Novel porous ambient temperature cured fly ash geopolymer for lead adsorption from wastewaters

ABSTRACT

This paper discusses the ability of the fly ash (FA) and abmbient cured Alkali activated Fly ash geopolymer (FAAG) for sequestering Pb (II) ions from aqueous solution. Various physiochemical properties such as the influence of pH and contact time were investigated for achieving the conditions for maximum removal via batch mode using powdered samples. The adsorbents were characterized by employing powder X-Ray diffraction, Attenuated Total Reflection Fourier Transform Infra-Red spectroscopy, and Scanning Electron Microscopy/EDAX before and after the treatment. The adsorption capacity of Pb²⁺ ions by raw FA and FAAG were examined by the Inductively coupled plasma mass spectrometry (ICP-MS). The results represented that the maximum adsorption capacity of Pb²⁺ ions by FAAG is 75 mg/g with attained equilibrium time of 120 min whereas raw fly ash at 150 min at 21.5 mg/g capacity. The pozzolanic reactivity of fly ash in water glass hardening resulted mainly N-A-S-H gel and traces of lead silicate due to the immobilization of lead in the network. This was conformed from the binding energy lines at 139.7 eV in XPS survey lines and lead silicate at 25 and 34° 2θ as identified in XRD phase assemblages. ICP-MS test results of leachate of lead immobilized geopolymer sample are devoid of lead ions and thus sorption sites of fly ash geopolymer lead to potential safety disposal of lead. Thus, recycling of fly ash into geopolymer by less energy intensive process and subsequent use in heavy metal disposal could achieve the concept of disposal waste and recycling, which could contribute to achieve the sustainable goals.

GRAPHICAL ABSTRACT

KEYWORDS:

• Fly ash
• geopolymer
• ICP-MS
• XPS
• lead immobilization

Highlights

• The alumino silicate network structure enables the Pb (II) immobilization.

• Physical adsorption of Pb (II) in fly ash does not alter the XRD pattern.

• Pb₃SiO₅ phases in geopolymer is from outer sphere ion exchange process.

• Network modification -O-Na to -O-Pb shifts binding energy of O_1s to lower end.

Acknowledgements

This work was supported by Science and Engineering Board, Government of India under the grant number SRG/2021/002467.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work was supported by the Science and Engineering Research Board [SPG/2021/002467].

Notes on contributors

Sivasakthi M

Dr. Sivasakthi M is an active researcher from Sathyabama Institute of Science and Engineering, Chennai. Possessing a research experience for 9 years, his notable works include development of the different geopolymer composites from industrial by-products for high temperature applications, published in reputed journals. His current research focus is on optimization of the one part alkali activator solution for geopolymer production with life time analysis, thermal energy storage applications and heavy metal encapsulation.

P Priyadharsini

Dr. P Priyadharsini has completed M.Sc. in Chemistry (2011) from NMCC, Manonmaniam Sundharanar University, M.Phil. in Chemistry (2013) from SJC, Manonmaniam Sundharanar University and Ph.D. (2022) from Sathyabama Institute of Science and Technology, Chennai. She worked as an assistant professor from 2013- 2015 at Infant Jesus College of Technology, Thoothukudi (2013-2014) and Prince Dr. K. Vasudevan College of Engineering, Chennai (2014-2015). She joined Sathyabama Institute of Science and Technology in December 2021. She has research publications in refereed international journals, national journals and book chapter in international publishers. She has organized and attended many workshops, trainings, symposiums, and seminars. She attended numerous national and international conferences. Her current research work includes biomass and biofuels, energy and environment, waste utilization and valorization, waste water treatment, phytochemicals and carbohydrate polymers.