Elimination of dust and smells in processing natural stone

Mario Zaniboni zamar.1970@libero.it

There are many situations in which the health of the workers is at risk. The lawmakers, conscious of it, have developed regulations for protecting their health. Therefore, the employers need to follow the norms so that the labour environment is not only not dangerous, but also pleasant.
 
 
In the natural stone industry, dust is one of these elements of risk. Dust can also be dangerous for the machinery with which the workers are in contact. This dust, by the action of wind, can spread to some distance, the distance depending on the intensity and speed of the air current and weight of the solid particles, disturbing the people nearby as well as the environment, leading to collateral problems. Among the many possible situations, we highlight the formation and expansion of fine particles (PM 10) and bad odors that need to be eliminated, and also, as far as possible, reducing the heat.
 
Over the years technology has advanced a lot as a result of interest shown by many companies in solving these problems.
There are several working environments in which clouds of dust and smells are formed: mines, quarries, steel factories, cement plants, warehouses of minerals, agglomerates and coal, conveyor belts, loaders and unloaders of trucks and ships, roads for transporting, etc. Unpleasant smells are also caused and extended through the air in garbage dumps, treatment plants and contaminated places, odors that need to be neutralized.
 
In the case of closed and not too big spaces it is a good solution to use suction system that makes the air mixed with dust pass through ultra-fine filters before releasing it in the atmosphere. This is when the presence of dust is not too invasive since, on the contrary, one would have to clean the filters very often and perhaps change them if the dust is especially erosive; in fact, it seriously affects the duration of the filters.
 
Therefore, the solutions proposed by the market are based mainly on the possibility of using water that, transformed into drops, is fired against the dust particles suspended in the air. When it comes to offering their products the companies speak of micronization or micro-sprinkling; whenever the water leaks in dimensions of the order of micras, with tubes designed for this effect. They work at pressure of between 10 and 20 bars, making a distinction between “big drops”/”fine drops”. This is one of the proposals. One also talks of “cool mist”. In any case, whatever the name given to this technology, the proposal of the water drops is the same: adhere to the surface of the dust particles so that they fall to the ground by their weight, but different from “rain effect”, without wetting the floor. That is, the atmosphere gets purified, it clarifies and becomes clean.
 
All this is applicable when the dust has already appeared.
 
But preventive measures can also be taken when we come across a material that we know beforehand that will release dust. Inside the building, or even outside, one can orient the water cannons to cover them with a campaign of sprinkling that blocks the spreading of dust.
 
Logically, the producers offer their machines praising the functional aspect, highlighting the distance reached by the waterjet, the special extension that can be treated, the size of the water particles produced, and the inclination angle of the cannons. And each potential client makes his choice in accordance with the most appropriate characteristics in his case.
 
With regard to the smells, at times unhealthy, that are formed and transmitted mostly in the storage and treatment of urban solid residues, in the treatment plants, in the factories, and, in general, in contaminating places, these can be eliminated with sprinkling of water. In fact, with water one can inoculate substances capable of activating the chemical process of pulverizing of smelling molecules. Each machine destined for this type of operation is provided with accessories for the inoculation of enzymatic perfumed products or specific bacteria and, if it is necessary according to the case, also of bacteria and insectoids.
 
It is necessary to highlight that the use of pulverized water also combats the heat that is released in the process.
Till now we have spoken of materials that emit dust and of its sprinkling with water to avoid the spreading of this dust. There exists another method specifically applicable to the mining sector, developed so as to resolve in a positive manner the ecological problems and of the environment associated with the processing of dry inert materials. A system of elimination of dust has been created, by means of application on the material, before its crushing and in the interexchange of the conveyor belts, of a foam produced from the mixture of air and water with an additive. The product, that ensures the agglomeration of dust with the sand and offers the advantage of not being affected by the action of the wind and does not affect the quality of the agglomerates, is used in minimum quantities and is biodegradable. It is not necessary that the water be clean, it can even be brackish water, which allows for considerable saving in costs.
 
One must highlight the case of big crushing and classification plants such as those installed in the marble quarries,that produce diverse elements of granulometrics, till they reach the dust, starting from the residues which, some years ago were thrown in the garbage dumps of the quarry. In this case, since these are a complex of big dimensions, ought to be within the structure from which the dust cannot escape, with the clear prohibition of entering in them except in cases of emergency or when the plant is shut down and has been submitted to an intense aspiration that cleans up the internal atmosphere of the suspending dust.