Study On Passivation Effect Of Iron Oxide Method And Heap Decay Method On Heavy Metal Mixed Contaminated Soil

Remediation of heavy metal-contaminated soils is one of the serious challenges in addressing environmental issues,which are difficult to degrade in the soil.Many researchers have proposed many methods to passivate heavy metals in soil,with excellent passivation efficiency but a complex and costly treatment process.In recent years,ferrite has developed rapidly in the removal of heavy metals from water,and composting has been effective in the treatment of heavy metals in sludge and animal manure.In fact,they have had far-reaching research implications in passivating heavy metal-contaminated soils.This paper investigates the stabilization efficiency of iron oxide method and heap rot method for passivation repair of heavy metal mixed contaminated soils using simulated chromium,cadmium,nickel and lead mixed contamination.The specific studies are as follows.?1?The effect of iron oxide heating method on the passivation efficiency of chromium in heavy metal contaminated soil was studied.The effects of Fe???/Fe???molar ratio,Fe/Cr molar ratio and pH on chromium passivation efficiency were investigated.The results show that the addition of a mixture of ferric sulfate and ferrous sulfate?0.35 mmol ferric sulfate and 3.2 mmol ferrous sulfate?will form iron oxide crystals in the chromium contaminated soil and passivate the chromium in the soil.When n(Fe²⁺)/n(Fe³⁺)=5,n?Fe?/n?Cr?=40,pH=9.0,the stabilization effect is the best.The soil that has been passivated by the iron oxide method passivation,continuous extraction through BCR found that loosely combined,the acid-extractable chromium decreased from 78.83%to 0.36%,the reducible state increased from 9.89%to 14.98%,the oxidizable state increased from 9.33%to17.88%,and the residue state increased from 1.95%to 66.78%.The stability of chromium is obviously enhanced,when the pH is 3.2,the chromium leaching rate after repairing is reduced from 56.47%to 0.16%.?2?The effect of room temperature iron oxide method on the passivation efficiency of chromium,cadmium,nickel and lead in heavy metal contaminated soil was studied.Some factors were investigated like the effects of Fe???/Fe???molar ratio,Fe/M molar ratio and pH on the passivation efficiency of chromium,cadmium,nickel and lead.The results show that the best passivation effect is appeared when the reaction time is 10d,n(Fe²⁺)/n(Fe³⁺)=7,n?Fe?/n?M?=50,and the pH is around9.0.At this time,the proportion of Cr in the residual state was 63.23%,Cd in the residual state was 38.78%,Ni in the residual state was 52.24%and Pb in the residual state was 68.31%.Through the BCR sequential extraction experiment,it was found that the normal temperature iron oxide method passivation repair.After that,the proportion of acid extractable Cr in the soil decreased by 67.64%,and the proportion of residual Cr increased by 63.24%;the proportion of acid extractable Cd in soil decreased by 37.58%,and the proportion of residual Cd increased.The percentage of acid-extractable Ni in the soil decreased by 42.34%,and the proportion of residual Ni increased by 48.44%;the percentage of acid-extractable Pb in soil decreased by51.26%,and the percentage of residual Pb The proportion increased by59.98%.Through the sulfuric acid nitric acid leaching experiment,it was found that after repair the leaching amount of chromium was reduced from 2695.00 mg/kg to38.75 mg/kg,the leaching amount of cadmium was reduced from 82.3 mg/kg to7.55 mg/kg.The leaching amount decreased from 1617.00 mg/kg to 47.00 mg/kg,and the leaching amount of lead decreased from 688.40 mg/kg to 7.6 mg/kg.The passivation effect is obvious,and the risk of environmental release is significantly reduced.?3?The effect of heap rot on the passivation of chromium,cadmium,nickel and lead in heavy metal mixed contaminated soil was studied.The passivation effect of different material ratios?CK1,CK2,K3,K4,K5?on heavy metal-contaminated soils was investigated,with CK1 being soil:leaf:sludge=4:0:1?anaerobic?,CK2soil:leaf:sludge=4:2:0?anaerobic?,K3 soil:leaf:sludge=4:2:1?anaerobic?,K4soil:leaf:sludge=4:2:1?aerobic?and K5 soil:leaf:sludge=4:2:1?anaerobic+aerobic?.The results show that the pH changes of the pile body under different treatments are all in the range of 5.56-7.19;after different pile decay treatment,due to the"relative concentration effect",the total amount of heavy metals Cr,Cd,Ni,Pb in the pile body increased,but the incremental difference between different treatments because of the difference in heavy metal species,Cr content increase:K5>CK2>K4>K3>CK1;Cd content increase:CK1>K5>CK2>K3>K4;Ni content increase:CK2>K5>K3>K4>C CK1;Pb content increase:K5>CK1>K4>K3>CK2;heavy metal species,the passivation effect of pile decay is different,the passivation effect on Cr is the best,Ni,Pb second,Cd passivation effect is weakest.The passivation effect of different heap rot raw materials and conditions on heavy metals is also different,comprehensive heap rot raw materials and oxygen supply conditions,CK2 treatment on Cr passivation effect is the best,oxidizable state and residue state Cr accounted for the highest ratio of 79.25%,followed by K5 treatment,different treatment on Cd passivation effect are general,oxidizable state and residue state Cd content accounted for the highest ratio of 32.69%,K5 treatment on Ni passivation effect is the best,oxidizable state and residue state Ni content is 54.64%,followed by K4 treatment;K4treatment on Pb passivation effect is the best,oxidizable state and residue state accounted for 60.13%followed by K5 treatment.Figure 36 table 16 reference 95...