离子强度和pH对可变电荷土壤与铜离子相互作用的影响

研究了离子强度和pH对可变电荷土壤表面电荷与铜离子吸附的影响。作为对照 ,也研究了它们对恒电荷土壤黄棕壤的有关性质的影响。结果表明 ,随pH升高 ,土壤的表面负电荷增加 ,正电荷减少。对于可变电荷土壤 ,可出现电荷零点 (pH0 )。随pH升高 ,土壤对Cu2 的吸附量增大。随着离子强度增大 ,恒电荷土壤对Cu2 的吸附百分率明显降低 ,可变电荷土壤对Cu2 离子的吸附百分率也降低 ,但降低的幅度比恒电荷土壤者小得多。土壤中氧化铁的含量越高 ,降低的幅度越小。对于含 2 1 %左右游离氧化铁的铁质砖红壤 ,即使支持电解质NaNO3的浓度高达 1molL- 1,对Cu2 的吸附仍然几乎没有影响。从离子强度和pH与土壤表面电荷和铜离子吸附的关系 ,可以推测在土壤对铜离子的吸附中 ,既存在电性吸附 ,又存在专性吸附。在可变电荷土壤对铜离子的吸附中 ,专性吸附较为重要

EFFECTS OF IONIC STRENGTH AND pH ON INTERACTION BETWEEN Cu2+ AND VARIABLE CHARGE SOILS

Four variable charge soils from south China and one constant charge soil from Nanjing were used to examine the effects of ionic strength and pH on the surface charge of soils and adsorption of Cu 2 ions. Adsorption of Cu 2 was measured at different pH in water, 0.01 mol L -1,0. 1 mol L -1 and 1 mol L -1 of NaNO 3 solutions was measured respectively. In the soils studied,the net surface charge decreased with an increase in pH. The pH at which the net surface charge was zero (pH 0) differed between the soils. The pH 0 was higher for soils dominated by variable charge components. For all soils studied,the adsorption of Cu 2 increased with an increase in pH and was closely related to the negative surface charge. The effect of ionic strength on Cu 2 adsorption differed between the soils. For constant charge soils,the adsorption of Cu 2 always decreased with an increase in ionic strength irrespective of pH. For variable charge soils,the effect of ionic strength on adsorption of Cu 2 was much smaller than that for constant charge soils. The higher the content of iron oxide in soil,the smaller the effect of ionic strength on Cu 2 adsorption. For iron oxide,the amount of Cu 2 adsorbed in 0.01 mol L -1 NaNO 3 solution was larger than that in water. The results suggest that the Cu 2 ions were retained by both non-specific and specific bonding. For constant charge soil,non-specific bonding played an important role in the adsorption of Cu 2 ; whereas for variable charge soil,specific bonding played an important role in the adsorption of Cu 2 ions.