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Cleaner production of soapstone in the Ouro Preto region of Brazil: a case study

Rodrigues, M.L.M., Lima, R.M.F.
Journal of cleaner production 2012 v.32 pp. 149-156
X-radiation, case studies, chemical composition, environmental impact, home furnishings, hydrochloric acid, insecticides, leaching, magnetic separation, packaging, pulp and paper industry, rocks, sieving, spectroscopy, Brazil
Soapstone is a metamorphic rock that is used for ornamental and construction purposes. Rock recovery during the exploitation process is low. Quarries in the state of Minas Gerais in Brazil sell small and low-quality blocks to artisans, who produce pans and souvenirs. This activity constitutes the main economic activity in several places within the Ouro Preto region, such as Santa Rita. Soapstone artisan workshops produce a large quantity of powder (approximately 10–15% rock recovery), which is discarded carelessly, often causing environmental problems. The objective of this study was to characterise and purify soapstone powder from the workshop of an artisan who works exclusively with rocks from Bandeiras-Santa Rita de Ouro Preto in order to identify potential applications for the residues and purified products. First, the mineralogical composition was determined by X-ray diffractometry, the size distribution was determined by sieving and the chemical composition of the residue was determined by inductively coupled plasma–optical emission spectroscopy (ICP-OES). Next, purification tests were performed by magnetic separation for fraction sizes larger than 74 μm. Fraction sizes smaller than 74 μm were purified by flotation and leaching with hydrochloric acid. This research shows that it is possible to recover almost all residues of both small and large size distributions for use as insecticide filler. In addition, it is possible to recover 100% and 96% of fraction sizes larger and smaller than 74 μm, respectively, for use in the paper industry (wallpaper and packaging). For more valuable applications, it is necessary to leach the purified material from flotation using hydrochloric acid. In addition to decreasing the environmental impact of soapstone powder discharge, it is possible for soapstone artisans to sell this powder for a profit, whether it is purified or not.