Study On The Acidification Characteristics Of Purple Soil By Electrodialysis

The acidification degree of purple soil is getting worse.Purple siol is one kind of non-zonal soil.The acidification characteristic of purple soil is different from the zonal red soil and yellow soil in southern China.Existing studies lack a complete study of the acidification characteristics and the acidification process of purple soil.Therefore,understanding the acidification process and acidification characteristics of purple soil is of great significance to the remediation of acidified purple soil.In this study,electrodialysis treatment was used to simulate the acidification process of purple soil.Electrodialysis,a technique for purification and separation,can acidify soil quickly and efficiently.Firstly,in this study,we compared the acidified effect of purple soil with the methods of electrodialysis and traditional acid leaching.Then,electrodialysis was applied to acidified different kinds of purple soils.These purple soils are developed from different parent materials?e.g.,Jurassic Suining Formation?J₃s?,Shaximiao Formation?J₃s?,Penglaizhen Formation?J₃p?,and Cretaceous Jiaguan Formation?K₂j??and developed from same parent material but with different development degrees?e.g.,sandstone,mudstone,stony sub-soil,half sand half mud,big-eyed mud,purple yellow mud?.The variation of soil chemical properties was monitored in the process of electrodialysis.Besides,the acidification potential of acid purple soil was evaluated by electrodialysis treatment.The experimental results are as follows:1.Compared with acid leaching treatment,electrodialysis can significantly increase the content of active acidity and potential acidity in purple soil during a short time as well as reduce the content of soil exchangeable base cations.Electrodialysis treatment can better achieve the rapid acidification of purple soils than that of acid leaching treatment.Even the strongly acid soil can be further acidified by elelctrodialysis treatment.The measurement process of electrodialysis is simple and convenient.Therefore,the electrodialysis can be used to simulate the acidification of purple soil.2.The parent material of purple soil significantly affected the acidification characteristics of purple soil.Purple soils with different parent materials had different characteristics of soil acidity.Purple soil developed from the sandstone of Jiaguan Formation had a relatively low CEC?cation exchangeable capacity?and pH value because of its mieral composition.However,this kind of soil had a slow acidification rate and low acidification degree after elelctrodialysis treatment.Generally,purple soil developed from mud shale of Shaximiao Formation,is rich in mineral composition.This kind of soil always has high CEC value and neutral or alkaline pH value.It had a serious acidification degree after the process of simulated soil acidification.This can be attributed to the high CEC value,which induced much more H⁺and Al³⁺can be absorbed on the soil surface than other soils.The purple soils developed from calcareous mudstone of Penglaizhen Formation and Suining Formation developed by are rich in carbonate.After the same electrodialysis treatment as other soils,the purple soils developed from calcareous mudstone always maintain their pH values around 8.It means that,with high content carbonate in the soil,these kinds of soils are had to be acidified.3.After electrodialysis,the acidification characteristics of purple soil with different development degree are not same.These purple soils are developed from the same parent rock but have different degrees of development and different acidification characteristics under the influence of topography of the hills.As the degree of soil development increases,the content of primary minerals and 2:1 clay minerals?montmorillonite and illite?in the soil decreased,and the degree of soil acidification increased.The parent rock at the top of the hills was rich in carbonate,which remained the pH value of soil in alkaline after electrodialysis treatment.After the carbonates are exhausted in stony sub-soil,half sand half mud,big-eyed mud,the cation exchange process begins to buffer soil acidification.The soil had a deeper acidification degree if the CEC of soil was higher.Consequencely,these soils?stony sub-soil,half sand half mud,and big-eyed mud?had a higher acidified degree than purple yellow mud after electrodialysis.4.High CEC values increased the potential acidification risk of acid purple.Compared to red soil and latosol,the acidic purple soils had higher content of base cations and high base saturation.However,after elelctrodialysis treatment,acid pruple soils had a higher content of soil acidity than that of red soil and latosol.At the beginning of soil acidification in the electrodialysis,the variation of soil acidity can be buffered by the reaction of soil exchangeable base cations.Unfortunately,with increasing electrodialysis time,more acidic ions(H⁺and Al³⁺)will be adsorbed on the colloidal surface of acid purple soils than that of red soil and latosol,which increased the potential acidification risk of acid purple soils.