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

点击翻译按钮获取中文摘要

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.