Mixed silica-alumina oxide as sorbent for dyes and metal ions removal from aqueous solutions and wastewaters

Abstract

Wastewaters containing organic and inorganic contaminants such as dyes, heavy metal ions, salts, and surfactants are considered to be a serious environmental problem in human society. Adsorption is the most popular technique for wastewater treatment. In this paper, a new mesoporous silica-alumina oxide (97% SiO2, 3% Al2O3) synthesized by pyrogenic method was proposed as a sorbent for acid (C.I. Acid Orange 7), reactive (C.I. Reactive Black 5) and direct (C.I. Direct Blue 71) dyes as well as for heavy metal (Co(II), Cu(II), Ni(II), Zn(II)) ions removal from the aqueous solutions and wastewaters. The batch method was employed. The parameters such as phases contact time (1–360 min), initial metal and dyes concentrations (10, 20, 30 mg/L), effect of hydrochloric acid concentration (0.1–6.0 M), anionic surfactant (0.1–1.0 g/L) and salt (5–20 g NaCl/L) as well as wastewater decolorization were studied. The kinetic and equilibrium studies were also performed. An equilibrium time of 1 min and >240 min was required for the adsorption of heavy metal ions and dyes onto mixed oxide, respectively. The experimental data were better fitted to the Freundlich equation than to the Langmuir one. The potentiometric titrations indicated that dyes and heavy metal ions adsorption influence the structure of electrical double layer at the mixed oxide - liquid interface which was evidenced by changes in the solid surface charge density. The results showed that the mixed oxide could be an effective adsorbent especially for heavy metal ions removal from aqueous and industrial wastewaters.