Modification of Iron-Tailings Concrete with Biochar and Basalt Fiber for Sustainability

Currently, less than 15% of waste iron tailings are utilized. Iron tailings can be used as fine aggregate in concrete, but this kind of concrete has no coarse aggregate, resulting in low strength. Additionally, iron tailings contain some heavy metals, which will cause environmental pollution if improperly treated. In this study, the mechanical properties, sulfate resistance, and pore structure distribution of basalt fiber-biochar-concrete (PFB) were studied. Where basalt is to enhance the mechanical properties of samples, and biochar is to adsorb heavy metals in iron tailings, to prepare environmentally friendly materials. Unconfined compressive strength (UCS) test, flexural strength (FS), sulfate immersion test, leaching behavior, and mercury intrusion porosimetry (MIP) test were used to study the performance of the samples, and X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), and scanning electron microscope (SEM) was used to characterize the samples, explaining the change mechanism of the macroscopic test. The results show that the compressive strength of PFB increased by 2.5% but the flexural strength increased by 12%. The basalt and biochar improve the pore size distribution of samples, that is, the pore size greater than 10 nm is reduced while the pore size between 2 and 6 nm is increased. Biochar can effectively adsorb heavy metals of Cu, Zn, Pb, and Cd, and their leaching concentration is reduced by 50–70%. Basalt fiber improves the mixing performance of concrete, while biochar with a small particle size fills the micro pores in concrete; this paper provides a new idea of sustainability for the preparation of environmentally friendly materials and the utilization of waste iron tailings.