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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 baghouse dust and slag. Table 1 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.
|
Table 1: |
Quantities of sand and other solid wastes generated by Queensland foundries |
|
Waste |
Tonnes/year |
|
Spent green sand |
11,322 |
|
Spent phenolic bonded sand |
9,799 |
|
Spent silicate bonded sand |
17,688 |
|
Spent furan-bonded sand |
3,496 |
|
Resin coated sand |
3,913 |
|
Spent silicate bonded zircon |
8 |
|
Core sand |
1,140 |
|
Baghouse dust (FFDC Dust) |
3,023 |
|
Shot-blast dust |
616 |
|
Furnace slag |
2,465 |
|
Dross |
127 |
|
Induction furnace lining |
114 |
|
standard firebrick |
8 |
|
ladle lining |
807 |
|
Furnace consumables - thermocouples etc. |
48 |
|
Sand reclamation dust |
132 |
|
Shot blast sand |
72 |
|
Clay graphite used pots (borden) |
1 |
|
General waste which cannot be recycled |
1 |
|
Approximate Total |
54,780 |
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. Baghouse 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 byproducts 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, baghouse 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 byproducts.
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:
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.
Figure 1: Sand Flows in the Queensland Foundry Industry
|
The Queensland Foundry Industry |
||
|
New Sand Purchased 48,700 tpa |
Spent Sand 46,400 tpa |
|
|
Sand Lost (< 5% baghouse dust & general loss) 2,300 tpa |
Landfill 85% Beneficial Reuse 15% |
As depicted in Figure 1, the average rate of internal sand reclamation for the Queensland foundry industry as a whole is currently 36%. Based on stated plans by several Queensland foundries, the industry average could potentially increase to 50% within the next two years.
Moving beyond 50% recovery will be relatively difficult. A further 5% may be gained if companies improve the efficiency of the current systems. Further gains will probably only be possible through the greater use of thermal reclamation, by improving moulding techniques to reduce the sand input, by changing to different casting processes or by identifying cost effective methods for sand reclamation at small foundries.
While significant work has already been undertake, most Queensland foundries recognise that there are many opportunities for continuous improvement in terms of by-product minimisation and for improving resource efficiency. Key areas identified by the sector include improved sand reclamation, metal yields, energy efficiency and the beneficial reuse of byproducts. All of these opportunities are discussed in further detail in this report.