CS197290B2 - Process for preparing photosphatic fertilizers - Google Patents

Description

The present invention relates to a novel process for the production of phosphate fertilizers from natural apatite calcium phosphate minerals. The phosphorus compounds contained therein have an apatite structure of the AsfPO + Z type, being in the form of an apatite. water-insoluble and, in fact, inaccessible to plants at all.

In the manufacture of phosphate fertilizers, compounds that are insoluble in water and unavailable for. plants, converted to compounds available to plants and soluble in water or weak acids.

One of the methods used to produce phosphate fertilizers to date consists of agglomerating phosphate rocks or apatites with soda, calcium carbonate and silica in rotary kilns at a temperature of 1100 to 1200 ° C.

The clinker produced is then ground in ball mills. The thermophosphates obtained, known under their trade names as Thomas slag or super slag, first of all contain water-insoluble calcium silicophosphate, which is converted only by the roots of the plants into the form available to the plants.

Thus, Thomas's slags and super slags are fertilizers to be spread in the fall.

Another commonly used process for producing simple superphosphates is a process consisting in the treatment of a water-insoluble tricalcium phosphate contained in natural minerals with a 62 to 70% aqueous sulfuric acid solution.

For the purposes of this procedure, sulfuric acid must first be produced (usually by contacting), stored and diluted to an appropriate concentration. Before the actual production process sc phosphate raw materials carefully. grind in a ball mill as it is mixed with sulfuric acid in a stirring mill. equipment and introduced into the production chamber, who in. presence of sulfuric acid insoluble phosphate. tricalcium converts. to a water-soluble compound, whereby gypsum is obtained as a by-product.

Stiff. . and dried product. crushed. granulated, the finished fertilizer obtained being used early in the spring for fast growing plants.

According to this method,. as a result of the reaction of sulfuric acid with the phosphorous feedstock, about 5% of the phosphorus contained in the crude rock converts to water-insoluble but soluble in the weak acids bi-, tri-, tetraa more aliphatic phosphates and cyclic metaphosphates, while over 90% of the phosphorus present in the feedstock. is a readily water-soluble dicalcium phosphate.

Because the water-insoluble superphosphate fertilizer components are slowly soluble in acids, they form the most valuable fertilizer component as they provide a sustained supply of phosphorus to the soil surface layer. Their availability is up to 90%, while - according to the 1968 Procedures issued by M. Niklewski and E. Wenglikowski from the University of Economics in Wroclaw - the use of water-soluble phosphorus compounds by plants does not exceed about 15-26%. Thus, over 75% of the phosphorus contained in a simple superphosphate, obtained by a wet process, remains unused due to its water solubility and is either eluted away from the field by rainwater, etc., or undergoes a retrograde process.

The so-called triple superphosphate, more concentrated than single superphosphate and produced by the reaction of a solution of aqueous phosphoric acid with phosphorus raw materials, also has the same highly disadvantageous properties.

It has been found that phosphate fertilizers can be produced from mineral raw materials in a simplified manner that requires neither high temperatures as in the thermal process nor an aqueous solution of sulfuric or phosphoric acid as necessary for the wet superphosphate process.

SUMMARY OF THE INVENTION The present invention provides a process for the production of phosphorous fertilizers from mineral raw materials which comprises grinding and drying the mineral raw materials, then reacting with a mixture of gases containing sulfur trioxide at a temperature between 180-350 ° C and after completion of the reaction and isolation of the reaction gases, the solid product is cooled.

For the production of phosphorous fertilizers according to the invention, phosphorous raw materials of any composition, different initial moisture and different grain sizes can be used. Sulfur dioxide gas obtained from any source and mixed with air, sulfur dioxide, nitrogen, oxygen or other inert gases may be used. The concentration of sulfur trioxide in the gas mixture may be in the range of 4-12 vol%. The temperature of the gaseous mixture may be in the range of 100 to 350 ° C.

According to the invention, the starting minerals are ground and dried and then treated with a gaseous mixture containing SO 3 at a temperature in the range of 180 to 350 ° C. When the sulfur trioxide-containing gas comes into contact with the grains of the phosphorus-containing feedstock, the reaction results in water-insoluble bi-, tri- and tetraphosphates of calcium, as well as the above condensed linear phosphates or metaphosphates.

After gas separation, the reaction product in the form of a free-flowing, non-hygroscopic and non-clumping powder is ready for use as a phosphorous fertilizer.

Over 90% of the phosphorus contained in the fertilizer thus obtained is available to plants due to the insolubility of the phosphorus compounds in water but their solubility in weak acids. The utilization of phosphorus (as available for plants) contained in the phosphorous fertilizers produced according to the present invention is more than three times higher than that found with single and triple superphosphates.

An embodiment of the invention is explained in more detail in the following exemplary embodiment.

Example

1 ton of crude phosphate rock is introduced into the ball mill and ground to 0.2 mm grain size. Then, the feedstock is dried at a temperature of 350 to 450 ° C in a drum furnace heated with fuel oil, the outlet gas temperature being 120 to 150 ° C.

The dried material weighing 865 kg, the moisture content of which was lowered below 1 ° / o, was fed directly from the furnace to a fluidization reactor where it was contacted with sulfur trioxide which was introduced as a mixture with oxygen and nitrogen in a ratio of 10% by volume. : 18: 72, the total amount of gas mixture introduced being 1150 Nm ³ .

The gas introduced into the reactor has a temperature in the range of 300 to 350 ° C and the average duration of the reaction is 20 to 30 seconds.

Then the material is cooled inside the cooling cylinder and transferred to a container from which it is discharged into bags.

A total of 1248 kg of phosphorus fertilizer is obtained in the form of a dry, non-clumping and non-hygroscopic powder of the following weight composition:

- phosphorus (converted to P2O5) - 23.5%, which includes 2% water-soluble phosphorus, 19.4% phosphorus soluble in 2% citric acid;

—CaO - 37.2% —SO3 - 34.1% —SIO2 - 0.61% —AI2O3 0.31% —РегОз - 0.02% —MgO - 0,12% —K2O + NažO - 0,96% —F - 1,6% —U - 0.003% -H2O - 0.4 ° / o

free acids - none.

Claims (4)

1. A process for the production of phosphate fertilizers from mineral raw materials, wherein the minerals are milled, dried and then reacted with a mixture of gases containing sulfur trioxide at a temperature ranging from 180 to 350 ^Q C, and after completion of the reaction and isolation of the solid reactant gases the product cools. 2. A process according to claim 1, characterized in that a gas mixture containing from 4 to 10 is used 12 volume% sulfur dioxide. 3. The process of claim 1, wherein gaseous sulfur trioxide mixed with sulfur dioxide, nitrogen and noble gases is used. 4. Process according to claim 1, characterized in that the reaction gases containing sulfur trioxide are used at a temperature of 100 to 350 ° C.