47. Ceramics - Fine, utilitarian and industrial

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Contents

1. Scope

2. Environmental impacts and protective measures

2.1 Air

2.1.1 Waste gases/flue gas
2.1.2 Dust

2.2 Noise
2.3 Water
2.4 Soils
2.5 Workplace
2.6 Ecosystems

3. Notes on the analysis and evaluation of environmental impacts

4. Interaction with other sectors

5. Summary assessment of environmental relevance

6. References

1. Scope

Fine, industrial and utilitarian ceramics cover the following industrial sectors:

- Ordinary ceramics: tiles, roof-tiles, earthenware, expanded clay, wall tiles and floor slabs, refractory products
- Fine ceramics: earthenware, pottery, fine earthenware, porcelain, electrical porcelain, sanitary products, grinding discs and abrasive wheels
- Technical ceramics

Most ceramics companies are established in the vicinity of clay deposits. (This environmental brief deals only briefly with the extraction of raw materials; for further details refer to the environmental brief Surface Mining. Advice on processing and transportation of raw materials is also given in the relevant environmental brief. The size of ceramic plants and their daily throughputs vary from a few kilograms for technical ceramic plants, normally 10 to 50 t/day for fine ceramics, to as much as 450 t/day in the tile industry. Since many companies operate different types of production, the total output of the works is often higher than the typical daily output of a specific product.

The fine, industrial and utilitarian ceramics industries use all types of clays, kaolins and fireclays (burnt clay), feldspars and sands as a raw material base. The refractory, abrasives and technical ceramics industries also use numerous high-temperature-resistant and abrasion-resistant oxides such as corundum (Al₂03), zirconium oxide (ZrO₂) and silicon carbide (SiC).

Besides using their own, readily available raw materials, many companies are increasingly purchasing ready-processed raw materials, particularly for refractory products, abrasives and technical ceramics, as well as the raw materials required for glazes and frits.

The following process sequence is typical of the production processes in industrial, utilitarian and fine ceramics:

- extraction, processing, forming, drying, partial glazing or enamelling, firing, sorting/packing and transportation.

Execution of the individual process stages varies according to the selected method. Generally speaking, casting, plastic or drying processes are employed, with smooth transitions between the process stages.

Table 1 - Production processes

- In the casting process the raw materials are dosed, wet-ground and poured into plaster moulds as so-called slip. During pressure casting, the slip is shaped to produce the blank under pressure in machines.
- In the plastic process the raw materials are normally prepared in the wet state, mixed and shaped with moisture content of 15 - 20% water.
- In the dry pressing process used in fine ceramics, the raw materials are frequently prepared in the wet state, then dried in a spraying tower to a residual moisture content of 5-7%. In the refractory industry the raw materials are mixed dry and are often processed with pressing moisture content of less than 2%, also using organic and inorganic binding agents.

The moulded products are dried and then fired. They are generally fired in high-power tunnel kilns; special products are fired mainly in individual, hood-type or batch kilns, while fast-burning products are fired in roller hearth kilns of various designs. In many countries, tile products in particular are often fired in self-built single-chamber and ring kilns or in charcoal kiln systems.

Many fine ceramic products are glazed or enamelled before firing.

Depending on the raw materials used, the firing temperatures in industrial, utilitarian and fine ceramics begin at 950°C for some tile products, for example, whereas most fine ceramic products are fired at between 1100°C and 1400°C. Refractory and technical ceramic products have firing temperatures of 1280 to 1900°C. (Pure glaze baking is done at lower temperatures.) The dual firing process is sometimes used for porcelain and very rarely for wall tiles.

Energy consumption depends on the product and the process; in the tile industry, because of the low firing temperatures, it is between 800 and 2100 kJ/kg of manufactured product, but in almost all other areas of industrial, utilitarian and fine ceramics it is on average much higher per manufactured product, and may be as much as 8000 kJ/kg of product.

After firing the products must be sorted and sometimes reworked, which will involve varying labour costs depending on the product.

2. Environmental impacts and protective measures

2.1 Air

2.1.1 Waste gases/flue gases

Hardly any waste gases are produced in the extraction, processing and moulding of ceramic products. Exceptions to this are the demoisturisation in the spraying tower, e.g. during the production of tiles, and the dry crushing plants used in clay processing, where harmless water vapour is given off.

During the glazing process, care must be taken to prevent glazing vapours, some of which contain heavy metals and other toxic substances, being discharged to the environment or being inhaled by personnel. Therefore only glazing plants which are equipped with the necessary extraction and wastewater discharge equipment should be licensed. Operating or maintenance personnel working in this area must be protected by breathing filters. When the glazed products are dried, mainly harmless water vapour is given off.

The amount of flue gas produced during firing depends on the emission of the fired product and on the type of fuel used. Volatile components are sometimes given off from the product mass and from the fuel.

The adverse environmental effects of fluorine emissions from the ceramics industry have come to be recognised as a serious problem, particularly in recent years, in view of the damage occurring in the vicinity of ceramic works (animals and plant diseases). Fluorides are present in all ceramic raw materials and are sometimes emitted in the waste gas during firing. Because of this, fluorine emissions from new plants built in Europe must be less than 5 mg/Nm³.

Because ceramic firing plants operate continuously, residual substances from other sectors such as waste oils or organic components from water treatment plants are sometimes used as fuel additives. Plants which use such materials are subject to special regulations because dangerous oxides may be introduced via these waste substances and re-emitted with the flue gas.

German companies must conform to the following values when burning waste substances:

- Total dust 10 mg/Nm³ max.

Sulphur dioxide 50 mg/Nm³ max.
Cd, Tl, Hg, 0.1 mg/Nm³ (per element)
(cadmium, tellurium, mercury)

Other heavy metals 1 mg/Nm³

Because of these conditions, waste substances cannot be used in the ceramic industry without the installation of additional water-spray separators.

Nitrous oxide emission during firing appears not to be a problem in most plants which are operated at relatively low temperatures, but special solutions must be found for high-temperature firing plants in the refractory industry for denitrifying the waste gases.

No waste gases are generally produced during sorting, packing, internal conveying, processing or refining. Only in very rare cases, e.g. during subsequent colouring or printing, may environmental pollution be caused by waste gases. These problems must be solved on a case-to-case basis.

2.1.2 Dust

Dust presents a latent risk in fine, industrial and utilitarian ceramic plants, particularly for the labour force. Fine quartz dusts < 5 µm may cause silicosis.

Depending on the geological and meteorological conditions, dusts may occur in pits during extraction of the raw materials which can be reduced by wetting and by the use of appropriate extracting and conveying methods. (See environmental brief Surface Mining).

Whilst hardly any dust is produced in the wet medium of the plastic processes, in the preparation, moulding and drying processes a variety of methods can be adopted to minimise dust formation, such as continuous cleaning of the works, concreting and sealing of floors, efficient dedusting systems and wet grinding of porcelain and sanitary products.

Silicosis in the German porcelain and refractory industry, particularly in the case of silicate products, has been successfully minimised by systematic dust control in all working areas, but in many countries it is still a problem. The statutory limits for quartz dusts impose a maximum allowable concentration (MAK) of 0.15 mg/Nm³ of fine dust, and the air may contain no more than 4 mg/Nm³ of fine dust containing more than 1% by weight of quartz.

In Germany according to TA-Luft [Technical Instructions on Air Quality Control] the total dust content must not exceed 50 mg/Nm³ in the waste gas at a mass flow of more than 0.5 kg/h, or 150 mg/Nm³ at a mass flow up to and including 0.5 kg/h.

During firing the dust burden is generally very slight. Dry filters are now frequently installed in kilns, water-spray separators more rarely. Dry absorption systems may create dust, thus care must be taken to ensure that when such systems are used the maximum dust quantity of 50 mg/Nm³ in the flue gas is not exceeded. These plants require regular maintenance to preserve their efficiency (see 3.1).

2.2 Noise

In most production processes in the ceramic industry, noise is emitted but rarely exceeds 85 dB(A) (see 2.5 - Workplace).

During the extraction of raw materials, noise and associated vibrations may occur for a short time as a result of blasting, sometimes causing a serious nuisance to residents living close by. However, such noise can be substantially reduced by means of suitable detonation methods. The machines used for mining can now be soundproofed to such an extent that they meet the noise protection requirements. (See environmental brief Surface Mining).

During dressing, noise pollution is liable to occur e.g. through the use of rebound crushers and mills for the crushing of hard materials. These crushing installations and the adjoining dressing installations can be encapsulated or soundproofed in such a way as to protect the environment from oppressive noise.

During the drying and firing phases, fans are used which may generate noise levels in excess of 85 dB(A). These noise sources must be installed outside permanent workplaces. During special ceramic production processes, e.g. when splitting cleaving tiles and when using sheet metal plates, frames or pallets for internal conveying systems, typical noise problems arise. However, such noise levels can be reduced by taking appropriate measures, e.g. encapsulating permanent workplaces and buffering mobile conveying systems with rubber.

To avoid noise nuisance the immission values for the residential areas located close to the ceramic production centres should not exceed 50 - 60 dB(A) during the day and 35 - 45 dB(A) at night. Housing developments should be sited at least 500 m from a ceramic factory.

2.3 Water

In Germany, ceramic works must comply with the administrative regulations regarding permitted substances in the wastewater.

Works laboratories must be established to monitor the works in question.

Table 2 - Maximum permissible values for direct dischargers according to the 17. VwV of the WHG
[17th Administrative Regulation of the Federal Water Act]

To avoid exceeding the applicable values, the water produced in the area of the pit must be fed through stilling basins, with the addition of sedimenting agents if necessary. The surface water occurring in the area surrounding the pit must be discharged separately.

Fresh water consumption in modern ceramic plants is low because the water required for the process is circulated internally. Some of the water used is driven off again as water vapour in the production of granulates in the spray tower and in the drying of the products. Wastewaters produced contain clay, flux and other ceramic raw materials which are precipitated and returned to the process by internal circulation.

Sanitary water produced in fine, industrial and utilitarian ceramic works must be discharged and disposed of separately.

2.4 Soils

Nowadays old clay pits are frequently used for storing waste products of all kinds, because of their relatively low water permeability. Soil damage may occur due to elutriation and water accumulation in old pits, because when the pit was worked, water management was not normally up to present-day environmental standards.

Soil is rarely impaired by spoil from ceramic works because the waste generated during production is reused in the plant’s own production or in other ceramic works, so that spoil dumps are only formed where the plant is operated inefficiently. Exceptions to this are the small quantities of gypsum produced during porcelain, sanitary and roof tile production, which have to be properly disposed of.

2.5 Workplace

Personnel working in ceramic plants may be endangered or oppressed by noise, dust and heat in certain work areas.

Permanent workplaces near sources of loud noise must be soundproofed. If the noise level is still not less than 85 dB(A) despite soundproofing measures, hearing protection must be made available, and from 90 dB(A) upwards it must be compulsorily worn to prevent resulting hearing impairment. Hearing protection must also be worn by personnel working in high-noise production areas for short periods.

During firing in tunnel, reciprocating, roll-over or bogie hearth kilns, temperature stress on personnel is relatively low in modern plants, but in plants with old single chamber and ring kilns, there may be considerable exposure to heat when the product is inserted and removed. In special cases, e.g. if a tunnel kiln car caves in, work must be carried out for a short time under conditions of extremely high temperature. In this case, strict protective measures, e.g. the wearing of thermal suits, must be complied with. Moreover, such work must only be carried out under appropriate supervision.

In fine ceramic works, particularly in the porcelain and silicate industry (refractory products), personnel may be at risk from continuous exposure to quartz dust. In addition to technical precautions, regular medical check-ups are essential here to ensure that fibrotic changes (changes in the pulmonary alveoli) are detected early, so that the employee in question can be protected from permanent injury through redeployment.

2.6 Ecosystems

When raw materials are extracted the landscape is impaired and there is an alteration to the surface (see environmental brief Surface Mining). Since the raw material requirement per plant is not very high, the individual mining areas are generally also relatively small. Many different types of clay are present in each clay pit, and with the introduction of suitable processing methods even low quality clays have been successfully processed in recent years, thereby reducing the amount of spoil in the vicinity of clay pits.

When selecting a site for a ceramic plant, due consideration must be given to the environmental aspects. In the case of locations in areas previously used for agriculture, possibilities for alternative employment must be examined, particularly for affected women. Besides complying with the regulations concerning waste gases, dust, noise and water, the conditions as regards the building land, integration in the landscape, and the infrastructure of the location must also be examined.

Infrastructural considerations include, amongst other things, the recruitment and housing of employees, transport systems and traffic density and the existing and planned industrialisation of the area.

Since the environmental impact is not limited to the factory area, the local population, including women and children in particular, should be given access to medical care.

Recycling of fine ceramic consumer goods, after use on or in buildings or in the home, is hardly feasible because of the variety of materials and small quantities involved at the points of consumption. On the other hand, in the refractory industry, particularly in steel works, over 30% of the refractory products are recycled.

3. Notes on the analysis and evaluation of environmental impacts

Emission limits for waste gas, dust and water have been formulated in the provisions of the German TA-Luft and TA-Lärm [Technical Instructions on Air Quality Control and Technical Instructions on Noise Abatement], in the guidelines adopted by the Association of German Engineers (VDI) and in the regulations specific to the various industries for dischargers (under the WHG - German Federal Water Act) and MAK (maximum allowable concentration) values have been established by the Berufsgenossenschaft (employers' liability insurance association) of the ceramic and glass industry for avoiding silicosis. These emission limits are being adopted in similar form by most European countries. The US regulations published by the Environmental Protection Agency (EPA) are frequently even more stringent than the German regulations, particularly in California.

For countries without their own environmental protection laws, these values must be examined taking into consideration the prevailing environmental conditions in the individual case and adapted to the particular circumstances. In exceptional cases, particularly for rehabilitation of plants, special regulations must be established, but new plants should conform to the standard values of environmental protection.

The Compendium of Environmental Standards offers advice on assessing environmental relevance for individual substances.

Table 3 - Limitation of hazardous substances under TA-Luft (Technical Instructions on Air Quality Control) and the 17th Administrative Regulation according to § 7a of the German Federal Water Act

When waste materials are used as fuel, the above emission limit values must on no account be exceeded, and regular inspection of the charge material, firing system and process, as well as of the waste gases and dusts, is essential (see 3.1).

It is vital that the dust regulations, based on the maximum allowable concentrations in the workplace, are adhered to, particularly in the porcelain and silicate industry. Non-compliance with these regulations leads to diseases with long-term consequential damage. Intensive dust abatement in all plants and in all sections of plants is imperative in this regard also.

The noise problem is underrated in many countries, but constant noise can lead to permanent damage. Here too, therefore, the prescribed noise limits must be adhered to in the workplace and in the surrounding residential areas, and encroachment on residential areas must be prohibited (see 2.2 and 2.5).

Managers of ceramic production plants must be alerted to the specific risks to employees and must be trained in the use of protective measures so that employees are not exposed to health hazards through ignorance (see 3.1). Suitable training must be given and personnel generally made aware of environmental concerns.

In all plants an internal water circuit must be carefully planned. Treated wastewaters which are discharged into receiving bodies of water are subject to minimum requirements which must be met to avoid damage to the ecosystem in areas close to the works.

All the parameters must be regularly checked by internal audits (see 3.1), and works laboratories must be set up to monitor adherence to the specified values.

3.1 Inspection and maintenance of environmental protection installations

A control centre independent of the production process must be established to comply with existing environmental protection regulations. The responsible personnel must be enabled to perform and monitor all inspection functions including measurements relating to environmental protection in the works. They should be available for consultation on investments and take charge of negotiations with environmental protection authorities. Moreover, this department is responsible for ensuring that all environmental protection installations are regularly maintained and upgraded. This internal environmental department is also responsible for staff training.

4. Interaction with other sectors

In the ceramic industry, interaction between different branches of production is common and is often necessary for a smooth production process. Fine, industrial and utilitarian ceramic works rely on numerous secondary operations, such as extraction plants, fuel stores, workshops and transport systems involving a number of other sectors.

Table 4 - Environmental impacts of adjacent sectors - fine, industrial and utilitarian ceramics -

All ceramic products must be packed, and the packing materials required for this purpose must be disposed of or recycled after use. Environmental impacts can be avoided in this area by making use of modern processes employed in the packaging industry. Moreover, the ceramic industry is highly transport intensive, since tiles, roof tiles, cleaving tiles and refractory products have high bulk weights and therefore require suitable means of transport.

5. Summary assessment of environmental relevance

The individual process stages in the industrial, utilitarian and fine ceramic industry do not generally give rise to severe environmental burdens.

Table 5 - Environmental impact of process stages (ceramics)

Key: 1 very slight; 2 slight; 3 moderate; 4 considerable
1) Depending on composition

Particularly dangerous in the case of free quartz with grain sizes smaller than 5 µm

Moreover, numerous measures to protect employees and the environment have been introduced through modernisation of the technologies applied and by installing protective equipment, e.g.:

- Surface mining: pit problems can be overcome by suitable mining planning, water management and recultivation.
- Internal water circuits and downstream stilling basins minimise the wastewater burden.
- Soundproofing of systems and processes prevents long-term hearing impairment.
- Fluorine and sulphur dioxide emissions are reduced to the required levels in the waste gas by controlling the firing processes or by means of downstream separation systems.
- The risk of silicosis is eliminated in relevant plants by technological improvements and dedusting systems, and is monitored by staff conducting routine preventive checks.

The environmental protection installations required in ceramic works may account for as much as 20% of the total investment costs. To achieve the desired results from the equipment in the long term, its efficiency must be guaranteed by proper maintenance. Improvements in the area of personnel and environmental protection can only be achieved by providing proper information and training.

Early involvement of neighbouring population groups in the planning and decision-making processes will enable measures to be devised to deal with any problems arising.

In countries which have no legal guidelines it should be ascertained as early as the planning stage, based on the raw materials to be used and the process technology applied, what environmental protection measures are necessary and appropriate. Environmental protection equipment provided should be of robust design so that the life of this equipment is appropriate to the overall project and so that simple, low-cost maintenance can be guaranteed.

6. References

Allgemeine Verwaltungsvorschrift über genehmigungsbedürftige Anlagen nach §16 der Gewerbeordnung - GewO.: Technische Anleitung zum Schutz gegen Lärm (TA-Lärm), 1985.

Siebzehnte Allgemeine Verwaltungsvorschrift über Mindestanforderungen an das Einleiten von Abwasser in Gewässer - 17. Abwasser VwV-, GMBL (joint ministerial circular) 1982.

Bauer, H.D., Mayer, P.: Zusammenführung staubtechnischer Daten und arbeitsmedizinischer Befunde am Beispiel von Asbesteinwirkungen, Sonderdruck aus "der Kompaß"91, Nr./1981.

Betriebswacht, Datenjahresbuch 1991: Berufsgenossenschaft der keramischen und Glas- Industrie, Würzburg.

1. Bundesimmissionsschutzgesetz (BImSchG), 1985.

Entwurf zur Abwasserverordnung Deutscher Industrie- und Handelstag, Anhang 17, Sept. 21, 1990.

Environmental Assessment Sourcebook: Environmental Department, November 1990, Draft, World Bank.

Industrial Minerals and Rocks: 5th Edition 1983.

Mayer, P.: Grenzwerte für Asbest am Arbeitsplatz und in der Umwelt unter besonderer Berücksichtigung der keramischen und Glas-Industrie "Sprechsaal" 1/80, 1980.

Mining and Mineral Processing: Environmental Department World Bank, October 1990, Draft.

Mineral Commodity Summaries U.S.: Department of the Interior, Bureau of Mines, 1991.

Guidelines of the German Federal Ministry of the Interior (Bundesdesministerium des Inneren) regarding BImSchG -Zugelassene Stellen zur Ermittlung von Luftverunreinigungen im Emissions- und Immissionsbereich nach BImSchG - Guidelines of the Council of the European Community

Schaller, K.H.; Weltle, D.; Schile, R.; Weissflog, S.; Mayer P. und Valentin, H.: Pilotstudie zur Quantifizierung der Bleieinwirkung in der keramischen und Glas-Industrie, Sonderdruck aus "Zentralblatt" Zbl: Arbeitsmed. Bd.31, Nr.11, 1981.

Schlandt, W.: Umweltschutz in der Keramischen Industrie, Beilage zur Keramischen Zeitschrift 36, Nr.10, 1984.

TA-Luft (Technische Anleitung Luft): Erste Allgemeine Verwaltungsvorschrift zum Bundes-Immissionsschutzgesetz (Technische Anleitung zur Reinhaltung der Luft - TA-Luft-), 1986.

Siebzehnte Verordnung zur Durchführung des Bundes-Immissionsschutzgesetzes 1990 (Verordnung über Verbrennungsanlagen für Abfälle und ähnliche brennbare Stoffe, 17. BImSchV).

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