Effect Of Residual Reducing Agent On Cr(?) Analysis In Chrome-contaminated Soil Treated With Sulfite/Pyrosulfite

With the improvement of environmental awareness among the people,the attention of soil pollution is increasing,the soil remediation market is gradually opening up,the research on the repair of chromium-contaminated soil is gradually increasing,and the repair methods are endless.The chemical reduction method is one of the most widely used techniques for the repair of chromium-contaminated soils.However,the residual reducing agent in the soil after repair may cause serious interference to the analysis of soil Cr(?),resulting in a wrong assessment of the repair effect.Therefore,eliminating the interference of residual reducing agent in soil on Cr(?)analysis of soil has important application value for chromium contaminated soil remediation technology and engineering acceptance.In this paper,the analysis of Cr(?)in chromium-contaminated soil treated with reducing agent(sulfite/pyrosulfite)is carried out to study the sources of bias,principle and elimination methods caused by residual reducing agent.The main contents and results of the paper are as follows:(1)The effect of sulfite on Cr(?)was analyzed by diphenylcarbazide spectrophotometry(DPC).The results show that in the presence of sulfite,according to GB 7467-87 chromogenic agent I method(that is,adding acid and then adding color developer)operation,it will lead to unacceptable analysis error;and according to GB 7467-87 chromogenic agent II method or EPA Method 7196a(adding coloring agent and then adding acid)can block the influence of sulfite on Cr(?)analysis to some extent,but if the sulfite concentration is too high,Methods can also lead to unacceptable analytical errors.(2)Flame atomic absorption spectrophotometry(FAAS)analysis of the effect of sulfite on Cr(?).The results show that sulfite does not affect the FAAS analysis of Cr(?).However,after the reduction of Cr(?)in Cr-contaminated soil by Cr(?),a large amount of soluble Cr(?)produced will affect the analysis of Cr(?)by FAAS.(3)The effect of pH adjustment operation on Cr(?)analysis in alkali digestion.The experimental results show that in the presence of sulfite,according to the alkali digestion + FAAS method(HJ687-2014),high concentration of sulfite will lead to Cr(?)reduction during pH adjustment,which can be corrected by FAAS method.The error caused by the reduction process;if the precipitation of Cr(OH)3 is formed in the sample storage,the correction effect will be greatly reduced.According to the alkali digestion + DPC method(EPA Method 3060 a + GB 7467-87 chromogenic II method),high concentrations of sulfite also lead to Cr(?)reduction during pH adjustment,resulting in unacceptable analytical errors.(4)A method of attenuating the effect of sulfite/pyrosulfite on Cr(VI)analysis by adding CaCl2 to form a calcium sulfite precipitate.The experimental results show that the sulfite/pyrosulfite is partially oxidized during the alkali digestion process,and the addition of CaCl2 after the completion of the alkali digestion contributes to the elimination of the remaining sulfite/pyrosulfite and reduces the sulfite/focus.The influence of sulfate on the analysis of Cr(VI)improves the accuracy of the data,and the analytical data meets the quality control requirements.(5)It has been found that a satisfactory spike rate of recovery does not necessarily guarantee the reliability of the data.Other relevant data needs to be provided to aid the judgment;for example,the results of the FAAS analysis and the results of the DPC analysis confirm each other.