Grantee Research Project Results
Final Report: Rare Earth Elements Recovery Using Food Waste
EPA Grant Number: SU840166Title: Rare Earth Elements Recovery Using Food Waste
Investigators: Zhang, Wencai , Amini, Hassan , Huang, Haibo , Jones, Baxter , Li, Qi , Lobeda, Katherine , Jin, Qing , Gibson, Kayla , Muhoza, Emmy
Institution: Virginia Tech
EPA Project Officer: Spatz, Kyle
Phase: I
Project Period: December 1, 2020 through November 30, 2021
Project Amount: $25,000
RFA: P3 Awards: A National Student Design Competition Focusing on People, Prosperity and the Planet (2020) RFA Text | Recipients Lists
Research Category: P3 Awards , P3 Challenge Area - Sustainable and Healthy Communities
Objective:
Organic acids of small molecules such as lactic acid can be produced from food waste by fermentation under proper conditions. These molecules have binary natures, i.e., acidity and complexation ability, enabling them to be used as efficient lixiviants for metal extraction. Recent studies by PI Zhang showed that REEs can be extracted from coal waste using mineral acids, whereas the acid consumption is too high to promote economic viability for commercialized production. We hypothesized that the acid consumption and operational cost will be reduced using the organic acids converted from food waste as lixiviants for REEs. Furthermore, flotation beneficiation of bastnaesite from ores also suffers from high reagent cost due to the similar surface characteristics of bastnaesite and its associated gangue minerals. Small-molecule organic acids converted from food waste normally carry hydroxyl and/or carboxyl groups. These chemicals can be potentially used as inhibitors to depress the floatability of the gangue minerals and thus improving the flotation performance. The primary objective of the Phase I project is to prove the above hypotheses by converting food waste into value-added, renewable, and environment-friendly chemicals and using these chemicals to improve the economic viability of REEs recovery. To achieve this objective, organic acid production from food waste, REEs leaching from coal waste, bastnaesite flotation, techno-economic analysis, and P3 approach teaching efforts were proposed in the Phase I project.
Summary/Accomplishments (Outputs/Outcomes):
Our Phase I project started on December 1, 2020 with a total performance period of 12 months. In the first half of the project (12/1/2020 – 5/31/2021), our team members primarily focused on laboratory experimental tests to assess the feasibility of our concept. A considerable amount of laboratory experimental tests have been completed by the students in our team. The knowledge and skills mastered by the students from the experimental tests will lay a solid foundation for the P3 approach teaching relevant to the environment, sustainability, and resource recovery, which will be one of the major focuses of the second half of our project (6/1/2021 – 11/30/2021). Moreover, techno-economic analysis will also be carried out in the second half of our Phase I project, using the experimental data obtained in the first half. The major activities that have been completed include: (1) Food waste collection and preparation; (2) Parametric food waste fermentation and organic acids production tests; (3) Coal sample collection and preparation; (4) Parametric rare earth extraction tests; (5) Bastnaesite, calcite, and barite pure minerals collection and preparation; and (6) Micro-flotation tests of the pure minerals using organic acids as the depressant. The major results and findings from the activities are presented as follows.
Organic Acid Conversion from Food Waste: Our results have demonstrated that food waste can be converted into lactic acid via fermentation with a high fermentation efficiency and yield. With the same sugar concentration (60.0 g/L), the fermentation of food waste produced a higher lactic acid (53.0 g/L) than that of the control glucose solution, which only produced 36.1 g/L lactic acid. This indicates that food waste is a superior feedstock for fermentation to produce lactic acid. Experiments were also conducted to identify the optimal conditions of food waste fermentation to produce lactic acid. The identified optimal condition is: 0.5% of yeast extract and peptone addition, 100 g/L of sugar concentration, and controlling fermentation pH at 6.0.
REE Leaching from Coal Waste: Coal waste samples of different density fractions (1.4-1.8 SG (specific gravity), 1.8-2.2 SG, and 2.2 SG sink) were collected and prepared for REE leaching test. With the same dosage, higher recoveries were obtained using lactic acid relative to succinic acid. Moreover, among the three different density fractions, the highest leaching recoveries were obtained from the 2.2 SG sink fraction. For example, a recovery of around 58% was obtained from the 2.2 SG sink material using 0.2 mol/L lactic acid, while only around 50% and 20% of the REE in the 1.8-2.2 SG and 1.4-1.8 SG materials were leached under the same conditions, respectively. Moreover, a lower recovery of around 40% was obtained from the 2.2 SG sink material using succinic acid of the same concentration. Comparisons between lactic acid and hydrochloric acid were conducted by running leaching tests at the same pH. When the solution pH was fixed at 2.0, a recovery of around 60% was obtained using 0.2 mol/L lactic acid, which is higher than that obtained using hydrochloric acid (around 50%). Therefore, the organic acid is more efficient than the inorganic acid for extracting REEs from coal waste.
Bastnaesite Ore Flotation: A series of micro flotation tests were conducted on the prepared pure calcite, barite, and bastnaesite ores using organic acids, i.e., lactic and succinic acids, as the flotation depressant. The impact of pH, collector dosage, and depressant type as well as dosage were investigated. A recovery of greater than 99% was obtained at pH 9.0 using 5.6×10-6 mol/L sodium oleate as the collector; however, under the same conditions, the recoveries of calcite and barite were also greater than 80%. Therefore, satisfactory flotation separation of bastnaesite from calcite and barite in the absence of depressant is challengeable. Adding organic acids, such as lactic acid, into the flotation systems effectively decreased the recovery of calcite, while the recovery of bastnaesite was barely affected. For example, with the addition of 2.85×10-5 mol/L lactic acid, the flotation of calcite was reduced to below 10%, whereas bastnaesite recovery remained above 95%. Therefore, organic acids can serve as efficient depressants for the flotation separation of bastnaesite from calcite. However, the organic acids are not effective in the flotation separation of bastnaesite from barite. Our team is evaluating the potential applicability of other organic reagents, such as starch, as barite depressant in bastnaesite flotation.
As aforementioned, the majority of our P3 approach teaching activities will be carried out in the second half of our project (6/1/2021 – 11/30/2021), however, our team members have completed some efforts, which include: (1) Stories and articles introducing our project and the P3 approach have been released on several social media, such as PIs’ research group websites, the news portal of PIs’ department, and Virginia Tech News; (2) In January 2021, Co-PI Huang gave a presentation to >100 students/scholars from 10 different universities regarding the resource recovery from food waste in an online teaching platform; (3) One of our undergraduate researchers, Katherine Lobeda gave a presentation about her lactic acid production research in the Annual Research Presentation of her department; (4) We have reached out the Virginia Governor’s School for Agriculture (GSA) and scheduled a series of presentations (a total of 5) in July to introduce the concept of food waste and resource conservations to 50 selected high school students. The preliminary efforts have brought positive effects; for example, a few industrial stakeholders have contacted PIs for the potential collaboration opportunities.
Conclusions:
As stated in the prior section, a considerable amount of laboratory experimental tests has been completed by our team members, focusing on three major technical aspects of our proposed concept: organic acid conversion from food waste, REE leaching from coal waste, and bastnaesite ore flotation. The primary conclusions for each aspect are listed as follows:
Organic Acid Conversion from Food Waste: (1) Food waste is a superior feedstock for lactic acid production via fermentation due to its high carbohydrate and other essential nutrients; (2) The fermentation of food waste can be improved by adding additional nitrogen nutrients, increasing initial sugar concentration, and controlling pH; and (3) Under the optimized fermentation conditions, 289.6 kg of lactic acid can be produced from 1 metric ton of food waste (dry basis).
REE Leaching from Coal Waste: (1) Coal waste can be used as potential sources for REE recovery; (2) The REEs existed in coal waste can be extracted using organic acids; (3) Lactic acid is a more efficient lixiviant than succinic acid for extracting REEs from coal waste; (4) Lactic acid is more efficient than inorganic acids (e.g., HCl) for extracting REEs from coal waste.
Bastnaesite Ore Flotation: (1) Organic acids converted from food waste may be used for the selective flotation of bastnaesite where calcite is considered as the main gangue minerals; and (2) The preliminary results showed that the flotation of barite may not be prevented using organic acids as the flotation depressant.
Overall, the data obtained from the experimental tests indicated that our concept of using organic acids converted from food waste for REE recovery is technically viable. In the second half of our project, the data will be used to conduct a techno-economic analysis to assess the economic viability of our concept. Moreover, the data will also be used to promote our P3 approach teaching efforts in the second half.
Journal Articles:
No journal articles submitted with this report: View all 2 publications for this projectSupplemental Keywords:
Food waste, fermentation, organic acid production, rare earth elements, critical elements, coal waste, bastnaesite ore, recovery, beneficiationRelevant Websites:
Wencai Zhang's Research Group Exit , HUANG LAB AT VIRGINIA TECH Exit , LInkedin Exit ,
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.