Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Alkaline earth metal
Patent
1999-01-15
2000-03-28
Griffin, Steven P.
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Alkaline earth metal
4231573, 423163, 423169, 423498, 4236585, C01F 100, C01F 532, C01B 2532, B01D 1100
Patent
active
060427949
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a process for the production of substantially anhydrous magnesium chloride (MgCl.sub.2) suitable for production of magnesium metal in electrolytic cells, and more particularly a process for selective leaching of magnesium from calcined Mg-containing minerals/ores using waterfree solvents.
In order to run a magnesium electrolysis process in an efficient way it is necessary to ensure that the applied MgCl.sub.2 feed is substantially anhydrous and free from impurities having a deteriorating effect on the electrolysis process and/or the resulting magnesium metal quality. Consequently, MgCl.sub.2 originating from natural or "artificial" brines or ores has to be subjected to a brine purification process (U.S. Pat. No. 5,120,514) and subsequently a dehydration process, e.g. by evaporation and drying of the solution of MgCl.sub.2 in water (brine) (U.S. Pat. No. 3,742,100) or by spray drying or granulation of brine in air and melt dehydration/chlorination by means of HCl gas (WO95/31401). It is also known that magnesium chloride hexammoniate (MgCl.sub.2.6NH.sub.3) is useful as an intermediate material for production of anhydrous MgCl.sub.2 (U.S. Pat. No. 3,966,888).
Thus, WO95/11859 describes a process where MgCl.sub.2 brines are complexed with an organic solvent, e.g. ethylene glycol, followed by removal of water by a distillation step and producing MgCl.sub.2.6NH.sub.3 by crystallization by adding NH.sub.3 to the waterfree ethylene glycol solution.
A common feature of all these known processes is that they start from an aqueous MgCl.sub.2 solution (brine) obtained by dissolving Mg-containing minerals/ores in hydrochloric acid (HCl in water) or from MgCl.sub.2 hydrates or brines being a by-product from e.g. the potash industry, something which necessitates complex and energy demanding dehydration processes and furthermore extra purification steps to remove impurities and unwanted contaminants (e.g. Ca).
It is therefore a principal object of the present invention to provide a new and improved process for producing substantially anhydrous magnesium chloride avoiding the necessity for major dehydration steps in the process.
Another object of the invention is to provide a process based on use of a weak acid as a dissolving/leaching agent promoting a selective dissolution of MgO from the raw materials, thus avoiding the need for extensive purification steps in order to achieve a high purity anhydrous MgCl.sub.2.
Still another object of the invention is to provide a low energy and a low capital investment demanding process for producing anhydrous MgCl.sub.2.
These and other objects/features of the process according to the present invention are achieved by provision of a new process as it appears from the accompanying patent claims.
The invention thus concerns a process for producing substantially anhydrous magnesium chloride suitable for electrolytic production of magnesium metal comprising steps of a) selective calcination of Mg-containing minerals/ores or other Mg-containing materials at temperatures within a range of 350-900.degree. C., b) selective leaching of magnesium from such calcined materials by using as a leaching solvent ammonium chloride dissolved in a substantially waterfree polar organic solvent, c) separation of insoluble impurities from the obtained solution of MgCl.sub.2 in the leaching solvent, d) precipitation of magnesium chloride hexammoniate by treating the solution with an excess amount of ammonia in a crystallizer without prior dehydration of the solution, e) separation of magnesium chloride hexammoniate crystals from the leaching solvent by filtration, centrifugation or other solid/liquid separation process, and finally f) thermal decomposition of the magnesium chloride hexammoniate crystals into magnesium chloride and ammonia.
It is preferred to use ethylene glycol or methanol as the polar organic solvent, but other solvents could also be used. In a preferred embodiment of the invention the leaching solvent necessary for the selective leaching step contains an am
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Amundsen Ketil
Eklund Hans Ragnar
Schmidt Ralf
Griffin Steven P.
Medina Maribel
Norsk Hydro ASA
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