Abstract

The 5 M sodium hydroxide (NaOH) chemical treatment was applied to the silt and clay fractions of three Chilean fertilized soils derived from volcanic materials tone Ultisol and two Andisols) in order to selectively concentrate iron oxides. The treatment was sequentially applied and results were followed by x-ray diffraction and Mossbauer spectroscopy. In all samples, dissolution chemical treatment concentrated iron oxides in variable degrees; and both, Mossbauer spectra and x-ray diffraction patterns were significantly improved after three successive hot NaOH treatments. Best results were obtained for the Ultisol sample which is the oldest soil with the lowest organic matter content. The Mossbauer spectrum after three NaOH treatments of Ultisol silt fraction reveals characteristic features of partially oxidized magnetite, leading to two probability profiles of the hyper-fine field distribution: one of them due to mixed valence iron (Fe3+/2+) ions in octahedral sites [delta =0.59 mm s(-1), 2 epsilon (Q)=0.02 mm s(-1), with a maximum hyper-fine field at B-hf(max)=46.2 tesla]; the other distribution profile encompasses contribution from Fe3+ in tetrahedral sites [delta =0.30 mm s(-1), 2 epsilon (Q)=-0.04 mm s(-1), and B-hf(max)=48.2 tesla].