Structural alteration within fly ash-based geopolymers governing the adsorption of Cu2+ from aqueous environment: Effect of alkali activation

• Published in: Journal of hazardous materials Vol. 377; pp. 305 - 314
• Main Authors: Darmayanti, Lita, Kadja, Grandprix T.M., Notodarmojo, Suprihanto, Damanhuri, Enri, Mukti, Rino R.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 05.09.2019
• Subjects: Alkali activation; Cu2+adsorption; Fly ash; Geopolymers; Structural alteration; Cu2+adsorption; Fly ash; Structural alteration; Geopolymers; Alkali activation
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2019.05.086

[Display omitted] •The fly-ash based geopolymers are synthesized using various alkali activation systems.•The structural alteration appears to be governed by the used alkali activation.•The Cu2+ adsorption isotherms and kinetics on the geopolymers are investigated.•The more organized structure leads to higher Cu2+ adsorption capacity. Fly-ash based geopolymers have been considered as a low-cost yet effective adsorbent for the removal of heavy metal cations, including Cu2+, from the aqueous environment. In the synthesis of geopolymers, the fly-ash needs to be alkali activated using several systems rich in either Na+ or K+. Herein, we investigate the effect of alkali activation on the structural alteration and its consequence on the adsorption capacity. Based on the series of detailed characterizations, the geopolymers formed in Na+–based alkali system is found to have more organized structure compared to that formed in K+–based alkali system. Moreover, the incorporation of additional silicate creates ancillary structure which positively contributes to the organization of the overall structure. All the samples, fly-ash and geopolymers, exhibits Cu2+ adsorption based on Langmuir isotherm and pseudo-second order kinetic. The geopolymers with more organized structure display higher Cu2+ adsorption capacity, which reaches 40 mg g−1 higher in comparison to 7 mg g−1 for fly ash sample. The structural alteration induces the formation of open-framework structure with more accessible sites which can accommodate more Cu2+. Our study provides a fundamental understanding for the design and fabrication of geopolymers as an effective adsorbent for the removal of heavy metal cations.