Decomposition Of Phosphogypsum Research Articles

Experimental study of preparing CaS from phosphogypsum with lignite

The reaction of phosphogypsum (PG) and lignite is complex, which depends on the reaction conditions and atmosphere. In the paper, it was carried out for reduction decomposition of PG to calcium sulfide under N2 atmosphere. Scanning electron microscopy and XRD were used to analyze the raw–material and decomposition solid production. The reaction mechanism of preparing CaS from PG with lignite were analyzed by Factsage 6.1 and thermodynamic analysis. The results indicated that the decomposition reaction temperature were between 800 °C and 1100 °C. These experimental conditions were also studied on Ca/C molar ratio, reaction temperature and reaction time in the N2 atmosphere. The results showed that the optimal result for production of CaS are found to be a lignite to CaSO4 molar ratio of 2.4 to 1, a temperature of 900-1000°C in reductive atmosphere. Under these conditions the conversion rate of CaS from phosphogypsum amount to no less than 97.3%.

Thermodynamic study of the desulfurization process of phosphogypsum

Abstract Phosphogypsum (PG) or chemical gypsum is a by-product generated in the manufacture of phosphoric acid. The world production estimated to 200 million tons per year (in Morocco 8 million tons per year) induces environmental threats and storage problems, which requires strict policies to limit pollution and encourage its valorisation. The purpose of this paper is to investigate the thermodynamic condition of the desulfurization process of phosphogypsum (PG). Theoretical approach and experimental setup were validated by using the actual data from desulfurization of PG. Theoretical results showed chemical decomposition of phosphogypsum is thermodynamically feasible only at low temperatures using the HSC chemistry 6.1 computer tool.

Investigation of Al2O3 and Fe2O3 transmission and transformation during the decomposition of phosphogypsum

Abstract Phosphogypsum (PG) is a solid waste produced in the phosphate fertilizer industry and is environmentally harmful. The decomposition of PG to recycle calcium and sulfur is a proper way to reutilize PG. Current work aims at enriching the basic theory of coal decomposition process of PG. The emphasis was laid on the exploration of impact of main impurities on the process. On the other hand, according to Reaction Module, Equilib Module, and Phase Diagram Module of FactSage, the simulation computation was done on the systems of pure gypsum mixed with coal, with or without impurities for avoiding other impurities interference. Later, possible reactions in the process were deduced. Additionally, experiments were conducted in a TG-DTA integrated thermal gravimetric analyzer and a tube furnace. The products from the experiments were characterized and analyzed to verify the accuracy of theoretical calculations. The results showed that these impurities can change the decomposition process of PG. For example, aluminum oxide was transformed to calcium sulfoaluminate, while iron oxide was transformed to dicalcium ferrite. Furthermore, the results help to further improve the basic theory of phosphogypsum decomposition.

Research on thermal decomposing properties of phosphogypsum with Fe addition under multi-atmosphere control

Phosphogypsum (PG) is a by-product of phosphor acid producing, which has become the primary barrier for the development of phosphate fertilizer industry. This paper proposes a series of technical process for the decomposition of PG with Fe addition. The FactSage 7.0 was used as feasibility analysis. Results from the TGA revealed that the initial decomposing temperature of PG was 590 °C, lower 300 °C than without FeCl3 immersion. The decompositions of PG and lignite in multi-atmosphere were performed at different molar ratio in the tube furnace, when the molar ratio of lignite and PG was 1.2:1, the purity of CaO in solid products could reach 90.6%. Fluidized bed experiments were done in a vertical tube furnace, results indicated that after a multi-atmospheres cycles experiment, target production CaO purity could achieve 93.8%. The present research proves that PG with Fe addition decomposed in fluidized bed under multi-atmospheres is feasible.

Decomposing properties of phosphogypsum with iron addition under two-step cycle multi-atmosphere control in fluidised bed.

Phosphogypsum is a solid industry by-product generated when sulphuric acid is used to process phosphate ore into fertiliser. Phosphogypsum stacks without pretreatment are often piled on the land surface or dumped in the sea, causing significant environmental damage. This study examined the reaction characteristics of phosphogypsum, when decomposed in a multi-atmosphere fluidised bed. Phosphogypsum was first dried, sieved and mixed proportionally with lignite at the mass ratio of 10:1, it was then immersed in 0.8 [Formula: see text] with a solid-liquid ratio of 8:25. The study included a two-step cycle of multi-atmosphere control. First, a reducing atmosphere was provided to allow phosphogypsum decomposition through partial lignite combustion. After the reduction stage reaction was completed, the reducing atmosphere was changed into an air-support oxidising atmosphere at the constant temperature. Each atmosphere cycle had a conversion time of 30 min to ensure a sufficient reaction. The decomposing properties of phosphogypsum were obtained in different atmosphere cycles, at different reaction temperatures, different heating rates and different fluidised gas velocities, using experimental results combined with a theoretical analysis using FactSage 7.0 Reaction module. The study revealed that the optimum reaction condition was to circulate the atmosphere twice at a temperature of 1100 °C. The heating rate above 800 °C was 5 [Formula: see text], and the fluidised gas velocity was 0.40 [Formula: see text]. The procedure proposed in this article can serve as a phosphogypsum decomposition solution, and can support the future management of this by-product, resulting in more sustainable production.

Analyses on the application of components in the phosphogypsum decomposition residue: Based on the study of migration and conversion rules of elements in the purification procedure of CaO

Phosphogypsum (PG), which is a solid waste in phosphate fertilizer industry, is harmful to the environment. The pyrogenetic decomposition is mainly used in the utilization of PG, and PG decomposition residue is produced in the decomposition process. In this paper, the migration and conversion rules of elements (Al, Si, P, K, Ca, and Fe) in the purification procedure of CaO in PG decomposition residue was investigated. The acid–base method was used to purify CaO. Content and chemical forms of elements in the purification procedure were analyzed by many characterization methods such as SEM and EDS. And moreover, changes on chemical forms of elements were supported theoretically by some ternary phase diagrams, which were made by the FactSage thermodynamics software. The result showed that, the soluble silicon dioxide and the acid‐insoluble material in PG decomposition residue were effectively removed by using the acid–base method. Meanwhile, impurities separated from CaO and the CaO sample were produced in the experiment, the former can be used to produce the building materials, refractories, insulating materials in various industrial fields, and CaO sample could be used as the filler, building materials, decolorant, etc. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 1020–1030, 2018

Mechanism of CO2 Capture Technology Based on the Phosphogypsum Reduction Thermal Decomposition Process

CO2 emission all over the world is constantly on the rise. In recent years, CO2 capture technology has been improved and innovated. Phosphogypsum (PG) is a solid product of industrial solid waste with an increasing annual accumulation. The research of this paper has carried out thermal decomposition of phosphogypsum under the reduction atmosphere to produce byproduct CaS and mineralization capture of CO2 in a gas–liquid–solid three-phase fluidized bed reactor. Results show that the fluidized bed is more effective and can effectually shorten the reaction time. Meanwhile, different liquid–solid (L/S) ratios, temperatures, and pressures have been researched to study the theory of CO2 capture by phosphogypsum. It has been found that the lower the L/S ratio is, the higher the CO2 capture capacity is. At the same time, theoretical calculations show that high temperature promotes the decomposition of CaCO3, thereby inhibiting the capture of CO2, so the whole carbonation process is operated under ambient temperat...

Effect of SiO2 on the melting characteristics of reaction between phosphogypsum and calcium sulfide

Currently, phosphogypsum (PG) pollution is a global problem. The reductive decomposition of PG to produce sulfuric acid is a good way to utilize this material. However, the solid–solid reaction between PG and calcium sulfide is an unavoidable step during this reaction. Silicon dioxide (SiO2) was the highest content of impurities during this reaction system, and it varies from 8 to 22 %. PG from different sources may differ with respect to the constituents and their amounts. Hence, the influence of the SiO2 on the melting characteristics of solid–solid reaction system was investigated in this paper. The melting phenomenon was clearly observed using scanning electron microscopy. Meanwhile, the melting temperature was decreased with an increased content of SiO2, which was illustrated using an ash fusion point determination meter and differential scanning calorimetry. Through phase diagram analysis, the reason for the changed melting temperature was discussed. The migration process of solid products was also illustrated. The results of the equilibrium analysis and phase diagram were obtained using FactSage6.1 software.

Recycling of Phosphogypsum in Complex Mineral Fertilizer

Background. In the production of phosphate fertilizers and phosphoric acid accumulation environmentally unsafe on the course – phosphogypsum. To date, in theterritory of Ukraine is in the dumps about 30 million tons of phosphogypsum. O bjective . To get from phosphogypsum with using waste technologies complex NPCaS-fertilizer. M ethods . Processing phosphogypsum in a relatively “soft” operating conditions, without the involvement of high-temperature (1173–1753 K) processes. Conducted a research of two-stage utilization processing of typical phosphogypsum into complex fertilizer with composition 7,9 % N, 37 % P 2 O 5 , 35 % Ca, 1,8 % S, containing phosphorus in the form of Сa(H 2 PO 4 ) 2 , СaHPO 4 (at a ratio ), and the nitrogen – in the form (NH 4 ) 2 SO 4 . The first stage of the process is implemented decomposition of phosphogypsum at temperature (323 ± 5) K by solutions of (NH 4 ) 2 СO 3 at pH > 5,1 with formed a precipitate (suspension) СаСO 3 in solution (NH 4 ) 2 SO 4 . In the second stage formed a thick slurry is processed (without filtration separation СаСO 3 ) by solutions of sub-standard phosphoric acid without external heating at the support of the pH of the medium to 6,8–6,9. The final solid fertilizer is drying of slurry in apparatus of type “fluid process” at temperature (390–423) K. Result s. The final solid fertilizer, consumer quality is tested on samples of soil for agricultural purposes. Conclusions. On the base of phosphogypsum is received a complete fertilizer for little-stage non-waste technology in environmentally sound conditions.

Purification of Calcium Oxide in Phosphogypsum Decomposition Residue Based on the Sucrose-CO2 Method

Phosphogypsum (PG) is a solid waste (by-product of the “wet process” phosphoric acid production) in phosphate fertilizer industry which is environmentally harmful. This paper studies purification of calcium oxide in the PG decomposition residue. The phase and the spectral signature of the purified sample were characterized and analyzed by XRD, SEM, and EDS. The experimental results indicate that impurities in the residue are effectively removed by sucrose solution. The reactions between calcium oxide and sucrose solution are well explained. In the purification process, soluble calcium sucrose is produced and almost all the impurities which are insoluble in sucrose solution are removed by filtration. Then the calcium carbonate synthesized by calcium sucrose and CO2 is calcined at 1173.15 K for 2 hours and the optimum mass ratio of the decomposition residue and sucrose solution is 5:100. It was concluded that the content of calcium oxide in the calcined products increased to 98.15% and it also had a compact structure, well-proportioned surface, and higher whiteness.

Mechanism Analysis of Ca, S Transformation in Phosphogypsum Decomposition with Fe Catalyst

Phosphogypsum (PG) is a solid waste (a byproduct of the “wet process” phosphoric acid production) in the phosphate fertilizer industry which is environmentally harmful. The thermal decomposition of PG to recycle the sulfur source and produce cement is a proper way for the utilization of PG. In the previous work of our group, the initial decomposition temperature of PG lowers largely with Fe catalyst and addition. In this paper, based on XRD (X-ray powder diffraction), XPS (X-ray Photoelectron Spectroscopy), and calculation of FactSage 6.1, the transformation of Ca, S in PG decomposition with Fe catalyst in CO atmosphere is explored further. There are a series of competitive gas–solid/solid–solid reactions. At a lower temperature (<1000 °C), the main existences of Ca are CaS and CaSO4 (anhydrite) during the PG decomposition. 1050–1100 °C is the interval area which the reaction of CaO, CaS competes intensively. The main product of PG decomposition is CaO and S exists as SO2 when the temperature is greater t...

PHOSPHOGYPSUM AS A RAW MATERIAL FOR THE PRODUCTION OF SO2 AND LIME IN CIRCULATING FLUIDIZED BEDS

The primary objective of this research is to investigate the possibility of producing sulfur dioxide and lime from phosphogypsum (PG) in a circulating fluidized bed (CFB) on a pilot scale. Thermal decomposition of PG was conducted in a CFB using anthracite as the reducing agent and fuel at temperatures in the range 900–1100°C. The gaseous decomposition products, which mainly consist of sulfur dioxide, were analyzed using a gas analyzer and X-ray diffraction. The results indicate that the reaction conditions required to produce sulfur dioxide and lime are an air flow rate of 94 m3/h, a temperature of 1100°C, and a PG consumption rate of 120 kg/h. Under optimal conditions, the maximum concentration of sulfur dioxide in the flue gas reached 8.2% (vol. %), and the maximum CaO concentration in the phospholime reached 62.57% (wt. %).

Calcium sulphoaluminate cements made with phosphogypsum: Production issues and material properties

Phosphogypsum (PG) is an industrial waste from the production of phosphoric acid. The impurities in PG limit its utilization in building materials, and make PG decompose easily at high temperatures. Calcium sulphoaluminate (CSA) cements are insensitive to the presence of impurities and show some desirable performance. The aim of this paper is to study the potential of producing CSA cement with PG and the decomposition behavior of PG during the production of CSA cement. Experimental results indicated that PG can be utilized to produce CSA cement, and the suitable firing temperature is between 1250 and 1300°C. Results also show that the decomposition of PG is closely connected to the firing temperature and the mix proportion. The decomposition of PG has a significant effect on the formation of calcium sulphoaluminate, and decreases compressive strengths of CSA cement.

Reaction Mechanism for Iron Catalyst in the Process of Phosphogypsum Decomposition

This paper proposes a catalyst to lower the decomposition temperature of phosphogypsum (PG) and investigates the reaction mechanism. PG is stable in the inert atmosphere, decomposed above 1100 °C, and unstable in the reducing atmosphere relatively. The PG decomposition temperature dropped to 800–1000 °C through previous study in a CO/coal reducing atmosphere, which is still high. The Ellingham diagram and FactSage6.1 were used as a guide to find catalyst to lower the PG decomposition temperature further and explore the reaction mechanism, respectively. The analysis of FactSage6.1 Reaction, Equilib, and Phase diagram module showed that Fe(+3) was reduced by CO and oxidized by S(+6) reacted in the molten state completely, which lowered the PG decomposition temperature significantly. PG powder was added to FeCl3 aqua and decomposed in a thermogravimetric analyzer (TGA). With different FeCl3 impregnation concentrations, CO flow rates, and heating rates, the decomposing properties of PG were investigated by thermogravimetric analysis (TG) and differential thermogravimetric (DTG). Impregnated by 0.8 mol/L FeCl3 and flowed 4 mL/L CO, the temperature of PG decomposition drops to 610 °C. This research proves that iron is a proper catalyst to lower the PG decomposition temperature and provides a new reaction path for PG decomposition through gas–solid reaction, liquid–solid reaction, and gas–liquid–solid reaction.

Production of SO&lt;sub&gt;2 &lt;/sub&gt;and Lime from Phosphogypsum Reduced with Lignite in a Nitrogen Atmosphere

In this study, using lignite as a reducer, the reaction characteristic of the reduction decomposition of phosphogypsum to SO2 and lime was investigated in a nitrogen atmosphere at different conditions. Scanning electron microscopy and XRD-ray diffraction were used to analyze the solid production. The gas production of SO2 was analyzed by the Gas Analyzers. The experiment results showed that the optimal conditions for production of SO2 are founded to be a molar proportion of C:CaSO4=0.8:1 and a decomposition temperature of over 1000°C.Under these conditions the maximum concentration of SO2 reached to 8.23% (vol. %). The CaO content of solid production increased to 62.57%. The desulfurization rate of phosphogypsum reached to 95.16%.

Effects of Additives on the Reductive Decomposition of Phosphogypsum in the CO Atmosphere

The effect of the reaction time and the amount of additives on the decomposition rate and temperature of phosphogypsum were studied in the weak reducing atmosphere of 3%Vol CO by using themixture of phosphogyp-sum and a certain percentage of CaCl2, Fe2O3and MgO additives. The resultshows that the decomposition rate of phosphogypsum reached 85% by adding CaCl2and Fe2O3, and the decomposition temperature of phosphogypsum was only 950°C which was 100 °C lower than the one of decomposition reaction of phosphogypsum without any adductives. And the addition of MgO had nosignificant effects on the decomposition of phosphogypsum under the same condition.

Cold Test of Circulating Fludized Bed Decomposition Phosphogypsum

Phosphogypsum is the gypsum as a byproduct of the processing of phosphate ore into fertilizer with sulfuric acid. It’s main components is CaSO4. Circulating fluidized bed(CFB) is the best reactor. In this paper the characteristics of phosphogypsum decomposition were analyzed via CFB reaction in cold test. And applied quantity of wind and bed material influenced bed pressure and the quantity of solides and solids concentration.

Thermodynamic study of phosphogypsum decomposition by sulfur

Phosphogypsum (PG) is one of the most significant industrial solid wastes from the phosphorus chemical industry. In order to utilize PG more effectively, a new decomposition process of PG by sulfur as a reducer is proposed in this work. Thermodynamic study of the sulfur reduction process including two-step reactions was carried out by both thermodynamic simulation and experimental research. The simulation results indicate that sulfur changes its form in a complex way with rising temperature. The final decomposition temperature of PG by simulation is 993K in the first-step reaction, and this is in good agreement with that obtained by the experiments. For the second-step reaction, however, the final PG decomposition temperature from the experiments is 250K lower than the simulation results predict. The reaction heat of the sulfur reduction process is 27.95% less than that of the traditional coke reduction process at T=1473K based on enthalpy change calculations. This new process can reduce the emission of CO2 effectively and is more suitable for resource utilization of PG than the coke reduction process, so it may be a promising method for sulfuric acid production from PG.

The Carbonic Acid Reaction of Phosphogypsum Decomposition Slag in the Three-Phase Fluidized Ded

Through the study on influence factors of the carbonic acid reaction of phosphogypsum decomposition slag in the three-phase fluidized bed, the effect of different factors on the transformation of CaS in the phosphogypsum decomposition slag was discussed. Experiments show that Increasing CO2 gas flow and extending reaction time have benefit for the transformation of CaS. The conversion rate of CaS was increased firstly and then tended to flatten with the increase of the liquid-solid ratio. The rise of reaction temperature has a weak inhibitory effect for the transformation of CaS. Comparing with tank reactor, three-phase fluidized bed reactor is more advantageous to the carbonic acid reaction of phosphogypsum decomposition slag.

Thermal and Kinetic Analysis of the Process of Thermochemical Decomposition of Phosphogypsum with CO and Additives

Phosphogypsum (PG) is a waste byproduct from the processing of phosphate rock by the ‘‘wet acid method’’ of fertilizer production. One of the main methods for reusing PG is to decompose and recycle Ca and sulfur contained in it. However, the decomposition reaction process is very complex because of its complicated contents, and very high temperature is needed for the reaction. In this paper, to decrease the reaction temperature, CO as a main reducer and some additives were added in the decomposition process. Results show that the decomposition temperature will decrease from 1000 to 809 °C with pure CO. When CaCl2 is used as an additive, the decomposition temperature can decrease to 790 °C, and at the same time the reaction rate will be increased, the main product being CaS at this condition. The thermal and kinetic action of this process has also been discussed.