Heavy Metals Removal on Dye – Modified Fly Ash Substrates

The fly ash is a cheap waste materials which can be an efficient substrate in wastewater treatment for the immobilization of heavy metals, mainly Cd, Pb, Ni, Zn, Cu, and for dyes removal. The use of FA for heavy metals removal, from wastewaters resulted in the dye finishing industry, faces a supplementary problem, related to the dyes affinity for oxide surfaces. Working with industrial wastewaters proved that there is a competitive adsorption process involving heavy metal cations and dyes. Still, some dyes fixed on the FA surface can act as complexion agents, increasing the adsorption efficiency of the heavy metals. The paper presents a comparative study of the efficiency obtained when modifying fly ash, by washing with ultrapure water followed by alkali treatment (NaOH 2N) and by dyes immobilization. The Pb, Zn removal efficiency on fly ash with and without dyes is investigated. The adsorption kinetic, the substrate capacities and the mechanisms are discussed correlated with the surface structure (XRD) and morphology (AFM). The results show that, fly ash with controlled surface properties allows the simultaneous removal of heavy metals and dyes, resulting waters that respect the discharge regulations. INTRODUCTION The degree of pollutants persistence in the environment varies from a few days up to several years and can affected the humans and the biota. Heavy metals, like Cd, Pb, Ni, Zn, Cu, Cr are among the most toxic pollutants, event hazardous, and can be found in waste waters, as resulting from mining, metallurgy, metal plaiting, smelting flux electrolysis, battery manufactories, petroleum refineries, paint manufacture, printing and photographic industries, etc. Most of industrial undertakings have developed small waste water treatment plants and are interested to develop various technologies targeting heavy metal removal from the wastewaters. World of Coal Ash (WOCA) Conference May 9-12, 2011, in Denver, CO, USA http://www.flyash.info/