CS274189B1 - Method of cobalt-zinc double cyclo-tetraphosphates preparation - Google Patents

Abstract

The invention is based on the calcination of a mixture of cobalt oxide, hydroxide, hydroxide-carbonate or carbonate and zinc oxide, hydroxide or carbonate in a quantity corresponding to the molar ratio Co/Zn = (2-x)/x with phosphoric acid in a quantity corresponding to the ratio P2O5/(Co+Zn) equal to 0.95 to l.4, whereas the rate of heating is less than 30 degrees C/minute up to a temperature of 250 to 800 degrees C, and the vapour pressure in the calcination chamber is higher than 20 kPa.

Description

The invention relates to a process for the preparation of cobalt-zinc cobalt double-phosphate phosphates.

The cobalt-zinc double cyclo-tetraphosphate is represented by the formula ο-Οο _{2 χ} Ζη _χ Ρ 0 ₄ 0 ^ ₂ , where x can range from values close to ee to zero up to values close to two. These compounds are characterized by high thermal and chemical stability and are blue-violet. The only process so far described for these compounds is to crystallize from a cooling melt containing phosphate anions in the necessary amounts together with cobalt and zinc cations. However, this process for the preparation of double cobalt tetra-zinc phosphate is particularly suitable for preparative laboratory purposes. It is possible to prepare very clean products, but it is not suitable for wider technological use. In fact, this method requires high energy, since it is necessary to transfer the starting mixture to the melt at high temperatures and then, in addition, it must be allowed to cool (under constant heating). Technological implementation of this method is also complicated by the necessity of providing a dry atmosphere or vacuum in the melt space.

Said drawbacks are eliminated pressurized feed vessels for preparing double cyclo tetrafoeforečnanů cobalt-zinc formula ^c ~ ^What 2_x ²ⁿ x ^P 4 ^O i2 ^»kd ® ^{X Moz} ® ^b e ^tv rozmszi ° d values close to zero up to a value approaching two, according to the invention, characterized in that the cobalt oxide, hydroxide, hydroxide-carbonate or carbonate 9pol with zinc oxide, hydroxide or carbonate in a Co / Zn ratio corresponding to a molar ratio of (2-x) / x is calcined with phosphoric acid in the starting mixture, of phosphate anions to divalent cations corresponds to a molar ratio P2Og / (Co + Zn) of 0.95 to 1.4, preferably 1 to 1.05, the starting mixture being prepared in such a way that the cobactate and zinc compounds are formed with phosphoric acid, preferably a concentration of 30 to 90 wt. % H3PO4, and the starting mixture is preferably allowed to continue to react for at least 1 hour, preferably with stirring, and thereafter heating rates of less than 30 ° C / min, preferably 1 to 8 ° C / min, to a temperature of 250 to 800 ° C, preferably to a temperature of 400 to 700 ° C, wherein in the calcination area the vapor pressure is higher than 20 kPa, preferably 60 to 100 kPa.

The relative ratio of cobalt and zinc compounds is initially selected according to the requirement for cobalt and zinc cations in the product. The zinc cation content (x) may range from near to zero to close to two. A value of zero or two cannot be used, since then it would not be a double product, but a pure dicobaltic cyclo-tetraphosphate c-Co ₂ P ₄ O ^ ₂ or pure disodium cyclo-tetraphosphate c-Zn ₂ P ₄ ° 12 * The amount of phosphoric acid in the starting mixture, expressed as a molar ratio of P ₂ Og / (Co + Zn), would be best used exactly by stoichiometry (i.e., said ratio equal to one) in the case of processing completely pure raw materials. However, according to the purity of the phosphoric acid used (metal content therein) and the purity of the cobalt and zinc raw materials (metal admixtures), the ratio should be adjusted within the range of 0.95 to 1.4, more preferably if the phosphate anions have a small excess ( 1 to 1.05) than their significant deficiency compared to etechiometry. The concentration of phosphoric acid is lower in terms of control of the condensation reactions and hence the yield and purity of the product; however, this lower concentration causes an increase in the energy requirement for the evaporation of excess water and increases the volume of the starting mixture, which moreover has the character of a slurry. Oil calcination then presents technical problems over a smaller volume calcination mixture which would be in the form of a solid or pasty that arises. When phosphoric acid is used, a concentration in the preferred range of 30 to 90 wt. %. P _by allowing the mixture containing phosphate, cobalt and zinc ions before kalcinacl least 1h spontaneously react, it is preferable for satisfactory completion of the initial reaction of the starting cobalt and zinc compounds with kyeelinou phosphoric i.e. neutralization reaction with hydroxide, or especially after the decomposition reaction of carbonates, since the released carbon dioxide and the resulting boiling of the mixture would complicate the calcination itself. Therefore, it is preferable to mix the reacting starting mixture. Heating of the mixture at a rate of less than 30 ° C / min and is selected so that the individual dehydration and condensation reactions gradually take place in the mixture

EN 274 189 81 at or near the temperatures at which they occur could occur as slowly as possible and thus with the highest yield. Otherwise, unwanted cleavage of the intermediates would result in the release of the phosphorous component, which would then condense separately to polyphosphoric cyeelines, thereby contaminating the main product and reducing its yield. When selecting a very low heating rate, a disproportionate increase in the product preparation time and thus a certain increase in material and energy requirements is to be expected. In addition, it will be more difficult in this case to maintain sufficient water vapor pressure in the space of the calcined mixture, thereby preventing the possible cleavage of the intermediates. The lower limit of calcination temperature (250 ° C) required is given by the temperature of the gradual formation of the first cobalt-zinc cobalt tetrafosphate double particles. The upper limit of the tacination temperature range (800 ° C) is related to the thermal stability of cobalt-zinc cobalt-zinc double-cyclophosphate, since some of them are non-congruent at this temperature. The preferred calcination temperature is in the range. 400 DEG-700 DEG C. is given by the fact that the double cyclo-tetraphosphates are formed at a temperature above 400 DEG C. with sufficient speed and the amorphous products initially formed are passed over. to the micro-crystals which are the most suitable form for the intended use. The upper limit of this preferred temperature range (700 [deg.] C.) is then determined by the fact that at this temperature the double cyclotetraphosphate formation reactions have already taken place (if advantageous heating rates have been used) even at higher water vapor pressures in the calcination space. Maintaining a water vapor pressure in the space of the calcined mixture above 20 kPa is necessary to prevent the formation of undesirable by-products of condensation and to prevent cleavage and separate condensation of the phosphorus component. Water vapor present The individual condensation reactions slow down somewhat, allow their more quantitative course and also prevent the formation of undesired non-porous crust on the surface of the particles of the calcined mixture, which would prevent the quantitative course of the dehydration reactions. It is advantageous to maintain the water vapor pressure above 60 kPa, when its action is sufficient in said direction. The upper limit for the advantageous pressure of water vapor in the space of the calcined mixture - 100 kPa - is given mainly by the necessity of increased constructional, material and energy demands on the calcining plant and the calcination line, using higher pressures than atmospheric pressure. In addition, increased braking of the condensation and dehydration reactions due to a water vapor pressure above 100 kPa would again disproportionately prolong the product preparation time.

The process according to the invention further comprises treating the product after calcination with hydrochloric, sulfuric, nitric or phosphoric acid, preferably a concentration of 0.5 to 10% by weight. This operation is optionally carried out as a purification of the obtained product in its pure form. By treatment with these acids, ee removes all unwanted byproducts as well as any residues of the starting mixture, which thus become dissolved. The cobalt-zinc double cyclo-tetraphosphates resist the action of these acids. If the cobalt-zinc cobalt phosphate double cyclophosphates were prepared under the preferred conditions of the present invention, this purification is not required.

The process makes it possible to prepare cobalt-zinc cobalt double-phosphate phosphates under technologically feasible conditions with sufficient yield and product purity. It also allows the use of lower quality raw materials - dilute and less pure phosphoric acid and less pure cobalt and zinc compounds.

The following are examples of the preparation of cobalt-zinc cobalt tetraphosphate double cycles according to the invention.

Example 1

100 g of cobalt carbonate (containing 49% Co) and 35.5 g of zinc carbonate (containing 51% Zn) were mixed with 369 g of phosphoric acid at a weight concentration of 60% HgPO4 and allowed to react spontaneously with occasional stirring. The mixture was then heated at a rate of 5 ° C / min to 480 ° C and held at this temperature for 2 h. The water vapor pressure in the space of the calcined mixture was maintained at 85 to 95 kPa. 252 g of a product were obtained which contained 96% of cobalt-zinc cobalt tetrachlorophosphate double c-Co | ₅ Zn _{Q 5}

CS 274 189 Bl

Example 2

100 g of cobalt hydroxide carbonate (containing 57% Co) and 175.7 g of zinc hydroxide slurry (containing 36% Zn) were carefully mixed with 387 g of 85 wt% phosphoric acid. % HgPO4 and allowed to react spontaneously with occasional stirring for 3 h. The mixture was then heated at a rate of 8 ° C / min to 550 ° C and held at this temperature for 1 h. The water vapor pressure in the space of the calcined mixture was maintained at 80 to 90 kPa. 460 g of product were obtained, which was further purified by leaching with 3 wt% HCl. After washing with water and drying at 110 ° C, 432 g of product containing 97% cobalt-zinc cobalt tetrasodium c-CoZnP ₄ O double cyclo-tartrate was obtained. ^ ₂ .

Claims (2)

CLAIMS 1. A process for the preparation of cobalt-zinc double cyclo-tetraphosphates of the formula ο-Οο ₂ _ _χ Ζη _χ Ρ ₄ 0 ^ ₂ , wherein x may range from near to zero to close to two, characterized in that the oxide, hydroxide, hydroxide carbonate or carbonate of carbonate together with zinc oxide, hydroxide or carbonate in a ratio of Co / Zn relative to the molar ratio (2-x) / x, is calcined with phosphoric acid at the starting point. mixtures wherein the amount of phosphate anions to divalent cations corresponds to a molar P ₂ Og / (Co + Zn) ratio of 0.95 to 1.4, preferably 1 to 1.05, wherein the starting mixture is prepared by treating the cobalt and zinc compounds phosphoric acid, preferably a concentration of 30 to 90 wt. % H ₃ PO ₄ , and the starting mixture is preferably allowed to react for at least 1 hour, preferably with stirring, and then heating is started at less than 30 ° C / min; preferably at a rate of 1-8 ° C / min, at a temperature of 250-800 ° C, preferably at a temperature of 400-700 ° C, wherein in the calcination space the water spring pressure is higher than 20 kPa, preferably 60 to 100 kPa. 2. Process according to claim 1, characterized in that the product after calcination is treated with hydrochloric, sulfuric, nitric or phosphoric acid, preferably a concentration of 0.5 to 10% by weight.