Mechanism of Extracting Germanium from Ge-Containing Solution with Tannins
Round 1
Reviewer 1 Report
Approach is good.
However, SEM part should be supported by EDS.
TEM analysis should be elaborated. TEM images should be explained properly and supported by other characterization studies made.
Author Response
Point 1：SEM part should be supported by EDS.
Response 1: This paper focuses on the morphological characteristics of tannic acid and tannic germanium as pure substances and therefore no EDS analysis has been carried out on them.By SEM analysis of tannic acid and tannic germanium, when tannin reacts with germanium, the germanium is deposited on the tannic acid molecules, i.e. the deposition pattern of tannic germanium is layer polymerisation.
Point 2：TEM analysis should be elaborated. TEM images should be explained properly and supported by other characterization studies made.
Response 2:The TEM examination in this paper is also primarily for morphological analysis. The images show that neither tannic acid nor tannic germanium has a distinct lattice structure when viewed at high magnification, indicating that they are not crystalline. It can be observed that the tannic acid has a clear lamellar structure and the tannic germanium is clearly stacked layer by layer, so it can be determined that the tannic germanium is deposited layer by layer on the tannic acid molecules as germanium.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The submitted manuscript by Kun Yang et al. regards the mechanism of extracting germanium from Ge-containing solutions with tannic acid. Infortuneally, the present work is trivial and lacks novelty. The introduction section is very poor and a clearer statement of the objectives is needed. The experimental results are not always comprehensive and do not support all conclusions of the work. I do not suggest this paper being published in Metals.
Specific comments:
The authors should identify the abbreviations the first time used (e.g. FT-IR, MIBK, etc).
282nd line: Why did you select a pH value close to 1.5? How did you maintain it constantly in the trials? The authors should specify and explain your choice of experimental conditions.
103rd line: “per-liquid”, “pre-liquid”. Please, revise.
150th line: “In the FT-IR curve…the diffraction peak” Please, revise.
5 252nd line: The authors should discuss the negative charge of the Ge-complex in the proposed mechanism.
Author Response
Point 1：The authors should identify the abbreviations the first time used (e.g. FT-IR, MIBK, etc).
Response 1:In the text Analysis and equipment. All test methods and test equipment are described and full names and abbreviations are mentioned.
Point 2：282nd line: Why did you select a pH value close to 1.5? How did you maintain it constantly in the trials? The authors should specify and explain your choice of experimental conditions.
Response 2: According to the literature, the optimum conditions for the precipitation of germanium by tannic acid are pH 1.50. Both the germanium solution and the tannic acid solution were adjusted to pH 1.50. The pH was tested every two minutes during the experiment
Point 3：103rd line: “per-liquid”, “pre-liquid”. Please, revise.
Response 3:The text has been revised with a different form of expression and the revision has been completed
Point 4：150th line: “In the FT-IR curve…the diffraction peak” Please, revise.
Response 4:The text has been revised with a different form of expression and the revision has been completed
Point 5：252nd line: The authors should discuss the negative charge of the Ge-complex in the proposed mechanism.
Response 5:The course of tannin coordination with germanium should be divided into two steps.The first step is that the phenol hydroxyl group in tannin is ionized to form phenoxy anion. The second step is the coordination of germanium with anion of phenoxy.It is inferred that the reaction process of tannin and germanium is that the two phenol hydroxyl groups in tannin react with Ge4+,which means the reaction mechanism of tannin reacts with germanium to produce tannin germanium is that the o-phenol hydroxyl groups in tannin react with Ge4+,sp3d2 hybridization is performed to form Ge-O covalent bond.
Author Response File: Author Response.pdf
Reviewer 3 Report
Mechanism of Extracting Germanium from Ge-containing Solution with Tannic Acid is very interesting paper. Some improvement is required.
Line 11, 12: The germanium complex with tannin process is the maturest technologies for extracting germanium from Ge-containing solution /what are conditions: temperature, pressure,…)
Line 29: Germanium is a rare metal (critical)
Line 55: In view of the above problems. (this statement is not finished. Please to check it)
Line 88, The germanium concentration was determined byinductively coupled (by inductively coupled)
Line 106. Figure 2. Germanium complex rate and germanium concentration at different tannins multiples (Please to explain the meaning of the red and blue color at Figure 2)
Line 119: it can be concluded that the tannins content of 30 times and germanium complex rate are the best. (Did you make comparison with other extraction reagent for germanium)
Line 194: The reaction solution is nitric acid. What is reason for this choice? Why not sulfuric acid?
Line 224: From Figure6a and b, the tannins is a three-dimensional spherical object, with a smooth surface. Do you use some EDX-analysis combined with SEM_analysis to confirm chemical composition of the
tannins
Author Response
Point 1：Line 11, 12: The germanium complex with tannin process is the maturest technologies for extracting germanium from Ge-containing solution /what are conditions: temperature, pressure,…)
Response 1：The best experimental conditions, based on the conditions of this experiment, are the reaction time of 60°C, the pH of 1.50, the reaction time of 30 minutes and the tannin addition of 30 times the germanium content.
Point 2：Line 29: Germanium is a rare metal (critical)
Response 2:Germanium is a typically rare and dispersed element.
Point 3：Line 55: In view of the above problems. (this statement is not finished. Please to check it)
Response 3：In view of the above problems, this paper investigates the complex process of tannin and germanium and the deposition pattern and complex mechanism of germanium-tannins through chemical coordination experiments.
Point 4：Line 88, The germanium concentration was determined byinductively coupled (by inductively coupled)
Response 4：The germanium concentration was determined byinductively coupled plasma-optical emission spectrometry(ICP-OES) using a PE-8000 spectrometer (Pekin-Elmer, Wellesley, MA).
Point 5：Line 106. Figure 2. Germanium complex rate and germanium concentration at different tannins multiples (Please to explain the meaning of the red and blue color at Figure 2)
Response 5:The graphs show the rates of germanium complexes at different tannin multiples and the concentration of germanium after the reaction is complete.Where the red line is the tannins germanium precipitation efficiency and the blue line is the germanium concentration of the liquid after the reaction is complete(marked on the diagram).
Point 6：Line 119: it can be concluded that the tannins content of 30 times and germanium complex rate are the best. (Did you make comparison with other extraction reagent for germanium)
In this paper, only one reagent, tannins, was chosen for the extraction of germanium and its mechanism was investigated.Single factor experiments were conducted to determine the optimum tannins consumption for the reaction of tannins with germanium, and no other reagents were chosen for comparison.
Point 7：Line 194: The reaction solution is nitric acid. What is reason for this choice? Why not sulfuric acid?
Response 7:Because tannic germanium does not dissolve in the sulphuric acid system, to explore the ionic form of Ge, it is necessary to do so under solution conditions. After dissolving all the tannic acid with nitric acid, it can be seen that although the ionic form of germanium is complex, most of it exists in the form of Ge4+, further proving the complex of Ge with tannin.
Point 8：Line 224: From Figure6a and b, the tannins is a three-dimensional spherical object, with a smooth surface. Do you use some EDX-analysis combined with SEM_analysis to confirm chemical composition of the tannins
Response 8: This paper focuses on the morphological characteristics of tannic acid and tannic germanium as pure substances and therefore no EDS analysis has been carried out on them.By SEM analysis of tannic acid and tannic germanium, when tannin reacts with germanium, the germanium is deposited on the tannins molecules, the deposition pattern of tannic germanium is layer polymerisation.
Author Response File: Author Response.pdf
Reviewer 4 Report
The recovery of Ge by precipitation as tannin complex is a very known process (Ge is more selective than precipitation by pH adjustment). Tannin method, it seems, is the most commonly accepted industrial process. The precipitation of germanium by tannin (or tannic acid), starting from weakly acid solutions with a concentration of 0.1 to 0.2 g/l, was discovered by Schoeller (1932) and put into practice as a quantitative analytical process by Davis and Morgan (1938).
Comments
1. Since germanium is extremely dispersed in the earth's crust and is associated with bauxite, lead-zinc, and coal mines
Pyro- and hydrometallurgical techniques have been developed for germanium recovery; these are usually used in conjunction in germanium-process industries. Generally, germanium-bearing materials are leached using mineral acids or other lixiviants, and then, germanium-containing solutions are obtained.
To separate germanium from these solutions, methods such as tannin precipitation, ferric hydroxide precipitation, ion exchange, and solvent extraction have been employed
2. resulting in the production of germanium mainly as a by-product of the zinc industry
Tannin and ferric hydroxide precipitation (e.g., hot acid leachate and liquid after iron removal, in jarosite processing) processes are usually used in zinc smelters
3. The zinc powder replacement method will produce toxic arsine gas
Do you mean Cementation Process?
4. Germanium recovery by extraction has the advantages of good selectivity and high recovery
This is solvent extraction process
5. However, many problems still need to be solved in order to realize the industrialization.
This is not true, solvent extraction is a very known process. Solvent extraction has advantages in terms of high efficiency, high selectivity, broad spectrum adaptability, large throughput, among others. Owing to these superiorities, solvent extraction has been industrially employed in the recovery of various metals, e.g., copper, nickel, cobalt, zinc, tungsten, and rare-earth elements.
6. For example, the extractant has high water solubility.
D2EHPA has very low solubility. The paragraph should be modified and low emulsification.
7. Tannins complex of germanium is the most widely used method, which has the advantages of environmental protection and high germanium recovery rate.
OK, but the process also has drawbacks in terms of high consumption, high cost, difficulty in filtration and reuse.
8. Germanium standard solution was obtained from the National Nonferrous Metals and Electronic Materials Analysis and Testing
OK, but the composition of the solution used for the precipitation of Ge-tannin complex depends on the source of initial material. Leachates from processing of coal fly ash or zinc refining by-products besides germanium may contain Zn as well as Ni, V, Sb, As, or Fe.
9. Gallnut tannins are hydrolyzed tannins, which are usually composed of one glucose and 5 ~ 12 gallic groups by ester or glycoside bonds
It should be noted that metal ions complex with tannins forming chelates with six and eight regular octahedron ligands and without a fixed structure.
In conventional germanium recovery by tannin process, a very known process, 99% of the germanium is precipitated, and the final germanium concentration is less than 0.5 mg/L
10. The glassware used in the experiment was immersed in 15% HCl and rinsed with DI water before use, then dried in a drying oven at 60℃ for 3 hours.
What for? 15% is too high and it is used in a pickling process. It should be omitted,
11. It can be seen from Figure 4 that C3H3GeO7 and C2H3GeO6 fragments appear.
It is not clear. Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) provides elemental, chemical state, and molecular information from surfaces of solid materials. How the Authors detected the above complexes?
Also, the average depth of analysis for a TOF-SIMS measurement is approximately 1 nm.
Author Response
Point 1: Since germanium is extremely dispersed in the earth's crust and is associated with bauxite, lead-zinc, and coal mines
Pyro- and hydrometallurgical techniques have been developed for germanium recovery; these are usually used in conjunction in germanium-process industries. Generally, germanium-bearing materials are leached using mineral acids or other lixiviants, and then, germanium-containing solutions are obtained.
To separate germanium from these solutions, methods such as tannin precipitation, ferric hydroxide precipitation, ion exchange, and solvent extraction have been employed
Response 1：Germanium is a typically rare and dispersed element and a trace component in the Earth’s crust and natural waters, which is the most important semiconductor material except silicon.
Point 2: resulting in the production of germanium mainly as a by-product of the zinc industry
Tannin and ferric hydroxide precipitation (e.g., hot acid leachate and liquid after iron removal, in jarosite processing) processes are usually used in zinc smelters
Response 2：This paper provides a mechanistic study of tannin germanium precipitation and an in-depth investigation of the reaction mode。
Point 3: The zinc powder replacement method will produce toxic arsine gas
Do you mean Cementation Process?
Response 3：The method mentioned in the article is zinc powder replacement precipitation.
Point 4: Germanium recovery by extraction has the advantages of good selectivity and high recovery
This is solvent extraction process
Response 4： Extraction method in the field of wet recovery of germanium has the advantages of good selectivity and high recovery rate, but to achieve industrial promotion still need to solve many problems, such as extractant water solubility is more prone to emulsification, high requirements for equipment, large losses, higher costs, can not be recycled.
Point 5: However, many problems still need to be solved in order to realize the industrialization.
This is not true, solvent extraction is a very known process. Solvent extraction has advantages in terms of high efficiency, high selectivity, broad spectrum adaptability, large throughput, among others. Owing to these superiorities, solvent extraction has been industrially employed in the recovery of various metals, e.g., copper, nickel, cobalt, zinc, tungsten, and rare-earth elements.
Response 5： Extraction method in the field of wet recovery of germanium has the advantages of good selectivity and high recovery rate, but to achieve industrial promotion still need to solve many problems, such as extractant water solubility is more prone to emulsification, high requirements for equipment, large losses, higher costs, can not be recycled.
Point 6: For example, the extractant has high water solubility.
D2EHPA has very low solubility. The paragraph should be modified and low emulsification.
Response 6： Germanium recovery by extraction has the advantages of good selectivity and high recovery in the field of germanium wet recovery.There are several extractants such as MIBK,HGS98 and D2HPA,KELEX100,LIX63,YW100,di-(2-ethylhexyl) phosphoric acid (P204)and Trioctylamine (TOA).
Point 7: Tannins complex of germanium is the most widely used method, which has the advantages of environmental protection and high germanium recovery rate.
OK, but the process also has drawbacks in terms of high consumption, high cost, difficulty in filtration and reuse.
Response 7:The problems you have mentioned are precise, and because they exist, we are studying their mechanisms in order to propose new directions that can reduce consumption and save costs.
Point 8: Germanium standard solution was obtained from the National Nonferrous Metals and Electronic Materials Analysis and Testing
OK, but the composition of the solution used for the precipitation of Ge-tannin complex depends on the source of initial material. Leachates from processing of coal fly ash or zinc refining by-products besides germanium may contain Zn as well as Ni, V, Sb, As, or Fe.
Response 8:In this paper, the mechanism of the reaction between tannins and germanium is to be investigated, therefore a germanium standard solution is used, which does not contain impurity elements, in order not to affect the experimental results.
Point 9: Gallnut tannins are hydrolyzed tannins, which are usually composed of one glucose and 5 ~ 12 gallic groups by ester or glycoside bonds
It should be noted that metal ions complex with tannins forming chelates with six and eight regular octahedron ligands and without a fixed structure.
In conventional germanium recovery by tannin process, a very known process, 99% of the germanium is precipitated, and the final germanium concentration is less than 0.5 mg/L
Response 9:
Point 10: The glassware used in the experiment was immersed in 15% HCl and rinsed with DI water before use, then dried in a drying oven at 60℃ for 3 hours.
What for? 15% is too high and it is used in a pickling process. It should be omitted,
Response 10：The addition of 15% HCl to the glassware is to exclude other impurities from interfering with the experiment. This condition has been removed in the text as per your suggestion.
Point 11: It can be seen from Figure 4 that C3H3GeO7 and C2H3GeO6 fragments appear.
It is not clear. Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) provides elemental, chemical state, and molecular information from surfaces of solid materials. How the Authors detected the above complexes?
Also, the average depth of analysis for a TOF-SIMS measurement is approximately 1 nm.
Response 11：TOF-SIMS is an extremely high resolution measurement technique for determining the mass of ions by exciting the surface of a sample with primary ions, striking extremely small amounts of secondary ions, and determining the mass of the ions according to the different flight times of the secondary ions to the detector due to their different masses.By striking the surface of a substance with secondary ions, many fragments are excited, and what is detected in the text is a fraction of its fragments, proving that germanium undergoes coordination reactions with tannins.
Author Response File: Author Response.pdf
