Using Sodium, Potassium and Calcium Carbonates as Fly Ash Activators to Achieve Higher Leachability of Aluminum

article in a collection out of WoS and Scopus

English

Based on extensive research, the key to finding a potentially universal method for all types of FA seems to lie in combining a thermal sintering reaction with a suitable activating agent, followed by leaching in a sulfuric acid solution, even at a low concentration of approximately 5 wt.%. The hightemperature activation reaction involves the chemical modification of fly ash composition, wherein the glass fraction or resistant minerals like mullite are converted into components that are more susceptible to degradation in an acidic environment. Experimental evidence has confirmed that alkaline ions, specifically sodium, potassium, and calcium, can serve as effective activating agents by inducing changes in the chemical composition and mineralogy of the samples. In this study, sodium, potassium, and calcium carbonates were selected as sintering agents, with varying ash-to-reagent ratios of 0.5, 1.0, 1.5, and 2.0 to FA. The temperature regime employed in the experiments was based on previous successful trials, involving gradual heating at a rate of 5–10 °C per min until reaching 1000 °C, followed by a 60 minu hold at this temperature and subsequent cooling to 500 °C at a rate of 5 °C per min. Finally, rapid cooling to room temperature was achieved within minutes. It was observed that excessively rapid cooling below 500 °C led to the autodisintegration of the materials into smaller fragments or fine particulate systems. Notably, samples activated with calcium carbonate exhibited a crumbly texture and could be easily ground by hand, whereas those sintered with sodium and potassium carbonates formed relatively solid balls that required grinding. Furthermore, the overall grindability of the material decreased with increasing amounts of activator added. The sintered precursors were subsequently subjected to extraction in a sulfuric acid environment, utilizing various concentrations corresponding to the proportion of the theoretical total stoichiometric reaction as 0.7, 0.8, 0.9, 1.0, 1.1, and 1.2 equivalents in sulfuric acid. During this process, the leachability of aluminum, iron, and titanium was continuously monitored over a period of time. The results demonstrated that when sodium and potassium activators were employed, the maximum leachability of aluminum, ranging from 70% to 80%, was achieved. Conversely, when the calcium reagent was utilized, an impressive leachability of up to 98% of the aluminum present was observed.

Fly ash, fly ash utilization, recovery of macro elements

MARKO, M.; OPRAVIL, T.; KŘIKALA, J.

22. 11. 2023

Slovenská chemická knižnica

Bratislava

978-80-8208-106-3

Chémia a technológie pre život 25. celoslovenská študentská vedecká konferencia s medzinárodnou účasťou

92

93

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https://www.uiam.sk/~oravec/svk/e_zbornik_svk_2023.pdf