几种有机酸对恒电荷和可变电荷土壤吸附Cu2+的影响

以恒电荷土壤(黄褐土和黄棕壤)和可变电荷土壤(红壤和砖红壤)为供试材料,研究了乙酸、草酸、酒石酸和柠檬酸对土壤吸附重金属铜离子(Cu2 )的影响。结果表明,在相同酒石酸浓度下,土壤对酒石酸的吸附量依次为黄棕壤(2 1 8mmolkg-1) >红壤(15 4mmolkg-1) >砖红壤(9 5mmolkg-1) ,土壤吸附有机酸后负电荷量增加,相同条件下增幅为砖红壤>红壤>黄棕壤;无有机酸配体时,供试土壤对Cu2 的吸附量为黄褐土>黄棕壤>砖红壤>红壤;加入有机酸时,随有机酸浓度增高,土壤对Cu2 的吸附一般表现为“峰”形曲线,峰所对应的有机酸浓度因有机酸类型而异,且随土壤可变电荷性质增强而增高;土壤吸附有机酸后对Cu2 的次级吸附不同于有机酸与铜共存时的竞争吸附,且因土壤性质表现迥异。这些结果意味着在存在有机酸配体的根际环境中,恒电荷土壤与可变电荷土壤对Cu2 的吸附明显不同,并将影响重金属离子在根际的转化与有效性

EFFECTS OF SEVERAL ORGANIC ACIDS ON COPPER ADSORPTION BY SOILS WITH PERMANENT AND VARIABLE CHARGES

Rhizosphere is a place where matters exchange and energy transfers concentratedly between soil and plants. In the rhizosphere, there are abundant organic ligands, of which the influence on copper adsorption by soils with permanent and variable charges have not yet been fully understood. Four soils (Yellow cinnamon soil, yellow brown soil, red soil and latosol), which were sampled from Hubei, Hunan and Hainan provinces, representing soils with permanent and variable charges, were used for investigating effects of organic acids on copper adsorption. The batch adsorption technique was employed in the experiments. The purpose of the study was to compare differences in copper adsorption between two types of soils with permanent and variable charges in the presence of organic acids so as to provide knowledge of copper uptake by plants. Results indicate that the adsorption of tartrate on the soils was dependent on the soil properties and tartrate concentration. In terms of maximum adsorption, the four soils were in a decreasing order of yellow cinnamon soil>yellow brown soil>red soil>latosol. The adsorption of organic ligands might result in increase in surface negative charges of soils, and the magnitude of the increase of the variable charge soils was greater than that of the permanent charge soils. The presence of organic acids increased the copper adsorption at lower concentrations, but decreased at higher ones. A peak appeared at a specific point of organic acid concentration. The point moved up higher with the intensification of variable charge properties of the soils. Moreover, secondary adsorption of copper after organic acids were adsorbed increased more remarkably in variable charge soil than in permanent charge soils. These results demonstrate that heavy metals might have different forms and fates in rhizospheres of the two soils different in charge properties due to difference in surface chemical behavior.