Utilisation of zeolitised coal fly ash as immobilising agent of a metallurgical waste

Abstract

In the work described in this paper, partially zeolitised coal¯y ash from a Spanish power station has been studied as the immobilising agent of an arc furnace dust waste (s-WA). s-WA is a dust coming from the collecting systems of particulate material in a carbon±steel electric arc furnace (EAF). The hazardous metals normally found in this kind of waste are lead, cadmium, and chromium. In addition, the dust usually has a high zinc content resulting from the use of galvanised scrap. Because of its heavy metal content, s-WA is classi®ed as hazardous waste, according to Spanish regulations. Different zeolitisation procedures, depending on the treatment of the¯y ash with NaOH and KOH alkaline solutions, using re¯ux heating and different times of attack were tested. The zeolitised products were studied using XRD in order to characterise the solid phases produced. The solidi®-cation/stabilisation (S/S) trials of s-WA were carried out using the zeolitised ashes, as well as the original coal¯y ash, in mixtures containing 20% (w/w) of ordinary Portland cement. To evaluate the ef®ciency of the immobilisation process, some speci®c criteria were de®ned, with regard to some physical (compressive strength) and chemical (pH and metal concentrations in TCLP leachates) characterists of the S/S solids. Finally, comparisons among the stabilising mixtures were made and the role of the zeolitisation of¯y ash in the S/S process was evaluated.

Síntese e caracterização de Zeólita pura obtida a partir de cinzas volantes de carvão

“…) que são livres para se moverem nos canais da rede e podem ser trocados por outros cátions em solução (Aguiar et al, 2002;Ferreira, 1998). Essa característica faz com que as zeólitas sejam excelentes trocadores de íons.…”

“…O que dá a variedade das zeólitas existentes, portanto, é a maneira como os tetraedros se unem, associado à possível substituição de silício por vários outros elementos, e ao tipo de íon presente nos poros (Ferreira, 1998).…”

“…Outras aplicações para as zeólitas de cinzas de carvão foram testadas para o tratamento de solos e melhoria no crescimento de plantas (Ferret, 2004); na inativação de íons metálicos tóxicos ou radioativos de solos (Lin et al, 1998;Moreno et al, 2001a;Umanã, 2002;; no tratamento de drenagem ácida de mina (Moreno et al, 2001b;Fungaro e Izidoro, 2006b, Paprocki, 2009; como agente imobilizador de resíduo metalúrgico (Fernández-Pereira et al, 2002); no descoramento de óleo vegetal (Fungaro e Izidoro, 2006c); como peneiras moleculares para purificação de gás (Querol et al, 2001), adsorventes em filtros de água e ar (García, 2001), na remoção de corantes em água (Fungaro et al, 2005;Fungaro et al, 2009a;Fungaro et al, 2009b;Carvalho et al, 2010), entre outras.…”

“…As cinzas de carvão brasileiras apresentaram diferentes conteúdos de ferro, que é considerado inibidor para a formação de zeólitas por não ser reativo durante a síntese (Ferret, 2004;Umaña, 2002, Ríos et al, 2009 maior é a capacidade de troca catiônica do material, já que para cada Si que foi substituído por um Al é gerada uma carga negativa, a qual é compensada por um cátion (Ferreira, 1998. Os valores encontrados variaram entre 0,96 e 1,34.…”

Physical, chemical and mineralogical characterisation of hydraulically disposed fine coal ash from SASOL Synfuels

“…The coal combustion process yields vast quantities of fly ash, the majority of which is disposed of either in dry or slurry form. Environmentalists and the public have a concern about coal ash despite its utilisation applications which include addition in cement and concrete manufacturing, agriculture, and waste stabilisation [1][2][3][4][5][6][7][8][9][10][11]. Furthermore, ash utilisation only consumes a small fraction of total fly ash production leaving the majority for internal disposal or landfilling.…”