Inhibition of calcium sulphate hemihydrate crystallization under simulated conditions of phosphoric acid evaporation

Abstract

Nucleation and crystal growth of CaSO 4 Á 0.5H 2 O (calcium sulphate hemihydrate) was studied under conditions simulating scale formation in phosphoric acid production evaporators. Phosphoric acid, calcium hydrogen phosphate, and sulphuric acid were mixed at 88 C. The induction time was determined using a turbidimeter across a range of supersaturation from 1.3-3.5. Crystallization equations, taking as input the induction time and supersaturation, were used to calculate surface energy, nucleation rate, free energy, and the critical nucleus radius of CaSO 4 Á 0.5H 2 O with and without the addition of 75 mg/L of various scale inhibitors: polyacrylic acid (PAA) 8000 g/mol, poly(diallyldimethylammonium chloride) (PDADMAC) <100 000 g/mol, or polyethyleneimine (PEI) 60 000 g/mol. The results suggest that PEI is capable of inhibiting crystal growth through the impediment of crystal nucleation.

Interfacial Engineering of Particulate & Surfactant Systems for Enhanced Performance in Industrial Applications

“…Solubility changes, SEM, FTIR, and XRD, were employed as investigative tools in the in-situ study of how additives affect mineral crystallization on surfaces. It was anticipated that a basic understanding of the scale formation process would allow the development of commercially viable other (greener) additives not only for phosphoric acid plants but also for other systems (Tanquero et al, 2021).…”

“…13 and data given in Tables 1 and 2. PF addition increased the induction time, reduced the surface free energy for nucleation, and delayed the growth of the gypsum (Carr et al, 2014;Tanquero et al, 2021;Zhang L. et al, 2015).…”

“…Note: the legend NA and PF represent without additive and with additive PhosFlow, respectively. Reprinted with permission from Ref (Tanquero et al, 2021)…”

Revealing Mechanism of Hemihydrate–Dihydrate Phosphogypsum Transformation and Minimizing Phosphorus Loss in Wet Process Phosphoric Acid

“…The sulfuric acid-based wet process phosphoric acid production − is the main method to produce phosphoric acid, which has the advantages of low production cost, low energy consumption, and environment-friendliness. Compared to traditional dihydrate (DH) wet process phosphoric acid production, the hemihydrate–dihydrate (HH–DH) wet process phosphoric acid recrystallization method , is a novel phosphoric acid production method that produces high content of P 2 O 5 (≥40 wt %) without a further energy-intensive concentration process to obtain the concentrated phosphoric acid.…”