Simultaneous Fe(OH)3 formation and silicon adsorption removal from reverse osmosis brine wastewater

Abstract

The reduce of the silicon concentration to low level (<5 mg·L−1) from the reverse osmosis brine wastewater is challenging and desirable for the maintain the membrane life and performance, as well as the wastewater treatment costs. This work focuses on the removal of silicon from the reverse osmosis brine wastewater by adding FeCl3 into the plant wastewater for simultaneous Fe(OH)3 formation and silicon adsorption. The effects of pH, FeCl3 dosing concentration, reaction time, and temperature on the silicon removal ratio were investigated. It was demonstrated that the silicon removal ratio could reach up to 94% and its residual concentration was 3.2 mg·L−1, which met the require of water quality in the reverse osmosis system. These results showed that Fe(OH)3 could effectively be formed by adding FeCl3 and realize the efficient silicon removal from the reverse osmosis brine wastewater, even when chloride ion (Cl-), sulfate anion (SO42-) and nitrate ion (NO3-) were present. Moreover, the adsorption thermodynamics, kinetics and isotherms during the process of the adsorption of silicon from the wastewater by Fe(OH)3 were studied. The calculated adsorption capacity of silicon could reach 612.74 mg·g−1, which was much larger than those of reported adsorbents. These results showed that the silicon removal process was spontaneously exothermic and mainly controlled by the physical adsorption and the monomolecular layer adsorption. This simple and cost-effective method could be used for the silicon removal from different kinds of Si-containing wastewater.