Adsorption Traits Of Se⁴⁺ In The Original Soil And Different Particle Sizes Of Micro Aggregate From Mingshan Old Alluvial Yellow Soil

As an essential trace element,Selenium(Se)is the micronutrient throughout the body,and Se is statistically relative to self-physical health status.However,Se cannot be automatically synthesized in the body,and can only be obtained through food and drinking water.Considering both of the two sources are from the soil directly or indirectly,making a study of the migration and transformation rule of Se in the soil is necessary.What is worthy of mention is that due to Se-enriched tea owns mutilple healthy care functions,which is favored by many people.Aiming to supply primary reference datas and theoretical basis for improving the Se content of tea,and producting Se-enriched tea,this paper has chosen the old alluvial yellow soil of Mengdingshan for the experimental material,which has been used for cultivating tea,worked on the adsorption traits of Se4+in the original soil and different particle sizes of micro aggregate(i.e.,particle size<0.002mm,0.002<particle size<0.053mm,0.053<particle size<0.25mm,0.25<particle size<2mm).Besides,this study processed the analysis of the influences from organic matter and free iron oxide on different particle sizes of micro aggregate adsorping Se4+.Main results are as followings:(1)The adsorption capacity is positively correlated with the initial concentration of Se4+ in the soil.In the preliminary stage,the adsorption of Se4+ in the original soil and different particle sizes of micro aggregate was increased remarkably with the increase of Se4+ concentration.Moreover,as the Se4+ concentration increases,the adsorption rate decreases,and the adsorption gradually comes to a balance.The order of Se4+ adsorption in the original soil and different particle sizes of micro aggregate in sequence is as following:size<0.002mm,0.002<particle size<0.053mm,then the original soil,and between 2mm and 0.25mm,and finally between 0.25mm and 0.053mm,which is in keeping with the distribution trend of organic matter and free iron oxide in the soil.The isothermal adsorption process simulated by thermodynamic equation shows that the equation of Langmuir has the best effect,and then Freundlich,which is impling that the Se4+ adsorption in the original soil and different particle sizes of micro aggregate is mainly single layer adsorption.(2)Se4+ adsorption in the original soil and different particle sizes of micro aggregate could be divided into two dynamic stages,i.e.rapid adsorption(non-obligatory adsorption)and slow adsorption(obligatory adsorption)respectively.In the first one hour,Se4+adsorption soares rapidly,and the rate of Se4+ adsorption shows the highest level at this time.Most worthy of mention is that the Se4+ content is almost reaching 90%-97%at the time of 720 minutes,then the adsorption trend is gradually gentle,Se4+ adsorption is going to be in equilibrium.The order of Se4+ adsorption in the original soil and different particle sizes of micro aggregate is as following:size<0.002mm,0.002<particle size<0.053mm,and then original,and then between 2mm and 0.25mm,and finally between 0.25mm and 0.053mm in sequence,which also is in keeping with the distribution trend of organic matter and free iron oxide in soil.Through proposing five common dynamics equation,this paper shows that the fitting effect of the Elovich equation on the adsorption process of selenium is the best,and the first-order diffusion equation has the worst result,which reflects that the kinetic adsorption of selenium in the different particle sizes of micro aggregate on the soil is not a single process,it may include additional processes except dissolution and diffusion.(3)When soil organic matter and free iron oxide are removed separately,the adsorption capacity of Se4+ in the different particle sizes of micro aggregate on the soil is as following:size<0.002mm,0.002<particle size<0.053mm,and then original,and then between 2mm and 0.25mm,and finally between 0.25mm and 0.053mm.This regular pattern is in according with the pattern in the untreated original soil.Comparing the adsorption rate and the adsorption capacity of Se4+ in original soil,both this two items in treated original soil and in treated different particle sizes of micro aggregate decreases instantly.Adsorption capacity of Se4+ in the original soil and in different particle sizes of micro aggregate that contains no free iron oxide is lower than in that contains no organic matter.The results comparing adsorption capacities of Se4+ in three kinds of soil are as followings:original soil,then the soil that contains no organic matter,and finally the soil that contains no free iron oxide.Both Langmuir equation and Freundlich equation can fit the Se4+ adsorption of the soil well,and the former one has the best fitting results.(4)After removing soil organic matter and free iron oxide separately,the dynamic adsorption traits of Se4+ in the original soil and different particle sizes of micro aggregate presents a trend that the index soars remarkably at first and then increases lower than before.In the first one hour,the rate of Se4+ adsorption can stay in high status,and the adsorption capacity rate of Se4+ adsorption rises rapidly during this time,and then increases slowly and gradually comes to the balance state after the time of 960 minutes.The adsorption capacity of Se4+ in the original soil and different particle sizes of micro aggregate is as following:size<0.002mm,0.002<particle size<0.053mm,and then original soil,and then between 2mm and 0.25mm,and finally between 0.25mm and 0.053mm.The adsorption rule is the same as which in the original soil that contains both soil organic matter and free iron oxide.Adsorption capacity of Se4+ in the original soil and in different particle sizes of micro aggregate that contains no organic matter is higher than in that contains no free iron oxide.The results comparing adsorption capacities of Se4+ in three kinds of soil are as followings:original soil,then the soil that contains no organic matter,and finally the soil that contains no free iron oxide.Through proposing five common dynamics equation,this paper shows that the fitting effect of the second-order diffusion equation on the adsorption process of selenium is the best in the soil that contains no soil organic matter,and Elovich equation is the best in the soil that contains no free iron oxide.Besides,but the first-order diffusion equation has the worst result.