Electrical Stimulation/H₂O₂ Oxidation-leaching Technology Research And Development Of Chromium Contaminated Site

Chromium and its compounds are indispensable industrial materials in electroplating,smelting,printing and dyeing,leather making,electronic and pharmaceutical industries.In recent years,with the rapid development of economy,because of the unreasonable and noneffective emissions of large amounts of chromium of"Three wastes"in the industrial production process,resulting in the deposition of chromium pollution in the soil,then causing soil chromium pollution,especially in chemical plant remains.Chromium pollutants have the characteristics of long time,concealment and great toxicity in the soil,and can endanger people's health and even life directly or indirectly through the food chain.Therefore,it is urgent to take effective measures to repair the chromium pollution site.In this paper,the technology of electric stimulation/H₂O₂ oxidation-leaching was applied to study the soil of chromium contaminated site in a chemical plant in Jinan to remove the heavy metal chromium in the soil of the contaminated site.Through the single factor experiment,the effect of power time,electric voltage,mass fraction of H₂O₂,solid to liquid mass ratio and pH on the transformation of Cr???into Cr???and the removal rate of total Cr have been discussed.On the basis of single factor experiment,the design and orthogonal experiment,the removal effect and economic cost,the repair of the best experimental conditions were determined,and the optimum condition analysis of environmental,economic and social benefits.In addition,the research results of this research group were compared and analyzed.The main conclusions of this paper are as follows:?1?The selection of chromate production workshop,ten thousand tons of chromate production workshop,in the north and east of chromium slag heap factory four sites in the soil,such as total chromium content seriously exceed national secondary standard of soil environmental quality(Cr_Total?250 mg/kg),the single factor index Pi value of 3.45-57.62,all belong to high levels of pollution..Among them,the content of total Cr in East chromium slag dump site was 14403.8 mg/kg,which was the most serious.The second was Chromic salt workshop,Ten thousand tons chromic salt workshop and North section of the plant with the content of total Cr was 2930.5,990.74 and 863.3 mg/kg respectively.The content of hexavalent chromium in different sites are not different,the content of hexavalent chromium was low in Ten thousand tons chromic salt workshop and North section of the plant with the concentration was respectively 7.75 and 8.11 mg/kg,but in Chromic salt workshop and East chromium slag dump site the concentration were 858.22 and 3549.12 mg/kg.The I of Ten thousand tons chromic salt workshop and North section of the plant is lower,respectively 0.0078 and 0.0094,and chromium migration activity was large and harmful.In the four sites,the pH value of the Ten thousand tons chromic salt workshop is 2.38,and the soil was acidic.The pH of the Chromic salt workshop,East chromium slag dump site and North section of the plant were 8.00,9.4 and 8.21respectively,all of which are alkaline.The content of organic matter in the four sites were between 6.8 and 31.3 g/kg,the contents of Ten thousand tons chromic salt workshop and North section of the plant were high,and the other two factories were very low.?2?The single factor experiment results of electrical stimulation and H₂O₂oxidation with chemical leaching shows that the removal rate of total Cr increased obviously with the increase in the power time in the four sites?Chromic salt workshop,Ten thousand tons chromic salt workshop,East chromium slag dump site and North section of the plant?,and the removal rate was more ideal when the power time was30 min;When the electric voltage was 20 V,the removal rate of total Cr were94.81%,53.53%,24.62%?30.15%in the four sites respectively,then the removal rate of total Cr grown slowly and even decreased with the electric voltage increase,suggesting that it can oxide part of Cr???under the condition of low electric voltage;When the concentration of H₂O₂ was 1%,the removal rate of total Cr were 71.90%,71.90%,14.42%and 35.34%respectively with ideal result.The effects of soil liquid ratio on the removal rate of total Cr were larger,and the removal efficiency was better with the increase of the solid to liquid mass ratio.The removal effect was ideal at 2:3,which were 91.44%,39.07%,19.33%and 11.90%respectively.The effect of pH on the total chromium removal rate is obvious,and the alkaline condition is better than the acidic condition,which is better for the removal of chromium pollutants.It is suggested that the soil pH should be adjusted to 8¹0.The results of single factor experiment showed that the total electric voltage was 20 V,the oxidant concentration was 1%,the soil liquid ratio was 2:3 and the pH range was 8¹0,and the total chromium removal was the best.?3?In single factor experiment based on orthogonal experiment,comprehensive consideration of total chromium removal effect,engineering,security,economic governance cost and ease of construction problems,and get the best four ground engineering parameters are as follows:The best engineering parameters of Chromic salt workshopwas that the power time was 20 min,the electric voltage was 20 V,the concentration of H₂O₂ was 3%,the soil liquid ratio of was 1:2,the pH was 10,the removal rate of total Cr reached 87.59%.For Ten thousand tons chromic salt workshop,the best parameter was that the power time was 20 min,the electric voltage was 20 V,the concentration of H₂O₂ was 3%,the soil liquid ratio was 1:2,the pH was10,the removal rate of total Cr was 73.95%.For East chromium slag dump site,the best parameter was that the power time was 20 min,the electric voltage was 20 V,the concentration of H₂O₂ was 1%,the soil liquid ratio was 2:3,the pH was 8,the removal rate was 51.83%.For North section of the plant,the power time was 40 min,the electric voltage was 20 V,the concentration of H₂O₂ was 1%,the soil liquid ratio was1:1,the pH was 10,the removal rate of total Cr was 42.61%.?4?The electrical stimulation/H₂O₂ oxidation-leaching technology in this paper,chromium contaminated soil,and our other scholars research of ultrasonic,microwave,UV improved H₂O₂ oxidation-leaching joint repair technology,compared to the repair effect of chromium contaminated soil repair effect is good,chromate production workshop,ten thousand tons of chromate production workshop and the northern factory three factory are able to meet.The total chromium pollution concentration in the soil of east chromium slag dump was up to 14403.8mg/kg.Improved H₂O₂ oxidation-leaching combined with microwave repair east chromium slag yard for chromium removal rate as high as 89.77%,and much higher than joint repair electrical stimulation/H₂O₂ oxidation-leaching 51.83%,therefore suggested that application of microwave improved H₂O₂ oxidation-leaching joint repair technology repair east chromium slag yard,and can be repeatedly repair oxidation or washed out to achieve.The research and analysis of the best governance scheme of the four polluted sites found that the technology was better than the traditional chromium contaminated soil restoration technique for the restoration of soil in the low-concentration chromium contaminated site.In addition,electric stimulation/H₂O₂ oxidation-leaching combined repair technology to repair every ton of chromium contaminated soil costs about 500⁹00 yuan,which is more economical than traditional technology.In summary,according to the actual situation of the polluted site,according to local conditions,different repair schemes are selected for different pollution sites.The results of this paper provide a basis for the repair of contaminated site in a chemical plant in Jinan.