Removal of dissolved silica from industrial waters using inorganic ion exchangers

Abstract

Dissolved silica is ubiquitous in impaired waters, a fouling agent in desalination membranes, resistant to existing antiscalants, and difficult to remove from power plant feed waters, thereby inhibiting long term reuse of industrial water. Herein we report a systematic materials study of an inorganic anion exchanger, hydrotalcite (HTC, (Mg6Al2(OH)16(CO3)•4H2O)), for the highly selective removal of silica from aqueous solutions. HTCs exist in two different forms: crystalline uncalcined and calcined (550°C) phases. Variables studied in ion-exchange studies include pH, HTC concentration, duration and selectivity with competing anions. Results indicate calcined HTC effectively removes silicate anion from different waters including simulated concentrated cooling tower water (CCTW), and waters with high concentration of competing ions, such as SO42− and Cl−. The non-optimized HTC can be easily regenerated and recycled. Calcined HTC has a silica adsorption capacity of 45mg SiO2/g HTC. The single path flow through (SPFT) studies indicate that using ∼1.1g/L calcined HTC effectively removes >90% of the dissolved silica from the CCTW. A pseudo-second order kinetic model was fit the experimental data of calcined HTC. Data is supported by Fourier transform infrared (FTIR), Thermogravimetric-Mass analyses (TGA-MS), Energy dispersive spectroscopy (EDS) and powder X-ray diffraction (XRD).