HU176308B - Process for producing phosphate-fertilizers - Google Patents

Abstract

Process for the production of phosphate fertilizers from phosphorus-containing minerals. in treating the minerals with gaseous sulfur trioxide, possibly in admixture with other gases.

Description

The present invention relates to a process for the production of phosphate fertilizers from phosphate ores, in particular from natural apatites, which are minerals containing calcium phosphate. The phosphorus compound contained therein is of the type A _s (PO ₄ ) ₃ Z, i.e. of apatite structure, insoluble in water and not at all usable by vegetation.

The purpose of making phosphate fertilizers is to make water-insoluble and inaccessible vegetation phosphorus compounds accessible to vegetation or soluble in water or weak acid.

One of the methods known so far for the production of phosphate fertilizers is the so-called thermal process, which involves the agglomeration of phosphate mineral or apatite with sodium carbonate, limestone and silica in rotary furnaces at 1100-1200 ° C. The resulting clinker is then ground in a ball mill. The resulting thermophosphates, which are marketed under the brand name Thomas slag or superfamily, contain predominantly water-insoluble calcium silicophosphates, which are converted to the form in which they are utilized by the organic acids selected by the root system of the plant. Therefore, thermophosphates are usually used as fertilizer in the autumn, ie applied to the area to be fertilized.

A known and widespread method for the preparation of simple superphosphates is the so-called wet process, which involves treating water-insoluble tricalcium phosphate, as it occurs in natural minerals, with a 62-70 percent aqueous solution of sulfuric acid. For this purpose, sulfuric acid must first be prepared (usually by contacting sulfuric acid), stored and diluted to a concentration suitable for digestion of tricalcium phosphate. In addition, the phosphate mineral must be carefully ground in a ball mill before it is excavated. Only then can the phosphate mineral be mixed in a suitable blender with sulfuric acid solution. The mixture thus obtained is then introduced into the digestion chamber where, in the presence of sulfuric acid, the water-insoluble tricalcium phosphate is converted into a water-soluble product, whereby gypsum, i.e. calcium sulfate, is formed as a by-product. The solidified and dried product is then crushed and preferably granulated to provide a ready-to-use fertilizer that should be used in early spring to fertilize fast growing vegetation. By this method, about 5 percent of the phosphorus in the crude mineral is converted into linear phosphates, not soluble in water 20 but weakly soluble in weak acids, and into higher cyclic metaphosphates as a result of the reaction of crude phosphate mineral and sulfuric acid, more than 90 percent of the phosphorus present is converted to water-soluble monocalcium phosphate.

The water-insoluble, but acid-soluble, components of superphosphate, which are slowly soluble in fertilizers, are considered to be the most valuable components for superphosphate fertilization, as they provide phosphorus for extended periods of time.

These acid-soluble components can be utilized by vegetation in 90 percent, while water-soluble phosphorus compounds can be utilized in vegetation by only 15 to 26 percent (see Niklewski, M, and Wenglikowski, E., in Proceedings of the College of Economics, Wroclaw, 1968). appeared). This means that more than 75% of the phosphorus content of the simple superphosphate produced by the wet process is not utilized because it is either washed away from the soil by rainwater or decomposed. The so-called triple superphosphate produced by reacting a phosphorus-containing raw material with an aqueous phosphoric acid solution, which is more concentrated than a simple superphosphate, has the same disadvantage, i.e. most of its phosphorus content is water-soluble.

It has been found that phosphate fertilizers, which are very effective in vegetation, can be obtained from mineral raw materials in a simplified manner by treating the mineral raw material with gaseous sulfur trioxide, optionally in the form of a mixture of sulfur trioxide with other gases. The use of this method does not require the use of high sulfuric acid or phosphoric acid aqueous solution which is essential for the thermal process and the wet process, so it is rightly a simplified process which is much simpler technologically than the methods previously used to produce superphosphate.

SUMMARY OF THE INVENTION The present invention relates to a process for the production of phosphate fertilizers from phosphorous minerals. According to the invention, the crushed raw material under 0.2 mm particle size is dried to a moisture content of up to 1% by weight and then treated with gaseous sulfur trioxide at 200-350 ° C, optionally in the form of a mixture with other gases.

Starting materials for the process of the present invention can be any composition of moisture, particulate or phosphorous minerals, in particular apatite or other phosphate minerals. Gaseous sulfur trioxide from any source may be used to treat the mineral raw material according to the invention, optionally in the form of a mixture with air, sulfur dioxide, nitrogen gas, oxygen gas or other reaction-inert gases.

When the phosphorus-containing particles of the raw material are contacted with sulfur trioxide-containing gas, a chemical reaction occurs which results in the formation of water-insoluble bi-, tri- and tetraphosphates of calcium, as well as higher condensed linear phosphates and metaphosphates. After separation from the treatment gas, the reaction product is a crumbly, non-hygroscopic and non-lumpy material which can be used directly as a fertilizer.

More than 90% of the phosphorus contained in the thus obtained phosphate fertilizers of the present invention can be utilized by vegetation, given that the phosphorus is present in compounds which are soluble in water but not in weak acids. Thus, for the phosphate fertilizers of the invention, the phosphorus is more than three times more utilized than the phosphorus content of the simple and triple superphosphates.

The following examples illustrate the invention.

Example 7

The ring mill is fed with 1 ton of crude phosphate ore and ground to a grain size of less than 0.2 mm. The milled raw material is then dried at 350-150 ^° C in a sieve drum heated with gas from the combustion of fuel oil, and the flow rate of the gas fed to the drying oven is controlled so that the outlet gas temperature is 120-150 ° C.

The 865 kg of material thus dried (having a moisture content below 1%) is then transferred from the drying furnace to a fluidized bed reactor where it is contacted with sulfur trioxide, using 10: 18: 72 by volume of oxygen and nitrogen as the total gas. Nm ^{3 was} fed into the fluidized bed reactor. The temperature of the gas fed to the reactor is 300-350 ° C and the average contact time between the feedstock and the gas mixture is 20-30 seconds.

The resulting product is then cooled in a grate drum and transferred to a storage container, whereupon it is filled into bags as desired.

This gives 1248 kg of phosphate fertilizer in the form of a dry, non-lumpy and non-hygroscopic powder having the following composition, expressed as a percentage by weight:

phosphorus (calculated as P ₂ O ₅ ) - 23.5%, of which 2% is soluble in water and 19.4% in 2% citric acid solution:

CaO - 37.2%

SO ₃ - 34.1% SiO ₂ -0.61% Al ₂ O ₃ -0.31% Fe ₂ O ₃ -0.02% MgO -0.12% K ₂ O + Na ₂ 0-0.96% F -1,6%

U-0.003%

H ₂ 0-0,4% free acid - not detectable.

Example 2

A rotary drum is fed with the phosphorous feedstock ground and dried in the same manner as in Example 1, followed by a countercurrent flow of a sulfur trioxide gas composition having the same composition as in Example 1. The temperature of the gas mixture fed to the rotating drum is 40-100 ° C. In the drum, the reaction temperature is 200-250 ° C and the residence time of the phosphorus-containing raw material is 15-30 minutes. The product leaving the drum is allowed to cool and stored in heaps or packed in bags. The resulting fertilizer has the same appearance and composition as the fertilizer prepared in Example 1.

Claims (1)

A patent claim Process for the production of phosphate fertilizers from phosphorous-containing mineral raw materials, characterized in that the raw material, which has been reduced to a particle size of less than 0.2 mm, is dried to a moisture content of up to 1% and treated with gaseous sulfur trioxide at 200-350C. in the form of a mixture.