Case Study: Brantner Fine Metal Recovery from Bottom Ash

 


Background

Incinerator bottom ash (IBA) is the residue of municipal and industrial waste–to-energy (WTE) plants. It consists mainly of inorganic (mineral or glassy) matter, unburnt organic matter and metals. Modern ash processing facilities are primarily trying to separate ferrous, aluminum, copper, stainless steel and zinc metal from the inorganic matter so the metals can be sold to smelters and the inorganic matter can be used as a construction aggregate or disposed of safely in a landfill. 

Since 2013 Brantner Oesterreich GmbH has operated a wet process plant with a capacity of 50 t/h raw IBA (0 – 300 mm). The plant utilizes magnets, a jig and an eddy current separator to recover coarse (+ 2 mm) ferrous and non-ferrous metals.

Challenges

  • While Brantner’s plant was doing a great job of recovering metals in the +2mm size fraction, all bottom ash smaller than 2mm were reporting to tailings.
  • Approximately 20-30% of ash is finer than 2 mm and contains ferrous metals, heavy non-ferrous (HNF) metals, mainly copper, zinc, lead and precious metals. Precious metals trace back to electronics and jewelry.
  • On average and across a range of WTE facilities from many countries, gold grades are 0.5ppm, silver grades are 11ppm and copper grades are 3,300ppm.
  • Branter believed there was an opportunity to profitably recover these fine metals. Additionally the metal content in the process tailings would be reduced providing for safer disposal and the potential to use the material as a construction aggregate.

Solutions

  • Sepro and Brantner worked together to develop a Fine Slag Treatment Plant that would fit within their existing bottom ash treatment plant.
  • Sepro designed a modular plant to speed up installation and commissioning at site.
  • Sepro and Brantner worked together after commissioning to optimize and improve plant performance, further increasing plant revenue and profitability

Results

  • The FSTP was installed and fully commissioned in three weeks
  • The FSTP produces approximately 70kg/h of fine heavy non-ferrous concentrate with an average metal content of 80% which is sold to copper smelters
  • While specific financial results are confidential, overall project economics have met expectations.

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