A Study of the Kinetics of the Reaction of Petroleum Coke with Phosphogypsum to Give Calcium Sulfide

J of Chemical Tech & Biotech

2023

BACKGROUND: Recent studies show that CaO is being produced from CaSO 4 by CO reduction using fixed-bed reactors. However, the product yield is low and the reaction time is long. Furthermore, the high cost of CO hinders its application in industrial processes. Therefore, a new process is proposed for preparing CaO by CaSO 4 decomposition using lignite under CO 2 . The influence of various process conditions on the production of CaO by CaSO 4 decomposition is investigated by combining kinetic and FactSage simulations. Finally, a typical industrial gypsumphosphogypsum (PG)is used for experimental verification.RESULTS: The study found that adding CO 2 during the coal reduction of CaSO 4 increases the CaO yield. The ideal conditions are 1.75 C/Ca molar ratio, 7.5% CO 2 concentration at 1100 °C with the maximum CaSO 4 decomposition rate and CaO yield of 99.63% and 99.28%, respectively. CaO generation is carried out using a two-step process. Initially, CaSO 4 is reduced to become CaS and CaO, and CaS interacts with CaSO 4 to produce CaO. Secondly, the reaction between CaS and CO 2 produces CaO. The nucleation and growth model with g(⊍) = −ln(1 − ⊍) is applicable to both processes. The experimental use of PG confirms the above conclusions, but SiO 2 in PG reacts with CaO to produce Ca 2 SiO 4 and affect the CaO yield.CONCLUSION: The addition of CO 2 promotes the conversion process of CaSO 4 to CaO. Increasing the temperature, C/Ca molar ratio and CO 2 concentration favor the decomposition of CaSO 4 into CaO. This study offers advice for using CaSO 4 products like PG as resources.

Section: Introductionmentioning

confidence: 99%

Experimental study on preparation of calcium oxide by coal reduction of calcium sulfate in carbon dioxide atmosphere

J of Chemical Tech & Biotech

2023

“…7 The type of reducing agent and the C/Ca molar ratio are the two most important factors influencing PG decomposition. The common reducing agents used for PG reduction mainly include solid reducing agents such as lignite, 8,9 anthracite, 10 high sulfur coal, 11 coke, 12 and gaseous reducing agents such as CO, 13 H 2 , 14 and H 2 S. 15 It is shown that pure graphite hardly reacted with CaSO 4 , while coal and char could effectively decompose PG. Moreover, when other conditions are the same, the PG decomposition rates of coals with low degrees of metamorphism (lignite and bituminous coal) are significantly better than those of coals with higher degrees of metamorphism (anthracite).…”

Section: Introductionmentioning

confidence: 99%

“…The type of reducing agent and the C/Ca molar ratio are the two most important factors influencing PG decomposition. The common reducing agents used for PG reduction mainly include solid reducing agents such as lignite, 8,9 anthracite, 10 high sulfur coal, 11 coke, 12 and gaseous reducing agents such as CO, 13 H 2 , 14 and H 2 S 15 . It is shown that pure graphite hardly reacted with CaSO 4 , while coal and char could effectively decompose PG.…”

Section: Introductionmentioning

confidence: 99%

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Preparation of calcium sulfide by sludge‐assisted rice husk reduction of phosphogypsum

Asia-Pacific J Chem Eng

Tian

2023

Reduction of phosphogypsum (PG) to calcium sulfide (CaS) using thermochemical methods solve the environmental problems caused by PG. However, the commonly used reducing agents are coal and CO. The use of the above‐mentioned reducing agents is not economically efficient. In this paper, rice husk (RH) is used as a reducing agent and sludge (SL) as an additive to reduce PG. The effect of the two on PG decomposition and the mechanism of the synergistic effect are also investigated in combination with kinetic calculations. It is found that decomposition rate of CaSO4 in PG is 99.99% and yield of CaS is 98.38% when 40% RH + 20% SL is used as the reducing agent at 900°C for 30 min. The combined use of RH + SL is superior to RH alone in reducing the initial decomposition temperature and Ea. The mechanism functions of both reduced PG are G(α) = −ln(1 − α). There is a synergistic mechanism between RH and SL. The Fe2O3 in SL increases the cleavage of nitrogen oxide‐containing compounds and PAHs in tar to monocyclic aromatic and aliphatic hydrocarbons while producing more CO, H2, and CH4. Meanwhile, SL ash can promote the reaction process of carbon with CaSO4, thus increasing the decomposition rate of PG.

“…Phosphogypsum (PG) is a solid waste generated during the wet process of phosphoric acid production in the phosphate fertilizer industry, and its main component is CaSO 4 ·2H 2 O or CaSO 4 ·0.5H 2 O 1 . As piling and burying PG residue not only occupies a large amount of land, but also tends to cause serious pollution to the atmosphere and groundwater, the pressure on environmental protection caused by PG emissions has become one of the important constraints to the development of the phosphate fertilizer industry 2 . Therefore, there is an urgent need for integrated and large‐scale utilization of PG to promote the recycling and sustainability of calcium and sulfur.…”

Section: Introductionmentioning

confidence: 99%

Experimental study of CaS preparation from lignite‐reduced phosphogypsum in a fluidized bed

J of Chemical Tech & Biotech

2022

BACKGROUND: Phosphogypsum (PG) is a solid waste. For a fluidized bed, current research has focused on the preparation of CaO and SO 2 by PG decomposition, while less research has been conducted with calcium sulfide (CaS) as the target product. Therefore, the effect of different conditions on the preparation of CaS by coal reduction of PG was investigated in a fluidized bed. The mechanism of the reaction between coal and PG was revealed through experiments and kinetic calculations.RESULTS: PG decomposition is a combination of solid-solid reaction (carbon reacting with CaSO 4 ) and gas-solid reaction (reducing gas reacting with CaSO 4 ), among which the solid-solid reaction plays a major role. A PG decomposition rate of 99.42% and CaS yield of 91.55% are obtained at 850 °C for 60 min when the Ca/C molar ratio is less than 0.25 and coal particle size is less than 0.075 mm. Lignite, bituminous coal and anthracite can promote the decomposition of PG. However, the higher viscosity of bituminous coal can lead to molten coking of the product, while anthracite is less economical, so lignite is the most suitable. Minerals in coal can improve the decomposition rate of PG. A fluidized bed improves the PG decomposition rate compared to a fixed bed.CONCLUSIONS: CaS is obtained by combined solid-solid and gas-solid reactions. Decreasing the Ca/C ratio and coal particle size as well as controlling the reaction temperature below 850 °C are beneficial for CaS generation. The minerals in coal can reduce the PG decomposition temperature and increase the PG decomposition rate.