Effects and mechanisms of Al substitution on the catalytic ability of ferrihydrite for Mn(II) oxidation and the subsequent oxidation and immobilization of coexisting Cr(III).

Al(III)-substituted ferrihydrite existing in natural soils is more common than pure ferrihydrite; however, the effects of Al(III) incorporation on the interaction between ferrihydrite, Mn(II) catalytic oxidation, and coexisting transition metal (e.g., Cr(III)) oxidation remain elusive. To address this knowledge gap, Mn(II) oxidation on synthetic Al(III)-incorporated ferrihydrite and Cr(III) oxidation on the previously formed Fe-Mn binaries were investigated in this study via batch kinetic studies combined with various spectroscopic analyses. The results indicate that Al substitution in ferrihydrite barely changes its morphology, specific surface area, or the types of surface functional groups, but increases the total amount of hydroxyl on the ferrihydrite surface and enhances its adsorption capacity toward Mn(II). Conversely, Al substitution inhibits electron transfer in ferrihydrite, thereby weakening its electrochemical catalysis on Mn(II) oxidation. Thus, the contents of Mn(III/IV) oxides with higher Mn valence states decrease, whereas those of lower Mn valence states increase. Furthermore, the number of hydroxyl radicals formed during Mn(II) oxidation on ferrihydrite decreases. These inhibitions of Al substitution on Mn(II) catalytic oxidation subsequently cause decreased Cr(III) oxidation and poor Cr(VI) immobilization. Additionally, Mn(III) in Fe-Mn binaries is confirmed to play a dominant role in Cr(III) oxidation. This research facilitates sound decision-making regarding the management of Cr-contaminated soil environments enriched with Fe and Mn.

[Simultaneous analysis of multi-elements in vegetation oils by inductively coupled plasma atomic emission spectrometry].

A simple, accurate and sensitive method for the simultaneous analysis of eleven trace elements (Fe, Cu, Co, Ni, Pb, Al, Zn, Cd, Cr, Mn and Mg) in vegetation oils by ICP-AES has been developed. The oils were digested by H2 SO4 ashing method. The detection limits (MDLs) of the method for the eleven elements were in the range of 0.1-3.6 microg x kg(-1). The average recoveries at three concentrations of 0.1, 0.5 mg x kg(-1) were between 70.4% and 113% with the RSD in the range of 1.01%-10.6%. The proposed method has been applied to the determination of the above elements in soy, peanut, sesame, rape, tea and blended oils with satisfactory results.