The potential recycling of boron sludges in ceramic tiles

DOMINGUEZ EDUARDO; C. IGLESIAS; ZANELLI, C.; DONDI, M.

PLINIUS

Società Italiana di Mineralogia e Petrologia (SIMP)

Lugar: Milán; Año: 2016 p. 680 - 680

1120-317X

Residues from beneficiation of borate ores have been extensively investigated in the world in the last decade. The recycled of boron-containing waste has been assessed in the clay bricks, ceramic tiles, as well as ceramic frits and glazes. All these studies agree about the technological feasibility of the utilization of borate residues, though with different amounts depending on the end-use. Such recommended percentages of waste are higher in clay bricks (< 30%) than in ceramic tiles (< 8%) and glazes (< 5%). The clay bricks can tolerate an amount of B2O3 widely spanning from around 1 to 5-6%. In the case of glazes, this percentage seems to be < 1%. The objective if this study was aimed at appraising the re-use of boron sludge, coming from Argentinian production factories, in porcelain stoneware tiles, addressing key-points in processing and product performance. The rationale consists in adding different waste amounts (2-5-10% wt.), then testing their technological behavior at the laboratory scale ad finally characterizing semi-finished and finished products in order to assess technological feasibility. The batches were designed by two different strategies: adding boron wase in replacement of ball clay in an ?Argentinian-style formation? and in replacement of sodic feldspar in an ?Italian-style body?. Argentina has an important boron production with a yearly output of 170.000 tn of borax and boric acid compounds. The waste sludge comes from the Tincalayu mine located at the western end of Salar del Hombre Muerto in the Salta province. The waste was taken directly during a routine industrial processing day; it came from the boric acid obtained after a hot water leaching for the borax solubilization. The waste sludge is composed by quartz (~ 20% wt.), plagioclase (~ 50% wt.), boro-muscovite (~ 20% wt.) and borates (~ 10% wt.). The percentage of iron oxide higher (~ 3%) and the relatively low loss an ignition (~ 11%) are the further features peculiar of the boron sludge. While the amount of iron is a limitation for its use in the white firing bodies, the latter is undoubtedly an advantage for its utilization in vitrification tiles. Boro sludge is characterized by a very strong ceramic flux and nearly 600°C below than a typical fluxes used in porcelain stoneware tiles. The boro sludge recycling is possible in the ceramic industrial practice only if a careful and controlled industrial deposition is done. During some steps of the conventional technological process such as milling and shaping, a slight reduction of the powder moisture, a fluctuation of expansion after pressing (i.e., 0.3-0.6 cm/m) and improved compaction (bulk density of dry bodies increased for addition over 2% of waste) were detected. Moreover, the waste implies an increase of reactivity: the firing temperature can be reduced according to the amount of waste added.