液相TD对砂质高岭土清洁浸铁分离反应机制的研究

In general, the presence of iron impurities can decrease the whiteness of sandy kaoline. Sodium dithionite, the conventional reducing agent for kaoline purification, has some disadvantages such as easily yellowing, high toxicity and contaminating the environment. Thiourea dioxide (TD) is a new type of green and strong leaching agent, whose reducing products do not increase the value of COD and BOD. However, the strong reduction potential of TD can only be achieved under the conditions of high temperature (>70℃) and strong alkaline. Thus, it is of significance to conduct studies on the enhancement of the reduction potential of TD at ambient temperature and low alkaline conditions (pH＜9). The aim of this project is to generate nonbonding and substitution reactions for TD by using nucleophilic agents, to study the process and control mechanism of TD reduction and activation under mild conditions, and thus enhancing the leaching efficiency of various types of iron impurities from kaoline. The meanchism of TD on various types of iron impurities in kaoline is explored by the calculation and analysis of apparent activation energy and reaction order in the reactions of TD with iron impurities in kaoline. Overall, based on the study of liquid TD, TD activation and iron leaching, this project is expected to optimize the reaction systems of iron leaching by TD under mild conditions, and to establish the kinetics of reaction between liquid TD and iron impurites in kaoline, laying a theoretical foundation for the innovative technology of sandy kaolin refining.

砂质高岭土常因铁杂质致使白度下降。高岭土传统还原除杂浸离剂：连二亚硫酸钠，存在矿产品易返黄、药剂毒性和环境污染等弊端。TD（二氧化硫脲）作为一种绿色强力浸离剂，其产物不产生COD和BOD。但TD的强还原性受强碱性及加热（＞70℃）限制，需深入研究温和条件下（室温且pH＜9）促进TD还原活性的科学问题。本课题拟用亲核试剂促使TD发生断键取代反应，开展温和条件下TD的还原活化过程及控制的研究，提高TD对高岭土中不同含铁杂质的溶离速率。 通过对液相TD浸铁反应表观活化能与反应级数的计算分析，探索TD对高岭土中不同铁杂质的作用机制；从液态TD-TD活化-浸铁三方面，优化温和条件下TD浸铁分离的反应体系,确立液相TD对高岭土清洁浸铁分离的动力学反应机制，为砂质高岭土精制技术创新奠定理论基础。

砂质高岭土常因铁杂质致使白度下降。二氧化硫脲（CH4N2SO2简称TD）作为一种绿色新型浸离剂，其产物不产生COD和BOD值，因其在强碱加热条件下具有强还原性能而被广泛应用，在矿石精制方面具有良好的应用前景。.为了突破TD应用条件的局限性，本项目在常温（25℃-40℃）弱碱（pH≤8）条件下研究了亲核攻击、超声波辅助、机械活化或自制稀土单/双配体有机配合物催化促使TD发生断键反应，获得高活性TD溶液，还原电位可稳定在-750~-860 mV，促进了TD对高岭土中含铁杂质的溶解浸离。弱碱性条件下，TD以FSA分子的存在形式为主。弱碱溶液可提供足量的OH-来中和FSA活化分解时产生的H+，Ce3+对二氧化硫脲的催化活化效果在弱碱条件下达到最大。TD在酸性、中性和弱碱条件下的活化，除了主要依靠FSA分子与Ce3+配位降低活化所需的能量之外，TD碳硫键断裂的关键因素在于水分子对TD分子的作用。.研究表明，当TD用量为高岭土的0.2%、煅烧1200℃时，北海砂质高岭土的白度可由84.5%提升至88.3%；星子砂质高岭土的白度可由68.02%提升至77%左右。.TD漂白高岭土动力学过程是高岭土泥浆在加入TD后，TD或FSA分子吸附在高岭土颗粒表面。随后，TD或FSA分子受OH-攻击和（或）H2O分子作用活化，反应生成尿素和次硫酸盐（SO22-）,新生成的活性物质SO22-可近距离直接攻击矿物颗粒晶体表面的结构铁或层间的浸染铁溶出，Fe3+随后又被SO22-还原成Fe2+。高岭土通过洗涤除去粘附在颗粒表面的Fe2+后，即实现了除铁增白。通过对TD漂白高岭土的机理研究，有利于改善和优化TD漂白高岭土工艺控制，使得TD作用高岭土的漂白效果达到最大功效。