A new insight into the restriction of Cr(VI) removal performance of activated carbon under neutral pH condition

Activated carbon has been widely used to remove hazardous Cr(VI); however, the impact of Cr2O3 precipitate on gradually declining removal ability as pH increases has received little attention. Herein, to investigate the effect of Cr2O3, SEM-EDX (scanning electron microscope-energy dispersive X-ray a...

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Autores principales:	Yi Fang, Ke Yang, Yipeng Zhang, Changsheng Peng, Aurora Robledo-Cabrera, Alejandro López-Valdivieso
Formato:	article
Lenguaje:	EN
Publicado:	IWA Publishing 2021
Materias:	activated carbon adsorption chromium neutral conditions passivation reduction Environmental technology. Sanitary engineering TD1-1066
Acceso en línea:	https://doaj.org/article/7f533ca915324cbc83cb9226b1a5d0a9
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spelling	oai:doaj.org-article:7f533ca915324cbc83cb9226b1a5d0a92021-11-23T18:40:53ZA new insight into the restriction of Cr(VI) removal performance of activated carbon under neutral pH condition0273-12231996-973210.2166/wst.2021.449https://doaj.org/article/7f533ca915324cbc83cb9226b1a5d0a92021-11-01T00:00:00Zhttp://wst.iwaponline.com/content/84/9/2304https://doaj.org/toc/0273-1223https://doaj.org/toc/1996-9732Activated carbon has been widely used to remove hazardous Cr(VI); however, the impact of Cr2O3 precipitate on gradually declining removal ability as pH increases has received little attention. Herein, to investigate the effect of Cr2O3, SEM-EDX (scanning electron microscope-energy dispersive X-ray analysis) coupling elements mapping of chromium-loaded powdered activated carbon (PAC) revealed that a chromium layer was formed on the PAC exterior after being treated with Cr(VI) at pH 7. XPS (X-ray photoelectron spectroscopy) study confirmed that 69.93% and 39.91% Cr2O3 precipitated on the PAC surface at pH 7 and pH 3, respectively, corresponding to 17.77 mg/g and 20 mg/g removal capacity. Exhausted PAC had a removal efficiency of 92.43% after Cr2O3 being washed by H2SO4 solution, which was much higher than the removal efficiency of 51.27 % after NaOH washing. This further verified that the intrinsically developed Cr2O3 precipitate on PAC under neutral conditions limited the durability of PAC as an adsorbent. Consecutive elution assessments confirmed that adsorption and reduction ability both declined as pH increased. Raman spectroscopy and C 1s spectra of materials demonstrated two distinct Cr(VI) removal mechanisms under pH 3 and pH 7. In conclusion, the exhausted AC after Cr(VI) adsorption can be rejuvenated after the surface coated Cr2O3 is washed by the acid solution, which can expand the longevity of AC and recover Cr(III). HIGHLIGHT In this work, we scrutinized the mechanism of poor removal capacity of commercial activated carbon on toxic heavy metal Cr(VI) under neutral pH conditions. Differing from the most accepted view that electrostatic repulsion is the main consideration, our study suggested that the relatively more Cr2O3 precipitate on the surface of activated carbon under higher pH led to the low Cr(VI) sequestration capability.;Yi FangKe YangYipeng ZhangChangsheng PengAurora Robledo-CabreraAlejandro López-ValdiviesoIWA Publishingarticleactivated carbonadsorptionchromiumneutral conditionspassivationreductionEnvironmental technology. Sanitary engineeringTD1-1066ENWater Science and Technology, Vol 84, Iss 9, Pp 2304-2317 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	activated carbon adsorption chromium neutral conditions passivation reduction Environmental technology. Sanitary engineering TD1-1066
spellingShingle	activated carbon adsorption chromium neutral conditions passivation reduction Environmental technology. Sanitary engineering TD1-1066 Yi Fang Ke Yang Yipeng Zhang Changsheng Peng Aurora Robledo-Cabrera Alejandro López-Valdivieso A new insight into the restriction of Cr(VI) removal performance of activated carbon under neutral pH condition
description	Activated carbon has been widely used to remove hazardous Cr(VI); however, the impact of Cr2O3 precipitate on gradually declining removal ability as pH increases has received little attention. Herein, to investigate the effect of Cr2O3, SEM-EDX (scanning electron microscope-energy dispersive X-ray analysis) coupling elements mapping of chromium-loaded powdered activated carbon (PAC) revealed that a chromium layer was formed on the PAC exterior after being treated with Cr(VI) at pH 7. XPS (X-ray photoelectron spectroscopy) study confirmed that 69.93% and 39.91% Cr2O3 precipitated on the PAC surface at pH 7 and pH 3, respectively, corresponding to 17.77 mg/g and 20 mg/g removal capacity. Exhausted PAC had a removal efficiency of 92.43% after Cr2O3 being washed by H2SO4 solution, which was much higher than the removal efficiency of 51.27 % after NaOH washing. This further verified that the intrinsically developed Cr2O3 precipitate on PAC under neutral conditions limited the durability of PAC as an adsorbent. Consecutive elution assessments confirmed that adsorption and reduction ability both declined as pH increased. Raman spectroscopy and C 1s spectra of materials demonstrated two distinct Cr(VI) removal mechanisms under pH 3 and pH 7. In conclusion, the exhausted AC after Cr(VI) adsorption can be rejuvenated after the surface coated Cr2O3 is washed by the acid solution, which can expand the longevity of AC and recover Cr(III). HIGHLIGHT In this work, we scrutinized the mechanism of poor removal capacity of commercial activated carbon on toxic heavy metal Cr(VI) under neutral pH conditions. Differing from the most accepted view that electrostatic repulsion is the main consideration, our study suggested that the relatively more Cr2O3 precipitate on the surface of activated carbon under higher pH led to the low Cr(VI) sequestration capability.;
format	article
author	Yi Fang Ke Yang Yipeng Zhang Changsheng Peng Aurora Robledo-Cabrera Alejandro López-Valdivieso
author_facet	Yi Fang Ke Yang Yipeng Zhang Changsheng Peng Aurora Robledo-Cabrera Alejandro López-Valdivieso
author_sort	Yi Fang
title	A new insight into the restriction of Cr(VI) removal performance of activated carbon under neutral pH condition
title_short	A new insight into the restriction of Cr(VI) removal performance of activated carbon under neutral pH condition
title_full	A new insight into the restriction of Cr(VI) removal performance of activated carbon under neutral pH condition
title_fullStr	A new insight into the restriction of Cr(VI) removal performance of activated carbon under neutral pH condition
title_full_unstemmed	A new insight into the restriction of Cr(VI) removal performance of activated carbon under neutral pH condition
title_sort	new insight into the restriction of cr(vi) removal performance of activated carbon under neutral ph condition
publisher	IWA Publishing
publishDate	2021
url	https://doaj.org/article/7f533ca915324cbc83cb9226b1a5d0a9
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A new insight into the restriction of Cr(VI) removal performance of activated carbon under neutral pH condition

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