Phase transitions relating to the pozzolanic activity of electrolytic manganese residue during calcination

Electrolytic manganese residue (EMR) is generated from electrolytic manganese metal (EMM) industry, and its disposal is currently a serious problem in China. The EMR were calcined in the interval 100–900°C to enhance their pozzolanic activity and characterized by the differential thermal analysis-thermogravimetry (TGDTA), X-ray diffraction (XRD), infra-red (IR) and chemical analysis techniques with the aim to correlate phase transitions and structural features with the pozzolanic activity of calcined EMR. From the phase analysis and compressive strength results, it is found that the EMR calcined within 700–800°C had the best pozzolanic activity due to the decomposition of poorly-crystallized CaSO₄ under the reducing ambient created by the decomposition of (NH₄)₂SO₄. The appearance of reactive CaO mainly contributes to the good pozzolanic activity of EMR calcined within 700–800°C. The crystallinity of Mn₃O₄ increases leading an unfavourable effect on the pozzolanic behaviour of EMR calcined at 900°C. The developed pozzolanic material containing 30% (mass fraction) EMR possesses compressive strength properties at a level similar to 42.5# normal Portland cement, in the range of 41.5–50.5MPa. Besides, leaching results show that EMR blend cement pastes have excellent effect on the solidification of heavy metals.