Tratamineto De Aguas Acidas

TRATAMIENTO DE RILES MINEROS ÁCIDOS POR PRECIPITACIÓN QUÍMICA Y FLOTACIÓN POR AIRE DISUELTO Luciana Cadorin, Érico Tabosa, Meise Paiva y Jorge Rubio1 Departamento de Engenharia de Minas - Laboratório de Tecnologia Mineral e Ambiental; Universidade Federal do Rio Grande do Sul Av. Bento Gonçalves, 9500 -Porto Alegre, RS, Brasil Fone: (+55) 51-3316-9479 – Fax: (+55) 51-3316-9477 1 jrubio@ufrgs.br;http://www.lapes.ufrgs.br/ltm ABSTRACT Aqueous effluents generated in mining activities (coal and metal sulfides mainly), especially the acid mine drainage (AMD), cause great environmental problems due to its high contamination potential for surface or underground water resources. AMD is often characterized by low pH values and high concentrations of toxic inorganic ions. This work summarizesalternatives to remove sulfate, molybdate and metal ions from mining effluents including neutralization, precipitation (or co-precipitation) under different reagents and pH conditions. In all cases, the solids (colloidal precipitates) generated are removed using microbubbles (DAF or dissolved air flotation). Among those ions, the removal of sulfate ions is one of the most difficult and costly processand for this reason the emphasis was posed in this element. The first alternative consisted in neutralization to precipitate hydrolysable metal ions (Me (OH)x) using lime. Should the wastewater contain Mn ions, the medium pH has to be raised up to about pH 8. No removal of sulfate is attainable with this alternative. When the effluent bears molybdate and sulfate ions (less than 1000 ppm) themethod is to remove them together using polyaluminum chloride (PAC), at pH 4.5 and at a PAC:SO4-2=7:1 mass ratio. With this alternative the Mn ions are not removed at all. The third alternative is to remove high sulfate ion concentration (>1000 ppm) and Mn ions altogether; this is possible at pH 12 (onwards whereby the pollutants are precipitated - the sulfate as ettringite) and the Mn co-precipitatedby addition of lime and aluminum salts at PAC:SO42 =2:1 mass ratio. The solids produced in all these precipitation treatments have been effectively separated by dissolved air flotation (DAF). DAF have been compared with settling and presents advantages regarding process kinetics and treated water quality. Best results were obtained at 15 m3.m-2.h-1 loading capacity yielding a residual turbidity of0,5 NTU. More, the floated solids after PAC addition might be recycled as “coagulant” or used in the cement industry because of the ettringite. Thus, it is believed that these precipitation alternatives, coupled with rapid flotation, have a great potential in the treatment of mining effluents with solids recycling and water reuse. RESUMEN Efluentes mineros (RILES), o aguas efluentes, generados enactividades mineras (carbón y sulfuros metálicos), especialmente el drenaje ácido de minas (DAM), causan grandes problemas ambientales debido al su alto potencial de contaminación de los recursos hídricos superficiales o subterráneos. Estas aguas ácidas de minas son caracterizadas por sus bajos valores de pH y elevadas concentraciones de iones inorgánicos tóxicos. Este trabajo resume lasalternativas para la eliminación de iones metálicos, sulfato y molibdato de los Riles incluyendo neutralización, precipitación (o co-precipitación) en diferentes condiciones de reactivos y pH. En todos los casos, los sólidos (precipitados coloidales) generados son removidos usando microburbujas (FAD o flotación por aire disuelto). Entre esos iones, la eliminación de los iones sulfato es uno de losprocesos más difíciles y costosos, y por esta razón el estudio fue enfocado en este elemento. La primera alternativa consistió en la neutralización para precipitar iones hidrolizables de metales (Me(OH)x) usando cal. Si los Riles contienen iones de manganeso, el pH del medio tiene que ser elevado hasta, en lo mínimo, pH 8. La eliminación de iones sulfato no es alcanzable con esta alternativa....