BY-PRODUCT MANAGEMENT ISSUES FOR THE QUEENSLAND FOUNDRY INDUSTRY

Although the foundry industry is traditionally been viewed as dirty and hazardous, modern foundry processes are relatively clean and impacts are generally related to environmental nuisance issues such as noise and odour rather than impacts that are hazardous to human health and the environment.

Most foundries have made considerable effort to minimise these impacts and foundries located in build up areas, have developed sophisticated noise and odour management systems and regularly monitor emissions from the site.

The most significant waste management issues for the foundry industry is the generation of large quantities of spent sand and other solid by-products such as bag-house dust and slag. The table below provides quantities of sand and other solid wastes generated by the foundry industry in Queensland. Historically, many foundries disposed of these materials on site, however this practice has given way to landfill disposal. As the costs of landfill disposal continue to rise, alternatives to disposal are being pursued.

Note: This table does not include the Maryborough and Bundaberg foundries. A survey conducted in 1995 by the MITA (now the Australian Industries Group) estimated the State’s waste foundry sands (including these foundries) to be approximately 75,690 tonnes per year. The economic downturn has reduced the volume of waste generated by the industry in recent times. Source: (EPA, 1999)

These waste and by-product streams are relatively benign, particularly those generated from ferrous foundries. Most chemical additives used for sand binding are inert or of organic origin which biodegrade relatively quickly (EPA,1999). For ferrous foundries, waste sand typically passes toxic characteristic leaching procedure (TCLP) tests and can therefore be sent to non-secured landfill. Non-ferrous foundry sands are usually sent to secured landfill due to the presence of heavy metals. Bag-house dust from ferrous foundries is also sent to secured landfill, due to the fact that the dust is extremely light so is a potential occupational health and safety issue.

In total, about 46000 tonnes of spent foundry sand is generated per year in Queensland, 85% of which is disposed to landfill. Around 4,920 tonnes is being used as night cover at landfill sites and a further 2,280 tonnes is being used as a composting material. Therefore around 15% of the total spent sand is currently being used for some form of beneficial reuse.

In response to the increasing costs of landfill disposal, beneficial reuse of foundry by-products has received considerable attention by the industry in recent years, culminating in the development by the Queensland EPA of an Environmental Guideline, Beneficial re-use of ferrous foundry by-products. Five of the major ferrous foundries in Queensland hope to achieve 100% beneficial reuse for their major waste streams, (i.e. sand, bag-house dust and slag) within the next five years. If these companies achieve their stated goals, the volume of material diverted from landfill could be realistically increased from the current level of 15% to around 70% over the next five years. This would reduce the volume of material going to landfill by 25,000 tonnes per year. Beneficial reuse options are generally more limited for non-ferrous foundries, small foundries, and foundries that are located a long way from potential users of the by-products.

While beneficial reuse will play an important role in by-product management, greater potential value can be gained from Cleaner Production. Beneficial reuse is an ‘end-of-pipe’ strategy that reduced the cost of waste once it has been generated. Cleaner Production stops the waste occurring in the first place so can potentially reduce the cost of purchasing materials as well as reducing the cost of unnecessary processing, handling and disposal costs.

In general, the outlook for Cleaner Production in Queensland’s foundry industry is quite promising with many of the ideas presented in this manual already being undertaken. Based on a recent survey of Queensand’s major foundries, companies have actively sought to minimise waste and maximise resource efficiency in a number of areas throughout the foundry. Some of the most interesting examples include:

· Beneficial reuse of industry by-products, particularly sand, bag-house dust and shotblast;

· On-site and off-site sand reclamation and reuse;

· Energy efficiency programs (e. g. covering ladles, energy management and production scheduling, ensuring equipment is turned off when not in use, capturing waste heat from the furnaces and heat treatment processes);

· Increasing on-site recovery and reuse of metals including shotblast, machining fines and bag-house dust metals;

· Better segregation of shotblast from sand to increase reclamation;

· Conversion of bag-house dust to slag to reduce disposal costs or increase beneficial reuse options;

· Regenerating machine cutting oils;

· Investigation of new resin systems;

· Changing energy sources (e.g. grid power to bagasse, propane to natural gas, diesel to electricity); and

· Improving layout and housekeeping practices.

Reclaiming sand for reuse within the foundry process is seen as an important means of reducing the amount of sand disposed to landfill. Many of the larger foundries currently undertake manual sand reclamation. For foundries that produce large, iron castings sand recovery rates for manual reclamation can be as high as 90-96%, however for most operations in Queensland, recovery rates for those foundries undertaking reclamation is typically around 70-80%.

A number of Queensland companies are in the process of installing manual sand reclamation systems or optimising the systems to increase recovery rates. Thermal reclamation has not been widely adopted in Queensland due to the high cost of the systems and the relatively small volumes of sand generated in the state. One Queensland foundry, using a shell casting process, has recently commenced thermal sand reclamation to recover 100% of its waste sand. Many of the conventional sand casting operations have investigated thermal reclamation and may invest in these systems in the future.