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 针对低环境影响（即低二氧化碳排放）的碱激发胶凝材料（或称地质聚合物，geopolymers）制备，学界已对多种富硅铝质材料开展了大量研究。若在制备地质聚合物砂浆与混凝土时，不仅用废弃物替代硅酸盐水泥，还以废弃物替代天然集料（砂、砾石），则可进一步提升其环境友好性。本文展示了以铁矿采矿尾矿制备地质聚合物的相关研究结果。所用地质聚合物基体由偏高岭土（MK）经硅酸钠+氢氧化钠溶液激发制得。研究中，以两种不同的铁矿石尾矿替代地质聚合物配方中的天然石英集料。测试评估的硬化性能包括抗压强度、吸水率、表观密度与孔隙率。此外，采用扫描电子显微镜（SEM）与X射线显微计算机断层扫描（µ-CT），分析了掺入尾矿后地质聚合物微观结构的变化。结果表明，使用铁矿石尾矿不会对地质聚合物的机械强度产生不利影响；但采用这类替代集料的地质聚合物可能具有更高的吸水率与孔隙率，因此仍需开展耐久性相关研究。