Effect of particles on the induction time of calcium carbonate in synthetic SWRO concentrate

Particles, which are naturally present in seawater, have been reported to affect the formation of CaCO₃ crystals. In this study the effect of foreign particles on induction time was explored. Induction time was monitored using a highly sensitive pH meter mounted in an air-tight glass reactor. Experimental work was performed with synthetic seawater prepared using ultra-pure water with a composition equivalent to 50% recovery SWRO concentrate (based on the composition of seawater from the Gulf of Oman). The prepared synthetic solutions were filtered through filters having different pore sizes namely 0.22 μm; 0. μm and 100kD (≈0.03 μm). In addition, glass beads of diameter 20–30 nm were added in volumes of (1; 0.5 and 0.1 ml) to synthetic seawater to yield an increase in glass/water contact area of 123%, 16% and 1% compared to the total reactor glass area in contact with the synthetic water. Different mixing speeds were applied namely 10; 50; 150 and 300 rpm to investigate the effect of mixing on experimental results. Results showed that fi ltering synthetic seawater and applying different mixing speeds had a negligible effect on the experimental induction time results. On the contrary, the addition of glass beads shortened the induction time substantially from 30% to 100% (immediate precipitation), depending on the amount of beads added.