Alum sludge as an efficient sorbent for hydrogen sulfide removal: Experimental, mechanisms and modeling studies

Abstract

This paper firstly reported a systematic study of using alum sludge (waterworks residue) for H₂S adsorption. Various trials were performed at ambient temperature in a fixed bed column to study the effects of H₂S flow rate, sorbent bed depth on the alum sludge adsorption efficiency of H₂S. The Breakthrough Curves were simulated by the Thomas model, Bed Depth Service Time model and Yoon-Nelson models. The mechanisms of H₂S adsorption onto alum sludge was examined by different physiochemical characterizations of exhausted and raw alum sludge. Moreover, the mass transfer coefficients were determined from mathematical descriptions of breakthrough curves. The alum sludge adsorption capacity was determined to be 374.2 mg of H₂S/g, slightly decreasing with the increasing flow rate and increasing with the increasing bed depth. All the three models successfully predict breakthrough curves which could be used for scaling-up purposes. The microporous structure, alkaline pH and the inherent metal species of the alum sludge promoted the formation of metal sulphate species. This study demonstrated that alum sludge could be used as cost-effective, largely available, and efficient sorbent for H₂S removal.

Keywords: Adsorption; Alum sludge; Breakthrough curves; Desulfurization; Fixed-bed reactor; Mass transfer coefficient.