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Types os Wastes
In the labouring of a processing plant or a quarry the inevitable production of wastes is always inherent to all the industrial process. The wastes produced can be divided in two great groups, the resultants directly from the activity (inert wastes without commercial value) and wastes resulting from the equipments and subsidiary materials, essential to the development of the activity.
In the industry of the ornamental stone are generated wastes that are common to several operations (called non specific since they are result from “subsidiary” proceedings); metal wastes, used tires, used oils, etc. The table bellow synthesizes for each area the wastes originated in a processing plant.
Wastes generated in a processing plant
The figure bellow represents the circuit of the main wastes (mud and stone waste) in the extraction and processing phases of the ornamental stone industrial process.
Layout of the main waste production in the extraction and processing phases
In what respects to the waste management it’s possible to present the most usual waste management procedures for each type of waste produced in the sector of the natural stone:
Rock without ornamental value
Corresponds usually to a great volume of stone that is extracted from the quarries and that does not fulfill the necessary parameters to go trough the rest of the process as ornamental stone. These wastes (rock without ornamental value) are the result of the normal extraction process since in the quarries from all the extracted material only about 20% to 30% are capable to be used in the ornamental stone industry. The rest of the material, 70% to 80%, is stored in huge landfills near the quarries (or smaller landfills in the processing plants).
This stone is considered as a waste by the European Waste List although in certain situations it can be considered has a raw material for other uses namely the processing of aggregates (on a crusher plant) or in the construction (has armor stone).
By the volumes that are involved this can be considered the main waste produced in the quarries, and the one that nowadays represents the most difficult management problems.
In the processing plants the quantities of this waste are not so evident although its management is the same.
Used oils and lubricants
This waste has its origin from the regular inspection to the machines, equipments and vehicles and is a liquid waste. The used oils are one of the most significant wastes produced in this sector in what respects to potential environmental impacts this leads to a management that has to be necessarily very exigent (we must also consider that the European legislation is very rigid in what respects to the used oils). This waste must be stored in the exploitation place (processing plant or quarry) during the industrial process, under special conditions in order to prevent potential spill over the soils, natural drainage system, etc.
The enterprises must store this waste only temporarily and under special conditions (in stanching cans over decanting basins) and when a certain volume is stored deliver the used oils to a specialized enterprise that collect them and take it to the appropriate treatment.
The European law obliges also the enterprises to have a regular and rigorous register of the oil quantities that is used and stored.
This waste is originated in the regular inspection of the vehicles and like the other dangerous wastes should be stored (only temporarily) under special conditions until the collection from a specialized enterprise to their final treatment.
These wastes are related with all the metallic items resulting from the exploitation and processing of the natural stone such as old cutting disks, wire, machines and pieces of machines out of use, old vehicles, etc..
This is a solid waste that should be temporarily stored in a non permeable place until its collection by an enterprise specialized in the treatment of this kind of materials.
This waste occurs both in the quarries and in the processing plants as a result from the regular maintaining of the mobile machinery. The used tires must be stored while in the exploitation site in an impermeable place (it’s possible to be the same place as for the metallic wastes). This storage must be only temporary and the wastes delivered to a specialized enterprise for their final treatment (recycling, reuse, etc.).
Paints, resins, etc.
This waste is referred to the raw material that is not used anymore in the industrial process and should follow the management process of the other wastes – stored temporarily in a protected and reserved place until the collection from a specialized enterprise for their final treatment. These industrial wastes due to their dangerousness should never be putted together with other types of wastes like for instance the urban wastes, and must follow a specific treatment that only specialized enterprises can assure.
Although there are some similarities the wastes produced in a processing plant have their own particularities, namely considering the most significant – stone mud.
Some of the natural stone transformation factories carry out pre-treatment actions before dumping the waste:
a) Disposal of solid rubble and transport to the dump site.
b) Piping of the liquid effluent to decanting tanks to recover the clean water to be circulated back to the cutting/machining devices for refrigeration, dragging, washing, etc.
c) After decanting then pumping the remaining phase, which is rich in sediment through filtering presses, obtaining wet lumps with an approximate content of 20% of water.
d) Transportation of this material to the dump site.
The slurry dragged by the water previously circulating through the process circuits is a low density mud. To recover the water it is homogenised in a tank by means of a stirring device and then sent to a filter using a volumetric pump. This filter works by the principle of mechanic filtering between two framed cloths that are compressed one against the other over guiding rolls. The pressure made by the cloths and the subsequent compression of the mud is obtained by means of a pneumatic piston with pressure regulators. The filtering cycle is automatic and commanded by control device and level sensors in the stirring tank. The filter output is a mud with a 80% maximum concentration of dry waste, well enough to be easily handled for loading and transportation by conventional means.
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