Research On The Applicable Conditions Of Extracting The Effective States Of Typical Elements With DTPA-LDHs-DGT

Soil heavy metal(loid)contamination is an important environmental problem facing human beings,and the harmfulness of heavy metal(loid)s mainly depends on their bioavailability.Diffusive gradients in thin films(DGT)technology is an excellent method for extracting the effective state of heavy metal(loid)s.The self-developed diethyltriaminepentaacetic acid-modified layered double hydroxide type DGT(DTPA-LDHs-DGT)is a cheap DGT that can simultaneously measure and co-adsorb anions and cations.In the early stage of research and development,the conditions for its adsorption of ions and the suitability of field have been studied,but they are not systematic and comprehensive.In this study,eight heavy metal(loid)s were taken as examples,and their performance of simultaneous adsorption of anions and cations was systematically analyzed.,and applied it to establish soil–rice Cd accumulation models.At the same time,available fraction analyzed via total Cd concentrations in the soils and soil solutions,concentrations determined via chemical extraction methods using acetic acid(HAc),composite organic acid,ethylene diamine tetraacetic acid(EDTA),and Ca Cl2,respectively,were compared.The main research results are as follows:1.In this study,by measuring the background blank of DTPA-LDHs-DGT,comparing the elution efficiency and elution time of different concentrations of dilute nitric acid to the binding gel,and the diffusion coefficient of the diffusion gel for eight ions,it was found that DTPA-LDHs-DGT has the characterization of low blank background value,rapid and complete dissociation with acid,The blank value of the per binding gel contains 29.91 ± 2.95 ng of Mn(?),677.23 ± 10.89 ng of Fe(?),0.67 ± 0.12 ng of Co(?),25.49 ± 1.77 ng of Ni(?),12.78 ± 0.70 ng of Cu(?),0.17 ± 0.02 ng of As(?),1.70 ± 0.11 ng of Cd(?)and 11.51 ± 0.46 ng of Pb(?);the eluent of binding gel was HNO3 with a concentration of 0.5 mol·L-1,the elution time was 10 min,and the average elution efficiency is 100% ± 5%;The diffusion coefficient(DDGT;E-6·cm2·s-1,25?)of the self-made diffusion gel is Mn(?)2.94,Fe(?)6.87,Co(?)2.56,Ni(?)2.63,Cu(?)2.67,As(?)3.56,Cd(?)2.68 and Pb(?)2.70.The diffusion coefficients of self-developed diffusive gel of DTPA-LDHs-DGT(DDGT;E-6·cm2·s-1,25 ?)are 2.94 for Mn(?),6.87 for Fe(?),2.56 for Co(?),2.63 for Ni(?),2.67 for Cu(?),3.56 for As(?),2.68 for Cd(?)and 2.70 for Pb(?).2.In this study,by measuring the adsorption effect of DTPA-LDHs-DGT on different ions under different p H and ionic strength conditions,the capacity of heavy(like)metals under different p H conditions,the coexistence of heavy(loid)s metals at different concentrations and the heavy(loid)s metal and different concentrations of HA coexistence of the existence of competition between the ions were studied,the results show that the range of p H and ionic strength was wide of DTPA-LDHs-DGT,the capacity was large,the competition effect between ions was weak,the competitive adsorption capacity for HA was strong enough.The p H application range was 5~8,and its the ionic strength application range is 0.005~0.1 mol·L-1 Na NO3.There was no effect of p H on the capacity of the test ions,the capacity of the test ions are 202.9 ?g·cm-2 for Mn(?),363.6 ?g·cm-2 for Fe(?),246.9 ?g·cm-2 for Co(?),88.8 ?g·cm-2 for Ni(?),99.5 ?g·cm-2 for Cu(?),75.3 ?g·cm-2 for As(?),159.8 ?g·cm-2 for Cd(?)and 671.7 ?g·cm-2 for Pb(?),and when the concentration of each ion in the solution is less than 90 ?g·L-1,there is no competitive adsorption effect among ions.For the heavy metal(loid)s-HA complex that can enter the DGT across the diffusion gel,the DTPA-LDHs-DGT binding gel can also adsorb it competitively.3.The application of DTPA-LDHs-DGT in the establishment of soil-crop model,and available fraction analyzed via total Cd concentrations in the soils and soil solutions,concentrations determined via chemical extraction methods using acetic acid(HAc),composite organic acid,ethylene diamine tetraacetic acid(EDTA),and Ca Cl2,respectively,the experimental results show that:DTPA-LDHs-DGT proved to be a better tool for extracting available Cd to establish the prediction models(R2=0.5854,0.9009,the coefficients of other methods are: total content 0.2932,HAc 0.3177,compound organic acid 0.3384,EDTA 0.3839,Ca Cl2 0.4796 and soil solution extraction 0.0146)for rice Cd accumulation than chemical extraction methods were as well as for distinguishing the effect of the soil bank supply capacity on Cd enrichment by rice.