水钠锰矿对Cr(Ⅲ)离子的吸附解吸及氧化行为

采取等温吸附热力学方法,探讨了锰氧化合物(水钠锰矿)对Cr(Ⅲ)离子的吸附解吸和氧化特征及温度、pH等因素对其影响。研究结果表明,随着Cr(Ⅲ)初始加入量的增加,总铬吸附量逐渐增大,用Langmuir方程可以很好地描述吸附等温线数据;达到反应平衡时,水钠锰矿对Cr(Ⅲ)离子的氧化量与加入初始Cr(Ⅲ)的浓度呈极显著线性正相关,而水钠锰矿对Cr(Ⅲ)的氧化率,随初始Cr(Ⅲ)浓度增加而减小;温度是影响水钠锰矿对Cr(Ⅲ)的吸附和氧化的重要因素,35℃时的吸附量显著低于25℃时的吸附量,而35℃时的氧化量、氧化率明显高于25℃时的氧化量、氧化率,表明升温对吸附反应不利,而对氧化反应有利;溶液酸度对于Cr(Ⅲ)的吸附和氧化有着不同的影响,随着pH的升高,Cr(Ⅲ)离子氧化量、氧化率增大,然而,水钠锰矿对总Cr的吸附量则随着pH的升高而减小,表明pH的升高有利于氧化反应,而对吸附反应不利。

Cr(Ⅲ) ADSORPTION, DESORPTION AND OXIDATION BY BIRNESSITE

Cr(Ⅲ) adsorption, desorption and oxidation by birnessite was studied in this paper. Results show that amount of total Cr(Ⅲ) increased with the amount of Cr(Ⅲ) added, and the adsorption process could be well described with the Langmuir equation. The concentration of Cr(Ⅵ) resulting from oxidation of Cr(Ⅲ) showed an extremely significant positive linear relationship with the initial concentration of Cr(Ⅲ) added, while the oxidation rate did a reverse one. Moreover, effects of pH, temperature on the adsorption and oxidation processes were also examined. The adsorption at 308.2 K was remarkably lower than at 298.2 K, while the oxidation and oxidation rate at 308.2 K were obviously higher than at 298.2 K, which suggest that high temperature favored oxidation, but disfavored adsorption. This finding could also be proved by thermodynamic parameters (ΔG°and ΔH°) of the adsorptive process. Adsorption decreased with increasing pH of the adsorption solution, while the oxidation and oxidation rate increased. The results indicated that high pH favored oxidation, but disfavored adsorption.