Alkali-activated materials : applications and the usage of sodium sulphate as an alternative alkali activator

Abstract

A large amount of sodium sulphate is accumulated every year as a by-product in industrial activities such as lithium-ion battery manufacturing, pulp production, and vanadium pentoxide recovery from spent catalysts. Although sodium sulphate's adverse health effects are relatively low, maintaining a commonly accepted sulphate limitation of 400 mg L-1 for sewer water is recommended. Therefore, the reuse of accumulated sodium sulphates is essential to enhance the circular economy.

Alkali-activated materials are a rapidly developing area of research where an aluminosilicate precursor such as blast furnace slag or metakaolin are activated using an alkali-activator to obtain a hardened solid material. Sodium sulphate has a significant potential to be used as an alternative alkali-activator instead of the commonly used activators such as sodium hydroxide or sodium silicates in alkali-activated material preparation. Careful monitoring of parameters such as the Si:Al ratio and calcium content of the aluminosilicate precursor, molarity of the alkali-activator, curing temperature, curing time, amount of water and the physical properties of the raw materials are essential in obtaining optimum characteristics of the materials. The prepared alkali-activated material with sufficient compressive strength has significant potential to be used as an alternative for Portland cement, adsorbent in water treatment and as a catalytic support material.

However, the preparation of alkali-activated material using sodium sulphate as the sole alkali-activator can be challenging given the lack of alkalinity that it produces. Additionally, challenges such as metal corrosion due to high salt content in such building materials and leaching of sulphates back into the environment are areas that needs to be addressed in future research work.

The focus of this thesis is to provide a detailed summary of the important aspects of alkali- activated material preparation, its applications, chemical and mechanical characterisation, and challenges through a comprehensive review of the literature covering alkali-activated material prepared using sodium sulphate and conventional activators.