Repurposing of steel rolling sludge: Solvent-free preparation of α-Fe

Steel rolling sludge (SRS) is the by-product of metallurgical industry with abundant iron content, which needs to be utilized for producing high value-added products. Herein, cost-effective and highly adsorbent α-Fe2O3 nanoparticles were prepared from SRS via a novel solvent-free method and applied to treat As(III/V)-containing wastewater. The structure of the prepared nanoparticles was observed to be spherical with a small crystal size (12.58 nm) and high specific surface area (145.03 m2/g). The nucleation mechanism of α-Fe2O3 nanoparticles and the effect of crystal water were investigated. More importantly, compared with the traditional methods of preparation cost and yield, this study was found to have excellent economic benefits. The adsorption results indicated that the adsorbent could effectively remove arsenic over a wide pH range, and the optimal performance of nano adsorbent for As(III) and As(V) removal was observed at pH 4.0-9.0 and 2.0-4.0, respectively. The adsorption process was consistent with pseudo-second-order kinetic and Langmuir isothermal model. The maximum adsorption capacity (qm) of adsorbent for As(III) and As(V) was 75.67 mg/g and 56.07 mg/g, respectively. Furthermore, α-Fe2O3 nanoparticles exhibited great stability, and qm remained at 64.43 mg/g and 42.39 mg/g after five cycles. Particularly, the As(III) was removed by forming inner-sphere complexes with the adsorbent, and it partially oxidized to As(V) during this process. In contrast, the As(V) was removed by electrostatic adsorption and reaction with -OH on the adsorbent surface. Overall, resource utilization of SRS and the treatment of As(III)/(V)-containing wastewater in this study are in line with the current developments in the environmental and waste-to-value research.