黄泥土对铜的吸附解吸及其pH变化

Sorption-desorption of Cu^(2+) by Paddy Soil and the pH Change of Equilibrium Solution

用平衡液吸附法和CaCl2与HCl溶液的连续解吸法研究了太湖地区黄泥土(水稻土)对重金属Cu2+的吸附和解吸特征以及吸附和解吸过程中平衡液pH的变化。结果表明,黄泥土对Cu2+吸附以Langmuir方程拟合为佳,模拟的最大吸附量达1600mg·kg-1以上。在最大吸附量以下,土壤对Cu2+的吸附容量随着外加Cu2+浓度的递增而升高,外加Cu2+浓度在100mg·kg-1下时,Cu2+吸附以专性吸附为主,而高浓度下非专性吸附占主要地位。外加Cu2+浓度在10￣160mg·kg-1范围内,观察到外加Cu2+吸附过程中平衡液pH的下降,其大小值依吸附量而变;同样,用CaCl2溶液解吸所吸附的外加Cu2+过程中平衡液pH也呈下降趋势,其大小依解吸量而变。不过,用HCl溶液解吸时观察到平衡液pH略有上升。可见,污染土壤中铜土壤吸附和解吸涉及土壤溶液pH的变化,因而土壤中Cu、Zn等金属污染也可能是导致土壤酸化的因素。

Adsorption-desorption of spiked Cu^2＋ by a typical paddy soil from the Tai Lake region, China and the pH change of at equilibrium solution was studied by using isothermal equilibrium adsorption method and continuing desorption method of dilute CaCl2 and HCl solution respectively. Adsorption of Cu^2＋ by the paddy soil could be best described with the Langmuir isotherm curve, with the maximum adsorption capacity over 1 600 mg·kg^-1. Before saturation, Cu^2＋ adsorption capacity showed in linear response to the concentration of spiked Cu^2＋ Specific adsorption predominated when spiked Cu^2＋ below 100 mg·kg^-1 while non-specific did at Cu^2＋ concentration over 100 mg·kg^-1. The pH decreasing of equilibrium solution was observed in proportional to the amount of absorbed Cu^2＋, similarly, the pH was also decreased during the desorption of the absorbed Cu^2＋by CaCl2. However, insignificant pH change could be detected when desorbed by HCl. Therefore, pH changes of soil solution could be involved in the adsorption and desorption of Cu^2＋ onto or from soil colloids of polluted metals. It is likely that soil heavy metal pollution, such as Cu and Zn, may result in soil acidification of paddy soils, which has been frequently reported in the polluted area.