Evaluation of the potential redistribution of chromium fractionation in contaminated soil by citric acid/sodium citrate washing

A new four-step approach, which removed fractions one by one based on the sequential extraction procedure proposed by the Community Bureau of Reference (BCR), was designed to study the variation of chromium (Cr) chemical fractionation after citric acid/sodium citrate (CA/SC) washing. Particular attention was paid to the potential redistribution of the acid soluble Cr fraction. The results indicated that CA/SC washing decreased the content of the reducible (R2) and oxidizable (R3) fractions during the four steps. During Step 1, the ratio of the acid extractable (R1) fraction with total Cr increased significantly. Through designing Steps 2, 3 and 4, it was proved that R1 was released from the R2, R3 and R4 (residual) fractions during washing. This indicated that CA/SC washing may be favorable for converting Cr from being difficult to extract into being easier extraction chemical fractionation. The results of this work revealed the high potential risk for the application of CA/SC washing in soil polluted with Cr because of the redistribution of its fractionation.