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Huzhamberdiev Sherzod Musurmonovich, Arifdzhanova Kamola Saifullaevna, Mirzakulov Holtura Chorievich, Tashkent Institute of Chemical Technology E-mail: [email protected]
SODIUM TRIPOLYPHOSPHATE FROM EXTRACTION PHOSPHORIC ACID ON THE BASIS OF PHOSPHORITE OF CENTRAL KYZYLKUM
Abstract. The article presents the results of obtaining sodium tripolyphosphate from the extraction phosphoric acid based on phosphorites of Central Kyzylkum.
Research processes of clearing extraction phosphoric acid and obtaining pure solutions of a mixture mono- and disodiumphosphates, their deep clearing from magnesium salts by gaseous ammonia and influence of duration of process dehydration and calcination temperature on a chemical compound sodium tripolyphosphate.
The optimal technological parameters of the dehydration process were established - temperatures of450-500 °C and a process duration of 2 hours. Thus sodium tripolyphosphate on a basis extraction phosphoric acid from phosphorites Central Kyzylkum contains not less than 57,00% P205.
Keywords: extraction phosphoric acid, desulfurination, defluorination, barium carbonates, sodium, ammonia, evaporation, filtration, drying, calcining
Introduction
The condensed phosphates of alkali metals are widely used in various industries, such as food, cosmetic, pharmaceutical, chemical, construction and etc. [1].
Depending on the application conditions and requirements for the properties, separate polyphosphates and mixtures of variable composition are used. Among alkali metal polyphosphates are the most commonly used sodium polyphosphates, which have significant restructuring properties and rather high solubility in water [2; 3].
Sodium polyphosphates are actively used for preliminary water treating and anticorrosive protection of pipelines of turnaround water supply. Sodium tripolyphosphate is one of the basic making synthetic washing-up liquids. For manufacture of sodium polyphosphate it is necessary phosphoric acid. The republic Uzbekistan has no high-quality phosphatic raw materials, suitable for reception of thermal phosphoric acid. Obtained of phosphorites Central Kyzylkum extraction phosphoric acid (EPA) is strongly polluted by various impurity [4]. The organisation of manufacture of sodium polyphosphate on the basis of EPA from phosphorites Central Kyzylkum is an actual problem of a chemical science and production workers.
Objects and methods. As a source of EPA used acid of manufacture ofJSC "Ammofos-Maxam", which are obtained in the dehydrate mode of washed burnt phosconcentrate Central Kyzylkum compound (mass.%): P2O5-18.31; SO3-2.32; Ca0-0.31; Mg0-0.68; Al203-0.77; Fe203-0.68; F-1.25.
Preliminary clearing of acid of fluorine and sulphates spent washed burnt $0CK0H^HTpaT0M, a carbonate and sodium metasilicate at their mass ratio 1.4:1. At the first stage at
introduction of metasilicate of sodium and a sodium carbonate in EPA reactions proceed:
H2SiF6 + Na2C03 * Na2SiF6 + C02 + H20 6HF + Na SiO * Na SiF + HO
2 3 2 6 2
Introduction of sodium metasilicate is necessary for fluorine linkage in sodium hexafluorosilicate, since EPA from phosphorites Central Kyzylkum contains no more than 0,15% of soluble silicates. Introduction of metasilicate of sodium allows to raise degree of sedimentation of fluorine from 38-40% to 80-85% [5; 6].
Washed burnt phosconcentrate contains to 57% оксида calcium from which 15-17% is in the form of Ca O. The introduction of washed burnt phosconcentrate promotes decrease in the maintenance of sulphates as a result of reaction course [7; 8].
H2S04 + CaO + H20 * CaS04 ■ 2H20
The cleared acid contains (mass.%): P205-16.98; S03--0.74; Ca0-2.09; Mg0-0.64; Al203-0.73; Fe203-0.65; F-0.34.
Analysis of the acid, intermediate and final products was performed using known methods of chemical analysis [9-11].
Results and discussion. The second stage clearing EPA Central Kyzylkum consists in neutralisation of the defluori-nated and desulphated acids with soda ash, as a result of which a number of chemical processes take place, described by the following equations:
2Н3РО4 + Na2C03 = 2NaH2P04 + C02 + H20 2Са(Н2РО4)2 + Na2C03 = 2CaHP04 j + 2NaH2P04 + C02 +
+ h2o
Fe, Al(H2P04)3 + Na2C03 = Fe, Al(P04)| + 2NaH2P04 + + C02 + H20
At increasing quantities of an entered carbonate of the sodium, the formed salt sodium dihydrophosphate, transmuted in sodium hydrophosphate on reaction: NaH2PO4 + Na2CO3 ■ Na2HPO4 + NaH2PO4 + CO2 + H2O Regulating the ratio Na2O : P2O5 it is possible to achieve the necessary maintenance mono- and disodiumphosphate in a solution. However, the obtained mixture of sodium orthophosphate contains 0,50-0,64% of magnesium oxide, which in final total reduces quality of sodium polyphosphate.
To reduce the content of magnesium oxide in neutralized with sodium ash EPA to pH = 6.1-6.5, gaseous ammonia was introduced in a molar ratio (NH3: MgO) of 1:1, 1.5:1 and 2:1. An increase in pH to 7.5-8.1 leads to the precipitation of magnesium in the form of crystallohydrates MgNH4PO4 x x6H2O and, accordingly, to a decrease in the content of magnesium oxide.
MgO + NH3 + H3P04 + 5H2O = MgNH4PO4 x 6H2O j In (table 1) results of influence of the molar ratio NH3 : MgO on the degree of magnesium deposition.
Table 1.- Influence of process ammoniation on a chemical compound of solutions of sodium phosphate
№ NH3/MgO pH Na,O P,05 SO3 CaO MgO AIP, Fe,0, F Nf„f
1. - 6.2 9.93 14.60 0.0009 0.0031 0.51 0.0024 0.0021 0.0020
2. 1.0 7.5 9.93 13.60 0.0010 0.0028 0.0035 0.0018 0.0016 0.0015 0.084
3. 1.5 7.8 9.89 13.54 0.0010 0.0022 0.0023 0.0016 0.0014 0.0012 0.111
4. 2.0 8.1 9.87 13.52 0.0010 0.0021 0.0022 0.0015 0.0013 0.0011 0.122
The table shows, that ammonia introduction in neutralised to pH = 6.2-6.5 a carbonate of sodium EPA sharply reduces the maintenance of magnesium oxide in a solution from 0.51% to 0.0035-0.0022% depending on the ratio NH3: MgO or pH 7.5-8.1. The content P205 in a solution
Table 2.- Influence of temperature on the filtration
makes 13.52-13.60%, Na2O 9.87-9.93%. The content of other impurity changes slightly.
In (table 2) shows the data on the influences of temperature on filtration speed of the ammoniated sodium phosphate solutions.
speed of neutralised and ammoniated solutions
№ Temperature, °C Filtration speed, kg/m2-h
on a pulp on a deposit on a filtrate
1. 20 6948 834 6114
2. 40 8900 1068 7832
3. 60 10080 1210 8870
4. 80 10685 1282 9403
An raising in the filtration temperature from 20 °C to 80 °C contributes to an increase in the filtration speed of the pulp from 6948 kg/m2 • h to 10685 kg/m2 • h. Accordingly, the filtration speed on a deposit make 834-1282 kg/m2 • h and on a filtrate 6114-9403 kg/m2 • h. The formed deposit magnesiumammoniumphosphate is filtered very well.
Table 3.- Influence of degree neutralization extraction phosphoric acid a sodium ash and ammonia on the rheological properties of the cleared solutions
In (table 3) shows values of density and viscosity of the ammoniated solutions after branch magnesiumammoniumphosphate in dependence on temperature for pH 7.5, 7.8 and 8.1.
pH Density, g/cm3 Viscosity, mPa • s
20 °C 40 °C 60 °C 80 °C 100 °C 20 °C 40 °C 60 °C 80 °C 100 °C
7.5 1.256 1.247 1.239 1.231 1.224 5.89 3.79 2.63 2.02 1.80
7.8 1.258 1.249 1.241 1.233 1.226 5.95 3.86 2.69 2.08 1.85
8.1 1.261 1.252 1.244 1.236 1.229 6.01 3.92 2.74 2.12 1.89
Density of solutions with increase pH with 7.5 to 8.1 raise and make 1.256-1.261 g/sm3 at 20 °C and 1.231-1.236 at 80 °C.
Viscosity of solutions with increase pH also raise and make 5.89-6.01 MPa-s at 20 °C and decrease to
2.02-2.12 MPa • s at 80 °C. The cleared solutions of sodium phosphate have good rheological properties.
For obtain sodium tripolyphosphate defluorinated and desulphated EPA have neutralized with sodium ash to pH 6.2,
parity Na2O : P2O5 = 0.73, ammoniated to pH 8.1, filtered, Influence of the process duration on the change in the
evaporated to a wet state, dried at temperature 100-105 °C chemical compound dehydrated sodium phosphates studied and calcinated. at 400 °C (tab. 4).
Table 4.- Influence of duration of process dehydration at temperature 400oC on a chemical compound of sodium phosphate, obtained at pH = 6.2 and Na2O : P2O5 = 0.73
№ T, min Chemical compound, mass.%
Na2O P2O5 SO3 CaO MgO AW F*2°3 F N total.
1. 30 40.43 55.38 0.0041 0.0084 0.0087 0.0062 0.0056 0.0014 0.0751
2. 60 40.78 55.86 0.0045 0.0088 0.0091 0.0069 0.0063 0.0016 0.0556
3. 90 41.02 56.19 0.0048 0.0091 0.0094 0.0075 0.0069 0.0018 0.0433
4. 120 41.18 56.41 0.0050 0.0093 0.0096 0.0080 0.0073 0.0019 0.0358
5. 150 41.20 56.43 0.0051 0.0094 0.0097 0.0082 0.0075 0.0019 0.0394
With increase in the duration calcination raises the con- the content Na2O under these conditions raises from 40.43% tent of all components. The P2O5 content with a calcination to 41.18%. Other components raise on 0.001-0.002%. The time of 30 minutes is 55.38%, after 120 minutes it is 56.41%, nitrogen content decreases from 0.0751% to 0.0394%.
Table 5.- Influence of temperature on a chemical compound of sodium polyphosphate at process duration 2 hours
№ T, oc Chemical compound, mass.% P2O* degree polimer. pH 1%-s' solut-s u.d.
Na2O P2O- 5tot. P2O5 2 Spoil. P2O5 2 5w-ater. SO3 CaO MgO ^2O3 Fe2O3 F Ntot.
1. 350 40.84 56.73 55.51 1.22 0.0051 0.0093 0.0100 0.0091 0.0085 0.0019 0.0510 97.85 9.6 0.13
2. 400 40.97 56.90 55.85 1.05 0.0054 0.0097 0.0104 0.0094 0.0089 0.0020 0.0364 98.15 9.6 0.13
3. 450 41.03 57.00 56.12 0.88 0.0059 0.0102 0.0108 0.0096 0.0094 0.0022 0.0280 98.45 9.6 0.12
4. 500 41.05 57.01 56.35 0.66 0.0061 0.0105 0.0109 0.0098 0.0092 0.0024 0.0215 98.84 9.7 0.12
5. 550 41.07 57.03 56.52 0.52 0.0063 0.0107 0.0111 0.0099 0.0094 0.0025 0.0172 99.10 9.7 0.12
An raising the temperature with 350 °C to 500 °C contrib- to polymerisation not less than 98.0%, 57.0% P205 contain-
utes to an increase the degree of polymerization from 97.85% ing not less. For this purpose it is necessary EPA to clear of
to 98.84%. The content P205 raises from 56.73% to 57.01, impurity by defluorization, desulfurization, deep clearing of Na2O from 40.84% to 41.05%. The optimal dehydration tem- sulphates, fluorine and the magnesium, the cleared solution
perature are 450-500 °C and the duration of process 2 hours. evaporated at temperature 450-500 °C within 2 hours.
Conclusion. Thus, the carried out researches have shown obtaining possibility sodium tripolyphosphate with sedate
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