赤铁矿对砷的吸附解吸及氧化特征

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

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.

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（ct-Fe2O3 ） surface were measured and the oxidation process was investigated, as a function of pH and 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 △rGm^θ, and △rH^θ of the adsorption. The pH of the solution had different effects on the adsorption and oxidation of As（ Ⅲ ）. The adsorption rates and amounts adsorbed were maximized at pH 8. However, the oxidation reaction rate and oxidation amounts both peaked at pH 6.