Physicochemical characterization of the chlorination of natural wolframites with chlorine and sulphur dioxide

The chlorination of natural wolframites (MnxFe1−xWO4) with chlorine and sulphur dioxide was studied in a vertical reactor with a static bed and upward flow of reactive gases. Wolframite samples collected from five different deposits of Argentina were carefully purified by hand under a binocular microscope. Upgraded specimens with this methodology had a variable ratio of divalent metals (0.06 < x < 0.84) for similar tungsten content (WO3 = 72.4–73.3%). Experimental conditions more appropriate to make chlorinations were established using the iron-rich wolframite. Under these conditions, the tungsten extraction was determined as a function of the ratio of iron(II) and manganese(II) present in each sample. Physicochemical characterization of the system involved measurement of wolframite cell dimensions, identification of reaction products formed from metallic elements (tungsten, iron and manganese) and reactivity evaluation of both divalent metals by means of thermodynamic parameters. Results obtained show that iron-rich wolframites had higher reactivity with respect to other solid solution specimens. Reaction products identified were all volatile, except manganese(II) chloride found in liquid state. Thermodynamic analysis confirmed that formation of iron oxychloride (FeOCl) as an intermediate chlorination product would be feasible, although it was not possible to observe any evidence of this reaction under experimental conditions used. Finally, it is indicated that the highest reactivity of iron-rich wolframites was attributed to the volatile nature of all their reaction products, to iron(II) oxidation easiness if compared with manganese(II) and to possible formation of iron oxychloride.