Valorisation of red gypsum through understanding of structure-processing-property relationships across scales

当矿物相的水分含量很高时，矿物悬浮液的有效和一致的过滤可能会受到不良流变效应的阻碍。红石膏就是这样一种材料，它是用石灰石、石灰或两者的混合物中和二氧化钛制造过程中产生的废硫酸而制成的。由于处理困难和杂质含量高，红石膏的可持续利用率很低，每年有大量红石膏被浪费在垃圾填埋场。以前的工作主要集中在红石膏的元素和微观分析上，以提出潜在的用途，但对工艺条件、颗粒结构发展和最终性能[1]之间的关系了解较少。在这项工作中，将对工业红石膏样品进行表征，以研究颗粒形态以及杂质或附加相的存在、数量和状态。这些将与基于过滤和流变学的性能测量相关联，以确定不良行为的潜在来源。重要的是要了解红色石膏的脱水程度，这是避免触变性等行为所必需的，以及如何将这种水掺入矿物结构中使其难以过滤。特别是，在考虑水通过滤饼渗透时，应控制颗粒形状和大小分布以及杂质和附加相的存在，以避免在过滤介质中潜在地积聚较小的颗粒或杂质。在实验室规模上复制石膏结晶过程，增加过程控制，将允许在条件上进行孤立的变化，以确定特性和性能的差异，这是目前在工艺规模上不可能实现的一步。加深对红石膏结构特性的了解有助于提高这种潜在有价值的工艺副产品的利用率和减少浪费。

Effective and consistent filtration of mineral suspensions can be hindered by undesirable rheological effects when moisture content of the mineral phase/s is high. Red gypsum is such a material and is produced when waste sulfuric acid from titanium dioxide manufacture is neutralised with limestone, lime, or a combination of the two. Sustainable utilisation of red gypsum is low and significant volumes are wasted in landfill annually, due to handling difficulties and high levels of impurities. Previous work has focused on elemental and microscopic analysis of red gypsum to suggest potential uses, but there is less understanding of the relationships between the process conditions, structural development of particles, and the resulting performance [1]. In this work, samples of industrial red gypsum will be characterised to investigate particle morphology and the presence, quantity, and state of impurities or additional phases. These will be linked to performance measures based on filtration and rheology to identify potential sources of undesirable behaviour. It is important to understand the level of dewatering of red gypsum that is required to avoid behaviour such as thixotropy, and how the incorporation of this water into the mineral structures makes it difficult to filter. In particular, particle shape and size distributions should be controlled alongside the presence of impurities and additional phases when considering permeation of water through a filter cake, in order to avoid potential build-up of smaller particles or impurities at the filter medium. Replication of the gypsum crystallisation process at the lab scale with increased process control will allow isolated changes in conditions to identify resulting differences in characteristics and performance, a step that is currently not possible at the process scale. Developing an understanding that can lead to improvement in the structural characteristics of red gypsum can contribute to increased utilisation and a reduction in waste of this potentially valuable process by-product.