Arsenic adsorption by different Fe-enriched biochars conditioned with sulfuric acid

Highly efficient removal of aqueous phosphate via iron-manganese fabricated biochar: Performance and mechanism

Biochar (BC) has emerged as a potential solution to phosphate removal from wastewater primarily resulting from global overuse of fertilizers. Further modification by embedment of iron (Fe)-manganese (Mn) oxides on BC can enhance phosphate removal; however, the modification method serves as a vital factor underlying distinctive removal performances and mechanisms, which have yet been systematically examined. Herein, two Fe-Mn modified BC, Fe/MnBC (comprised of Fe3O4 and MnO2) and Fe-MnBC (comprised of MnFe2O4), were comprehensively investigated for gaining insights into the unsolved perspectives. The results indicated that Fe-MnBC exhibited a markedly greater maximum phosphate adsorption capacity of 135.88 mg g-1 than that of Fe/MnBC with 17.93 mg g-1. The comparative results based on microstructure and spectroscopic analyses suggested that different Fe and Mn oxides were successfully loaded, which played a distinctive role in phosphate removal. Further characterizations unveiled that the key mechanisms for phosphate removal by Fe/MnBC are inner-sphere complexation and precipitation, while electrostatic interaction and outer-sphere complexation are the dominant mechanisms underlying the notable performance of Fe-MnBC. The delicately designed Fe-MnBC with special structure and property also enabled a superior regeneration capacity, which presented a promisingly high phosphate removal efficacy of over 81.34% after five cycles. These results enhance comprehension regarding the impact of biochar modification techniques on phosphate removal, offering positive indications for the remediation of excessive phosphate and other pollutant-containing water through feasible design and green chemicals.

Removal of Fe(III)/Al(III)/Mg(II) by phosphonic group functionalized resin in wet-process phosphoric acid: Mechanism and intrinsic selectivity

The removal of iron ions (Fe(III)), aluminum ions (Al(III)), and magnesium ions (Mg(II)) in phosphoric acid (H₃PO₄) solution is vital for the production of H₃PO₄ and supply of phosphate fertilizer. However, the mechanism and intrinsic selectivity for removal of Fe(III), Al(III), and Mg(II) from wet-process phosphoric acid (WPA) by phosphonic group (-PO₃H₂) functionalized MTS9500 are still unclear. In this work, the removal mechanisms were determined via combined analysis of FT-IR, XPS, molecular dynamics (MD), and quantum chemistry (QC) simulations based on density functional theory (DFT). The metal-removal kinetics and isotherms were further studied to confirm the removal mechanisms. The results indicate that Fe(III), Al(III), and Mg(II) interact with the -PO₃H₂ functional groups in MTS9500 resin with sorption energies of -126.22 kJ·mol^-1, -42.82 kJ·mol^-1, and -12.94 kJ·mol^-1, respectively. Moreover, the intrinsic selectivities of the resin for Fe(III), Al(III), and Mg(II) removal were quantified by the selectivity coefficient (S_i/j). The S_{Fe(III)/Al(III)}, S_{Fe(III)/Mg(II)} and S_{Al(III)/Mg(II)} are 18.2, 55.1 and 3.02, respectively. This work replenishes sorption theory that can be used in the recycling of electronic waste treatment acid, sewage treatments, hydrometallurgy, and purification of WPA in industry.

Phosphate Removal Mechanisms in Aqueous Solutions by Three Different Fe-Modified Biochars

Iron-modified biochar can be used as an environmentally friendly adsorbent to remove the phosphate in wastewater because of its low cost. In this study, Fe-containing materials, such as zero-valent iron (ZVI), goethite, and magnetite, were successfully loaded on biochar. The phosphate adsorption mechanisms of the three Fe-modified biochars were studied and compared. Different characterization methods, including scanning electron microscopy/energy-dispersive spectrometry (SEM-EDS), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), were used to study the physicochemical properties of the biochars. The dosage, adsorption time, pH, ionic strength, solution concentration of phosphate, and regeneration evaluations were carried out. Among the three Fe-modified biochars, biochar modified by goethite (GBC) is more suitable for phosphate removal in acidic conditions, especially when the pH = 2, while biochar modified by ZVI (ZBC) exhibits the fastest adsorption rate. The maximum phosphate adsorption capacities, calculated by the Langmuir-Freundlich isothermal model, are 19.66 mg g^-1, 12.33 mg g^-1, and 2.88 mg g^-1 for ZBC, GBC, and CSBC (biochar modified by magnetite), respectively. However, ZBC has a poor capacity for reuse. The dominant mechanism for ZBC is surface precipitation, while for GBC and CSBC, the major mechanisms are ligand exchange and electrostatic attraction. The results of our study can enhance the understanding of phosphate removal mechanisms by Fe-modified biochar and can contribute to the application of Fe-modified biochar for phosphate removal in water.