Effect of reaction temperature on the size and morphology of scorodite synthesized using ultrasound irradiation

Abstract

Synthesis of scorodite (FeAsO·2HO) using dynamic action agglomeration and the oxidation effect from ultrasound irradiation was investigated. The effect of different reaction temperatures (90, 70, 50, and 30°C) on the size and morphology of scorodite particles synthesized under O gas flow and ultrasound irradiation was explored because the generation of fine bubbles depends on the solution temperature. At 90°C, the size of scorodite particles was non-homogeneous (from fine particles (<1μm) to large particles (>10μm)). The oxidation-reduction potential (ORP) and yield at 90°C showed lower values than those at 70°C. The scorodite particles, including fine and non-homogeneous particles, were generated by a decrease in the oxidation of Fe(II) to Fe(III) and promotion of dissolution caused by the generation of radicals and jet flow from ultrasound irradiation. Using ultrasound irradiation in the synthesis of scorodite at low temperature (30°C) resulted in the appearance of scorodite peaks in the X-ray diffraction (XRD) pattern after a reaction time of 3h. The peaks became more intense with a reaction temperature of 50°C and crystalline scorodite was obtained. Therefore, ultrasound irradiation can enable the synthesis of scorodite at 30°C as well as the synthesis of large particles (>10μm) at higher temperature. Oxide radicals and jet flow generated by ultrasound irradiation contributed significantly to the synthesis and crystal growth of scorodite.

Disposal of high-arsenic waste acid by the stepwise formation of gypsum and scorodite

“…A Fe/As ratio in the range of 1.0-3.0 is available for the synthesis of scorodite in different conditions by using pure chemical reagents. 32,35,38,46,47,49,62 The inuence of Fe/As ratio on the scorodite synthesis was investigated in the range of 1.0-2.0, as shown in Fig. 8.…”

“…40 | RSC Adv., 2020, 10, [29][30][31][32][33][34][35][36][37][38][39][40][41][42] This journal is © The Royal Society of Chemistry 2020 into account balances of minimal arsenic loss and maximal removal rate of sulfuric acid, a nal pH of 0.5 is xed in Stage-I. The nontoxic gypsum with an As leaching concentration of 3.36 mg L À1 below the regulatory limit was obtained, resulting in a sulfuric acid removal rate of 80% with a negligible arsenic loss.…”

“…27,28 Owing to the above properties, scorodite is recognized as the best arsenic-stabilization mineral and attracts widely attentions. 16,17,[29][30][31][32][33][34][35][36][37][38][39][40][41][42] The synthesis of scorodite is of great importance for arsenic removal rate from a arsenic-bearing solution. 6,35 The hydrothermal method was proposed using Fe(III) and As(V) starting solution at temperatures higher than 125 C in the pHs range of 0.2-1.8 to synthesize scorodite.…”

Utilization of carbon dioxide to synthesize large scorodite particles under ultrasound irradiation

“…In a previous work, we reported that oxidant radicals generated under 200 kHz ultrasound irradiation and O 2 gas flow contribute to the oxidation reaction to synthesize scorodite. 11,12) Thus, when the gas mixture contains more than 50 vol % of CO 2 , the oxidation reaction during the ultrasound agglomeration process is inhibited because of the reduction in O 2 gas and oxidant radicals, which are responsible for oxidation. Therefore, a large proportion of CO 2 gas (≥50 vol %) prevented nuclei formation by oxidation of radicals and O 2 gas during ultrasound irradiation (10 min) at the early reaction stage.…”

The effect of precursor speciation on the growth of scorodite in an atmospheric scorodite synthesis

“…In addition, the particle size of scorodite is influenced by its precursor. Larger scorodite is synthesized when the size of the precursor is increased by agglomeration [19][20][21]. Even though the precursor plays a significant role in the growth of scorodite during atmospheric scorodite synthesis, the speciation of the precursor has not been characterized.…”