MANUFACTURE OF AN ABC EXTINGUISHING POWDER FROM PHOSPHOGYPSE

Abstract

The present invention relates to a method for preparing an ABC extinguishing powder from phosphogypsum (PG).

Description

Title of the invention: MANUFACTURE OF AN ABC EXTINGUISHING POWDER FROM PHOSPHOGYPSE FIELD OF INVENTION

[0001] The present invention relates to a process for preparing an ABC extinguishing powder from phosphogypsum (PG). TECHNOLOGICAL BACKGROUND

[0002] ABC class extinguishing powder is a powder designed for extinguishing fires caused by the combustion of hydrocarbons or solid materials, class A fires (wood, paper, cardboard, rags, plastics, etc.), class B fires (gasoline, oil, alcohol, solvents, petroleum products) and class C fires (gas fires). It is composed mainly of phosphates and ammonium sulfate.

[0003] Ammonium salts have the property of melting under the effect of heat and forming a crust on the surface of solids, insulating them from the air. This makes this powder usable for Class A, B, or C fires. Other additives are generally used, e.g., minerals from the mica group, muscovite (potassium aluminum hydroxysilicate), or fuller's earth (magnesium aluminum silicate) to make the powder less volatile. Finally, fractions of silicone oil (methylated and hydrogenated polysiloxane) are included to prevent the powder from clumping under the effect of humidity. It is non-toxic, dielectric, non-freezing, fine, and very fluid, and forms a heat shield.

[0004] Different mixtures of ABC class powder are available depending on the content of monoammonium phosphate (MAP) and ammonium sulfate (NH4)2SO4. Table 1 below shows different mixtures of a dry ABC powder.

[0005] [Tables 1] Powder ABC 90 ABC 95 ABC 80 ABC 70 ABC 50% of MAP 90 95 80 70 50% (NH4)2SO4 5 5 15 20 30

[0006] Table 1: Different compositions of ABC extinguishing powder

[0007] Ammonium sulfate is a by-product of the manufacture of certain organic materials; it enhances the activity of a multipurpose powder on smoldering fires. Most ABC extinguishing powders contain a certain mass percentage of ammonium sulfate mixed with MAP.

[0008] Ammonium sulfate is thermally unstable, however its decomposition is gradual and only completes above 500 °C. It is fairly soluble in water, and of a Its hygroscopicity is slightly higher than that of MAP. It is also non-toxic. It does not attack iron or its alloys, nor even light metals, and it exhibits low reactivity towards certain copper and zinc alloys. Phosphogypsum is a by-product of the reaction of phosphate with sulfuric acid according to the following equation:

[0009] [Math.l] [Cas{POArisCaFs * WH.SG, * 2ÔHaO * WfCaSO. 2H2O) * 2HF Generally, the production of one ton of phosphoric acid is accompanied by the production of more than four tons of gypsum (calcium sulfate, Ca2SO4). Gypsum is a problematic product, large quantities of which are released into the environment. Morocco is one of the world's leading producers of phosphate and phosphoric acid, generating nearly 15 million tons of PG annually (1). Until 2006, the total amount of PG produced worldwide was estimated at around 6 billion tons, with an annual production of approximately 160 million tons (2). However, 85% of this by-product is disposed of without any treatment, generally by dumping it into the oceans or by storing it in special areas, which causes environmental problems (3).

[0010] Recently, research has focused on this area in order to valorize phosphogypsum tailings. This by-product is thus particularly used in construction materials such as bricks, cement, and plasterboard (4) and in agriculture as a source of calcium Ca2+ and sulfate SO42 (5) for soil amendment or as fertilizer. It is also transformed into basic building blocks by a thermal decomposition process in the presence of a solid fuel (coal or shale) to produce sulfur dioxide SO2 and calcium oxide CaO (6). However, this process has several drawbacks. It is, in fact, highly energy-intensive and requires the use of toxic and corrosive combustion gases.

[0011] Furthermore, its transformation into elements of value has also been studied (6).

[0012] The conversion of phosphogypsum is also carried out by carbonation, after dissolution of the phosphogypsum. Another study involves treating PG with 8 M sulfuric acid at a solid-liquid ratio of 1:4 at 80 °C before the production of ammonium sulfate (7). The results show that optimal conversion is obtained at this ratio with an amount of 3% ammonium sulfate, a stirring speed of 150 rpm for 4 h, and at 55 °C. Barium chloride is added to remove radium from the ammonium sulfate produced (7).

[0013] Another study was based on bubbling CO2 through a solution of ammonia NH3 in distilled water to produce ammonium carbonate (NH4)2CO3. The latter then reacts with phosphogypsum to produce ammonium sulfate. (NH4)2SO4, under a pressure of 1.2 MPa to CO2. A conversion of 97% is observed after 10 min (8).

[0014] Hannu-Petteri Mattila et al. used this same process for the production of an ammonium sulfate solution which is then concentrated by reverse osmosis (9). The conversion of PG to ammonium sulfate also produces calcium carbonate which can be used in various fields such as the remediation of acid mine drainage to control the acidity of waste (10) or in construction and cement manufacturing (11).

[0015] Several patents (12, 13, 14, 15) have described the preparation of an ABC extinguishing powder from ammonium sulfate obtained from a mixture of gaseous ammonia and water vapor, introduced into a reactor containing a saturated solution of ammonium sulfate and approximately 2 to 4% sulfuric acid at 60°C. Ammonium sulfate can also be obtained by spraying sulfuric acid into a chamber containing gaseous ammonia.

[0016] Nevertheless, there remains a need for the provision of a process for preparing an ABC extinguishing powder, which is economically attractive compared to existing processes and which gives pride of place to the valorization of industrial by-products, including phosphogypsum. BRIEF DESCRIPTION OF THE INVENTION

[0017] The present invention relates to a method for preparing an ABC extinguishing powder comprising the following steps:

[0018] 1) supply of phosphogypsum;

[0019] 2) preparation of ammonium sulfate from phosphogypsum;

[0020] 3) mixing the ammonium sulfate obtained in step 2) with at least phosphate monoammonium (MAP) to give an ABC extinguishing powder.

[0021] Other aspects of the invention are as described below and in the claims. FIGURES

[0022] [Fig.1] Fig.1 is a synoptic diagram of the process for manufacturing ammonium sulfate from phosphogypsum according to one embodiment.

[0023] [Fig.2] Fig.2 is a block diagram of the powder manufacturing process ABC extinguishing from ammonium sulfate obtained according to the process described in [Fig.1].

[0024] [Fig.3] Fig.3 represents an X-ray diffraction pattern of the phos phogypsum.

[0025] [Fig.4] Fig.4 shows the effect of different parameters on the conversion of SO42 a) concentration in (NH^COs, b) liquid-solid ratio, c) reaction time.

[0026] [Fig.5] Fig.5 shows the effect of temperature on the conversion rate of SO42 ions from PG.

[0027] Figures 6a and 6b represent the X-ray diffraction patterns of the synthesized products, i.e., ammonium sulfate and calcium carbonate. [Fig. 6a] a-Evaporated filtrate, [Fig. 6b] b-Precipitate at 55 °C, c. (NH4)2CO3=3.84M, reaction time=60 min and stirring speed 250 rpm.

[0028] Figures 7a and 7b show the Fourier transform infrared (FTIR) spectra of phosphogypsum and the evaporated filtrate. [Fig.7a] a- Phosphogypsum, [Fig.7b] b- Evaporated filtrate derived from the PG conversion by ammonium bicarbonate.

[0029] [Fig.8] Fig.8 shows images obtained by scanning electron microscopy of phosphogypsum (a, b) and calcium carbonate resulting from the attack of PG by ammonium bicarbonate (c, d). DETAILED DESCRIPTION OF THE INVENTION

[0030] The inventors have developed a process for preparing an ABC fire extinguishing powder from ammonium sulfate derived from phosphogypsum, meeting the stated requirements. The economically competitive process reduces industrial waste by using phosphogypsum, a by-product of the phosphate industry, to prepare the ammonium sulfate used in the composition of such ABC fire extinguishing powders. Advantageously, the process does not generate effluents harmful to the environment.

[0031] The process for preparing an ABC extinguishing powder according to the invention comprises the following steps:

[0032] 1) supply of phosphogypsum;

[0033] 2) preparation of ammonium sulfate from phosphogypsum;

[0034] 3) mixing the ammonium sulfate obtained in step 2) with at least phosphate monoammonium (MAP) to give an ABC extinguishing powder.

[0035] Preparation of ammonium sulfate from phosphogypsum (step 2)

[0036] The preparation of ammonium sulfate from phosphogypsum can be carried out in the following manner:

[0037] (a) washing of phosphogypsum;

[0038] (b) preparation and stirring of a mixture comprising phosphogypsum and a aqueous solution comprising ammonium (NH4+) and carbonate (CO32) ions;

[0039] (c) separation of the liquid phase and the solid phase of the mixture obtained in the step (b);

[0040] (d) evaporation of the liquid phase so as to collect the ammonium sulfate.

[0041] Phosphogypsum typically comes from industrial waste containing calcium sulfate. In preferred embodiments, phosphogypsum is obtained from processes preparation of phosphoric acid by the action of a strong acid on natural phosphate.

[0042] Phosphogypsum is typically washed with water. The phosphogypsum washing step removes soluble and floating impurities. Advantageously, the water is obtained from the ammonium sulfate preparation process (recycled at the end of the process following step d). The phosphogypsum is typically washed with water at a liquid / solid mass ratio of 2:1. The washing can be carried out by stirring a mixture of phosphogypsum and water, preferably at room temperature. The mixture is typically stirred for a period of 5 to 30 minutes, preferably for about 15 minutes.

[0043] Filtration is typically carried out to separate the wash water containing the impurities from the phosphogypsum.

[0044] Typically, after washing, the phosphogypsum is dried, ground, and sieved, preferably to obtain phosphogypsum with a particle size of less than 250 µm. Drying can be carried out by placing the phosphogypsum at a temperature ranging from 40 to 100°C, preferably at about 60°C, for a period of 2 to 20 hours, preferably about 12 hours.

[0045] A mixture comprising phosphogypsum and an aqueous solution comprising ammonium (NH4+) and carbonate (CO32+) ions is then prepared. Typically, the phosphogypsum is placed in a reactor and a solution containing the free forms CO32+ and NH4+ is added to the reactor.

[0046] The assembly is agitated, typically by mechanical agitation. The agitation is typically carried out at a speed ranging from 100 to 500 rpm, preferably at a speed of 200 rpm.

[0047] The mixture is typically stirred for a period of 2 to 300 min, preferably 5 to 200 min, or 10 to 100 min, or 20 to 80 min, or 30 to 70 min, or 40 to 70 min. Preferably, the mixture is stirred for approximately 60 min. An optimal conversion rate of sulfates from phosphogypsum is thus obtained after 60 minutes of reaction.

[0048] The mixture is typically stirred at a temperature ranging from 20 to 100°C or from 20 to 60°C. Preferably, the mixture is stirred at a temperature of at least 50°C or approximately 56°C. Above 56°C, the conversion rate tends to decrease due to the decomposition of bicarbonate into CO2 and NH3.

[0049] The aqueous solution comprising ammonium (NH4+) and carbonate (CO32) ions typically has a pH ranging from 11 to 12. Preferably, the pH of the solution is about 10.26.

[0050] In some embodiments, the NH4+ ions are derived from an ammonium salt, preferably ammonium carbonate, ammonium bicarbonate, chloride ammonium or ammonium nitrate or a mixture thereof.

[0051] In some embodiments, the concentration of ammonium salt in the aqueous solution ranges from 0.01 M to 1.5 M. Preferably, the ammonium salt is present in the aqueous solution at a concentration ranging from 0.4 to 1.3 M. In some embodiments, the concentration of ammonium salt in the aqueous solution is approximately 1.08 M. An optimal conversion rate of phosphogypsum sulfates is thus obtained for concentrations on the order of 1 M.

[0052] In some embodiments, the CO32 ions are derived from ammonium carbonate, ammonium bicarbonate or any other source of carbonate.

[0053] Preferably, the CO32 and NH4+ ions are derived from ammonium carbonate. Thus, in some embodiments, step (b) comprises the preparation and stirring of a mixture comprising phosphogypsum and an aqueous solution of ammonium carbonate. In some embodiments, the concentration of calcium carbonate in the mixture is from 0.01 M to 1.5 M, preferably from 0.4 M to 1.3 M. In other embodiments, the concentration of ammonium carbonate in the mixture is approximately 1.08 M.

[0054] Preferably, the stoichiometry (molar ratio) between the ammonium salt and the phosphogypsum in the mixture is from 1.1 to 1.3, preferably it is 1.2.

[0055] The liquid / solid mass ratio in the mixture, i.e. the mass ratio between the ammonium salt solution and the phosphogypsum, typically varies from 50:1 to 1:1, preferably from 30:1 to 1:1, or from 20:1 to 2:1 or from 10:1 to 1:1. Preferably, the ammonium salt is ammonium carbonate.

[0056] In embodiments, the liquid / solid mass ratio in the mixture, i.e. the mass ratio between the ammonium salt solution and the phosphogypsum, is 10:1.

[0057] In some embodiments, the liquid / solid mass ratio in the mixture, i.e. the mass ratio between the ammonium salt solution and the phosphogypsum, is 20:1.

[0058] The conversion of PG increases proportionally with the liquid / solid mass ratio, thanks to better solubilization of PG, which results in a higher conversion yield.

[0059] Agitation of the mixture comprising phosphogypsum and a solution comprising ammonium ions (NH4+) and carbonates (CO32) promotes contact between the chemical species and allows the conversion of calcium sulfate, the main component of phosphogypsum, into ammonium sulfate.

[0060] The conversion of calcium sulfate to ammonium sulfate begins with the dissolution of calcium and sulfate ions present in phosphogypsum in an aqueous medium. The sulfate ions thus combine with ammonium ions, supplied, for example, by carbonate ammonium, to form ammonium sulfate (NH4)2SO4 according to the following reaction (equation 1):

[0061] [Math.2] (HH^COs M +CaSp4.2HîO(S)--------- + CaCOH<: +COHs) + 3H3O (1)

[0062] After stirring, the liquid phase (also called the filtrate) and the solid phase are separated. The solid phase comprises calcium carbonate. The liquid phase comprises sodium sulfate. The separation is typically carried out by filtration.

[0063] The collected solid phase is typically rinsed with water and dried in an oven for 24 hours.

[0064] Advantageously, after filtration, the liquid phase, in other words the ammonium sulfate solution, has a solids content of less than 1% by weight, preferably less than or equal to 0.02% by weight.

[0065] The liquid phase is evaporated / dried so as to collect the ammonium sulfate formed in step (b). According to embodiments, the evaporation step is carried out at a temperature ranging from 100 to 400°C, preferably from 200 to 300°C, and even more preferably from 200 to 250°C.

[0066] This step makes it possible to obtain ammonium sulfate of high purity (on the order of 95 to 99% molar or mass).

[0067] The conversion rate of PG to ammonium sulfate is determined by the following equation:

[0068] [Math.3] • m(SO42 )PC is the mass of sulfate in the initial amount of PG. • m(SO / ) / is the mass of sulfate extracted in the filtrate, which is determined by the The gravimetric method described in the Indian Standard (17) is based on the precipitation of sulfates as BaSO4 using a BaCl2 solution. m(SO4 / ) / is calculated by the following equation:

[0069] [Math.4]

[0070] The water collected during the evaporation / drying step can be recycled upstream in the process to wash the phosphogypsum.

[0071] The collected ammonium sulfate is typically ground and sieved, preferably so as to obtain ammonium sulfate with a particle size less than 100 microns.

[0072] According to some embodiments, the preparation process is as shown in [Fig. 1]:

[0073] (El) washing of phosphogypsum;

[0074] (E2) filtration to separate the wash water containing the impurities from the phosphogypsum.

[0075] (E3) stirring of a mixture comprising phosphogypsum and an aqueous solution including ammonium ions (NH4+) and carbonates (CO32);

[0076] (E4) separation of the liquid phase and the solid phase of the mixture obtained in the step E3;

[0077] (E5) evaporation of the liquid phase so as to collect the ammonium sulfate.

[0078] Preparation of ABC extinguishing powder from ammonium sulfate obtained in step 2

[0079] ABC extinguishing powder is prepared by mixing the ammonium sulfate obtained in step 2) with at least monoammonium phosphate (MAP).

[0080] MAP can be derived from industrial waste or be a by-product of the phosphoric acid preparation process when the latter is formed by the action of a strong acid on natural phosphate.

[0081] The MAP useful for the preparation of ABC extinguishing powder is preferably ground and sieved, preferably the MAP has a particle size of less than 100 pm.

[0082] The mixing is typically carried out in a double-shaft, paddle mixer in order to obtain a homogeneous mixture of the different components of the ABC extinguishing powder.

[0083] The mixing is typically carried out at a speed of 2 to 20 rpm, preferably 5 to 10 rpm. The mixing time is 5 to 30 min, preferably 5 to 10 min.

[0084] ABC extinguishing powder can be prepared by mixing the ammonium sulfate obtained in step 2) with monoammonium phosphate (MAP) and conventional additives, such as a fluidizer, an anti-caking agent, a dye, a tracer, or mixtures thereof. Thus, various additives can be added to the mixer, such as a fluidizer, an anti-caking agent, as well as dyes and tracers and mixtures thereof.

[0085] Advantageously, the addition of a fluidizer increases the contact of the ammonium sulfate / MAP mixture and facilitates drying.

[0086] The fluidizer is preferably silicon dioxide.

[0087] The anti-caking agent may be aluminum silicate (Mica), silicate of calcium or hydrated magnesium silicate.

[0088] The addition of colorants and tracers gives the powder an identifiable color. Preferably, the colorant is an organic colorant.

[0089] Typically, the powder comprises, in relation to the total weight of the composition:

[0090] a) from 10 to 90%, preferably from 75 to 85%, by weight of MAP;

[0091] b) from 10 to 90%, preferably from 15 to 85% or from 15 to 25%, by weight of sulfate ammonium (derived from PG);

[0092] c) 3 to 10%, preferably 4 to 5%, by weight of conventional adjuvants.

[0093] At the end of the mixing step, the resulting mixture, generally in the form of powder, is typically dried, ground and sifted.

[0094] Advantageously, a water-repellent agent can be added to the resulting mixture. Thus, the preparation of ABC extinguishing powder generally includes a step of adding a water-repellent agent to the resulting mixture. Preferably, the water-repellent agent is a hydrophobic grease prepared by combining a silicone oil with a thickener.

[0095] Advantageously, the addition of a water-repellent agent makes it possible to obtain a stable, homogeneous and conforming ABC extinguishing powder.

[0096] The powder obtained is generally stored in dry premises, preferably at a temperature slightly higher than that of the places where it is likely to be used and preferably protected from light.

[0097] In embodiments, the ABC extinguishing powder comprises, relative to the total weight of the composition:

[0098] a) from 10 to 90% by weight of MAP;

[0099] b) 10 to 90% by weight of ammonium sulfate derived from PG;

[0100] c) 3 to 5% by weight of muscovite mica (potassium aluminium silicate; anti-caking agent);

[0101] d) 3 to 5% by weight of fuller's earth (magnesium aluminium silicate; fluidizing agent).

[0102] According to some embodiments, the process for preparing ABC extinguishing powder is as shown in [Fig. 2]. EXAMPLES

[0103] Example 1: Optimization of the conditions for preparing ammonium sulfate from phosphogypsum

[0104] The composition of phosphogypsum depends on several parameters: the source and nature of the phosphate rock, the transformation process which influences the morphology, solubility, level of purity as well as the conversion of phosphogypsum.

[0105] The PG is washed with distilled water at a liquid-to-solid ratio of 2. The mixer is stirred for 15 min at room temperature to remove water-soluble impurities. The phosphogypsum is then dried overnight at 60°C, at constant mass. The X-ray diffraction pattern of the phosphogypsum is shown in the [Fig.3].

[0106] The optimal parameters for the carbonation of phosphogypsum by ammonium carbonate were determined by a series of discontinuous reactions. Effect of ammonium carbonate concentration

[0107] Figure 4 presents the results obtained. Different concentrations of ammonium carbonate (0.48, 0.72, 0.97, 1.08, 1.15, and 1.2 M) were studied, and their effects on the conversion rate of calcium sulfate (CaSO4·2H2O) to ammonium sulfate (NH4)2SO4 were evaluated. The liquid / solid ratio was 10, and the residence time (reaction time) was 60 min. Figure 4(a) shows that increasing the ammonium carbonate concentration from 0.48 M to 0.72 M resulted in conversion rates of 34% and 52%, reaching an optimum of 95.3% at a concentration of 1.08 M at room temperature.

[0108] When the concentration of (NH4)2CO3 is 1.15 M, the leaching of sulfates is complete, resulting in supersaturation of the solution. The excess of carbonate ions in the filtrate affects the purity of the final product.

[0109] Effect of the liquid / solid ratio between (NH₄CO₃) and phosphogypsum

[0110] The influence of varying the liquid-to-solid ratio (L / S) (4, 5, 6.66, 10, and 20) between PG and ammonium carbonate solution (1.08 M) on the conversion yield is shown in [Fig. 4] b). The residence time (reaction time) was set at 60 min. The results show that the conversion of PG increases proportionally with the L / S ratio, due to improved solubilization of PG, resulting in a higher conversion yield. The reaction yield is generally limited by the diffusion of Ca2+ and SO42 ions in the solution, according to the kinetic study carried out by V. Danielik et al. (16). Effect of reaction time

[0111] Figure 4(c) shows the effect of reaction time (10, 30, 60, 120, and 180 min) on the SO42 extraction rate. After 60 min of reaction, the sulfate conversion rate reaches 96%. No significant improvement is observed when the reaction time is increased to 120 and 180 min, meaning that the reaction time is sufficient to complete the leaching reaction. Effect of temperature

[0112] In order to further increase the conversion of PG, the effect of temperature was also investigated. The results presented in [Fig. 5] show that the conversion of PG to ammonium sulfate increases progressively with rising temperature, reaching an optimal value of 92% at 56°C. As the temperature continues to rise, the conversion rate decreases due to the decomposition of bicarbonate into CO2 and NH3 at these elevated temperatures.

[0113] Characterization of the components of the evaporated filtrate and the precipitate by X-ray diffraction

[0114] X-ray diffraction (XRD) analysis of the PG and the synthesized products (ammonium sulfate, calcium carbonate) shows the characteristics of the different samples. The phases were identified by comparing them to the diffraction profiles referenced in the standard COD data (CaSO4.2H2O: 96-901-3165, (NH4)2SO4: 96-900-9883). The main crystalline phases of PG observed are CaSO4.2H2O ([Fig. 3]) with traces of quartz appearing at 26.6°C in the precipitate, which was identified as CaCO3 ([Fig. 6b]).

[0115] [Math.5] (aq) + ^-$3 (aq) CaCO3^py

[0116] Characterization of the components of the evaporated filtrate by infrared

[0117] Figure 7b shows the FTIR analysis spectra of PG with the presence of a strong sulfur-oxygen (OSO) stretching vibration at 1090 cm⁻¹ and a bending vibration giving rise to two bands at 668–602 cm⁻¹. The band group at 3545–3248 cm⁻¹ and the bands at 1686–1621 cm⁻¹ belong to the OH stretching and bending of water molecules adsorbed and crystallized in PG. Furthermore, the conversion to ammonium sulfate is characterized by the appearance of new vibrations at 2983 cm⁻¹ and 1606 cm⁻¹. These vibrations correspond respectively to the v(NH₄) stretching band and the ô(NH₄) deformation band. In addition, the X-ray diffraction results are in agreement with those of infrared spectroscopy.

[0118] [Tables2] Vibration Mode Frequency (cm1) PG Ammonium sulfate Stretching vibrations °OH of water 3545-3248 3493-3331 Stretching vibrations °NH of ammonium - 2983 Stretching vibrations °0-S-0 of SO42 2240-2115 2360-2337 Bending vibrations of water 1686-1621 - Bending vibrations °NH of ammonium - 1606 Stretching vibrations °0-S-0 of SO42 1143-1113 1169 Bending vibrations SO42 668-602 614

[0119] Table 2: Attribution of infrared vibrations of crude PG and leaching filtrates

[0120] The images shown in [Fig. 8] illustrate the morphological structure of PG and the prepared samples. As can be seen in [Fig. 7a], the particles have a hexagonal crystalline structure. This morphology depends primarily on the composition of the phosphogypsum (impurities, syncystalized PO42 ions) and the state of crystallization (nature of the rock, etching process, etc.). Furthermore, the size of these crystals ranges from 10 to 150 pm. Comparing the SEM images of PG with those of precipitated calcium carbonate reveals a change in morphology. The SEM images show that the CaCO3 particles are organized and agglomerated into thin scales. The average diameter of the scales is 1–5 pm. It should be noted that the impurities and elements contained in the phosphogypsum can significantly alter the morphology and structure of the precipitated particles.The removal of P2O5 by washing produces a precipitate with an increase in particle size, thus facilitating the filtration process.

[0121] Table 3 summarizes the elemental analysis, by inductively coupled plasma atomic emission spectroscopy (ICP-AES), for the three compounds. The major elements were determined by chemical titration and gravimetric methods. The results show a high purity of the product (NH4)2SO4 during the aqueous carbonation process.

[0122] [Table 3] Carbonation by (NH4)2CO3 Element Unit PG (NH4)2SO4 CaCO3 SO3 % 44.71 60.7 12 CaO % 32.95 0.0011 46.26 F % 0.94 0.07 1.05 P2O5 % 3.48 0.9 1.32 SiO2 % 0.99 - 0.62 Al2O3 % 0.12 <0.0005 0.1933 Fe2O3 % 0.011 <0.0005 0.0118 K2O % 0.008 0.0003 0.0196 MgO % 0.031 0.0003 0.0194 Na2O % 0.024 0.0017 0.7446 Cd ppm 3 0.0015 2.992 V ppm 16 <0.0010 9.205 Cr PPm 9.3 0.0091 11.6

[0123] Table 3. Main elements present in the PG and conversion products

[0124] Example 2: Preparation of ammonium sulfate from phosphogypsum

[0125] Ammonium sulfate was prepared according to the process described in [Fig.1].

[0126] The phosphogypsum used comes from the phosphoric acid production units of Jorf Lasfar.

[0127] The latter is washed with water with a liquid / solid ratio of 2 then dried overnight at 60°C, ground and sieved to less than 250 pm.

[0128] An ammonium carbonate solution is prepared in a reactor and vigorously stirred. Washed phosphogypsum is added to the reactor and the mixture is stirred at 200 rpm for 90 min.

[0129] The liquid phase is separated from the solid phase by filtration. A precipitate containing mainly calcium carbonate is obtained.

[0130] A washing of the residues (RI) with water followed by drying in an oven for 24 hours is carried out.

[0131] The filtrate is evaporated to collect ammonium sulfate. The latter is ground and sieved to less than 100 microns. The yield varies from 92 to 95%.

[0132] This process makes it possible to produce ammonium sulfate from 1.54 t of PG, It and 1.07 kg of calcium carbonate. The use of PG in this process allows for a massive reduction of phosphate by-product, thus offering an environmental and economic advantage.

[0133] Example 3: Manufacture of ABC 80 extinguishing powder from PG

[0134] In a double shaft paddle mixer, 80% by weight of ammonium phosphate (MAP) and 20% by weight of ammonium sulfate prepared according to example 2 are added.

[0135] 3-5% by weight % of muscovite mica and 3-5% by weight of fuller's earth relative to the Weights of MAP and ammonium sulfate are added. Table 4 presents the characterization of the resulting ABC extinguishing powder.

[0136] [Tables4] Characteristics Apparent Density (g / ml) Particle Size Analysis (%) Moisture Content (%) Hygroscopicity Resistance to Agglutination Thermal Stability (°C) >125 pm >63 pm >40 pm ABC Powder 80 / 20 0.85-0.98 0-5 15-2 5 15-2 5 <0.25 Positive Positive -60 to 90

[0137] Table 4: Characteristics of the ABC extinguishing powder obtained by mixing 80% MAP and 20% ammonium sulfate

[0138] The ABC powder obtained is dried at a temperature of 110°C for 2 hours and 30 minutes, then sieved through a vibrating sieve. 2% by mass of silicone oil was then added to reduce the wettability of the particles.

[0139] Particle size analysis is carried out by sieving.

[0140] The ABC powder's behavior was tested in real-world conditions on fires of different classes (A, B, and C). The fires were successfully extinguished. Furthermore, it was verified that the fire did not reignite within twenty minutes of extinguishment.

[0141] Example 4: Manufacture of ABC 70 extinguishing powder from PG

[0142] ABC 70 powder is prepared according to Example 3, except that the MAP and ammonium sulfate contents are modified to 30% by weight of ammonium sulfate and 70% by weight of ammonium phosphate. Table 5 presents the characterization of the resulting ABC powder.

[0143] [Tables5] Characteristics Apparent Density (g / ml) Granulometry Analysis (%) Moisture Content (%) Hygroscopicity Resistance to Agglutination Thermal Stability (°C) >125 pm >63 pm >40 pm ABC Powder 70 / 30 0.85-0.98 0-5 15-2 5 15-2 5 <0.25 Positive Positive -60 to 90

[0144] Table 5: Characteristics of ABC extinguishing powder obtained by mixing 70% MAP and 30% ammonium sulfate

[0145] This powder, tested in real-life situations, enabled effective extinguishing of fires of different classes (A, B and C). REFERENCES

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Claims

Claims

1. A method for preparing an ABC extinguishing powder comprising the following steps: 1) providing phosphogypsum; 2) preparing ammonium sulfate from the phosphogypsum; 3) mixing the ammonium sulfate obtained in step 2) with at least monoammonium phosphate (MAP) to give an ABC extinguishing powder.

2. A method according to claim 1 wherein the preparation of ammonium sulfate from phosphogypsum comprises the following steps: (a) washing the phosphogypsum; (b) preparing and stirring a mixture comprising the phosphogypsum and an aqueous solution comprising ammonium (NH4+) and carbonate (CO32) ions; (c) separating the liquid phase and the solid phase of the mixture obtained in step (b); (d) evaporating the liquid phase so as to collect the ammonium sulfate.

3. A method according to claim 2 wherein the ammonium ions are derived from an ammonium salt, preferably ammonium carbonate, ammonium bicarbonate, ammonium chloride or ammonium nitrate.

4. A method according to claim 3 wherein the concentration of ammonium salt in the aqueous solution is 0.01 to 1.5 M, preferably 0.4 to 1.3 M.

5. Method according to one of claims 2 to 4 in which the aqueous solution comprising ammonium (NH4+) and carbonate (CO32) ions is an aqueous solution of ammonium carbonate.

6. Method according to one of claims 3 to 5 in which the molar ratio between the ammonium salt and the phosphogypsum varies from 1.1 to 1.3, preferably is 1.

2.

7. Method according to one of claims 2 to 6 in which the mixture in step (b) is stirred for a period ranging from 2 to 300 min, preferably for approximately 60 minutes.

8. A method according to any one of claims 2 to 7 wherein the mixture in step (b) is stirred at a temperature ranging from 20 to 100°C, preferably at a temperature of approximately 56°C.

9.

10.

11.

12.

13. Method according to one of claims 2 to 8 in which step (c) is carried out by filtration. Method according to one of claims 2 to 9 in which step (d) is carried out at a temperature ranging from 200 to 250°C. Method according to one of claims 2 to 8 in which the mixture of ammonium sulfate and mono-ammonium phosphate further comprises conventional adjuvants. The method of claim 11 wherein the conventional adjuvants are a fluidizer, an anti-caking agent, a colorant, a tracer or mixtures thereof. Method according to claim 11 or 12 in which the ABC extinguishing powder comprises, relative to the total weight of the composition: a) from 10 to 90%, preferably from 75 to 85%, by weight of mono-ammonium phosphate; b) from 10 to 90%, preferably from 15 to 85%, by weight of ammonium sulfate; c) from 3 to 10%, preferably from 4 to 5%, by weight of conventional adjuvants.

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