Historical Lead Smelting Slag Harmlessness and Valuable Metals Recovery: A Co-Treatment of Lead Slag and Zinc-Bearing Material in Rotary Kiln

Round 1

Reviewer 1 Report

Reviewer: Minor revision

This paper reports a detailed study about the harmlessness treatment of historical lead smelting slag located in Gejiu, Yunnan province, China, and valuable metals recovery from this slag were investigated with a co-treatment of lead slag and zinc oxide ore in rotary kiln. The proposed approach is very meaningful, and the manuscript organization is satisfied. So, I think that this paper deserves to be published in Sustainability after minor revision of some issues as follows:

1- Authors must ensure that the quality of English is improved (i.e., make all efforts to rectify any grammatical mistakes, typos, double spaces, missing spaces etc.).

2- Can the author add a table containing a comparison with the previous works in the same field? It will probably help the readers to understand the manuscript better.

Author Response

Dear reviewerRe: Manuscript ID: sustainability-1903913 and Title: Historical lead smelting slag harmlessness and valuable metals recovery: A co-treatment of lead slag and zinc-bearing material in rotary kiln

Thank you for your comments concerning our manuscript entitled “Historical lead smelting slag harmlessness and valuable metals recovery: A co-treatment of lead slag and zinc-bearing material in rotary kiln” (sustainability-1903913). Those comments are valuable and very helpful. We have read through comments carefully and have made corrections. Based on the instructions provided in your letter, we uploaded the file of the revised manuscript. Revisions in the text are shown using red highlight for additions. The responses to your comments are presented following.

We would love to thank you for allowing us to resubmit a revised copy of the manuscript and we highly appreciate your time and consideration.

Sincerely.

Minting Li.

 

Reviewer #1:

Q1.  Authors must ensure that the quality of English is improved (i.e., make all efforts to rectify any grammatical mistakes, typos, double spaces, missing spaces etc.).

Response：We apologize for some grammatical errors in the manuscript. We have corrected some grammatical errors in the manuscript.

Q2.  Can the author add a table containing a comparison with the previous works in the same field? It will probably help the readers to understand the manuscript better.

Response：This is good advice. However, it is a pity that we have not published relevant articles on our preliminary work. So, there is no way to make a comparison.

Author Response File: Author Response.pdf

Reviewer 2 Report

 This manuscript reported the harmless treatment of lead smelting slag with zinc oxide ore in rotary kiln. This work is of great significance. The authors have done a lot of work. However, the experimental design is questionable. If the zinc oxide ore content is greater than 50 wt%, the treatment is almost nonsense because the treatment is not on waste, but zinc oxide. It makes more sense to narrow the range of zinc oxide content although the authors claimed that lead smelting slag with 20 wt% zinc oxide is an optimal choice. 

Increasing zinc oxide ore content means the decrease of lead smelting slag to zinc oxide ore ratio. Some related descriptions in Page 5 and 6 are wrong. 

In section “Valuable metals recovery”, Zn recovery and As recovery data is not 97.37% and 43.34%, respectively. 

The EDS images are not clear: the letters in the picture are not clear at all. The letters in BSE images are incomplete. 

In page 10, “Fe, which is an alkali metal” is wrong completely. 

The letters in EPMA images are unclear also. From element mapping, Pb existed in the WQS as metal sulfide particle, i.e. Pb existed as PbS. Whether or not PbS can be found in XRD patterns?

 The first occurrence of the abbreviation should be given the full name.

Author Response

Dear reviewerRe: Manuscript ID: sustainability-1903913 and Title: Historical lead smelting slag harmlessness and valuable metals recovery: A co-treatment of lead slag and zinc-bearing material in rotary kiln

Thank you for your comments concerning our manuscript entitled “Historical lead smelting slag harmlessness and valuable metals recovery: A co-treatment of lead slag and zinc-bearing material in rotary kiln” (sustainability-1903913). Those comments are valuable and very helpful. We have read through comments carefully and have made corrections. Based on the instructions provided in your letter, we uploaded the file of the revised manuscript. Revisions in the text are shown using red highlight for additions. The responses to your comments are presented following.

We would love to thank you for allowing us to resubmit a revised copy of the manuscript and we highly appreciate your time and consideration.

Sincerely.

Minting Li.

 

Reviewer #2:

Q1. This manuscript reported the harmless treatment of lead smelting slag with zinc oxide ore in rotary kiln. This work is of great significance. The authors have done a lot of work. However, the experimental design is questionable. If the zinc oxide ore content is greater than 50 wt%, the treatment is almost nonsense because the treatment is not on waste, but zinc oxide. It makes more sense to narrow the range of zinc oxide content although the authors claimed that lead smelting slag with 20 wt% zinc oxide is an optimal choice.

Response：From the point of view of harmless treatment of lead slag, it is more meaningful to reduce the proportion of zinc oxide ore. However, if the addition amount of zinc oxide ore is too small, the treatment energy consumption and cost are high (as shown in Fig. 7(b)). Hence, a zinc oxide ore addition of 20% was recommended on base of energy cost and processing capacity of lead smelting slag(LSS). Whether the proportion of zinc oxide ore can be further reduced still needs to be investigated in the following industrial application process. According to the results of our experiments, 20% is a relatively optimal choice. 

Q2. Increasing zinc oxide ore content means the decrease of lead smelting slag to zinc oxide ore ratio. Some related descriptions in Page 5 and 6 are wrong. 

Response：We agree with the comment and re-wrote the sentence in the revised manuscript.

Q3. In section “Valuable metals recovery”, Zn recovery and As recovery data is not 97.37% and 43.34%, respectively. 

Response：We are grateful for the suggestion. As suggested by the reviewer, we have modified the Zn and As recoveries from 97.37% to 95.99% and from 43.34% to 40.07%, respectively in the revised manuscript (red number in page 10).

Q4. The EDS images are not clear: the letters in the picture are not clear at all. The letters in BSE images are incomplete. 

Response：EDS pictures are too many and small, resulting in unclear letters. So we removed these pictures. In order for reader to see the BSE image clearly, we have enlarged it appropriately.

Q5. In page 10, “Fe, which is an alkali metal” is wrong completely. 

Response：The sentence “Fe, which is an alkali metal, has a strong buffering for acid solution to decrease the leaching of heavy (Chai et al., 2015). “ was modified to “Fehas a strong buffering for acid solution to decrease the leaching of heavy (Chai et al., 2015).” In revised manuscript.

Q6. The letters in EPMA images are unclear also. From element mapping, Pb existed in the WQS as metal sulfide particle, i.e. Pb existed as PbS. Whether or not PbS can be found in XRD patterns?

Response：EPMA images are too many, and the letters are too small to see clearly. Therefore, we put the corresponding letter in the upper left corner of each picture. Due to the low lead content in the water-quenched slag, PbS could not be found in the XRD pattern.

Q7. The first occurrence of the abbreviation should be given the full name.

Response：We have changed the abbreviation in “2.2 Rotary kiln tests and sampling” in revised manuscript (red words).

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors present a good literature review with clear logical conclusions. However, given the level of the journal in the work, I would like to see the current state of the environment in the sphere of influence of the object under study. Hypothetical assumptions about the negative state, not confirmed by field studies, are presented.

Sampling is a key moment in the development of processing technology. The authors indicated that the samples of the material were taken from the bottom of the heap. However, taking into account the classical processes of material segregation occurring in the body of an object, it is rather difficult to assess the quality of the selected samples of the material. It is recommended to indicate material sampling points on the map, possibly with reference to geodata. It is recommended to specify the depth of selection, as well as the method of excavation.

The authors are recommended to indicate the primary characteristics of the material, namely: granulometric, chemical and mineralogical composition of raw materials, humidity.

Why was the material mixed with the original ore?

What equipment was used for leaching tests?

Based on what principles were the presented mixtures of acids selected?

The description of the process is rather difficult to understand. Why did the authors not provide a technological scheme of processing with qualitative and quantitative indicators?

Figure 5 is basically unreadable. As a reader of this article, it is not clear why to add such drawings in the work.

It is necessary to describe how what happens to acids after leaching.

Conclusion: The work has a pronounced practical emphasis. One gets the impression that the authors were approached by an enterprise that wanted to recycle waste. The material is quite interesting, but in my opinion it is not finalized to the level. Big questions are raised by the drawings in the article. The authors need to clearly state the purpose and objectives of the work, present a processing flow chart with all indicators. Scientific novelty must be indicated. Given the specifics of the journal, describe what impact the processing of raw materials will have on the state of the environment and public health.

Author Response

Dear reviewerRe: Manuscript ID: sustainability-1903913 and Title: Historical lead smelting slag harmlessness and valuable metals recovery: A co-treatment of lead slag and zinc-bearing material in rotary kiln

Thank you for your comments concerning our manuscript entitled “Historical lead smelting slag harmlessness and valuable metals recovery: A co-treatment of lead slag and zinc-bearing material in rotary kiln” (sustainability-1903913). Those comments are valuable and very helpful. We have read through comments carefully and have made corrections. Based on the instructions provided in your letter, we uploaded the file of the revised manuscript. Revisions in the text are shown using red highlight for additions. The responses to your comments are presented following.

We would love to thank you for allowing us to resubmit a revised copy of the manuscript and we highly appreciate your time and consideration.

Sincerely.

Minting Li.

 

Reviewer #3:

Q1. The authors present a good literature review with clear logical conclusions. However, given the level of the journal in the work, I would like to see the current state of the environment in the sphere of influence of the object under study. Hypothetical assumptions about the negative state, not confirmed by field studies, are presented.

Response：The current state of the environment in the sphere of influence of the object was investigated by toxicity characteristic leaching procedure (TCLP) and sulfuric and nitric acids leaching test (SNAL) tests (as shown in Table 4). The results of TCLP and SNAL tests indicated that the LSS is a dangerous solid waste, The leaching concentration of lead, zinc, arsenic and cadmium in the LSS exceeded the threshold value [U.S. EPA, 1986; U.S. EPA, 1990; GB 5085.3−2007] (Table 4). However, the leaching concentration of lead, zinc, arsenic and cadmium in the WQS obtained from carbonthermal reduction decreased significantly, showing that the environment implication of WQS was small. The purpose of this paper is to develop an economical and feasible technical route for harmless treatment of lead slag, focusing on the recovery of valuable metals and the solidification of toxic and harmful elements.

 

Q2.  Sampling is a key moment in the development of processing technology. The authors indicated that the samples of the material were taken from the bottom of the heap. However, taking into account the classical processes of material segregation occurring in the body of an object, it is rather difficult to assess the quality of the selected samples of the material. It is recommended to indicate material sampling points on the map, possibly with reference to geodata. It is recommended to specify the depth of selection, as well as the method of excavation.

 

Response：According to the reviewer's suggestion. material sampling points on the map and possibly with reference to geodata were was added in the revised manuscript (as shown in Fig. 1). The depth and method of digging was added also (red sentence in revised manuscript in 2.1 section).

Q3.  The authors are recommended to indicate the primary characteristics of the material, namely: granulometric, chemical and mineralogical composition of raw materials, humidity.

Response：The date on the granulometric, mineralogical composition of raw materials and humidity of mixed sample was added in revised manuscript at 2.1 section. The chemical composition is shown in Table 2.

Q4.  Why was the material mixed with the original ore?

Response：The economic feasibility of treating the LSS is low because of the low content of valuable metals in the LSS. At present, there is no alone treatment method for LSS. Hence, the harmlessness treatment of historical lead smelting slag was investigated with a co-treatment of LSS and zinc oxide ore in rotary kiln to improve the economic feasibility of LSS treatment.

Q5.  What equipment was used for leaching tests?

Response：The TCLP tests was conducted in a 20 mL polyvinyl bottle. The sulfuric and nitric acids leaching test (SNAL) was rotated in a rotary oscillator at 30 r/min for 18 h. This part of content has been added into the revised manuscript (red sentence in 2.3 Leaching tests).

Q6.  Based on what principles were the presented mixtures of acids selected?

Response：The selection of mixed acids is based on the Environmental Protection Industry Standards of the People's Republic of China (HJ/T 299−2007. Solid waste-extraction procedure for leaching toxicity-sulphuric acid & nitric acid method (as shown in Reference).

Q7.  The description of the process is rather difficult to understand. Why did the authors not provide a technological scheme of processing with qualitative and quantitative indicators?

Response：The LSS and zinc oxide ores were treated in an industrial-scale rotary kiln (ϕ2.8m×L44m) by carbothermic reduction method. We designed five ratios of LSS to zinc oxide ore (100% slag, 80% slag + 20% ore, 60% slag + 40% ore, 40% slag + 60% ore and 20% slag + 80% ore). The purpose is to find an optimal ratio to achieve economic feasibility and solidification effect of heavy metals. The main parameters of reduction process have been given in Section 2.2 Rotary kiln tests and sampling. Due to the fluctuations of production, some small changes in process parameters may occur. Hence, we give a range of these process parameters. The technological process is shown in Fig. 2.

Q8.  Figure 5 is basically unreadable. As a reader of this article, it is not clear why to add such drawings in the work.

Response：Fig.5 (EDS) pictures are too many and small, resulting in unclear letters. So, we removed these pictures.

Q9.  It is necessary to describe how what happens to acids after leaching.

Response：The toxicity characteristic leaching procedure (TCLP) is useful in identifying the potential hazards of solid waste with a co-disposal assumption. Several metallurgical wastes (such as slag), have been classified using this procedure. The main limitation of the conclusions obtained from the TCLP for slag is related to the acid-neutralizing capacity of the specific slag, which lessens over time during the procedure, resulting in amphoteric metals being leached. Therefore, the results are not reliable for long-term stability studies. In the present case, despite the fact that co-disposal of the slag in the landfill and municipal solid waste did not occur, the use of the TCLP test is interesting in that it can simulate the effect of the eventual interaction of the slag with low-molecular-weight organic acids.

The sulfuric and nitric acids leaching test (SNAL) was applied to simulate leaching characteristics of solid waste under specified conditions of acid rain.

 

The TCLP and SNAL leaching tests were used to evaluate the stability of slag. Therefore, this work did not focus on the changes of acid after leaching.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The article lacks a technological scheme with specific qualitative and quantitative values

Author Response

Q1. The article lacks a technological scheme with specific qualitative and quantitative values

Response：The technological scheme used in this work was shown in Fig. 3 in the second manuscript.