Reusing Most of the Materials
Thermal waste treatment produces residues which can be either reused or landfilled. The principal components are slags and ashes, consisting mostly of non-combustible waste constituents such as glass, minerals or scrap metals. Flue gas cleaning also forms reaction products. The volume and nature of the residues produced depend mainly on the composition of the waste and the process used in the particular treatment concept. With an intelligent secondary treatment process, large parts of these materials can often be reused.
InovaRe by HZI – Efficiently Recovering Metals from Waste
Maximum metal recovery to high standards of purity, less need for landfill, and a reduced burden on the environment: InovaRe by HZI enables valuable metals such as copper, silver, palladium, and even gold to be recovered from waste.
Thermal treatment in the furnace is followed by a dry discharge of bottom ash, which is then processed. This allows metals such as iron, aluminum, copper, gold, silver, and palladium to be recovered – all while maximizing energy efficiency and without additional emissions. The high level of purity achieved by this process means large volumes of precious materials can be recovered, creating a source of substantial earnings over the long term. InovaRe also is a major contributor to saving resources and protecting the environment.
Visit ZAR, the development center for sustainable management of recyclable waste and resources (www.zar-ch.ch).
InovaRe (1.5 MB)
Fly Ash Washing
Stabilization and Product Recovery
If fly ash is collected separately from bottom ash and flue gas cleaning residues, two different methods may be applied to remove or immobilize fly ash contaminants:
- Acid washing of fly ash using acidic scrubber blowdown removes heavy metals in a recyclable form and produces a fly ash which can be disposed with the bottom ash.
- Neutral washing followed by solidification by adding binders to condition the fly ash into a leach resistant matrix
Acidic Fly Ash Washing
This process is an ideal combination of two flue gas cleaning residues: Acidic fly ash washing uses acidic scrubber blowdown to wash out the heavy metals from fly ash. Heavy metals can be recovered in the effluent treatment stage and recycled.
Neutral Fly Ash Washing
The aim of this process is to transform fly ash into a stable, leach proof matrix. Neutral, easily soluble salts are extracted in a cascade of stirred vessels. By controlling pH in a slightly alkaline range, soluble heavy metals are precipitated. Washing liquid is separated from the solids by filtration and cleaned in the effluent treatment stage. Dewatered solids are mixed with hydraulic binders to form a solid, stable and leach resistant matrix when landfilled.
Capture and Recycle Contaminants
The effluent treatment process neutralizes blowdown from wet flue gas scrubbers or from fly ash washing and removes contaminants such as heavy metals, ammonia or persistent organic pollutants (POPs). Depending on the plant configuration, some contaminants such as mercury or zinc can be recovered for recycling. The only remaining components in the cleaned effluent are naturally occurring salts such as sodium and calcium chlorides and sulfates.
Set the pH
Often lime slurry is used to neutralize acidic scrubber effluents. In a first step the pH is controlled to transform dissolved heavy metals into less soluble complexes. Induced flocculation enhances the precipitation of fine particulates, gypsum and metal complexes which allows separation in a sedimentation tank or a filter. Thereafter the pH is adjusted to the neutral range and a second purification is carried out with specific ion exchangers and activated carbon beds. After a final quality control, the clean effluent is discharged. The precipitated sludge is dewatered in a filtration system for final disposal.