Highlights
- Researchers assess the technoeconomic and environmental impact of recovering didymium oxide from hard drive shreds using acid-free dissolution recycling.
- The process shows potential for reducing dependence on mining, stabilizing REE market prices, and minimizing environmental impact of e-waste.
- Results indicate economic feasibility with optimization potential and lower greenhouse gas emissions compared to traditional recycling methods.
Energy engineer Esther Sanchez Moran MS (opens in a new tab), mechanism engineering, Iowa State University along with Mark Mba Wright (opens in a new tab), Associate Professor, Department of Mechanical Engineering, Iowa State University, Ames, Iowa and the Ames National Laboratory (US DOE) and colleagues approach the topic of electronic waste (e-waste), that rich source of rare earth elements (REE). The authors claim that “E-waste REE recovery can lower the dependence on mining, stabilize REE market prices, and reduce the environmental impact of landfilling.”
The need for technologies involving the recovery of REE from e-waste only grows, and this article presents a technoeconomic (TEA) and environmental (LCA) assessment of didymium oxide recovery from hard drive shreds through acid-free dissolution recycling. With an aim of assess the economic feasibility and the environmental impacts of the process, the authors summarize their findings.
Professor Mark Mba Wright
Before delving into those findings a brief description of the process and technologies.
Recovering didymium oxide (a compound primarily made of praseodymium and neodymium oxides, used in glass and magnets) from shredded hard drive materials via acid-free dissolution recycling involves a specialized process to selectively extract rare earth elements.
This approach is increasingly explored as an environmentally friendly alternative to traditional acid-based methods for rare earth recovery, which generate significant chemical waste and are costly due to acid handling and disposal.
Rare Earth Exchanges provides a brief breakdown of the steps involving acid-free dissolution recycling for Didymium Oxide:
| Step | Summary |
|---|---|
| Shredding and Pretreatment | Hard drives are first shredded into small particles, exposing materials like neodymium magnets embedded within. These shreds are often subjected to mechanical or thermal treatment to release embedded rare earth metals, primarily neodymium (Nd) and praseodymium(Pr). |
| Dissolution Using Selective Solvents | An acid-free solvent, typically an ionic liquid or other complexing agents, is introduced. These solvents are tailored to selectively dissolve rare earth elements without impacting other materials such as aluminum or iron. Ionic liquids are especially useful due to their ability to break down metal bonds at lower temperatures and without acid involvement. |
| Separation and Precipitation | Once dissolved, rare earth elements can be separated through precipitation techniques. Conditions are adjusted to allow Nd and Pr ions to crystallize as didymium oxide, minimizing impurities from other metals present in the hard drive. |
| Purification | The didymium oxide precipitate is purified to remove remaining contaminants. This may involve washing, magnetic separation, or further refinement depending on the purity required. |
| Recycling of Solvents | Many acid-free dissolution processes allow for recycling of the solvents, reducing waste and further lowering the environmental impact. |
Some Advantages
This acid-free approach offers key benefits by reducing the chemical waste associated with conventional recycling methods and preserving the integrity of valuable metals for reuse in magnets and other applications. Acid-free recycling also can align with circular economy goals by allowing for the sustainable reuse of critical materials in high-tech and green technologies, such as electric vehicle motors and wind turbines. Such techniques are still emerging, with ongoing research focused on improving the efficiency, cost, and environmental benefits of acid-free dissolution recycling.
Iowa State University Study Results
As reported in the peer-reviewed journal ACS Sustainable Chemistry & Engineering (opens in a new tab), the results reveal that a facility with an annual processing capacity of 342.42 tonnes of hard drive shreds per year collects 2.53 tonnes of didymium oxide.
With an estimated minimum didymium oxide price point at $130/kg, the Iowa-based authors’ sensitivity analysis points to additional optimization of the recycling technology could potentially reduce the cost to approximately $73/kg.
What about greenhouse gas (GHG) footprint? The authors write that this would be estimated at 4.91 kg CO2/kg REE. Additional sensitivity analysis evidences REE and CuSO4 recovery efficiency and HDD content are the primary factors impacting the MSP. When comparing hydrometallurgical and electrometallurgical processes they found that “acid-free dissolution is an attractive e-waste strategy.
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