盐湖共存元素在水氯镁石热处理过程中的物理化学行为及其应用研究

A number of bischofite by-product is eagerly needed to develop newly comprehensive utilization in salt lake in Qinghai Province. On the other hand, the high cost and property of conventional sintered MgO at high temperature (1600℃) result in high cost of MPC, which is adverse for the popularization and application. The coexistent elements such as B, Li and K in salt lake remarkably affect the pyrolyzation-sintering process of bischofite and the performance of resultant MgO. The property of coexistent elements inspire that we want to study the prepared method of MPC by the low reactive MgO made from thermal decomposed bischofite and then sintered at low temperature (for example no more than 1200℃) in this proposal. The transfer rule of coexistent elements and the influence on sintering MgO are studied. The element composition of the resultant derived from pyrolyzation and sintering processes are analyzed, the transfer model of coexistent elements in the thermal processes of bischofite will be made as well as the transfer laws and influence factors will be understood. The phase composition and crystal structure of sintered MgO are resolved, and the mechanism of coexistent elements affected on MgO sintering at low temperature will be discovered. The hardening performances of MPC that derived from the sintered MgO are tested, and the hydration mechanism and durability will be clarified. In this research, the new idea for developing a promising utilization method for the larger number of bischofite in salt lake and simplifying a preparation technology and lowing cost of MPC will be presented. It offers the theoretical and technical support for the future utilization of bischofite and popularization of MPC.

盐湖资源开发副产大量的水氯镁石亟需综合利用；而传统高温（≥1600℃）烧结MgO的性能和成本导致其制备的磷酸镁水泥（MPC）难于推广应用。共存元素（如锂、钾和硼等）显著影响水氯镁石的热解和烧结过程及产物MgO的性能。本项目基于元素助烧结原理，拟将水氯镁石热解、低温（≤1200℃）烧结制备低活性MgO并用于制备MPC；研究其工艺条件、共存元素的迁移和对烧结的影响等物理化学行为以及MPC的基本性能。分析热解和烧结产物的元素组成，建立共存元素在水氯镁石热解和低温烧结过程中的迁移模型、明确迁移规律及影响因素；解析烧结产物的物相组成及结构，揭示共存元素影响MgO低温烧结的动力学机制及相互作用；测试MPC的凝结硬化性能，明确低温烧结MgO制备MPC的水化机理、强度发展规律及耐久性。本项目提出由水氯镁石低能耗、低成本制备MPC的新思路，为开拓水氯镁石高值化利用及促进MPC推广应用提供理论和技术支持。

盐湖资源开发副产大量的水氯镁石亟需综合利用；传统高温（≥1600℃）烧结MgO的高成本导致磷酸镁水泥（MPC）难于推广应用。盐湖常见共存元素因熔点低而影响MgO的烧结性能。本项目基于共存元素的助烧结原理，将盐湖水氯镁石脱水、热解、低温烧结（≤1200℃）制备低活性MgO，并进一步考察其制备MPC的可能性。分析热解及烧结产物中元素含量，研究共存元素在水氯镁石热解及其产物低温烧结过程中的迁移规律；测定烧结产物的烧结收缩率、中和反应时间、物相组成和形貌，研究共存元素种类和含量、烧结条件对氧化镁低温烧结的影响及助烧结机制；测定凝结时间、抗压强度、组成和结构、体积稳定性等，研究低温烧结氧化镁制备MPC的可能性。.研究表明，Li、Na、K、Ca和B对水氯镁石的起始热解温度影响不明显。热处理的时间和温度是共存元素在热解/烧结时迁移的主要影响因素，延长时间及提高温度均有利于共存元素迁移溢出；挥发性是影响金属元素及Cl在烧结时迁移的重要因素。氯化钠和氯化钾在烧结过程中较易溢出，提高烧结温度和延长烧结时间可促使氯化钙的迁移溢出。通过低温烧结可将水氯镁石热解烧结产物中的Cl含量降低至0.019%。B在低温易形成液相促进MgO烧结，Na/K和Cl共存时诱MgO的形貌改变，促进烧结。Si诱导烧结体系更易形成液相，促进MgO烧结。水氯镁石的低温烧结产物可以用于制备MPC。不掺缓凝剂时浆体的凝结时间长于30min；浆体硬化后强度较高，浸水60天未发现MgO二次水化引起开裂现象；MPC砂浆棒脱模后先收缩后膨胀。以管式炉为热解和烧结设备时，推荐水氯镁石热解-烧结制备低活性氧化镁的烧结温度为1100~1200℃，烧结时间为1~3h。本项目提出由水氯镁石热解低温烧结制备MPC的新思路，具有能耗低、成本低和简化MPC制备的优点，经济和环境效益明显，为开拓水氯镁石高值化利用及促进MPC推广应用提供理论和技术支持。