Study On Extraction Method For Available Ni、Co In Soil In A Sewage Library Surrounding Farmland Soil In Xinjiang

Ni and Co are the necessary trace elements of plants. But the high content of Niand Co not only affect on the normal growth of plants, but also on human healththrough the food chain. Previous studies showd that the environmental behavior ofheavy metals in soil and ecological effect mainly depend on their existence form,biological state, effectively. The chemical extraction method which is divided intosequential extraction and single extraction according to the extracting procedure oftenbe used to extracted available heavy metal.In this paper, the extraction rate and the extraction condition were discussed andthe differences of Tessier and BCR to extract Ni and Co were compared. The suitableextration method was chosen by evalating the extraction rate, stability and biologicalof experimental results. EDTA-enhanced Phytoremediation were import to repairNi-contaminated soil. And the remediation effect of EDTA were discussed. The mainresult as follows:(1) The extration amount of Ni and Co in soils varied relatively large withdifferent types of extraction agents. The sequence of extraction contents for Ni is0.1mol/L citric acid>0.005mol/L DTPA-TEA>0.02mol/L EDTA>0.5mol/LNH4OAc>0.2mol/L Ca(NO3)2. The sequence of extraction contents for Co is0.1mol/L citric acid>0.02mol/L EDTA>0.005mol/L DTPA-TEA>0.5mol/LNH4OAc>0.2mol/L Ca(NO3)2. In addition to0.2mol/L Ca(NO3)2, the rest of thefour types of extractants has better coefficient of variation. There is good correlationbetween the amount of the extracted available Ni and Co which were extracted by thefive extractants and the Ni, Co content in the alfalfa samples.(2) Except0.2mol/L Ca(NO3)2, other four extratants can increase extrcationrates of Ni by supersonic extraction (SE) were uch higher than that by conventionalextraction (CE) method in some degree. Among which, SE using EDTA asextractant can increase51.33%than that of CE to Ni, and50.2%to Co.(3) Variance analysis show that the extract time have great influenced to theextraction rates of Ni and Co by EDTA, DTPA and citric acid, but little by NH4OAcand Ca(NO3)2. There is significant differences between the amounts of Ni and Coextracted by5extractants in different ratios of solution to soil. The concentration ofNi extracted by EDTA is influenced by pH much bigger than that extracted by Ca(NO3)2.(4) The amount of Ni’s forms extracted by Tessier different from that extractedby BCR. The sequence of Ni’s forms extracted by BCR is Redu＞RF＞AS＞Oxid.The sequence of Ni’s forms extracted by Tessier is Oxid＞RF＞AS＞Redu. There aresame sequence of Co’s forms ratio for BCR and Tessier. It is Oxid＞RF＞Redu＞AS.(5) The amount of EX and CARB of Ni extracted by Tessier achieve significantcorrelation with the concentration of Ni in the alfalfa sample. The amount of AS of Niextracted by BCR has great correlation with the concentration of Ni in the alfalfa’saboveground. There no significant difference for MF of Ni between BCR and Tessier.In addition to the residual form, the content of rest four forms (EX, CARB, Fe-Mn,OM) and Co-content in the alfalfa samples have obvious correlation. There are similarcorrelation results of Co between BCR and Tessier. The MF with BCR is higher thanthat with Tessier. Tessier sequential extraction was more suitable for Ni,Cofractionation with smaller relative error in the present study.(6) When the concentration of EDTA is0.5g/kg, the dry weight of alfalfa’s root,stem and leaf is higher than those in low concention Ni contaminated soil. When theconcentration of EDTA is1～8g/kg, the dry weight of alfalfa’s root, stem and leafshow the trend of decreasing. With the concentration of EDTA increasing, alfalfa’sroot, stem and leaf showed the trend of decrease, and was lower than that in highconcention Ni contaminated soil. High concentration of EDTA has stronger inhibitoryeffect than low concentration for alfalfa growth. In high concentration of Nicontaminated soil the concentration of EDTA impact the growth of alfalfa moresignificant than that in low concentration of Ni contaminated soil.(7) EDTA can increase the available Ni and significantly promote the enrichmentof Ni to alfalfa. When the concentration of EDTA is2g/kg, the amount of Niaccumulated by the aboveground of alfalfa reached maximum. TF and BCF of Nireached maximum by2g/kg EDTA. When the concentration of EDTA is0.5g/kg, theamount of Ni accumulated by alfalfa reached maximum in the condition of300mg/kgNi. TF and BCF of Ni reached maximum by0.5g/kg EDTA.