TREATMENT OF METAL INDUSTRIAL WASTEWATER BY FLY ASH AND CEMENT FIXATION By C. H. Weng, 1 and C. P, Huang, z Member, ASCE ABSTRACT: A process for the treatment of industrial wastewater containingheavy metals, using fly ash adsorption and cement fixation of the metal-laden adsorbent, was investigated. Results show that the fly ash can be an effectivemetal adsorbent, at least for Zn(II) and Cd(II) in dilute industrial wastewaters. Fly ash adsorption capacities for Zn(II) and Cd(II) were 0.27 mg/g and 0.05 mg/g, respectively. A mortar specimenprepared with 10% metal-laden fly ash showed a 56-daystrength, about the same or even greater than that of cement alone. Leachates from the fixed metal-laden fly ash, obtained by using both the ASTM and U.S. Environ- mental Protection Agency-extractionprocedure (USEPA-EP) leaching tests, ex- hibit metal concentrations lower than the drinking water standards. Compressive strength and leaching test results suggest that metal-laden fly ash can be considered for use in secondary construction materials. INTRODUCTION Heavy metal pollution is extremely pernicious because these metals are environmentally persistent and toxic. Unlike most organic pollutants, heavy metals are generally refractory and cannot be degraded or readily detoxified biologically. Safe and effective disposal of heavy-metal-containing waste- water is always a challenging task for the industries due in part to the fact that the cost-effective treatment alternatives are not readily available. In the United States, most metal-rich wastewaters are treated by the conven- tional alkaline-neutralization-precipitation (ANP) process (Peters and Ku 1985). In the ANP process, soluble metal ions are removed as insoluble metal hydroxide precipitates. This process has several disadvantages. The presence of aqueous organic ligands in wastewater can hinder metal hy- droxide precipitation, which may result in residual metal concentrations that may no longer meet the increasingly stringent effluent discharge standards (Luo et al. 1992; Peters and Ku 1987). Moreover, the disposal of metal hydroxide sludge is rather difficult due to its limited settleability and de- waterability (Peters and Ku 1987). With the selection of a proper adsorbent, the adsorption process can be a promising technique for the removal of heavy metals from wastewater streams (Huang and Elliott 1981; Huang and Wirth 1982; Huang et al. 1986; Huang and Coracioglu 1987; Tien and Huang 1987; Huang and Rhoads 1989; Huang and Hao 1989; Huang et al. 1990). These suggested adsorbents are alumina, silica, ferric oxide, and activated carbon, which generally have high metal adsorption capacity, but are expensive and difficult to be sep- arated from the wastewater after use. Fly ash, a finely divided residue from coal-burning plants, requires ulti- mate disposal. The annual production of fly ash from coal-burning power ~Doctoral Student, Dept. of Civ. Engrg., Univ. of Delaware, Newark, DE 19716. 2Distinguished Prof. of Envir. Engrg., Dept. of Civ. Engrg., Univ. of Delaware, Newark, DE 19716. (To whom correspondence should be addressed.) Note. Discussion open until May 1, 1995. To extend the closing date one month, a written request must be filed with the ASCE Manager of Journals. The manuscript for this paper was submitted for review and possible publication on November 20, 1992. This paper is part of the Journal of Environmental Engineering, Vol. 120, No. 6, November/December, 1994. 9 ISSN 0733-9372/94/0006-1470/$2.00 + $.25 per page. Paper No. 5151. 1470 Downloaded 18 Sep 2010 to 128.175.10.174. Redistribution subject to ASCE license or copyright. Visit http://www.ascelib