Effect of the surfactant loading on the magnetite content and the saturation magnetization of magnetic-organo-montmorillonite systems

BARRAQUÉ,FACUNDO; MONTES, MARÍA LUCIANA; M. A. FERNANDEZ; CANDAL, ROBERTO; TORRES SÁNCHEZ, ROSA MARÍA; MERCADER, ROBERTO CARLOS

Conferencia; Conferencia; Latin American Conference on the application of the Mössbauer Effect 2018; 2018; 2018

Montmorillonite (Mt) has been widely used as sorbent of heavy metals and organic compounds, due to its large surface area, cation-exchange capacity, swelling ability, abundance, eco-friendliness and low cost. The incorporation of quaternary amino compounds to montmorillonite has proved to extend and improve its organic pollutants sorption spectrum, due to the contribution of non-polar groups. Besides, the production of magnetic clays has attracted scientific interest due to its sorbent ability and isolation capacity by application of external magnetic fields, which reduces the pollutant exposition. This work reports the structural, magnetic and hyperfine characterization of three magnetic-organic-Mt samples, produced by 1) loading montmorillonite with HDTMA, (hexadecyltrimethylammonium bromide) at 50, 100 or 150% of its cation exchange capacity (CEC) and 2) further synthesizing magnetite by controlled alkaline oxidation of iron (II) sulfate. Magnetite was also synthesized on untreated montmorillonite. The XRD patterns indicate the existence of Fe oxides. Mössbauer spectra reveal the existence of magnetite as the major magnetic Fe oxide (around 60 %), a minor contribution of goethite (around 5%), the paramagnetic sites characteristic of montmorillonite, and a superparamagnetic relaxation. The magnetic-organic-Mt with 100% of the CEC exchanged displays the highest saturation magnetization, Ms = 20.3±0.5 Am2/kg. There is a clear linear dependence of Ms on the CEC percentage exchanged, despite the low Ms value for magnetic-organic-Mt with 150% CEC. The linear behavior between HDTMA amount exchanged and the Ms value is attributed to the HDTMA presence at the Mt interlayer space which produces a steric hindrance to iron and consequently enhances the magnetite/goethite formation at the outer surface. After 100% CEC of HDTMA loading, the saturation of the interlayer space and outer surface prevents the Fe interaction with the clay surface, thus decreasing the magnetite/goethite formation in the Magnetic-organic-Mt systems.