Selective recovery of magnesium compounds from serpentinites of the Arvaten deposit

This article presents the results of an MgO-containing serpentinite processing study using phosphoric acid in the stoichiometric standard range of 90 to 115 %. The crystal lattice of serpentinite was fractured by calcining at 850 °C when exposed to air and phosphoric acid in order to selectively bind magnesium compounds into magnesium phosphate. The calcined middlings were then treated with a solution of nitric acid under mild conditions to transfer Mg into the solution in the form of magnesium nitrate. The study identifies the distribution of components in the sediment and solution depending on the amounts of phosphoric and nitric acids. It has been shown that, with higher acid content, the MgO conversion rate increases from 88.18 to 97.48 %. X-ray analysis also demonstrates the lack of peaks, generally characteristic of magnesium compounds, in the first sediment after serpentinite treatment with phosphoric and nitric acids under optimal conditions, which indicates complete Mg recovery into the solution in the form of magnesium nitrate. In this case, the first sediment has the following composition: SiO2 at 75.76 wt%; Al2O3 at 3.87 wt%; Fe2O3 at 9.67 wt%; CaO at 5.78 wt%; MgO at 0.07 wt%. The X-ray diffraction pattern for the second sediment contains bands mainly attributable to MgNH4PO4. The optimal parameters for magnesium removal from serpentinite have been established, as required to obtain a concentrate with silicon dioxide, which is the raw material for the manufacture of amorphous silica and iron-containing concentrates. Middlings in the form of crystalline MgNH4PO4 and an ammonium nitrate solution have also been obtained, which may be used in the manufacture of mineral fertilizers.

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