ENVIRONMENTAL CERAMIC TESTS: LEACHING AND EMISSION POTENTIALS

DOMINGUEZ,E A; IGLESIAS, C; DONDI,M

Córdoba

Congreso; I Reunión Argentina de Geoquímica de la Superficie; 2009

 Growing environmental concern is promoting the necessity of testing new ceramic raw formulations before its utilization in industrial developments.  In traditional ceramic plants several laboratory studies are done before acceptating new raw material. These studies are based on the identification of physical and chemical characteristics of the clays and their responses to ceramic processes..   The use of unknown clays and new materials with potential contamination conditions requires further studies to demonstrate that the ceramic piece encapsulates the pollutant and that during its firing it does not produce the emission of unacceptable harmful volatile elements. The objective of this work was to perform both tests in a ceramic paste made with slip casting wastes and electro-plating residues. The leaching methods for determining the encapsulation of potential harmful elements are usually performed following the TCLP EP-Tox (USA EPA, 1986). There are no universally accepted laboratory methods to test the potential volatile emissions during the firing. Having precise chemical analysis of both green and fired brick pieces, the problem of the losses during the firing can be solved by the gain/losses techniques used in geological studies (Lindgren, 1900; Domínguez y Ullman, 1996). In particular it is useful the Isocon method that permits a quick visualization of the lost elements (Gresens, 1967; Grant, 1982). Once the volatile elements had been determined their amount can be additionally calculated with the method proposed by Fabbri and Dondi (1995) or with an adaptation using the crude/fired brick ratio densities. The leaching test was performed using the TCLP EP-Tox norm. A brick piece was previously crushed to obtain particles smaller than 9.5 mm so as to reach the worst weathering conditions.  The chemical analyses were carried out at Argentina Alexander Stewart Laboratories (Protocol M0720929). The leaching tests indicate that the ceramic brick does not produce harmful leachates according with the Argentinean specifications. The leachates of B and Ca are high. Ca does not seem a problem while the B content is beyond the permitted contents for aquatic life protection and also higher than animal drinking standards.  It is suggested that a lower leaching content would be achieved bathing the brick after its firing in a diluted acid solution. To identify samples with volatile elements, a green and fired brick were used. Accurate and complete chemical analyses were done at ACTLABS-Canada (Protocol A08-3775). The fired brick has a density of 1.818 g/cm3 whereas the green has one of 1.726 g/cm3. The fired brick has a water absorption of 9.9%. Volatilized elements are silver, bromine, mercury, sulfur, selenium, fluoride and chlorine plus water. The loss of water during firing is in the usual range and the emissions of Ag, Br, and Se are so low that are practically inexistent. For F and Cl the liberation of 100 mg/kg is in the lower ranks of the European reported data. In the case of S, the emitted amount is among  the highest published. Since industrial emissions are measured on the chimney gases, the extrapolation of laboratory data is only possible with the assumption that the volume of air needed for firing a brick is 2.5 to 5 Nm3/kg. (Bouscaren 1993). Considering an air volume of 2.5 Nm3/kg, emission rates were found to be of 1040 for S, and 40 for both F and Cl, which fall within the safe reported amounts.  It has been found that emissions are minimal and environmentally acceptable. References Fabbri, B y Dondi M (1995) Caratteristiche e Difetti del Laterizio. Gruppo Editoriale Faenza Editrice- Italia. Grant, J A (1976) The Isocon Diagram – A Simple solution to Gresens´ Equation for Metasomatic Alteration. Economic Geology Vol 81 pp 1976-1982. Domínguez, E A and Ullman R (1996) ¨Ecological bricks “ made with clays and steel dust pollutants. Applied Clay Science 11, 237-249. Kemp J F (1949) A Handboock of Rocks. FF Grout ( Editor) Van Nostrand, New York 300pp Lindgren W (1900) Metasomatic  Processes in Fissure Veins. Trans. Amer. Inst. Mining Eng. V 30,pp 579-692. Bouscaren R (1993) Atmospheric pollution in brick and tile production. Tile and Brick Int 9,6, pp 364-367. Gresens R L (1967) Composition-volume relationships of metasomatism. Chemical Geology v 2 pp 47-55.