INVESTIGATION ON THE PHOSPHORIC ACID PRODUCTION FROM LOW GRADE PHOSPHORITES WITH HIGH CONTENT OF MAGNESIUM

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1 Journal Israiljan of Chemical T. Shamshidinov, Technology ahramon and Metallurgy, G. Gafurov, 51, Mubosher 2, 2016, M. Ikramov INVESTIGATION ON THE PHOSPHORIC ACID PRODUCTION FROM LOW GRADE PHOSPHORITES WITH HIGH CONTENT OF MAGNESIUM Israiljan T. Shamshidinov, ahramon G. Gafurov, Mubosher M. Ikramov Namangan Engineering-Pedagogical Institute 12a, st. Do stlik, , Namangan, Uzbekistan E -mail: bse-chemist-68@mail.ru Received 20 April 2015 Accepted 05 January 2016 ABSTRACT The effect of MgO content of the pulp liquid phase on the decomposition of high magnesia low grade phosphorites by sulfuric acid was studied. The phosphoric acid (EPhA) and phosphogypsum obtained were analyzed and the optimal parameters of process taking place were defined. The latter provided the formation of scaly and needle type of phosphogypsum crystals of dimensions 100 mm х 24 mm, 120 mm х 20 mm, 220 mm х 20 mm, 360 mm х 28 mm, 400 mm х 80 mm, 500 mm х 80 mm. This resulted in increase of the extraction pulp s filtration rate and the values of the technological indicators ( e.c. - the decomposition coefficient, l.c. - the extraction coefficient, w.c. - the washing coefficient, y.f. - the yield factor) of the process studied. The EPhA obtained under optimal processing conditions corresponds to the requirements referring to amorphous and other kinds of phosphate fertilizers production based on it. eywords: high magnesia low grade phosphorite, sulfuric acid decomposition, dehydrate condition and filtration rate. INTRODUCTION At present, the phosphorous containing fertilizers production is limited by raw material resources consumption. The performance of the plants producing phosphate fertilizers depends exclusively on the quality of phosphate raw materials. In Uzbekistan the low grade phosphorites of Central yzylkum are the basic raw materials for the production of phosphorus containing fertilizers. Currently, at the yzylkum phosphate plant (PP), washed and calcined phosphorus concentrate (WCPC) of a capacity 400 thousand tons per year is produced. It is directed to Joint Stock Company (JSC) Ammofos-Maxam for EPhA production by sulfuric acid extraction and ammophos. The main drawbacks of WCPC production is not only the high calcium module, but the high magnesium content of the ore as well. The processing of higher magnesia low grade phosphates containing 15 % - 20 % and up to 3.0 % % МgО to fertilizers is planned. It is known [1] that wellfiltrating calcium sulfate is formed in the presence 1 % - 2 % (on the round of the total weight) zinc, magnesium, iron, nickel and copper sulfates. The magnesium content increase above 1.5 % affects negatively the values of (EPhA) obtained from phosphates. It is shown [2, 3] that the extraction degree of from the solution and the filtration properties are improved at low content of magnesium phosphate (less than 1 % %) based on the extraction phosphoric acid from apatite concentrate. But they deteriorate in case the magnesium content is higher than of the ore. The decomposition coefficient value in the presence of 2 % - 3 % МgО is 3 % - 4 % less than that in pure solution. Patents [4, 5] describe methods of phosphoric acid production through wet extraction process in presence of low magnesium and fluorine content providing 157

2 Journal of Chemical Technology and Metallurgy, 51, 2, 2016 naphthenates introduction to the circulating solutions of phosphoric acid. Ref. [6] suggests ionite purification of phosphoric acid circulating solutions from magnesium. Its application to decomposition of high magnesium containing phosphorites is also considered. The phosphoric acid extraction from magnesium containing phosphates requires the preliminary enrichment of the raw material [7-12]. For example, ref. [11] describes the ovdor s apatite concentrate used which contains (mass %): , СаО; MgO; Al 2 ; Fe 2 ; SiO 2 ; СО 2 ; F and insoluble residue. The phosphate concentrate obtained under optimal technological conditions contains % of and 1.0 % % MgO. The present study is aimed at defining the optimal conditions of sulfuric acid extraction using high magnesia raw material but in absence of any preliminary enrichment. EXPERIMENTAL Materials High magnesia low grade phosphorite was used in the present study. It contained (mass %): , СаО; MgO; Al 2 ; Fe O ; SiO 2 ; СО 2 ; F and insoluble residue, as well as a mixture of sulfuric (92,5 %, H 2 SO 4 ) and phosphoric acids. The phosphorite was ground and 8 % of it referred to particles size of 0 mm 70 mm, 19.5 % to 70 mm -100 mm, 24.5 % to 100 mm 160 mm, 32.0 % to 160 mm 200 mm and 16.0 % to more then 200 mm. The formulas used The decomposition coefficient ( d.c. ) was calculated on the ground of СаО:S present in the phosphorites: 0,7 100 d.c. =,% CaO /SO where 0.7 stands for the theoretical weight ratio of СаО and S in gypsum. The extraction coefficient of in the solution was determined on the ground of the total and the watersoluble forms of present in phosphogypsum in accordance with: (Ctotal C water solible. ) Gg.n ex.c. = , % C phos. where C total is total content of in the phosphogypsum, %, С water-soluble is the water-soluble content of in phosphogypsum, %; С phos stands for content in the phosphate (referred to an absolutely dry substance), %; G g.n. is the gypsum number, i.e. the yield of dried phosphogypsum (СаSO 4. 2Н 2 О calculated on the ground of СаО content in the raw material referred to an unit phosphate; The washing coefficient of phosphogypsum allowed to estimate losses of water-soluble : Cwater sol. Gg.n. 100 w.c. = 100, % C phos. ex.c. The technological yield factor characterized the degree of distribution of between the initial phosphate and the phosphoric acid. It was determined by multiplication of the extraction coefficient of from the solution and the washing coefficient of phosphogypsum: 100 ex.c. w.c. y.f. =,% The filtration rate calculation was carried out in accordance with: θθ = mm SS tt, where was the filtration rate, кg/m 2 h, was the mass of the wet phosphoric concentrate, кg, S was the area of the filtrated surface, m 2, while was the filtration time, hour. Experimental procedure The experiments were carried out at a laboratoryscale plant of a continuous mode, which consisted of two-sectional stainless steel AI-943. The latter was isolated by an electric heating coat. It was equipped with a stirrer and feeders for acids and phosphorites flour. The plant capacity was 150 g of phosphorites raw material, the pulp stay time was hours, the extractors capacity was 2.5 l. The phosphorite decomposition process was performed with a mixture of sulfuric (92,5 % - H 2 SO 4 ) and phosphoric acids in a dehydrating regime at temperature of 85±1 о С. The system worked without a circulating pulp. Prior to the start the extractors were filled by extraction pulp obtained from the raw material used. The mixing velocity was revolutions per minute (rpm) in the first reactor, while it was rpm in the second one. The mixing duration was hours. The ratio of the liquid and solid phases was about 2.5, while the sulfate ion content was g/100ml in terms of S

3 Israiljan T. Shamshidinov, ahramon G. Gafurov, Mubosher M. Ikramov in the liquid phase. The concentration of S and in the pulp as well as the liquid and solid phases state were continuously followed during the process of extraction. The phosphoric acid and the circulating solution obtained were analyzed in respect to the content of, СаО, MgO, S, Аl 2, Fe 2, F, the density and viscosity in the 20 о С - 80 о С temperature range. The filter cake (phosphogypsum) was 3 fold washed using a counter flow scheme. The water weight referred to that of phosphogypsum varied from 160 to 100. The filtration was carried out using Buchner funnel at pressure 0,65 kg m -2. The phosphogypsum was analyzed for the content of total, water-solble, СаО, MgO, S and F. The investigation of magnesium ion influence on the production data and the quality of EPhA was carried out in several stages. A model solution of phosphoric and sulfuric acid was used as a circulating mixture. It contained S and magnesium oxide referring to the manufacturing one. The first and the second filtrates were used to follow the circulating solution composition. Methods of analysis The dried phosphogypsum, EPhA and the filtrate were subjected to chemical analysis. All forms of P 2 O 5 contained [total (t), acceptable by citric acid (ac.c.a.) and acceptable by EDTA (ac. EDTA) and water-soluble] were determined calorimetrically using CPhC-3 ((l = 440 nm) [13] with an error ± 1 %. The sulfur content was determined gravimetrically [14]. The total (t) amounts of CaO and MgO were determined by a complexometric titration with 0.02N EDTA using calcein or chrome navy-blue as an indicator [15]. Fluorine was determined in accordance with the technique described in ref. [16] using ionomer EV-74. The density of the extraction pulp and EPhA was determined by the bottle method, while the viscosity was measured using a glass capillary viscometer (GCV-2) with a diameter of 0.77 mm at 20 o C. The size and the form of crystals were defined by microscope IPM-8. Таble 1. Chemical composition of EPhA and the extraction pulp as a function of magnesium oxide content of the system. Components Content of MgO in pulp liquid phase, % Circulating solutions of phosphoric acid, mass % SО 3, g/100 ml MgO t, mass % Extraction pulp Density (ρ), g cm Ratio of L:S Filtration rate, kg m -2 h Productive EPh, mass % SО 3, g/100 ml CaO t, mass % MgO t, mass % Аl 2, mass.% Fe 2, mass % F, mass % Density (ρ), g cm Viscosity (η), cps, at 20 o С

4 Journal of Chemical Technology and Metallurgy, 51, 2, 2016 RESULTS AND DISCUSSION The data referring to the chemical composition of EPhA and the extraction pulp depending on magnesium content is shown in Table 1. It is seen that content in the circulating solution varies from % tо % with МgО decrease from 1.80 % tо 0.10 % in the liquid phase. SО 3 content varies from 1.52 g tо 2.01g in 100 ml. The extraction pulp density decreases insignificantly with МgО content decrease from 2.30 % tо 0.74 %, i.е times in the liquid pulp. It is also seen that inadmissable impurities content in the acid such as that of Аl 2, Fe 2 and F decreases 4.14, 4.05 and 2.30 times, respectively. content in the acid increases from % tо % but the subsequent decrease of МgО presence in the system decreases it from % tо %. The filtration rate of the phosphoric acid pulp changes as well. For example, the decrease of МgО content from 2.30 % tо 1.52 % in the pulp liquid phase results in the filtration rate decrease from kg m -2 h -1 tо kg m -2 h -1. Further decrease of МgО content up to % in the liquid phase brings about a filtration rate decrease up to kg m -2 h -1. This data is in correspondence with that presented in Table 2. The latter shows also the data referring to variation of phosphogypsum s chemical composition and the decomposition process s technological indicators with decrease of magnesium s ions content in the system. It is seen that the decrease of magnesium ions content in the system leads to increase of the raw material decomposition degree. Thus in case of MgO content of 2,30 % in the pulp liquid phase, the decomposition coefficient is (for decomposition duration of hours), while the extraction coefficient ( ex.c. ) and yield factor ( y.f. ) are 93.6 and 92.6 %, correspondingly. However, MgO content decrease to 1.52 % % promotes the increase of the decomposition coefficient, the extraction coefficient and the yield factor to 97.5 % %, 95.8 % % and 94.8 % %, respectively. A subsequent decrease of magnesium oxide content in the system has a similar impact on the technological indicators. Habitus and calcium sulfate crystals are found out in presence of defined regularities between magnesium ions content and calcium sulfate crystallization. A significant effect of magnesium cations on the crystals form and size is observed. Таble 2. Chemical composition of phosphogypsum and technological indicators of the decomposition process with decrease of magnesium oxide content of the system. Values Content of MgO in the liquid phase of pulp, mass % Phosphogypsum content, mass % Н 2 О total, mass % total, mass % w.s., mass % S, mass % СаО t, mass % R 2 (Fe 2 + Аl 2 ), mass % F, mass % Process technological indicators, % К d.c., % К ex.c.., % К w.c., % К y.f., % The sizes of phosphogypsum crystals, µm Rhombic crystals with size 80х60, 60х60, 40х40, 20х20, 10х10, much small druse Scaly and needlelike crystals with size 100х24, 120х20, 220х20, much 500х80, 400х80, 360х28 and seldom 100х16, 80х60 Heterogenous 520х40, 248х36, 212х24, 180х24, 80х8, 80х4, 60х2 much small fraction 160

5 Israiljan T. Shamshidinov, ahramon G. Gafurov, Mubosher M. Ikramov Phosphogypsum rhombic crystals of a size of 80 μm х 60 μm, 60 μm х 60 μm, 40 μm х 40 μm, 20 μm х 20 μm together with many minute crystals of a size of 10 μm х10 μm are formed in case MgO content in the liquid phase is kept in the range of 2.30 % %. Scaly and needlelike crystals of a size of 100 μm х 24 μm, 120 μm х 20 μm, 220 μm х 20 μm are formed together with crystals of a size of 60 μm x 80 μm, 400 μm x 80 μm and rarely 80 μm х 60 μm and 100 μm х 16 μm are formed in case of MgO content decrease to 1.52 % %. Further MgO content decrease leads to the formation of inhomogeneous crystals of calcium sulfate of a size of 520 μm х 40 μm, 180 μm х 24 μm, 80 μm х 8 μm, 80 μm х 4 μm, 60 μm х 2 μm together with a large number of much minute crystals. It is reported [2] that the phosphate decomposition coefficient and the cake filtration properties deteriorate in presence of magnesium compounds in the range % MgO. The explanation refers to the retardation of the phase transition of hemihydrates into gypsum and apatite surface coating of gypsum (minute crystal) in presence of 1.50 % % MgO in the phosphoric acid. Thus, magnesium ions participate directly in calcium sulfate crystallization and affect essentially the habitus and size of the crystals formed. The decrease of phosphorites decomposition coefficient can be explained with the increase of magnesium cations amount (> 1.5 % MgO in the extraction pulp). The latter affects also the crystallization, i.e. system supersaturation with minute crystals, it brings about retardation of hemihydrates phase transition to gypsum as well as particle coating, it deteriorates the diffusion process. Similar processes take place in the system with decrease of magnesium ions content to less than 1 % in presence of sulfuric acid. The optimal content of magnesium cations (calculated on the ground of MgO) in the liquid phase should be 1.16 % %. The yield of phosphoric acid containing % % of reaches 95.8 % % in case a high magnesia low-grade phosphorites ore (24,8 % ) is used. Coarse-grinding in the heating dehydrate regime is required. CONCLUSIONS The principle possibility of EPhA production on the ground of high magnesia low grade phosphorites was outlined in the present study. The optimal parameters of the process are as follows: MgO concentration of 1.16 % %, S content of 3.36 g/100 ml g/100 ml, decomposition and crystallization temperature of 85± 1 о С, a liquid to a solid ratio of 2.6:1 and process duration of 4,5 h. Scaly and needlelike crystals of gypsum of a size of 100μm х 24 μm, 120μm х 20 μm, 220μm х 20 μm and 500μm х 80 μm, 400μm х 80 μm, 360μm х 28 μm are formed. They facilitate the increase of the extraction pulp filtration rate and the values of the corresponding technological indicators (К d.c., К ex.c., К w.c. and К y.f. ). Acknowledgements We thank Dr. Bokhodir E. Sultonov, senior staff scientist at the Laboratory of Phosphoric Fertilizers for his valuable suggestions concerning the manuscript presentation and Dr. Umar. Alimov, senior staff scientist at the Laboratory of Phosphoric Fertilizers for the translation of the text. REFERENCES 1. M.E. Pozin, Technology of mineral salts, Leningrad, Publishing House Chemistry, 1989, (in Russian). 2. T.T. ozlova, B.A. opilev, Concerning magnesium affect to sulfuric acid decomposition of apatite, Collection studies.: Technology of mineral fertilizers, Leningrad, 4, 1973, 74-84, (in Russian). 3. T.G. ozlova, Ph.D. thesis, Investigation of physicchemical conditions for sulfuric acid extraction of phosphoric acid from magnesium containing phosphorites, Leningrad, 1974, (in Russian). 4. Patent for invention 4504 (Rep. of Uzbekistan), Method of wet process phosphorous acid preparation, 1997, (in Russian). 5. Patent for invention 5698 (Rep. of Uzbekistan), Method of wet process extraction phosphoric acid obtaining, 1998, (in Russian). 6..G. Gafurov, I.T. Shamshidinov, Ionite purification of circulating solutions of phosphoric acid from magnesium and use it at decomposition of high magnesium containing phosphorites, Scientific-technical journal of Fergana polytechnic institute, Fergana, 2, 2005, , (in Russian). 7. Patent for invention (USA), Purification of phosphoric acid,

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