镉在土水系统中的迁移特征

TRANSPORT CHARACTERISTICS OF CADMIUM IN SOIL-WATER SYSTEM

本文研究了4种红壤和水体系中镉的迁移特征。结果表明：镉扩散系数D变化在5．6×10(－8)-9．3×10(－7)cm2／sec；通过比较单、双表面Langmuir方程的参数，发现四个土壤的高能位吸附常数远远大于低能位吸附常数，高能位的最大吸附量b1明显小于低能位的最大吸附量b2，即镉被土壤吸附是以低能位为主，导致镉在土水体系中高度迁移性；四种土壤对镉的吸附量随土水系统中pH的变化，可分为三个区域，即pH＜ZPC（电荷零点）的低吸附量区、ZPC＜pH＜6．0的稳定吸附区，以及pH＞6．0的强吸附和沉淀区，在稳定吸附区镉吸附量与pH呈正相关。pH6以下被吸附的镉中生物有效态镉量随pH的升高而增加，pH6以上被吸附的镉中生物有效态镉量随pH升高而降低。

Transport characteristics of cadmium in 4 soil-water systems were studied. Theresults showed that the diffusion coefficients of cadmium ranged from 5.6 × 10-8 to9.3 × 10-7cm2 /sec. Comparison betWeen the Parameters from the single and tWo-surfaceLangmuir equations demonstrated that the maximum adsorption capacity (b2) oflow-energy sites was much greater than the maximum adsorption capacity (b1) ofhigh-energy sites, resulting in high 0transPortability of cadmium in the soil-watersystem. The variation of adsorption capacity of cadmium with PH had three distinctstages, i. e., low adsorption stage at PH < ZPC, stable adsorption stage at ZPC <PH < 6.0 and strong adsorption and precipitation stage at PH > 6.0. The adsorptioncapacity of cadmitim was Positively correlated with PH at the stable adsorption stage.The bioavailability of adsorbed cadmium increased with increasing PH when PH < 6but decreased with increasing PH when PH > 6.