Preparation and adsorption behavior of new hollow-like spherical sludge chars for methylene blue

Abstract

A new pyrolytic process was successfully used to prepare hollow-like spherical sludge chars (HSC). In the process, pre-formed cotton spheres with a low density were firstly coated by a layer of sludge paste containing ZnCl₂ to form cotton fiber@sludge spheres and then pyrolyzed at 500 °C for 2 h. The resulting HSC possessed a diameter of about 3 mm, a low density of 0.1008 g cm⁻³ and a high surface area of 1008 m² g⁻¹. The column adsorption behavior showed that the adsorption capacity and rate constant of HSC for methylene blue reached 186.4 mg g⁻¹ and 0.232 mL min⁻¹ mg⁻¹. The adsorption capacity is about 8.4 and 12 fold of the adsorption capacities of GAC (22.28 mg g⁻¹) and SC (15.26 mg g⁻¹), respectively, and the adsorption rate constant is about 1.3 fold of that of GAC and SC. The great adsorption capacity and rate constant can be considerably dependent on the special hollow-like spherical structure of HSC.