Effect of B2O3 on the removal of phosphate ions from an aqueous solution in borosilicate glasses

Recently, it was found by the authors of this study that glasses of a special composition have an ability to remove some hazardous ions from waste solutions. In the present study, a SiO2-B2O3-CaO-Na2O glass system has been chosen to remove phosphate ions from an aqueous solution. Several glasses with different amounts of B2O3 in the SiO2-B2O3-CaO-Na2O glass system have been prepared, and these glasses have been reacted with a solution containing 155 ppm of phosphate ions. A silica-rich layer is first formed on the glass surface by leaching Na+ and Ca2+ ions from the glass, and then the Ca2+ and PO43− ions in the solution have been uptaken on the silica-rich layer to precipitate hydroxyapatite crystals. In this manner, the phosphate ions could be removed from the solution. The efficiency of removing the phosphate ions was found to depend strongly on the B2O3 contents. With increase of B2O3 contents in the glass, more Ca2+ ions can be leach out of the glass, promotes the precipitation of hydroxyapatite. Therefore, the removal efficiency increases with increased B2O3 content. The phosphate ion removal efficiency was also sharply enhanced by increasing the surface area of the glasses and decreasing the pH of the solution.