Optimization Of EDTA Recovery And Utilization For Heavy Metals Removal From A Contaminated Soil And Fertilizing Extracted Soil

In this study,the soil polluted by heavy metals in Liling City,Hunan Province was selected as the research object.First of all,the most effective extractant and extraction conditions were determined through modeling experiment;and the recycling was carried out on soil extract by resin;then plant cultivation was conducted on the soil after extraction,and further recovered the level of soil fertility.It can provide a certain technical experience for large-scale soil chemical remediation in the future.The main conclusions were as follows:(1)Through the analysis of soil samples,the content of Pb?Zn?Cu?Cd were respectively 95.53mg·kg-1?23.84mg·kg-1?148.25mg·kg-1?0.81 mg·kg-1.The Cd pollution was more serious,which was 3.2 times over national qualified standard and it comes with a certain degree of Pb pollution.(2)From the comparation among extraction effects of organic acids and three kinds of EDTA salt,they had certain effects on Pb?Zn?Cu?Cd in soil,Among the organic acids,the extraction effect of salicylic acid on Pb?Zn?Cu?Cd was the best,and the extraction rates were respectively up to 8.83%?5.74%?4.45%?47.66%;secondly are tartaric acid and citric acid;and the glutamate acid and aspartic acid are the worst.In addition,the removal effects of EDTA solutions on Pb?Zn?Cu?Cd in the soil were higher than the organic acid solution.Removal rates on different heavy metals were: Cd>Pb>Cu>Zn.The removal effects of the three kinds of EDTA appeared as: NH4-EDTA>Na-EDTA>Ca-EDTA.(3)Determined eluant turbidities of Na-EDTA?NH4-EDTA and Ca-EDTA were 98.6 NTU?88.0 NTU?7.6 NTU.It was shown from the experimental result that extraction turbidity of the Ca-EDTA was the lowest,which were beneficial to the treatment of soil extract.Therefore,Ca-EDTA was selected as the extractant to carry out further experiments.(4)Optimal conditions of Ca-EDTA are : concentration of 2.5 mmol·L-1,solid-to-liquid ratio of 1:5,washing time is 2h;Under these conditions,the removal rate of the Pb?Zn?Cu?Cd in soil were respectively 45.29%?13.03%?18.54%?68.94%.(5)The static adsorption experiment is conducted on EDTA metal-complex in soil extracts by chloride type 717 anion exchange resin.And the effects of solid-liquid ratio,PH,time and temperature on resin adsorption EDTA metal-complex were investigated.Results show that with the increase of EDTA metal-complex in extract,the adsorption capacity of resin is decreasing.When the solid-liquid ratio is 1:30,the removal rates on Pb?Zn?Cu?Cd in extract were respectively 96.35%?66.92%?87.06%?93.53%;when p H was 5.6,the removal rates of resin on Pb?Zn?Cu?Cd are respectively 96.42%?68.14%?87.94%?93.38%;in addition,when the time was 30~45 mins,the adsorption of resin on Pb?Zn?Cu?Cd in extract reaches balance;when the temperature reaches to 25-35?,the removal effect of resin on Pb?Zn?Cu?Cd in extract was best,and the removal rates were respectively up to 95.38%?68.73%?86.53%?93.24%.(6)Adsorption treatment was conducted on EDTA metal-complex in extract by dynamic column adsorption method.Results show that with the increase of flow rate,the faster the breakthrough point and saturation point will be and show the tendency to the left.When the flow rate is 4m L·min-1,the treatment capacity of resin on extract reached maximum,and the breakthrough capacity and saturation capacity on Pb were respectively 4.04 mg·g-1 and 5.93 mg·g-1,and for Cd were respectively 0.089 mg·g-1 and 0.121 mg·g-1,Cu were respectively 0.621 mg·g-1 and 1.61 mg·g-1,and for Zn were respectively 1.27 mg·g-1 and 7.28 mg·g-1.(7)Dynamic elution recovery was conducted on EDTA metal-complex in resin by using salt solution as regenerant.Results show that the elution effect of the four kinds of regenerants on EDTA metal-complex in resin is:Fe2(SO4)3>Mg SO4>Ca Cl2>KCl,among it,the effect of Fe2(SO4)3 was the best,and the elution volume is 60 m L.(8)The continuous 5 adsorption-regeneration experiments on resin were conducted by using the regenerant(Fe2(SO4)3).Results show that when the flow rate is 2m L·min-1,after 5 times of adsorption-regeneration,the elution efficiency on Cd remains 75.65%~84.19%,and the removal rate on Cd keeps in 76.64%~93.43%;the elution rate on Pb kept in 68.37%~78.32%,and the removal rate on Pb kept in 68.69%~95.38%;the elution efficiency on Cu remains 62.95%~71.65%,and the removal rate on Cu kept in 63.73%~87.26%;the elution rate on Zn keeps in 55.83%~66.34%,and the removal rate on Zn kept in 52.77%~67.82%.(9)The treatment of concentrate.First of all,the acidification was conducted on regeneration concentrate to recovery the EDTA,and the recovery rate reached to 72.17%~78.93%;in addition,adding alkali(Ca O)to the filtrate,adjusting the p H to 9~10,and the removal rates of the three kinds of metal-ion(Cd?Pb?Fe?Cu?Zn)were respectively 93.87%?98.59%?99.07%?99.84%?99.19%.(10)The soil fertility recovery experiment after extraction was carried out by two common plants.Result show that the biomass in each part of alligator alternanthera and myriophyllum were both increase;in addition,compared with the soil after extraction,the content of soil nutrients and organic matter were increased in the soil after recovery.Among which,the total N? total P?total K?effective N?effective P?effective K?Ca2+?Mg2+?Mn2+ and the organic matter were respectively increased 7.11%?4.9%?24.79%?69.84%?24.65%?74.08%?3.47%?19.10%?24.34%?13.33% compared with the soil after extraction;and the nutrient elements and organic matter in the soil after recovery basically reached the content of each index in the original soil.