柠檬酸对茶园紫色土微团聚体竞争吸附Zn、Cd影响

采用批量培养和平衡吸附法,选取原土及微团聚体颗粒组为对象,研究Zn(II)、Cd(II)单一存在、二元竞争及竞争体系中加入柠檬酸(0.1,1,10mmol/L)等3种处理的等温吸附特性及影响。结果表明:(1)以专性吸附方式为主的多层吸附随Zn~(2+)、Cd~(2+)强度增加逐渐饱和,吸附能力以0.002mm最优、0.05~0.002mm和原土次之,0.25~0.05mm和2~0.25mm结合能力稍差,不同条件下Cd较Zn更易积累。吸附过程为自发吸热反应,热力学Freundlich方程(Zn:R2=0.960~0.997;Cd:R2=0.957~0.995)拟合结果优于Langmiur方程(Zn:R2=0.952~0.995;Cd:R2=0.913~0.991)。最大吸附量与有机质含量具有显著相关性。(2)单一处理Zn、Cd的固持效果明显、共存处理时Zn、Cd竞争行为表现为彼此削弱,Zn对Cd的吸附具有更强抑制作用。(3)添加不同浓度柠檬酸后Zn、Cd吸附水平介于单一及共存处理之间呈动态变化(Zn、Cd接近),0.1~1mmol/L利于Zn、Cd固持,增至10mmol/L后加速淋洗,仅0.002mm粒径富集量持续提升。表明柠檬酸作为一种调节剂,能适度保持土壤Zn供给并弱化Cd迁移活性,缓解茶园土壤复合污染。

Effects of Citric Acid on Competitive Adsorption of Zn and Cd by Soil Micro-aggregates in a Tea Plantation

In order to investigate the effects of citric acid on isothermal adsorption of Zn(Ⅱ) and Cd(Ⅱ) under conditions of single element,coexistence of two elements,and adding citric acid into the competitive system (a form of shorthand:the first,second,and third condition) by the purple bulk soil and micro-aggregates of different particle sizes in a tea plantation.The experiment was carried out by using methods of siphon settlement and centrifugal freezing thawing.The results showed that:(1) The multilayer adsorption dominated by specific adsorption was saturated gradually with increase of the Zn2+ and Cd2+ concentration.The adsorptive amount order was ＜0.002 mm ＞ 0.05-0.002 mm ＞ bulk soil.The Zn and Cd accumulating ability of the micro-aggregates of 0.25-0.05 mm and 2-0.25 mm particle sizes were relatively lower.Under different conditions,Cd was easier to accumulate than Zn.The adsorption of Zn and Cd on soil surface was spontaneous and exothermic.The fitting results of the Freundlich equations were better than those of the Langmiur equation.At the same time,there was a significant correlation between the maximum adsorption capacity and organic matter content.(2) Under a single processing mode,the holding effects of Zn and Cd were obvious.When Zn and Cd coexisted,their competitive behaviors weaken each other,with Zn having a stronger inhibitory effect on Cd.(3) Citric acid promoted the adsorption of Zn and Cd when the concentration was 0.1-1 mmol/L,but accelerated leaching when the concentration was increased to 10 mmol/L.The retention of Zn and Cd by micro-aggregates (＜0.002 mm) was further increased after adding citric acid at different concentrations.The results showed that citric acid could be used as a regulator to maintain the supply of Zn in the soil appropriately while weakening the migration of Cd,in order to alleviate the compound pollution in the soil in tea plantations.