Dissolution, Adsorption, and Redox Reaction in Ternary Mixtures of Goethite, Aluminum Oxides, and Hydroquinone

Abstract

To better understand the oxidative reactivity of iron oxides in the fate of contaminants in acidic environments, we examined the reactivity of goethite in binary mixtures with Al 2 O 3 by carrying out oxidation experiments of hydroquinone (HQ) in the presence of goethite and/or Al 2 O 3 at pH 3. Kinetic results revealed inhibiting effects of 0.2−20 g/L of three different types of Al 2 O 3 on the oxidative reactivity of goethite. Surprisingly, soluble Al ions of 0.18−18 mM had a negligible impact on the reactivity. It turned out that the Fe 3+ dissolved from goethite partly contributed to the observed HQ oxidation and the Al 2 O 3 adsorbed the Fe 3+ to lead to the slower HQ oxidation. The observed pseudo-first-order rate constants in HQ oxidation had a strong linear correlation with Fe 3+ concentration in various goethite and Al 2 O 3 mixtures. Separate experiments confirmed the reactivity of Fe 3+ toward HQ and the linear correlation between [Fe 3+ ] and HQ oxidation reactivity. Finally, sedimentation experiments showed negligible heteroaggregation between goethite and AluC−Al 2 O 3 or nAl 2 O 3 but intensive heteroaggregation between goethite and Alu 65−Al 2 O 3 , which explained the observed highest inhibition effect of Alu 65. Overall, oxide mixtures are very complex whose reactivity is determined by many factors such as oxide dissolution.

Fe(II) Redox Chemistry in the Environment

“…It is well-known that Fe­(II) can form abiotically during the reduction of different iron­(III) (oxyhydr)­oxides by organic and inorganic compounds (e.g., sulfide and phenolic substances). − In the reductive dissolution, surface Fe­(III) is reduced to Fe­(II) and the detachment of iron becomes more energetically favorable due to the weaker bonds between the reduced iron and its neighboring irons. Therefore, the generated Fe­(II) is readily released into the solution.…”

Oxide– and Silicate–Water Interfaces and Their Roles in Technology and the Environment

“…Regarding Fe-oxides, the effects of metal ions and ligands on their oxidative reactivity are reportedly similar to those on Mn-oxides . However, different from the above mechanisms for binary oxide mixtures containing MnO 2 , in binary mixtures of Al- and Fe-oxides at pH 3, the Al 2 O 3 strongly inhibits the oxidative reactivity through adsorbing dissolved Fe 3+ , pointing to the complexity of multicomponent mixtures and the need to continuously examine them.…”

“…At far-from-equilibrium conditions, experimental data on dissolution rates disagree with eq or predictions. To address this problem, eqs or were modified into two types of power-law expressions that are still widely applied. ,,, A constant, n , was introduced to the exponential term such that γ dis = k + true[ 1 − normalexp ( n Δ G R T ) true] or γ dis = k + true[ 1 − ( IAP K sp ) n true] where n is not necessarily equal to 1.0. − In this form, the dissolution rate becomes constant as the degree of undersaturation increases at far-from-equilibrium conditions. The approach was rationalized with PDB because eq reduces to the expected linear form at near-equilibrium conditions, where n Δ G < RT .…”

Redox reactions of iron and manganese oxides in complex systems

“…Similar to MnO 2 , the oxidation of iron oxides is also considered as surface-related (LaKind and Stone, 1989;Zhang and Huang, 2007;Zhang et al, 2019). Therefore, the addition of metal ions, ligands and second metal oxides can influence the surface properties of iron oxides and thus their reaction kinetics.…”

“…In a recent work, Zhang et al (2019) attempted to elucidate the interactions between goethite and Al 2 O 3 , and to understand how the interactions affected the oxidative reactivity of goethite (Zhang et al, 2019). Not surprisingly, Al 2 O 3 exhibited a strong inhibitory effect on the oxidative degradation of hydroquinone by goethite at pH 3.…”