| "The national soil pollution survey bulletin"published by the Ministry of environmental protection in 2014 pointed out that"the overall situation of the national soil environment is not optimistic,and the soil environment problems in the waste land of petrochemical,electroplating,coking,metallurgy and other industrial and mining enterprises are outstanding".Cyanide is an important soil pollutant in the contaminated sites of the above industrial enterprises.The study shows that cyanide in soil mainly exists in the form of complexation,and mainly is ferricyanide complex,and there is no simple cyanide.Ferricyanide is a strong complex,with high stability and strong adsorption with mineral colloid,which is not conducive to degradation and removal.At present,there are few researches on remediation and treatment technology of cyanide bearing soil at home and abroad.Therefore,it is necessary to carry out research on soil remediation technology in cyanide contaminated site.In this paper,the low temperature heat treatment technology is applied to repair the contaminated soil of cyanide,and some kinds of complex ferrocyanide,such as potassium ferrocyanide,potassium ferrocyanide and ferrocyanide,are used as the target pollutants,and the soil with different concentrations of cyanide is artificially prepared.The effects of heat treatment temperature,time,atmosphere,soil particle size,cyanide shape and concentration on the removal efficiency of cyanide in the soil are investigated,and the optimum process conditions and technological parameters are obtained.The experiment shows that temperature and time have significant effect on cyanide removal.Under 200 ~oC conditions,cyanide removal efficiency in cyanide bearing soils was lower than 60%.When heat treatment temperature is 300~oC,the removal rate of ferricyanide and ferrocyanide in contaminated soil can reach more than 99%,and the removal rate of ferrocyanide is only 71%,and the removal rate of ferrocyanide can be increased to more than 94%by increasing temperature to above 400~oC.In addition to temperature,time has an important effect on the effect of heat treatment.Under the condition of 300 ~oC,the heat treatment time is 0.5h,the removal rate of cyanide is about 90%,the prolonging time to 1h,the removal rate of cyanide can be increased to over 99%.The form and concentration of cyanide have a certain effect on the removal of cyanide.The degree of cyanide removel by different cyanide forms is Potassium ferrocyanide is superior to potassium ferricyanide and iron cyanide is inferior to both.In the same form of cyanide,the effect of cyanide concentration in soil on the removal rate of pollutants is not very large,but more cyanide will enter the tail gas absorption solution in the form of easy-released cyanogen in the low concentration cyanide condition.The effect of heat treatment atmosphere and soil particle size on cyanide removal is not significant.It is concluded that under the air atmosphere,and when the heat treatment temperature is300~oC,the removal rate of cyanide in the soil polluted by potassium ferricyanide and potassium ferricyanide can reach more than 99%after heat treatment for 1h.For the soil polluted by ferrocyanide,the better removal efficiency can be achieved by increasing the temperature to above 400~oC.It is necessary to collect and reclaim cyanide containing waste gas in the process of cyanide bearing soil heat treatment.In this study,the cyanide containing tail gas is absorbed by high concentration alkaline solution,and then the cyanide in the alkaline waste liquid is concentrated and adsorbed by activated carbon.The factors that affect the adsorption efficiency of activated carbon,such as the amount of activated carbon,the time of adsorption,the pH value of the waste liquid and the temperature of the reaction system,are discussed in detail.In addition,the activated carbon after adsorption of cyanide containing wastewater is treated by heat treatment.The results show that the amount of activated carbon is 10g/L,and the pH of cyanide containing wastewater is about 8,adsorbed for 12h at room temperature,activated carbon shows good adsorption effect on cyanide,and the total cyanogen adsorption efficiency can reach more than 70%.In the process of thermal regeneration of activated carbon with cyanide,the process conditions are set at 300~oC,and the adsorption performance can be recovered after the heat treatment time 1h.After four reuses,the adsorption efficiency is23.06%,the regeneration efficiency is 32.50%,and the carbon loss rate is 18.39%.According to the conclusion of the paper,the remediation of cyanide containing soil by low temperature heat treatment is a better soil remediation technology,which has the advantages of wide application,high efficiency,complete safety and no second pollution.The technology is combined with activated carbon adsorption method to treat waste gas absorption tail liquid,and the activated carbon after adsorption is recycled and recycled through heat treatment.It can effectively realize the whole process of remediation and remediation of cyanide containing soil and waste gas,which is environmental protection and efficient,and has a bright future. |
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