CH140435A - Process for the preparation of sodium ammonium phosphate Na NH4 HPO4 intended for use as fertilizer. - Google Patents

Description

Process for the preparation of sodium and ammonium phosphate Na N114 HP04 destW to be used as eugrais.

It is known that the great solubility of the ammoniacal phoiphates hitherto employed as fertilizers requires that, for their manufacture, one should use concentrated phosphoric acid and then concentrate and evaporate the solutions of the phosphates. These evaporations impose a large expense on fuel and must be carried out in expensive apparatus. The costs for the maintenance of these devices are considerable because the phosphoric acid, as well as the solution of acid phosphates, attacks the heated material with which they come in contact. Finally, the concentration of phosphate solutions is always accompanied by greater or lesser losses of ammonia than by the effect of their dissociation.

The object of the present invention is a process for the preparation of sodium ammonium phosphate Na NH, HP04 for use as fertilizer.

According to this process, natural phosphates, such as mineral phosphates (phos-

pho,rites) or of animal origin (bones) finely ground, are treated with a mineral acid, for example sulfuric, hydrochloric or nitric acid, etc., in the presence of an alkaline sulphate. The bolution thus obtained is separated from the sulphate precipitate, for example by means of filtration or settling.

In the clear solution obtained, a sodium salt is dissolved and ammonia is then introduced in the form of gas, for example, until a monoammonium sodium salt ( Na HNH, P0.), which has a neutral reaction when it is not dissociated, for example at ordinary temperature, and when Von precipitates at a temperature not higher than 25 C.

This precipitate separates from the mother waters, for example by decantation filtration, removes crystallization water from these waters, which causes the solutions to concentrate spontaneously and the process does not require any. evaporation, and it does not even happen that, in subsequent operations, the liquids become

at least to the point that they can be considered lost, or that they cause filtration or settling difficulties.

These operations are repeated with the same raw materials and in the same way, by bringing the mother waters which result from a Phase back into the cycle of successive operations in such a way as to. establish a constant regime, so that a product of constant P20',-, and N content is obtained. The separation of the sulphate precipitate. of the solution can be carried out without difficulty Ms; an can in fact operate under conditions such that complex sulphates of calcium and alkali are formed, precipitating in sandy and coarsely granulated form.

0n can indeed, to form sulfa your calcium-.% lcalins double and even triple @ in Brande quantity, add ä. 1a<B>,</B> acid solution with which the pliosphorites are attacked, a much higher quantity of alkaline sulphate than the quantity stoichiometrically necessary to fix the calcium under 1a. form of calcium.

But if the artifice just mentioned (i.e. adding an excess of sulphate alcahn) is advantageous for the precipitation and the filtration, it makes it necessary for the precipitate to recover the acid and aleali or alkaline metal which have remained precipitated as Alkaline Calcium Sulfates by treating the mixture of Sulfates with ammonia and carbonic acid.

Example of a case of application of the pro c6d6 according to the invention: 1.00 kg of phosphate with 69% finely ground tricalcium phosphate are attacked with 112 kg of sulfuric acid at 68% and 100 kg of ammonium sulphate. In the phosphoric acid solution separated by filtration from the sulphate precipitate, 22 kg of sodium chloride are added.

The reaction is carried out in three successive phases following one another in the opposite direction to that of the movement of the acidic liquids, that is to say quo la. natural phosphorite viet in contact with the most exhausted liquid, while the second mud undergoes the action of natural aeide; in the. Interphase

medium to add the mother water from the previous operation. The reaction ends with a double wash with approximately 120 liters of water. After each of the three phases, the mixture of reactants is sent to the filters and, by filtration, it obtains clear liquids and relatively dry residues. The final liquid from filtration and containing Ammonia Phosphate, Alkali Chloride and possibly small quantities of phosphoric and sulfuric acid, is sent to the saturation apparatus and neutralized with oxygen gas. 'a.mmoniaque which is absorbed6. During this operation, the temperature tends to rise. but it is maintained at 35-40 h C, thanks to cooling. The neutralization having been obtained and the cooling continuing, the temperature drops to 16-20° C. and then crystallization of the sodium ammonium phosphate takes place. The crystals which would be naturally colorless are soiled by phosphates of aluminum and iron of a colloidal character which give the mass, while it is humid, a brown color. On desiccation, the mass discolors and becomes whitish. The content of the dried product contains 3.6 to 37% P20 and 9 to 10% N,.

The muddy water is recirculated. 0n makes los react. sludge containing polybasic sulphates with ammonia and carbonic acid and thus obtains carbonate of lime and alkaline sulphates, with a preponderance of ammonium sulphate.

In the application as a fertilizer of sodium and ammonium phosphate, the latter has; valuable properties: it is rich in fertilizing elements P20 and N2; its agricultural value is remarkable, which can be expected from its composition and which is confirmed by the fact that guano, containing precisely sodium and ammonium phosphate, is considered one of the best fertilizer; its solubility in water is limited so that it is assimilated by plants, atmospheric precipitation cannot remove it from the ground on which it has been spread; finally, unlike other ammoniacal phosphates, it is completely

stable and non-hygroscopic. The product is presented as a granulated, chestnut-white, dry powder, which does not clump together, even if pressed in the hand, and can be stored unaltered for a long time in containers or in heaps.

Claims (2)

CLAIM Process for the preparation of sodium phosphate and 4'ammoniurn Na NH, HP04 intended to be used as a fertilizer, characterized in that a finely ground natural phosphate is treated with a mineral acid in the presence of an alkaline sulphate, an separates the firm m6e solution from the sulphate precipitate, an dissolves a sodium salt in this solution, puls an adds the ammonia until an ammoniacal sodium salt is obtained which is precipitated at a temperature below 25 C , separating this precipitate from the mother waters, from which <B>11</B> removes water of crystallization, and repeating the operations with the same raw materials and in the same way, bringing in each time the mother waters of calf in the cycle of the following operations, so as to establish a constant regime and to obtain a sodium and ammonium phosphate of constant <B>P205</B> and N` content and presenting itself like a granulated, whitish, dry powder, which does not accumulate in lumps. SUB-REQUESTS 1 Process according to the claim, characterized by 1'emploi Jans phas-e attack, an excess of alkali sulfate, in order to cause the formation with .1e Sulfate mo nocalcium, alkaline ealcium complex sulfates. 2 Process according to claim and sub-claim 1, characterized by the treatment of calcium-alkaline sulphates with carbonic acid and ammonia, so as to recover the teaatives used in excess.