DE2444828A1 - Condensed phosphates prodn from wet phosphoric acid - bbyaan eihh--stag cobbinddp process giving reduction in phosphate loss - Google Patents

Abstract

Condensed phosphates, esp. sodium triphosphate, are produced from wet phosphoric acid, with a phosphate loss 12% by (1) pptg. calcium by addition of excess crude phosphate to the untreated wet H2PO4 at 60-100 degrees C, pref. 80 degrees C; 2) Pptg. fluorine by neutralisation, pref. wiht NaOH lye, at 70-100 degrees C, pref. 90 degrees C, to a mol. ratio of NA:P of 0.1-0.4, pref. 0.2; (3) cooling to 10-40 degrees C, pref. 25 degrees C, separating the ppt. adn opt. utilising the ppt. as settling accelerator for concrete; (4) pptg. the rate earth components by neutralisation with NaOH lye or sod at 70-100 degrees C, pref. 90 degrees C to a mol. ratio of NA:P of 0.6-0.7, pref. 0.65, separating the pptg. and opt. recovering the rate earth components from the ppt; (5) pptg. the sulphates by addition of BaCO3; (6) pptn. of the polyvalent cations (e.g. Fe3+, Al3+, Ca2+) by neutralisation, pref. with NaOH lye at 70-100 degrees C, pref. 90 degrees C to a mol. ratio od Na:P of 1.2-1.4, pref. 1.25, separating the ppt. and opt. working up the ppt. to produce fertilisers; (7) Neutralising pref. with NaOH lye, to a mol. ratio of Na:P of 1.66) and concentrating to a 30-33% of P2O5 content; (8) working up the sodium ortho-phosphate soln. obtained to condensed phosphates in known manner. Method gives marked reduction of phosphate loss as compared with know processes. all byproducts are utilisable further.

Description

"Process for the preparation of condensed phosphates" The invention relates to a process for the production of condensed phosphates, in particular Sodium trip @ osphat, from wet phosphoric acid and the necessary cleaning of the Wet phosphoric acid.

In contrast to therinic phosphoric acid, which because of its Extraction from pure elemental phosphorus sufficiently pure for most technical Applications is called wet phosphoric acid or extraction phosphoric acid technical phosphoric acid obtained by digesting rock phosphates with sulfuric acid and which due to this origin is obtained by large amounts of fluorine, sulfuric acid, Silicic acid, caleium, aluminum, iron and other substances is contaminated. For extraction of the desired products, the impurities must be largely removed.

This is done according to known methods either by liquid-liquid extraction with organic solvents, by ion exchange processes, by precipitation Sufficiently pure phosphates from wet phosphoric acid and subsequent processing these phosphates, by volatilization of part of the impurities, in particular of fluorine and silicic acid, or by precipitation and separation of the debris in the course of the neutralization which is necessary anyway for the production of phosphoric acid salts.

The process belonging to the latter group, heutralization and cleaning are linked to one another because of their technological simplicity great importance too. They come with relatively simple reaction apparatus that do can be easily controlled and mastered, and need to carry them out no expensive or hard-to-reach chemicals than. Raw and auxiliary materials.

All known, technically used neutralization processes exist from one or more reaction steps in which precipitation means, for example Calcium or barium compounds for the precipitation of sulfates, or neutralizing agents, like soda, caustic soda or ammonia are added to the phosphoric acid, which thereby Precipitated compounds containing the impurities are in or in separated from several stages.

The known methods differ in their type and number of the individual reaction steps, through the precipitation and neutralization auxiliaries used and by the technique of separating those containing the individual impurities Precipitation products. The choice of these process parameters is not limited to the ones available Raw materials and the quality requirements of the main product, but also depending on the intended use for the by-products.

Zwn example, one proceeds according to a known method so that one the crude wet phosphoric acid neutralized with calcined soda and thereby up to near heated to boiling. The resulting precipitate is separated on filter presses wash it off with hot water and use it in superphosphate production. Sodium triphosphate is obtained from the filtrate by spray drying and calcining.

Another known method is used to neutralize wet phosphoric acid with alkali carbonates, optionally activated carbon, barium carbonate or iron (II) sulfate added, initially at 30 ° C up to the metallic titer (molar ratio Na: P) 1.0 up to 1.2 and then at 70 ° C up to the metallic titer 1.67. From the subsequent Filtrate obtained by filtration produces Inan Polyphosphate using precipitate man in fertilizer production.

Another known process is crude wet phosphoric acid initially concentrated in an immersion burner system to a P205 content of 54%, then stirred with rock phosphate to remove sulfate and with to remove fluoride Soda is added to precipitate the fluorosilicic acid that is present. Afterward is filtered on filter presses at room temperature. Ground barium carbonate in the filtrate and carbon black is added, after which it is neutralized with soda at 80 ° C.

Sodium triphosphate is produced from the filtrate and the separated one Precipitation is processed in the fertilizer industry.

Another known method is to remove from wet phosphoric acid by adding soda and limestone first sulphate and fluorine, filtered on vacuum filters, removes the remaining sulfate with barium carbonate and neutralizes with help concentrated soda solution at 80 OC.

The resulting neutralization sludge is filtered by means of pressure filters separated and by means of water-thinned filter sludge from a previous one Stage washed out, Sodium triphosphate, the neutralization sludge, is obtained from the filtrate is used in the manufacture of fertilizers.

According to several known methods, the neutralization sludge with an alkali solution, in some cases with the addition of silicates, to further Alkali phosphate solution and a low-phosphorus sludge reacted to yield the phosphate to increase. However, this requires an additional reaction and filtration stage, which makes the process more complicated and expensive.

With all known ones, only described here to a small extent Process is the yield of phosphate, based on the amount of phosphoric acid used, relatively low. The phosphate losses are distributed over the individual process steps slightly different, but their total always reaches 20 to 30. Most of the loss However, it is always omitted from the neutralization sludge.

The phosphate is not absolutely lost, because it is the Jleietellunr of fertilizers used, it goes; however, from the relatively highly refined Form, which it possesses in the form of phosphoric acid, into the relatively inferior one Form of the neutralization sludge and is therefore only at the same value such as a rock phosphate can be used.

The state of the art laid down in the literature shows that daP the deficiency of the nickel supplement formed during the neutralization of the polyvalent cations primarily responsible for the loss of phosphorus is. The defensiveness of this neutralization precipitate is not solely due to depending on the conditions prevailing during the neutralization, but also in strong ones Dimensions of the pretreatment of the solution to be neutralized. You have it here clearly to do with a complex of influencing factors that are also mutually exclusive influence and the overall effects of which cannot easily be overlooked.

The purpose of the present invention is to alleviate the main deficiency the well-known neutralization process, which consists of a high loss of phosphate.

The invention is therefore based on the object of a method for Processing of wet phosphoric acid into phosphoric acid salts, which are used for production condensed phosphates is suitable to find that on the one hand only little phosphorus can get into the by-products and, on the other hand, as rational as possible Use of all inevitable by-products permitted.

It has now been found, surprisingly, that condensed phosphates, especially sodium triphosphate, from wet phosphoric acid with phosphate losses of less than 12% through a combination of process steps known per se in unexpected can produce a favorable extent.

According to the invention, the processing of wet phosphoric acid is used in the following way; 1. Addition of rock phosphate to untreated wet phosphoric acid at a temperature of 60 to 100 OC, with over 100% of the stoichiometrically required The amount of rock phosphate used to fill the CaSO4 sulfate present is required, 2. Neutralization, preferably using sodium hydroxide solution at 70 to 100 ° C up to the metallic titre 0.1 to C, 4, where the alr; Fluosilicic acid The fluorine present is precipitated as Na2SiF6.

3. Crystallization at 10 to 40 ° C, separation of the CaSO4.2H2O and Na2SiF6 existing precipitate.

4. Neutralization using caustic soda or soda at 70 to 100 ° C up to the metallic titer 0.6 to 0.7, separation of the rare earth phosphate precipitated in the process.

5. Addition of barium carbonate to precipitate the remaining sulfate.

6. Precipitation of the multivalent cations (e.g. Fe3 +, Al3 +, Ca2 +) through @Neutralization preferably by means of sodium hydroxide solution at 70 to 100 ° C up to metallic Titer 1.2 to 1.4, separation of the neutralization precipitate obtained in this way, Wash out with water.

7. Neutralization using sodium hydroxide solution up to a metallic titer of 1.667, Evaporation to a content of 30 to 32% P205, separation of the during evaporation resulting recurrence.

8. Process the purified sodium orthophosphate solution in a conventional manner Way, for example in a spray tower or in a return condensation process, to sodium triphosphate.

In the case of this type of procedure, the loss of phosphate exceeds which was introduced in the form of wet phosphoric acid, not more than 12%. As the main product Sodium triphosphate is obtained with a degree of purity over 92%, which is less contains than 0.25% of water-insoluble substances and that has a reflectivity for white light over 91%. The gypsum-sodium fluorosilicate- @ enic obtained as a by-product can be used e.g. in construction as a setting accelerator for concrete. That continues Occurring by-product rare earth phosphate contains 24-26% oxides after drying of rare earths in addition to 40 -45% P2O5, 1 - 3% CaO and 2 - 2.5% Fe2O3, it represents a valuable rare earth material, which after one of the usual processes for Example by dissolving in nitric acid with subsequent precipitation of the rare ones Earthing through oxalic acid, to rare earth concentrations @@ 1 A Finally, that falls to his @enge by far the most important by-product, the neutralization sludge, after separation, Wash and squeeze out in an easily transportable and easy-to-dry form at. It can be used both directly in complex fertilizer production, for example in the production of nitrophosphate fertilizers, as well as dried as a stand-alone Use phosphate fertilizers that contain at least 35% P2O5 (of which 30 to 50 '' water soluble) and approx.

Contains 3% @gO.

The invention is detailed below in an exemplary embodiment explained.

Example: Wet phosphoric acid was operated in a continuously Apparatus processed in the following way (the quantities given refer to a t wet phosphoric acid with 32% P2O5, 2.0% SO and 0.35% CaC): In a stirred tank with a residence time of 2 hours, the untreated wet phosphoric acid was at 80 ° C with 24.2 kg of kola apatite concentrate (39.2% P2O5, 52% CaO).

The calcium sulfate suspension obtained in this way was in one further agitator vessel at 90 0C by matron lye to a metallic titer (Na: P molar ratio) of 0.2 neutralized. The now additionally containing Na2SiF6 The suspension was cooled to 25 ° C. in a tube cooler and at this temperature stirred for six hours.

Ifiernach the solid was separated with the help of a centrifuge, mashed with water and centrifuged again, with 66.1 kg of moist CaSO4.2H2O-Na2SiF6 sludge with a P205 content of 3.3% were obtained.

By adding a maximum of 0.62% of this dried sludge to fresh Concrete has a setting time of 30 - 35 minutes down to 0.2, when using Portland cement from 30 - 35 minutes up to shortened to 5 minutes. The flexural and compressive strengths of the iertig set Concrete was not affected by the additives.

The filtrate after the separation of CaSO4.2H2O and Na2SiS6 was combined with the wash filtrate in a further agitator vessel at 90 ° C with sodium hydroxide solution Neutralized to a metallic titer of 0.65 and centrifuged the precipitated Rare earth phosphate separated, mashed again with water and centrifuged became. 7.42 kg were obtained moist rare earth phosphate with the following composition: 28.6% P2O5 36.1% water, 16.5 oxides of the rare alder, , 97% CaO and 0.83% Fe2O3.

The filtrate from the rare earth separation was charged with 7.25 kg of darium carbonate to complete the sulphate precipitation of the added and immediately afterwards 90 0C neutralized with sodium hydroxide solution up to a metallic titre of 1.25. In a automatic air chamber filter press, the neutralization sludge was separated, washed with 274 l of hot water and then squeezed out. There were 163 kg of moist sludge with a P2O5 content of 17.0 0%.

This neutralization sludge became after drying and agglomeration tested with water as an agglomeration aid for its suitability as a fertilizer. It was featured that he is just as good fertilizer properties with regard to the Has phosphate activity, as do the commonly used P and PK fertilizers with low water solubility.

The washing filtrate of the neutralization sludge separation was in the continuously operated neutralization process returned. The filtrate was evaporated to a P2O5 content of 32.1%, with a slight turbidity occurring, which was separated in a centrifuge. 3.7 kg of moist sludge fell with it a P205 content of 19.6% and C, 925 t of clarified filtrate with a P2O5 content from 32.1, v.

The yield of P205 in the form of purified sodium orthophosphate solution was thus 92.7%, based on the amount of P2O5 introduced in the form of wet phosphoric acid.

After the addition of 1.5% concentrated nitric acid, the filtrate became (based on the amount of filtrate), evaporate and heat the powdered salt 400 0C sodium triphosphate with Gehlaten of 0.68% orthophosphate, 4.4% pyrophosphate, 0.90% trimetaphosphate and 0.25% insolubles obtained that a white grail @@@@ lexi @ n capacity for white light) of 91.5% and thus meets the requirements of detergent manufacturers.

Claims (1)

Claim Process for the production of condensed phosphates, in particular Sodium triphosphate, from wet phosphoric acid with phosphate losses of less than 12 %, characterized by the combination of the process steps known per se 1. Precipitation of calcium by adding excess rhodium to untreated Wet phosphoric acid at 60 to 100 ° C., preferably at 80 ° C., 2. Precipitation of the fluorine by neutralization, preferably using matron liquor at 70 to 10 ° C, preferably at 90 ° C, up to a molar ratio Na: P of 0.1 to 0.4, preferably 0.2, 3. Cooling to 10 to 40 ° C, preferably 25 ° C, separating the precipitate and if necessary, use of the precipitate as a setting accelerator for concrete, 4. Precipitation of the rare earths by neutralizing with rutron lye or soda at 70 to 100 ° C, preferably at 90 ° C, up to a molar ratio Na: P of 0.6 to 0.7, preferably 0.65, separating the precipitate and optionally Use of the precipitate for the extraction of rare earths, 5. Precipitation of the Sulphate tea by adding barium carbonate, 6. Precipitation of the polyvalent cations (e.g. Fe3 +, Al3 +, Ca2 +) by neutralizing, preferably using sodium hydroxide solution 70 to 100 ° C, preferably at 90 00, up to a Na: P ratio of 1.2 up to 1.4, preferably 1.25, separation of the precipitate and, if appropriate, use for further processing on dilution media, 7. Neutralize preferably by means of sodium hydroxide solution up to a molar ratio N: P of 1.667 and evaporation a content of 30 to 33% P2O5, 8. processing of the sodium orthophosphate solution obtained according to 7. in the usual way to condensed phosphates.