| Human activities(such as mining,"three wastes" emissions and agricultural production,etc.)result in increasingly serious soil Cd pollution.Soil Cd pollution not only affects crop yield and quality,but also endangers human health through the food chain.Therefore,it is necessary to repair and treat soil Cd pollution.For Cd contaminated paddy soil,it is recommended to select the in-situ remediation technology--electric remediation technology,which has little impact on soil physical and chemical properties,short remediation cycle,can reduce the total amount of soil Cd,has little impact on the environment and does not affect the normal planting of rice,and is suitable for the treatment of low permeability soil.There are two main problems in traditional electric remediation technology :(1)electric remediation technology can only remove movable dynamic Cd in soil,and better reduction effect can only be achieved after activated treatment of soil Cd,and the selection of activators with good activation effect on soil Cd and little influence on soil physical and chemical properties needs to be further studied.(2)the focusing phenomenon caused by electrode corrosion and alkaline soil pH on the cathode side in the process of electric remediation can affect the remediation effect of soil Cd and even cause secondary pollution.In view of the above problems,inorganic salts(such as calcium chloride)were selected as activators and combined with natural organic weak acids(such as humic acid)to improve the activation effect of soil Cd on the premise of having little impact on soil physical and chemical properties.Use naisuanjian corrosion electric geotextile composite materials(electrokinetic geosynthetics,EKG)as the electrode of electric repair,because of its filter,drainage and conductive function,not only avoid the electrode corrosion,and through the role of the drainage EKG electrode to avoid the electrode in the process of electrolysis of water of OH-too much into the soil,caused the cathode side soil pH alkaline soil Cd is focused on the phenomenon,improve the removal effect of soil Cd.Based on this,this study takes hunan liuyang Cd pollution in paddy soil as the research object,discusses the effect of humic acid calcium chloride activation of paddy soil Cd and its influencing factors,humic acid,calcium chloride activation were examined under the action of soil Cd electric removal performance and electric drainage process parameters,so as to paddy soil Cd repair management provide a new way of thinking.The main conclusions are as follows:(1)the effect of humic acid-calcium chloride on the activation of Cd in soil was investigated,and it was found that humic acid-calcium chloride as the activation solution could improve the activation efficiency of Cd in soil by 6.5% and 10.7%,respectively,compared with the single calcium chloride and humic acid.The activation rate of Cd in soil was 12.1% and 8.5%,respectively,and the pH of soil decreased slightly from 5.90 to5.49.The main influencing factors(activation concentration,activation time,and activation pH)of humic acid-calcium chloride activated soil Cd were identified,and it was found that when the humic acid concentration in humic acid-calcium chloride increased from 0% to 10%,the activation rate of cadmium in the soil showed a trend of first rising and then falling,with the highest around 1%,and the activation rate was about20.9%.The activation time of Cd in soil increased from 0d to 6d,and the activation rate of Cd in soil increased from 10.5% to 22.1%.The activation time was greater than 2d,and the activation rate of Cd in soil did not increase significantly.The activation rate of Cd in the soil increased with the decrease of the pH value of the activated solution,and the activation rate of Cd in the soil increased from 13.9% to 29.1% when the activated pH increased from 6 to 2.On the premise of ensuring little impact on soil physical and chemical properties,suitable conditions for activating soil Cd were selected as follows:activator concentration was 1% humic acid + calcium chloride,activation time was 2d,and activation pH was 5.(2)the performance of soil Cd removal by electric drainage under the activation of humic acid-calcium chloride was revealed.The paddy field soil was activated under theappropriate conditions described in(1).Electric drainage was conducted for 12 h with electrode spacing of 50 cm and voltage gradient of 1V/cm.The soil pH on the cathode side increased slightly from 6.19 to 6.48,which greatly weakened the soil alkalization phenomenon,thus avoiding the soil Cd enrichment on the cathode side.The total Cd content and available Cd content in the soil on the cathode side decreased from1.39mg/kg and 0.349mg/kg before electric drainage to 1.14mg/kg and 0.261mg/kg,respectively.(3)the process parameters(power on time,voltage gradient,and electrode spacing)of humic acid-calcium chloride activated electric dewatering were optimized,and it was found that increasing the power on time and voltage gradient was conducive to improving the removal effect of soil Cd,but the energy consumption would also increase correspondingly,while increasing the electrode spacing would reduce the removal effect of soil Cd.From 2h to 32 h,the removal rate of soil Cd increased from 13.95% to 37.79%,but after 12 h,the removal rate of soil Cd did not increase significantly.When the voltage gradient increased from 0V/cm to 2V/cm,the removal rate of soil Cd increased from13.14% to 35.47%.When the electrode spacing increased from 50 cm to 150 cm,the removal rate of soil Cd decreased from 20.12% to 15.13%.Based on the energy consumption,repair cycle and field operability of electric water withdrawal,the optimal process parameters for electric water withdrawal are selected as follows: power on time12 h,voltage gradient 2V/cm,and electrode spacing 50 cm. |
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