Formation of chukanovite in simulated groundwater containing

Abstract

ABSTRACTChukanovite (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 , OH−, and Fe2+ concentrations and the ratios (R = [Fe2+]/[OH−] and R′ = []/[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 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+, . 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.