Patent ID: 12221342

EXAMPLE 1

Preparation and Characterization of a Phosphate Rock Pulp

From a phosphate rock pulp, which is an aqueous suspension comprising water and particles of phosphate material, the characteristics of this suspension are determined. The phosphate material comes from three deposits near Khouribga (Morocco). The pulp is prepared by mixing water and crushed and ground phosphate rock, and optionally the anionic polymer according to the invention.

If necessary, the pulp can be concentrated by centrifugation or diluted by adding water. Particle size of phosphate material:

The particle size distribution of phosphate rock pulp is measured using a Malvern Mastersizer 2000 laser diffraction granulometer. The results are shown in Table 2.

TABLE 2median particle sizesize (μm)d1013.33d50130.65d90280.67
Pulp Density:

The density is determined at 25° C. using a pycnometer of size 1,501/100 (Sheen S230729) with a volume of 100 cm3. The clean pycnometer is weighed empty. The homogenized phosphate rock pulp is introduced into the pycnometer; the air present is purged and the pycnometer is closed. The full pycnometer is weighed. The mass of the empty pycnometer is subtracted from the mass of the full pycnometer, the value of this difference is multiplied by 10 and the density of the phosphate rock pulp is obtained. The results are shown in Table 3.

TABLE 3solids content(% by weight)densitypolymer-free pulp511.538polymer-free pulp581.709pulp with polymer (P3) 0.3% by weight701.905

The use of a polymer according to the invention significantly increases the phosphate rock solids content and the density of the pulp while allowing easy handling of this concentrated pulp.

Viscosity of the Pulp:

300 g of phosphate rock pulp are introduced into a 250 mL beaker at 25° C. under mechanical stirring (600 rpm—for 2 min). If necessary, the polymer according to the invention is added in the dry/dry amounts of dry polymer relative to the amount of dry phosphate rock shown in Table 3. Stirring is stopped and, after 90 s, the viscosity is measured at 25° C. by means of a Brookfield viscometer equipped with a type S63 spindle at a rotation speed of 100 rpm. The results are shown in Table 4.

TABLE 4solids contentviscosity(% by weight)(mPa · s)polymer-free pulp70not measurablepulp with polymer (P1) 0.2% by weight>70230pulp with polymer (P3) 0.3% by weight>70260

Whereas polymer-free pulp does not allow viscosity to be measured, the pulp comprising polymer according to the invention has a controlled viscosity which makes it easily handled and transportable, in particular by gravity.

Pulp Stability—Phase Shift Measurement:

200 mL of phosphate rock pulp are introduced into a 250 mL beaker at 25° C. under mechanical stirring (2,050 rpm—for 2 min). If necessary, the polymer according to the invention is added in the dry/dry amounts relative to the amount of dried phosphate rock shown in Table 4. Then, 100 mL of pulp are poured into a graduated test tube and the volumes of the different phases that form are recorded over time. During sedimentation, two phases may appear. Phase 1, which is water and does not include particles of phosphate material due to the occurrence of a pulp separation phenomenon. Phase 2, which includes water and particles of phosphate material. The measured phase 1 volumes (mL) are shown in Table 5. This is a measure of the phase shift over time related to the sedimentation rate.

TABLE 560% pulp with polymer (P1)time (h)50% polymer-free pulp0.15% by weight10.5021031.5019852496

It can be seen that the presence of the polymer according to the invention makes it possible to obtain a suspension which is more concentrated in particles of phosphate material and which is more stable. In fact, the amount of phase-shifted pulp is nil or very much reduced in comparison with pulp containing no polymer.

Pulp Stability—Determination of Dilatancy:

The dilatancy of the phosphate rock pulp is measured with a Haake Rheostress 600 rheometer equipped with a CC20Ti cylindrical spindle. The dilatancy at 30° C. of a pulp sample (16 mL) is determined by measuring the viscosity regularly by increasing the speed of the spindle from 0 to 1,500 rpm (0 to 660 s−1) in 120 s. The results obtained are shown in Table 6. Such a viscosity measured at varying shear rates makes it possible to evaluate the dilatancy of the pulp. Thus, if the viscosity increases as an increasing shear rate is applied, the slurry expands.

TABLE 6pulp (solidsviscosity (mPa · s)content-% by weight)at 2 s−1at 600 s−1polymer-free pulp (>70)not measurablenot measurablepulp with polymer (P3)7,290960.1% by weight (60)

Once again, while the pulp without polymer does not allow viscosity measurement, the pulp comprising polymer according to the invention has a controlled viscosity which makes it easily handled and transportable, in particular by gravity. Moreover, it can be seen that its viscosity does not increase with increasing shear rate; the suspension according to the invention is not dilatant.

EXAMPLE 2

Preparation of Phosphoric Acid and Characterization of its Quality

The phosphate material particles of an aqueous suspension according to Example 1 are treated in a manner known as such with sulfuric acid. A slurry is obtained which is filtered to separate the phosphogypsum and to obtain an aqueous solution of phosphoric acid. A solution of strong phosphoric acid is obtained. If necessary, it can be concentrated by evaporation of water under suction. Washing the phosphogypsum with an aqueous solution of phosphoric acid or with water or sulfate-rich water can produce medium or weak phosphoric acid solutions.

A similar procedure is used for different suspensions prepared according to Example 1. The quality of phosphoric acid is characterized by different parameters. The filtration time provides information on the shape of the phosphogypsum crystals present in the phosphate material. The filtration time also provides information on the quality of the phosphoric acid produced. The density indicates the titer of the phosphoric acid produced and must be above 1.266 at 25° C. to reach a generally acceptable quality.

The amount of free sulfate present in the acid (g/L) is estimated from the level of residual sulfuric acid that did not react during the treatment of the phosphate material particles in the suspension. A high level means a low phosphoric acid titer and a high phosphogypsum filtration time. Preferably, the aqueous phosphoric acid solution contains residual sulfate ions in a weight concentration of 20 to 35 g/L. More preferably, the aqueous phosphoric acid solution comprises residual sulfate ions in a weight concentration ranging from 22 to 26 g/L. The filterability of the phosphate material suspension (tons P2O5/m2/day) enables the production capacity of strong phosphoric acid to be evaluated. The filterability of phosphogypsum is linked to its crystallinity. Particular shapes of phosphogypsum crystals can lead to piling up which degrades the efficiency of filtration or to filter clogging. Filterability should range from 5 to 7, preferably from 6 to 7, on a scale of 1 to 7. Filterability F is calculated according to the formula:

F=A(1-B1⁢0⁢0)*t⁢1+t⁢2+t⁢3

whereA=17.80 measuring technique specific constant,B=moisture content of the phosphogypsum (% by weight),t1=filtration time of strong phosphoric acid (s),t2=average phosphoric acid filtration time (s),t3=filtration time of weak phosphoric acid (s).

The results obtained are shown in Table 7.

TABLE 7pulp (solids content-% by weight)filterabilitypolymer-free pulp (60)5pulp with polymer (P1) 0.2% by weight (>70)7pulp with polymer (P3) 0.3% by weight (>70)6

The presence of polymer according to the invention in the aqueous suspension of particles of phosphate material makes it possible to obtain a filterability maintained or even improved while making it possible to increase the solids content. The efficiency of the method for producing strong phosphoric acid is improved.

Density of the Strong Acid:

After acid treatment and filtration of the phosphate material suspension, the density of the strong phosphoric acid is measured with a densimeter, graduated from 1,200 to 1,300 or from 1,300 to 1,400, and at a temperature of 25° C. The results obtained are shown in Table 8. Quality of the phosphoric acid produced: density and titer of the strong acid

After acid treatment and filtration of the phosphate material suspension, the density of the strong phosphoric acid is measured with a densimeter, graduated from 1,200 to 1,300 or from 1,300 to 1,400, and at a temperature of 25° C. The titration of the phosphoric acid solution is carried out in a manner known per se. The results obtained are shown in Table 8.

TABLE 8pulp (solids content-% by weight)densityfilterabilityP2O5titerpolymer-free pulp (60)1.2745.425.33pulp with polymer (P3) 0.3%1.2976.128.30by weight (>70)

The presence of polymer according to the invention in the aqueous suspension of particles of phosphate material makes it possible to prepare a highly concentrated pulp with very improved properties. The P2O5titer is improved. Similarly, the acid density is improved.

When phosphoric acid is prepared by treating the aqueous suspension of phosphate material particles with sulfuric acid, the phosphogypsum (calcium sulfate) crystals must have controlled dimensions to improve their separation by filtration. The sizes and dimensions of the crystals of different filtration retentate are determined using an optical microscope (Olympus SZX-ILLD200, DF PLFL 1.6* PF objective) producing images processed with Imagej software. Different crystal forms are present: acicular (A), tabular (B) or compact crystals or polycrystalline aggregates (C). For these crystals of different shapes, several size ranges are present. Among these crystals are oblong crystals of about 250 μm or 220-350 μm in size (Q1), semi-oblong crystals of about 150 μm or 125-160 μm in size (Q2) and more compact or star-shaped crystals of about 50 μm or 40-85 μm in size (Q3). Type (Q3) crystals provide the best filterability results.

The relative amounts of type (Q3) crystals are increased and the filterability of phosphogypsum crystals is improved.

Evaluation of Losses of Phosphoric Acid Produced:

In the preparation of phosphoric acid expressed in P2O5equivalent, the overall chemical yield of the phosphoric acid preparation may be reduced due to acid losses. Generally, the method of acid preparation leads to losses of acid in different forms. These losses can be identified and measured. Part (A) of the product losses corresponds to the phosphoric acid present in the phosphate rock which is not attacked during acid treatment. Part (B) of the phosphoric acid product losses is related to the acid trapped in syncrystallized form within the phosphogypsum crystals. Part (C) of the phosphoric acid product losses results from the presence of acid in solution in the wash waters. The results are shown in Table 9.

TABLE 9pulp (solids content-P2O5losses (% by weight)P2O5yield (%% by weight)ABCby weight)polymer-free pulp (60)0.120.810.8292polymer-free pulp (>70)0.120.670.6794.3pulp with polymer (P3)0.080.680.2595.30.3% by weight (>70)

In addition to a strong improvement in the overall efficiency of the phosphoric acid preparation reaction, the use of a polymer according to the invention in the aqueous suspension of particles of phosphate material reduces the various losses of phosphoric acid. In particular, the acid losses resulting from the unattacked phosphate material during acid treatment are greatly reduced.

The conditioning method according to the invention therefore confers special properties on the particles of phosphate material as well as on the mixture of particles of phosphate material and polymer according to the invention.