Research Of A Method Based On Diffusive Gradients In Thin Films (DGT) For Extracting And Analyzing Heavy Metals Availability In Soil

The biological toxicity of heavy metals in soil depends on heavy metals availablity.As a technique for extracting the available heavy metals in soils,Diffiisive gradients in thin films(DGT)has become a research hotspot in recent years.However,the traditional Chelex-100-DGT is expensive and the dissociation ability of heavy metals is poor.The research of DGT in our country are mostly for one or two heavy metals with low adsorption and esorption.In this study,ZnAl-LDH,ZnAl-EDTA-LDHs,PGA,and SA-PGA gels were prepared and the adsorption performance of four gels for chromium,nickel,copper,cadmium and lead were analyzed.And we selected SA-PGA binding phase gel to assemble the new DGT(SA-PGA-DGT or New DGT in short)to study the adsorption properties of the new DGT for five heavy metals(chromium,nickel,copper,cadmium and lead).We also explored the practical application value of the new DGT and the results showed:(1)The diffusion coefficients(25?)of Cr,Ni,Cu,Cd and Pb in SA-PGA-DGT are 7.38×10-6cm2s-1,6.04×10-6cm2s-1,6.15×10-6cm2s-1,and 6.76×10-6cm2s-1 and 8.51×10-6cm2s-1.The adsorption of chromium,nickel,copper,cadmium and lead by SA-PGA-DGT reaches equilibrium within 2h with the 90%adsorption amount of the total,which is in line with the pseudo-second-order kinetics.The desorption efficiency of 3mol/L nitric acid to chromium,nickel,copper,cadmium,and lead are all over 91%,which is significantly better than the elution efficiency of Chelex-100-DGT(80%).(2)SA-PGA-DGT can accurately measure Cr,Ni,Cu,Cd and Pb especially for Pb and Cd at pH is 5-9 and ionic strength is 1-50 mmol/L.And the adsorption capacity shows lead>cadmium>nickel>copper>chromium.(3)The adsorption capacities of SA-PGA-DGT for Cr,Ni,Cu,Cd and Pb is 0.60 meg/g.SA-PGA-DGT can accurately determine the available heavy metals at a low concentration(one-tenth of the limits of spectrophotometric detection)for 24 hours,which is suitable for determining trace heavy metals.(5)In the slightly contaminated soils with pH between 7.7 and 8.9,there is a very positive linear correlation between the DGT technology and the traditional method of chemical extraction of available chromium,nickel,copper,cadmium,and lead in the soil.The DGT technique can be used To predict the bioavailability of heavy metals.And the DGT technology is less affected by the physical and chemical properties of the soil and is more suitable for the enrichment of the available heavy metals than the traditional chemical extraction method.