Immobilization of Pb, Cd and Cr by Synthetic NaP1 Zeolites from Coal Bottom Ash Treated by Density Separation

Abstract

This paper describes a study of the immobilization of Pb²⁺, Cd²⁺ and Cr³⁺ by synthetic zeolites formed as a result of the hydrothermal treatment of coal bottom ash (CBA) in alkali-solution after physical separation in below 1.8 specific gravity. The majority zeolite formed at 120°C was a NaP1 species (Na₆Al₆Si₁₀O₃₂·12H₂O) showing gismondine-type appeared in large clusters of tetragonal prisms. The CBA was separated into four kinds depending on specific gravity(S); below 1.8S, 1.8–2.2S, 2.2–2.5S and above 2.5S. NaP1 zeolite could be more synthesized by using the CBA in below 1.8S. The adsorption behavior of hydrothermally treated CBA in 2M NaOH at 120°C after density separation in below 1.8S was studied with respect to Pb²⁺, Cd²⁺ and Cr³⁺ in order to consider its application to purify wastewater. The Langmuir model was found to describe the adsorption process well, offering a maximum adsorption capacity of 15.4 mg/g Pb, 12.7 mg/g Cd and 5.4 mg/g Cr.