Adsorption And Desorption Behavior Of Antimony Under Different Redox Situation

The adsorption of soil clay minerals,iron and aluminum oxides to antimony has effect on the migration and transformation of antimony.Also the change of pH and Eh in the environment will affect the transformation and forms of antimony.The purpose of this paper is to lay a foundation for the the migration and transformation study of antimony in soil.In this paper,the release behavior of antimony in heavily polluted soil(the total content of antimony in soil about 719.85mg/kg)is discussed.The characteristics of antimony release from the soil under different extraction liquid pH(pH=2.00,4.00,5.00,6.15,8.00)were investigated.Because the adsorption of antimony on soil composition will affect the migration of antimony,this paper focuses on the adsorption and desorption characteristics of Sb(III)and Sb(V)on the four adsorbents: kaolinite,vermiculite,ferric hydroxide and aluminum hydroxide.The adsorption effect research of Sb(III)and Sb(V)on the adsorbents includes: the sorption kinetics,isothermal adsorption and adsorption effect under the influence of pH.In addition,the change of pH and Eh in the environment influences the forms of antimony.Acording to this,the fitting parameters of adsorption isotherm before and after flooding were compared.And the desorption efficiency of antimony under different flooding time was studied as well.It is expect to achieve weak reduction conditions by flooding treatment.And then the adsorption and desorption effect of antimony on the four adsorbents under different redox conditions is discussed.The results of antimony release from mining polluted soil show that the release of antimony increased with the raising suspension pH.And Sb(Ⅴ)is the major valence state of the release of antimony from the soil,which accounts for more than 90% of the total release antimony concentration.Antimony release concentration is rapid increasing in the first 24 hours.While the rate of rise gets much lower within the next 24 hours,and then tends to equilibrium.The adsorption characteristics of the four adsorbents to trivalent and pentavalent antimony shows that the best adsorption of trivalent antimony is shown on vermiculite and ferric hydroxide,while the absorb-ability of vermiculite to Sb(Ⅴ)is weak.Pentavalent antimony can be adsorbed better by ferric hydroxide and aluminum hydroxide,but aluminum hydroxide shows poor adsorption effect of trivalent antimony.The results of the sorption kinetics show that both Sb(Ⅲ)and Sb(Ⅴ)adsorption on the four adsorbent gradually become stable after 24 hours.In addition,the adsorption of trivalent antimony on vermiculite and ferric hydroxide decreased after reaching the peak value at 8h.For example,the adsorption of Sb(Ⅲ)on ferric hydroxide was 23.19μg/g at6 h,while the adsorption decreased to 19.75 μ g/g at 72 h.The decline of adsorption and the increase concentration of Sb(Ⅴ)determined in supernatant indicates the oxidation of Sb(Ⅲ)during the adsorption process.The pH of background solution was adjusted to study the adsorption effect within different p H conditions.The result suggests the both valence antimony have anion adsorption characteristics,for the adsorption decreases with the raising pH.For instance,the adsorption of Sb(Ⅲ)on kaolin increased from 10.12μg/g to 37.89μg/g with theequilibrium solution pH decreased from 4.82 to 2.12.Compared with the isothermal adsorption before and after flooding,the differences of the adsorption effect of antimony with the four adsorbents basically remain unchanged.According to the fitting parameters of Langmuir model,the Qm(maximum adsorption capacity)increases after flooding.Such as the Qm for ferric hydroxide to Sb(Ⅲ)increases from 180.369μg/g to 302.26μg/g,and the Qm for aluminum hydroxide to Sb(Ⅴ)increases from 111.36μg/g to 155.91μg/g after flooding.No matter pre-adsorption or not,the Eh value of the suspension decreases with the flooding process,and tends to be stable in 14 days.The suspension pH of both ferric hydroxide and aluminum hydroxide decreases within flooding,such as the pH value of aluminum hydroxide suspension decreased from 8.90~9.04 to 8.05~8.16,and the suspension pH charge of kaolin and vermiculite is relatively stable.In the situation of pre-adsorption,the adsorption of both trivalent and pentavalent antimony decreases during flooding process,and and stabilizes in 4~7 days.For example the adsorption of ferric hydroxide to Sb(Ⅲ)decreases from 16.46μg/g to 12.62μg/g during the first 7 days.And till the final day of flooding,the adsorption is 12.95μg/g.The desorption rate of antimony decreases during flooding.Such as the desorption rate of kaolin to Sb(Ⅲ)decreases from 23.12% to 7.53%,the desorption rate of vermiculite to Sb(Ⅴ)decreases from 47.06% to 26.29% and the desorption rate of aluminum hydroxide to Sb(Ⅴ)decreases from 6.24% to 1.02%.