Adsorption Potential and Mechanism of Sludge-Based Activated Carbon Modified with Fly Ash for Removal of Heavy Metals

Abstract

The treatment of sludge has received a lot of attention due to its intractable status and potential resource value. In order to explore methods of sludge resource utilization and to reduce the harm of heavy metals in municipal sewage, this study analyzed the preparation method of a modified sludge adsorbent (MSA). Another common waste (fly ash) was added to raw domestic sludge (RDS) in a certain proportion and developed to have the ability to adsorb heavy metals through multiple steps such as drying, mixing, activation and carbonization. The adsorption performance of the modified sludge adsorbent (MSA) was verified by simulating wastewater containing Cu2+ and Cd2+, and the surface and structural properties were studied from a microscopic perspective with the aid of SEM and XRD. This study showed that the MSA was characterized by increased microporosity, an enlarged surface area and enhanced activity of functional groups, and the best performance for heavy metal adsorption was found when the RDS was mixed with fly ash at a ratio of 4:3 and a pH of 8. The highest removal rates for the heavy metals Cu2+ and Cd2+ were 99.6% and 99.7%, respectively. The adsorption kinetics and adsorption isotherms indicated that the adsorption behavior of the MSA was controlled by both physical and chemical adsorption, and the best fit of the Langmuir adsorption isotherm model revealed the predominance of monolayer adsorption. The present study is a meaningful exploration of the resource utilization of sludge and fly ash and can provide a cheaper and more effective material for addressing heavy metal pollution in domestic sewage.