Rheology and apparent activation energy of alkali activated phosphorous slag

This paper focused on determining the rheological behavior and apparent activation energy of activated phosphorous slag (AAPS) with sodium silicate and NaOH at different SiO2/Na2O (S/N) and Na2O/Al2O3 (N/A) molar ratios. The results showed that the AAPS paste behaved like a shear-thinning fluid, its rheological behavior obeyed the Herschel-Bulkley model, and its apparent viscosity decreased with increasing of shear rate. The chemical composition of activator affected the rheological properties and fluidity of AAPS paste but had no significant effect on shear thinning parameters. It was found that shear thinning behavior of AAPS paste was depend upon the changes done in the nature of phosphorous slag after activation process. It was observed that the initial rest time before increase of shear stress during the time was decreased as the S/N and N/A was increased due to increase in the slag dissolution rate and more gel formation. Increase in chemical composition of the activator also caused to accelerate the geopolymerization reactions and hence increased the shear stress. Apparent activation energy of AAPS paste based on Arrhenius viscosity model at temperatures of 10, 25, and 40 °C was measured in the range of 39.2–44.5 kJ/mol. It was found that lower silica content in the activator, i.e. decrease of S/N molar ratio, and higher alkaline content in the activator, i.e. increase of N/A molar ratio, result in decrease of the apparent activation energy. The accuracy of Arrhenius viscosity model was confirmed by determining the activation energy of OPC as the blank sample that was measured as 36.7 kJ/mol.