Green sand & the environment: the European scene.

Environmental pressures on all aspects of industrial operations are high and are growing. For foundries in most Western European countries, there are national regulations which govern the internal working environment and others which control emissions to the external environment.

Much of the environmental legislation now being introduced in European countries originated in the regulations and directives issued by the European Community (EC). In 1987 the Single European Act amended the Treaty of Rome to include a section on the environment thereby establishing the legal status of the EC environmental policy. Based on this legislation, the EC has adopted the policy that "preventive action should be taken, that environmental damage should be rectified at the source and that the polluter should pay."

As each member state of the EC at present issues its own legislation on environmental pollution control, there is a huge and sometimes confusing fund of such legislation. Many of these directly affect foundries as well as the materials and processes they use. Green sand molding is a good example of how foundries are being affected by current and proposed EC environmental regulations.

Air Emissions

The major emissions associated with green sand molding are particulates, gases and vapors. The new Environmental Protection Act in the U.K. will require control of these emissions. A Guidance note on iron, steel and nonferrous foundry processes lists the control requirements to meet the BATNEEC (Best Available Technology Not Entailing Excessive Cost) principles. Limits for emissions to the external atmosphere will be set for particulates and for some specific gases and vapors. For particulates, it is expected that the limits will be 50 mg/ml. Limits for amines, ammonia and hydrogen sulfide at 5 ppm, 18 mg/ml and 5 mg/ ml respectively, will probably not affect the operation of the green sand process, but a general limit for volatile organic compounds (VOC) of 50 mg/m.sup.3 could pose problems.

The requirements to control particulates to 50 Mg/m.sup.3 Will require collection and arrestment of dusts generated at all shakeout and cleaning operations. For arrestment of particulates in exhaust air from shakeout operations, there may be some problems. The particulates contain considerable amounts of active clay which absorb water and swell, possibly resulting in blinding of the fabric used in bag filter units and resulting in poor efficiency. in the past it was thought that the only effective method would involve wet arrestment, usually by induced-spray wet collectors.

The efficiency of these units is now being questioned, however, in the context of meeting low particulate emission limits. While for most purposes it is believed that they could achieve 50 Mg/m.sup.3, it is unlikely that they would be able to reduce emission levels to below 20 mg/m.sup.3. (The U.K. figure of 50 mg/m.sup.3 is likely to be reduced in the future. In Scandinavia and Germany, limits of 20 mg/m.sup.3 already are in force.) In view of this, the use of bag filters for control of shakeout dust emissions may become essential. There are believed to be several successful bag filter operations in Scandinavia and Germany and at least one is running successfully in the U.K.

The important feature of all these installations is that the ducts carrying the exhaust air are heated and insulated to maintain the relative humidity of the air in the duct below 70%. This reduces condensation and is reported to eliminate blinding problems on the filters.

Treatment Options

The VOC limit will probably lead to increased expense for many foundries using green sand as it is believed that the concentration of VOCS in the smoke above poured molds and from the casting cooling line could well exceed 50 mg/m.sup.3. Some form of fume treatment will probably be required. The options for treatment are chemical scrubbing, incineration, catalytic combustion and adsorption.

Chemical scrubbing with water would reduce VOC emissions and the technology is well established. The problem is that wastewater emissions are produced and the phenol content may render the water unacceptable for discharge without treatment.

Incineration, if carried out at a sufficiently high temperature (>1472F/ 800C), is effective in destroying VOCS, but it is wasteful in fuel consumption and carbon dioxide emissions are increased. Other gases such as S0.sub.2 HCI and NO., all of which are severe atmospheric pollutants, also may be released after incineration.

Catalytic combustion using raised temperatures (392-752F/200-400C) and supported catalyst beds, often used with noble metals such as platinum or palladium, can be very effective in reducing fumes to basic elemental constituents including nitrogen and hydrogen, and eliminating VOCS. Capital costs are high and some catalysts can be readily poisoned which reduces treatment bed lifetimes and increases operating costs.

Adsorption techniques involve trapping the offending chemicals onto packed beds of materials such as activated charcoal. This technology is widely used and is especially effective if the materials trapped in the adsorbents can be recovered and reused. For foundry fume cleaning, it is extremely unlikely that the mixture obtained would have any commercial value and would have to be destroyed by incineration, thus increasing costs. This method still may prove attractive however as the adsorption stage concentrates the exhausted chemicals at relatively low cost and the incineration of the collected materials would involve considerably less fuel than for incineration of a high-volume, low-concentration stream directly at the exhaust dust.

As control of VOCS is new to the U.K. foundry industry it is not possible to give detailed guidance on these options, but scrubbing or adsorption techniques should suffice for achieving the 50 mg/ ml limit, if treatment is necessary.

In Germany, there is a general limit for VOCS of 150 mg/m.sup.3, but there also are limits for specific organic chemicals including benzene, formaldehyde, phenol, cresols and amines. For benzene, emissions must be reduced as low as possible and should not exceed 5 mg/m.sup.3. A similar limit applies to amines but for the remainder, the limit is 20 mg/m.sup.3. It is understood that most foundries exercise control by means of scrubbing with chemical treatment of wastewaters to meet water discharge requirements.

Water Emissions

There are few water discharges associated with greens and foundries. The only area is where wet arrestment is used to treat exhaust air from shakeout areas. Frequently the water is recirculated and some reused as makeup water for the system sand carrying with it some of the active clay collected as dust and suspended in the water. Where water from this source is discharged into sewers, foundries can have problems as it often contains high levels of clay minerals and sometimes has a significant phenol content >5 ppm).

At present, most foundries can discharge the water without too much trouble. But recently one or two foundries have had to make special provisions that involved treating contaminated water prior to disposal, again increasing costs. In the future, this may be less important if foundries have to use bag filters to meet particulate emission standards.

Sand Disposal

In the past, waste disposal of green sand has not been a problem, in fact the sand often was welcomed by disposal site managers as an inert capping material. In the West Midlands, considerable quantities of waste foundry sands, much of it green sand, have been used in land reclamation projects for landfill and consolidation, for road foundations and for lining pipe trenches.

In the last 20 years, more than 17 million tons of foundrys and have been used for land reclamation in the West Midlands with no apparent ill-effect on the environment. Now a new guidance note to local authorities on the control of landfill gases effectively requires waste disposal contractors to monitor and, if necessary, control methane gas emissions on all landfill sites. Such monitoring has to be continuous and performed until the methane content of the gases falls to below 1% of the total for a period exceeding two years. Only then can the site be used for development.

For development companies using foundry sand for land reclamation purposes, this has made the process uneconomical and now the only sites suitable for waste foundry sand are the licensed landfill sites taking all other controlled industrial waste. This has led to a 300% increase in disposal charges, in the West Midlands, in the last year.

There are no other major requirements for waste green sands at present unless there is a risk of heavy metal contamination. Local authorities are increasing requesting increasingly analysis of the heavy metal contents of the sands together with tests for Chemical Oxygen Demand (COD), pH and free phenol content. For waste sands from nonferrous foundry operations there is a greater risk of subsequent metal contamination of wastesands and a higher potential for water leachates from these sands containing unacceptably high levels of some metals such as aluminum, lead, copper and zinc.

One problem in the disposal of waste foundry material in the U.K. is that of mixed loads. Generally, waste sands, whether they be clay bonded or chemically bonded, are accepted at licensed waste disposal sites with little or no problem. There are other wastes from foundries which are more difficult to dispose and some of these should be regarded as 4special wastes' within the definitions of the 1980 Special Waste Regulations. These include some slags, especially those containing carbides and carbide residues from desulfurization, and any waste resins, catalysts or other binder chemicals.

Disposal in the EC

In EC countries there are apparently more problems with waste disposal than in the U.K. at present. In Germany, the authorities are more concerned with waste sand containing phenol. Disposal of such sands, which in many German states are referred to as hazardous, is expensive as there are few sites available for their disposal. There is strict scrutiny of these sands to ensure that there is no risk of pollution to rivers or groundwater supplies following disposal.

The processes giving rise to much concern for waste disposal appear to be the shell and the alkaline phenolic resin-based binder processes. Green sands contain some free phenol, distilled from coal, but generally the levels are low. However, the presence of some core sands in waste green sand can lead to consignments being treated as phenol-containing waste.

There is considerable pressure in Germany to reclaim both green sand and core sands, and thermal reclamation processes are gaining in popularity. There are at least four plants in Germany reclaiming shell process sands and mixtures of green sands and core sands. One of these is reclaiming more than 60,000 tons annually.

Elsewhere in Europe, Scandinavia is apparently less concerned about phenol-containing sands, allowing them to be disposed of at domestic sites because the high level of bacteria in the domestic waste destroys the phenol rapidly. Nevertheless, there are very strict controls on disposal of all types of foundry waste in Sweden.

The situation in France is believed to be changing quickly in a way similar to that in Germany as there is greater interest now in thermal reclamation of sand, although few details are available.

In Finland, waste sands containing more than 100 mg of phenol/kg of sand (100 ppm) cannot be disposed of at normal licensed disposal sites and special arrangements have to be made.

In Spain, there are general limitations on waste disposal in line with EC policy. For example, there are severe restrictions on the disposal of a number of highly toxic compounds included in the EC'Black List,'which was issued in 1976 for the control of discharge of dangerous substances to water. There are also restrictions on the disposal of highly acidic or alkaline compounds (pH <2 or >12.5, respectively). There do not appear to be problems in the disposal of waste foundry sands, provided that they do not contain significant quantities of heavy metals.

There is no doubt that in the future all environmental legislation will be more strictly enforced. Once the means of controlling emissions from factories is established, it is likely that the emission limits for particular pollutants will be steadily reduced in line with one of the main goals of EC environmental policy: reducing the pollutant emissions into any medium to a minimum.

Harmonizing Policy

There is pressure to harmonize pollution control standards across Europe and many of the recent EC directives have been issued with this goal in mind.

These pressures will increase after the completion of the internal market in December 1992 and also with the formation of the European Environmental Agency (EEA) established by regulation in May 1990. As soon as a 'home'is established for the EEA in one of the member states, it will be charged with gathering information on the present and foreseeable state of the environment across Europe. it will also be responsible for promoting the harmonization of environmental measurement methods and forecasting techniques and for stimulating exchange of information on the best techniques for preventing or reducing environmental damage. It is expected that there will be new or increased environmental control requirements in a number of areas detailed below.

VOC Air Emissions

Today, most national legislation on chemical emissions introduces the concept of controlling VOCS volatile organic compounds) following another EC directive that VOC emissions must be reduced progressively with the aim of eliminating organic solvent processes in industry.

For green sand foundries where generally only small amounts of solvents are used (for degreasing, pattern cleaning, mold coatings and a few resin binders), it is difficult to see that this control will substantially affect the environment. But it could impose high costs for control of mixed organic vapor emissions associated with the casting process and mold and core binder breakdown.

In the U.K. it is likely that at the first review of the authorization given under the Environmental Protection Act, within four years of the first authorization in 1992-93, the local authorities backed by Her Majesty's Inspectorate of Pollution (HMIP) will press for the removal of processes using organic solvents. if this is to be achieved, improved technology will be required rapidly to provide water-base cleaning and coating systems that will give comparable performance with existing organic-solvent-base systems.

Waste Classification

Increased concern of the contamination of soils and groundwater supplies by leachates from wastes deposited on tips (landfill) will lead to increased monitoring requirements on wastes particularly with regard to some organic compounds and heavy metals as already discussed.

The classification of wastes also is changing. Where in the past hazardous or special wastes were defined largely on the basis of their harmful actions on man, there is now a move to consider the direct environmental effects.

For example, the U.K.'s Department of the Environment is about to introduce a new set of regulations for special waste and the first draft issued last year used all of the original definitions of special waste and introduced a new section dealing with the 'ecotoxicity' of the waste. Thus, any waste which can cause harm to biological systems could be considered as special waste under the new definitions.

If the ecotoxic classification is maintained there would be substantial implications for the foundry industry. Phenol, cresols, formaldehyde and other components of resin binders and acids and alkalines used as catalysts, which would be present in many waste foundry sands (including green sand), would probably result in the waste being treated as special waste. This would inevitably increase costs dramatically, probably increasing disposal costs from typically 510-20/ton at present to upwards of 530/ton. With these costs, green sand reclamation would begin to look considerably more attractive.

All bag filter residues would be classed as special wastes in the new regulations and disposal costs would increase for these materials. Although quantities are relatively small (compared with waste sand or slags) these residues are very fine and careful handling procedures will have to be adopted to avoid creating severe dust emission problems. Site storage of the residues prior to disposal and disposal in sealed bags/containers or covered vehicles also will increase disposal costs.

Sludge Disposal

Sludge dragged out of wet arresters from sand plant and shakeout dust control systems can contain very high levels of active clay and even with high-performance filter presses, the pressed cake cannot be dried to better than about 6070% solids content. This sludge cake is difficult to handle and disposal costs can be high. One large U.K. foundry is paying more than 51000 per week for sludge disposal.

A recent EC directive requires that member states initiate legislation banning the disposal of any sludge containing more than 10% water, if it also contains potentially polluting substances such as phenol or heavy metals. As far as is known, no draft legislation on this matter has been produced by any member states, but it could result in large increases in the costs of sludge disposal if they have to be dried prior to disposal. This would increase further the pressure on foundries to switch to bag filters for control of dust emissions from sand handling plants and shakeout.