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 °C). The precipitates were characterized by SEM, XRD, and XPS, and confirmed that it was calcium borate (Ca2B2O5.H2O). Pseudo-first order kinetic model fits the reaction satisfactorily. The activation energy (Ea) 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 °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 °C. Experimental results showed that precipitation process using lime was very effective and efficient to remove boron from concentrated wastewater.

Graphical abstractThe optimum dose of Ca(OH)2 was 10 g/L, at which 87% of boron was removed from both synthetic and optoelectronic wastewater at 60 °C.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A greener and more cost-effective treatment method for boron removal in which lime reacts with boron. ► Calcium borate forms under moderate temperature as confirmed by XPS and XRD. ► Calcium borate does not re-dissolve during cooling. ► The precipitation reaction rate was controlled by surface chemical reaction.