Recycling of residual boron muds into ceramic tiles

Waste recycling has become an important issue in the environmental sustainability of mining operations. Beneficiation of borate ores produces a boron-bearing sludge, which utilization in ceramic manufacturing may lower the process energy demand. A case-study was carried out on a sludge coming from the processed ore of an evaporite located at the Tincalayu mine in the Salta province, Argentina. The use in vitrified tiles of this sludge was appraised addressing key-points in processing and product performances. The sludge was added to stoneware batches (up to 10% wt.) and tested at the laboratory scale. It consists of feldspars, quartz, illite and chlorite, plus ulexite (6.4% B2O3) that turns this sludge into a powerful flux. The waste had a minor effect during milling but allowed an improved compaction. The reactivity during firing was increased: the maximum temperature can be reduced from 1200°C down to 1140°C, according to the amount of sludge added. Stoneware tiles have a suitable technical performance, but the sludge tends to lower bulk density and increase closed porosity. Although the influence on phase composition is apparently limited, the sludge can significantly change the melt composition (enriched in boron and alkaline-earth oxides) which governs the sintering behavior. The actual amount of boron sludge recyclable in vitrified tiles is up to 5% by weight.