Treatment of textile dye wastewater using modified silica

In this work a ‘carrier’ was selected that would separate an anionic reactive dye from aqueous solution, and would display an intense white colour and a high adsorptive capacity. In this context, a commercial, highly dispersed precipitate, Syloid® 244 silica was employed to remove C.I. Reactive Blue 19. The adsorption resulted in blue pigmentation of the silica carrier; the ensuing pigment was subjected to a comprehensive physicochemical analysis, including particle size, particle size distribution, polydispersity, tendency to form primary and secondary agglomerates and the morphology of the particle surface. It was found that a preliminary surface modification of the silica adsorbent with an NH2-silane compound was necessary. The aminosilane-modified silica could be used as a selective adsorbent in the purification of waste dye solutions; its application secured highly efficient removal of dye from solutions (in most cases over 90% and in some cases even 100%). The silica-carrier product was then used as a pigment within an exterior acrylic paint. Optimum properties were obtained using 5% silane; the ensuing pigment displayed very low polydispersity (0.030), low mean particle diameter (428 nm) and no tendency to form secondary agglomerates.