Influency of the thermal treatment in the development of iron sulphate from mill scale iron waste

Full text: Wastes are being studied because of the environmental and economic issues that they represent and of the search for sustainable development. This research, with the mill scale iron waste, that is an iron oxide obtained from the hot lamination process of steel; propose the development of iron sulphate. The chemical route for this material production consists in: chemical reaching by sulfuric acid, heating with agitation, filtration, concentration, cooling and crystallization. The waste is constituted by 98% of iron oxides (wustite, magnetite and hematite), according to the XRF and XRD results, respectively. Aiming the improvement of the obtaining process of the iron sulphate, the waste passed through a thermal treatment in an inert atmosphere of N₂, varying the temperature with a dwell time of 2h, with the objective of reduce the oxides that delay the process. Characterizations by XRD were done to identify the crystalline phases being at each case. In all treatments, was possible to reduce the hematite amount, this phase is stable and is difficult to being reached by acids. Comparing the iron sulphate production from the mill scale that was not thermal treated with the one obtained by the tree thermal treatments (T1-600 deg C, T2-500 deg C and T3-400 deg C), can being show that the T2 showed the more adequate thermal treatment for iron sulphate production. This behavior happened because the magnetite was found as the major phase by XRD, while the hematite was not identified and the wustite had weak peaks, mainly comparing the presence of that oxide in T1 and T3. This mineralogical composition allowed the increasing in the temperature in the chemical route and facilitated the crystallization of the present phase (Fe₂SO₄.H₂O), that brought stronger peaks of XRD. The mill scale had shown as a great precursor of iron sulphate yet, however was observed an optimization of the process with the thermal treated mill scale application. (author)