Iron Adsorption on Clays Inferred from Atomistic Simulations and X-ray Absorption Spectroscopy

Effect of sulfidation on nitrobenzene removal from groundwater by microscale zero-valent iron: Insights into reactivity, reaction sites and removal pathways

While it has been recognized that sulfidation can effectively improve the reactivity of microscale zero valent iron (mZVI), there is limited understanding of nitrobenzene (ArNO₂) removal by sulfidated mZVI. To understand the reduction capacity and pathway of ArNO₂ by sulfidated mZVI, ball-milling sulfidated mZVI (S-mZVI^bm) with different S/Fe molar ratios (0-0.2) was used to conduct this experiment. The results showed that sulfidation could efficiently enhance ArNO₂ removal under iron-limited and iron excess conditions, which was attributed to the presence of FeS_x sites that could provide higher Fe(0) utilization efficiency and stronger passivation resisting for S-mZVI^bm. The optimum ArNO₂ reduction could be obtained by S-mZVI^bm with S/Fe molar ratio at 0.1, which could completely transform ArNO₂ to aniline (ArNH₂) with a rate constant of 4.36 × 10^-2 min^-1 during 120-min reaction. FeS_x phase could act as electron transfer sites for ArNO₂ reduction and it could still be reserved in S-mZVI^bm after reduction reaction. The product distribution indicated that sulfidation did not change the types of reduction products, while the removal of ArNO₂ by S-mZVI^bm was a step-by-step reduction progress along with the adsorption of ArNH₂. In addition, a faster reduction of ArNO₂ in groundwater/soil system further demonstrated the feasibility of S-mZVI^bm in the real field remediation.

A comparative study for phosphate adsorption on amorphous FeOOH and goethite (α-FeOOH): An investigation of relationship between the surface chemistry and structure

Eutrophication is generally caused by excess nitrogen and phosphorus being released into surface waters by runoff. Developing adsorbents for adsorbing phosphate within soil buffer zones and/or water treatment columns may be effective methods to mitigate this problem. In this study, an amorphous FeOOH (AF) and a well-crystallized α-FeOOH (CF) was formulated to compare phosphate adsorption behavior. The physicochemical properties between these species showed significant differences in morphology, crystallization, zeta potential, and specific surface area. The AF exhibited higher phosphate uptake than CF. X-ray photoelectron spectroscopy (XPS) verified that the hydroxyl groups within AF were 13.28% higher than that in CF. The triply coordinated hydroxyl groups (μ₃-OH) associated with AF and CF appeared at different positions as shown in the diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analyses, confirming that AF contains more adsorption reactive sites (μ₃-OH). Mechanisms for monodentate formations and a stable six-member ring structure were proposed. The X-ray absorption near the edge structure (XANES) and XPS results suggested that the iron valence in AF was dominated by Fe (III). XANES also demonstrated that the amorphous structure found in the AF was caused by the disordered tetrahedron and octahedron alignments, leading to a higher phosphate adsorption.

Organic Carbon Linkage with Soil Colloidal Phosphorus at Regional and Field Scales: Insights from Size Fractionation of Fine Particles

Nano and colloidal particles (1-1000 nm) play important roles in phosphorus (P) migration and loss from agricultural soils; however, little is known about their relative distribution in arable crop soils under varying agricultural geolandscapes at the regional scale. Surface soils (0-20 cm depth) were collected from 15 agricultural fields, including two sites with different carbon input strategies, in Zhejiang Province, China, and water-dispersible nanocolloids (0.6-25 nm), fine colloids (25-160 nm), and medium colloids (160-500 nm) were separated and analyzed using the asymmetrical flow field flow fractionation technique. Three levels of fine-colloidal P content (3583-6142, 859-2612, and 514-653 μg kg^-1) were identified at the regional scale. The nanocolloidal fraction correlated with organic carbon (C_org) and calcium (Ca), and the fine colloidal fraction with C_org, silicon (Si), aluminum (Al), and iron (Fe). Significant linear relationships existed between colloidal P and C_org, Si, Al, Fe, and Ca and for nanocolloidal P with Ca. The organic carbon controlled colloidal P saturation, which in turn affected the P carrier ability of colloids. Field-scale organic carbon inputs did not change the overall morphological trends in size fractions of water-dispersible colloids. However, they significantly affected the peak concentration in each of the nano-, fine-, and medium-colloidal P fractions. Application of chemical fertilizer with carbon-based solid manure and/or modified biochar reduced the soil nano-, fine-, and medium-colloidal P content by 30-40%; however,the application of chemical fertilizer with biogas slurry boosted colloidal P formation. This study provides a deep and novel understanding of the forms and composition of colloidal P in agricultural soils and highlights their spatial regulation by soil characteristics and carbon inputs.