Mechanochemical Activation On The Pozzolanic Activity Of Siliceous Tailings

Silica tailings are one of major mine tailings in China. The basic chemical compositions contain mainly SiO2 and Al2O3, which are similar with pozzolanic materials. There is potential pozzolanic activity that could react with alkaline compounds such as Ca(OH)2. In this paper, the study purpose is to improve pozzolanic activity of tailings by mechanochemical activation. The studies consist of effect of mechanical grinding and chemical activator on pozzolanic activity of tailings, application of tailings activated used in composite cement.Researches showed that the pozzolanic activity of tailings could increase with increase of the specific surface area by mechanical grinding.Compared with raw tailings whose specific surface area was 223.20m2/kg,the 28d activity index was 53.89%, when specific surface area was 495.10m2/kg during grinding for 5min, the 28d activity index was 65.65%.When the specific surface area was 849.40m2/kg, the 28d activity index reached 80.94%. When ratio of tailings and fly ash was 1:1, the specific surface area was 1169.80m/kg,the compressive strength of sample reached 50.25MPa in 28d, the 28d activity index was as high as 94.56%.That performances were higher than that of tailings whose specific surface area was 1161.70m2/kg, and the compressive strength of samples reached 37.61MPa in 28d, the 28d activity index was 73.78%. There are obvious differences in reinforced pozzolanic activity of tailings by chemical activator. CaO and CaCl2 could effectively improve the compressive strength of the cement in the early hydration process. While the appropriate amount of CaO was 2% and the specific surface area was 880.40m2/kg, the 3d compressive strength of the cement was 22.25MPa, and 28d activity index was 81.88%. The 3d compressive strength of the cement was 22.14MPa,and 28d activity index was 81.74%,while CaCl2 was about 1%and the specific surface area was 903.90m2/kg.By study for tailings used in composite cement, it found that the setting time decreased gradually with the increase of the specific surface area of tailings, but the water consumption of cement standard consistency increased. When the specific surface area was 840.30m2/kg, flexural strength and compressive strength of cement with 30% of tailings were 6.86MPa and 43.91MPa in 28d, and the setting time was 201min and 253min, the water consumption of cement standard consistency was 28.20%, stability qualified, which could meet the requirements of P·? 425.Tailings and fly ash were mixed by 1:1 in composite cement, specific surface area was up to 1175.50m2/kg, it could meet requirements of P·?425 in amount of 50%. Its properties were that the flexural and compressive strength of cement in 28d were 7.09MP and 43.77MPa, and the setting time was 237min and 311min, the water consumption of cement standard consistency was 29.80%, stability qualified.