Variation Of Arsenic(As), Antimony(Sb) And Fe Oxide In The Soils In Wet-Dry Rotation Environment

This paper focused on the soils near Qinglong antimony mine area in Guizhou Province. The concentrations, speciation and bio-availability of arsenic(As) and antimony(Sb) in 21 topsoil samples were measured. The pollution characteristic and potential ecological risk of As and Sb were analysed based on the local soil background concentration and environmental quality standard for soils. Researches about variation of As, Sb and Fe oxide in wet-dry rotation environment were carried out in laboratory simulation. HG-AFS was applied to the determination of As and Sb in the soils with microwave assisted sample digestion. The distribution characteristics of the speciations for soil As and Sb were analysed using the sequential extraction procedure(GB/T 25282-2010) in21 soil samples. The results showed:Results showed that the contents of As and Sb were high in the study area. As concents in the topsoil samples was 12.38-127.85 mg·kg-1, 0.61-6.39 times of Guizhou soil background values, the average concentration of soil As was 43.52 mg·kg-1, exceeded the TypeⅡ limit(As>30 mg·kg-1)set by Chinese environment quality standard for soils and the local soil background concentration(As>20 mg·kg-1). Sb concentrations in the topsoil samples was 171.9-603.8 mg·kg-1 and the average concentration was 267.5 mg·kg-1, 76.75-269.54 times and 119.42 times of the local soil background concentration(Sb>2.24 mg·kg-1). Based on the single factor pollution index assessment results, the antimony mine area had a high pollution level, following the order of Sb>As. And the whole potential ecological risk of the two metals in the antimony mine area was high and the order of Sb>As.The analysis of the speciations for soil heavy metals indicated that, soil As gave priority to the residual fraction(52.87%-87.58%), followed by the reducible fraction(2.49%-19.59%) and oxidisable fraction(3.68%-20.46%), the mild acido-soluble fraction was low(0.16%-3.86%), the water-soluble fraction was very low(0.02%-0.77%). The distribution of the speciations for soil Sb showed a same characteristic when were 76.30%-91.47%, 0.58%-7.16%, 0.77%-7.34%,0.05%-1.51% and 0.01%-1.10%, respectively. There were significant positive correlation with As different fractions, Sb different fractions and As and Sb fractions. The concentration of easilybioavailable antimony was 0.15-14.60 mg·kg-1 and the percentage was 0.05%-2.46%, while0.12-2.94 mg·kg-1 and 0.21%-4.37% for arsenic.During flooding period, the contents of As and Sb in soils water rose up at first, then relatively stable, and varied along with the flooding days. The percentages of As(Ⅲ) and Sb(Ⅲ) varied with the flooding days, as well as variance of it. The contents of Sb different fractions in 3 kinds of soil for TH-CF, TM-CF and TL-CF fall off with the flooding days when the contents of As different fractions rose up or fall off, but Sb residual fraction fall off. There were significant positive correlation with As different fractions or Sb different fractions during flooding period.During flooding period, flooding significantly increased the content of amorphous Fe oxide accompanying with a sharp decrease of crystalline Fe oxide in the tested soils. The content of amorphous Fe oxide was increased 133.42%, 137.79% and 326.53% when the content of crystalline Fe oxide was decreased 36.46%, 43.57% and 51.89%, after 84 flooding days. The Fe oxide activation ratio was also increased, as well as variance of amorphous Fe oxide, and there was significant for TL-CF soil.During wetting-redrying period, the contens of As and Sb different fractions varied along with wetting-drying in the test soils for TH-DW, TM-DW and TL-DW. The contents of As(Ⅲ) and Sb(Ⅲ)in soil different fractions also varied with wetting-redrying. During flooding period, the contents of As and Sb different fractions were increased, following the distribution order of water-soluble fraction>mild acido-soluble fraction>reducible fraction and oxidisable fraction. During the drying period, the contents of As and Sb different fractions were increased or decreased, water-soluble fraction and mild acido-soluble fraction fall off, residual fraction rose up, reducible fraction and oxidisable fraction rose up or fall up. During flooding period, the contents of As(Ⅲ) and Sb(Ⅲ)were increased, the percentages of As(Ⅲ) and Sb(Ⅲ) were also increased. During the drying period,there were increased. There were significant positive correlation with As different fractions or Sb different fractions during flooding period.During wetting-redrying period, the contents of amorphous Fe oxide and the crystalline Fe oxide varied along with wetting-redrying in the 3 test soils. During flooding period, flooding significantly increased the content of amorphous Fe oxide accompanying with a sharp decrease of crystalline Fe oxide in the 3 test soils. During the drying period, drying decrease the content of amorphous Fe oxide accompanying with a sharp increase of crystalline Fe oxide, but varianceamplitude was different.