Effect of supersaturation on morphology and stability of atmospheric pressure scorodite under As(Ⅴ)-Fe(Ⅱ) system

According to the problem that low solution supersaturation was the key factor in the process of scorodite synthesis under atmospheric pressure, the effect of pH on the oxidation rate of ferrous iron, the relationship between the oxidation rate of ferrous iron and supersaturation, and the effect of supersaturation on the precipitation percent of arsenic and iron, the content of scorodite components, particle size, morphology and stability were investigated in an As(Ⅴ)-Fe(Ⅱ) system by slow oxidation of ferrous ions. The results show that the oxidation rate of ferrous ions decreases with the decrease of initial pH value, while the supersaturation of solution decreases with the decrease of oxidation rate of ferrous ions. Lower initial supersaturation is not conducive to the precipitation of As and Fe, and has no significant influence on the content of arsenic and iron in the synthesized scorodite but has a greater impact on the sulfur content in synthesized scorodite. The initial supersaturation increases from 7.86 to 78.86, and the arsenic iron precipitation percent increases from 77.05% and 53.9% to 88.66% and 61.79%, respectively, and the contents of arsenic, iron and sulfur in the scorodite are 30.74%, 24.14% and 0.58%-0.17%, respectively. The particle size of scorodite first increases and then decreases with an increase of initial supersaturation. When the initial supersaturation is 11.7, the particle size reaches a maximum of 87.5μm. The initial supersaturation is in the range from 7.86 to 24, the spheroidoid particles are synthesized. The initial supersaturation is in the range from 24 to 78.86, it is irregular scorodite particles. By controlling the initial supersaturation in the range of 7.86-78.86, the stability of the synthesized scorodite is high, and its leaching toxicity is less than 1 mg/L. © 2020, Science Press. All right reserved.