Formation of chukanovite in simulated groundwater containing [Formula: see text]

Chukanovite (Fe₂(OH)₂CO₃) is one of the secondary mineral precipitates on the surfaces of zero-valent iron (ZVI) barriers in groundwater containing carbonates. Synthesizing experiments were conducted in FeCl₂, NaOH, and Na₂CO₃ solutions to investigate the effect of carbonate concentration on the formation of Fe₂(OH)₂CO₃ and estimate the stability field of Fe₂(OH)₂CO₃ on the potential-pH diagram. Results revealed that Fe₂(OH)₂CO₃ is a unique product based on X-ray diffraction. The [Formula: see text], OH^-, and Fe²⁺ concentrations and the ratios (R = [Fe²⁺]/[OH^-] and R' = [[Formula: see text]]/[OH^-]) are important parameters in the formation of the Fe₂(OH)₂CO₃. Fe₂(OH)₂CO₃ was better formed in the R = 1.1, R' = 0.9 system than in the R = 1.1, R' = 0.7 system. The crystallization of Fe₂(OH)₂CO₃was increased with the concentration of [Formula: see text] increased from 0.018 to 0.18 mol/L. The standard Gibbs free energy of the formation of Fe₂(OH)₂CO₃ was -1151.1 ± 5.3 kJ/mol from the equilibrium conditions between Fe₂(OH)₂CO₃ and Fe²⁺, [Formula: see text]. Potential-pH diagram of iron, including Fe₂(OH)₂CO₃, was drawn in the Fe-C-H₂O system. In this diagram, the stable domain of Fe₂(OH)₂CO₃ was 7.87 < pH < 10.34, -740 mV < Eh < -400 mV, which can be converted into FeCO₃ in low pH value in the 0.18mol/L carbonate solution. This work will aid in predicting the potential for mineral precipitation, as well as estimating the reactivity, porosity, and hydraulic performance of ZVI permeable reactive barriers.