Dust is generated at aggregates exploitations (at gravel pits as well as quarries) when carrying out tasks such as blasting, loading, crushing, classifying, etc. In other words, throughout the entire process of extracting and treating the rock until the aggregate is dispatched at its final grain size, dust is released to the atmosphere.

Gregorio Ezquerra, Technical Sales Manager of Solintal

This dust is comprised of very small size elements, which based on their nature, may harm workers at the exploitation site as well as cause damage to vehicles located at the homes near the extraction centres.

Figure 1- Releasing of dust at the crushing and classification installation..

However, not all the aggregates extracted from the exploitations have silica in their composition and therefore the dust that is generated does not contain crystalline silica. Also, the percentage of silica varies greatly depending on the composition. The percentage of breathable crystalline silica in limestone is normally less than 1%, while quartzite exceeds 95%. Therefore, depending on the type of material that is extracted from an aggregate exploitation, workers will be more or less exposed to breathable crystalline silica, which could cause them (in a greater or lesser extent) to develop lung disorders. Although this is not always the case, generally aggregates originating from igneous (Volcanic and plutonic) and metamorphic rocks contain more silica than sedimentary rock and therefore, working with these types of rocks generates more breathable crystalline silica.

Figura 2- Loader moving aggregates..

What was known by many and ignored by others is now something that is completely controlled by the European Union. The recently approved European regulation on crystalline silica makes this carcinogen agent an element that needs to be considered in aggregate exploitations. The releasing into the atmosphere of dust containing a breathable fraction of crystalline silica in recent months has become a very high risk aspect in aggregate exploitations and controlling how they are handled is strictly regulated.

In the next two years, affected mining exploitations in Spain must comply with a very strict regulation that will affect workers as well as the aggregates extraction and production environment. In other words, we must also control the dust that is generated at aggregate exploitations that contaminates adjacent areas directly affecting the communities located near gravel pits and quarries.

Figure 3- Dump truck operating at an aggregates exploitation site

Currently several options are available for mitigating the dust emissions to the atmosphere. These options, applied with a certain laxity, will be of required compliance in the next two years.

Irrigation equipment and even drilling machines with dust collection equipment are available for use during drilling operations. Water cannons are available to minimise the amount of dust that is released to the atmosphere during the loading and transport operations. At the tracks, the most practical option is irrigation while at the crushing and classification plant there is the possibility of covering all the conveyor belts and also of installing an irrigation system with surface active elements on crushing equipment, at unloading areas, sieving areas, etc. To control the dust generated from aggregates that fall off (especially for the smallest aggregates) there is the possibility of installing gutters and also of using water cannons to minimise the emission of particles into the air by air currents. In addition to all these options, there is the possibility of encapsulating the entire plant and of storing the aggregates in hoppers and silos; an option that is very expensive but 100% effective.

THE TRACKS; FIRST DUST GENERATOR

Although generally all aggregate extraction tasks generate dust, one of the areas that generate dust the most is the tracks; in other words, the dirt roads used by the dump trucks to transport the material from the front of the exploitation to the crushing and classification plants. Dust can also be generated on used tracks when the transport units are transporting the material from the extraction area to the storage area or on the tracks used by the trucks for transporting the different size materials that are manufactured from their collection point under the conveyor belt to the final storage area, pending delivery to the different interested clients.

Figure 4- Dump truck with Solintal cistern irrigating the tracks.

The lengths of these tracks vary between several hundred metres long to kilometres, which usually presents a problem. These roads are wide enough for dump trucks to pass each other. With ascending and descending slopes, these roads allow the trucks to reach high speeds with the subsequent increase in the generation of dust in areas near the cut as well as in other areas near the boundaries of quarries and consequently, the neighbouring area.

As a result of the operation of these dump trucks (weighing between 70 tons empty and 250,000 kilos loaded) a large amount of rock is crushed, releasing an increasing amount of fine dust into the atmosphere.

In conclusion, controlling the dust on the tracks is one of the most important aspects of these types of operations and as such, it is mainly predominant in the summer and at those exploitation sites that are located in arid areas or in areas with a low annual precipitation.

SOLINTAL, MANUFACTURER OF CISTERNS

The wetting down of tracks and aggregates is therefore an essential and fundamental aspect of aggregate exploitations and require having transport equipment with water storage cisterns or bowsers mounted on them to mitigate the generation of dust through irrigation.

Solintal is one of the few manufacturers world wide with more than 50 years of experience designing, manufacturing and selling these types of bowsers. Solintal markets bowsers capable of holding 20,000 to 180,000 litres with internal breakwater, water cannon and sprinklers, independent irrigation pump and different finishes and treatments depending on the pH of the water.

Figure 5- Installation of a Solintal bowser on a Komatsu truck

The most striking feature of this company from Madrid is its technical department, which is focussed on devising tailor made solutions and in providing advice regarding what type of bowser to select based on the specific needs of each client. This way, Solintal provides solutions for mounting the bowsers on dump trucks from any manufacturer and with different types of irrigation devices.

Sollintal's water bowsers are capable of holding 20,000 to 180,000 litres and an internal breakwater is incorporated in all the designs to minimise the water movements inside the bowser, which could produce accidents such as tipping over the vehicle, increasing the braking distance, etc.

All bowsers are designed with two inlet fillers to facilitate filling and also incorporate two irrigation systems. On the one hand it incorporates a water cannon that is controlled from the cabin by the truck operator using a joystick. This is a very practical feature when you need to direct the water stream to specific areas such as dump sites, etc.

Figure 6 - Filling a Solintal bowser with water at an aggregate exploitation site.

The second option is the use of sprinklers. Sprinkler heads with valves installed at the rear of the bowser that are also controlled by the operator, who can decide to use all the sprinklers, the left side sprinklers, right side sprinklers or the system using a reel, all from a button panel that is located in the cabin of the dump truck.

Figure 7 - Transport of a Solintal bowser to the location where it will be installed on a rigid dump truck

From a technical perspective, to build these water bowsers, Solintal uses steels of the highest quality and proven durability as well as stainless steel piping. Additionally, this company from Madrid offers different finishes and treatments for metallic as well as ceramic materials based on the pH of the water. All the bowsers incorporate a water pump and an independent motor for the pump, which may be hydraulic or thermal diesel depending on the particular needs of each client. This design provides the possibility of continuing to irrigate with the vehicle's engine shut down. If the hydraulic option is selected, a Vickers motor is mounted and if the diesel option is selected, then the motor that is mounted is made by Kohler. The pumps for both types of actuation are Wilo-CronoNorm-NL.

The irrigation assembly incorporates a valves system that is air piloted and operated by a 24V solenoid valve for opening and closing the valves. The compressor that generates the air operates at an optimum pressure of 8 bar.

In conclusion, Solintal designs, manufactures and sells all types of bowsers that can be adapted to any dump truck on the market and with specifications that meet the needs of each client based on the capacity, pH of the water, type of actuation (diesel or hydraulic), type of irrigation, etc. Solintal bowsers are a necessary option for any aggregate operation that will help comply with current regulations regarding the emission of crystalline silica particles to the atmosphere.