Production of high-purity magnesia

• Localización: Industrial Minerals, ISSN 0019-8544, Nº. 548, 2013
• Idioma: inglés
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• Resumen

  • In the early 1970s such an application with a capacity of 50,000 tpa of MgO sinter was built in connection with the potash production from the Dead Sea waters in Israel, by ICL. The plant is still in operation and has been extended to three spray roaster units, with a combined capacity of 70,000 tpa, which feed a common washing, calcination (supplied by CMI NESA), briquetting, and sintering line. About 700,000 tpa of HCl (18-20% w/w) is produced as a by-product which is used in the production of phosphoric acid and other phosphates from phosphate ores. A similar installation was built in Germany which processed MgCl 2 brines produced by leaching an underground bischofite deposit.

    These were leached in a semi continuous leaching process using 18% w/w regenerated HCl and giving a solution of not more than 300 g/l MgCl 2, therefore pre evaporation was necessary. Further developments included an acidulation instead of a pre- evaporation in order to reduce energy consumption. The first application using acidulation was located in Hacava (Slovakia), a 25,000 tpa installation for the production of +99% w/w MgO sinter using locally mined magnesite and flue dust. The use of acidulation achieved the most economic MgCl 2 concentration, of about 420g/l.

    The isotropic concentration limit of the HCl solution may be avoided by feeding not simply water, but also magnesite ore fines suspended in water to the adiabatic absorption column (acidulation). Thus, HCl reacts in the absorber with the magnesite producing magnesium chloride, enabling the solution to absorb additional hydrogen chloride. The concentrations of HCl and MgCl 2 in the solution are therefore only dependent on their solubilities in water at actual operating conditions. The acidulation process is controlled at a concentration of about 390 g/l of MgCl 2 in the acidic liquor. In this way, not only the production of pure magnesium chloride brines but also the thermal decomposition to magnesia is achieved in a single continuous process. HCl is needed only for the initial start-up of the plant and to make up chloride losses arising from the presence of metals which do not hydrolyse in the Spray Roaster.