Formation of chukanovite in simulated groundwater containing
2016
Chen, Ri | Chen, Juan | Hong, Mei | Zhang, Wenjing
Chukanovite (Fe ₂(OH) ₂CO ₃) 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 FeCl ₂, NaOH, and Na ₂CO ₃ solutions to investigate the effect of carbonate concentration on the formation of Fe ₂(OH) ₂CO ₃ and estimate the stability field of Fe ₂(OH) ₂CO ₃ on the potential–pH diagram. Results revealed that Fe ₂(OH) ₂CO ₃ is a unique product based on X-ray diffraction. The , OH ⁻, and Fe ²⁺ concentrations and the ratios (R = [Fe ²⁺]/[OH ⁻] and R ′ = [ ]/[OH ⁻]) are important parameters in the formation of the Fe ₂(OH) ₂CO ₃. Fe ₂(OH) ₂CO ₃ 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 Fe ₂(OH) ₂CO ₃was increased with the concentration of increased from 0.018 to 0.18 mol/L. The standard Gibbs free energy of the formation of Fe ₂(OH) ₂CO ₃ was −1151.1 ± 5.3 kJ/mol from the equilibrium conditions between Fe ₂(OH) ₂CO ₃ and Fe ²⁺, . Potential–pH diagram of iron, including Fe ₂(OH) ₂CO ₃, was drawn in the Fe–C–H ₂O system. In this diagram, the stable domain of Fe ₂(OH) ₂CO ₃ was 7.87 < pH < 10.34, −740 mV < Eh < −400 mV, which can be converted into FeCO ₃ 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.
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