土壤对铜离子的专性吸附及其特征的研究

供试土壤专性吸附铜的等温线均符合Langmuir方程。红壤吸附量最低,砖红腹与黄泥土最大吸附量相近,但在铜浓度低时砖红壤吸铜量远低于黄泥土,而在高浓度则反之。土壤专性吸附铜是在溶液中Na⁺浓度比Cu²⁺高8.3—100倍条件下,Na⁺离子仍不足以与之竞争的那些专性吸附点所吸持的铜。按其解吸条件区分为松结合铜(可为N NH₄Cl解吸)和紧结合铜(仅能为0.1 N HCl解吸)两种。紧结合铜受平衡溶液铜浓度影响很小,所占据的吸附点对Cu²⁺有较强亲和力。松结合铜则随平衡铜溶液浓度增大而增加,符合Langmuir方程。对于砖红壤和黄泥土,在铜浓度低时紧结合铜>松结合铜;浓度高时则反之。红壤专性吸附铜始终以松结合铜为主。三种土壤比较,紧结合铜是砖红壤>黄泥土>红壤;松结合铜则是黄泥土>砖红壤>红壤。造成这些差别的原因可能与土壤性质、氧化物、有机质和粘土矿物组成等不同有关。用平衡法研究三种土壤专性吸附铜在不同浓度NH₄Cl和HCl溶液中的解吸表明,可进一步区分为三或四种不同的结合状况。红壤对铜吸附容量最小,且最易解吸。

STUDY ON THE SPECIFIC ADSORPTION OF COPPER ION BY SOILS AND ITS CHARACTERISTICS

The present paper deals with the effect of the components of soils on the specific adsorption of copper ion and its characteristics. Latosol, red earth and paddy soil (neutral) were used in this paper. The specific adsorption of Cu²⁺ ion was determined in the presence of 0.5 M NaCl as supporting electrolyte, and the initial pH of solution was 4.00.The results showed that Cu specific adsorption isotherms of tested soils followed the Langmuir equation (Table 2). The specific adsorption of Cu by latosol and paddy soil was greater than that of red earth. By comparison of maximum adsorption, the specific adsorbed Cu of latosol and paddy soil was about 3.1 times and 3.0 times the amount of adsorbed Cu of red earth respectively.Desorption experiments reveled that there existed two types of specific adsorbed Cu, one was with a low bonding energy and could be desorbed by 1 N NH₄Cl (pH 5.0) and the other was with a high bonding energy and could only be desorbed by 0.1 N HCl, corresponding to the loosely bonding and tightly bonding fractions of copper respectively.The tightly bonding Cu was independent of the concentration of Cu added, once the specific sites were filled with this fraction of copper (Fig. 3, 4, 5), it had greater affinity with the specific sites. The loosely bonding Cu increased with increasing concentration of copper added, and followed the Langmuir equation (Fig. 3, 4, 5). Thus there must be a fixed number of specific sites at a given pH from which copper is less readily desorbed (tightly bonding Cu), and with increasing concentration of copper added, there will be an increasing proportion of the adsorbed Cu at that pH which can be readily desorbed (loosely bonding Cu).At lower concentration of copper added, tightly bonding Cu was more than loosely bonding Cu for latosol and paddy soil, and vice versa. Loosely bonding Cu dominated in specific adsorbed Cu for red earth. The amount of tightly bonding Cu in soils was in the order: latosol>paddy soil>red earth; while that of loosely bonding Cu in soils was in the order: paddy soil>latosol>red earth. This distinct difference in specific adsorbed Cu for the tested coils is probably related to the different content and properties of hydrous oxides, organic matter and composition of clay minerals of soils.