Mineral Dust Exposure: Environmental Effects, Properties, Equipment Failures & Safety Standards

Drilling, crushing, and other mechanical processing of rocks and minerals inevitably generate mineral dust, which has a negative impact on both the environment and human health. To mitigate its effects on human life and industrial operations, mineral dust regulation has been introduced, requiring the implementation of specialized cleaning systems to meet these standards.

The mineral dust composition depends on the source materials from which it is generated. Silicon and aluminum oxides typically make up the bulk of the mass, while magnesium, calcium, iron, potassium, clay minerals, sulfides, feldspars, and carbonates can also be part of the chemical composition of mineral dust.

For example, the crusher dust mineral content typically includes quartz, feldspars, mica, and carbonates, along with iron sulfides, copper sulfides, or aluminum oxides, depending on the type of material being crushed (such as granite, limestone, or ore).

While the rock dust mineral content includes feldspars and quartz with a small admixture of mica and pyroxenes (for granite), or calcite with a small percentage of quartz (for limestone).

Fine inorganic particles are highly hard and abrasive, whereas clay-based materials tend to adhere in humid environments. Taken together, these properties create significant challenges for any cleaning system, as they must be addressed simultaneously. Moreover, hazardous components such as heavy metals, asbestos, crystalline silica, and other harmful rock dust trace minerals must be reduced to near-zero levels.

The mineral dust size distribution ranges from coarse particles larger than 100 microns, which settle quickly under gravity, down to submicron particles smaller than 1 micron that move randomly in the air and pose the greatest inhalation hazard.

Some inorganic particulate matters tend to clump upon absorbing water vapor; they rapidly clog filters and require special preventative measures. The highest mineral dust hygroscopicity is characteristic of soluble salts such as carnallite, halite, sylvite, and sodium and potassium nitrates. Clay minerals like kaolinite, halloysite, and montmorillonite, as well as diatomite and opoka, also exhibit increased hygroscopicity.

The primary health effects of mineral dusts lie in their ability to cause connective tissue growth in the lungs. Crystalline silica, fine and long asbestos fibers, coal solids, talc, kaolin, and graphite are considered the most hazardous.

To select an effective air purification system, it is first necessary to establish the mineral dust definition, its characteristics, and the limitations of certain devices. For example, if the particles tend to clump together, a wet scrubber is contraindicated.

The effects of mineral dusts on equipment operation are significant, so maintaining clean air in the work area is essential. Bearings and gearboxes are particularly vulnerable. Small abrasive particles, especially quartz, mix with bearing lubricant, turning it into an abrasive paste. This results in ball and roller raceway pitting, increased play, overheating, and seizure of the bearing, often accompanied by a metallic grinding sound during rotation.
Settling on conveyor drive and idler pulleys, small particles disrupt belt adhesion. With constant abrasive action on the rubber conveyor lining, they can cause tearing. If particulate matter accumulates between the screw and the conveyor chute, it can lead to motor overload, shaft twisting, or extrusion of end bearing seals. There is also a risk of insulation breakdown, which can be caused by the deposition of graphite and metal particles on windings and commutator plates, as they form conductive bridges.

Impurities clogging is a problem for both pneumatic equipment (valves, compressors) and hydraulic equipment (pumps, distributors). In both cases, it causes jamming and blockages, which reduce performance and lead to premature wear. For control and measuring instruments, fine particles are dangerous because they cause a loss of accuracy, which negatively impacts the operation of the entire process control system.

Given the toxic potential of mineral dusts, the following requirements have been introduced to regulate permissible exposure limits. Special attention is paid to silicon dioxide concentrations due to their high risk to human health, as they cause silicosis. For this concentration, OSHA has set a threshold of 0.05 mg/m³ over an eight-hour work shift.

For other types of inorganic solids, particle size-specific limits have been established:

• for the fine (respirable) fraction – 5 mg/m³;
• for the remaining fraction – 15 mg/m³.

Violations of these standards are subject to fines, the amount of which depends on the severity of the violation, the number of non-compliance items identified, the facility's history of previous inspections, and the category of the violation (serious or repeat).

Fines are not the only enforcement measure. Failure to correct the violations within the timeframe specified by the supervisory authority will result in more severe penalties. A company may also be placed on probation, during which its activities are strictly monitored, and any new violations occurring in this period will result in the harshest possible punishment.

Criminal charges may be brought not for accidentally exceeding standards, but for intentional violations. For example, at the federal level, a deliberate violation of standards resulting in death carries a prison sentence of up to six months, and a repeat violation carries a prison sentence of up to one year.

Penalties can be avoided by reducing inorganic particulate matter concentrations to acceptable levels using an effective aspiration system and continuous monitoring. For example, dust control in big mineral crushing plants requires a comprehensive system to capture dust generated at all stages of processing large volumes of rock, from primary crushing to finished product loading. The main component of such a system is an industrial aspiration system with intelligent monitoring. Additional measures include spraying water mist above crushers or conveyors, sealing transfer points, and ensuring personnel protection through the use of personal protective equipment.

However, standards require not just installing filters, but also proving their effectiveness. This requires the use of outlet monitoring sensors and SCADA systems that enable reporting to regulatory authorities.

The most widespread dust mineral use is for soil remineralization and crop yield enhancement. This is explained by the fact that, when crushed, silicate rocks become a source of a wide range of trace elements that are lacking in arable land, as they are eventually washed out of the soil.

In metallurgy, rock dust mineral powder is used to produce zinc oxide, which is used in zinc smelters, while the iron-containing residue is used as an additive to blast furnace charge or sent to cement production.

The most valuable type of particulate matter used in construction is microsilica. When added to cement, it fills voids, increasing the strength of concrete. Bridges, high-rise buildings, and airfield slabs are built from this mixture. Basalt waste is also used in construction, forming mineral wool from it.

Stages of use:

1. Composition analysis is performed to determine further use.
2. Mixed with binders and formed into briquettes.
3. Processed if required or mixed with other components to produce the final product.