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Environmental Aspects of Ornamental Stones: Recent Developments

Ornamental StoneAn ornamental stone is a natural stone that is used for decorative purposes in construction and monumental sculpture. The utility of ornamental stone in construction arises from its aesthetic value, and the quantum of its utility depends on the purpose for which it is being used. Ornamental or decorative stones are mainly used in construction, flooring, cladding, counter tops, curbing, engraving, etc.

The dimension stone industry, though not widely known or appreciated within the mainstream mining industry, has grown at an average of over 7 per cent per annum since 1980, and is estimated to currently have a global turnover in excess of $60 billion per annum. Production technologies, particularly in the developed world, where labour costs are high, have developed rapidly over the past two decades.

Accompanied with modernisation and urbanisation, the growth in use of dimension stone products has accelerated in recent years. The major application of dimension stone is within the construction sector, which accounts for over 80 per cent of consumption as detailed below:

• Floors and paving 35%

• Steps 3%

• Internal wall cladding 9%

• External wall cladding 8%

• Special works 18%

• Structural works 7%

• Memorial art 18%

• Other uses 2%

Though the usage of ornamental stones has given a new impetus to modern life, the process of ornamental stone extraction undoubtedly has big consequences for the environment. Such an activity nowadays follows severe rules concerning the environmental impacts, which must be carefully evaluated, starting from the planning of a new quarry. The environmental degradation arising out of extraction of ornamental or dimension stone much depends on the method of mining technology adopted for their extraction. In mining dimension stone, it is necessary to split or cut the stone into successively smaller pieces until the final desired block size is achieved, and saleable blocks are produced. The mining methods utilised in the extraction of dimension stone range from relatively simple and low technology methods to some quite technologically advanced methods. In general, marble is extracted using relatively advanced non-explosive cutting technologies and is even quarried in underground situations, while granite tends to utilise more low-tech drilling and splitting technologies. Mining of slates and quartzites generally utilises the simplest technologies. They are quarried by splitting blocks or slabs from the body of the stone using drilling, and splitting with plug and feathers, or in some cases, sawing. These are then cleft along the bedding planes to produce thin sheets for paving or roofing purposes.

Environmental Impacts

Though the mining technology adopted can determine the quantum of environmental degradation it leads to, it is unrealistic to assume that it will not affect the environment. Natural and artificial stone industry generates large volume of stone waste. It is classified to various forms such as powder or fines, aggregates, larger stone pieces and cobbles, damaged blocks or slabs and stone slurry. Stone slurry is a semi-liquid substance consisting of particles originated from the sawing and polishing processes and water used to cool and lubricate the sawing and polishing machines. These generated wastes cause environmental, health and economical drawbacks.

The environmental impacts caused by the industry include soil, water, air, vegetation, landscape, ecology, noise, vibration, dust, traffic and so on. The magnitude of these effects depends on various other-associated factors. Quarrying of decorative stones in an area with vegetable coverage can lead to accelerated erosion whose consequences are not only the quick degradation of the landscape, but also pollution of surface waters and the aquifer.

The environmental impact of all works regarding excavations and trenches involves, besides landscape problems, aeromechanical stability problems of the ground, which could get even worse if the mining activity stops and a proper mould is not provided. The removal of natural barriers can cause ground changes (e.g. structure, texture, permeability, etc.) and disarrangement or, in general, the increase of dangers for the natural environment and the anthropic community.

Waste from quarry and fabrication operations can be unsafe and environmentally detrimental. When stone slurry is disposed in landfills, its water content is drastically reduced and the stone dust resulting from this, presents several environmental impacts. In dry season, the stone powder drops in the air, flies and deposits on vegetation and crop. In some cases, stone dust disposed in the riverbank and around the production facilities causes reduction in porosity and permeability of the topsoil and results in water logging. Manufacturing wastes, such as antifreeze and lubricants, can create environmental problems if they are leaked onto the ground or into a waterway. The atmosphere also suffers the direct and indirect consequences of the strong exploitation of natural resources. In the extraction process, airborne dust is produced during different operations, such as drilling, detonation, sawing, transportation and unloading. At times, in the extraction areas, the dust of some harmful minerals reaches such a high concentration in the air that its inhalation causes serious illnesses, such as silicosis and asbestosis.

Corrective and Preventive Measures

Keeping in view the harmful effects of extraction of ornamental stone, it is prudent to think how best the environmental impacts can be either minimised or prevented in order to strike a balance between industrial growth and clean environment.

Waste Management

All the activities related to the natural stone sector, extraction and transformation have associated the production of some type of wastes that must have a correct management in order to prevent and minimise the occurrence of impacts in the surrounding environment. There are some wastes that are common to the stone extraction and to the processing plants; others are specific to each “sub-sector”. The wastes can be classified according to their dangerousness, which is defined in the European normative (included in the national legislation of each country). According to these definitions, we can identify the more significant wastes that are produced in natural stone industry and the way that they are usually managed during the exploitation.

The most rational way of waste reduction and consequent lessening of the environmental damage is to reuse waste of different forms in different applications as detailed below:

Different applications for stone waste reusing (after E. K Shirazi 2011)

Table 1: Best Techniques

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It is possible to ensure waste reduction at the origin, essentially through the use of equipment that allows maximising the exploitation of the stone and therefore minimising waste production. There are many pieces of equipment or technologies that permit waste reduction, many of them already assumed in by the enterprises as essential to the productive process (1. Ashmole, 2008). In this group are included the diamond tools that are used in circular tools, gang saws and wire saws and band sawing. These pieces of equipment, besides bringing better performances, saving time and money, are very important in waste reduction. In the front line of the most modern equipment or under investigation are the thin tools that will make waste production even smaller.

Land Rehabilitation

Land rehabilitation is the process of returning the land in a given area to some degree of its former state after some process has resulted in its damage. While it is rarely possible to restore the land to its original condition, the rehabilitation process usually attempts to bring some degree of restoration. Modern methods have in many cases not only restored degraded land but actually improved it, depending on what criteria are used to measure ‘improvement’.

In the past, land reclamation was not considered to be an important component of quarry exploitation and the soil resource was often treated as part of the overburden material. As a result, soils were completely lost during mining due to the mixing with spoil or other materials or to improper handling and storage. Presently, the topsoil resource is considered to be vitally important to aid in the reclamation process. Most of the regulations oblige to remove the soil materials from a site prior to disturbance and to replace the soil at the surface after the site is out of its planned usage.

Control of Water Pollution

Each quarry and each processing entity producing ornamental stones use water as the main fluid in sawing operations because of its two important functions: to drain off disintegrated dust of stony materials and to cool the cutting tools. Besides, during the extraction and cutting of ornamental stones, water is also intensely used to cool the instruments and to remove abrasive agents and small particles produced by the cut and polishing. Even not having harmful addictive in the water circuit, the fine particles of stone or metal are forbidden in effluents and underground waters.

To extract and transform ornamental stones, quarries and processing plants have to prevent losses of hydrocarbures to maintain equipment and to foresee accidents loosing oils in waters and ground by careful and complete recuperation of used oils, careful distribution of oils, greases and fuel, cleanly storage, efficient lubrication systems, use of biodegradable oils wherever possible, cleaning flows correctly treated (purification of dirty water from cleaning vehicles, engines and all kinds of mechanical components), etc. Provision should also be made to recycle water and to treat effluent water before it is discharged outside the mine or quarry.

Landscape Recovery

The landscape recovery of quarries comprises the use of certain techniques and the conduction of certain natural processes that make possible the conversion of open pit exploration areas in zones within the region environment. The definition of landscape recovery is described in the legislation as being the “biological, economical and scenical revitalisation of the space affected by the exploration, giving it new use, with view to the establishment of the equilibrium in the ecosystem, or restoring its primitive ability.”

Environmental Management

The environmental management of an organisation is the management of the activities that have had or can have environmental impacts, where the management of the produced wastes has an important weight. The definition of Environmental Management System (EMS) in Norm NP EN ISO 14 001:2004 says that an EMS is part of the management system of an organisation that includes the organisational structure, planning of activities, responsibilities, procedures, processes and resources used to develop and implement the environmental politics and manage the environmental aspects. An Environmental Management System is build through environmental activities or management instruments. These activities are implemented aiming to fulfil a perfectly defined objective – environmental protection. The implementation of an environmental management system in an organisation conduces to benefits not only internal but also in the relation of the enterprises with the external agents. The main benefits of EMS are conformity with the environmental legislation, sustainable management of the natural resources, costs reduction from good management and treatment of the pollution source, prevention of environmental accidents, etc.

Conservation

One of the problems that beset the practical conservation of stone buildings is the fragmentation of the disciplines involved. A substantial environmental damage that is caused due to exploitation of the ornamental stone can be prevented by adopting best practices of either conserving or recycling the ornamental stones. Several heritage monuments (e.g. the Taj Mahal) are under severe threat of damage caused due to growing industrialisation and urbanisation. Increasing environmental pollution in urban areas has been endangering the survival of carbonate stones in monuments and statuary for many decades.

Numerous conservation treatments have been applied of late for the protection and consolidation of these works of art. Most of them, however, either release dangerous gases during curing or show very little efficacy and appeared to display insufficient consolidation and plugging of pores. Recent researches (C.R. Novarro et al., 2003), have indicated that the bacterially induced carbonate mineralisation has been proposed as a novel and environmentally friendly strategy for the conservation of deteriorated ornamental stone. The bioremediation through the application of the bacteria Myxococcusxanthus- induced calcium carbonate precipitation efficiently protects and consolidates porous ornamental limestone.

Recycling of decorative stones from damaged old buildings or monuments is a unique idea of conserving scarce natural resources and thereby reducing the environmental damage. Recycling of dimension stone can occur when structures are demolished, along with other construction materials. Stone recycling is usually done by specialists that monitor local demolition activity, looking for stone- containing houses, buildings, bridge abutments and other dimension stone structures scheduled for demolition. Particularly treasured are old hand-carved stone pieces, local stones that are no longer quarried or that are quarried in a different shade of colour or appearance. The recycled dimension stone is used in old stone buildings being renovated (to replace deteriorated stone pieces), in fireplace mantels, benches, veneer, or for landscaping.

Conclusion

Natural resources, be they ornamental stones or minerals, are non-renewable resources. They need to be properly harnessed and conserved for prosperity. Mining or quarrying is inevitable to extract the ornamental stone, which, in turn, is bound to damage the environment. In order to minimise the damage caused due to mining, a thorough assessment of environmental impact is needed. Besides, proper planning to implement the Environmental Management System needs to be built into the project cost to ensure some degree of semblance to restore the damaged land, soil, air and water. By choosing appropriate mining technology and by adopting the best practices of environmental management, the damage caused due to extraction of ornamental stone can be minimised. Further, reuse of stone wastes, recycling of old decorative stones and conservation of the monuments will go a long way towards sustaining ornamental industry with minimal damage to the environment.

This is the text of the paper presented by
Dr. K.V. Krishna Murthy, Director,
RSAS, Geological Survey of India, Bangalore,
at a seminar held at Bangalore’s STONA 2014.

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