The effect of CO (sub 2) and oxidation rate on the formation of goethite versus lepidocrocite from an Fe(II) system at pH 6 and 7
The effect of CO (sub 2) and oxidation rate on the formation of goethite versus lepidocrocite from an Fe(II) system at pH 6 and 7
Clay Minerals (March 1990) 25 (1): 65-71
- aqueous solutions
- carbon dioxide
- carbonaceous composition
- chloride ion
- chlorine
- clay mineralogy
- crystal chemistry
- crystal growth
- crystal structure
- crystallinity
- experimental studies
- ferrous iron
- goethite
- halogens
- infrared spectra
- iron
- iron oxides
- lepidocrocite
- metals
- minerals
- Ohio
- oxidation
- oxides
- pH
- phase equilibria
- polymorphism
- spectra
- synthetic materials
- United States
Samples were synthesized by oxidizing FeCl (sub 2) solutions with air/CO (sub 2) mixtures at ambient T and pH 6 and 7. The proportion of lepidocrocite in the mixtures decreased from 100 to 0% with increasing [HCO-,3] in solution and with decreasing average oxidation ratio. At a given [HCO-,3], more goethite was formed at pH 6 than at pH 7. IR spectra showed two broad bands at approx 1300 and 1500 cm (super -1) which can be assigned to distorted carbonate adsorbed at the goethite surface; identical bands were also found in a young, poorly crystalline goethite formed from coal mine drainage in Ohio. It is suggested that carbonate anions direct the polymerization of the double band of FeO (sub 3) (OH) (sub 3) octahedra common to both minerals towards a corner-sharing arrangement, and thereby to goethite, whereas chloride permits edge-sharing as in lepidocrocite.
