淋溶毒性及其资源化是研究者关注的热点问题，然而常温常压下不锈钢渣的固相氧化和碳酸化动力学研究还很不充分，老化过程中铬形态转化的研究尚属空白，胶凝固化对铬淋溶毒性的影响规律还存在很大争议。申请者在前期研究中发现不锈钢渣连续淋溶液中含有毒性更强的Cr(VI)，因此本项目以AOD和EAF不锈钢渣为研究对象，以堆存和资源化涉及的自然老化、雨水淋溶和建筑材料制备过程为主线，采用热力学模拟和实验室实验相结合的研究方法，探索氧化、碳酸化和水解对不锈钢渣矿相及铬存在形态的耦合作用，明确二次相生成、溶解、取代、竞争性吸附等过程对铬淋溶的控制机理，揭示建筑材料制备过程中水化反应、胶凝反应及固化包裹作用对铬淋溶毒性的内在影响。研究成果不仅能够极大丰富不锈钢渣关于冶金学、矿物学、电化学和材料学等方面的科学内涵，相关理论研究的外延也为不锈钢渣再利用途径的探索提供重要理论支撑，具有重要的学术价值。

在分析了不锈钢渣中可碳酸化相的热力学基础上，采用薄膜和悬浆加速碳酸化法，研究了不锈钢渣的碳酸化机理；采用连续静态淋溶实验研究了碳酸化对不锈钢渣中铬淋溶特性的影响；采用长期动态淋溶实验，研究了研究了淋溶液pH值和淋溶气氛对AOD渣中铬淋溶特性的影响；采用标准方法测定了不锈钢渣的胶凝活性以及固化作用对渣中铬淋溶特性的影响；采用Factsage 7.0和HSC Chemistry 5.0热力学软件研究了氧化对不锈钢渣中铬赋存形态的影响。项目研究过程中，共培养博士生1名，硕士生5名，申请发明专利2项，已发表学术论文15篇，其中SCI索引7篇、EI索引1篇、中文核心3篇，科技核心1篇，会议论文3篇，并获得以下理论成果：.不锈钢渣中可碳酸化矿相被碳酸化的难易程度由易到难依次为：自由氧化钙>硅酸二钙>方镁石>镁铬尖晶石；碳酸化能降低不锈钢渣浸出液的pH值和电导率，而溶解氧则变化较小；经薄膜法碳酸化后AOD渣中铬的淋溶能力呈先降低后增加，经悬浆法碳酸化后EAF渣中铬的淋溶能力随碳酸化率的升高而升高；不锈钢渣经过长期动态淋溶后，淋溶残渣会有C-S-H胶凝相和碳酸钙等淋溶二次相生成，在淋溶过程中，Cr2O3控制着铬的淋溶；AOD渣具有一定的胶凝活性，满足用于水泥、混凝土中的第二等级钢渣的要求，随着AOD渣掺入量增加，复合胶凝材料达到标准稠度的需水量逐渐升高，初凝与终凝时间延长；AOD 渣整个水化过程中只出现一个放热峰，其前期水化分为三个阶段，随着 AOD 渣掺入量增加，复合胶凝材料水化过程逐渐呈复杂化，累积放热量逐渐降低；当AOD渣掺入量小于20%时，可以制备出满足42.5级强度要求的复合硅酸盐水泥；当AOD渣掺入量为30~40%时，可以制备出满足32.5级强度要求的复合硅酸盐水泥；静态连续淋溶实验表明，胶凝固化能降低铬的淋溶能力，随着养护时间的增加和AOD渣掺入量的减少，对铬的固化作用增强；不锈钢渣中的Cr2O3在纯氧中不能自发地发生氧化反应，但是在碱性环境中能被氧化为六价铬，不锈钢渣中富集铬元素的尖晶石相中FeCr2O4 最容易被氧化。