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CONSEQUENCES OF SIMPLE ACID-PRETREATMENTS ON GEOPOLYMERIZATION AND THERMAL STABILITY OF RED MUD-BASED GEOPOLYMERS Kardelen Kaya, Samira Fatma Kurtoglu, Alper Uzun, and Sezen Soyer Uzun Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b00920 • Publication Date (Web): 03 May 2018 Downloaded from http://pubs.acs.org on May 5, 2018
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Industrial & Engineering Chemistry Research
CONSEQUENCES OF SIMPLE ACID-PRETREATMENTS ON GEOPOLYMERIZATION AND THERMAL STABILITY OF RED MUD-BASED GEOPOLYMERS
Kardelen Kayaa,‡, Samira Fatma Kurtoğlub,c,‡, Alper Uzunb,c,d, Sezen Soyer-Uzuna,*
a
Department of Chemical Engineering, Bogazici University, Bebek, 34342 Istanbul, Turkey
b
Department of Chemical and Biological Engineering, Koç University, Rumelifeneri Yolu, Sariyer 34450, Istanbul, Turkey c
Koç University TÜPRAŞ Energy Center (KUTEM), Koç University, Rumelifeneri Yolu, Sariyer 34450, Istanbul, Turkey d
Koç University Surface Science and Technology Center (KUYTAM), Koç University, Rumelifeneri Yolu, Sariyer, 34450 Đstanbul, Turkey
‡
These authors contributed equally.
* Corresponding Author: E-mail address:
[email protected] (S. Soyer-Uzun) Tel.: +90 2123596469; fax:+90 2122872460.
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Abstract
Red mud, a solid waste residue that forms as a by-product of the Bayer process in alumina production, is structurally modified by simple acid treatments (using 2M and 6M HCl with digestion temperatures of 85 and 220 °C, respectively) followed by calcination at 800 ºC prior to employing it as a raw material in geopolymer synthesis. The raw materials and their geopolymers are characterized by combining X-ray diffraction, Fourier transform infrared spectroscopy, X-ray fluorescence spectroscopy, thermogravimetric analysis, pore volume and surface area analysis, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. Results reveal that acid modification of red mud followed by calcination plays an important role in activating red mud significantly leading to enhanced geopolymerization and increased thermal stability of the corresponding geopolymers. The findings presented here can offer new opportunities for effective large-scale utilization of other waste materialbased systems in geopolymerization.
Keywords: Geopolymer; Red mud; Acid modification; Characterization; Thermal stability
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Industrial & Engineering Chemistry Research
1. Introduction Geopolymers are aluminosilicate binders synthesized by a chemical heterogeneous reaction between aluminosilicate sources and alkali silicate or alkali metal hydroxide solutions in highly alkaline and mild conditions forming a polymeric Si-O-Al and Si-O-Si framework.1-2 Although geopolymers represent similar chemical structures to zeolites, their structures are considered as partially or totally amorphous.3 These materials are potential future alternatives to ordinary Portland cements displaying high mechanical strength, high resistance in acidic or alkaline environments and high stability under high temperatures.2 Aluminosilicate sources having the ability to dissolve in an alkaline solution can be utilized in geopolymerization process.4 Various aluminosilicate sources have been studied for geopolymer synthesis including metakaolin,5-7 fly ash,8-10 granulated blast furnace slag,11 red mud together with different aluminosilicate sources12-20 and combinations of these materials. Raw material selection and processing conditions have a huge effect on the structural and mechanical characteristics of the geopolymers.21 As different raw materials display diverse chemical compositions, Si/Al ratios, reactivity and different amorphous and crystalline phases, raw material selection designate the usage area of the final product.15 Red mud (RM) is a solid waste residue which occurs as a result of Bayer process in the production of alumina (Al2O3) from bauxite ores.12-13 Approximately 1.5 tons of RM is discharged during the production of 1 ton of alumina22 and approximately 150 million tons of RM is generated annually. Unfortunately, only less than 4 million tons of this bauxite residue are used for beneficial purposes.23 It is estimated that
