Abstract
Studies on the transformation of calcium sulphate dihydrate to hemihydrate in the wet process phosphoric acid production The influence of the process temperature from 85°C to 95°C, the content of phosphates and sulphates in the wet process phosphoric acid (about 22-36 wt% P2O5 and about 2-9 wt% SO4 2-) and the addition of αCaSO4·0.5H2O crystallization nuclei (from 10% to 50% in relation to CaSO4·2H2O) on the transformation of calcium sulphate dihydrate to hemihydrate has been determined. The wet process phosphoric acid and phosphogypsum from the industrial plant was utilized. They were produced by reacting sulphuric acid with phosphate rock (Tunisia) in the DH-process. The X-ray diffraction analysis was used to determine the phase composition and fractions of various forms of calcium sulphates in the samples and the degree of conversion of CaSO4·2H2O to αCaSO4·0.5H2O and CaSO4. It was found that the transformation of CaSO4·2H2O to αCaSO4·0.5H2O should be carried out in the presence of αCaSO4·0.5H2O crystallization nuclei as an additive (in the amount of 20% in relation to CaSO4·2H2O), at temperatures 90±2°C, in the wet process phosphoric acid containing the sulphates and phosphates in the range of 4±1 wt% and 27±1 wt%, respectively.
Highlights
The world phosphoric acid production amounted to 39.8 million tons of P2O5 in 2009, and, according to forecasts, will increase to 46.9 million tons of P2O5 by 2013 1,2.The largest consumption of phosphoric acid in 2009 was in Asia (30%), United States (22%) and Southwest Asia (10%) 3.The phosphoric acid is produced by two commercial methods: wet process and thermal process
1. an increase of the process temperature and/or the content of SO42- and/or PO43- in the phosphoric acid affected the increase of the degree of transformation of CaSO4.2H2O to CaSO4.0.5H2O, 2. a higher reaction temperature enables to carry out the conversion under milder conditions in relation to the 3
CothnetenatddoiftiSoOn42o- fan dCPaOSO43-4.i0n.5tHhe2Ophcorsypshtoarlliiczaatciiodn, nuclei enabled the achievement of a high degree of
Summary
The world phosphoric acid production amounted to 39.8 million tons of P2O5 in 2009, and, according to forecasts, will increase to 46.9 million tons of P2O5 by 2013 1,2.The largest consumption of phosphoric acid in 2009 was in Asia (30%), United States (22%) and Southwest Asia (10%) 3.The phosphoric acid is produced by two commercial methods: wet process and thermal process. The wet process phosphoric acid can be obtained by the decomposition of phosphate rock with sulphuric acid by the following methods: dihydrate (DH-process), hemihydrate (HH-process) and by combined processes [4,5,6,7,8,9,10,11,12,13,14,15]. The phosphates content in the calcium sulphate hydrate depends on the production method used Their content results from the presence in this waste of unreacted phosphoric raw material, unwashed phosphoric acid and due to the cocrystallization of CaHPO4.2H2O with CaSO4.nH2O4,5
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
