ABSTRACT
The widespread use of geopolymer cement (GPC) has been hindered by a lack of scientific knowledge that still exists regarding its synthesis process. Key points, such as the release of aluminosilicate species from the raw materials and its link to the properties of GPC, have still not been completely studied. As a result, most of the GPC formulations covered in the literature are based on precursors' elemental analysis using XRF (X-ray Fluorescence), or other equivalent analysis methods, and consider that the total aluminosilicate content of the precursors is available for participating in the geopolymerization process, which seems very unlikely. In this study, the amounts of aluminate and silicate species released from metakaolin (MK), electric arc furnace slag (EAFS), and biomass fly ash (BFA) in alkaline dissolution tests were determined by simple spectrophotometric methods. It was found that MK yields the highest aluminosilicate dissolution amount, about 2.1 mmol of silicate + aluminate per gram of MK, while EAFS and BFA yield about 0.53 and 0.32 mmol/g precursor, respectively. These results were used to estimate the total amounts of dissolved aluminosilicates in a series of GPC mortars prepared from these raw materials, which were thereafter subjected to mechanical tests. It was shown that the mortars' compressive strength (which ranged from 1 to 63 MPa) is linearly correlated with their estimated total amount of dissolved aluminosilicates, with the best linear fit yielding a coefficient of determination above 0.99. It was concluded that by using the results of the dissolution tests, the estimation of compressive strength is greatly improved when compared to using the elemental analysis obtained by XRF, which yields a coefficient of determination of 0.88 and a larger dispersion of data points. The results reveal the usefulness of this simple method for evaluating the potential of inorganic industrial waste streams as precursors for GPC.
ABSTRACT
Water pollution poses a global threat to ecosystems and human health and is driven by the presence of various contaminants in wastewater, including nano- and microplastics. Despite the magnitude of this problem, the majority of global wastewater is released untreated into water bodies. To combat this issue, a multi-strategy approach is needed. This study explores a circular economy-based solution for treating emerging pollutants, particularly wastewater from ophthalmic spectacle lens production. Our approach integrates solid waste materials into polymeric and cement matrices while also utilising wastewater for microalgae cultivation. This innovative strategy focuses on biomass generation and economic valorisation. By adopting a circular economy model, we aim to transform environmental pollutants from wastewater into valuable organic products. A key component of our approach is the utilisation of microalgae, specifically Nannochloropsis sp., known for its high lipid content and resilience. This microalgae species serves as a promising biobased feedstock, supporting the production of innovative biobased products, such as biopolymers, for ophthalmic lens manufacturing. Our interdisciplinary approach combines microalgae technology, analytical chemistry, cement production, and polymer processing to develop a sustainable circular economy model that not only addresses environmental concerns, but also offers economic benefits. This study underscores the potential of harnessing high-value products from waste streams and underscores the importance of circular economy principles in tackling pollution and resource challenges.
