DD280745A1 - METHOD FOR PRODUCING MAGNESIUM OXIDE WITH HIGH CORN WEIGHT - Google Patents

Abstract

The invention includes a process for producing high grain weight magnesium oxide. It relates to a process for the conversion of coarse disperse, reaction MgEG in magnesium hydroxide in saline aqueous media for the production of reactive MgO in particular for further processing to sintered magnesia with a high particle weight. According to the invention, the hydration in the aqueous medium with the addition of carboxylic acids or their salts (CnH2n1 COOH with n0, 1, 2) in molar proportions of 0.001 to 0.2 mol / mol, based on MgO, specific reaction conditions of 10 to 40 kg Mg (OH ) 2 / m3h. There are obtained Mg (OH) 2 products with surface areas up to 55 m 2 / g, which are equal or superior in their properties to the precipitated hydroxides.

Description

Field of application of the invention

The invention relates to a process for the conversion of coarse disperse magnesium magnesium oxide (MgO) into magnesium hydroxide (Mg (OH) ₂ ) in salt-containing aqueous media for the production of reactive magnesium oxide, in particular for further processing into sintered magnesia, with a high particle weight.

Characteristic of the known state of the art

In the seawater magnesium process, Mg (OH) _{2 is} precipitated from MgCl ₂ and milk of lime (precipitated dihydroxide), which can be further processed with sufficient reactivity.

The situation is different in the MgO production by thermal processes, in which magnesium chlorides are decomposed at high temperatures. Such MgO products, which consist of aggregated particles of hollow spherical structure (made of MgCl ₂ ), according to Gardner and others (Ceramic Bulletin - 63 [1984] 12 - p 1498-1501) have too low reactivity. In OD WP 74461 and DD WP 220951 it is therefore proposed to largely eliminate the difficultly destructible air-filled hollow spherical structures of the MgO particles from the MgC 2 split process, for example by the action of mechanical or thermal energy in suitable milling aggregates or by treatment in water at boiling temperature. However, such processes are very energy-consuming, in addition, the hollow spheres are not sufficiently destroyed in water.

It is also known that by adding MgCl ₂ -CaCl ₂ -, NH ₄ Cl solution (WP 246971 and WP 241247) crucial changes in the basic structure in the hydration process can be achieved without the dio particle size changed significantly. The reaction reaction is significantly accelerated, and in the further processing of these MgO products sintering can be produced with very high particle weights.

The disadvantage is that these products are practically not brikettierfährig and thus not enough briquettes for the sintering process can be produced.

With respect to compaction and sintering, finely dispersed products are favorable. After an extensive investigation Uzberg (Izv Akad. Nauk, Neorg, Mat. 1983, 1492ff.) Concluded, for example, that one of the most important factors for achieving high grain-space weights in the sintering of MgO powders with good Brikettierverhalten fineness

Object of the invention

The object of the invention is to improve the quality of the MgO produced from the thermal MgCl ₂ splitting process, whereby the energy expenditure is to be reduced.

Explanation of the essence of the invention

The technical problem to be solved is to produce a fine-grained reactive Mg (OH) ₂ or MpO from coarsely dispersed, inert MgO from theoretical processes, which can be processed into sintered products with a high particle weight.

Surprisingly, it has been found that when small amounts of carboxylic acids or their salts are added in aqueous solution, starting MgO products are converted into finely dispersed Mg (OH) ₂ . If the finely dispersed Mg (OH) _{2 is} used. calcination, the decomposition of unreacted carboxylic acids or salts thereof may additionally have a positive effect on the dispersity of the calcined product. Finely dispersed MgO is of crucial importance for a high grain weight after the sintering process with good Brikettiervarhalten. The carboxylic acids formic acid, acetic acid, propionic acid or salts thereof are used in substoichiometric amounts of from 0.001 to 0.2 mol / mol, preferably from 0.002 to 0.1 mol / mol, based on the starting MgO product.

MgO + 2HR- * Mg ²⁺ + 2FT + H ₂ O

MgO + 2Mtr-R -> Mg ²⁺ + 2R "(R ² ") + Me ₂ O (MeO)

Me: cation

The additives are simply added to the suspension so that no major interventions in an existing process are required. The additives also make hydration more "spontaneous", that is, in addition to decreasing the particle diameter, the time and temperature for hydration can be reduced Formic acid, acetic acid and propionic acid are technical products of the chemical industry Example in the acylation of salicylic acid (Acesalsynthese) and the ethanal representation of ethyne (butadiene synthesis).

The salts can, inter alia, be prepared by double reaction from the acids.

The additional amount of carboxylic acids can not be increased arbitrarily, since with increasing concentration, the i-tltrierzeiten the Mg (OH) ₂ suspension increase and the humidity of the filter residue increases. It must therefore be found in determining the addition amount an optimum between the respective degree of dispersion of the generated Mg (OH) ₂ and technical controllability of the filter processes and the economy of the overall process. The chosen hydration conditions and the geometry of the containers and design of the agitators have a great influence.

According to the invention, the hydration with continuous process control, and mixed homogeneously at specific throughputs of 10 to 40kg Mg (OH) ₂ / m ³ h the reaction chamber should preferably 25kg Mg (OH) ₂ / m ³ h at pulp densities between 400 end 550 g Mg (OH) ₂ /! Suspension in the temperature range between 70 to 95 ° C are performed. Thereafter, the calcination of Mg (OH) ₂ in the temperature range between 600 to 1000 ⁰ C and the workup to sinter with high particle weights § 3.4g / cm ³ by known methods

 The invention will be explained in more detail in the following embodiment.

embodiment

Selected parameters: throughput temperature head density

27kg / m ³ h 9O ⁰ C 500g Mg (OH) ₂ /! suspension

additive amount Mg (OH) ₂ Kornan Mg (OH) ₂ MgO causter briquetting sinter mol / mol part (%) behavior based filter <16 pm BET value KRG aufMgO wet 20.0 95.2 (g / cm ³ ) bad (g / cm ³ ) (%) 25.7 97.9 Well vinegar 0.15-1C- ² 23 50.3 99.3 5.3 very well 3.37 acid 0.75-10 " ² 25 55.7 99.7 9.7 very well 3.42 1.45-10 " ² 27 53.7 99.8 11.2 Well 3.44 2.20 x 10 " ² 30 60.1 100.0 13.9 Well 3.46 7.Ö0-10- ² 32 90.0 100.0 20.1 bad 3.43 10,90-ΙΟ " ² 41 40.3 3.44 14.50-TO- ² 50 55.0 3.42

Claims (3)

1. A process for the preparation of magnesium oxide with a high particle weight from inert, coarsely dispersed Spa't-MgO from thermal processes by hydration of the starting MgO, followed by calcination of the resulting magnesium hydroxide and sintering of the MgO causer by known methods, characterized in that the hydration in aqueous medium with the addition of carboxylic acids C _n H _2n + 1COOH with η = 0 to 2 or their salts in mole fractions of 0.001 to 0.20 mol / mol, based on MgO, with continuous process control and homogeneous mixing at specific reaction conditions of 10 to 40 kg Mg (OH) ₂ / m ³ reaction space · h and cloud densities of 400 to 550g Mg (OH) ₂ /! Suspension in the temperature range of 70 to 95 ° C is performed. 2. The method according to claim 1, characterized in that the carboxylic acids or salts thereof are preferably added in molar proportions of 0.002 to 0.10 mol / mol, based on MgO. 3. The method according to claim 1, characterized in that the reaction is preferably carried out at specific reaction conditions of 25kg Mg (OH) ₂ / m ³ · h.