Biomass waste as a clean reductant for iron recovery of iron tailings by magnetization roasting

The enrichment and transformation mechanism of Pb and Cu in suspension magnetization roasting and magnetic separation from iron tailings

Magnetic iron concentrate (MIC) and nonmagnetic tailings (NT) are obtained from magnetization roasting of iron tailings (IT). MIC containing Pb adversely affects blast furnace ironmaking, while Cu in NT poses leaching risks. This study utilizes fast pyrolysis-suspension magnetization roasting to recover iron from IT. The enrichment of Pb, Cu, and the phase transformation mechanism of Cu in the process of suspension magnetization roasting and magnetic separation were clarified. Results show 96.13 % of Cu in IT is in limonite and 47.23 % of Pb is associated with iron. At 750 °C, with 10 % dosage of biomass pyrolysis and 10 min roasting, Pb, Cu and Fe contents in MIC are 0.96, 2.14 and 3.17 times that of NT. Increasing roasting temperature enhances Cu associated with iron enrichment into the MIC, while oxidation of free copper oxide associated with iron forms magnetic copper ferrite. Increased pyrolyzed biomass leads to over-reduction of magnetite associated with Cu to FeO associated with Cu, promoting magnetic copper ferrite decomposition into FeO and free copper oxide. This research holds significant importance in controlling the quality of MIC and the storage risk of IT, and provides theoretical guidance for the regulation and recovery of valuable metals in subsequent processes.

Eco-friendly strategy for preparation of high-purity silica from high-silica IOTs using S-HGMS coupling with ultrasound-assisted fluorine-free acid leaching technology

Iron ore tailings (IOTs), a typical hazardous solid waste, seriously threaten human health and the ecological environment. However, the abundance of quartz, particularly in high-silica IOTs, renders them useful. Yet, state-of-the-art technologies have rarely reported the preparation of high-purity silica from high-silicon IOTs. Thus, this study proposed an eco-friendly technology for producing high-purity silica from high-silica IOTs through the coupling of superconducting high gradient magnetic separation (S-HGMS) preconcentration with leaching followed by the use of ultrasound-assisted fluorine-free acid solution. Following an analysis of the separation index and chemical composition, the optimum conditions for the quartz preconcentration were determined as a magnetic flow ratio of 0.068 T s/m, a slurry flow velocity of 500 mL/min, and a pulp concentration of 40 g/L. Consequently, the SiO₂ grade increased from 69.32% in the raw sample to 93.12% in quartz concentrate following the application of S-HGMS, with the recovery reaching 45.24%. X-ray diffraction, vibrating sample magnetometer, and scanning electron microscope analyses indicated that quartz was effectively preconcentrated from the tailings by S-HGMS. Subsequently, employing the "ultrasound-assisted fluorine-free acid leaching process," impurity elements were removed and high-purity silica was produced. Under optimal leaching conditions, the SiO₂ purity of silica sand increased to 97.42%. Following a three-stage acid leaching process with 4 mol/LHCl +2 mol/LH₂C₂O₄, the removal efficiency of Al, Ca, Fe, and Mg exceeded 97% for all cases, and the SiO₂ purity in high-purity silica reached 99.93%. Thus, this study proposes a new strategy for the preparation of high-purity quartz from IOTs, which facilitated the effective realization of the high-value utility of the tailings. Furthermore, it provides a theoretical basis for the industrial application of IOTs, which is of great scientific significance and practical application value.

Insights into direct reduction iron using bamboo biomass as a green and renewable reducer: Reduction behavior study and kinetics analysis

Biochar is a renewable, carbon-neutral energy source that can replace traditional fossil fuels for iron and steel production, so it is of great significance to reduce carbon emissions and reduce pollution. In this paper, the reaction characteristics and kinetics between biomass (bamboo powder) pyrolysis gas, biochar, and iron ore powder are studied by a thermogravimetric analyzer (TG). Comparing the samples with four different C/O ratios (C/O = 0.375, 0.5, 1, 3), it is found that the sample with C/O = 1 can completely reduce hematite. The mass loss process is divided into the following four stages: de-crystal water, hematite to magnetite, magnetite to wustite, and wustite to metallic iron. Among them, the latter three stages are following the kinetic model of random nucleation (n = 1, 2) and three-dimensional diffusion, and the activation energy of the three stages increases and then decreases. Through scanning electron microscopy (SEM), the surface of hematite particles changed from relatively flat to porous and finally the reduced metal iron aggregated, and connected into large pieces. By using online Thermogravimetry-Fourier Transform Infrared Reflection (TG-FTIR), when the reduction temperature is lower than 700 °C, biochar plays a leading role. On the contrary, the CO produced by biochar gasification plays a leading role.

Recovery of iron from iron tailings by suspension magnetization roasting with biomass-derived pyrolytic gas

A major industrial solid waste, iron tailings occupy a large area and pose long-term pollution risks. The pyrolysis gas of biomass was used as reducing agent to suspension magnetize and roast iron tailings to recover iron in this study. The process conditions, phase transformation and microstructure evolution of the iron tailings, pyrolysis gas production, and reaction regulations were investigated to explain the mechanism of iron recovery by suspension magnetization roasting (SMR) under the action of biomass pyrolysis gas. These studies were conducted using X-ray diffraction, scanning electron microscopy, vibrating sample magnetometer, thermo-gravimetric and differential scanning calorimetry, brunauer-emmett-teller specific surface area, and gas chromatography. The results showed that, after the grinding-magnetic separation process, the iron recovery rate was 93.32 %; the iron grade of the iron concentrate was 61.50 %. The optimal process conditions were determined as follows: fast pyrolysis temperature of 600 °C, SMR temperature of 700 °C, biomass dosage of 10 %, and SMR time of 4-5 min. The formation of Fe₃O₄ from the surface to the interior of the particles during the reduction process, and formation of pores and cracks led to an increase in the specific surface area. The SMR temperature not only improved the heat and mass transfer effect in the reduction process but also generated more CO and H₂ through the reverse reaction of methanation, which work together to increase the saturation magnetisation of the unit sample. This method can be used to efficiently recover high quality iron from refractory iron ores.