Reuse of iron ore tailings in the production of geopolymer mortars

Abstract A great variety of silica and alumina-rich materials have been investigated in the production of alkaline activated binders (or geopolymers) with low environment impact, e.g. low CO2 emissions. Geopolymer mortars and concretes may be more environmentally friendly if not only Portland cement but also natural aggregates (sand, gravel) are replaced with waste materials. This article presents results of geopolymers made with tailings from the iron mining industry. The geopolymer matrices are composed of metakaolin (MK) activated with a sodium silicate + sodium hydroxide solution. Two different iron ore tailings replaced a natural quartz aggregate in the geopolymers’ formulation. The hardened properties assessed were compressive strength, water absorption, apparent density and porosity. Scanning electron microscopy (SEM) and x-ray micro computed tomography (µ-CT) were used to assess the changes in the microstructure when the tailings were incorporated into the geopolymers. Results show that the employment of iron ore tailings is not detrimental to the mechanical strength of geopolymers; however, geopolymers containing those alternative aggregates may present higher water absorption and porosity, and durability studies are required.摘要：为制备低环境影响（即低二氧化碳排放）的碱激发胶凝材料（又称地质聚合物），学界已针对多种富硅铝材料开展了广泛研究。若不仅以废弃材料替代波特兰水泥，还替代天然集料（砂、砾石），地质聚合物砂浆与混凝土将具备更优异的环境友好性。本文报道了以铁矿选矿尾矿制备地质聚合物的相关研究成果。该地质聚合物基体由偏高岭土（metakaolin，MK）经硅酸钠与氢氧化钠混合溶液激发制得。研究中采用两种不同的铁矿尾矿，替代地质聚合物配方中的天然石英集料。本次研究评估的硬化性能包括抗压强度、吸水率、表观密度与孔隙率。借助扫描电子显微镜（scanning electron microscopy，SEM）及X射线显微计算机断层扫描（x-ray micro computed tomography，µ-CT），分析了掺入尾矿后地质聚合物微观结构的变化情况。研究结果表明，使用铁矿尾矿并不会损害地质聚合物的力学强度；但采用这类替代集料的地质聚合物可能具备更高的吸水率与孔隙率，因此需开展相关耐久性研究。