A calorimetric study of hydration of magnesia-ferriferous slag mechanically activated in air and in CO.sub.2 atmosphere

Hydration behavior of mechanically activated magnesia-ferriferous slag has been investigated by isothermal calorimetry. The slag is a waste of pyrometallurgical processing of Cu-Ni ores. Hydration activity of the slag is low in comparison to that of blast furnace slag. It has been shown that mechanical activation of the magnesia-ferriferous slag in CO.sub.2 atmosphere considerably increases its hydration activity. In the course of milling in planetary mill in CO.sub.2, the slag absorbs carbon dioxide molecules in the form of carbonate ions not only on the surface, but also in the bulk of the slag particles. This accelerates dissolution of the slag in water and the consequent formation of hydration reaction products. As a result, the slag is hardened at ambient temperature without addition of alkali agents or other chemical activators. Calorimetric measurements show that for the slag milled in CO.sub.2 the acceleration period comes without the induction period immediately following the initial exothermal peak. For the slag milled in air, the induction period lasts for about 20 days. Milling of the slag in CO.sub.2 results in higher intensity of the main heat evolution rate peak and larger cumulative hydration heat as compared to those for the slag milled in air. The compressive strength of the slag milled in CO.sub.2 is 12-14 MPa after the main hydration stage, whereas that of the slag milled in air is only about 1 MPa. This can be explained by the mechanically induced carbonization of the slag resulting in its higher reactivity and faster hydration relative to those for the slag milled in air.