(385au) Influence of Reactive Conditions on Metal Oxidation States: Critical Metal Recovery from Municipal Solid Waste (MSW) and Corrosion Behavior in Extreme Environments

Approximately half of the MSW produced in the US is disposed of in landfills. A viable alternative to this is Waste-to-Energy (WtE) facilities that produce electricity by combusting MSW and thus reducing waste volume. The economic growth has increased the demand for critical materials, leading to the recovery of valuable materials from MSW. The flue gases released by burning this MSW significantly impact the WTE plants through high-temperature corrosion. Particularly in the U.S., the WTE industry allocates approximately one-third of its annual maintenance budget to corrosion-related maintenance, which can account for around 10% of the annual turnover. The experimental investigations for this work were conducted within two distinct research efforts; the first part is the introduction of additives to the WTE stream for recovery of critical elements, and the second part focuses on evaluating new materials that may provide resistance to corrosion to extend the life of the superheaters in the WTE plant. Investigations were made on the alterations in metal oxidation states influenced by gas-solid, gas-gas, and solid-solid reactions.

1. Additives in waste stream: This work is primarily focused on solid additives that modify the oxidation states of valuable metals in WTE bottom ash (BA) by the introduction of different additives. The experimental results from techniques like XRD, SEM/EDS, TGA, FTIR, and micro-GC demonstrated noteworthy alterations in the oxidation states of elements like Mn, Ti, Al, and Fe, resulting in an approximate 20-40% increase in their extraction efficiency.
2. Corrosion in superheater WTE alloys: In the context of WTE plants, the impact of flue gas on the change in the oxidation states of metals in superheater alloys was studied. Various alloys containing different weight percentages of elements like Nickel (Ni), Chromium (Cr), Silicon (Si), Tungsten (W), and Molybdenum (Mo) were examined. Characterization techniques revealed that the presence of elements like Ni, Mo, W, and Si improved the alloys' corrosion behavior. Changes in oxidation states of metals Fe (+3), Ni (+2), Cr (+6), Si (+4), W (+6), and Mo (+6) were observed, which are attributable to the formation of metal oxide and chloride scales. About a 60% decrease in corrosion mass loss was observed in an alloy with high amounts of Ni (+2), Mo (+6), and W (+6) with time compared to the other alloys tested.

Thus, this research work elucidates how alterations in oxidation states of elements in diverse environments contribute to material recovery potential as well as to material loss, offering valuable insights into waste-to-energy processes and material science.

Research Interests

1. Utilization of various analytical techniques: My focus is on the implementation of different analytical techniques to study new materials to understand their properties and behaviors by developing appropriate characterization methods. Analytical techniques provide detailed information about the material structure, composition, and morphology. This information can be used to predict changes at the molecular level when modifications are made to the material.
2. Development of advanced materials: My interests lie in developing and enhancing the performance of different materials in terms of properties like improved strength, corrosion resistance, slagging, and fouling resistance. This involves designing and synthesizing new alloys and coatings that exhibit good mechanical properties and durability in harsh environments. Also, developing sustainable and efficient synthesis processes of advanced materials.
3. Process optimization and scale-up: Having developed efficient processes for the synthesis of advanced materials at a laboratory scale, my interest involves scale-up and process intensification.