Electrokinetic Remediation Of Fluorine-Contaminated Soil By Separate Electrolytic Cell System Coupled With Enhancer

Endemic fluorosis is a global geochemical disease resulting from overtaking of fluorine.Human body takes fluorine mainly through drinking water and eating foods.Soil fluorine is a major source for underground/surface water and food fluorine.Therefore,it is of great practical significance to remediate fluorine-contaminated soil.Electrokinetic technique has been widely used to remediate soil,sludge and sediment contaminated by heavy metals as well as organic pollutants.Literatures have suggested that such technique can also be used to remediate fluorine-polluted soil.However,when traditional integrated electrolytic cell system is adopted to remediate fluorine-contaminated soil by electrokinetics,it is easy for fluorine to cumulate in the central part of the soil body.As a result,the difference of fluorine content between each part is greater,the removal rate of soil fluorine is lower,and the difference of soil pH near the two poles is also obvious.On that account,with self-made separate electrolytic cell system,under 0.5,1.0 and 1.5 V?cm^-11 voltage,using deionized water as an electrolyte and ammonia of different concentrations as an enhancer,this paper used various methods—pulsed electric fields,exchanging electrode periodically,adding Al₂O₃ as adsorbent in the central chamber of the separate electrolytic cell system—and investigated the mechanism of electrokinetic remediation of fluorine-contaminated soil,the variation of soil pH within each part after remediation,the difference in residual fluorine content as well as the power consumption during the remediation process by using separate electrolytic cell system.The conclusions are as follows:1.Using deionized water as an electrolyte,separate electrolytic cell system has better effect for electrokinetic remediation of fluorine-contaminated soil,the residual fluorine content is between 394.98⁶35.15 mg·kg^-11 after remediation,with a significant decline compared with the soil fluorine content 1197.2 mg·kg^-11 before the experiment and a smaller difference of residual fluorine content between each part.The soil fluorine removal rate is positively correlated with voltage gradient,and the removal rate is higher compared with the traditional integrated electrolytic cell system.2.With separate electrolytic cell system,the current can be greatly enhanced by using ammonia as anode electrolyte during the remediation process,the current is in positive correlation with the ammonia concentration,and the electrolyte pH increases with the rise of the ammonia concentration.Ammonia promotes the desorption of fluorine in the soil,increases the electroosmotic flow,which results in an increase of soil fluorine removal rate from 61.86%to 79.50%.The difference of soil pH is smaller between each part after remediation and similar to the original soil pH.3.With the same voltage gradient,the current can be obviously enhanced by using pulsed electric fields during the remediation process,and the soil fluorine removal rate is significantly increased,with a highest value of 73.46%.In contrast to a stable voltage,energy efficiency increases by 27.5³3.2%,and the energy consumption and cost is lowered.4.Exchange electrode-electrokinetic remediation of fluorine-contaminated soil by separate electrolytic cell system can remove soil fluorine efficiently and the difference of soil pH near the two poles reduces obviously after remediation.But compared with a stable voltage mode,the energyconsumption is greater and the energy efficiency is somewhat reduced.5.Under electrokinetic remediation for fluorine-contaminated soil by using separate electrolytic cell system coupled with Al₂O₃ adsorbent,the residual soil fluorine content is 265.14⁵61.87 mg·kg^-11 between different soil parts after remediation,with an obvious decline compared with the method without adding Al₂O₃.The soil fluorine removal rate accordingly increases almost 10 percentage points,but the difference of soil pH between each part is greater.6.In contrast to the electrokinetic remediation by using a stable voltage mode,12h exchange electrode-electrokinetic coupled with Al₂O₃ adsorption has a certain removal effect,but the removal rate is not significantly increased,and the difference of soil pH between each part is smaller.Electrokinetic remediation of fluorine-contaminated soil by separate electrolytic cell system could effectively remediate the fluorine-contaminated soil.When it is in the practical application,the effectiveness,soil physicochemical properties after remediation,and the remediation cost should be taken into account,and then selecte the appropriate intensifiers and power mode to remediate the contaminated soil.