不同NaNO3浓度下可变电荷土壤铜离子解吸率的分配及影响因素

DISTRIBUTION OF CU(Ⅱ) DESORPTION RATE IN VARIABLE CHARGE SOILS RELATIVE TO CONCENTRATIONS OF NANO_3 AND ITS AFFECTING FACTORS

研究了江西红壤和昆明铁质砖红壤在去离子水中和在0．1molL^-1 NaNO3溶液中吸附铜离子后，依次在包括去离子水在内，浓度由低到高的NaNO3溶液中解吸时，铜离子解吸率在不同吸附pH段的分配规律。结果表明，随着吸附pH的升高，可在去离子水中解吸的铜离子解吸率变化规律与在NaNO3溶液中者完全不同。在所研究的吸附pH范围内，大致以吸附pH3．7～4．0为界，低于此值时，吸附性铜离子基本以在去离子水中解吸为主，反之则基本为交换性解吸。土壤中氧化铁含量和吸附时溶液的NaNO3浓度越高，则能被交换解吸的铜离子所占总解吸率的比例越低。其原因与不同pH段各种铜离子吸附态在不同吸附条件下的比例分配以及解吸对体系pH的影响有关。

An adsorption and desorption test was conducted of two variable charge soils （Ali-Haplic Acrisol from Jiangxi and Hyper-Rhodic Ferralsol from Kunmin of Yunnan ） to explore distribution of desorption rates of pre-adsorbed Cu （ Ⅱ ） from the soils in NaNO3 solution relative to concentration of the solution and pH, at which Cu （Ⅱ） was adsorbed during the pre-adsorption phase. For the test, the soil samples were first put into de-ionized water and 0.1 mol L-1 NaNO3, separately, for pre-adsorption of Cu （Ⅱ） and then into de-ionized water and NaNO3 solutions varying in concentration gradually from low to high, sequentially, for desorption of Cu （ Ⅱ ） . Results show that with rising pH, Cu （ Ⅱ ） desorption rate varied sharply with NaNO3 solution. In de-ionized water, Cu （Ⅱ） desorption rate declined monotonously with the rise of pH in the Cu （ Ⅱ ） pre-adsorption phase; while in NaNO3 solutions, Cu （ Ⅱ ） desorption ratefollowed a peak-shaped curve, but the total Cu （ Ⅱ ） desorption rate also declined monotonously with the rise of pH in the Cu （ Ⅱ ） pre-adsorption phase. The Cu （ Ⅱ ） desorption rate was the highest in the solution of 0.1 mol L-1 NaNO3. In short, desorption rates of the Cu （Ⅱ） desorbable in de-ionized and in NaNO3 solutions were distributed mainly in the high and low sections, respectively, of the range of pH studied. Desorption rate of the Cu （ Ⅱ ） desorbable in NaNO3 was closely related to content of ferric oxide in the soils and NaNO3 concentration in Cu （ Ⅱ ） pre-adsorption, so the higher the content of ferric oxide in the soil, or the higher the NaNO3 concentration in pre-adsorption at pH 〉 4.0 - 4.5, the lower the proportion of Cu （ Ⅱ ） desorbed by NaNO3. The cause of such a phenomena is believed to be associated with the effect of ion-strength, specific weight of exchangeable Cu （ Ⅱ ） relative to adsorption condition and the effect of desorption on pH of the system. Besides, comparison was also made between sequential desorption in solutions constant in NaNO3 concentration and that in solutions varying in NaNO3 concentration.