Incinerator bottom ash is the ash product leftover from waste incineration facilities. It contains non-combustible materials which may include precious metals like gold, silver and platinum group metals.  Historically, recovering these fine materials was not possible and all fine particles were sent to the local landfill. However, we now have the technology to selectively recover fine heavy and precious metals while using the remaining ash as construction aggregate. At Sepro, we’ve pioneered a wet process to recover these metals using a system of screens, gravity concentrators, strong magnets, and more. Here’s how it all works. 

The Basics of Incinerator Bottom Ash

Incinerator bottom ash often contains precious metals and heavy metals that can be a challenge for disposal facilities. However, if these metals are selectively recovered, they can be sold directly to recyclers and metal refiners, giving incineration facilities an extra stream of revenue.

In addition, many jurisdictions, especially in Europe, are encouraging or mandating the treatment of fines and the washing of fine incinerator bottom ash so that it can be used as construction aggregate material.

Dry Processing of Incinerator Bottom Ash Cannot Recover Fine Material

Until recently, most incinerator bottom ash has been treated using dry processing methods to recover metals. Unfortunately, dry processing methods are not effective on fine material (typically below 6mm and certainly below 2mm). This finer material is often just sent to landfills.

Using the Wet Treatment Increases Fine Metal Recovery Rates

Wet treatment simply means that water is used as the transportation medium through the process and many of these plants are already in operation. Because of their success, more and more wet treatment incinerator bottom ash plants are being commissioned every year. 

Sepro’s Wet Treatment Incinerator Bottom Ash Process

Sepro’s wet treatment plant will first screen material at 40mm or 50mm. A belt magnet then removes coarse ferrous material.

Incinerator bottom ash then goes to a jig. Uncombusted material floats off the top of the jig. +2mm material is separated into a light fraction and a heavy non-ferrous fraction. This light fraction can be sent to eddy current separators for aluminum and stainless steel removal and can then be used as construction aggregate. The heavy non-ferrous can be sold directly to smelters or further separated for the creation of specific non-ferrous products.

The -2mm goes to the Sepro Fine Slag Treatment Plant (FSTP) which consists of several gravity separation processes [link to FSTP video]. The FSTP generates a -2mm light fraction that can be mixed with the +2mm aggregate and used as construction aggregate. The -2mm ferrous fraction can also be sold directly or mixed with the coarse ferrous material from the first belt magnet. The -2mm heavy non-ferrous metal fraction can be sold directly or processed further

Removal of the fine metals through the FSTP removes much of the leachable metal particles that have a high surface area. This dramatically improves the free use of the aggregate product without physical isolation measures to prevent metal leaching. 

The water treatment system removes and dewaters the slimes from the process. The dewatered slimes can be mixed back with the light aggregate product and/or landfilled depending on the amount of slimes and the aggregate specifications for fine particle content. 

Want to Learn More about Incinerator Bottom Ash Recovery?Many incineration facilities are taking advantage of wet processing bottom ash, like the Brantner Oestereich’s incinerator bottom ash processing operation in Austria. If you’re looking to recover fine metals from incinerator bottom ash, or want to discuss a custom urban mining solution, contact the experts at Sepro Urban Mining.