拜耳法铝酸钠溶液中有机物的累积行为及氧化去除机制

Sodium aluminate solution is an important intermediate production in alumina industry, the accumulation of organic matter in it has seriously impacted the normal Bayer process. Moreover, being accumulated organic matters are very difficult to be removed from sodium aluminate solution. Therefore, it is significant to research the accumulating mechanism of organic matter in sodium aluminate solution and found the reasons of hard being removed so that the best organic matter removal method will be explorated in future. Based on this, different types of organic matters, such as humic acids, flotation reagents, small molecule matters and flocculants, were respectively tested to study the distribution proportions and the existing states of them in sodium aluminate solution by the cyclling process of high pressure digestion or sedimentation and separation of red mud. The reaction mechanism and the interaction rules of those organic matters in different conditions were deeply analysed to found the main reasons of causing accumulation and hard removal. In addition, the experiments were carried out to study different types of organic matters being removed easily or difficultly from sodium aluminate solution by H2O2 oxidation method, and the reaction mechanism were analysed. The results will provide a sound theoretical basis for removal organic matters from sodium aluminate solution by H2O2 oxidation method.

铝酸钠溶液是氧化铝生产过程中的重要中间产物，其在拜耳循环过程中逐渐累积的有机物严重影响着企业的正常生产，因此从机理上探索铝酸钠溶液中有机物累积的原因，指导寻求高效的拜耳法铝酸钠溶液中有机物去除方法有着重要的意义。本课题基于拜耳法铝酸钠溶液中有机物的累积及难以去除的技术难题，通过系统的研究腐殖酸类、浮选药剂类、小分子类和絮凝剂类有机物在高压溶出和赤泥沉降分离过程及拜耳循环过程进入铝酸钠溶液中的分布比例及其形态的转变规律，深入分析不同类型有机物在铝酸钠溶液中的反应机理及其相互作用规律，进而揭示造成其在铝酸钠溶液中累积及难以去除的主要原因；并针对逐渐累积的有机物研究其氧化去除的反应机制，重点研究H2O2对逐渐累积的不同形态有机物氧化去除的难易程度及其对晶种分解析出氢氧化铝过程及产品质量的影响，深入分析H2O2氧化去除有机物的反应机理，为氧化法去除铝酸钠溶液有机物的条件优化提供理论基础。

本项目针对拜耳法铝酸钠溶液中有机物的累积及难以去除的技术难题，以揭示其在铝酸钠溶液中累积及难以去除的主要原因为目的，围绕有机物在高压溶出过程的分布规律、存在形态、对赤泥沉降分离和铝酸钠溶液晶种分解的影响、对H2O2氧化去除的影响等问题开展拜耳法铝酸钠溶液中有机物的累积行为及氧化去除机制研究。揭示了氧化铝生产过程腐殖酸类有机物是造成铝酸钠溶液中总有机碳和草酸钠累积的重要来源，而絮凝剂和浮选剂对有机物累积的贡献较小。同时，发现这些类型的有机物在铝酸钠溶液分解时，对分解率的影响有相似的规律，即铝酸钠溶液中有较少量的这些类型有机物时，有利于提高晶种分解率，而这些类型有机物含量提高到一定程度后才会降低分解率，草酸钠比腐殖酸和絮凝剂更容易使结晶氢氧化铝颗粒细化，这一发现对指导实际生产有着重要的科学意义。铝酸钠溶液中的有机物经循环高压溶出后用H2O2氧化去除的难度增加，这也正印证了实际生产过程铝酸钠溶液中的有机物难以氧化去除的原因。H2O2氧化去除部分有机物后的铝酸钠溶液有利于提高晶种分解率，结晶过程中晶面平整，颗粒表面不易破损，有利于氢氧化铝晶体继续长大趋势。本项目的研究结果，为有机物氧化去除工艺方法提供理论依据，有着一定的工业应用前景。