Application Of Water Bath Oscillation Extraction-inductively Coupled Plasma Mass Spectrometry In Analysis Of Hexavalent Chromium In Soil

Hexavalent chromium is the first class carcinogen identified by WHO.It is also a basic item of Soil environmental quality risk control standard for soil contamination of development land.Due to historical reasons,a large number of chromium residue produced by chromite industry has not been properly disposed of for a long time,resulting in a large range of soil chromium pollution in China.The current testing standard for hexavalent chromium in soil in China is Soil and sediment-Determination of Cr（VI）-Alkaline digestion/flame atomic absorption spectrometry（HJ 1082-2019）.This method has some shortcomings,such as inadequate extraction,high detection limit,poor stability and so on.More importantly,when detecting hexavalent chromium in the repaired soil,this method will be affected by excessive reducing agents in the soil,making the analysis results lower than the true value and seriously misleads to evaluate the remediation effect.In this study,the leaching mechanism of soil hexavalent chromium and its associated REDOX reaction were studied based on the main line of leaching process.Three main factors leading to inadequate extraction in the current standard were identified and optimized: extraction equipment,sample particle size and extraction time.At the same time,combined with the characteristics of the extract,the better performance of the extract detection method was selected.On this basis,a method of water bath oscillation extraction and inductively coupled plasma mass spectrometry was established for the analysis of soil hexavalent chromium.The detection limit of the method was 0.07mg/kg,the spiked recoveries were 93.7%-98.3%,and the one-hour stability（relative standard deviation）was 4.2%-6.3%,which were all better than the current standard.Aiming at the interference of excessive reducing agent in soil after reducing agent restoration,two pretreatment procedures of reducing agent were established in this paper to reduce the influence of reducing agent on the analysis results before alkali solution leaching of soil hexavalent chromium.Experimental results show that the pretreatment program can significantly reduce the interference of reducing agent to analysis,and increase the recovery rate from 0% to more than 75%.More reliable analysis results of hexavalent chromium can be obtained by using the reductant pretreatment program established in this study to treat the soil repaired with ferrous sulfate and calcium polysulfide.