Significant amount of mineral waste is generated by metal, construction, forest, energy industries, which remain largely without effective utilization around the globe. To protect the environment and to ensure sustainable growth, new production technologies are needed to utilize these wastes as a valuable resource. Alkali-activation (or geopolymerization) is becoming more widely accepted method to prepare low carbon dioxide (CO2) binder, other products and materials from several industrial mineral wastes.
One of the challenges in alkali activation is the low reactivity i.e. dissolution of the mineral wastes. Current approach is to use concentrated alkaline solutions, typically a mixture of sodium hydroxide and sodium silicate solutions, to improve the reactivity. However, alkaline solutions cause most of the environmental impact of alkali-activated materials (AAMs); they are user non-friendly due to the high alkalinity; they are the most expensive component of the mix; and cause efflorescence and instability of the binder and thus their use is not preferred.
The proposed project will tackle the problem of low reactivity of mineral wastes by developing and searching for chelating agents that will improve the solubility of the mineral components without the need for high concentrated aggressive alkaline media.
The effect of controlling the availability of dissolved species in the aqueous phase during the dissolution of minerals and gelation and hardening of AAMs cannot be underestimated. The hypotheses of the project are that by introducing chelating agents to AAM mixes they will: enhance the dissolution of mineral wastes; they will act as ion transport facilitators enabling the modification of binder gel formation; and they will increase the content of dissolved species in AAM mixes up to concentration that the mix will not freeze at below zero centigrade. Finally, they will enable the use of low concentration alkaline solutions as alkali activators.
The proposed project will result substantial new information about the chemistry related to dissolution mechanism of mineral wastes; chelating agents; gel formation of AAM binders; and the effect of chelates to mechanical properties of AAM binders. If the dissolution of minerals could be significantly increased, several currently underutilised industrial side streams could be used in alkali-activated materials. Due to high industrial relevance, the project is done in close collaboration with Saint-Gobain Finland Oy.
Keywords: Chelating agents, geopolymer, mineral wool, alkali-activated material