Effects of sodium hydroxide in a selective chemical treatment of Peruvian peloids

M.L. Cerón Loayza,* M.E. Mejía Santillán and J. A. Bravo Cabrejos
Facultad de Ciencias Físicas, Universidad Nacional Mayor de San Marcos, Apartado 14-0149, Lima 14, Perú
Received August 21, 2010
The main purpose this work is to apply the NaOH treatment to the silt and clay fractions of Peruvian peloids in order to selectively concentrate iron oxides [1] by dissolving and removing phyllosilicates, for a better identification of oxides in the mineralogical composition of samples. For the mineralogical characterization of the samples that contain iron, especially for those that show magnetic ordering, transmission Mössbauer spectroscopy (TMS) was applied using the 14,4 keV resonant nuclear transition in the B7Fe isotope; which allowed the detection of sesquioxides and other minerals that contain iron. For the identification of crystalline phases we use the X ray diffractometry (XRD) technique. The NaOH treatment was applied sequentially to each sample and monitored by TMS and XRD. The results by TMS show paramagnetic doublets and the presence of partially oxidized magnetite. The XRD results of the samples without treatment show the presence of quartz and phyllosilicates such as vermiculite and halloysite. After selective chemical treatment the phyllosilicates were eliminated almost in their totality whereas the main (311) reflection belonging to iron oxide spinel was evident. As a general trend, the NaOH-treatment was significantly effective in concentrating iron oxide minerals in the studied peloids. The applied analytical techniques corroborate these results.
Keywords: Peloids, Mössbauer spectroscopy, X ray diffractometry.