PROJECT DESCRIPTION
BACKGROUND
The Estremoz area of Portugal is well-known for its natural and ornamental stone industry, the “jewel” being marble production. This industry represents an expanding market, bringing with it great social and economic benefits. However the large amount of waste generated by the industry creates a growing environmental problem. The major concern is caused by two by-products, stone rubble from the extraction process, and “natas”, a chalky, milky waste produced during the cutting and polishing of calcareous ornamental stones. The latter is composed of a fine white dusty residue of essentially carbonated nature, (calcium carbonate, aluminium, magnesium and iron oxides) which when mixed with water create a milky slurry. It is calculated that each 1.000m3 of marble produce between 500 and 650 tons of “marble slurry”. These “dumps” create not only a visual eyesore, but cause risks of water pollution, both at surface and subterranean levels, and lead to the proliferation of insects and rodents through nests created in their midst. The beneficiaries were concerned to solve the existing environmental problem by finding viable recycling outlets for these by-products. Initial tests carried out by the Estremoz Town Council had indicated that the “nata” slurry could be recycled into an efficient material for sealing municipal dumps.Detailed studies were needed to evaluate the effectiveness and viability of this option for recycling this key industrial waste product..
OBJECTIVES
The overall purpose of the project was to resolve the environmental hazard caused by key waste by-products in the natural and ornamental stone industry, particularly stone slurry and abandoned quarries,by converting them into value-added products. The project aimed to evaluate and build on initial tests carried out on these by-products through a further series of detailed studies. These included: 1) Evaluation of the pilot test carried out on sealing the municipal dump with the marble slurry, including technical validation of the work (testing subterranean water quality, sources and levels of pollution.) 2)Geo-mechanical and Viability tests on the slurry by-product 'natas' to explore recycled usage (permeability; compacting capacity etc.) 3) The environmental recovery of a specific quarry, as a landfill or tip for building waste.
RESULTS
The project first consolidated their knowledge of the salient characteristics and possible uses of marble slurry, through comparing data from existing studies with new tests carried out with the help of LNEC, Departamento de Geotecnica-nucleo de fundaçaoes. It then quantified existing and future accumulations of the slurry waste residue and carried out detailed evaluation of the pilot usage for sealing rubbish dumps in the Estremoz area. Although, studies had shown more than 17 different possible uses, 3 of the most positive findings were to recycle “nata” in compact marble for use in paving and covering materials, as a substitute for calcium carbonate in the ceramic industry and as a medium to seal potentially hazardous rubbish dumps. A test for the latter process was carried out previously by the Estremoz local council through enclosing the urban solid waste residues in cells of hardened marble slurry on a base of compacted slurry (20cm) and covered by a slurry cap of 15 to 20 cm. The process, involved a rigorous compacting phase to reduce the volume of the residues and to increase the efficiency of the level of impermeability of the slurry. Detailed monitoring was then carried out on impermeability, compactness and the filtration and seepage of residual wastewater to subterranean supplies. The main conclusions of the studies were that the marble slurry could offer similar characteristics of impermeability and operate as a substitute for clay as a sealant medium . Secondly, given the lack of clay fields in the area, and the predicted excessive dumps of marble waste slurry, there was added pressure to consider the benefits of this usage. Thirdly, the detailed evaluation of the slurry-covered rubbish dumps carried out by the municipality test revealed the effectiveness of the slurry in terms of reducing pollutant seepage, outcrops of vermin, fire risk etc. and its viability in cost terms. The overall conclusion was that the use of “natas” marble slurry as an innovative sealant of problematic rubbish dumps, eradicated two environmental problems of industrial waste and seepage from municipal rubbish tips, as well as providing a value-added product to the stone industry. The project first consolidated their knowledge of the salient characteristics and possible uses of marble slurry, through comparing data from existing studies with new tests carried out with the help of LNEC, Departamento de Geotecnica-nucleo de fundaçaoes. It then quantified existing and future accumulations of the slurry waste residue and carried out detailed evaluation of the pilot usage for sealing rubbish dumps in the Estremoz area. Although, studies had shown more than 17 different possible uses, 3 of the most positive findings were to recycle “nata” in compact marble for use in paving and covering materials, as a substitute for calcium carbonate in the ceramic industry and as a medium to seal potentially hazardous rubbish dumps. A test for the latter process was carried out previously by the Estremoz local council through enclosing the urban solid waste residues in cells of hardened marble slurry on a base of compacted slurry (20cm) and covered by a slurry cap of 15 to 20 cm. The process, involved a rigorous compacting phase to reduce the volume of the residues and to increase the efficiency of the level of impermeability of the slurry. Detailed monitoring was then carried out on impermeability, compactness and the filtration and seepage of residual wastewater to subterranean supplies. The main conclusions of the studies were that the marble slurry could offer similar characteristics of impermeability and operate as a substitute for clay as a sealant medium . Secondly, given the lack of clay fields in the area, and the predicted excessive dumps of marble waste slurry, there was added pressure to consider the benefits of this usage. Thirdly, the detailed evaluation of the slurry-covered rubbish dumps carried out by the municipality test revealed the effectiveness of the slurry in terms of reducing pollutant seepage, outcrops of vermin, fire risk etc. and its viability in cost terms. The overall conclusion was that the use of “natas” marble slurry as an innovative sealant of problematic rubbish dumps, eradicated two environmental problems of industrial waste and seepage from municipal rubbish tips, as well as providing a value-added product to the stone industry.
