38. Minerals-handling and processing

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1. Scope

2. Environmental impacts and protective measures

2.1 Handling
2.2 Crushing, screening, milling, classifying
2.3 Separation, flotation
2.4 Roasting
2.5 Storage and handling of concentrate; recultivation

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

Processing constitutes the technological link between the extraction, or mining, of raw minerals and their conversion into industrially useful working materials. The techniques applied are designed to separate the valuable from the barren material while upgrading, or concentrating, the former. The large variety of raw materials and the many different types of deposits in which they are found naturally necessitate an accordingly broad array of processing routes, from the simple classification and washing of sand and gravel to the more elaborate methods of processing hard coal, and on to the material beneficiation of disseminated metal ores. Ores processing (dressing) does not, however, include the various stages of metallurgical processing described in the brief dealing with the production of nonferrous metals.

In many cases, the environmental relevance of a given stage of processing increases in relation to its scope and/or degree of difficulty. The present brief therefore focuses on the environmental aspects of ore processing facilities as the source of most damage potentials.

It must be noted in that connection that no account is made of special cases such as uranium ore processing, which is already subject to special statutory regulations around the world. Likewise, no processes are dealt with that serve in the reclamation or reprocessing of spent merchandise such as worn-out batteries, scrap glass, etc.


2. Environmental impacts and protective measures

2.1 Handling

The loading and unloading of trucks and railroad cars can generate large amounts of dust. During transportation, fine dust is lost to relative (head) wind, while trucks emit pollutant-laden exhaust gases, and both trucks and trains are noisy. Transportation by truck or rail entails the consumption of land area for roads and railways. The construction and use of traffic routes can have detrimental effects on nature and residential quality; cf. briefs dealing with transport and traffic planning, provision and rehabilitation of housing, and road traffic.

In the interest of environmental protection, the mineral processing plant should be located either directly on or in the immediate vicinity of the mine premises. That way, the ore can be moved from the mine to the processing facility by conveyor belt instead of by truck or rail. If transportation by truck is unavoidable, the haul roads should be provided with a course of bituminous road-building material or concrete and kept clean at all times. A wheel-washing stand and/or routine washing of the vehicles helps reduce dust emissions. Low-emission, noise-abated trucks are designed to help reduce overall emissions of carbon monoxide, hydrocarbons, oxides of nitrogen, soot and noise. Other in-transit protective measures include moistening the load with water, tarping it over, or using closed containers. Dust extraction and control devices are required for loading and unloading operations, i.e., on loading equipment such as downcomers, and on unloading equipment such as dumping chutes. When filling closed containers with dust-generating products, the displaced air must be dedusted. The required degree of dust extraction depends on the hazardousness of the dust in question. Cyclone separators and fabric filters are inherently suitable.

Conveyor belts should be encapsulated as a pollution-prevention measure (not for maintenance purposes), i.e., as a means of restricting dust and noise emissions. The conveyor drives at the corners (diversion points) emit sound intensity levels reaching as high as 120 dB (A). Any sound insulation employed should be harmonized with that used for other noise sources within the processing plant. The use of noise locks on bunkers also helps reduce noise emissions, since the size of the opening is decisive for the amount of sound radiated during unloading.

2.2 Crushing, screening, milling, classifying

The rock material is preferably rough crushed in jaw crushers and subsequently screened, with the oversize being returned for recrushing. The normal fractions are collected in a surge bin. A conveyor transfers the material from there to the fine crusher. Classification to standard sizes involves continuous feedback of the oversize and interim storage of the standard-size fractions. Additional classification and particle-size reduction can be effected in rod or ball mills, with separation of the desired size fractions and raw materials.

All of the above processing steps involve dust and noise emissions that can emburden both the workplace and the environment.

There are no generally applicable values for the dust quantities encountered, because they depend on the crystalline structure of the minerals and of their geological association, requisite extent of crushing and various engineering factors. However, in view of now-common ore throughputs of up to 50 000 t/d, even minimal proportional dust emissions can put pressure on the soil and vegetation around ore processing facilities. In particular, the attendant deposition of heavy metals can jeopardize human health by way of the food chain, and the presence of fibrogenic dust at the workplace can cause silicosis or asbestosis.

In order to minimize dust pollution, the machinery should be encapsulated. Wherever that would be unfeasible for technical reasons, the dust-laden exhaust air should be collected and put through a dust precipitator. The type of filter to be used depends on the composition and particle-size distribution of the dust. Generally, cyclone filters are used for coarse filtering, while fabric filters serve to remove fine dust particles. Such equipment can achieve residual dust contents (clean gas dust loads) of less than 10 mg/m3. Equipment operators at dusty workstations must be required to wear dust masks (particle respirators). Masks designed for use in very warm climates should have appropriately large filtering surface areas.

In the interest of noise control, such facilities must have enclosures with a minimal number of openings. Since processing plants operate around the clock, suitable noise control measures in the form of safety distances, embankments, shielding walls and the like must be planned in at an early stage to preclude excessive prejudice to adjacent residential areas.

The only real options for limiting the workplace noise nuisance is to automate and install control centers. The operators of noisy equipment generating high acoustic intensities must be provided with ear protectors and made aware of their importance for preventing noise-induced deafness.

2.3 Separation, flotation

Ore processing facilities use water for separating buoyant and nonbuoyant, i.e. floating and nonfloating, materials: in cyclones and screen classifiers for grading by gravimetric separation or for pulp preparation, where water serves as a working medium for separating the useless material by gravimetric means and for eliminating suspended solids from the concentrate. The overall water requirement varies widely, depending on the type of raw material, the nature of the deposit, and the processes employed.

Dense-medium techniques are used exclusively for the coarse-size range, with medium solids consisting of magnetite, lead glance (galena), ferrosilicon and, occasionally, heavy spar (barium sulfate). Between 0.3 and 1 g of sodium hexametaphosphate can be added per liter of pulp to reduce its consistency. The water used in heavy media separation processes should be recirculated. Accordingly, the entrained solids have to be separated out in settling tanks, irrigated electrostatic precipitators or hydrocyclones. Even if the water from pulp regeneration is recirculated, the fresh water requirement can still amount to 0.5 - 1.5 m3/ton of crudes.

Concentration by flotation is achieved with the aid of flotation agents. Special chemicals induce physicochemical surface reactions that are useful for separating and separately concentrating mixed and disseminated ores that have been sufficiently comminuted to eliminate most intergrowth between the constituents of interest. Consequently, the solid contents of flotation slimes in part occupy the microfine to colloidal size range. Since such slimes sediment out very slowly, part of the process water can be recovered more quickly by dewatering the flotation products in thickeners. The still-wet mining wastes (tailings) are then pumped into settling tanks and given ample time - perhaps a week - for extensive sedimentation of solids. The liquid phase can be recaptured as gravitation water.

Among the various flotation agents, distinction is made between collectors, frothers and modifiers. Collectors, or collecting agents, are surface-active substances that make the surface of the ore water-repellent. Organic compounds serving as collectors are selectively employed according to the type of ore. In the flotation of sulfide ore, for example, between 10 and 500 g of xanthate is needed per ton of ore, while anywhere from 100 to 1000 g of sulfonates or unsaturated fatty acids are consumed per ton of nonsulfide ores.

Frothers, or frothing agents, which influence the size of air bubbles and help stabilize the froth in the flotation apparatus, include terpenes, cresols, methyl isobutyl carbinol, and monomethyl esters of various propylene glycols. Consumption levels run between 5 and 50 g/t for flotating crude sulfide ores.

The modifiers, or modifying agents, include chemicals for regulating the pH: lime, soda and caustic soda for adjusting the alkalinity, and predominantly sulfuric acid for acidification. Passifiers and actifiers, which are used to intensify the differences between the water-repelling properties of the ores to be separated, include copper sulfate and zinc sulfate. Alkali cyanides serve in the selective flotation of sulfide ores. Cyanides can only be added to an alkaline pulp; otherwise, hydrogen cyanide could evolve and be released to the atmosphere. The amounts required range from 1 to 10 g/t ore. Sodium sulfide, dichromate, water glass and complexing agents also belong to the group of selective flotation agents.

Many flotation agents and other chemical additives constitute a hazard to water. Consequently, carefully monitored dosing apparatus is required to preclude overdosing, and special safety requirements must be met by plant and equipment used for storing, decanting, handling and using such hazardous-to-water flotation agents. The facilities must be designed to safely preclude contamination of surface water and groundwater to an extent reflecting both the pollutive potential of the substances in question and the protection requirements of the relevant locations, e.g., potable water protection areas. Impervious, chemical-resistant, drainless collection and holding vessels must be provided to the extent

necessary for intercepting in a controlled manner any media that may escape as a result of leakage, overfilling or accidents. The retention volume must suffice to hold back the escaped substances until such time as appropriate countermeasures can be brought to bear. Additional safety precautions include double-walled storage tanks, overflow prevention devices and leakage sensors.

All requisite measures and precautions for avoiding hazards due to potential water pollutants in the form of flotation agents should be stipulated and communicated via appropriate handbooks. Plans pertaining to monitoring, repair and alarm response to malfunctions should also be compiled in handbook form. In addition, occupational safety measures must be instituted and monitored in connection with the handling of potentially dangerous flotation agents.

Sensitization and training measures are of essential importance, because the inexpert handling, storage and transportation of working agents are frequent sources of environmental pollution.

Along with the depleted material, small amounts of flotation agents, leaching chemicals and/or heavy medium can get into the tailings ponds. The gravitation water collecting in the drains should be tested for the presence of flotation agents and chemicals prior to its return to the process water circuit. Most of the agents and chemicals remain in the floated concentrate. When the concentrate is dewatered, the agents and chemicals are washed out and re-injected into the fine-grinding cycle.

Once the concentrate has been thickened, filtered and dewatered, its residual moisture content will amount to roughly 8 %. Thus, the freshwater requirement for such processing facilities can amount to about one third of the overall process water consumption rate of about 5 m3/ton of ore. The water consumption of a given concentration plant must be carefully attuned to the existing original water budget, i.e., to the available volumes of groundwater and surface waters, in order to avoid both detrimental effects on the environment and problems with the supply of drinking water.

The process water should be appropriately treated and recirculated. Processes in which the water is discharged into a recipient body on a once-through basis can cause silting and contamination of the receiving water due to high sediment contents and residual chemical additives.

The disposal of barren rock and tailings is also problematic in that it consumes land area. As the percentage of valuable material diminishes, the throughput quantities increase, and the long-term areal requirement rises proportionately. An ore processing facility with a throughput of approximately 45000 tons/d, for example, requires a settling basin measuring some 400 to 500 hectares in area and 300 to 350 million m3 in volume for 20 years of operation. In some cases, the tailing ponds can be kept somewhat smaller by extracting dried material for use in refilling underground mines. Due to the altered material properties, however, this option is only conditionally appropriate and would never be able to fully replace tailings ponds and rubbish dumps.

Large settling basins should never be constructed prior to painstaking pertinent investigation including precise specification of the physical and chemical compositions of the tailings as well as of the geological and, above all else, the hydrological set-up. The permeability of soil strata, for example, and natural drainage systems are very important with regard to groundwater protection. Since many tailings ponds stay in service for decades on end, building up all the while, the relevant accident analysis must consider a possible dam failure due to excessive surface runoff.

Rubbish dumps must be established with due attention to the fact that precipitation can induce leaching processes with attendant pollution of surface and gravitation water. Any mining waste containing large amounts of water-soluble substances or heavy metals can jeopardize the groundwater, unless the soil under the dump is sufficiently impermeable. Thus, the essential protective measures include an adequately dense subgrade, minimal sprinkling and the collection of runoff water. Before the first load of material is dumped, observation wells should be sunk for monitoring the groundwater.

It would be impossible to preclude all dust generation in connection with dump operations, but it can be minimized by keeping the discharge heights of dry tailings as low as possible and by encapsulating the transfer points. Wind erosion can be limited by compacting the surface, sprinkling the pile, applying suitable, environmentally benign binders to the surface, or planting the windward side of the heap. The equipment required for dump operation (pumps, dump trucks, conveyor belts, bulldozers, ...) can be quite noisy. Noise control measures in the form of quiet tools and vehicles, acoustical barriers, etc. are called for whenever sensitive legitimate residential areas are located nearby.

The surface and gravitation water (percolation) from rubbish dumps should be collected by way of an impermeable peripheral trench and tested before being released to a recipient body. Moreover, before the water is discharged, its settleable solids content must have been ascertained as appropriate to the outlet channel's own sensitivity and intended use. Depending on the material composition of the tailings in the pond and/or of the rubbish in the dumps, additional testing for the presence of environmentally relevant pollutants such as heavy metals and processing chemicals may be necessary. The treatment required for the impounded water may consist merely of settling in an appropriate basin or, depending on the entrained substances, of physicochemical processes (precipitation, flocculation, chemical oxidation, evaporation, ...).

Long-term, if not permanent, monitoring of the surface runoff and gravitation water is called for, because the nature and extent of discharge can change over time due to weathering (surface disintegration).

In addition to flotation, leaching and amalgamation also serve as separation processes. In gold mining, for example, the gold is extracted from the gravity-separated concentrate by making it react with metallic mercury to form amalgam. The concentrated residue is then leached with a cyanide solution. Both processes have negative environmental impacts that are very difficult to control. The mercury content of the effluent is particularly problematic, if the wastewater is discharged to the outlet channel without having been treated. It is still an open question as to whether or not the new ion-exchanger resins will, in the long run, be able to bind enough mercury to meet the residual concentration requirements. Leaching involves the use of numerous different chemicals. In gold processing, for example, these include cyanide, lime, lead nitrate, sulfuric acid and zinc sulfate. The processes themselves also jeopardize the air, water and soil. All measures and precautions that would apply to the concerns of environmental protection and occupational safety in connection with an industrial-scale inorganic chemical process must be allowed for at the planning stage. This would include, for example, capturing the exhaust vapors from the reaction tanks and vessels and installing vapor scrubbing equipment (vapor stacks) to prevent harmful emissions. The aqueous solutions emerging from filter presses should be recirculated, and the waste sludge from suction filters must be tested for disposability and treated as necessary. The wastewater from amalgamation and leaching processes requires periodical monitoring.

2.4 Roasting

The processing of sulfide ores includes roasting. The roasting gases contain large amounts of sulfur dioxide and therefore require gravitational separation (inertial impaction) and electrostatic precipitation. Further processing of the incidental sulfur dioxide should be obligatory, because release of the unprocessed roasting gases would unavoidably destroy most of the vegetation around the roasting plant. It is particularly important that the feed and discharge devices on the roasting furnace be airtight. Fabric filters mounted on the roasted-ore silo can extensively preclude dust emissions. To the extent that the blowers give off too much noise, their encapsulation is recommended. A chlorinating roasting process may involve the formation of polychlorinated dibenzodioxins and furans in the exhaust gas, the roasting residue and/or the slag, depending on the operating conditions and on the nature and extent of organic substances. Whenever the formation of any such harmful substance is detected in connection with a chlorinating roasting process, the operating conditions must be altered such as to minimize the level of emissions.

2.5 Storage and handling of concentrate; recultivation

If concentrates are stored outdoors and unprotected, wind- and precipitation-induced erosion can pollute the air, the soil and the waters.

The ground in the storage area should be sealed to prevent contamination of the topsoil. Continuous maintenance of adequate surface moisture and/or covering the ground with mats does not always suffice to prevent all wind erosion. Consequently, the concentrate storage area should be roofed over and enclosed, and appropriate measures, e.g., low dumping heights, should be taken to minimize dust generation during loading and unloading.

The measures to be taken in connection with hauling correspond to those described in section 2.1.

The extent to which planned heaps and sedimentation facilities would occupy the former life space, i.e., the habitats, of local flora and fauna must be ascertained on a case-by-case basis. The possibility of promptly recultivating slopes should also be examined as a means of preventing wind- and water-induced erosion while achieving a certain degree of ecological compensation. The nature and extent of early recultivation must be discussed and coordinated with those responsible for regional/landscape planning and defined in a catalogue of measures. If the area in question is to be used for agricultural or horticultural purposes, the anthropogenic pollutive burdens in the stored material and their mobility (pollutant transfer factors) must be accounted for by appropriate measures such as sealing or compacting of the subsoil to interrupt the paths of emission. Even at the planning stage, information should be gathered on the availability of cultivable materials fit for land restoration.


3. Notes on the analysis and evaluation of environmental impacts

The processing, handling and transportation of raw minerals can cause substantial environmental pollution by dust evolution. The most effective available means of dust collection and precipitation must be applied to dust containing cadmium, mercury, thallium, arsenic, cobalt, nickel, selenium, tellurium or lead. Quartzose dust (silica dust) can cause silicosis and therefore must be allowed for as an occupational safety consideration. Depending on the mass flow, the material must be analyzed for the presence of the aforementioned heavy metals, and clean-gas limits need to be defined, whereas those for cadmium, mercury and thallium should be lower than those pertaining to the other heavy metals. The workplace dust concentrations must be monitored as a basis for controlling the silicosis hazard. Industrial medical care must be provided for the workers.

The local vegetation is liable to be destroyed by the caustic effects of mineral constituents dissolved by rain. Also, a thick layer of dust can so strongly impede the plants' natural assimilation process that they die off. The soil around processing facilities for ores containing heavy metals can eventually become contaminated. The geogenic contents of the soil should be determined prior to erection of any such facility.

Well-proven dust collecting and precipitating devices are available for use in controlling dust emissions. Their adequate separation efficiency in continuous operation must be monitored. The nature and extent of inspections, preventive maintenance and repair of precipitators should be specified in a service manual.

Under certain unfavorable conditions, an accumulation of heat, an overheated bearing or a spark can trigger the ignition or fulmination of fine dust. Good ventilation, possibly in combination with inertization, pressure-surge-proof encapsulation and/or the use of pneumatic drives, can substantially reduce the hazard.

Substances constituting a hazard to water in connection with ore dressing processes can lead to soil and water pollution due to leakage, carelessness, accidents, etc. Consequently, all facilities required for storing, decanting, handling and using potentially water-polluting substances must be designed and operated such as to avoid contamination of the soil and water. Appropriate precautionary measures also must be taken for the transportation and disposal of the chemicals, and pertinent occupational safety measures must be specified for handling them. The potential environmental hazards emanating from the chemicals (cyanides, mercury, etc.) and from the acidic roasting gases involved in separation and concentration processes based on leaching, amalgamation and roasting can be particularly severe. Thus, appropriate measures must be taken to hold back the mercury, cleanse the roasting gases, control the leaching process, and otherwise contribute toward the minimization of emissions.

Tailings ponds, settling basins and rubbish dumps for the residues of dressing processes all have substantial space requirements. Knowledge of the subsoil structure is important for properly assessing the effects of harmful emissions. With a view to ensuring the long-term protection of groundwater and surface waters, relevant special studies and analyses must be conducted at the planning stage. There are as yet no official limit values for acceptable levels of ground contamination by mill slurries from the processing of raw minerals. Consequently, planners of new facilities have to rely on experiential values gleaned from settling basins for similar dressing plants. In the case of coal mud heaps, good compaction is required to prevent spontaneous combustion.

To the extent that farmland and, hence, income potential must be sacrificed for processing activities, the consequences for the affected subpopulation, women in particular, must be investigated and suitable alternatives developed as necessary. Early involvement of the local populace in the dissemination of information and decision-making processes is an effective means of avoiding or alleviating conflicts in advance.

The effluent from mineral processing activities and the gravitation water emerging from tailings ponds and rubbish dumps may contain heavy metals or potentially water-polluting chemicals that pose a hazard to surface water, groundwater and the soil. Special attention must be given to the possible jeopardization of potable water supplies. In case of excessive sediment contents, the river bed is liable to silt up and accumulate harmful substances. The wastewater from ore processing plants therefore has to be continuously monitored. Depending on the nature and extent of settleable solids, heavy metals or chemicals posing a hazard to water, the effluent will require appropriate treatment.

Properly sized equipment enclosures with adequate acoustic insulation properties are very important for reducing the amount of noise emitted by processing plants. Appropriate safety clearances should also be planned in for between the plant and neighboring residential areas. Suitable noise control measures also should be applied to the operation of tailings ponds and rubbish dumps located in the near vicinity of residential areas.

Permissible noise emission levels are specified in Germany's TA-Lärm (Technical Instructions on Noise Abatement). The site surroundings - e.g., an industrial zone, commercial area or residential district - are decisive for the maximum allowable noise intensity level.

As in Germany, ore processing plants should have immission-control, water-pollution-control and waste-management officers, whose positions should be independent of the production division. A safety officer and an occupational physician should be available for matters concerning occupational safety.


4. Interaction with other sectors

As a rule, mineral processing plants are attached directly to the relevant mining operations. The environmental briefs pertaining to mining therefore apply.

The large area required for a processing plant necessitates its coordination with present and planned regional land use. As such, the environmental briefs Spatial and Regional Planning, Planning of Locations for Trade and Industry should also be consulted.

If the processing plant cannot be installed directly at the mine, appropriate roadbuilding measures become necessary, in which case important details can be found in the briefs Road Building and Maintenance, Building of Rural Roads.

In arid regions, the water neeeded for operating the processing equipment is a very important resource, and its judicious use must be incorporated into Water Framework Planning.


5. Summary assessment of environmental relevance

If the planned site of a processing plant is located in a thinly populated area, it must be brought in line with the goals of regional development planning. In selecting the site, importance should be attached to choosing a location with a relatively low level of ecological sensitivity and which is not crucial to the vitality of the regional natural household.

Most processing plants emit large amounts of material- and process-generated dust and noise. Within the plant premises, such nuisances/pollution can be reduced to tolerable levels by the use of suitable enclosures and dust retention devices. Dust emissions from dry heaps and dumps, however, is more difficult to control, particularly when finely comminuted material is exposed to wind and weather. Such material must be kept moist and/or covered, and the surface should be consolidated or sown over.

Large volumes of low-grade material accumulate at processing plants and have to be pumped into tailings ponds for sedimenting. Before any such settling basin is established, its long-term environmental impacts must be carefully analyzed, because it could well remain in operation for several decades, becoming larger and larger all the while. The analysis must cover important aspects of protection for the soil and groundwater, stability (e.g., in case of flooding) and subsequent recultivation, including definition of appropriate measures.

Prior to establishing and operating rubbish dumps, the site-specific hazard potentials for the subsoil, groundwater and surface waters must be carefully investigated. The subgrade must be sealed and a means of collecting all surface runoff and gravitational water provided.

Old tailings ponds and dumps should be given close-to-natural shapes prior to their recultivation in order to fit them into the landscape in a manner appropriate to their planned future use.

Process effluent and gravitational water from processing plants, tailings ponds and rubbish dumps must be put through wastewater treatment facilities, the nature and extent of which depend on the sensitivity and manner of utilization of the recipient body. Silting should be avoided, of course, and pollution by mercury and other heavy metals should be minimized. Observation wells should be sunk to allow monitoring of the groundwater.

Bulk transportation by road or rail can have negative impacts on the environment: through construction of the required hauling routes (and attendant erosion potential) and in the form of airborne dust and noise. Dust emissions can be avoided by hauling the material in closed containers. Quiet, low-emission trucks should be given preference. Fine-grained material should not be stored in the open air for any length of time. Otherwise, wind- and precipitation-induced erosion could cause pollution of the soil and water. Frequently, the cost of relevant environmental protection measures is more than offset by resultant reductions in the loss of resources.


6. References

Rules and Regulations

Anforderungskatalog für HBV-Anlagen: Anforderungen an Anlagen zum Herstellen, Behandeln und Verwenden wassergefährdender Stoffe (HBV-Anlagen) Ministerialblatt für NRW, Nr. 12, 1991, p. 231 - 234.

Deutsche Forschungsgemeinschaft: Liste maximaler Arbeitsplatzkonzentrationen (MAK-Wert-Liste), 1990, Mitteilung XXVI, Bundesarbeitsblatt 12, 1990, p. 35.

EC Directives: Protection of workers from the risks related to exposure to noise at work, May 12, 1986 - 86/188/EEC, and of June 14, 1989 - 89/392/EEC - on the approximation of the laws of the Member States relating to machinery.

Environmental Protection Agency (EPA): Standard of Performance for Nonmetallic Mineral Processing Plants, EPA 40, Part 425 - 699 (7-1-86 Edition) 60, Subpart 000, Preparation Plants and Coal Preparation Plants, EPA 40, Part 425 - 699 (7-1-86 Edition) 434.23.

Katalog wassergefährdender Stoffe: Lagerung und Transport wassergefährdender Stoffe. LTWS Reihe No. 12, 1991, Umweltbundesamt [German Federal Environmental Agency] Berlin.

Technische Anleitung zum Schutz gegen Lärm: TA-Lärm, (Technical Instructions on Noise Abatement) vom 16.07.1968, Beilage BAnz. (supplement to the Federal Gazette) Nr. 137.

Unfallverhütungsvorschriften: Hauptverband der gewerblichen Berufsgenossenschaften, Bonn - u.a. UVV-Lärm, VBG 121 v. 01.01.1990.

VDI Guideline 2560: Personal Noise Protection, December 1983.

VDI Guideline 2058, sheet 1: Assessment of Working Noise in the Vicinity, September 1985.

VDI Guideline 2263, sheets 1 to 3: Dust Fires and Dust Explosions; Hazards, Assessment, Protective Measures, November 1986, November 1989, May 1990.

Erste Allgemeine Verwaltungsvorschrift zum Bundes-Immissionsgesetz, vom 27.02.1986 (Technische Anleitung zur Reinhaltung der Luft - TA-Luft), GMBI. (joint ministerial circular) 1986, Ausgabe A, p. 95.

16. Allgemeine Verwaltungsvorschrift: Mindestanforderungen an das Einleiten von Abwasser in Gewässer. Steinkohleaufbereitung und Steinkohlebrikettfabrikation. GMBI. (joint ministerial circular) No. 6, 1982.

27. Allgemeine Verwaltungsvorschrift: Mindestanforderungen an das Einleiten von Abwasser in Gewässer, Erzaufbereitung. GMBI. (joint ministerial circular) No. 8, 1983, p. 145.

Wiedernutzbarmachung von Bergehalden des Steinkohlebergbaus Bellmann Verlag, Dortmund, Verlags-No. 614, 1985.

Zulassung von Bergehalden: Richtlinien für die Zulassung von Bergehalden im Bereich der Bergaufsicht, MBI. NW. (North-Rhine/Westphalia ministerial circular), p. 931, dated July 13, 1984.

Technoscientific Contributions

Alizadeh, A.: Untersuchungen zur Aufbereitung von Golderzen. Aufbereitungstechnik 5, 1987, p. 255 - 265.

Alizadeh, A.: Grundlagenuntersuchung zur mathematischen Beschreibung der Flotation von oxidischen Eisenerzen. Aufbereitungstechnik 2, 1989, p. 82 - 90.

Atmaca, T.; Simonis, W.: Freistrahlflotation von oxidischen und sulfidischen Erzen im Feinstpartikelbereich. Aufbereitungstechnik 2, 1988, p. 88 - 94.

Diesel, A.; Lühr, H.P.: Lagerung und Transport wassergefährdender Stoffe, Erich Schmidt Verlag, 1990.

Kirshenbaum, N.W.; Argall, G.O.: Minerals Transportation, Proceedings of First International Symposium on Transport and Handling of Minerals, Vancouver, 1971.

Sciulli, A.G. et al: Environmental approach to coal refuse disposal, Mining Engineering, 1986.

Ullmanns Enzyklopädie der technischen Chemie, 4. Auflage: Band 2 Verfahrenstechnik I, 1972, Band 6, Umweltschutz und Arbeitssicherheit, 1981, Verlag Chemie, Weinheim.

Williams, R.W.: Waste Production and Disposal in Mining, Milling and Metallurgical Industries, Miller Freeman Publ., San Francisco, 1975.

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