Study On Remediation Of Pb And Cd In Soil By Solidification And Its Stability

With the development of industry and agriculture,the pollution of heavy metals in soil is becoming more and more serious in China.In this paper,soil samples from simulated lead and cadmium contaminated soil were studied by chemical solidification,and the transformation rule and repair effect before and after soil solidification were studied by Tessier continuous extraction and TCLP detection.The soil was characterized by XRD,and the mechanism of the curing agent was discussed.Simulated acid rain and pot experiment were used to evaluate the stability of soil after curing.The main conclusions are as follows:?1?Curing agent screening test results show that for 5×500mg/kg of lead-contaminated soil,ferrous ammonium phosphate has a good curing effect with a stable efficiency of 89.4%;for 100×1mg/kg of cadmium-contaminated soil.The curing effect was better when the calcium magnesium phosphate fertilizer was combined with ammonium polyphosphate?mass ratio 0.5:1.5?,and the stability efficiency was 77.8%.?2?Optimum process conditions for Pb and Cd solidification:The solidification time of Pb-contaminated soil with ferrous ammonium phosphate is 21 days,and the corresponding amount of curing agent when the Pb contamination multiple is 1,3,5,8,and 10 times.For 0.5%,1.2%,1.5%,2%,2.3%,the relationship between the amount of curing agent added and the multiple of pollution is y=0.0031x³-0.0628x²+0.5484x;Calcium magnesium phosphate fertilizer and ammonium polyphosphate combined repair Cd contaminated soil,The curing time is14 days.When the contamination multiples of Cd are 30,40,50,70,and 100 times,the corresponding amounts of curing agent are 0.2%,0.5%,1.0%,1.5%,2.0%,and the amount of curing agent added.The relationship with the multiple of contamination is y=-6E-06x³+0.001x²-0.0159x.?3?Under the acid rain leaching conditions,the leaching toxicity of the solidified soil is small,and the stability of Pb and Cd after curing is good.?4?Study on the mechanism of curing agent:After curing,lead phosphate?PbH₂PO₄,Pb₃?PO₄?₂?and phosphorite?Pb-PO₄-Cl/OH?and mixed heavy metal precipitates?Fe-PO₄-Pb-OH?;Cd in contaminated soil and curing agent form precipitates such as cadmium phosphate,cadmium phosphate,and phenyl phenyl phosphate cadmium hydrate,and compete with each other through the elements Antagonism and other processes reduce the bioavailability of Cd in contaminated soils.?5?Pot experiment results showed that in the solidified soil,the growth status of plants in low-pollution soil was good,and the content of heavy metals in plants was in line with the standard;the biomass in high-contaminated soil was small,and the content of heavy metals in plants was relatively high.