土壤—水体系中离子反应平衡时间的电导法检测

采用电导法检测了土壤—水体系中离子反应达到平衡所需的时间。5种土壤和硝酸盐溶液(10-4/3z mol L-1)配制的20种悬液(30 g kg-1)的电导率时间变化曲线表明,所有悬液的电导率均呈下降趋势,在平衡100~300 h后不再变化。含Cu(NO3)2和Pb(NO3)2溶液(10-4mol L-1)的黄棕壤悬液(10 g kg-1)的Wien效应曲线的位置和形状随平衡时间而变,但当平衡时间≥480 h,曲线出现重叠。含NaNO3和KNO3溶液(2×10-4mol L-1)的黄棕壤悬液(10 g kg-1)的电导率与离心清液中Na 和K 离子浓度随平衡时间呈同步变化趋势,平衡初期均不断下降,分别在平衡70 h和30 h后趋达稳定。这些实验结果表明,电导法确是一种检测土壤—水体系中离子反应平衡时间的简易手段。

DETERMINATION OF EQUILIBRIUM TIME OF IONS IN REACTION IN SOIL-WATER SYSTEM BY MEASURING ELECTRICAL CONDUCTIVITY

By measuring electrical conductivity (EC),the time it takes for ions to reach equilibrium in reaction in the soil-water system was investigated.The EC-time curves of 20 soil suspensions (30 g kg^-1) prepared out of 5 tested soils and 4 nitrate solutions of 10^-4/3z mol L^-1 showed that ECs of the suspensions all decreased until the ion reaction reached equilibrium after 100~300 hours.The curves of Wien effect of two yellow-brown soil suspensions (10 g kg^-1) that contained 10^-4mol L^-1 Cu(NO₃)₂ and Pb(NO₃)₂,respectively,varied with the equilibrium time in location and shape,and overlapped when the equilibrium time reached or exceed 480 hours.The EC value of suspensions (10 g kg^-1) of yellow-brown soil containing 2 10^-4mol L^-1 NaNO₃ and KNO₃ and the concentrations of Na⁺ and K⁺ions in their supernatants showed a similar tendency at first and reached equilibrium after 70 hours and 30 hours,respectively.These experimental results show that conductometry is indeed a simple means to determine time it takes for ions to reach equilibrium in reaction in the soil water system.