What Does it Mean?
Incinerator bottom ash (IBA) is produced from municipal and industrial waste to energy and incineration facilities. It is the material left over after incineration which does not fully burn. In Canada approximately 97% of the waste requiring final disposal is sent to landfills and 3% is incinerated. In Europe, 20-25% of waste is incinerated with some European countries incinerating over 60% of municipal solid waste.
Approximately 20-30% of this ash is finer than 2 mm and contains precious and heavy metals, mainly gold, silver, platinum, copper, stainless steel, zinc and lead.
Why is Incinerator Bottom Ash an Exciting Topic?
Did you know that precious metals can be extracted from the left-over ash from incinerators?
There are over 800 waste incinerators worldwide and over 400 in Europe. In Europe alone, 20 to 30 million tonnes of IBA is produced annually. About 25% of this contains recoverable valuable metals.
Approximately 90% of copper, 70% of silver and 80% of the gold in IBA can be recovered. Once recovered, some of these metals can be sold directly to metal refiners for profit. In addition, some of the material can be reused to make products and construction materials. Your current electronics, jewellery, or pipes may contain metals recovered from incinerator bottom ash!
This type of mining is called urban mining. What is urban mining? Urban mining is the process of recovering compounds and elements from used products, buildings, or e-waste. This is an ecofriendly process as the elements are recovered from discarded material instead of being mined from the earth.
A Fine Slag Treatment Plant can easily be integrated into existing incineration facilities, increasing their profit and reducing the amount of ash sent to landfills. The ability to produce construction aggregates from the processed ash minimizes the need for landfilling. Wet process solutions lead to higher resource recovery, lower footprint, minimized dust emissions and the ability to produce quality construction aggregates. Fine slag treatment plants (FSTP) can be added to both dry and wet existing IBA treatment plants.
What is the Value in Mining Incinerator Bottom Ash?
There is significant metal value in incinerator bottom ash. Fine IBA contains metals including gold, silver, platinum, aluminum, copper, stainless steel, zinc, and ferrous material. Using Sepro’s Falcon Centrifugal Concentrators along with other gravity separation devices, these metals can be recovered and sold to metal refiners and recyclers for a nice profit.
After the metals have been recovered and recycled, the remaining ash material can also be used in the construction industry. Since extracting aggregates from quarries is a very energy-intensive and costly process, infrastructure projects should use as many recycled materials as possible. IBA can be used as bulk fill, concrete, cinder blocks, and other cement materials depending on local regulations. Recycling IBA also reduces expensive landfill fees.
Rejected ash is then sent to landfills with minimal metal contaminants which can harm the environment.
How is Incinerator Bottom Ash Processed?
Bottom ash is fed into a wet jig or screen, which separates the fines. In the first step, a low intensity magnetic separator removes ferrous particles from the slurry, and the resulting concentrate can be sold to smelters for use in special smelting applications.
The fraction containing most of the precious metals is then sent to the rest of Sepro’s proprietary Fine Slag Treatment Plant (FSTP). The non-ferrous slurry is treated by slot separators, shaking tables, and Falcon gravity concentrators. The low G slot separator stage recovers larger heavy metal particles, and the high G stage recovers smaller heavy metal particles which includes most of the precious metals. These processes minimize heavy metal and leachable contaminants in the leftover ash which is sent to landfills.
Using a combination of screening equipment, gravity concentrators, and magnetic separators, two valuable products are produced: a ferrous metal concentrate as well as a non-ferrous metal concentrate containing copper and precious metals. In addition, a cleaner final ash material is produced that is often used in higher value construction projects.
Once the ash has been processed, the separate ferrous and non-ferrous concentrates are produced and bagged. The fine heavy non-ferrous concentrate is sold to copper smelters or upgraded to separate the precious metals for sale to refiners. Concentrates which are not sold to smelters are cleaned further. The leftover ash is dewatered and then sent to landfills with minimal remaining metals.
Why is Wet processing better than Dry?
Easier separation and less equipment wear are the main reasons that wet separation is used rather than dry or air separation, especially for very fine particles.
Ash processing technology for IBA is either wet or dry. Conventional dry technology has physical limitations with separation. The moisture content in dry ash can make heavy non-ferrous metal recovery ineffective.
Conventional dry processing plants require the ash to be aged for 4-6 weeks, and the moisture reduced to about 10% before metal can be effectively separated. In addition, the ash may also need to be crushed to increase metal liberation. It is then sized, ferrous metal is removed and fed into eddie current (EC) separators for recovering metals. Sometimes oversize material is sorted by hand or sensor-based machines. Fine metals are lost in a dry process, as most remains unliberated or respond poorly to EC separators.
The adaptation of a conventional facility to include wet processing provides many benefits. There is no aging period, less storage is required, and dust is mostly eliminated because the fines are separated in a wet process and the coarse fractions remain moist. Material buildup on conveyors and chutes is also minimized. Existing conventional process plants require no technical modifications. Better liberation allows for higher metal recovery rates.
For further information, call Sepro at 1-800-990-5568 or contact our team.