Haul Mining

For as long there is mining as an economic activity dust suppression is and always will be a priority in the design and maintenance considerations of haul mining roads and as the Science Newsletter of 1936 reads ‘Respirators Cannot Take Place of Dust Control’. The transitional drive from abatement to complete elimination of inhalable and respirable dust in haul mine road applications has evolved over time. In this period, a lot of changes have occurred for the better which has been evident in more research and factually based approaches to the problem. As a result, this has led to more targeted and improved product development of dust suppressants with a shift from traditional to more non-traditional dust suppressants factoring in sustainability and eco-friendliness. The article will focus on the generation and occupational health concerns of dust in haul mine roads, the developmental history of dust suppressants over time and the pros and cons of the preferred dust suppressants used in haul mining roads.

Defining Dust

Dust is a term that refers to particles that are smaller than 10 micrometres (PM10) and are susceptible to airborne transport. The background to the problem of dust in haul mine roads revolves around the use of mining haul trucks in all surface mine operations. Transit of mining materials within or from mining premises results in haul trucks generating the majority of the dust emissions which is approximately 78% to 97% of total dust emissions. The short-term challenge posed by dust is as a safety hazard through impairing visibility of haul truck and road grader operators thus increasing the chances of accidents. Consequently, the long-term hazard to prolonged and overexposure to respirable and inhalable dust is penetration into the respiratory system and settling in the alveolar region of the lungs. Pulmonary inflammation is triggered leading to toxic responses and eventually, the condition of clinical silicosis develops. The type of dust, its concentration and duration of exposure determine whether it is acute, accelerated or chronic silicosis.

Managing Dust

Haul trucks, in general, can work at a reduced speed, watering of the haul road and treatment of haul roads with dust suppressants are some of the methods used to suppress dust. Minimizing wearing course disturbance of the haul road at low operating speeds can reduce dust but is not always ideal given targets that have to be met from a business perspective. Instead, it is imperative to focus on methods that are long-lasting and do not compromise on production. Whilst still focusing on longevity alternatives, a balance should be achieved between incentive for less repetition and considerations for durability through stabilization in attaining good dust control efficiencies. In essence, the tendency is to deviate from just one centred approach but rather a multi-purpose and cost-saving approach from the operation of the mine whilst fulfilling given operational and business targets. The oldest and most used form of dust control in haul mine roads has been watering. Comparisons between unwatered and watered dust emission rates have been assessed before. It has been shown that on a haul mine road a water truck operating once an hour achieves 40% reduction in total suspended particles. Increase in frequency of watering to every 30 minutes, improves the control efficiency of total suspended particles to 55%. Dust control efficiency of water varies on its application rate. The more L/m² the longer dust suppression duration even at a slightly lower percentage of total suspended particles. The opposite is true at a lesser L/m² application rate.

The need for more comprehensive, robust and sustainable dust control regimes led to the development of non-traditional dust suppressants as better options to traditional dust suppressants. Traditional dust suppressants/stabilising agents include fly ash, lime, cement and bitumen emulsions whereas non-traditional suppressants include salts, lignosulfonates, natural and synthetic polymers, acids, enzymes and tree resins. Some of the dust suppressants that have been developed for mine haul roads factor in a combination of dust suppression and stabilization. Introduction of traditional dust palliatives as an effective option to water was met with a lot of industry acceptance at the beginning with dust suppression results far superior. Consistency in their use without thought of the environment became one of the biggest elusive challenges which have taken years to resolve as the greater need was dust suppression which unfortunately overshadowed the burden of post dust control environmental assessment. Haul mine roads are assets and the principles of asset management stipulate the role maintenance plays through rehabilitation of the existing infrastructure with the functionality of the haul mine road to be kept at its operational best. In recent decades the need for better application performance, lower resource and energy consumption and drive for environmentally friendly products has seen the popularity of non-traditional dust suppressants.

Modern Dust Management Approaches

Product development of non-traditional dust suppressants in the modern era factors in the source, whether it is environmentally benign, water-solubility, benefits and drawbacks. Sources come in different forms with options for synthetic, by-products of production processes such as paper and timber and natural-based feedstocks. Depending on breakdown and degradation chemistry of the dust suppressant by-products some can be toxic to the environment depending on the effect of UV radiation and enzymatic action of biota in the soil. Some of the benefits to consider are ease of application with good efficiency, adaptability to wet conditions, fast action with no interruption to the mining activities, non-hygroscopic to create long-lasting protection, suitability to arid regions owing to water solubility and good water retention capacity. However, they are drawbacks which include susceptibility to thermo-oxidative aging and photo-oxidation, high costs, poor adaptability to wet conditions for some products and failure to render mechanical properties which leads to haul road poor performance.

Knowledge is Power

In the last two decades selecting the right palliative has improved remarkably with methodologies based on average daily traffic, climate, fines content and geometry. Ranking the sums of the different palliatives in addition to life cycle costs completes the process of selection. The decision to be made is based on knowledge of what the non-traditional dust suppressants offer and the key is to determine the dosage rate which is soil type dependent. Dust suppression for haul mine roads is still progressing and implementation of strict legislative and non-compromising dust control laws will complement the calls for greater health and safety rather than a temporary substitute for dust prevention.

REFERENCES

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