Calcium Silicates as Lime Substitute

Abstract

An experimental study has been carried out of the removal of iron from solutions of ferric chloride by lime, beta-dicalcium silicate (C2S) and alpha-monocalcium silicate (CS) and of the treatment of the resulting sludge. C2S promoted the flocculation of iron precipitates to achieve higher settling, thickening and dewatering rates. The effect of first minute settling time is especially evident that 60% and 22% of the iron respectively was removed when 0.39 g/l of C2S and 0.21 g/l of lime were applied to solutions containing 100 mg/l Fe3+. 99% and 48% of the iron respectively was removed in the first two minutes of settling period when 3.90 g/l of C2S and 2.10 g/l of lime were applied to solutions containing 1000 mg/l Fe3+. Zone settling and thickening of the iron flocs below a sludge blanket formed were observed and zone settling velocities were determined as 4.6 and 3.7 cm/minute for C2S and lime, respectively. When C2S was used as precipitant for different iron concentrations i.e. 10, 100, 1000 mg/l Fe3+, the sludges produced had lower specific resistance to filtration (5.38 x 10(12), 1.75 x 10(12), 1.13 x 10(12) m/kg) than that (6.77 x 10(12), 5.76 x 10(12), 3.98 x 10(12) m/kg) when lime was used, respectively. C2S treatment significantly increased the filter yield hence reduced the size of the dewatering plant.