Solubility enhancement of silicate with polyamine/polyammonium cationic macromolecules: Relevance to silica-laden process waters

This paper reports the inhibition efficiency of a family of synthetic amine/ammonium-containing cationic polymers in colloidal silica particle growth. Three polymeric additives were tested and compared to control samples. These are polyethyleneimine (PEI), polyallylamine hydrochloride (PALAM), and poly(acrylamide-co-diallyldimethylammonium chloride) (PAMALAM). Two sets of experiments were carried out: long term (0-72 h) and short term (0-8 h). There is a strong dependence of silica inhibition on additive dosage. The optimum dosages are 10 ppm for PEI, 20 ppm for PALAM, and 80-100 ppm for PAMALAM. PEI (at 10 ppm dosage) reaches 55% inhibitory efficiency at 24 h (defined as reactive silica in ppm at the time of measurement divided by 500 ppm, or multiplied by 100 for % efficiency). PALAM shows 65% inhibitory activity at 20 ppm, after 24 h. PAMALAM at 80 ppm dosage exhibits 60% inhibition. Inhibitory activity is reduced upon longer silicate polymerization times (48 and 72 h). Inhibition within the first 8 h is efficient with all three inhibitors exhibiting small differences in performance. There is similar to 130 ppm silicate stabilization over the control after 72 h of polymerization. These inhibitors present potential for water treatment applications.