(590d) Impact of Reactive Conditions on Wte Ash for Recovery of Elements and Waste Management

The economic growth in society has spurred a substantial increase in metal production, notably in modern high-technology industries, where precious, critical, and rare earth elements (REEs) are in high demand. To overcome this high demand, currently the US imports about 95% of these elements from different countries. Moreover, the escalating production of these elements is accompanied by growing challenges related to the limited availability of natural resources and costs associated with their extraction. To address these challenges, it is crucial to prioritize reducing the depletion of natural resources and improving the utilization of elements from waste. The considerable accumulation of materials within waste presents an opportunity to retrieve essential elements crucial for industrial applications. Notably, these elements are abundant in the ash derived from Waste-to-Energy (WTE) facilities, providing an avenue for efficient resource recovery and seamless integration into the circular economy.

This research focuses on the treatment of WTE ash with waste from other streams like gypsum waste from the construction and demolition sector and spent Fluidized Catalytic Cracking catalyst (FCC) from chemical industries. WTE ash is thermally treated (up to 1500℃) with these additives in 15, 30, and 50 weight percentages in reactive conditions to investigate the transformation in the crucial elemental compounds and how they can be converted into more extractible forms.

Various characterizations like XRD, SEM/EDX, gas chromatography (evolved gas analysis), and thermal analysis, are utilized to study the changes in the elemental compounds at different temperature ranges, after their exposure to reactive environments. The introduction of the additives has already demonstrated the modifications in the transition elemental compounds. This work is focused on studying the changes in precious and REE compounds. The results showed the formation of different oxides, elemental compounds with aluminum or silicon, and alumino-silicate compounds by altering the oxidation state of the elements. These precious and REEs compounds formed are soluble in different acids which can lead to ease in their extraction via the acid leaching process. Thus, elements present in the WTE ash can be recovered by including gypsum and/ or spent FCC catalysts.

Furthermore, combining the equilibrium calculations with the characterization results showed the formation of various mineral compounds that impact the slagging behavior of the ash. The mineral compounds formed after the incorporation of the additives elevated the ash fusion temperatures (AFTs) by 100-200℃, leading to a reduction in the slagging of ash at low temperatures. This improvement is because of the formation of alumina-silicate compounds which have higher melting points than the original compounds in the ash causing an increase in the AFTs.

This presentation will show comparative results for several conditions and discuss possible restates, mechanisms leading to the transformations in elemental compounds and their oxidation states, and the gases evolved.