RESUMEN
In the present investigation thermal treatment of galvanizing waste with clay and fly ash has been carried out to immobilize Cr, Zn, Cu and other metals of the waste at temperature range 850 degrees C to 950 degrees C. Leaching of the metals from the waste and solidified product was analyzed using toxic characteristic leaching procedure (TCLP). Results indicated that the composition of waste and clay treatment temperature are the key factors in determining the stability of solidified product. After heating at 950 degrees C, the solidified specimens of 10% waste with clay have shown comparatively a high compressive strength and less water absorption. However, a decrease in compressive strength and increase in water absorption were noticed after addition of 15% of waste with clay. The leachability of all the metals present in the waste was found to reduce considerably with the increase of treatment temperature. In the case of Cr and Zn, their leachabilty was found at unacceptable levels from the treated product obtained after heating at 850 degrees C However, their leachability was reduced significantly within an acceptable level after treatment at 950 degrees C. The thermal treatment has shown an increase of re-oxidation trend of Cr (III) to Cr (VI) up to 900 degrees C of heating and this trend became almost zero after heating at 950 degrees C. Addition of fly ash did not show any improvement in strength, durability and leachability of metals from the thermally treated product. X-ray diffraction (XRD) analysis of the product confirmed the presence of mixed phases of oxides of toxic metals.
Asunto(s)
Silicatos de Aluminio/química , Carbono/química , Residuos Industriales , Metales Pesados/química , Material Particulado/química , Eliminación de Residuos/métodos , Cromo/química , Arcilla , Ceniza del Carbón , Fuerza Compresiva , Cobre/química , Calor , Metales Pesados/aislamiento & purificación , Solubilidad , Difracción de Rayos X , Zinc/químicaRESUMEN
Waste generated from galvanizing and metal finishing processes is considered to be a hazardous due to the presence of toxic metals like Pb, Cu, Cr, Zn, etc. Thermal treatment of such types of wastes in the presence of clay and fly ash can immobilizes their toxic metals to a maximum level. After treatment solidified mass can be utilized in construction or disposed off through land fillings without susceptibility of re-mobilization of toxic metals. In the present investigation locally available clay and fly ash of particular thermal power plant were used as additives for thermal treatment of both of the wastes in their different proportions at 850, 900 and 950 degrees C. Observed results indicated that heating temperature to be a key factor in the immobilization of toxic metals of the waste. It was noticed that the leachability of metals of the waste reduces to a negligible level after heating at 950 degrees C. Thermally treated solidified specimen of 10% waste and remaining clay have shown comparatively a higher compressive strength than clay fired bricks used in building construction. Though, thermally heated specimens made of galvanizing waste have shown much better strength than specimen made of metal finishing waste. The lechability of toxic metals like Cr, Cu, Pb and Zn became far below from their regulatory threshold after heating at 950 degrees C. Addition of fly ash did not show any improvement either in engineering property or in leachability of metals from the solidified mass. X-ray diffraction (XRD) analysis of the solidified product confirmed the presence of mixed phases of oxides of metals.
Asunto(s)
Silicatos de Aluminio/química , Carbono/química , Calor , Residuos Industriales , Metales Pesados/química , Material Particulado/química , Arcilla , Ceniza del Carbón , Fuerza Compresiva , Residuos Peligrosos , Ensayo de Materiales , Agua/análisis , Difracción de Rayos XRESUMEN
Thermal treatment of metal finishing waste with locally available clay, in their varying ratios, was carried out at 850 degrees C and above temperatures. In the presence of 1:1 ratio of waste and clay a solidified product was obtained at 950 degrees C. Measurement of an appreciably high compressive strength, approximately 500 kg cm(-2) and a very small (0.4%) water absorption from the solidified product indicated its stable nature. Toxicity Characteristic Leaching Procedure (TCLP) test of the waste showed nearly 85 to 90% decrease of leaching of Fe, Cu, Ni, Zn, Mn and Cr after thermal treatment compared to their leaching without treatment. No hexavalent chromium (Cr(VI)) was observed from the leachate of the solidified product. This indicates the absence of re-oxidation phenomena of chromium during thermal treatment up to 950 degrees C. X - ray diffraction (XRD) of solidified product indicated the presence of hematite, and aluminum silicate as main phases of the solidified product. Involvement of the above waste metals with these phases during thermal treatment could be the reason for their immobilization.