Column leaching of chromium and nickel from a contaminated soil using EDTA and citric acid

This study investigates the column leaching of a soil contaminated mainly with Cr and Ni by using two chelants: citric acid (biodegradable) and EDTA (non-biodegradable) followed with water rinse. The chelants lead to Cr and Ni leaching, in addition to major elements (Ca, Fe, Mg, Al, Mn and Zn) showing the dissolution of soil mineral constituents. EDTA leaches more major elements and Ni than citric acid related to the respective stability of metal–chelant complexes; citric acid leaches more Cr than EDTA, certainly because of a substitution reaction with Cr(VI). In the case of alternating chelant/water applications, leaching occurs during the chelant applications, but also during water applications. In the case of chelant/water applications followed by continuous water application, both Cr and Ni leach over time. This increased mobility could be due to the residual chelant present in soil as well as to the dissolution/mobilization of mineral or organic soil fractions.

► Column leaching of an industrial soil contaminated with chromium and nickel.
► Citric acid or EDTA were used alternatively or followed with water rinse.
► Chelants lead to Cr and Ni leaching and the dissolution of soil mineral constituents.
► Leaching of these two metals proceeds continuously during water rinse.
► Chelants deeply impacted Cr and Ni mobility.