热活化温度对拜耳法赤泥-水泥基复合砂浆的影响研究

Study on the effect of thermal activation temperature on Bayer method red mud-cement based composite mortar

为提高拜耳法赤泥在水泥基材料中的利用率,通过高温热活化改性了拜耳法赤泥的相组成和溶出碱能力,研究了不同温度热活化改性赤泥的掺入对赤泥-水泥复合砂浆力学强度、矿相组成和微观形貌的影响规律。研究结果表明:经500~800℃热活化处理后拜耳法赤泥中的钙霞石、方解石等矿物相分解,有助于促进游离碱Na^(+)的溶出,提高了浸出液pH至11.13~11.59。当掺入20%拜耳法赤泥的掺入量,随着拜耳法赤泥热活化温度的升高,复合砂浆的工作性能有所降低,28 d的抗压强度呈现先升高后降低的变化趋势。其中,掺入700℃热活化赤泥的复合砂浆试件的28 d抗压强度最高,可达46.5 MPa,与掺入未经热活化赤泥的复合砂浆相比提高了15.38%。这主要是因为赤泥中硬水铝石经高温热活化分解成了活性更高的无定型氧化铝,而且赤泥中碱性离子含量增加可以更好地激发浆体中活性矿物的水化反应,反应生成更多的AFt和C-S-H凝胶,使试件的微结构更加致密,更有利于后期力学强度的发展。

In order to improve the utilization of Bayer red mud in cementitious materials,it modified the phase composition and dissolved alkali capacity of Bayer red mud by high-temperature thermal activation,and investigated the effect law of incorporation of thermally activated modified red mud at different temperatures on the mechanical strength,mineral phase composition and microscopic morphology of red mud-cement composite mortar.The results showed that the decomposition of mineral phases such as calcium chalcocite and calcite in Bayer method red mud after thermal activation treatment from 500℃to 800 ℃ helped to promote the dissolution of free alkali Nat and increased the leachate pH from 11.13 to 11.59.When the admixture of 20%Bayer red mud was added,the working performance of the composite mortar decreased with the increase of the thermal activation temperature of Bayer red mud,and the 28 d compressive strength showed a trend of first increasing and then decreasing.Among them,the 28 d compressive strength of the composite mortar specimens mixed with 700℃thermally activated red mud was the highest,reaching 46.5 MPa,which increased by 15.38%compared with that of the composite mortar mixed with non-thermally activated red mud.It is mainly because the hard alumina in red mud is decomposed into more active amorphous alumina by high temperature thermal activation,and the increased alkaline ion content in red mud can better stimulate the hydration reaction of active minerals in the slurry,and the reaction generates more AFt and C-S-H gels,which makes the microstructure of the specimen more dense and more conducive to the development of mechanical strength at a later stage.