Cr(VI) heavy metal adsorption from aqueous solution by KOH treated hydrochar derived from agricultural wastes

The solidification/stabilization (S/S) is one of the effective methods that are used for the heavy metals treatment. It was known that one of the main issues of this method is that the heavy metal is stayed inside the matrices, not destroyed nor adsorbed, which may cause serious problems for the environment once the matrices would be crashed. Agricultural wastes have shown a great capacity to the heavy metal adsorption from solid and liquid wastes. This paper reviews the incorporation of the agricultural wastes as heavy metals’ adsorbents inside the matrices of the S/S method. In addition, changes in particle sizes, pre-treatment, temperature and other factors have also been discussed towards the heavy metal adsorption. Nevertheless, research regarding the incorporation of the agricultural wastes into the S/S method is very minimal, and almost all the previous researches were only focusing comprehensively on the leaching characteristics of the method.

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Regeneration of chitosan-based adsorbents used in heavy metal adsorption: A review

Separation and Purification Technology ◽

10.1016/j.seppur.2019.05.040 ◽

2019 ◽

Vol 224 ◽

pp. 373-387 ◽

Cited By ~ 63

Author(s):

Mohammadtaghi Vakili ◽

Shubo Deng ◽

Giovanni Cagnetta ◽

Wei Wang ◽

Pingping Meng ◽

...

Keyword(s):

Heavy Metal ◽

Metal Adsorption ◽

Heavy Metal Adsorption

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Combined Influence of Low-Grade Metakaolins and Natural Zeolite on Compressive Strength and Heavy Metal Adsorption of Geopolymers

Minerals ◽

10.3390/min11050486 ◽

2021 ◽

Vol 11 (5) ◽

pp. 486

Author(s):

Alcina Johnson Sudagar ◽

Slávka Andrejkovičová ◽

Fernando Rocha ◽

Carla Patinha ◽

Maria R. Soares ◽

...

Keyword(s):

Heavy Metals ◽

Heavy Metal ◽

Compressive Strength ◽

Natural Zeolite ◽

Metal Adsorption ◽

Low Grade ◽

Heavy Metal Adsorption ◽

Adsorption Model ◽

X Ray ◽

Adsorption Capacities

Metakaolins (MKs) prepared from low-grade kaolins located in the Alvarães (A) and Barqueiros (B) regions of Portugal were used as the aluminosilicate source to compare their effect on the compressive strength and heavy metal adsorption of geopolymers. Natural zeolite, an inexpensive, efficient adsorbent, was used as an additive in formulations to enhance geopolymers’ adsorption capacities and reduce MK utilization’s environmental footprint. Geopolymers were synthesized with the replacement of MK by zeolite up to 75 wt.% (A25, B25—25% MK 75% zeolite; A50, B50—50% MK 50% zeolite; A75, B75—75% MK 25% zeolite; A100, B100—100% MK). The molar ratios of SiO2/Al2O3 and Na2O/Al2O3 were kept at 1 to reduce the sodium silicate and sodium hydroxide environmental impact. Geopolymers’ crystallography was identified using X-ray diffraction analysis. The surface morphology was observed by scanning electron microscopy to understand the effect of zeolite incorporation. Chemical analysis using X-ray fluorescence spectroscopy and energy dispersive X-ray spectroscopy yielded information about the geopolymers’ Si/Al ratio. Compressive strength values of geopolymers obtained after 1, 14, and 28 days of curing indicate high strengths of geopolymers with 100% MK (A100—15.4 MPa; B100—32.46 MPa). Therefore, zeolite did not aid in the improvement of the compressive strength of both MK-based geopolymers. The heavy metal (Cd2+, Cr3+, Cu2+, Pb2+, and Zn2+) adsorption tests exhibit relatively higher adsorption capacities of Barqueiros MK-based geopolymers for all the heavy metals except Cd2+. Moreover, zeolite positively influenced divalent cations’ adsorption on the geopolymers produced from Barqueiros MK as B75 exhibits the highest adsorption capacities, but such an influence is not observed for Alvarães MK-based geopolymers. The general trend of adsorption of the heavy metals of both MK-based geopolymers is Pb2+ > Cd2+ > Cu2+ > Zn2+ > Cr3+ when fitted by the Langmuir isotherm adsorption model. The MK and zeolite characteristics influence geopolymers’ structure, strength, and adsorption capacities.

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