New insights into silica scaling on RO-membranes

The polymerization of silica in hard water was investigated by using different supersaturation levels of silica at pH 7 and 8. The results indicate a kinetically stable range up to similar to 400ppm [SiO2] under the chosen conditions at pH 7, whereas no such range is present at pH 8. Additionally, polyvinylpyrrolidone and polyethers were tested for their silica inhibition capabilities. It was found that the performance is depending on molecular weight as well as dosage of the polymers, respectively. From these results, a mechanism for inhibition at pH 7 and 8 was suggested.