Precious Metal Recovery from Waste Electrical and Electronic Equipment through Oxidative Refining
Round 1
Reviewer 1 Report
This study presents a refining process of master alloy from WEEE to recycle precious metals. However, some problems are existed.
(1) The introduction of experimental process is too brief. Vital information is missing. For example, what is the crucible size and furnace was used? What was the gas injection method? was a tube immersed into the bath directly?
(2) Oxidation refining is an exothermic process, different gas-injection time and oxygen contents could cause enormous temperature fluctuations; this effect should be taken into consideration.
(3) Compared with previous approaches, what is the new finding of this work?
(4) The EDX pattern (curve) in figures should be added.
(5) What is the separation result of metal from the slag after refining? Macro and micro images of the slag-metal boundary must be presented.
Author Response
Dear Reviewer,
We would like to thank you for your invaluable guidance and feedback. We are deeply appreciative of the meticulous comments and outstanding suggestions that have significantly improved the quality of our paper. In the following sections, we offer a detailed response to each of the comments, aiming to address the reviewers' concerns thoroughly.
Point 1: The introduction of experimental process is too brief. Vital information is missing. For example, what is the crucible size and furnace was used? What was the gas injection method? was a tube immersed into the bath directly?
Response 1: We have addressed your concerns by providing additional details in the 'Materials and Methods' section of the manuscript, specifically in lines 99 through 106, where we describe the experimental process in more depth. We have also included a schematic diagram of the refining process in Figure 1 to visually illustrate key aspects of the experimental setup. We believe that these additions will help provide a more comprehensive understanding of the experimental process. Your suggestions have been invaluable in improving the clarity and completeness of our manuscript.
Point 2: Oxidation refining is an exothermic process, different gas-injection time and oxygen contents could cause enormous temperature fluctuations; this effect should be taken into consideration.
Response 2: Regrettably, we did not account for temperature fluctuations during the process due to the absence of a system for direct temperature measurement of the sample. However, to guarantee complete melting of the metals and their retention in a liquid state, the samples were preheated to the desired temperature for one hour prior to the refining process and were consistently heated throughout to sustain the necessary temperature. Nevertheless, it would be of great interest to explore the temperature dynamics during gas injection. Therefore, we are considering modifying our device to include a temperature measuring system, enabling a comprehensive study of temperature fluctuations during the process.
Point 3: Compared with previous approaches, what is the new finding of this work?
Response 3: First and foremost, it's essential to highlight that our study utilized real electronic scraps, including PCBs and lead frames, providing a direct representation of practical recycling scenarios. Furthermore, our unique advantage lies in our capability to conduct the entire pyrometallurgical process, encompassing both smelting and refining stages, at a laboratory scale.
Initially, we employed an arc smelting process to extract metal alloys from electronic scraps, an achievement that sets our investigation apart. Subsequently, we executed a refining process employing the recovered metal alloy from the smelting phase, effectively enhancing the concentration of precious metals. This holistic approach allowed us to optimize the recycling process, demonstrating our commitment to transforming initial materials into valuable precious metals.
Point 4: The EDX pattern (curve) in figures should be added.
Response 4: The patterns of all EDX measurements can be found in ‘Appendix A’ section.
Point 5: What is the separation result of metal from the slag after refining? Macro and micro images of the slag-metal boundary must be presented.
Response 5: Following the refining process, it's crucial to note that the slag and metal alloy achieved complete separation. Consequently, there was no slag-metal boundary observed in this particular instance. As a result, we do not possess macro and micro images of the slag-metal boundary to present. The effectiveness of our separation process was such that the two components were distinctly and fully separated.
Reviewer 2 Report
In this study, the authors propose a study regarding the optimization of the recycling parameters to obtain precious metals from recovered waste Electrical and Electronic Equipment (WEEE). This paper should be revised in minor revision of the manuscript before it is suitable for publication.
-The characterization conditions such as calibration curves and methods should be provided in detail.
-For the waste treatment process, it is recommended to provide a flow chart with optimization conditions.
-The conclusive parameters seem missing since the purpose of this study is to find the optimum conditions for the WEEE recycling.
Author Response
Dear Reviewer,
We would like to thank you for your invaluable guidance and feedback. We are deeply appreciative of the meticulous comments and outstanding suggestions that have significantly improved the quality of our paper. In the following sections, we offer a detailed response to each of the comments, aiming to address the reviewers' concerns thoroughly.
Point 1: The characterization conditions such as calibration curves and methods should be provided in detail.
Response 1: Detailed information regarding the experimental processes for oxidative refining can be found in the 'Materials and Methods' section, spanning from lines 99 to 106. Additionally, specific details of the ICP measurement process have been provided in lines 298 through 302.
Point 2: For the waste treatment process, it is recommended to provide a flow chart with optimization conditions.
Response 2: We have included a flow chart of the recycling processes along with optimization conditions in Figure 1 to provide a visual representation of the waste treatment process. Additionally, we have detailed the experimental process, including specific process conditions, in the 'Materials and Methods' section, which can be found in lines 83 through 113 of the manuscript. We believe that these additions will enhance the clarity and comprehensibility of the waste treatment process in our study.
Point 3: The conclusive parameters seem missing since the purpose of this study is to find the optimum conditions for the WEEE recycling.
Response 3: We have addressed your concern by adding a section in the conclusion (lines 331 through 334) that summarizes the optimized refining process conditions. This addition provides a clear overview of the key parameters that were determined through this study to enhance WEEE recycling.
Reviewer 3 Report
The authors present a study on the extraction of precious metals from Waste Electrical and Electronic Equipment (WEEE) using a pyrometallurgical technique. The focus of the investigation lies in the impact of temperature and air pressure on the resulting refining purity. The findings underscore that optimal temperature and pressure conditions yield precious metals with remarkable purity levels. The experimental dataset not only reinforces these outcomes but also offers substantial contextual information. The reviewers have some comments as follows:
1. To enhance reader comprehension, it is recommended that the authors include a schematic diagram outlining the refining process.
2. The manuscript title could be improved by removing the abbreviation "WEEE" and using the complete term.
3. While the complete name of the chemical element should be mentioned, subsequent references can employ abbreviations.
4. It would be valuable for the authors to elucidate the distinctive merits of their work in comparison to existing literature.
5. Is the purity of precious metals significantly influenced by the presence of oxygen content?
6. The abstract should encapsulate specific conclusions drawn from the study.
Moderate editing of English language required
Author Response
Dear Reviewer,
We would like to thank you for your invaluable guidance and feedback. We are deeply appreciative of the meticulous comments and outstanding suggestions that have significantly improved the quality of our paper. In the following sections, we offer a detailed response to each of the comments, aiming to address the reviewers' concerns thoroughly.
Point 1: To enhance reader comprehension, it is recommended that the authors include a schematic diagram outlining the refining process.
Response 1: we have included a schematic diagram outlining the refining process in Figure 1 to enhance reader comprehension. Additionally, we have provided a detailed description of the experimental process, including the equipment used, in the 'Materials and Methods' section (lines 99 to 106) to ensure clarity and transparency in our methodology.
Point 2: The manuscript title could be improved by removing the abbreviation "WEEE" and using the complete term.
Response 2: Following the suggestion of reviewer, the abbreviation ‘WEEE’ was deleted and the title was revised to ‘Precious Metal Recovery from Waste Electrical and Electronic Equipment through Oxidative Refining’.
Point 3: While the complete name of the chemical element should be mentioned, subsequent references can employ abbreviations.
Response 3: We will ensure that the complete names of chemical elements are mentioned upon their first reference, and subsequent references will use abbreviations for clarity and consistency.
Point 4: It would be valuable for the authors to elucidate the distinctive merits of their work in comparison to existing literature.
Response 4: The merits of our work are particularly noteworthy when compared to existing literature. We took a unique approach by utilizing genuine electronic scraps, encompassing PCBs and lead frames, which closely replicate real-world recycling scenarios. This method ensures that our findings directly relate to practical electronic waste recycling processes.
In our 'Conclusion' section (lines 314 through 320), we have highlighted these merits.
Point 5: Is the purity of precious metals significantly influenced by the presence of oxygen content?
Response 5: Yes, the presence of oxygen content does significantly influence the purity of precious metals. As demonstrated in our ICP results, the concentrations of precious metals were notably improved after undergoing the oxidative refining process. Oxygen plays a crucial role in the selective oxidation of impurities while preserving and enhancing the concentration of precious metals, leading to increased purity.
Point 6: The abstract should encapsulate specific conclusions drawn from the study.
Response 6: The conclusion of this study has been added in abstract.
This is new version of abstract: This study delves into the application of oxidative refining for the recovery and concentration of precious metals, namely palladium (Pd) and gold (Au), from WEEE recycling, leveraging pyrometallurgical techniques. The primary objective is to optimize refining parameters, encompassing variations in gas pressure, temperature, and gas composition, to maximize the extraction and purification of precious metals from recycled materials. Through an array of comprehensive characterization techniques, encompassing microstructural analysis, elemental composition assessment, and metal concentration measurement, this study scrutinizes the potential of oxidative refining. The conclusive findings underscore the remarkable potential of oxidative refining in augmenting the efficiency and effectiveness of metal recovery from waste printed circuit boards (PCBs), with a pronounced emphasis on the concentration of Pd and Au. This research not only highlights the promise of oxidative refining but also concludes that optimizing process parameters, such as a N2/O2 mixed gas pressure of 4 l/min, process time of 40 min, and a temperature of 1400 °C, is imperative for achieving the highest efficiency in metal recovery from electronic waste, especially precious metals like Pd and Au. It further contributes to the sustainable management of electronic waste and the strategic extraction of valuable precious metals.
Reviewer 4 Report
Pyrometallurgical recycling is mature and commonly performed in recycling industries to recover valuable metals. Throughout the article, scientific novelty can be barely found although this is a relatively comprehensive study (with various parameters). In addition, due to lack of description or schematic drawing of the equipment and proper digestion method, the results are not very convincible with some semi-quantitative analysis, such as EDS and XRF.
The English writing is good.
Author Response
Dear Reviewer,
We would like to thank you for your invaluable guidance and feedback. We are deeply appreciative of the meticulous comments and outstanding suggestions that have significantly improved the quality of our paper. In the following sections, we offer a detailed response to each of the comments, aiming to address the reviewers' concerns thoroughly.
Pyrometallurgical recycling is mature and commonly performed in recycling industries to recover valuable metals. Throughout the article, scientific novelty can be barely found although this is a relatively comprehensive study (with various parameters). In addition, due to lack of description or schematic drawing of the equipment and proper digestion method, the results are not very convincible with some semi-quantitative analysis, such as EDS and XRF.
Response: We appreciate your thoughtful feedback and observations regarding our study. We acknowledge the importance of scientific novelty, and we would like to emphasize several distinctive aspects of our research:
- Real Electronic Scraps: Our study employed actual electronic scraps, including PCBs and lead frames, which closely mirror practical recycling scenarios. This approach ensures that our findings are directly applicable to real-world electronic waste recycling processes.
- Schematic Diagram: To enhance the clarity of our experimental setup, we have included a schematic diagram of the refining process in Figure 1. This visual representation offers readers a clearer understanding of key aspects of our research.
Regarding the semi-quantitative nature of EDS and XRF analysis, we recognize the limitations of these techniques. To address this, we performed ICP analysis to obtain more precise quantitative results. We found that the results from EDS, XRF, and ICP analysis were consistent with each other, further validating our findings.
Round 2
Reviewer 1 Report
The manuscript has been revised based on the comments and can be accepted in the present form.
Reviewer 4 Report
N.A.
N.A.
