Formation of Ta-rich magnetite phases in WEEE recycling slags through modification and controlled cooling

在过去的几十年里，电子设备的发展推动了诸如Ta， In, Te, Ga， Se和几种稀土元素（REE）等元素的消费，这些元素在技术圈中是稀缺的。在大多数情况下，这些战略元素的使用是ppm，因此，它们的回收率小于1%。如今，从废旧电气电子设备（WEEE）中提取这些原材料是过程冶金的一大挑战。它们通常存在于报废电子电气设备处理后的火法冶炼渣中，无法回收，因为它们的浓度较低，在传统技术条件下不适合进一步提取。除了稀缺性之外，天然资源还存在于欧洲边界之外，由于其技术重要性，被欧盟宣布为关键原材料（CRM）。有色冶金利用铁矾渣处理几种金属废料，如铅、铜和报废电子电气设备，因为它们的粘度低，熔点低，铁在渣中不动。在冷却过程中，铁矾石部分分解成磁铁矿和二氧化硅。磁铁矿与其他化合物具有反尖晶石结构，在特定条件下表现出磁性，可以使用磁选机回收。该项目旨在了解人工磁性矿物的形成和生长机制，以富集和选择性捕获CRM为重点，重点是WEEE中的钽。这种现象受工艺条件的影响很大，如液相温度、冷却速度、熔体中的氧分压以及炉渣中不同离子的氧化状态。这些不同的现象控制了铁尖晶石相的偏析和析出，并在此过程中捕获了几种有价元素。在温度依赖系统中，生成用于建模和设置热物理性质（如粘度和密度）的数据，提高了控制目标结构形成的可能性。

During the last decades, the evolution of electronic devices push up the consumption of elements like Ta, In, Te, Ga, Se, and several Rare Earth Elements (REE), having a scarce presence in the technosphere. In most cases, the use of these strategic elements is in ppm, and thus, their recovery rate is smaller than 1%. Today, extract these raw materials from Waste Electrical and Electronic Equipment (WEEE) is one of the big challenges of process metallurgy. Typically found in pyrometallurgical slags from WEEE treatment, they are not recovered as their low concentration makes them economically unsuitable for further extraction under the conventional state of the art. Besides their scarcity, natural sources are found outside European borders and, due to their technological importance, are declared as Critical Raw Materials (CRM) by the European Union.Nonferrous metallurgy utilises fayalitic slag to treat several metal scraps such as lead, copper and WEEE because of their low viscosity, melting point and iron immobilisation in the slag. During cooling, fayalite partially decomposes into magnetite and silica. Magnetite share is inverse spinel structure with other compounds that under specific conditions show a magnetic behaviour and can be recovered using magnetic separators. Several authors have reported these strategies to concentrate Fe, Ti and V.This project aims to understand the formation and growing mechanism of artificial magnetitic mineral to concentrate and selectively capture CRM, focusing on Tantalum from WEEE. This phenomenon is strongly affected by the process conditions such as liquidus temperature, cooling rates, oxygen partial pressure in the melt, as well as the oxidation state of different ions in the slag. These different phenomena control the segregation and precipitation of Fe inversed spinel phases from fayalite and capturing several valuable elements during this process. The generation of data for modelling and setting the thermo-physical properties such as viscosity and density in a temperature-dependent system improves the possibilities to achieve control over the formation of the targeted structures.