Comment: Pilot-Scale Test for a Phosphate Treatment Using
Sulfate-Coated Zeolite at a Sewage Disposal Facility
by Jae-Woo Choi, Kyu-Sang Kwon, Soonjae Lee, Byungryul
An, Seok-Won Hong, Sang-Hyup Lee
Emmanuel I. Unuabonah& Nurudeen A. Oladoja
Received: 14 February 2014 / Accepted: 9 April 2014 #Springer International Publishing Switzerland 2014
Abstract The article, Pilot-Scale Test for a Phosphate Treatment Using Sulfate-Coated Zeolite at a Sewage Disposal Facility by Jae-Woo Choi, Kyu-Sang Kwon, Soonjae Lee, Byungryul An, Seok-Won Hong, Sang-Hyup Lee, is replete with some fundamental scientific flaws which have the potential to misinform readers. This comment seek to correct these flaws.
Keywords Sulfate-coated . Phosphate . Pilot-scale . Zeolitic material . Calcination
In the recent paper, Pilot-Scale Test for a Phosphate Treatment Using Sulfate-Coated Zeolite at a Sewage Disposal Facility, by Choi et al. (2014), the authors stated that the objective of their study was to evaluate a zeolite ball coated with sulfate (ZBCS) for the removal
of phosphate in a batch, lab-scale column, and pilot-scale plant. The authors, though, have done a good study with the pilot-scale test, but the article is replete with scientific flaws.
The authors did not provide sufficient scientific evi-dence to prove that the zeolitic material used in their study was truly “sulfate-coated.” The mechanism by which the sulfate coating occurred on the zeolite mate-rial and the underlying mechanism of phosphate remov-al from aqueous solution by the prepared materiremov-al were not presented. The justification for the calcination of the supposed sulfate-coated material using mixed gases is not convincing, i. e., why the use of mixed gases (inert and non-inert) and what informed the choice of the ratio of the gases used? This should be clearly stated in the manuscript. The proposal for efficient regeneration of ZBCS and phosphate recovery (Section 3.4) was based on non-scientific evidence which leaves a lot of unanswered ques-tions in the minds of esteemed readers of Water Air
& Soil Pollution journal articles. For example, how
was struvite (NH4MgPO4·6H2O) recovered from the regenerated sulfate-rich solution and why was the regenerating solution enriched with sulfate ion?
The evidence provided by the authors, relating to the characterization of the prepared samples, are not sufficient and tend towards mere speculations. Scan-ning electron microscopy (SEM) cannot be used to confirm the presence of any chemical functional species on the surface of particles. It is meant for elucidating the surface morphology of particles. The electron probe microanalyzer (EPMA) mapping tool Water Air Soil Pollut (2014) 225:1969
DOI 10.1007/s11270-014-1969-y
E. I. Unuabonah (*)
Environmental and Chemical Processes Research Laboratory, Department of Chemical Sciences, Redeemer’s University, PMB 3005, Mowe, Ogun State, Nigeria
e-mail: iyaemma@yahoo.com
N. A. Oladoja
Department of Chemistry, Adekunle Ajasin University, Akungba Akoko, Ondo State, Nigeria
N. A. Oladoja
Technische Universitat Munchen,
Chair of Urban Water Systems Engineering, Am Coulombwall,
employed would definitely reveal the presence of sulfur, but it does not differentiate between the dif-ferent species of sulfur-containing compounds deriv-able from the hydrolysis of sulfuric acid (i.e., HSO4−, the bisulfate anion, and SO42−, the sulfate anion). The use of Fourier transformed infrared (FTIR), violet Raman, and/or diffuse reflectance ultra-violet spectroscopic techniques would have been more informative. It should be noted that immersion of a zeolitic material (an aluminosilicate) in 10 % s u l p h u r i c a c i d w o u l d l i k e l y c a u s e s o m e dealumination (dissolution of the alumina fraction of the zeolite) which should be accounted for. This dealumination results in the increase of Bronsted acidity of the regenerated material (Yan et al. 2003). How this material with Bronsted acidity sites will adsorb phosphate ion is still unclear except with the use of its pores. This obviously indicates that sulfate ion was not involved in the removal of phos-phate ion from aqueous solution in their study.
While the title of this work suggests a surface reac-tion between the zeolitic material and a sulfate salt in an aqueous medium (surface reaction), the actual prepara-tion of the material in the article indicates a surface coating of a zeolitic material with a polymer (acrylic binder), calcination of the product, and subsequent acti-vation with sulfuric acid. At the temperature of calcina-tion (750 °C) and the time for calcinacalcina-tion (3 h), the polymer is expected to be transformed to carbon
basically. Unfortunately, the procedure for the acrylic coating was not even discussed.
Thus, because the authors have not provided scientific evidence to prove that their zeolitic ma-terial is sulfate-coated, they lack the strength to use the term sulfate-coated in their title and in the entire article. To this end, the current title of the article is misleading and the entire article has the potential to strongly misinform scientists who have just picked interest in surface modification of ma-terials. We therefore suggest that Choi and his colleagues call for an erratum of this article, change the current title of the article using a more appro-priate term in place of sulfate-coated, and perhaps provide further evidence of the nature of the mate-rial used in this study in another article.
References
Choi, J.-W., Kwon, K.-S., Lee, S., An, B., Hong, W., & Lee, S.-H. (2014). Pilot-scale test for a phosphate treatment using sulfate-coated zeolite at a sewage disposal facility.Water, Air, and Soil Pollution, 225, 1835.
Yan, Z., Ma, D., Zhuang, J., Liu, X., Liu, X., Han, X., Bao, X., Chang, F., Xu, L., & Liu, Z. (2003). On the acid-dealumination of USY zeolite: a solid state NMR investiga-tion.Journal of Molecular Catalysis A: Chemical, 194, 153–
167.
