Optimized Metals Separation for Remanufacturing of Product-Centric Recycled and Reclaimed Scrap

Gupta, Akanksha

Etd

Optimized Metals Separation for Remanufacturing of Product-Centric Recycled and Reclaimed Scrap

Public Deposited

The increasing complexity of products has made recycling and reclamation of metals a challenge due to chemical and thermodynamic interactions between the various elements. A product centric view of recycling is at the heart of recycling for such complex multi-material products at their end-of-life as it takes the entire material into account instead of one-metal-at a time view. Metal substrates are often coated with metal coatings, refractory coatings, or other types of coating to prevent corrosion and erosion of the metal substrate during service conditions. These coating must be removed from the substrate before effective recycling can be conducted so that there is minimal contamination in the final recycled product. This project is focused on the recycling and recovery of bi-material composites which consists of metal-based coatings on metal-based substrates. The recovery techniques are studied for three bi-metallic composites – Tantalum coated steel, CrC-Nichrome coated stainless steel and Tin coated steel. The objective of this study is to review coating separation techniques, optimize coating separation techniques for aforementioned samples and provide a general guideline for coating separation techniques for diverse types of bimetallic composites. The three bi-metallic samples differ in type of coating and its composition, its bonding to steel substrate and the grade of steel substrate used. Separation of tantalum from steel is achieved by high-temperature oxidation wherein tantalum is recovered as value added product of tantalum pentoxide. The optimal temperature for oxidation is 700°C but optimal time is a factor dependent on the coating thickness. For CrC-Nichrome coated stainless steel, remelting, and casting into secondary steel was investigated because the coating chemistry consists of major alloying elements for stainless steel substrate. A mathematical model based on linear programming was formulated to determine the amount of steel scraps to be mixed to obtain the desired secondary steel concentrations. Modelling was validated through induction furnace experiments. Moreover, recovery rate of chromium was determined with and without the use of flux as well as hardness testing was done to prove the feasibility of this process. In the case of tin coated steel, two electrochemical processes were evaluated to selectively electrodeposit tin metal on a suitable cathode. Various electrodeposition parameters like type of anode and cathode, current density, temperature, and time, oxidizing agent, among others, were investigated. Current efficiency was found to be very high when electrodeposition was carried out with pure tin compared to tinplate. It was concluded that there is a critical tin concentration needed in electrolyte for high current efficiency.

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