Environmental Aspects on the Use of Bayer's Process Bauxite Residue in the Production of Ceramics

Abstract

Bauxite Residue (BR) is the main waste generated during the alumina-producing Bayer process. With the aim to utilize BR in the production of traditional ceramics, the potential impact such a use might have on the leaching behaviour and radioactivity levels of the final products was investigated. Leaching behaviour of Cr, Ni and V on calcined BR was studied according to the maximal availability test, NEN 7341. Firing atmosphere, firing temperature and soaking time were the investigated parameters. Results demonstrate that the soluble fraction of Cr is higher for oxidizing atmosphere whereas the soluble fraction of V and Ni increases for inert and reducing atmosphere, respectively. For assessing radioactivity, the activity concentrations of 226Ra, 40K, and 232Th were determined by means of gamma ray spectroscopy. For an excess gamma dose less than 1mSv/a, the maximum quantity of BR that can be introduced replacing the raw materials ranges from 14wt.% up to 100wt.%, depending on the type of product and the extent of use in the dwelling.

The role of nano-perovskite in the negligible thorium release in seawater from Greek bauxite residue (red mud)

“…Thus, V appears to be the most mobile element, perhaps due to its major association with rather soluble phases. This is in accordance with previous leaching NEN7341 tests concerning BR calcined in inert and reducing atmosphere 11 , as well as in good agreement with recent studies about V in Hungarian BR 1 7 . According to the latter studies, presenting X-ray absorption near-edge structure (XANES) spectroscopic data of vanadium (V K -edge), V in Hungarian BR is pentavalent associated with a Ca-Al-hydroxysilicate phase, corresponding to “hydrogarnet”-type phase.…”

“…As per previous regulations, the plant was allowed to pump the BR directly to the bottom of the sea, at the depth of >100 m. Since 2007, this practice has gradually ceased and through substantial investments (i.e., four filter presses to deliver a semi-dry cake, a new disposal area, a number of research projects for valorization trajectories and more) BR is currently industrially utilized in cement production, with ongoing efforts in the area of ceramics and metallurgy e.g. 11 12 13 . Due to the former disposal practice, millions of metric tones of BR are still remaining on the sea bed of the Antikyra bay e.g.…”

“…Previous studies have been carried out to elucidate the basic chemical composition and distribution of the discharged BR onto the bottom of sea e.g. 14 15 and to address the issue of the nature of actinides in BR 11 12 . Claims on elevated radioactivity, mainly due to 232 Th-series, and potential release of radionuclides in the environment of the Antikyra Bay were also indicated 16 17 18 .…”

“…The fact that Th, which is primarily present in the minerals of the initial bauxite ore e.g. 27 28 , is subsequently transferred into BR through the Bayer process 11 12 , puts forward the claim that the deep knowledge about the localization of this actinide is mandatory, due to its environmental concern in the mining and metallurgical industry. However, the exact nature of this actinide element in the above natural (parent bauxite) and synthetic (bauxite metallurgical residue/BR) materials has been rather unknown, until the present paper.…”

Effect of firing atmosphere and soaking time on heavy clay ceramics with addition of Bayer's process bauxite residue

“…2,8,9 and being safe for the humans and the environment. [10][11][12] Previous results 2,9 have demonstrated that the addition of up to 30 wt-%BR in a Greek clay mixture suitable for heavy clay production, results in ceramics with slightly inferior or comparable physical and mechanical properties. For a higher addition, there is a decline in properties.…”