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Natural limonite, which contains mainly nano-sized iron and manganese oxides, is widely distributed worldwide. This study investigated the kinetics, thermodynamics, and the effects of pH, ion strength, and anions on the adsorption of Sb(III) via limonites sampled from Xinqiao and Yeshan (Tongling, China). Results show that adsorption equilibrium is achieved after 24 h for all experiments. Under initial Sb(III) = 200 mg/L, pH = 3.0, and temperature = 25 °C, Sb adsorption quantities for X1 (Mn-free limonite from Xinqiao), X2 (Mn-containing limonite from Xinqiao), Y1 (Mn-free limonite from Yeshan), and Y2 (Mn-containing limonite from Yeshan) are 10.92, 12.97, 27.12, and 89.34 mg/g, respectively. Manganese oxides in limonites promote Sb removal through oxidizing Sb(III) to Sb(V). The adsorption processes for all four limonites are fitted with a pseudo-second-order model. All adsorptions except for X1 fit with the Freundlich model; for X1, the Langmuir adsorption model is better. All adsorptions are spontaneous reactions (ΔG < 0). All adsorptions except for Y1 (ΔH < 0, exothermic reaction) are endothermic reactions (ΔH > 0). Antimony adsorption is independent of solution pH for Mn-free limonites but is negatively related to solution pH for Mn-containing limonites. Generally, ion strength has a weak positive effect on Sb adsorption. The effects of anions on Sb adsorption are grouped into three types: weak negative (NO3− and SO42−), negative (CO32−, SiO44−, and PO43−), and equivocal (humic acid). This study indicates that due to a much higher surface area, Yeshan (124.8 m2/g for X1 and 171.7 m2/g for X2) rather than Xinqiao (13.7 m2/g for Y1 and 12.8 m2/g for Y2) limonites are better materials for Sb(III) removal in an aqueous solution. The key factors for the better use of limonite as an Sb(III) treatment material include temperature, pH, ion strength, and Mn content. [ABSTRACT FROM AUTHOR]

A series of Fe–rich palygorskite supported manganese oxide (X%Mn–Pal) catalysts were prepared by co-precipitation method and used as catalysts for toluene oxidation. The components and structure of the as-prepared catalysts were characterized by XRD, Raman, TEM, XPS, and in situ DRIFTS. The results showed that the 15%Mn–Pal catalyst exhibited the highest catalytic activity (T90 = 227 °C) and excellent cycling stability for the oxidation of toluene compared with other catalysts. The characterization results indicated that remarkable activity of the 15%Mn–Pal catalyst for toluene oxidation should be ascribed to the abundant surface oxygen vacancies. In situ DRIFTS results elucidated that benzoate was the main intermediate, which can be further oxidized into H2O and CO2. The objectives of this study are to (i) investigate the synergistic effect between Fe and Mn for toluene oxidation, (ii) develop an efficient catalyst for toluene abatement with high activity and low–cost, and (iii) promote the application of natural Fe–rich palygorskite in the control of VOCs. [ABSTRACT FROM AUTHOR]

In our previous study on petrogenesis of quartz syenite and granite porphyry, the host rocks of the Late Mesozoic Shapinggou Mo deposit in the Qinling–Dabie orogenic belt, we found that the initial Sr isotopic composition of the host rocks is strongly affected by the degree of K-alteration. Here, we provide further isotopic evidence of the host rocks and their minerals to investigate the geochemical behaviour of trace elements and isotopes during the alteration and to explain the phenomenon of decoupling of Sr–Nd isotopic composition. The quartz syenite and granite porphyry are altered by K-alteration in varying degrees and have high K2O and Rb contents and low Na2O, CaO, Sr, and Ba contents. Rock samples of both quartz syenite and granite porphyry have variable Rb/Sr ratios and initial 87Sr/86Sr values (even < 0.70) but contain quite homogeneous εNd(t) values (−12.8 to −14.8). Minerals from the rocks of moderate to intense K-alteration have very low initial 87Sr/86Sr values (even < −17), while those from the weakly altered rocks have 87Sr/86Sr(t) values of 0.7044 to 0.7084. The same phenomenon of the decoupling in Sr–Nd isotopic composition can be observed from several Mo deposits within the eastern Qinling–Dabie orogenic belt. This fact suggests similar hydrothermal features and a comparable origin for both the magmatic rocks and hydrothermal fluids in this belt. A comparison between porphyry Mo and porphyry Cu deposits shows that elements and the Rb–Sr isotope system have different behaviours during the K-alteration, implying distinct material sources and igneous rocks for porphyry Mo and porphyry Cu deposits, respectively. [ABSTRACT FROM AUTHOR]

Jarosite residues produced by zinc hydrometallurgical processing are hazardous solid wastes. In this study, monoclinic pyrrhotite (M-Po) was prepared by the pyrolysis of jarosite residues in H2S atmosphere. The influence of gas speed, reaction temperature, and time was considered. The mineral phase, microstructure, and elemental valence of the solids before and after pyrolysis were analyzed using X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy, respectively. The performances of the prepared M-Po on the removal of Zn and Pb from aqueous solution were evaluated. The results show M-Po to be the sole product at the reaction temperatures of 550 to 575 °C. Most of the M-Po particles are at the nanometer scale and display xenomorphic morphology. The phase evolution process during pyrolysis is suggested as jarosite → hematite/magnetite → pyrite → pyrite+M-Po → M-Po+hexagonal pyrrhotite (H-Po) → H-Po. The formation rate, crystallinity, and surface microtexture of M-Po are controlled by reaction temperature and time. Incomplete sulfidation may produce coarse particles with core–shell (where the core is oxide and the shell is sulfide) and triple-layer (where the core is sulfate, the interlayer is oxide, and the shell is sulfide) structures. M-Po produced at 575 °C exhibits an excellent heavy metal removal ability, which has adsorption capacities of 25 mg/g for Zn and 100 mg/g for Pb at 25 °C and pH ranges from 5 to 6. This study indicates that high-temperature sulfidation is a novel and efficient method for the treatment and utilization of jarosite residues. [ABSTRACT FROM AUTHOR]

In this work, a nano-structured iron-manganese oxide composite was prepared by calcining natural manganese-rich siderite at different temperatures (450, 500, 550, 600 °C, labeled as H450, H500, H550, H600, respectively), and their performances of selective catalytic reduction (SCR) of NO by NH3 were investigated. XRD, XRF, BET, XPS, SEM, and TEM were used to investigate the morphology, composition, and surface characteristics of the catalyst. The results showed that the decomposition of siderite occurred from 450 °C to around 550 °C during the calcination in air atmosphere; moreover, the siderite could be converted into nano-structured α-Fe2O3. The specific surface area of the material increased, and Mn2+ was transformed into Mn4+, which were beneficial to the SCR. Among these catalysts, H550 had the best SCR performance, with NO removal of 98% at a temperature window from 200 to 250 °C. The presence of water vapor and sulfur dioxide can inhibit the SCR performance of the catalysts, but this inhibition effect was not obvious for H550 at the optimum reaction temperature (250 °C). The findings presented in this study are significant toward the application of the Mn-rich siderite as a precursor in preparing the Fe-Mn oxides for catalytic de-NOx by SCR. [ABSTRACT FROM AUTHOR]

The removal of Hg(II) from aqueous solutions by pyrrhotite derived from the thermal activation of natural pyrite was explored by batch experiments. The adsorption isotherms demonstrated that the sorption of Hg(II) by modified pyrite (MPy) can be fitted well by the Langmuir model. The removal capacity of Hg(II) on MPy derived from the Langmuir model was determined to 166.67 mg/g. The adsorption process of Hg(II) on MPy was well fitted by a pseudo-second-order model. The sorption of Hg(II) on MPy was a spontaneous and endothermic process. The removal of Hg(II) by MPy was mainly attributed to a chemical reaction resulting in cinnabar formation and the electrostatic attraction between the negative charges in MPy and positive charges of Hg(II). The results of our work suggest that the thermal activation of natural pyrite is greatly important for the effective utilization of ore resources for the removal of Hg(II). [ABSTRACT FROM AUTHOR]

Manganese (Mn) oxide is a ubiquitous metal oxide in sub-environments. The adsorption of Cd(II) on Mn oxide as function of adsorption time, pH, ionic strength, temperature, and initial Cd(II) concentration was investigated by batch techniques. The adsorption kinetics showed that the adsorption of Cd(II) on Mn oxide can be satisfactorily simulated by pseudo-second-order kinetic model with high correlation coefficients (R² > 0.999). The adsorption of Cd(II) on Mn oxide significantly decreased with increasing ionic strength at pH < 5.0, whereas Cd(II) adsorption was independent of ionic strength at pH > 6.0, which indicated that outer-sphere and inner-sphere surface complexation dominated the adsorption of Cd(II) on Mn oxide at pH < 5.0 and pH > 6.0, respectively. The maximum adsorption capacity of Mn oxide for Cd(II) calculated from Langmuir model was 104.17 mg/g at pH 6.0 and 298 K. The thermodynamic parameters showed that the adsorption of Cd(II) on Mn oxide was an endothermic and spontaneous process. According to the results of surface complexation modeling, the adsorption of Cd(II) on Mn oxide can be satisfactorily simulated by ion exchange sites (X₂Cd) at low pH and inner-sphere surface complexation sites (SOCd⁺ and (SO)₂CdOH - species) at high pH conditions. The finding presented herein plays an important role in understanding the fate and transport of heavy metals at the water-mineral interface., Competing Interests: The authors declare no conflict of interest.