Ultrasound assisted seed preparation and subsequent application for desupersaturation of calcium sulphate as a measure for scaling control

Abstract

To increase the water recovery from brine for zero liquid discharge (ZLD) desalination system, precipitation of salts and its subsequent removal is one of the desired solutions to prevent the scaling of heat exchanger or membrane surfaces, which leads to improved operation. Present work focuses on synthesis of better-quality calcium sulphate seed crystals using different strategies based on different initial sources, varying reagent concentration, washing with different solvents, varying the aging period and also providing ultrasound (US) at different stages of synthesis. It was elucidated that using only US at optimized conditions of 100 W US power, 70% duty cycle and 2 h irradiation time could reduce the supersaturation from 2.05 to 1.33 at 60 °C. Use of only seeding under optimized conditions required 4 h for reducing supersaturation from 2.02 to 1.21. The combination of US with the seeds synthesized at optimized condition resulted in the complete elimination of the supersaturation i.e. from the initial supersaturation of 2.02 to final of 1.03. Better desupersaturation is attributed to the increased nucleation rate and crystal growth by the synergy of US and seeding. Overall, an effective approach based on the combination of US and seeding for the desupersaturation of CaSO4 has been demonstrated.