Hydration Activity and Carbonation Characteristics of Dicalcium Silicate in Steel Slag: A Review

Dicalcium silicate is one of the main mineral phases of steel slag. Ascribed to the characteristics of hydration and carbonation, the application of slag in cement production and carbon dioxide sequestration has been confirmed as feasible. In the current study, the precipitation process of the dicalcium silicate phase in steel slag was discussed. Meanwhile, the study put emphasis on the influence of different crystal forms of dicalcium silicate on the hydration activity and carbonation characteristics of steel slag. It indicates that most of the dicalcium silicate phase in steel slag is the γ phase with the weakest hydration activity. The hydration activity of γ-C2S is improved to a certain extent by means of mechanical, high temperature, and chemical activation. However, the carbonation activity of γ-C2S is about two times higher than that of β-C2S. Direct and indirect carbonation can effectively capture carbon dioxide. This paper also summarizes the research status of the application of steel slag in cement production and carbon dioxide sequestration. Further development of the potential of dicalcium silicate hydration activity and simplifying the carbonation process are important focuses for the future.

Effect of Gas Holdup on CO2 Biofixation by Spirulina sp. in the 20-liter Airlift Bioreactor

The rise of CO2 concentration in the Earth is a major environmental problem, which cause global warming. To solve this issue, several methods have been applied, but among these solutions using microalgae is an eco-friendly and cost-effective way of reducing carbon dioxide, as they can efficiently sequestrate CO2 and produce biomass as valuable products. In this study, hydrodynamic parameters, bubble sizes and carbon dioxide uptake were investigated in an airlift bioreactor. Experiments were studied at two different superficial gas velocities (0.185 and 0.524 cm/s) for Spirulina sp. microalgae into a 20-liter airlift bioreactor to find out the amount of carbon dioxide sequestration and cyanobacterial biomass. The highest efficiency of carbon dioxide removal and maximum dry weight of Spirulina sp. were achieved 55.48% and 0.86 g/L respectively at 5% CO2 (v/v) and superficial velocity of 0.185 cm/s. This experiment was conducted in 7 days, light intensity (2600 lux/m2), temperature (30\(\pm\)2 °C) and a light-dark cycle (12–12), which all were constant. The hydrodynamic parameters studied by Spirulina sp. demonstrated a capability of CO2 sequestration in this airlift photobioreactor.