Synthesis of thermostable geopolymer from circulating fluidized bed combustion (CFBC) bottom ashes

• Published in: Journal of hazardous materials 2010-03, Vol.175 (1), p.198-204
• Main Authors: Xu, Hui, Li, Qin, Shen, Lifeng, Wang, Wei, Zhai, Jianping
• Format: Article
• Language: English
• Subjects: Alkali activation; Applied sciences; CFBC bottom ashes; Chemical engineering; Compressive Strength; Exact sciences and technology; General treatment and storage processes; Geopolymer; Hazardous Substances; Hazardous Waste; Hot Temperature; Hydroxides - chemistry; Industrial Waste; Microscopy, Electron, Scanning - methods; Particulate Matter - chemistry; Pollution; Polymers - chemistry; Potassium Compounds - chemistry; Pressure; Refuse Disposal - methods; Safety; Sodium Hydroxide - chemistry; Spectroscopy, Fourier Transform Infrared - methods; Thermal history; Thermal stability; Thermogravimetry - methods; Wastes; X-Ray Diffraction
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2009.09.149

Circulating fluidized bed combustion (CFBC) bottom ashes (CBAs) are a class of calcined aluminosilicate wastes with a unique thermal history. While landfill disposal of hazardous element-containing CBAs poses serious challenge, these wastes have long been neglected as source materials for geopolymer production. In this paper, geopolymerization of ground CBAs was investigated. Reactivity of the CBAs was analyzed by respective dissolution of the ashes in 2, 5, and 10N NaOH and KOH solutions. Geopolymer pastes were prepared by activating the CBAs by a series of alkalis hydroxides and/or sodium silicate solutions. Samples were cured at 40 °C for 168 h, giving a highest compressive strength of 52.9 MPa. Of the optimal specimen, characterization was conducted by TG-DTA, SEM, XRD, as well as FTIR analyses, and thermal stability was determined in terms of compressive strength evolution via exposure to 800 or 1050 °C followed by three cooling regimes, i.e. cooling in air, cooling in the furnace, and immerging in water. The results show that CBAs could serve as favorable source materials for thermostable geopolymers, which hold a promise to replace ordinary Portland cement (OPC) and organic polymers in a variety of applications, especially where fire hazards are of great concern.