ES2332300B1 - PROCEDURE FOR REDUCTION OF THE CONCENTRATION OF AMMONIA IN DEJECTIONS OF LIVESTOCK. - Google Patents

Abstract

Procedure for the reduction of ammonium concentration in farm dropouts Livestock

The present invention describes particles. solids with a size less than 500 microns containing Mg and P in a molar ratio between 75: 1 and 1: 1, obtainable by means of a procedure comprising: a) calcining the natural magnesite or the natural dolomite at a temperature between 600ºC and 1000ºC during the time needed to completely decompose carbonate from magnesium; b) react the product obtained in step a) with phosphoric acid and, optionally, add water in a range from 15% to 500% by weight with respect to the product obtained in the stage a); c) optionally drying the product from step b), and d) if it is necessary, reduce the particle size to a size Approximately less than 500 microns. The invention is useful for reducing the ammonium concentration in farm dropouts Livestock

Description

Procedure for the reduction of ammonium concentration in farm dropouts Livestock

The present invention relates to particles solids comprising P and Mg, to a procedure for its preparation and a method to reduce the concentration of ammonium in dejections of livestock farms.

State of the art

Reduction of nitrogen concentration contained in livestock farms, commonly known as slurries, especially on large farms, is a problem of great magnitude and importance throughout the world. The intensive livestock, which is necessary to increase the farm productivity, produces a polluting waste which is difficult to manage and is very dangerous for the environment ambient.

When these wastes are used as fertilizers on cultivated land, the presence of ammonium ion, Generally in concentrations between 2 and 10 g / L, it has very harmful in aquifer systems. The main cause of these negative effects is the oxidation of ammonium ion to ions Water soluble nitrite and nitrate, which accumulate in the underground aquifers up to levels dangerous to health human

Some of the usual procedures for treatment of livestock farm dropouts are based on the stages of methanization, composting of the solid phase and finally, treatment of the liquid phase in a treatment plant biological In this last phase the oxidation of the ion takes place Ammonium to nitrite and nitrate. Subsequently these two ions are oxidized to nitrogen and oxygen.

Currently, the energy consumption of Methanization and debugging procedure is much greater than the energy contained in the methane produced, doing the procedure economically unfeasible.

On the other hand, from the point of view technological, the separation of the liquid and solid phases of the waste during processing of farm dropouts Livestock has operational problems. Separation by solid phase decantation of the liquid is almost impossible even after long periods of time and filtration or centrifugation needed for this separation present difficulties requiring specific technical means.

It is well known that the introduction of magnesium in the liquid phase of the liquid dejections of farms livestock, preferably in pig manure, allows precipitate the ammonium ion in the form of struvite (NH4 MgPO4), according to the following chemical reaction:

PO4 {3-} + NH4 + + Mg2 + + 6H2 O → NH 4 MgPO 4 .6H 2 O

Struvite-shaped ammonium ceases to be soil contaminant, because its subsequent oxidation and mobility towards groundwater they are disabled. Also the ion potassium is also fixed in the form of a similar compound named K-struvite (KMgPO_ {4}):

PO4 {3-} + K + + Mg 2+ → KMgPO_ {4}

Finally, the soluble phosphates present in slurries are generally insufficient for both reactions are carried out completely, therefore it is necessary the addition of external phosphates to the system.

Different literature have been described procedures for adding magnesium in the form of chloride, hydroxide, sulfate, oxide, carbonate or bicarbonate to slurry. Although the use of struvite for the removal and recovery of phosphates and ammonium following these procedures is technically feasible, in practice it does not apply due to the high cost of magnesium compounds However, it is possible to use fonts of magnesium such as low grade magnesium that make the economically viable procedure.

The document Recents Progres in Genie des Procedes 1995, vol. 9, (43, Boues Industrielles; Traitements, Valorisation), pp. 81-86 describes a procedure for the treatment of slurries with phosphoric acid and magnesium oxide. In this document, no previous reaction between these two reagents is described, nor is there any indication about the origin of the reagents or the order of addition thereof.

ES 2264377 describes the addition of magnesium from low grade in solution or suspension to slurries to precipitate the Struvite in a Mg: P molar ratio of 1.6. In this procedure, a first stage of aeration is needed to eliminate carbonates present in slurry. This document does not exist any indication of the source of phosphorus.

There is a need to develop new procedures for the treatment of dejections generated in the intensive livestock that are technically as well as economically viable, and simple to implement.

Summary of the Invention

The inventors have found that certain solid particles with a specific composition containing P and Mg, and with specific physical characteristics, reduce the concentration of ammonia in livestock farms through an economic and simple procedure, without the operational difficulties of the other known methods. For example,  there are no exothermic reactions and, consequently, it is not strict control of reagent quantities or the control of the temperature or the speed of addition of reagents

In contrast to the use of reagents separated, magnesium oxide and phosphoric acid, from treatments already known, the solid particles described herein invention as a single solid reagent are safe and easy handling and dosage. Actually, you don't need to calculate a stoichiometric dose of solid particles, given that an excess of them is not problematic for the reduction procedure of the concentration of ammonium, nor for subsequent use of the treated dejections. In any case, the only effect of the addition of an excess of solid particles of the invention to dejections of livestock farms is that the fixation of Contaminant components thereof are insured. For the Therefore, prior or subsequent analysis of the dejections of livestock farms.

Thus, a first aspect of the present invention is related to solid particles with a particle size approximately less than 500 µm, comprising Mg and P in one molar ratio between 75: 1 and 1: 1, obtainable by means of a procedure comprising: a) calcining magnesite or dolomite natural at a temperature between 600 and 1000ºC during the time necessary to completely decompose magnesium carbonate; b) react the product obtained in step a) with acid phosphoric and, optionally, add water in an interval from the 15 to 500% by weight with respect to the product obtained in step a); C) optionally dry the product of step b), and d) if it is necessary, reduce the particle size to a size approximate less than 500 µm.

The invention also comprises a method for the preparation of solid particles as defined previously comprising: a) calcining magnesite or dolomite natural at a temperature between 600 and 1000ºC during the time necessary to completely decompose magnesium carbonate; b) react the product obtained in step a) with acid phosphoric and, optionally, add water in an interval from the 15 to 500% by weight with respect to the product obtained in step a); C) optionally dry the product of step b), and d) if it is necessary, reduce the particle size to a size approximate less than 500 µm.

A third aspect of the invention is related to a method to reduce the concentration of ammonium in dejections of livestock farms until reaching the desired ammonium concentration, which comprises contacting solid particles as defined above with the dejections of livestock farms.

Aspects of the present invention will be described later in the detailed description section that follow. Unless defined otherwise, all terms scientists and technicians used have the same significance as commonly understood by the person skilled in the art to whom the Present invention belongs. Throughout the description and the claims the word "comprises" and its variants not they intend to exclude other technical characteristics, additives, components or steps. For experts in the field, others objects, advantages and features of the invention will come off partly from the description and partly from the practice of invention.

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Detailed description of the invention

As described above, the particles solids of the invention have an approximate size of less than 500 \ mum. The particle size of the solid is important for get a good reactivity of them. In one embodiment preferred, the approximate particle size of the solid is smaller than 200 µm. In an even more preferred embodiment, the size of Approximate particle of the solid is less than 100 µm.

In another preferred embodiment, the particles of The invention contains Mg and P in a 8.8: 1 molar ratio. In a most preferred embodiment, the particles of the invention contain Mg and P in a molar ratio of 2.2: 1 or 2.1: 1.

Alternatively, the molar ratio of Mg and P is it can also express in% of the oxides MgO and P2O5 respectively. Therefore, the Mg / P molar ratio of 75: 1 corresponds to 85% MgO by weight and 2% by weight of P 2 O 5. In general, the solid particles of the invention show a Mg / P molar ratio such that% MgO can be located from 30% by weight to 85% by weight of MgO and the percentage of P 2 O 5 can be between 2% by weight and 45% by weight, with the proviso that the total percentage of both components is 100% In a preferred embodiment, the solid particles of the invention has a Mg / P molar ratio such that% MgO is between 30% and 85% by weight and% P2O5 can be from 20% by weight to 40% by weight, with the condition of that the sum of both components is 100%.

The particles of the present invention contain among other components Mg (OH) 2, MgHPO4 .3H2O, CaCO3, and may also contain others oxides such as iron oxide, aluminum oxide, or oxide of silicon. The presence of these oxides does not interfere with the formation of the struvite and remain unchanged in the final solid, increasing its decantability and filterability. Generally the solid particles contain SiO2 in a range between 1% in weight and 10% by weight, preferably between 1% by weight and 3% by weight, with the proviso that the total percentage of components is 100% In another particular embodiment, the solid particles also contain CaO in a range between 5% by weight and 50% by weight, preferably between 6% by weight and 10% by weight with the condition that the total percentage of the components is 100%

An advantage of the particles of the invention is that since the risks of transport and handling are virtually eliminated.

The procedure to prepare the particles solid of the invention comprises, in a first stage, the calcination of natural dolomite or natural magnesite for the time necessary to achieve decomposition Complete of magnesium carbonate.

Magnesite (Magnesium Carbonate (MgCO3) mineral) and dolomite (calcium magnesium carbonate (CaMg (CO 3) 2, mineral found in everyone and whose reservations are virtually unlimited), are the most important natural sources of low grade magnesium.

In a preferred embodiment, the calcination of Magnesite is carried out at a temperature of 750 ° C. In other preferred embodiment, the calcination of dolomite is brought to out at 650 ° C.

Generally the time required for the decomposition of all magnesium carbonate is between 1 and 5 hours.

As shown in the examples of the In the present invention, both sources of magnesium have proven to be equally efficient for fixing ammonium.

In a second stage of the procedure, the product obtained in the first stage is reacted with acid phosphoric. In a preferred embodiment, phosphoric acid is used. concentrated. This reaction is optionally carried out by adding A certain amount of water. The addition of water is carried out. on the product obtained in the first stage before adding the phosphoric acid or, alternatively, can be added to the mixture in reaction once phosphoric acid has been added. In a particular embodiment, no water is added to the reaction mixture. In a preferred embodiment, water is added to the resulting product of calcination in an amount between 15% and 500% by weight with respect to the product resulting from calcination and then add phosphoric acid. In a more preferred embodiment, the water is added to the product resulting from calcination in a quantity between 15% and 25% by weight with respect to the resulting product from calcination and then phosphoric acid is added.

In another preferred embodiment, the reaction is carried out at a temperature below 60 ° C.

The product previously obtained from the reaction of the calcined product and phosphoric acid can be optionally dried. In a preferred embodiment, the product is dried at 110 ° C. When water is added to the reaction mixture it is drying operation is carried out to obtain a product solid. Drying means an operation that removes water from the reaction. The person skilled in the art will determine in each case the better way to eliminate water, depending on the quantity used to carry out the reaction.

If necessary you can reduce the size of particle and particles can be screened to get a particle size less than 500 µm. Particle size desired can be achieved by several methods known in the prior art, for example using mills and other equipment of fragmentation. Alternatively, particles of a certain size they can be obtained by reaction from a product that already has the appropriate particle size. Sieves can be used to get a uniform particle size.

The solid particles of the invention are useful for reducing the concentration of ammonia in dejections of livestock farms. The procedure to reduce the concentration of ammonia in livestock farms comprises contacting the solid particles as they are have previously defined with farm dropouts Livestock The time required for this treatment will be determined in each case by the expert in the field. In one embodiment In particular, the treatment is carried out over a period of time which is between 24 and 72 hours. In a preferred embodiment, the Time used is 24 hours.

Dejections of livestock farms and especially slurries contain large amounts of carbonates and bicarbonates. Direct addition of phosphoric acid, already known in the state of the art, it causes a strong effervescence of carbon dioxide which forces degassing previously the dejections before the addition of salts of magnesium. On the contrary, the addition of solid particles of the The present invention does not cause effervescence and eliminates the need of the degassing stage, as will be shown in the examples.

As previously mentioned, the formation of struvite by the addition of magnesium phosphates contained in the solid particles of the invention is not as exothermic as the corresponding separate addition of phosphoric acid and salts of magnesium. The particle size of the particles of the invention Improves struvite formation by slowly growing the crystal, which later facilitates the filtration of treated injections. Consequently, the use of flocculants, the decanting volume and the surface of the filter cloths, it They reduce considerably.

Solid particles are obtained as result of the reaction of low grade magnesium sources with phosphoric acid In this reaction only part of the magnesium oxide it becomes magnesium hydrogen phosphate, capable of reacting with the ammonium ion in a sample, for example in a dejection of livestock exploitation, to produce struvite:

MgHPO4 + NH 4 + + NH 4 MgPO 4 + H +

Also, the solid particles of the invention are also able to react with the potassium ion of The sample to give K-struvite:

MgHPO4 + K <+> KMgPO_ {4} + H +

The low reactivity of magnesium sources Low grade used in the present invention, as well as excess of the same used in the procedure, cause the solid particles of the invention show an important content of unreacted magnesium oxide in the form of hydroxide of magnesium, magnesium hydroxide reacts with anions slurry phosphate and soluble phosphate concentration in it It is reduced too. Magnesium hydroxide remains stable during the procedure of treatment of the dejections and fixed pH at appropriate values for struvite formation, of so that the use of caustic hydroxides for adjustment is eliminated of pH.

Actually, to get a good fix of the ammonium and potassium ions of a sample a pH is required between 9 and 9.5. The solid particles of the invention have the advantage of producing a buffer effect that brings the pH to a value included between these two values. In addition, the presence of unreacted magnesium hydroxide has the advantage that the product obtained after the treatment of the injection of Livestock farms can be used to correct the acidity of the soils.

In a preferred embodiment, the amount of solid particles used in reducing the concentration of magnesium in livestock farm injections is one to twice the stoichiometric amount required by ammonium Present. The concentration of ammonium can be reduced until reaching the desired ammonium concentration, usually up to Ammonium concentration that complies with applicable regulations. Generally, the final concentration of ammonium is reduced to 100 ppm or less Preferably the final concentration of ammonium in the Sample is equal to or less than 40 ppm.

As a result, the procedure for the treatment of livestock farm dropouts and the reduction of ammonium concentration is simplified and allows an in situ treatment of the dropouts by non-specialized personnel.

Additionally, the procedure to reduce the Ammonium concentration works well regardless of origin of the dejections of livestock farms. On the other hand, the solid particles of the invention are equally active against recent dejections, embalmed for weeks or months, or previously digestated in a methanizer, as shown in the following examples.

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Examples

The following examples are described for facilitate understanding of the invention and are not intended to be Limitations of the present invention.

Phosphate ion concentrations were determined by inductively coupled plasma optical emission spectroscopy (ICP-AES). In all experiments the concentration of ammonium was determined by the Kjeldall method (IMKolthoff et al ., "Quantitative Chemical Analysis", 1986sixth edition).

Example comparative

Treatment of the liquid fraction of a slurry with acid phosphoric and calcined magnesite

The initial composition in ammonium and phosphate of the Sample to be treated is shown in Table 1.

TABLE 1

one

To fix the ammonium, a sample of low grade magnesium obtained by calcination of natural magnesite at 900 ° C for two hours. Its composition is shown in Table 2. The particle size distribution was determined by an analyzer particle size by laser dispersion, Beckam Coulter LS 13 320.

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TABLE 2

2

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To facilitate the formation of struvite it added the stoichiometric amount of phosphoric acid of 85% necessary to combine with the ammonium ion present in the sample of slurry (13.5 mL per liter).

The addition of phosphoric acid and magnesite calcined to the sample produces an exothermic reaction, with vigorous effervescence, due to the elimination of HCO 3 - of the ejection in the form of CO2. To avoid splashing the acid addition was done carefully by small additions

Subsequently, calcined magnesite was added in each experiment, and the pH value was determined after stir as well as the concentrations of ammonium and phosphate ions in the reaction medium as a function of the contact time and the Amount of magnesite calcined per liter of slurry.

Residual concentrations of ammonium below 25 ppm and the final pH of the system was 9 (20-25 grams of calcined magnesite per liter of slurry and contact time greater than 6 hours).

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Example 1 Treatment of slurry samples with FIXASOL obtained from of calcined magnesite Preparation of FIXASOL

They were introduced into a beaker of 1 L, 115 grams of phosphoric acid 85% by weight. Later, 171 grams of calcined magnesite were gradually introduced for three minutes

The mixture was kneaded for one minute to homogenize the product obtaining a solid whose composition a Dry time is shown in Table 3. Data were obtained by inductively coupled plasma optical emission (ICP-OES) Perkin Elmer Optima 3200 spectrophotometer RL The granulometric distribution was determined by a Beckman laser dispersion particle size analyzer Coulter LS 13 320.

TABLE 3

3

Sample treatment with FIXASOL

With the reagent obtained (FIXASOL), they were treated Three slurry samples:

- Sample A: recent slurry.

- Sample B: damped slurry: Time of stay approximately 6 months.

- Sample C: embalmed slurry. Time of stay approximately 2 months.

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The treatment consisted of introducing the FIXASOL in 100 mL of slurry leaving the system unturned or agitated sporadically every 6 hours. The contact time was 72 hours. The results are shown in Table 4.

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TABLE 4

4

In all samples a final pH was observed next to 9 and an improvement in phase separation. Of the two separated phases one contained the organic matter and the reagent already loaded with ammonium and the other phase, corresponding to the layer superior, it did not contain organic matter. System filterability  once the procedure was over, it was much larger than the slurry original. With the addition of FIXASOL and the reaction time adequate, improved the release of the solid from the liquid, improving the slurry treatment in the separation stage solid-liquid

The solid obtained after the treatment of the Sample A has practically no smell what the fixation demonstrates Ammonium

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Example 2 Treatment of slurry slurry samples with FIXASOL

The digestion procedure was carried out by mixing slurry with different vegetables to increase the carbon / nitrogen ratio and optimize gasification efficiency. 1 L of anaerobically digested slurry (E.Campos et al ., "Guide deis tractaments de les dejaccions ramaderes", Residus Agency of Catalonia, Generalitat de Catalunya, 2004 and J.Prats, Manual de Gestió deis purins i de la seva utiiització Agricultural, Residus Board, Generalitat de Catalunya ISBN: 84-393-3236, 1995) was treated with 20 g of FIXASOL. After 24 hours of contact with sporadic agitation, the concentration of ammonium was analyzed, as well as the pH.

5

Example 3 Treatment of slurry samples with product obtained from from calcined dolomite Preparation of the product derived from calcined dolomite

500 g of dolomite were placed in an oven CARBOLITE CWF 1300 and kept at 750 ° C for 2 hours. Be produced a 28% weight loss obtaining a compound with a 60% by weight MgO content.

115 g of acid were introduced into a container phosphoric of 85% by weight and 215 g of subsequently added calcined dolomite To homogenize the product, the Mix manually for 1 minute. Product composition obtained after drying is shown in Table 5 (data is have obtained by plasma optical emission spectroscopy inductively coupled (ICP-OES), spectrophotometer  Perkin-Elmer Optima 3200 RN). The distribution Granulometric was determined with a size analyzer particle by laser dispersion, Beckman Coulter LS 13 320.

TABLE 5

6

Treatment of samples with the product obtained from calcined dolomite

The treatment consisted of introducing 3 g of the product previously obtained in 100 mL of slurry leaving the system at rest and stirring sporadically every 6 hours. The system is left in contact for 72 hours. This procedure allowed reduce the concentration of ammonium from 5660 to 135 ppm.

Claims (12)

1. Solid particles with a particle size approximate less than 500 µm, containing Mg and P in a ratio molar between 75: 1 and 1: 1 obtainable by a procedure that understands: a) calcinate natural magnesite or dolomite natural at a temperature between 600ºC and 1000ºC during the time necessary to completely decompose magnesium carbonate; b) react the product obtained in the step a) with phosphoric acid and, optionally, add water in a range from 15% to 500% by weight with respect to the product obtained in stage a); c) optionally drying the product of the stage b), and d) if necessary, reduce the size of particle up to an approximate size of less than 500 µm.

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2. Solid particles according to claim 1, which have an approximate particle size less than 200 \ mum. 3. Solid particles according to claim 2, which have an approximate particle size less than 100 \ mum. 4. Solid particles according to any of the claims 1-3, comprising Mg and P in a 2.1: 1 or 2.2: 1 molar ratio. 5. Solid particles according to any of the claims 1-4, further comprising Si and AC.

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6. Procedure for the preparation of solid particles as defined in claim 1, which understands: a) calcinate natural magnesite or dolomite natural at a temperature between 600ºC and 1000ºC during the time necessary to completely decompose magnesium carbonate; b) react the product obtained in the step a) with phosphoric acid and, optionally, add water in a range from 15% to 500% by weight with respect to the product obtained in stage a); c) optionally drying the product of the stage b), and d) if necessary, reduce the size of particle up to an approximate size of less than 500 µm.

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7. Method according to claim 6, where the calcination of natural magnesite is carried out at a approximate temperature of 750ºC and the calcination of dolomite Natural is carried out at an approximate temperature of 650ºC. 8. Procedure according to any of the claims 6-7, further comprising the step of drying the product at a temperature of 110 ° C. 9. Procedure to reduce concentration of ammonia of cattle droppings until reaching the concentration of desired ammonium, which comprises contacting the particles solids defined in any one of claims 1 to 5 with the dejection of livestock exploitation. 10. Method according to claim 9, where the particles defined in any of the claims 1 to 5 are contacted with the injection of livestock exploitation for 24 hours. 11. Procedure according to any of the claims 9-10, wherein the ejection of Livestock exploitation is a slurry. 12. Procedure according to any of the claims 9-11, further comprising a previous stage of digestion of the exploitation injection Livestock