碱激发-碳养护对铜尾矿固化砖的作用机理研究

以细粒级铜尾矿作为主要原材料,水玻璃为激发剂,辅以少量水泥和粉煤灰,通过碱激发反应、压制成型及碳养护制备铜尾矿固化砖。采用X射线衍射、热重-差示扫描量热法、压汞法和扫描电子显微镜-能谱仪等对试样的物相组成、碳化产物、孔隙分布和微观产物形貌进行分析,探讨碱激发-碳养护对铜尾矿固化砖性能提升的影响规律。结果表明,水玻璃可以激发铜尾矿的部分胶凝活性,生成更多絮凝状C-S-H凝胶,改善铜尾矿固化砖的微观孔结构进而提升其抗压强度。碳养护的时机选择至关重要,固化砖成型后立即进行碳养护,碳化反应会与碱激发反应竞争OH^-,生成文石型和方解石型CaCO₃,导致C-S-H凝胶的生成量减少,孔隙率增大,抗压强度降低。固化砖密封养护84 h后再碳养护84 h,其7 d抗压强度可提高20.9%,碳化产物CaCO₃填充内部孔隙,有害孔和多害孔数量大幅减少,无害孔数量增加,整体结构密实程度提高,从而解决铜尾矿固化砖表面泛霜的问题。

Mechanism of Copper Tailings Cured Bricks by Alkali Activation-Carbonated Conservation

By alkali activation reaction, compression moulding and carbonated conservation, copper tailings cured bricks were prepared using fine-grained copper tailings as main raw material, sodium silicate as activator, with a small amount of cement and fly ash. The phase composition, carbonized products, pore distribution and microscopic morphology of different samples were analyzed by X-ray diffraction (XRD), thermogravimetric-differential scanning calorimetry (TG-DSC), mercury intrusion porosimeter (MIP) and scanning electron microscope-energy dispersive spectrometer (SEM-EDS). Then, the synergistic mechanisms of alkali activation-carbonated conservation on the performance improvement of copper tailings cured bricks were discussed. The results show that sodium silicate can stimulate part of the gelling activity of copper tailings, and generate flocculated calcium silicate hydrate (C-S-H) gels to improve the microscopic pore structure and the compressive strength of the cured bricks. Timing of carbonated conservation is critical. If the cured brick is carbonated conservation immediately after forming, the carbonization reaction will compete with the alkali activation reaction for OH^- to generate aragonite-type and calcite-type CaCO₃, resulting in the reduction of C-S-H gel generation, and then causing increasing porosity, and compressive strength reduction. When the cured brick is cured for 84 h in airtight condition and then carbonated cured for 84 h, the 7 d compressive strength would increase by 20.9%, and the internal pores are filled with the carbonized product CaCO₃, in which the volume of harmful pores and multi-harm pores greatly reduce and the number of harmless pores increases, thus improving the overall structure density, there by solving the problem of efflorescence on the surface of the copper tailings cured brick.