Zinc is successfully recycled from its main uses: galvanized steel is re-melted, and the protective zinc coating finds its way back into zinc smelters for recycling. Brass is recycled in the copper industry, and zinc metal scrap is re-melted. Zinc’s end-of-life recycling rate represents 55% in Europe, 50% in North America, and 45% at the global average. Still, there is room for improvement and the global call for an increased circular use of materials moves those zinc fractions into focus that are not yet recycled today.
Often waste incineration is seen as the ultimate solution for treating waste, that may even be used for energy production. Metals that are less volatile such as copper and steel survive the incineration process in the so-called bottom ash. These are sorted and recycled. But other metals and compounds that are more volatile, such as zinc, lead, and part of copper end up in fly ash. Zinc can be recycled from fly ash, but often landfilling is cheaper.
In Switzerland, fly ashes were landfilled in the past. But it appears that the landfill capacity in Switzerland is quite limited and expensive. Also, exporting fly ashes for treatment outside the country goes against Swiss environmental regulations. The Swiss energy from waste (EfW) plant KEBAG supported by the BSH Umweltservice AG already in 2010 decided to develop a recycling process that would allow the recycling of metals contained in the fly ash and at the same time reduce the landfill capacity needed. Today KEBAG produces 250 tons of SHG zinc per year, treating 6500 t of fly ashes from two EfW. With the enforcement of the new Swiss regulation (VVEA) in 2015, metals from waste incineration fly ashes must be recycled after 2021. The project SwissZinc aims at recycling metals from fly ashes of all Swiss EfW plants. A production of 2000 t of SHG zinc is envisaged.
The Swiss way is unique, and its feasibility heavily depends on the country specific regulatory framework. Nevertheless, it is an example for unleashing valuable metals from waste thus contributing to circularity and UN SDG 12 responsible consumption and production.
IZA spoke with Dr. Stefan Schlumberger, head of the competence center for hydrometallurgical operations at Swiss foundation ZAR.
Could you briefly present KEBAG AG and its activities?
KEBAG in Zuchwil, Switzerland is responsible for energetic use of flammable municipal waste from 188 communities with about 483.000 inhabitants. 138 communities are shareholders of KEBAG AG. From 220000t municipal waste annually, KEBAG produces 165000 MWH electricity and an additional 165000 MWh district heat. About 6000 t Iron and other metals are recovered from the bottom ash.
What makes the KEBAG process different from every other waste incineration plant?
Fly ashes from the waste incineration process have been landfilled in underground disposal sites for a long time. In later years these have been washed or hydraulically bound . Fly ashes consist of 4% zinc, 3% aluminum, 2% iron, 1% titanium, and lead, copper and antimony below one percent. Landfill capacity is Switzerland is scarce and expensive. Since 2012, KEBAG recycles zinc, copper, cadmium, and lead from fly ashes from two waste incineration facilities.
Could you describe the FLUREC and the FLUWA processes? What is the added value of combining these two methods?
An acidic filter ash leaching process (FLUWA) removes heavy metals from the filter ash. The remaining metalliferous filtrate is processed by the FLUREC process which involves leach purification and electrolysis. Copper, lead and cadmium are recovered in a cement by-product which is sold as secondary raw material to metal smelters. About 250 t of Special-High Grade (SHG) zinc, a high-purity metal is sold as product. The combination of FLUWA and FLUREC allow for not only limiting the need for landfill capacity but also contributes to circularity. Valuable metals are recovered from a waste stream that had been landfilled before.
Is it the economic value of the metals or rather the specific Swizz regulatory framework that makes the process viable?
The high costs for landfilling and the additional revenue from the recovered metals contribute meaningfully to the overall economical result of the process. Nevertheless, it’s also due to the specific and very strict Swiss environmental regulatory framework that the mid-to long-term perspective of our technology is quite promising: With the enforcement of the new Swiss waste regulation (VVEA) in 2015, metals from waste incineration fly ashes must be recycled after 2021.
Are there new developments foreseen in the coming years?
In Switzerland, metals are recycled from fly ashes of 12 waste incineration plants. This covers about 65% of all ashes today. To reach the goal of 100% coverage for Switzerland, 2-3 new FLUWA plants will be built to leach the remaining fly ashes. Metals will then be recycled from the resulting heavy metal concentrate in a centralized plant in Zuchwil. Under the brand name SwissZinc AG, presently the Swiss Waste incineration plants unite their joint activity of setting up a new production facility at Zuchwil for the additional metal cement and zinc production. Once the new plant is in full production in 2025, an annual zinc production of 2500 t is the goal.
IZA thanks Mr. Schlumberger for accepting the interview