| In coastal area,groundwater has high salinity,the depth of groundwater is low and a lot of salt easily accumulate to the surface of the soil,which cause soil salinization phenomenon.The high salinity of coastal saline-alkali soil makes its utilization limited,which not only wastes of land resources,but also damages the ecological environment.Therefore,the use of this kind soil is the important action to solve the problems such as population,resource,environment and so on.This thesis took coastal saline-alkali soil in Tianjin as the research object,using the overlapping of diffuse layers on saline-alkali soil colloids with negative charge and magnesium aluminum hydroxides with positive charge to decrease the adsorption capacity of the soil to the base cations and realize desalination of saline-alkali soil.Five kinds magnesium aluminum hydroxides(MAH)of different magnesium aluminum mole ratios were made in experience,the ratios were 3:1(MAH1),2:1(MAH2),1:1(MAH3),1:2(MAH4)and 1:3(MAH5)respectively.Firstly,the experiment took MAH1 as an example and researched improvement mechanism of MAH to coastal saline-alkali soil.Secondly,the experiment screened the best MAH and its optimal dosage through measuring major indexes of the mixed soil solution with different ratio(0,10,25,50,75 and 100 mg/g)of MAH and saline-alkali soil.Thirdly,the experiment used soil column leaching to contrast and analyze the desalting process and effect of the control group made by saline-alkali soil and the improved group made under the best option.The experimental results indicated that:(1)In the 5 kinds MAH,MAH1,MAH2 and MAH3 were alkaline and pH was around 9,MAH4 and MAH5 were acidic and pH was around 5.The Zeta potential of MAH had the trend of decreasing,rising and declining with pH generally,which was mainly related to the morphology of Mg and Al in MAH under the different pH.It was proved that there was an overlapping the diffuse layers between MAH1 colloids and saline-alkali soil colloids through the Zeta potential of mixed system and took it as the improvement mechanism of MAH to coastal saline-alkali soil.The overlapping of diffuse layers also existed in alkaline environment,that proved the feasibility of MAH application in coastal saline-alkali soil improvement.The study showed that the addition amount of MAH and the pH value of the mixed system were two important factors that influenced the overlapping degree of the diffusion layers.(2)In optimization study of improvement schemes,two kinds acid MAH were better than three basic MAH in improving the pH and the removing the salinity of saline-alkali soil.The slightly more acidic MAH5 in 2 kinds acid MAH had the best desalting efficiency,and MAH5 was significantly superior than MAH4 on the removal of the major harmful Na~+in coastal saline-alkali soil.The MAH5 had a significant effect on the removal of main salinity ions,agglomeration of soil and fixation of nutrients(N,P)in the low additive amount.Therefore,screening the best improvement scheme that was adding 1%MAH5 to coastal saline-alkali soil by comprehensive analysis.(3)According to the experimental study of soil column leaching,it could be seen that MAH5 could improve the coastal saline-alkali soil in all aspects.Firstly,the addition of 1%MAH5 improved the soil physical properties from saturated hydraulic conductivity and soil aggregated particle structure.Secondly,it inhibited the alkalinization of soil effectively during the leaching process,removed soil salinity quickly in low-volume leaching solution and decreased the exchangeable Na~+in saline-alkali soil.Additionally,it fixed the nutrients(N,P)effectively in soil and inhibited the leaching of nutrients from saline-alkali soil in the process of leaching. |
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