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HSE Facts and Environment

  • Health and Safety of Silica

  • Occupational Exposure Limits for Quartz and other minerals in European countries


  • Silica and Sustainable Development

       Case study on the improvement of water quality
       - Kings Lynn Norfolk Site (United Kingdom)
       Case studies on incremental restoration during the lifetime of a quarry
       - Boudeau quarry (France)
       - Snive Quarry - Robilante (Italy)



    Health & Safety Aspects of Crystalline Silica Dust Exposure

    In Brief:

    Exposure to crystalline silica (i.e. quartz, cristobalite) is ubiquitous on earth and is one of the most common occupational exposures. Prolonged overexposure to respirable particles of crystalline silica may lead to silicosis, a progressive fibrosis of the lung, which has been known for years. Although in continuous decrease, this preventable occupational disease has not yet been totally eliminated. The cases reported today are mainly inherited from the past when safety and hygiene conditions failed, but also sometimes from lack of contemporary compliance with the prescribed occupational exposure limits. Since the 80s, a suspicion of lung cancer occurrence in workers exposed to crystalline silica dust has been extensively explored, but the data accumulated remain controversial. In 1997 the International Agency for Research on Cancer, IARC, published a review of crystalline silica literature concluding that in some industrial circumstances crystalline silica inhaled at work is a human carcinogen. This has put the issue in the forefront of health authority concerns. After consideration, scientific evaluations are generally translated into preventive measures by regulatory agencies. The scientific evidence showing that the hazard related to crystalline silica dust exposure is limited to some occupational circumstances, and that the actual risk of lung cancer remains very limited in the absence of silicosis, a strict compliance with current occupational exposure limits would prevent any risk of cancer.

    In the meantime and to efficiently improve workers' health protection, EUROSIL and IMA-Europe have convinced some 15 European employers' organisations and two European workers' unions to negotiate and sign a Social Dialogue Agreement on Workers Health Protection through the Good Handling and Use of Crystalline Silica and Products Containing it.

    Through the implementation of Good Practices, the Agreement aims at improving the protection of over 2 million workers employed in the EU by the signatory sectors from exposure to respirable crystalline silica (RCS) and at enhancing compliance with EU and EU Member States' existing workers' health & safety legislation. The Agreement also aims at increasing knowledge about the potential health effects of RCS and about Good Practices.

    The text of the "Social Dialogue Agreement on Workers Health Protection through the Good Handling and Use of Crystalline Silica and Products Containing it" is (notably) available (in English, French and German) from the European Commission's social dialogue website click here, as well as the Good Practices Guide containing more than 50 different task sheets - click here.

    A special website on the Social Dialogue Agreement containing all needed information and documents is available at http://www.nepsi.eu .

     

    Safety data sheets: EUROSIL Members apply REACH (Title IV/Annex II) and ISO 11014 for the development of their safety data sheets.




    Silica and Sustainable Development


    The industrial silica industry has come very far in integrating sustainable development into its management practices. As shown in a few examples here below, the efforts achieved by the industry in terms of environmental protection during and after the lifetime of a quarry are so important that quarries are now seen as significant developers of habitat variety and biodiversity.



    Improvement of water quality

    Desacidification of a lake after quarrying
    Kings Lynn Norfolk Site (United Kingdom) - Silica sand

    A silica sand producer excavates vast quantities of sand. The resulting large holes extend below the water table and so pumps are used to facilitate dry working conditions. When the excavation ceases, the holes fill with ground water to form lakes. The sand is worked until it becomes too rich in iron to be commercially useful for glassmaking. The iron is combined with sulphides in the form of iron pyrite which, on exposure to air, undergoes oxidation to produce sulphuric acid. The water in the newly formed lakes becomes very acid with a pH of 3 or less. There is an interest in using these artificial lakes for recreational purposes, including sailing and fishing. In their untreated state, the lack of biological productivity and unattractive appearance precludes such use. Treating the lake with lime would ameliorate the situation, but only temporarily and it was highly desirable to establish a self-regulating system.

    The company has launched a research project in order to upgrade and stabilise this ecosystem. The principle is to apply a combined treatment, using lime, to raise the pH, and organic matter forming a uniform layer over the surface of the sediment. Decomposition of the organic material leads to reducing conditions, so that sulphate is converted to sulphide which is precipitated as iron sulphide. This reducing zone, situated at the sediment water interface, acts as a "chemical filter", removing sulphate as it enters the lake via the ground water. The large area of reducing sediment also prevents oxygen from coming into contact with the groundwater, thus slowing down, and eventually stopping, the production of sulphate. The organic matter also acts as a nutrient into the system and encourages primary productivity. This productivity leads to the accumulation of additional carbon, from atmospheric CO2, which is continuously added to the lake and accumulates as organic-rich sediment. Photosynthesis is effectively used to combat acidification and a new balanced pH is established.

    This principle has been applied at real size in the lake and a long-term monitoring of the effect has been put in place. So far, the results show a stabilisation of the pH and no side effect. The certitude that the ecosystem is self-sufficient and stable is not yet established. It has offered a real-size laboratory for developing a new environmental engineering technique, the interest of which extends much beyond this specific case.



  • Incremental restoration during the lifetime of a quarry

    Boudeau quarry (France) - Quartz pebbles and silica sand

    This quarry exploits a sandy-clay ore-body containing quartz pebbles (300,000 tonnes/year). The overall plan was designed in order to allow simultaneous working and restoration of the site.

    The working area is maintained at less than 4 ha and the "active area" (from clearing of vegetation through to replantation with trees) does not exceed 15 ha.

    The working is carried out in basins of limited size, about 10m deep. Once the working is completed, the basin is used to collect the clay mud resulting from the washing of the ore-body during the process. These clays progressively fill up the exploited basins. The amount of carrying water released in the basins with the mud was minimised by introducing a cyclone concentration of the mud at the outlet of the process. The water is recycled in the process.

    The complete drying of a basin occurs in 2 to 3 years, mainly through evaporation. For final restoration, the overburden material is put back in place and is eventually covered with the vegetal earth, which was carefully kept for this purpose. The final remodelling of the soil is carried out in harmony with the local topography.

    Depending on the initial vegetation on the site, it can be rapidly converted back to agricultural use (e.g. one area has already been used again for cereal production three years after starting the working), or it can be planted as a forest. Forestry research has been carried out, with the support of specialised institutions support, in order to optimise the plantation, both from ecological and forestry points of view. It resulted in the development of mixed forests of pine and chestnut trees.

    The unique aspect of this case lies mainly in the rapidity with which the site was returned to its initial use.



    Sibelco Italia S.p.A. Snive Quarry. Robilante (Italy)

    The Snive Quarry, which was opened in 1971 for the mining of a large quartzite deposit, is situated at the confluence of two secondary valleys in the province of Cuneo - "Vallone degli Agnelli" and "Vallone Brignola" - between the altitudes of 1,100 and 1,450 meters above sea level.

    The area involved covers a total of about 40 hectares.

    Sibelco Italia S.p.A. (called SIRO S.p.A. up to 31/11/1998) extracted about 40 million cubic meters of quartzite from this site which, after sorting at the nearby Robilante plant, supplied more than 50 percent of the siliceous sand required by the Italian glassworks. The product is also used in the ceramics, iron, chemical and building industries.



    The mineral deposit consists of a massive deposit of quartzite from the Permo-Triassic era (225 millions of years ago). Originally it was a huge deposit of loose sand, then, as a result of the geologic phenomena, it has been compressed in quartz rock layers between chlorite schist and dolomite limestone. The thickness of the quartzite block ranges from 70 meters (which is the average for this type of formations) up to more than 200 meters, with several material foldings.

    Chemically, at large scale the deposit is of an even quality, but at small scale it becomes quite heterogeneous. The variations in Fe2O3 and Al2O3 contents, even though they are slight, are unacceptable by glass industry and therefore it becomes necessary to activate a homogenisation process of the extracted material, starting from the quarry heaps.

    Mining is performed according to the horizontal descendant step method, starting from the top of the deposit, with subsequent steps every 15 meters on two or more floors, in order to obtain a first homogenisation directly during the loading phase and allowing immediate environmental regeneration activities in the exploited areas.

    The mining phases can be summarised as follows:

    1. Preparation of the mining area: it consists in removing inert covering minerals, the schist inside the mined seam, the contaminated quartzite, and in preparing the access paths to the benches and the regime for quarry watercourses.

    2. Drilling and mines explosion: it is an essential step for material blasting and pulverization.

    3. Material loading and transport: it consists in collecting the material from the quarry yards and in transporting it (by six trucks) to the nearby crushing installation, which reduces the extracted mineral to <40 mm fractions. Then the material reaches a silo and is sent to the downstream treatment installation, which is about 440 meters below, by means of a 2,100 meters long belt conveyor, 1,208 meters of which are in a tunnel. This conveying plant has proved to be a cost-effective solution, with successful results for the environment too. In fact, the installation, also called "stone power plant", during the braking phase produces 0.84 kWh/t, and the use of the belt conveyor eliminated the need for 30 trucks which had to drive 7 km over and over again to get to the downstream treatment plant, with consequent sound and air pollution.

    4. Landscaping of the mined out sections of the deposit and replanting initiatives for their reintegration into the surrounding landscape, by using innovative solutions and techniques to obtain best results.

    Environmental regeneration activities have so far been carried out over a total land area of about 10 ha. The interventions made are:

    - landscaping of the surface and reduction of gradients, where necessary, to between 30 and 35 degrees so to guarantee long-term stability.

    - construction of counterslope terraces to contain and control waters.

    - taking back of the agricultural soil removed during the preparation of the mining area. The soil is spread over the newly prepared surfaces so that it can be reused for growing.

    - construction of hedges or positioning of jute nets to prevent surface runoff and permit the rapid and regular replanting of land surfaces.

    - planting with herbaceous plants that can take root rapidly, even on highly siliceous soils. Various kinds of clover, grasses and barley are the most frequently used.

    - planting of indigenous tree species on the regenerated land surfaces.

    Environmental regeneration of the mined out sections of the deposit has always been based on the surrounding natural habitat, which is a typically alpine landscape whose mountain slopes are covered with forests and woodland containing beech, birch (Betula verrucosa), willow (Salix capreai), oak (Quercus pubescens and Quercus petrea), chestnut (Castanea sativa), cherry trees (Prunus avium), ash (Fraxinum excelsior), sycamore (Acer pseudoplatanus) and black alder (Alnus glutinosai) and with meadowland used as pasture, interrupted by the occasional rocky outcrop.

    The new slopes that have been created have therefore been designed to imitate alpine pastures or been replanted with thousands of specimens of the tree species listed above. The sides of the quarry in the mined out area have been reshaped so as to eliminate, where possible, the harsh horizontal outlines left by the mining terraces, and only the hardest of the rocky outcrops have been left visible.



    Although the quarry is still being mined, it is not unusual to see species of wild animal of the Maritime Alps: mammals such as foxes (Vulpes vulpes), wild boars (Sus scrofa), roe deer (Caprolus capreolus), badgers (Meles meles), weasels (Mustela nivalis), squirrels (Sciurus vulgaris), hedgehogs (Erinaceus europaeus) and the common hare (Lepus capensis); reptiles such as green lizards (Lacerta viridis), grass snakes (Natrix tassellata) and adders (Vipera aspis); and birds such as buzzards (Buteo buteo), robins (Erithacus rubecula), jays (Garrulus gladarius) and hawks (Pernis apivorus).







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