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The use of calcined clays as supplementary cementitious materials provides the opportunity to significantly reduce the cement industry’s carbon burden; however, use at a global scale requires a deep understanding of the extraction and processing of the clays to be used, which will uncover routes to optimise their reactivity. This will enable increased usage of calcined clays as cement replacements, further improving the sustainability of concretes produced with them. Existing technologies can be adopted to produce calcined clays at an industrial scale in many regions around the world. This paper, produced by RILEM TC 282-CCL on calcined clays as supplementary cementitious materials (working group 2), focuses on the production of calcined clays, presents an overview of clay mining, and assesses the current state of the art in clay calcination technology, covering the most relevant aspects from the clay deposit to the factory gate. The energetics and associated carbon footprint of the calcination process are also discussed, and an outlook on clay calcination is presented, discussing the technological advancements required to fulfil future global demand for this material in sustainable infrastructure development.

Suitability of TBP for recovery of uranium(VI) from dilute HNO3 using LEM extraction is investigated. TBP co-extracts significant amount of HNO3 along with U(VI). Beyond a critical time, extraction of U(VI) ceases due to attainment of critical acid level when the strip phase is unable to break TBP-U(VI) complex. The observed critical time is in good agreement with that estimated from rate of acid extraction. Optimal conditions at which the relative extraction of HNO3 is minimal with respect to U(VI) is arrived at. The extraction efficiency of TBP is compared with other ligands viz., TiAP, TEHP, TOPO, TOA and D2EHPA.

The response surface methodology is used to obtain optimal rate and extent of extraction of low concentration U(VI) (a parts per thousand currency sign100 mg/L) by liquid emulsion membrane technique. Three different ligands viz. Tri-n-octyl phosphine oxide (TOPO), Tri-n-octyl amine (TOA) and Di-(2-ethylhexyl)phosphoric acid (D2EHPA), are used. 2(3) factorial design is applied to generate second order regression equation for studying the effect of concentration of ligand, surfactant and feed acidity. The regression model is in good agreement with the experimental data for all ligands. The rate of extraction of U(VI) by LEM is found to be in the order TOA > TOPO > D2EHPA.