Crystallization study of reverse osmosis desalination scales at low salinity with and without inhibitor

Abstract

Crystallization study of calcium sulfate dihydrate was studied under conditions of scales formation using pure chemicals and at low salinity. Calcium chloride and sodium sulfate were mixed in deionized water, and the conductivity of the reaction mixture was measured at different time periods to determine the induction time of gypsum crystal formation. Induction time was measured under different high supersaturation ratios (SR) ranging from 5.9 to 7.0. Using crystallization Downloaded by [University of Lethbridge] at 23:59 26 June 20162 equations that relate induction times with supersaturation ratios, the free energy barrier and critical nuclei radius were calculated with and without addition of scale inhibitor (Tri-Sodium Phosphate, TSP). The nucleation rates at supersaturation ratio of 5.9 are 7.6 × 10 26 nuclei/cm 3 .s and 2.3 × 10 26 nuclei/cm 3 .s with and without TSP addition, respectively. The surface energy increases with TSP compared to the baseline (without TSP). Numbers of molecules required for formation of stable nucleus are calculated to be from 15 to 22 molecules depending on supersaturation ratios and presence or absence of TSP.

Experimental Study of Salicylic Acid as a Calcium Sulfate Dihydrate Scale Inhibitor, Analyzed from Surface Properties and Crystal Growth

“…The solubility of CSD is from 0.213 to 0.266 g/100 cm 3 when the solution temperature ranges from 20 to 60 °C. 15 …”

“…The supersaturation ratio ( S ) was calculated as follows: where η is the scale inhibition ratio, %; C a is the equilibrium residual concentration of Ca 2+ in the presence of the scale inhibitor, mg/L; C b is the equilibrium residual concentration of Ca 2+ without the scale inhibitor, mg/L; C 0 is the initial concentrations of Ca 2+ , mg/L; S is the ratio of supersaturation; c is the CSD concentration, g/100 cm 3 ; and c * is CSD (solute) solubility under the experimental conditions. The solubility of CSD is from 0.213 to 0.266 g/100 cm 3 when the solution temperature ranges from 20 to 60 °C …”

“…The solubility of CSD is from 0.213 to 0.266 g/100 cm 3 when the solution temperature ranges from 20 to 60 °C. 15 2.3.2. Dynamic Simulation Scale Inhibition Experiments.…”

Initial Stages of Gypsum Nucleation: The Role of “Nano/Microdust”

“…In both cases A and B solutions reach similar levels. The conductivity measurements are very useful and common for the gypsum induction time (t ind ) estimations [27,[37][38][39]. Thus, this method was chosen for gypsum nucleation monitoring in the bulk aqueous phases with different nano/microdust content, Figure 5.…”