Valorization of MSWI Bottom Ash as a Function of Particle Size Distribution, Using Steam Washing
, Caterina Caviglia 1,*, Davide Bernasconi 1, Erica Bicchi 2, Renato Boero 3, Costanza Bonadiman 4, Giorgia Confalonieri 5, Ingrid Corazzari 6, Giuseppe Mandrone 7, Linda Pastero 1, Alessandro Pavese 1, Francesco Turci 6 and Quentin Wehrung 2Round 1
Reviewer 1 Report
Paper “Valorization of MSWI bottom ash as a function of 2 particle size distribution, using steam washing” presents studies on reducing the leaching of contaminants (chlorides, sulphates, heavy metals) in MSWI bottom ash by means of steam washing and carbonation. The authors show the results of complete tests for separate particle size classes, demonstrating the results of leaching, and others – XRPD, optical microscopy, SEM and EDS, TGA, and SSNMR results and their analysis.
I would like to show some of the problems noted in the reviewed paper. Please find them below:
- The authors describe many different tests, but the results of some of them are not given in the main text but in the supplementary material. I think that all important results should be included in the main text.
- The section “Conclusions” does not correspond to the conclusions of the research, but rather the summary. Conclusions should be reformulated.
- Please explain why whole graining of sample of MSWI bottom ash was not tested, but only fractions 1-4.75 mm.
- Moisture of sample should be given in % not in wt% (line 76). I do not know unit for bulk density: Kg/L (line 78). For solid material it should be given in Mg∙m−3.
- In my opinion the intervals for four particle classes are wrongly established from Figure S1 or Figure S1 is wrong. Four classes: s ≥ 4.75, 4.75 > s ≥ 2, 2 > s ≥ 1 and s < 1 mm, correspond to 36%, 24%, 13%, 27%, respectively. In civil engineering the different determining the axis of the Figure S1 should be used. OX axis should be reversed scale.
- Each SEM image, please provide the full specification from test, not only the scale. Please specify the applied magnification in optical microscope and SEM images.
Author Response
Reviewer 1:
Paper “Valorization of MSWI bottom ash as a function of 2 particle size distribution, using steam washing” presents studies on reducing the leaching of contaminants (chlorides, sulphates, heavy metals) in MSWI bottom ash by means of steam washing and carbonation. The authors show the results of complete tests for separate particle size classes, demonstrating the results of leaching, and others – XRPD, optical microscopy, SEM and EDS, TGA, and SSNMR results and their analysis.
I would like to show some of the problems noted in the reviewed paper. Please find them below:
Point 1. The authors describe many different tests, but the results of some of them are not given in the main text but in the supplementary material. I think that all important results should be included in the main text.
Response1. The most relevant results have been included in the main text, as SEM analysis after steam washing and TGA, XRPD, SSNMR after bottom ash carbonation. Please see paragraphs 3.1.2. and 3.2.
Point 2. The section “Conclusions” does not correspond to the conclusions of the research, but rather the summary. Conclusions should be reformulated.
Response 2 Conclusions have been reformulated in the text.
Point 3. Please explain why whole graining of sample of MSWI bottom ash was not tested, but only fractions 1-4.75 mm.
Response 3.
The fractions on which the steam washing was applied were respectively: s≥ 4.75, 4.75 > s ≥ 2, 2 > s ≥ 1 and s < 1 mm. The fractions were treated separately as a different result was observed depending on the particle sizes. The separation allowed to define in detail the quantities of steam required for the individual particle sizes and the effectiveness of the treatment by providing information on which portions of the BA were suitable for reuse without further treatment.
On the fraction <1mm it has been verified that the steam washing treatment is not applicable as the treated material tends to aggregate first and then solubilize in significant quantities in the waste water.
Accelerated carbonation has therefore been proposed for this fraction as the method is more effective if applied to materials with higher specific surfaces.
Point 4. Moisture of sample should be given in % not in wt% (line 76). I do not know unit for bulk density: Kg/L (line 78). For solid material it should be given in Mg∙m−3.
Response 4. We have corrected both the units, % and Mg∙m−3 (line 85 in the revised text)
Point 5. In my opinion the intervals for four particle classes are wrongly established from Figure S1 or Figure S1 is wrong. Four classes: s ≥ 4.75, 4.75 > s ≥ 2, 2 > s ≥ 1 and s < 1 mm, correspond to 36%, 24%, 13%, 27%, respectively. In civil engineering the different determining the axis of the Figure S1 should be used. OX axis should be reversed scale.
Response 5. We have corrected in the text the percentage of the material because they were wrong. The right one are 36%, 24%, 13% and 27%, as shown by the reviewer. Figure S1 (supplementary material) was changed as requested.
Point 6. Each SEM image, please provide the full specification from test, not only the scale. Please specify the applied magnification in optical microscope and SEM images.
Response 6. We have specified all the details for SEM images (figure 5 and figure 9): experimental conditions: W filament, accelerating voltage 15 kV, working distance 10 mm, high probe current, magnification 200x; we have also specified the magnification for each optical microscope images (fig. 4 a-f) in the figure captions.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Thank you for this very interesting paper!
Minor changes
Line 23 : treatments
Line 211 : the residual leaching capacity of the treated BA, : the residual soluble fraction of the treated BA
Table 1 Replace n.d. by <LOQ and mention the LOQ
L 283 It shows that Na/K-chloride and Ca-sulfate underwent dissolution into water (pKsp= -1.58, -0.85, 4.36 and 4.58, respectively). : there are 3 species and 4 solubility products
Table 5: mention if wt% is expressed on dry weight ; Weight loss of the BA fraction
Author Response
Reviewer 2 comments
Thank you for this very interesting paper!
Minor changes
Point 1. Line 23 : treatments
Response 1. Corrected, it was a typing error.
Point 2. Line 211: the residual leaching capacity of the treated BA,: the residual soluble fraction of the treated BA
Response 2. Corrected in the residual soluble fraction. Line 213 in the revised text.
Point 3. Table 1 Replace n.d. by <LOQ and mention the LOQ
Response 3. n.d. was replaced by LOQ and LOQ was specified in the Table 1 captions, and in the Table 4, too.
Point 4. L 283 It shows that Na/K-chloride and Ca-sulfate underwent dissolution into water (pKsp= -1.58, -0.85, 4.36 and 4.58, respectively). : there are 3 species and 4 solubility products
Response 4. It was corrected removing 4.58 (line 292 in the new text).
Point 5. Table 5: mention if wt% is expressed on dry weight ; Weight loss of the BA fraction
Response 5. wt% is expressed on dry weight, we added in the table 5 caption.
Author Response File: Author Response.pdf
