| The soil pollution is becoming more and more serious.The main pollutants are cadmium,nickel,copper,arsenic,mercury,lead,DDT and PAHs.,it is urgent to control them.In the remediation and treatment of heavy metal pollution in agricultural land,soil washing is a kind of remediation technology with simple operation,quick effect and high removal efficiency of heavy metals,which can completely remove heavy metals from soil.The purpose of this study was to investigate the effect of humic substances?HS?extracted from different sources and extracts on soil leaching removal of Pb and Cd.lastly,evaluated the changes of soil overall properties after washing.The details are as follows:three different extractants?extract?:1.0 mol/L Na OH,extract?:0.1 mol/L Na OH+0.1mol/L Na4P2O7,extract?:0.1 mol/L KOH+0.1mol/L K4P2O7?were selected to derive HS from five sources?Leonardite,Sewage sludge,Chicken manure,Peat soil,Cow dung?.Next,the soil was washed and the leaching conditions were optimized by orthogonal experiments.Fourier Transform Infrared Spectroscopy?FTIR?was used to analyze the differences of humic functional groups.,and scanning electron microscopy?SEM?combined with energy spectroscopy?EDS?was used to compare the changes of apparent structure and element content before and after soil leaching.BCR three-step extraction method was used to study the change and moving coefficient of Pb and Cd occurrence in soil.Conclusively,the risk of HS washing soil was assessed by discussing the changes of soil physicochemical properties,heavy metal morphology,enzyme activity,and wheat germination toxicity experiments after leaching.The main conclusions are as follows:?1?Among the five sources of HS,the total acid groups of chicken manure and cow dung were lower,mean that the groups could react with heavy metals were less.HS properties are quite different,and the TOC concentration of lignite and sludge extraction was higher.Except for lignite,the extraction HS of extract?was better than that of extract?and?.?2?The washing of soil with p H 4.0 HS results in different changes but the change trend of soil p H values was the same.Overall,the order of soil p H after washing was as follows:extract?;extract?;extract?.The removal rate of Pb was not very high which the best effect was HM?.The Pb content decreased from 2738.58 mg/kg to 1916.63 mg/kg,and the removal rate was 30.01%.HM?removal rate of Cd was most significant?p<0.05?.And the content of Cd decreased from 18.63 mg/kg to 10.23 mg/kg.In all processing groups the maximum removal rate of single washing was 45.78%.?3?The removal rate of Pb and Cd in treatment group 24 was significantly higher than other treatments after orthogonal experiment optimization of solid-liquid ratio,p H and elution time.When the solid-liquid ratio was 1:40,the p H was 7.0 and the elution time was960 minute,the washing removal rates of Pb and Cd were 43.74%and 52.80%for single washing,respectively.?4?The main removal of Pb and Cd by HS leaching is the weak acid extracted and reducible in the soil.?5?The leaching of HS solution had no effect on soil p H value and total nitrogen,but the total phosphorus,total potassium and organic matter content increased significantly.The activity of catalase and sucrase decreased significantly compared with before and after washing.Instead,it would promote dehydrogenase activity.There was no change of urease activity after washing.?6?Changes of soil particles before and after washing were compared by scanning electron microscopy and combined with EDS energy spectrum analysis,it was found that the particle size of soil aggregates did not change significantly before and after leaching The EDS energy spectrum showed that the phosphorus and potassium elements increased after washing,which proved that the total potassium and total phosphorus content could be increased by HS leaching.?7?After comparing wheat germination rate,germination potential,germination index and vigor index,it was found that the soil after washing was more favorable for wheat germination. |
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