It is estimated that around 20 billion tons of raw materials are extracted annually in the world, some of which are renewable, but most of which are not. Over time, the awareness that resources are finite has become real, and their rational use, reuse and recycling is urgent.

In this dimension stone extraction and processing industry, the various production stages generate large losses, with a significant volume of waste. Although there is a concern for the environment, most of the time, waste is deposited directly in the ecosystem without any prior treatment. The sludge generated in this process is not considered a hazardous waste, but it is an environmental problem.

This industry generates several types of waste:

  • Residues from block extraction
  • Sawdust waste to fit standard dimensions
  • Waste from the sawing and polishing process

Geological resources are essential for modern life, as they are raw material for a large number of economic activities and for a reasonable number of transformation industries, increasing their importance with the development of society.

The exponential development and technological advancement of nations call into question the planet’s ability to respond to world demand, especially in terms of mineral resources, which leads to the discussion of the conflict between exponential growth and consumption of raw materials and the limits of geology.

It is estimated that over the next 30 to 35 years, in order to respond to market needs, the mining industry will have to produce a volume of resources similar to everything it has produced to date, aggravating the fact that it has not made major advances or discoveries in the sector. and the depletion of some of the large conventional deposits.

The responsible exploitation of geological resources is an important means of development, being a lever for improving the performance of the national economy. As such, it is crucial to consolidate sustainability policies and measures, promoting the circular economy, in order to contemplate in an integrated way the economic, social and environmental aspects, as well as the definition of an efficient legal and institutional framework.

The stone quarrying industry generates large volumes of waste (from natural inert materials), for example in the marble industry waste can represent 80-90% of the total soil and stone extracted.

The way these residues are treated directly affects the impacts generated in this industry, as well as the environmental performance of the materials produced.

The waste generated in the ornamental stone production industry is generated mainly in the cutting and sawing phases, which generate solid particles when cutting the stone.

The larger the cut, the more material is destroyed by the process and resource efficiency becomes less. About 5% of these particles are released into the air and the remainder is removed by the cooling water stream, which is subsequently subjected to a decantation process resulting in mud residues.

The production of significant amounts of stone dust, sludge and stone remains/shavings in the ornamental stone sector, as mentioned above, has provided a continuous study and development of new technologies and applications, not only with a view to solving environmental problems, but also to find new synergies and industrial symbioses that can promote circular economy strategies that contribute to new life cycles of new products with different characteristics and potential uses.

There are several solutions for the recovery of this waste and some industrial sectors have shown willingness to incorporate them into their production processes, as well as their reuse in the ornamental stone sector itself, namely when the remains/stone chips are reused for the manufacture of other products of different sizes and/or used in the landscaping recovery of quarries.

Several investigations have been carried out to assess the feasibility of incorporating sludge and stone remains/shavings in different types of construction materials, namely in the production of concrete, mortar, ceramic products and glass.

The use of sludge becomes more complicated in industries with more demanding specifications when the transforming units work with ornamental rocks of different nature, resulting in a mixture that is difficult to guarantee the characteristics, however, in this case they can be used in less demanding applications from the point of view chemical point of view. The use of these wastes as aggregates in road paving, filler material in civil construction works, material for foundations, binder in construction works, are examples of possible recycling solutions.

Ceramics Industry

Ceramic products have been the subject of several studies to determine the viability of incorporating granite mud as a raw material in their manufacture, being used as a substitute for feldspar, sand and some of the necessary clay minerals. Several conclusions emerged from these studies:

Use of granite mud as a substitute for pigment additives in ceramic bodies after firing. These sludges facilitate the drying phase by reducing the amount of water needed and allow reducing heating temperatures in drying and cooking operations. These products have similar or even superior technical properties to conventional products.

  • The recycling of marble waste in the production of ceramics without stoneware as raw material for its manufacture, with optimal incorporation of up to 27%.
  • It is possible to incorporate high concentrations of marble mud into ceramic compositions.
  • 30% marble mud can be added to the tile production paste, not only without reducing the properties of the final product, but also with the possibility of using lower firing temperatures.

Civil Construction – Concrete

Concrete and mortar were also studied as possible destinations for waste from the stone sector. Some of the examples are:

  • The use of marble and granite chips can replace cement (up to 30%) in the manufacture of concrete.
  • Replace 10% of cement needs with granite and marble sludge and produce quality concrete.
  • Marble slurry can be incorporated up to 20% of the total density in concrete and conventional concrete compounds to improve physical and mechanical properties.
  • Add up to 20% marble slurry and super plasticizer to conventional concrete.

Civil Construction – Mortars

In the case of mortars, it is possible to use marble mud to completely replace the CaCO3 filler in the production of plastering mortars, with the complementary function of adding color.

Civil Construction – Bricks

It is possible to replace the conventional aggregates used in the manufacture of concrete bricks with granite and marble chips and dust. Its filling capacity and distribution in the size of its grains allow a good performance in replacing conventional materials.

Bricks made from recycled waste have physical and mechanical properties that make them suitable for use in the construction sector, reaching optimal values in terms of technical and mechanical characteristics, with 10% of waste incorporation.

Landscape Decoration

Stone remains/shavings, depending on their size, can be reused for landscape restoration or decoration, for example, strategically placed to form paths.

Glass Industry

The glass industry can also recycle waste from the ornamental stone sector, marble mud can be used in the manufacture of colored glass in place of silica sand, or as filler in the molding of plastics such as PVC.

Rubber Industry

He found that marble mud can also be used as a filler for natural rubber compounds in order to reduce costs.

Farming

Granite mud is an effective alternative to traditional alkalizing correctives used in the acid neutralization of agricultural and forest soils, acting as a source of essential nutrients for plants.

Waste Treatment

Marble sludge can be added to sediment polluted with heavy metals, leading to a decrease in available metallic forms and sediment toxicity.

They can also be used as a sealing material for municipal landfills and possible waterproofing solution due to their low expansion and low permeability, low organic matter content and high safety when placed close to or under concrete structures.

Application Examples

Currently, there are cases of reuse of waste from the ornamental stone sector on the market.

One of them is Stone Paper, a combination of CaCO3 with a small amount of non-toxic polyethylene resins that act as a binder. This product reuses the minerals present in waste from the stone sector to produce a type of paper that is durable, resistant to fungus and waterproof.

But the main use of residues from the extraction of dimension stones is in civil construction and public works such as roads and dams. Civil construction incorporates, in various activities (road paving, filling material, material for foundations, bonding material), waste from the ornamental stone sector (granite and marble) as a secondary raw material, thus reducing the consumption of raw materials. natural raw material and promoting a more sustainable final destination for waste that would otherwise

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