Comparation Of Methods On Pretreatment Of Speciation Analysis On Heavy Metals, Extraction And Fixation Of Heavy Metals In Sediments

The heavy metals pollution in sediments has been getting serious as the accelerating urbanization and industrialization.The Shandong Peninsula coastal zone,the Jiehe River and the Jiaolai River were selected as the study areas to study the restoration of heavy metals in sediments.There were two parts on the heavy metals restoration study in the present study.Firstly,heavy metals toxicity is mainly determined according to their chemical fraction.Additionally,the analysis accuracy of the heavy metals fraction extraction should be affected by different heavy metals samples pretreatment methods.Therefore,the influence of three kinds of pretreatment methods?fresh,air-dried and freeze drying methods?on the analysis accuracy of sedimentary lead?Pb?,arsenic?As?and cadmium?Cd?fraction extraction using the Tessier sequential extraction method.Secondly,the gold mining can discharge excessively high concentrations of heavy metals to sediments,which seriously damage the sediment quality Consequently,various studies on sedimentary As and Cd extraction methods,and the removal of As and Cd in the extracting solution were conducted in the Jiehe River located in the gold mining areas.The main conclusions were as follows:1)There were significant differences in the distribution of Cd and Pb between river sediments and marine sediments.The Cd and Pb existed mainly in organic matter bound fraction and residual fraction in river sediments.Both of them accounted for more than90%of the total content.However,the relative distribution of residual fraction was at the highest level and the organic-bound fraction was at the lowest level in marine sediments.Nevertheless,the AS regularities distribution in river and maine sediments were consistent?residual fraction>the other three fractions>the Fe-Mn oxide bound fraction?.2)Results showed that different pretreatment methods could dramatically influence the heavy metals fraction analysis method accuracy.The determined concentrations of Cd,As and Pb in fresh sediments significantly deviated from the true values.The measured concentration of Cd in exchangeable,organic and residual fraction,and As in exchangeable,and Fe-Mn oxide,organic and residual fraction in river sediments were close to the true values.In addition,the Pb in all fractions,and As in exchangeable,organic and residual fraction in marine sediments were also close to the true values.However,concentrations of each fraction in freezing drying samples were generally lower than average values.Most of Cd forms in marine sediments and Pb forms in river sediments were closer to the true values.We concluded that the method of sediment air-drying was the most suitable sediment pretreatment.It was important to select a suitable pretreatment method to guarantee the accuracy of sediment sequential extraction for the following study.3)In this study,a sediment sequential extraction method about As and Cd and the As and Cd removingmethod in the extracting solution were studied.Both of the two heavy metals were extracted using a single reagent extraction and a sequential chemical extraction medod and then removed through neutralization method and sulfide precipitation method.The results showed that the 0.1 mol/L oxalic acid?OX?single reagent extraction method and the sequential chemical extraction of 0.01 mol/L EDTA combined the 0.1 mol/L Na₂S₂O₃ had the best extraction efficiency for As and Cd?approximately 100%?,respectively..And there was a high removal efficiency for As in the HCl extraction solution using the neutralization precipitation method?pH?6?.Additionally,the As removal efficiency in the EDTA-OX extraction was significant through the sulfide precipitation method?reaction time,15 min?.And the Cd in both of the two above extraction solutions could be effectively removed via the neutralization precipitation combined the sulfide precipitation?Na₂S=0.05 mol/L,p H=7?.