Valorisation of Sidestream from lithium Refining - Activation of Analcime

Abstract

The European Union has an ambitious goal to transition from linear to circular economy [1]. In circular economy, the old saying of "one's waste is the other's treasure" is being implemented. An industrial side stream, traditionally branded as waste, is the raw material for the formation of the next product. Analcime is a reject from spodumene refining at a Finnish lithium hydroxide plant, currently in piloting stage, but is also found as a natural zeolite. With a channel size of 4.2-8.9 Å [2], analcime can be used as sodium cation exchange for NH4 + [3], Pb 2+ and Cu 2+ [4], and to a lesser extent and at elevated temperatures for K + , Ag + , Tl + , Rb + [5]. Being an energy minimum, the α-analcime structure is inert towards mild activation methods. Therefore, in this paper the valorisation of analcime by thermal and chemical activation and possible ways of obtained materials' use are discussed. Several procedures were considered in order to change raw material properties: alkaline, acid, and thermal activation. Raw analcime is inert towards alkaline activation (geopolymerisation) under all room temperature reaction in a solid to liquid ratio of 1:1.1 with NaOH/NaSiO3 or KOH/KSiO3 solution. Rinsing with 1 and 2 M HCl did not facilitate the geopolymerization, nor did heating at 700 °C. Calcination at 900 °C for 2 h resulted in complete phase change from analcime to nepheline, as characterized by XRD. Treating analcime with sulfuric acid of at 3, 4, and 5 M strength resulted in breakdown of the alumino-silicate structure of analcime and the formation of Na2AlSO4. XRD and XRF confirm the preferential dissolution of aluminate. After acid activation, geopolymerization occurred rapid and exothermic. Mixing analcime with metakaolinite as an additional binder had also resulted in the geopolymerized solid material. The structural properties, XRF, and XRD characterization of activated analcime products are discussed. Adsorptive properties of the new materials were tested for ammonium and compared to the raw side stream analcime. In all cases, the ammonium sorption were low. Activation with 5 M H2SO4 and subsequent geopolymerization (adsorbent ANA-5M-GP) doubles the adsorption capacity at 50 mg/L NH4 + and dose of 2 and 5 g/L. The competition of ion exchange sites Ca 2+ cations at concentrations found in municipal wastewater (40-100 mg/L Ca 2+) is discussed and investigated under complex matrix of Kajaani municipal waste water. Inert analcime side stream can undergo harsh chemical and thermal treatment to form new products with potentially interesting properties. Geopolymerization of acid treated activation of inert analcime greatly influences the structural and chemical properties of the raw substance. ANA-5M-GP has a higher adsorption capacity for ammonium than raw analcime. Additionally, the fast geopolymerization reaction could find applications in fast-hardening low carbon concrete substituents. Acid activation with at least 3 M H2SO4 therefore valorises the side product and enhances its properties for new applications...

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“…An alternative is the treatment of the analcime with hydrochloric acid, which causes a fourfold increase in the specific surface area of the material [69]. The acid activation with subsequent geopolymerisation also doubles the ion exchange capacity and promotes the removal of the ammonium ion [74]. Unfortunately, this requires the use of chemicals.…”

Geopolymers and Alkali-Activated Materials for Wastewater Treatment Applications and Valorization of Industrial Side Streams

“…Although the ultimate set of preferable conditions to form a GP instead of a zeolite are still under discussion, ratios Si:Al > 1.5 have been empirically established as providing more amorphous structures [60]. α-Analcime is a reject from spodumene refining at a Finnish lithium hydroxide plant, currently in piloting stage, and estimated to start the production in 2024, but is also found as a natural zeolite [3]. The small cavity size of analcime facilitates ionexchange only for small mono-and divalent cations such as ammonium and Cu 2+ , and also K + ,Ag + ,Tl + ,Rb + (at elevated temperatures), and with low adsorption capacity.…”

“…The small cavity size of analcime facilitates ionexchange only for small mono-and divalent cations such as ammonium and Cu 2+ , and also K + ,Ag + ,Tl + ,Rb + (at elevated temperatures), and with low adsorption capacity. Raw analcime is inert to alkaline activation and analcime requires either chemical activation by 3-5MH 2 SO 4 or thermal activation above 700°C [3].…”

“…Upcycling often requires further energy sources to achieve higher valuable material. In geopolymeration or alkaline activation this means the addition of chemicals, and in some occasions, such as analcime tailings, the addition of thermal energy [3].…”