Utilization of drinking water sludge and modified coal fly ash as adsorbents of metals and metalloids

Abstract

The presence of toxic trace metals and trace elements has drastically increased in recent decades as a consequence of industrialization and a growing demand for natural resources. These toxic metals and elements can be severely harmful to human health and to the environment in general, if they are not properly contained and treated. In the recent years, many papers on the use of low-cost adsorbents to remove toxic metals and metalloids from wastewaters have appeared in the literature. In the category of low-cost adsorbents, coal fly ash or products synthesized from it are commonly studied but drinking water sludge is much less used. This study is aiming at using waste products to clean the water stream from mine tailing ponds, and developing a new material, which is efficient, and of high performance. Fly ash, sludge and modified fly ash as low-cost adsorbents are presented in this paper and their performance for the removal of metals and metalloids from contaminated water is compared. The adsorption phenomenon could be generally modeled by Langmuir and Freundlich isotherms. Factors that can affect oxyanions (AsO43-, SeO32-, CrO42- and MoO42-) adsorption by sludge and fly ash influence the mobility of these inorganic anions in wastewater. This research attempted to compare the adsorption capacities of inorganic anions on sludge and fly ash commonly found in Canada in a tailing pond system. The effects of sample modification, pH and matrix on adsorption were studied; the adsorption kinetics and adsorption capacity if different materials and matrix were investigated. The main goal of this study is to provide some information concerning the use of industrial waste materials as adsorbents for the removal of toxic elements (inorganic anions) from mining wastewater. It is also to determine the chemical mechanisms of toxic elements in water treatment and optimize systematic parameters to be more efficient on the removal of toxic elements from water streams.