Reusing electrolytic manganese residue as an activator: The effect of calcination on its mineralogy and activity

Abstract

Electrolytic manganese residue (EMR) is a potential activator for alkali and salts activated binders. However, the high contents of water and organic substances in EMR restricts its use. Calcination is one of the most practical pretreatment methods to improve the quality of EMR, but little is known about the proper calcination temperature. This study investigated the effects of calcination temperature on the mineralogy and activity of EMR. The results show that gypsum in EMR totally transforms to CaSO4·0.5H2O at 160℃. Then, CaSO4·0.5H2O continues to dehydrate, and most of it transforms to CaSO4 at 360℃. At higher calcination temperature, the CaSO4 phase seems unchanged. CaSO4·0.5H2O shows much higher solubility than CaSO4 in alkaline environment. As a result, the EMR calcined at 160℃ obtains the highest activity among all the calcined EMRs. Regarding the EMR activated slag, the binder containing 160℃-calcined EMR shows the highest main exothermic peak and compressive strength. However, calcination at 160℃ slightly increases the leaching concentration of Mn, but it can be totally stabilized in the alkaline environment.