CS266785B1 - Process for the preparation of cobalt-magnesium double-cyclo-tetraphosphates - Google Patents

Abstract

The method consists in calcining a mixture of oxide, hydroxide, carbonate or hydroxide-carbonate of cobalt and magnesium in an amount corresponding to the molar ratio Co/Mg = (2-x)/x and phosphoric acid in an amount corresponding to the ratio P2O,-/(Co+Mg) equal to 0.98 to 1.3?, with the heating rate being less than 50 °C/min, to a temperature of 260 to 1060 °C and the water vapor tension in the calcination space being higher than 20 kPa.

Description

The invention relates to a process for the preparation of double cobalt-magnesium cyclophosphates.

The double cobalt-magnesium cyclophosphates are expressed by the formula c-Co _{2 χ} ^ 8χ ^ 4θΐ2 ' ^x can range from values approaching zero to values approaching two. These compounds are characterized by high thermal and chemical stability. So far, the only mentioned method of preparation of these substances consists in their crystallization from a cooling melt containing in the required amounts phosphate anions together with cobalt and magnesium cations. However, this process for the preparation of double cobalt-magnesium cyclophosphates is particularly suitable for preparative laboratory purposes. Although it is possible to prepare very pure products, although for wider technological uses that do not require completely pure products, this method is only slightly suitable. This method has high energy requirements, since it is necessary to convert the starting mixture into a melt at high temperatures, and this must also be allowed to cool in a controlled manner (with constant heating). The technological implementation of this method is also complicated by the need to provide a dry atmosphere or vacuum in the melt space.

These disadvantages are eliminated by the process for the preparation of double cobalt-magnesium cyclophosphates of the _{formula c-Co 2} _ _{χ Μ§ χ} Ρ ^ Ο ^ ₂ , where x can range from values approaching zero to values approaching two, according to the invention, characterized in that the cobalt oxide, hydroxide, carbonate or hydroxide-carbonate together with the magnesium oxide, hydroxide, carbonate or hydroxide-carbonate in a Co / Mg ratio corresponding to the molar relationship (2-x) / x is calcined with phosphoric acid in the starting material. mixtures where the amount of phosphate anions to divalent cations corresponds to a molar ratio

P 2 O 2 / tCo + Mg) equal to 0.96 to 1.3, preferably 1 to 1.05, the starting mixture being prepared by treating the cobalt and magnesium compound with phosphoric acid, preferably at a concentration of 50 to 85 by weight, and H ^ PO ^ ^and the starting mixture is preferably allowed to continue at least 2 hours freely react, preferably with stirring, then begins to heat up rate of less than 50 ° C, preferably at a rate of 1-8 ° C / min, to a temperature of 260 to 1060 ° C, preferably a temperature of 350 to 800 ° C, the water vapor pressure in the calcination space being higher than 20 kPa, preferably 60 to 100 kPa. .

The mutual ratio of cobalt and magnesium compounds in the starting mixture is chosen according to the requirement for the content of cobalt and magnesium cations in the product. The content of magnesium cations (x) can range from values approaching zero to values approaching two. A value of zero or two cannot be used, because then it would not be a double product, but a pure dicobaltic cyclo-tetraphosphate c-Co ₂ P ^ 0 ^ ₂ , resp. o pure dibasic magnesium cyclophosphate cM 2 P 2 O 2. The amount of phosphoric acid in the starting mixture, expressed by the molar ratio PgO 2 / 1Co + Ug), would be most suitable in the case of processing completely pure raw materials exactly according to the stoichiometry (i.e. said ratio equal to one). However, depending on the purity of the phosphoric acid used (metal ion content therein) and the purity of the cobalt and magnesium feedstock (metal impurities), the ratio should be adjusted to the above range of 0.96 to 1.3, with small amounts of phosphate anions being preferred. excess (1 to 1.0?) than, on the contrary, their more pronounced deficiency compared to stoichiometry. The concentration of phosphoric acid is more preferably lower in terms of controlling the condensation reactions, and thus the yield and purity of the product; however, this lower concentration in turn causes an increase in the energy requirements for the evaporation of the excess water and increases the volume of the starting mixture, which in addition has the character of a slurry. Its calcination then presents technical problems compared to the calcination of a mixture of a smaller volume, which would be in the form of a solid or a paste which is formed if phosphoric acid is used in a concentration in the preferred range of 50 to 85 wt. 2. Allowing the mixture containing phosphate, cobalt and magnesium ions to react spontaneously for at least 2 hours before calcination, it is advantageous for sufficient initial reaction of the starting cobalt and magnesium compound with phosphoric acid, i.e. neutralization reaction using hydroxides, or especially decomposition reactions of carbonates , since the carbon dioxide released and the effluent of the mixture caused by it would complicate the calcination itself. For this reason, it is also advantageous to stir the reacting starting mixture. The heating of the mixture at a rate of less than 50 ° C / min is chosen so that the individual dehydration and condensation reactions successively taking place in the mixture can proceed as slowly as possible at (or near) the temperatures at which they occur, and thus in the highest possible yields. . Otherwise, undesired cleavage of the intermediates would occur, releasing the phosphorus component, which would then condense separately to polyphosphoric acids, thereby contaminating the main product and reducing its yield. When choosing a very low heating rate, it is again necessary to take into account the disproportionate extension of the product preparation time, and thus a certain increase in material and energy requirements. In addition, in this case it will be more difficult to maintain a sufficient water vapor pressure in the space of the calcined mixture, and thus to prevent the possible cleavage of the intermediates. The lower required limit of the calcination temperature (260 ° C) is given by the temperature of gradual formation of the first particles of double cobalt-magnesium cyclophosphates. The upper limit of the calcination temperature range (1060 ° C) is related to the thermal stability of the double cobalt-magnesium cyclophosphates, which may melt uncongruently even at this temperature. The preferred calcination temperature in the range of 350 to 800 ° C is due to the fact that the double cyclo-tetraphosphates are formed at a temperature above 350 ° C at a sufficient rate and the initially formed amorphous products are converted into microcrystals, which are its most suitable form for the intended use. . The upper limit of this preferred temperature range (800 ° C) is then given by the fact that at this temperature the reactions of the formation of double cyclo-tetraphosphates have already taken place (if the preferred heating rates have been used), even at higher water vapor tensions in the calcination space. Maintaining a water vapor pressure in the calcined mixture space of more than 20 kPa is necessary to prevent the formation of undesired condensation by-products and to prevent the cleavage and separate condensation of the phosphorus component. The presence of water vapor slows down the individual condensation reactions somewhat, allows them to proceed more quantitatively and also prevents the formation of undesired non-porous crusts on the surface of the calcined mixture particles, which would prevent the quantitative course of dehydration reactions. It is advantageous to keep the water vapor pressure above 60 kPa, when its action in this direction is sufficient. The upper limit for the advantageous water vapor pressure in the calcined mixture space - 100 kPa - is mainly due to the need for increased design, material and energy requirements for calcination equipment and calcination conduction, when using higher pressures than atmospheric pressure. due to a water vapor pressure above 100 kPa, it would again disproportionately prolong the product preparation time.

The essence of the process according to the invention further consists in that the product, after calcination, is treated with hydrochloric, sulfuric, nitric or phosphoric acid, preferably with a weight concentration of 0.5 to 10 .mu.l. This operation is performed ev. as purification of the obtained product when needed in pure form. The action of these acids removes all undesirable by-products, even ev. residues of the starting mixture, which thus go into solution. Double cobalt-magnesium cyclophosphates resist the action of these acids. If the double cobalt-magnesium cyclophosphates were prepared under the conditions according to the invention mentioned as preferred, this purification does not need to be carried out.

The process allows the preparation of double cobalt-magnesium cyclophosphates under technologically feasible conditions, with sufficient yield and with sufficient product purity. It also allows the use of lower quality raw materials - dilute and less pure phosphoric acid and less pure cobalt compounds. Under the conditions of preparation of the product according to the invention as preferred, almost pure double cobalt-magnesium cyclophosphates can be prepared. If less pure products are obtained, they can be purified according to the process of the invention.

. The following are examples of the preparation of double cobalt-magnesium cyclophosphates by the process of the invention.

Example 1

100 g of cobalt carbonate (containing 49% Co) and 69.7 g of magnesium carbonate (containing 29% Mg) were mixed with 511 g of phosphoric acid with a concentration of 65% H 2 PO 2 ^and allowed to react spontaneously with occasional stirring for 3 hours. The mixture was then heated at 5 ° C / min to 450 ° C for 1 h at this temperature. The water vapor pressure in the calcined mixture space was maintained at 85 to 95 kPa. 339 g of product were obtained, which contained 98% of double cobalt-magnesium cyclophosphate of the formula c-CoMgP 2 O 2. ...

(containing 57% Co) and 22.4 g of hydroxide-carbon-mixed with 573 g of phosphoric acid, stirring occasionally for 2 h.

at a temperature of 500 ° C with a holding time of 1 h at this temperatureExample 2

100 g of magnesium cobalt hydroxide carbonate (containing 35 X Mg) had a concentration of 45 wt. % H ^ PO ^ ^and allowed for Ames was then heated at a rate 8 ° C / min-ture. The water vapor pressure in the calcined mixture space was maintained at 75 to 85 kPa. 258 g of product were obtained, which was further purified by leaching with 4 wt. % HCl. After washing with water and drying at 110 ° C, 254 g of product containing 99.5% of c-Co .5 Mg _{Q 5} ^Ρ 4 ° ₁₂ ·

Example 3 g of cobalt carbonate (containing 49% Co) and 126.3 g of magnesium hydroxide slurry (containing 24% Mg) were carefully mixed with 391 g of phosphoric acid by weight. S> H-.P0. and allowed to react spontaneously with occasional stirring for 1 h. The mixture was then heated at a rate of 10 DEG C./min to a temperature of 400 DEG C. for 2 hours at this temperature. Water tension.

steam in the space of the calcined mixture was maintained at 80 to 90 kPa. Was obtained 322 g of product which contained 98.5 and double-entry cyclo-tetraphosphate cobalt-magnesium formula C-Co _{Q (^} 0, _2>

Claims (2)

OBJECT OF THE INVENTION A process for the preparation of double cobalt-magnesium cyclophosphates of the formula wherein x can range from values approaching zero to values approaching two, characterized in that the cobalt oxide, hydroxide, carbonate or hydroxide-carbonate together with the oxide, magnesium hydroxide, carbonate or hydroxide-carbonate in a Co / Mg ratio corresponding to the molar ratio (2-x) / x, are calcined with phosphoric acid in the starting mixture, where the amount of phosphate anions to divalent cations corresponds to the molar ratio P 2 O / (Co + Mg). ) equal to 0.98 to 1.3, preferably 1 to 1.05, the starting mixture being prepared by treating the cobalt and magnesium compound with phosphoric acid, preferably a concentration of 50 to 85 wt. The H 2 PO 2 ^{and the} starting mixture are preferably allowed to react freely for at least 2 hours, preferably with stirring, and then heated at a rate of less than 50 ° C / min, preferably at a rate of 1 to 8 ° C / min, to a temperature of 260 to 1060 ° C, preferably to a temperature of 350 to 800 ° C, the water vapor pressure in the calcination space being higher than 20 kPa, preferably 60 to 100 kPa. 2. The process according to claim 1, characterized in that the product after calcination is treated with hydrochloric, sulfuric, nitric or phosphoric acid, preferably with a weight concentration of 0.5 to 10