CS257746B1 - Method of double cobalt-calcium cyclo-tetraphosphates preparation - Google Patents

Abstract

The method consists in calcining the mixture oxide, hydroxide, carbonate or hydroxide cobalt carbonate in calcium a phosphoric acid, with a rate heating is less than 45 ° C / min, to temperature 280-885 ° C and in the calcination area the vapor pressure is greater than 20 kPa. Solution can be used in chemistry and technology phosphate compounds, in technology production of anti-corrosion paint pigments mass, glazed colors and agrochemistry in the preparation of microelement fertilizers.

Description

The present invention relates to a process for the preparation of cobalt calcium calcium double cyclotetrophosphates.

The cobalt-calcium double cyclo-tetraphosphates are expressed by the formula:

where x can range from zero to one. These compounds are characterized by high thermal and chemical stability as well as intense blue-violet color and can be used as colored anticorrosion hygienic and environmentally friendly anticorrosion pigments in paints, as a glazed paint in ceramics or in various high-temperature materials or as micro-element fertilizers with prolonged effectiveness. . The only method so far disclosed is to crystallize them from a cooling melt containing phosphate anions together with cobalt and calcium cations in the necessary amounts.

However, this process for the preparation of cobalt calcium calcium cyclotrophosphates is particularly suitable for preparative laboratory purposes. Thus, very pure products can be prepared, but this method is of little use for a wider technological application to produce products for pigmentary or agrochemical purposes that do not require completely pure products. This is because the energy requirements of this method are high, since it is necessary to transfer the starting mixture to the melt at high temperatures and, in addition, it must then be allowed to cool in a controlled manner (under constant heating). Technological implementation of this method is also complicated by the necessity of providing a dry atmosphere or vacuum in the space.

These drawbacks are eliminated by a process for preparing double cyclo tetrapolyphosphate cobalt-calcium of the formula ^c * ^'Co 2-x ^Ca x ^P 4 ^C) i2' ^x may range from values approaching zero to the value one, according to the invention wherein wherein the cobalt oxide oxide, hydroxide, carbonate or hydroxide-carbonate together with the calcium / calcium carbonate in a Co / Ca ratio corresponding to the (2-x) / x molar ratio is calcined with phosphoric acid in the starting mixture, wherein the amount of phosphate anions to divalent cations corresponding to a molar ratio of P ₂ O 4 / (Co + Ca) of 0.96 to 1.30, preferably of up to 1.04, the starting mixture is prepared by treating the cobalt and calcium compounds with phosphoric acid %, preferably a concentration of 30 to 95 wt. % and the starting mixture is preferably allowed to continue to react freely for at least 1 hour, preferably with stirring, and then started to heat at less than 45 ° C / min, preferably at 1 to 8 ° C / min, to 280 to 885 ° C, preferably at a temperature of 350 to 650 ° C, wherein the water vapor pressure in the calcination space is higher than 20 kPa, preferably 60 to 100 kPa.

The ratio of cobalt and calcium compounds in the starting mixture is chosen according to the requirement for cobalt and calcium cations in the product. The calcium cation content (x) may range from values close to zero to a value equal to the cobalt ion content (x - 1). Zero values cannot be used, since then they would not be a double product, but a pure dicobaltic cyclo-tetraphosphate c-COjP ^ ° 12 'The value x = 1 cannot be exceeded again, since the cobalt-calcium double-cyclo-tetraphosphates with calcium than it corresponds to the formula c-CoCaP? O? cannot be prepared.

If a larger amount of calcium compound is used in the starting mixture than is equal to x = 1, by-products of the condensed calcium phosphate type, in addition to the double cyclotetraphosphates, will be produced to an increased extent. The amount of phosphoric acid in the starting mixture, expressed as a molar ratio of P 2 O 4 / (Co + Ca), would be best to use exactly by stoichiometry (i.e., said ratio equal to one) when processing completely pure raw materials. However, according to the purity of the phosphoric acid used (the content of the metal ions therein) and the purity of the cobalt and lime raw materials (metal admixtures), the ratio should be adjusted in the range of 0.96 to 1.3, more preferred if the phosphate anions are small (1 to 1.04) than their significant deficiency compared to stoichiometry. 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 in turn 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.

Its calcination then presents technical problems over the calcination of a smaller volume mixture, which would be in the form of a solid or pasty which arises when phosphoric acid is used in the preferred range of 30 to 85% by weight. %. Allowing the mixture containing phosphate, cobalt and calcium ions to react spontaneously for at least 1 hour is advantageous for the initial reaction of the starting cobalt and calcium compounds with phosphoric acid to proceed sufficiently; this is a neutralization reaction using hydroxides or, in particular, a decomposition reaction of carbonates, since the released carbon dioxide and the resulting loosening of the mixture would complicate the calcination itself.

For this reason, it is also preferred to stir the reacting starting mixture. Heating with a mixture rate of less than 45 ° C / min is selected so that the individual dehydration and condensation reactions gradually taking place in the mixture can occur at (or near) the temperatures at which they occur as slowly as possible and thus with the highest possible yield. Otherwise, unwanted cleavage of the intermediates would result in the release of the phosphorous component, which would then condense separately into polyphosphoric acids and thereby contaminate the main product and reduce its yield.

When selecting a very low heating rate, a disproportionate increase in 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 and thereby prevent the possible breakdown of the intermediates.

The lower limit of calcination temperature (280 ° C) required is given by the temperature of the gradual formation of the first cobalt calcium-calcium double-cyclo-tetraphosphate particles. The upper limit of the calcination temperature range (885 ° C) is related to the thermal stability of double cobalt calcium calcium phosphates, which melt non-congruently at this temperature. The preferred calcination temperature in the range of 350 to 650 ° C is given by the fact that double cyclo-tetraphosphates are already formed at a temperature above 350 ° C at a sufficient rate and the amorphous products initially formed are converted to the microcrystals which are . The upper limit of this preferred temperature range (650 ° C) is due to the fact that, at this temperature, double cyclo-tetraphosphate 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 of the calcined mixture space 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. The water vapor present somewhat slows down the condensation reactions, allows them to be more quantitative, 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 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 advantage of the steam pressure in the space of the calcined mixture - 100 kPa - is given above all by the necessity of increased constructional, material and energy demands on the calcining plant and the calcination line, using higher pressures than atmospheric pressure. Moreover, 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.

Furthermore, the process according to the invention consists in 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 performed as ev. Purification of the obtained product in its pure form. The action of said acids removes all unwanted by-products and ev. residues of the starting mixture which thus pass into solution. The cobalt-calcium double cyclo-tetraphosphates resist the action of these acids.

If the cobalt calcium calcium cyclotaphosphates are prepared for pigment or micronutrient fertilizer use, and in particular if they are prepared under the preferred conditions of the invention, such purification is not required.

The process makes it possible to prepare double cobalt calcium calcium cyclophosphates under technologically feasible conditions, with a sufficient yield and with a sufficient purity of the product. 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 identified as preferred in the present invention, nearly double cobalt-calcium-calcium cyclophosphate can be prepared. if less pure products are obtained, they can be purified by the process according to the invention.

The following is an example of a process for the preparation of cobalt calcium calcium double cyclotetaphosphates according to the invention.

Example 1

100 g of cobalt hydroxide carbonate (containing 57% Co) and 143.6 g of calcium slurry (containing 27% Ca) were mixed with 590 g of phosphoric acid at a concentration of 65% Η ^ ΡΟ ^ and left stirring spontaneously for 5 hours respond. The mixture was then heated at 3 ° C / min to 550 ° C for 2 hours at this temperature. The water vapor pressure in the space of the calcined mixture was maintained at 85 to 95 kPa. 418 g of product were obtained which contained 94% of cobalt-calcium-calcium double cyclo-tetraphosphate c-CoCaP ^ O ^^ ·

Example 2

100 g of cobalt carbonate (containing 49% Co) and 27.8 g of calcium carbonate (containing 40% Ca) were carefully mixed with 488 g of 45 wt% phosphoric acid. %

And allowed to react spontaneously with occasional stirring for 6 hours. The mixture was then heated at 6 ° C / min to 500 ° C for 3 h at this temperature. The water vapor pressure in the space of the calcined mixture was maintained at 75 to 85 kPa. 241 g of product were obtained, which was further purified by leaching with 4% hydrochloric acid. % HCl. After washing with water and drying at 160 ° C afforded 232 g of product containing 97.0% Co-C ^ ^Ca 5 Q 5 ^P 4 ° i2 '

Claims (2)

OBJECT OF THE INVENTION. A process for the preparation of cobalt-calcium double cyclo-tetraphosphates of the formula c-Co ^^^ Ca ^ P ^ O ^^ / wherein x can range from values above zero to one, characterized in that the oxide, hydroxide, carbonate or cobalt (II) hydroxide-carbonate together with a calcium / calcium carbonate in a Co / Ca ratio corresponding to a molar ratio of (2-x) / x, are calcined with phosphoric acid in the starting mixture, where the amount of phosphate anions to divalent cations is ^{Co + Ca} J equal to 0.96 to 1.3, preferably 1 to 1.04, wherein the starting mixture is prepared by treating the cobalt and calcium compounds with phosphoric acid, preferably a concentration of 30 to 85 wt. %, ^{And the} starting mixture is preferably allowed to react for at least 1 hour, preferably with stirring, and then heated at a rate of less than 45 ° C / min, preferably at a rate of less than 45 ° C / min. at a temperature of 280 to 885 ° C, preferably at a temperature of 350 to 650 ° C, wherein in the calcination space the water vapor pressure is higher than 20 kPa, preferably 60 to 100 kPa. Method according to claim 1, characterized in that the hay product, after calcination, is treated with hydrochloric, sulfuric, nitric or phosphoric acid, preferably a concentration of 0.5 to 10% by weight.