What is Required for the Viability of Metal Recovery from Municipal Solid-Waste Incineration Fly Ash?

– Design and Assessment of a Process Pland for Copper Extraction

Abstract

The incineration of municipal solid waste produces large amounts of fly ashes, today in Sweden around 200 000 tons/yr. The ashes normally contain a considerable amount of valuable and hazardous metals. To fulfil the environmental regulations, most of these fly ashes can be deposited only in specific sites. This handling costs, requires energy and leads to emissions in the transportation to the deposit site. This work, taking departure in laboratory experiments for crucial steps, discusses possible chemical processing schemes and from this develops an overall design of a plant for the extraction and production of copper from the fly ash generated in a fluidized bed waste incineration plant. It also addresses the economic viability and environmental impact of the suggested processing in comparison to current handling, which involves transport to and disposal of the fly ash in Norway. The proposed process involves a leaching step, a solvent extraction process, a stripping step where the copper is transferred to an aqueous phase and finally electrolysis. By quantitative modelling and cost estimates of the processing steps of the proposed plant we identify the most important factors for the economics and environmental impact of the plant. In addition, we quantify the necessary recycling rates of the different process chemicals for achieving profitability. We conclude that a crucial factor is the recycling rate of the used organic solvent. Important parameters are also the handling costs and transportation needs of the rest products. For instance, a major benefit of the process is if treated fly ash can be reclassified such that it is allowed to be disposed into the own close-up hazardous waste landfill thus lowering the costs and environmental impacts. An extension of the process to include also the extraction of metals other than copper, for instance zinc, should be an interesting further development to consider.