Treatment of boron-containing optoelectronic wastewater by precipitation process

A greener and more cost-effective process was studied for boron removal from synthetic and optoelectronic wastewater by precipitation with lime (Ca(OH)(2)) under moderate temperature (45-80 degrees C). The precipitates were characterized by SEM, XRD, and XPS, and confirmed that it was calcium borate (Ca2B2O5 center dot H2O). Pseudo-first order kinetic model fits the reaction satisfactorily. The activation energy (E-a) of the reaction was 45.1 kJ/mol, implying that the reaction rate was controlled by surface chemical reaction. The calcium borate precipitate formed at 60 degrees C was cooled to room temperature gradually and no re-dissolution of boron was found, indicating that calcium borate was a stable compound. Boron removal in both synthetic wastewater and optoelectronic wastewater increased with increasing pH and stabilized at equilibrium pH of 12.4 +/- 0.1. The optimum dose of Ca(OH)(2) was 10 g/L, at which 87% of boron was removed at 60 degrees C. Experimental results showed that precipitation process using lime was very effective and efficient to remove boron from concentrated wastewater. (C) 2011 Elsevier B.V. All rights reserved.