Experimental Research On Non-Hazardous Treatment Of Cyanide Contaminated Soil

Cyanide is known as highly toxic and harm to humans,animals,plants and aquatic organisms through many ways,even endanger to human life.Therefore,the treatment of cyanide pollution is very urgent.Among many kinds of soil treatment technologies,the leaching technology has the advantages of wide range,quick effect,large capacity,remarkable effect,low processing cost,etc.,and has been widely used in soil remediation.In this paper,cyanide in contaminated soil was treated by leaching method.The cyanide leaching process was studied by jar test,column test and continuous test.The cyanide leaching liquid was treated by ozone advanced oxidation process.The realization of cyanide soil detoxification and cyanide contaminated wastewater treatment provide a theoretical basis for real application.In addition,the slope stability of actual heap was discussed in this paper.In this study,raw soil with cyanide contaminated from Tianjin was used as the experimental sample.The treatment of cyanide-contaminated soil by leaching method shows that:Solid-liquid ratio,stirring strength and leaching concentration had no significant effect on cyanide leaching.Temperature and soil particle size were the key factors affecting cyanide leaching.The leaching process could be inproved by higher leaching temperature and less particle size of soil.The effects of leaching intensity and soil particle size on cyanide from contaminated soils were studied by column test.The results showed that:for 0.5 mm<r0?1 mm soil,it had no significant effect on cyanide leaching rate with leaching intensity.While with particle sizes of 1 mm<r0?2 mm,2 mm<r0?3 mm,3 mm<r0?4 mm and 4 mm<r0?5 mm,the best leaching effect of cyanide was achieved under the leaching intensity of 42 L/(m2·h),52 L/(m2-h),65 L/(m2·h)and 79 L/(m2·h),respectively,and the leaching time was 715 min,430 min,350 min,280 min and 230 min,respectively.When the leaching intensity increased from 15 L/(m2·h)to 32 L/(m2·h)and 79 L/(m2·h),and the leaching time was decreased by 21%and 62%,respectively.With the same leaching intensity and time,the residual cyanide concentration in the soil was increased with particle size.The leaching processes were all belong to deceleration stage,which could be divided into the first stage and the second stage.The leaching rate decreased with cyanide concentration.Since there was some content cyanide in leaching liquid,the non-hazardous treatment of cyanide contaminated wastewater was studied.The effect of ozone and its combination process on the contaminated wastewater treatment was studied.The results show that different ozone dosages had different effects.The removal rates of total cyanide was 12.9%and 46.7%when the ozone dosage was 0.3 g/h and 4 g/h respectively after 20 h treatment.The hybrid process with ozone(0.3 g/h)and activated carbon has little promotion on cyanide(about 10.9%).However,by adding ultraviolet(UV)to ozone,it has a significant effect on cyanide removal.The total cyanide concentration decreased below the detection line after 2h treatment,which indicated that the ozonic-UV hybrid process was a fast and effective method for treating cyanide wastewater.The non-hazardous treatment of cyanide contaiminated soil and leaching liquid were studied by a column test with the leaching-ozone-UV process that the rinsing intensity was 79 L/(m2·h),the dosage of ozone was 0.3 g/h,the ultraviolet reacto intensity was 145?w/cm2 and the hydraulic detention time(HRT)was about 1.17 min.After 30 h of treatment,total cyanide concentration in contaminated soil was decreased from 68.95 mg/kg to 6.70 mg/kg,the total cyanide in the leaching liquid decreased from 14.78 mg/L to 0.97 mg/L,and the total cyanide in the circulating water was below 0.5 mg/L.The concentration of cyanide in the treated soil reached the requirement of soil risk control standard of soil environmental quality construction land(GB 36600-2018)for residential land less than 9.86 mg/kg.And the cyanide in the treated wastewater reached the requirement of less than 0.5 mg/L in GB 8978-1996.The heap is unstable state and the higher the heap is,the less the area will be,but it will cause slope collapse and even heap accident.In order to determine the stability of the heap,the FLAC3D numerical simulation method was conducted to study the slope stability.The simulation results showed that:when heap-load height was 5.2 m,the plastic zone and potential slip surface of the heap was not through,the calculation was convergent and the displacement did not change.The safety factor calculated by FLAC3D numerical simulation method was 3.85,which is larger than 1.25 in the Design Code for Non-ferrous Metals Mine dump(GB 50421-2007).It indicates that the whole heap was in a stable state under the design conditions and will not produce landslides.