Effect of desulfurized gypsum whiskers on the adsorption performances of red mud-based ceramsites for lead ion

In order to realize the reutilization of industrial waste red mud and desulfurized gypsum whiskers, a novel ceramsite was fabricated using red mud and desulfurized gypsum whiskers for the adsorption of Pb(II). The study investigated the impact of red mud / desulfurized gypsum whiskers mass ratio, coupling agent dosages and calcination temperature on the Pb(II) adsorption by desulfurized gypsum whiskers modified red mud ceramsites. The resulted optimum factor was the mass ratio of red mud / desulfurized gypsum whiskers as 2:1 with silane-coupling agent dosage as 0.1% at 900 °C, and the maximum absorption capacity of Pb(II) reached 173 mg.g⁻¹ (at 298 K). Sintering process made red mud and desulfurized gypsum whiskers adhere evenly and closely, inducing the spilling out of crystal water to form porous structures favorable for the adsorption of Pb(II). The adsorption performance of Pb(II) onto red mud-based ceramsites followed the second order kinetics model and the isothermal adsorption curve conformed to Langmuir model. The changes of thermodynamic parameters indicated that the adsorption process was feasible, spontaneous and endothermic. The adsorption process includes ion exchange (53.0%), electrostatic attraction, surface precipitation and physical adsorption. In brief, the fabricated ceramsites were clarified to be a promising candidate as an effective and economical adsorbent for Pb(II) removal, making it prospective in simultaneous resources-utilization of many solid wastes and treatment of heavy-metal contaminated water.