CS252011B1 - A method of preparing anhydrous magnesium chloride - Google Patents

Abstract

The essence of the solution is the conditions of dehydration of magnesium chloride hexahydrate or its concentrated solutions in a multi-stage fluidized dryer to mono- or dihydrate and subsequent complete dehydration in a fluidized bed in a protective atmosphere containing chlorine, leaving the electrolysis of magnesium production. The advantage of this method is in the quality of chloride, speed and completeness of dehydration, associated with savings in specific electrical energy for magnesium production.

Description

232011

The present invention relates to a process for the preparation of anhydrous magnesium chloride from hexahydrate or from magnesium chloride solutions, for the purpose of electrolytic production of magnesium. In the prior art, the preparation of magnesium chloride for the subsequent electrolytic production of magnesium is carried out in several ways: 1. Chlorination of magnesium oxide obtained from marine water or salt lakes by calcination of magnesium hydroxide, or chlorination of magnesium oxide by obtaining magnesite. By chlorination, it is necessary to carry out a briquetted batch electric furnace at 800-900 ° C using an almost 10% binder addition of a reducing agent.

In order to produce pure magnesium chloride, high purity magnesium oxide is required in the process, since almost all admixtures pass chlorides to chlorides and cause product contamination, increase chlorine sides, and eliminate operational problems only after shutdown. The process consumes 400-400 kWh of electrical energy and 0.8-0.95 tons of chlorine gas to produce 1 tonne of material, making this technology considerably more expensive. Certain e-economic advantages are possible in parallel production of titanium, in which anhydrous magnesium chloride is produced as a by-product and magnesium production is limited. 2. Dehydrate the hexahydrate to mono-resp. magnesium chloride dihydrate in stage and rotary driers, respectively. with the addition of ammonium chloride, which is added to the molten MgCl2.6 H2O to inhibit hydrolysis. Further dehydration is carried out in an electric furnace from the molten charge of the spent electrolyte in the hydrogen chloride protective atmosphere, respectively. ammonium chloride decomposing, which is required to be recycled in the outgoing gas to be used for the preparation of so-called "ammonium carboxylate" (NH 4 Cl, MgCl 2, 6 H 2 O).

The final dehydration in the electric furnace is carried out at a temperature of 700-750 ° C for a relatively long time and with the addition of barium chloride, which is necessary due to the increasing weight of the electrolyte dehydrating only on the melt surface. 3. The process by DOW Chemical (USA) is used in seawater treatment. The magnesium hydroxide solution obtained is dissolved in dissolved hydrochloric acid to produce magnesium chloride solutions, the concentration of which is to give hexa- or hexa-3-ol. magnesium chloride tetrahydrate. Dehydration is carried out in two stages, in a furnace and a rotary kiln. The product obtained in the granule form represents almost monohydrate (containing 1.25 - 1.5 mol H2O), with magnesium chloride decomposed partially by magnesium chloride. Such a material without complete dehydration is used for the electrolytic production of magnesium in specially treated electrolytic cells leaving the mixed gas formed with hydrogen chloride and chlorine to absorb water, to prepare the leachate solution. The main disadvantage of this method is that the water present causes a partial decomposition of the electrolyte and an increase in the electricity demand by more than 2,000 kWh per tonne of magnesium produced.

The shortcomings of the three magnesium chloride processes described can be summarized as follows:

The first is to obtain the highest quality magnesium chloride, but its production is very costly and requires a high-grade feedstock, which rarely suits the magnesite process.

The application of this process in technological practice is increasingly rare, and even more so in the form of the so-called "mixed method" together with the production of titanium by the Croll process.

In a second way, anhydrous chloride is prepared with some decomposed chloride in the form of MgO, the amount of which depends on the proportion of added ammonium chloride, barium chloride or the concentration of hydrogen chloride used as a protective atmosphere over the molten magnesium chloride. Thus, complete dehydration is always associated with chloride losses and with considerable demands on electrical energy. The third method utilizes, for partial dehydration, similar to the previous procedure, conventional drying ovens in which the drying is relatively long (24-48 h). Electrolysis of such chloride is much more expensive.

The above drawbacks are substantially obviated by the method of preparation according to the invention, wherein the iron hydroxahydrate or magnesium chloride solutions are dehydrated in a fluidized bed at an initial temperature of 80 ° C until 180 ° C at a heating rate of 1-6 ° C zamin. to obtain magnesium chloride monohydrate which is further dehydrated to a temperature of 210-260 ° C in an air atmosphere containing 10-30% by volume of chlorine.

In this way, it is possible to obtain fully dehydrated magnesium chloride with a minimal amount of oxide at substantial times, which in the first stage as well as in industrial scale it should not overwhelm 90 minutes and 30 minutes.

Contrary to a similar method of dehydration of carnality, it is important to adhere to said temperature regime, which maximally suppresses the possibility of hydrolysis and at the same time does not fuse the surface of the material due to the large flow rate. The optimum temperature for drying the hexahydrate to monohydrate showed a temperature of 140 ° C. Further dehydration is in view of the desired concentration of hydrogen chloride or chlorine in the protective

Claims (1)

A process for the preparation of anhydrous magnesium chloride from hexahydrate or magnesium chloride solutions, for the electrolytic production of magnesium, characterized in that the hexahydrate or magnesium chloride solutions are dehydrated in the fluidized bed at an initial temperature of 80 ° C to 180 ° C at a heating rate of 1 to 6 ° C / min to obtain magnesium chloride monohydrate, which is further dehydrated at 210 to 260 ° C in an air atmosphere containing 10 to 30% chlorine by volume.