锌、镉在紫色土中的竞争吸附

Competitive sorp-desorption of zinc and cadmium in purple soil

研究了3种紫色土及2种黏土矿物对Zn、Cd的吸附特点.结果表明,中性紫色土中Zn、Cd的吸附特点相似,等温吸附符合Langmuir方程,最大吸附量分别为147.9,104.7mg/kg;其吸附动力学过程先快后慢,符合一级动力学方程与Elovich方程,快速吸附段的吸附量与易解吸量相近,且符合一级动力学方程,为交换吸附;慢速吸附段的吸附量与难解吸量相近,且满足Elovich方程,可能属于深层吸附或专性吸附,3种紫色土及2种黏土矿物对Zn、Cd的吸附量及其土壤理化性质的相关分析表明,CEC与最大吸附量显著相关,表明紫色土对Zn、Cd的吸附机理为交换吸附所控制.Zn、Cd共存时吸附速度与吸附量降低,表明二者对吸附位的竞争,竞争吸附服从质量作用定律,高浓度者占优,高浓度Zn对Cd的吸附有明显抑制,完善的土壤重金属阈限指标应包含复合污染的考虑.

Sorption character of zinc and cadmium in three kinds of purple soil and two kinds of clay miller were studied. In neutral purple soil the sorption character of zinc and cadmium were similar, the isothernal sorption of zinc and cadmium conformed to the Langmuir equation; their maximum sorption quantities were 147.9 and 104.7mg/kg respectively, their sorption kinetic processes were rapid first and followed slow in accordance with one order kinetic equation and Elovich equation; the sorption quantity of the slow sorption section was close to that of difficult sorption and belong to deep layer and special sorption＇s. Correlation analyses showed CEC was related markedly to the maximum sorption quantity of zinc and cadmium. This indicated the sorption mechanism of purple soil on zinc and cadmium was controlled by exchangeable sorption. When Zn, Cd existed together, the speed and the quantity of sorption lowered, showing their competition of sorption place, and the competition obeyed the mass law, high concentration dominated the competition, zinc of high concentration restrained the sorption of cadmium obviously, complete threshold index of soil heavy metals should take complex pollution into account.