3.1.1. Intermediate chemical softening
Chemical softening of the primary RO concentrate has been
accomplished with lime softeners, pellet softeners or fluidized
bed crystallizers. Gabelich et al. [33] utilized lime slurry (Ca(OH)2)
for primary RO concentrate treatment. When chemical softening of
primary RO concentrate was integrated with a secondary RO system,
overall feed water recovery was enhanced to 95%. Calcium
was removed as calcium carbonate while silica was removed by
co-precipitation with magnesium hydroxide; metals (such as barium)
were also removed by co-precipitation [33]. In another study,
Ordóñez et al. [36] utilized flocculants that enhanced floc formation
and promoted the removal of hardness ions.