摘要
为进一步了解离子强度对可变电荷表面吸附性铜离子连续性解吸的影响,研究两种可变电荷土壤在去离子水和0.1mol·L^-1NaNO3溶液中吸附铜离子后,依次在去离子水和浓度由低到高的NaNO3溶液中连续解吸时,离子强度变化对不同pH段铜离子解吸的影响。结果表明,解吸过程中离子强度变化方向对解吸分值随pH升高的变化趋势的影响完全不同,当离子强度由大变小时,解吸分值曲线的总体趋势是随着pH的升高而降低,反之,曲线呈现为钟形,且当去离子水第一次解吸在0.1mol·L^-1NaNO3溶液中吸附的铜离子时,两种可变电荷土壤的第一次去离子水解吸均可出现重吸附现象,但铁质砖红壤解吸分值绝对值要小于红壤。整个解吸过程中,两种可变电荷土壤的铜离子吸附性铜离子的解吸特征与高岭石基本相似,但可变电荷土壤与高岭石以及两种可变电荷土壤之间,解吸分值的变化规律均存在一定的差异性,可变电荷土壤中的氧化铁含量多少被认为是导致这些差异的主要原因。
【Objective】To investigate in depth effects of ionic strength on desorption of Cu(Ⅱ)pre-adsorbed on surface of variable charges, two variable charge soils, Ali-Haplic Acrisol and HyperRhodic Ferrasol were employed in a successive desorption experiment, in which the soils had been pretreated with copper ions in de-ionized water or 0.1 mol·L-1 NaNO3 for adsorption and were then treated with a series of NaNO3 stripping solutions with concentration ranging from low to high, to desorb the preadsorbed Cu(Ⅱ) from the soils. 【Method】In this study, the two variable charge soils were pretreated with electrodialysis and then subjected to a series of adsorption and desorption tests with varying pH in an attempt to characterize copper ion(Cu(Ⅱ)) desorption from clay minerals.【Result】Similar to the findings in the studies on kaolinite, Cu(Ⅱ) adsorption of the soils increased rapidly from 0.05 to nearly 1 in score value within the range of the pH set for this research(pH 3.0~6.3). No matter what concentration of the electrolyte used, all the adsorption score value curves could be fitted with Fischer equation and the degree of fitting reached as high as 0.996 or more. Also it was noteworthy to note that when adsorption occurred in de-ionized water or 0.1 mol·L-1 NaNO3 solution, the same in pH, Cu(Ⅱ) adsorption was always higher in de-ionized water than in 0.1 mol·L-1 NaNO3 solution in score value, which was attributed to the effect of the high concentration of electrolyte in the solution inhibiting Cu(Ⅱ) adsorption. The findings of this experiment indicate, 1) that the adsorbed copper ions can be desorbed in de-ionized water and the desorption will decline in score value with desorption going on round after round in the waters the same in pH;2) that in most cases, pH of the equilibrium liquid remains basically the same, around pH5.0, when the desorption lowers down to almost zero in score value;and 3) that the phenomena of re-adsorption will occur during the first round of desorption in de-ionized water only with pH above a specific pH, when the soils are pre-treated in 0.1 mol·L-1 NaNO3 solution, which means the copper ions will be adsorbed rather than desorbed when the equilibrium liquid is above this specific value in pH. Compared to Ali-Haplic Acrisol, Hyper-Rhodic Ferrasol is much lower in Cu(Ⅱ) re-adsorption threshold. Similar to what happens in kaolinite, the results of sequential Cu(Ⅱ) desorptions with NaNO3 solutions varying in concentration from low to high after the soils that had been pre-treated in either de-ionized water or 0.1 mol·L-1 NaNO3 solution, were subjected to three rounds of desorption with de-ionized water demonstrate 1) that Cu(Ⅱ) that could not apparently be desorbed by de-ionized water, can be desorbed by NaNO3 solution, and all the score value curves of pH-desorption follow a trend of rising first and then declining with rising pH regardless of concentration of NaNO3 or rounds of desorption;2) that the score value of Cu(Ⅱ) desorption peaks in0.1 mol·L-1 NaNO3 solution;and 3) regardless of the concentration of NaNO3, there is a relatively gradual rise process before the desorption begins to soar up in score value. In all the case, Ali-Haper Acrisol is higher than Hyper-Rhodic Ferrasol in Cu(Ⅱ) desorption score value, and in most cases the desorption score value curve has an apparent turning point where the desorption score value abruptly soars up, regardless of concentration of NaNO3 and rounds of desorption. Although the desorption equilibrium suspensions are not consistent in pH at the turning points, however, the pH at the turning points corresponding to the pHch of the desorption equilibrium suspensions are quite consistent, lingering around a special pH, that is, pH3.5,for Cu(Ⅱ) adsorbed in de-ionized water, and pH3.18 or pH3.39 for CU(Ⅱ) adsorbed in 0.1 mol·L-1 NaNO3 solution, which means that the copper ions adsorbed near the turning points of the pH-adsorption curves under any adsorption conditions exhibit a similar tendency in the desorption tests, that is climbing gently first and then abruptly soaring up with rising pH of the system. 【Conclusion】All the above-descrobed phenomenon and differences can be attributed to the difference between the two variable charge soils in content of iron oxide and the difference between iron oxide and kaolinite in nature of the surface charge.
作者
邹献中
陈勇
谢卓文
艾绍英
ZOU Xianzhong;CHEN Yong;XIE Zhuowen;AI Shaoying(Institute of Agricultural Resources and Environment, Guangdong Academy of Agricultural Sciences,Key L aboratory of Plant Nutrition and Fertilizer in South Region, Ministry of Agriculture, Guangdong Key L aboratory of Nutrient Cycling and Farmland Conservation, Guangzhou 510640, China;Agricultural Technology Service Promotion Center of Gaoming District, Foshan City, Foshan, Guangdong 528500, China)
出处
《土壤学报》
CAS
CSCD
北大核心
2019年第3期672-681,共10页
Acta Pedologica Sinica
基金
广东省自然科学基金项目(2015A030313567)
广东省属科研机构改革创新领域项目(2016B070701009)
广东省应用型科技研发专项资金项目(2016B020240009)资助~~
关键词
可变电荷土壤
铜离子
重吸附
特征pH
解吸峰
Variable charge soil
Copper ions
Re-adsorption
Characteristic pH
Desorption peak
