Arsenite Oxidation and Treatment by Ultrasound/Iron in Aqueous Solutions

Shinoda

et al. 2022

The effect of 200 kHz ultrasound on scorodite synthesis at 70 °C and 3 h reaction conditions was investigated using sulfuric acidic solutions of various pH (3.0, 2.0, 1.5, 1.0, and 0.0). In contrast to the case of only O2 gas flow without ultrasound irradiation, oxidizing radicals generated by ultrasound irradiation promote Fe(II) oxidation in solution and precursor, allowing scorodite to synthesize with high crystallinity (>99%), which relates to low solubility, even in strong acid solution at pH 1.0. During synthesis, particle shape was changed to polyhedral or spindle type depending on the pH of 0.0 to 3.0. The spindle-shaped scorodite was probably formed by the decrease of precursor amount produced in initial stage of the synthesis. Furthermore, porous maghemite obtained by alkali treatment of scorodite showed initial discharge capacities of 146 mAh/g (polyhedron) and 167 mAh/g (spindle), indicating that its potential use as a cathode material for lithium-ion batteries.

Section: Resultsmentioning

confidence: 99%

Synthesis of porous γ-Fe₂O₃ from scorodite synthesized using ultrasound irradiation and evaluation of its battery performance

Kitamura

Shinoda

et al. 2022

“…This suggested that As is removed from scorodite to the solution via alkali treatment. Figures (6) and (7) show the XRD patterns and SEM observations of the precipitated sample deposited post alkaline treatment. The precipitated sample post alkali treatment was identified as maghemite (γ-Fe 2 O 3 ) in Fig.…”

Section: Separation Of Arsenic From Scorodite and Battery Performance...mentioning

confidence: 99%

“…Therefore, we consider that differences in size and morphology of scorodite particles synthesized in the solution at various pH values are related to the difference in the amount of precursor generated in the reaction. In a previous study, we synthesized polyhedral large-sized (>10 μm) scorodite particles using oxidation [5][6][7][8][9][10][11][12][13] and agglomeration effects 14) by applying 200 kHz ultrasound irradiation at 70 °C for 3 h in a sulfuric acidic solution at pH 2.0. [15][16][17] The contribution of ultrasound irradiation to the synthesis of the large scorodite particles is due to two important factors: (i) a decrease in the number of precursor particles by the agglomeration effect of ultrasound at an early stage of the experiment, and (ii) the enhancement of crystal growth with oxidation of the precursor to nuclei by oxidants [e.g., OH radicals (OH•) and HO 2 radicals (HO 2 •)] generated during ultrasound irradiation.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of porous γ-Fe₂O₃ via alkaline treatment of size controlled scorodite particles synthesized using ultrasound irradiation and its evaluation as a cathode for lithium-ion battery

Kitamura

Shinoda

et al. 2019

Herein, we synthesized scorodite particles using ultrasound irradiation in a strong sulfuric acidic solution (pH 0.5) and investigated the scorodite particles' size and morphology. The highest crystallinity of scorodite (96%) was synthesized using 200 kHz ultrasonic treatment, and maximum yield of scorodite was obtained in three conditions: 200, 28 kHz, and stirrer. The oxidant generated through 200 kHz ultrasound irradiation enhanced Fe(II) oxidation in the solution resulting in crystal nuclei formation. The crystal nuclei were transformed to scorodite by oxidation with a supply of solute [Fe(III)] from the solution and ostwald ripening. Clustered scorodite (4 μm in size) was obtained via synthesis using 200 kHz ultrasound (pH 0.5). Arsenic could be separated from the clustered scorodite via alkaline treatment; scorodite was changed to porous γ-Fe 2 O 3 comprising nanosized particles. Porous γ-Fe 2 O 3 was evaluated as a cathode in a lithium-ion battery, which showed a 149 mAh g −1 discharge capacity with a 0.

“…The use of ultrasound for the oxidation of As(III) was reported previously. [15][16][17][18][19][20][21] It was found that while ultrasound is effective for the oxidation of As(III) to As(V), Ascontaining solutions gradually become acidic under ultrasound irradiation. This prevents the use of adsorbents that dissolve in the acidic solution, such as ferric hydroxide.…”

Section: Introductionmentioning

confidence: 99%

Removal of arsenious acid from sulfuric acidic solution using ultrasound oxidation and goethite

Yoshikawa

Hosokawa

et al. 2015

We investigated the properties of synthetic goethite for the adsorption of As from strongly acidic solutions in ambient atmosphere under ultrasound irradiation. The goethite was successfully synthesized from iron-containing sulfuric acidic solution (1271 ppm) using an autoclave apparatus for 1 h at 0.12 MPa and 121 °C. The ratio of the iron eluted from the synthetic goethite to the acidic solution was only 0.58% at pH 2.1. Ultrasound irradiation (200 kHz, 200 W) was applied to oxidize 10 ppm of As(III) to As(V) at pH 2.2 for 60 min under various atmospheric conditions. Remarkably, the oxidation ratio of As(III) to As(V) is quite high (89.7%) at pH 2.2 in ambient atmosphere and is close to those obtained for Ar (95.3%) and O2 (95.9%) atmospheres. The As(III) removal ratio reached 94.5% after 60 min of irradiation. Therefore, goethite is a promising material for As adsorption using ultrasound oxidation in the acidic region in ambient atmosphere.