几种土壤粘粒表面Pb^(2+)吸附-解吸不可逆性特征

Irreversible characteristic of lead(Ⅱ) adsorption-desorption on soil clays

为了探讨土壤粘粒表面Pb2+吸附-解吸的不可逆性特征,采用一次平衡法研究了陕西4种土壤粘粒对Pb2+的吸附和解吸特征。结果表明,在恒定pH条件下,残留吸附常数Kd与吸附常数Ka的比值称为吸附-解吸的不可逆性特征参数,Kd/Ka=1,表示吸附-解吸过程是可逆的;Kd/Ka≠1,表示该过程不可逆;在不同解吸溶液中,供试土壤粘粒表面Pb2+Kd/Ka值由大到小依次表现为N aNO3、草酸、柠檬酸,不可逆程度大小与此相同。在不同pH条件下,供试土壤粘粒表面Pb2+络合常数log Kiant与解吸常数log Kidnt的比值也可作为过程不可逆性特征参数;在不同介质中,其绝对值由大到小依次为N aNO3、柠檬酸、草酸,不可逆程度大小与此相反。

In order to investigate the irreversibility of the adsorption and desorption of Pb^2＋ on soil clays,one equilibrium method was used to study the characteristics of the adsorption and desorption of Pb^2＋ on soil clays in Shaanxi. The results were that the ratio of residual adsorption constant Kd to adsorption constant Ka was defined as the irreversible parameter of adsorption-desorption for Pb^2＋ on the soil clay. If Kd/Ka= 1 ,the process of adsorption and desorption was reversible. If Kd/Ka≠1 ,the process of adsorption and desorption was irreversible. The ratio Kd/Ka of soil clays showed the feature of NaNO3〉oxalic acid〉citric acid at a constant pH,the irreversible degree showed the same sequence. So,concerning pH, the ratio of log K^intd/log Kinta （the intrinsic desorption constant/surface intrinsic complexation constant） Pb^2＋ on soil clays was defined as the parameter of irreversible,the ratio showed NaNO3〉 citric acid〉 oxalic acid in different mediums ,the irreversible degree was just the opposite.