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环境化学

Characteristics of isothermal adsorption and desorption,and oxidation of As(Ⅲ) ion on a hematite surface

摘要：采用等温吸附热力学的方法,研究了赤铁矿(α-Fe₂O₃)对三价砷离子的吸附和氧化特征,以及温度、pH值等因素对吸附和氧化效果的影响.研究结果表明,Langmuir方程可以很好地表述吸附量与初始三价砷离子浓度的关系(R²=0.9939);随着初始砷离子浓度的增大,溶液中As(V)的浓度(氧化量)也逐渐增大,然而氧化率却随着初始砷离子浓度的增大而减小;35℃条件下的吸附量和吸附率、氧化量和氧化率都比25℃时大,表明升高温度有利于赤铁矿对砷离子的吸附和氧化作用.溶液酸度对于As(Ⅲ)的吸附和氧化有着不同的影响,在pH<8时,吸附量和吸附率随pH上升而增加,在pH=8时达到最大,随后随pH上升而减小;当pH低于6.0时,随着pH的增加As(Ⅲ)氧化量、氧化率逐渐增大,而当pH高于6.0时,随着pH增加As(Ⅲ)氧化量反而降低,最大氧化量出现在pH=6.0处.

Abstract：Arsenic can be adsorbed into soils by reaction with iron-containing minerals such as hematite. The As(Ⅲ) adsorption and desorption isotherms on the hematite(α-Fe₂O₃) surface were measured and the oxidation process was investigated,as a function of pHand temperature. The Langmuir equations describe the relationship of adsorption amount to the original concentration of As(Ⅲ) well(p<0.05). The concentrations of As(V) (oxidized) in the solution increased but the oxidation rates decreased as the initial As(Ⅲ) concentration increased. Temperature is an important factor influencing both the adsorption and oxidation of As(Ⅲ) ion on the hematite surface. The adsorption amounts,adsorption rates,oxidation amounts and oxidation rates at 35℃ were all greater than those at 25℃,which suggested that higher temperature favored the adsorptive and oxidation reactions. This is also confirmed by the thermodynamic parameters Δ_rG_m^θ and Δ_rH^θ of the adsorption. The pHof the solution had different effects on the adsorption and oxidation of As(Ⅲ). The adsorption rates and amounts adsorbed were maximized at pH8. However,the oxidation reaction rate and oxidation amounts both peaked at pH6.