Fluorine, chlorine and sulphur emissions from the Andalusian ceramic industry (Spain)—Proposal for their reduction and estimation of threshold emission values

Abstract

The aims of this paper are concerned with the evaluation of F, Cl and S emissions, originated from the raw material used in Andalusian ceramic factories, which are affected by the European directive. Forty-one ceramic factories were sampled corresponding to the most important production centres in Andalusia, with production rate ranging from 30 to 400 t/day. One hundred and sixty-three samples were studied, including raw materials, extrusion moulded samples, and fire products. Concerning fluorine emission, the lower values (<208 ppm) correspond to materials with low fluorine contents and/or high carbonate content, and firing temperature ≤850 °C. High fluorine emission (208–399 ppm) occurs when initial fluorine contents are high and/or the firing temperature exceeds 900 °C, or well carbonates are lacking. Problematic values higher than the 90th percentile (389 ppm) are usually when the temperature control is not efficient (Hoffman kiln) and exceeds 850 °C. Chlorine emissions are directly related to its content in the raw material. Factories exceeding the emission 90th percentile (1141 ppm) work with raw material containing halite and low percentage of illite, being fired at temperature around 850C. Sulphur emissions will happen only when raw materials of high sulphur contents (>4600 ppm) and low calcite percentage (<15%) are used because if firing temperature is ≥850 °C the CaO can react with SO2 and form efflorescence of gypsum/anhydrite on the fired product.The following measures can be implemented in order to diminish the F emission rates: (a) an accurate temperature control, not exceeding a maximum firing temperature of 850 °C (tunnel kiln is highly recommended); (b) fix fluorine by means of common carbonates if the content in the raw material is <10%; (c) use, alternatively, loams with lesser F contents, if it is possible; (d) for special products fired at higher temperatures (∼1000 °C) solution should be focussed on installing filters in the kiln's chimneys because F emission would usually be high. Finally, to avoid chlorine emissions, raw materials without halite should be used, and if the original loam contains S, emissions can be controlled by calcite content (or additions).