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In this study, scandium extraction from Bauxite residue based on sulfuric acid leaching is presented. Scandium dissolves at elevated temperatures under high acid concentration reaching recovery yields up to 90%. It was found that increasing acid concentration in the range of 3-4 mol/L at elevated temperature, increase Sc recovery whereas simultaneously overcoming silica gel issues that occur from Si dissolution obtaining fast filtration rates while working at high pulp densities. Upon H2SO4 leaching, the main elements present in Bauxite residue such as Fe, Ti and Al co-dissolve, resulting to a pregnant solution of several g/L and Sc concentration in the range of 10-20 mg/L. Neutralisation of leachate for Iron precipitation as well as direct solvent extraction were applied to successfully remove iron or directly extract Sc from solution.

Conventional perlite expansion suffers certain well-known shortcomings compromising its viability and the adherence of expanded perlite to modern technical specifications for high-quality insulation materials. A new perlite expansion process has been designed and a vertical electrical furnace for perlite expansion has been constructed to overcome such drawbacks, with concurrent modeling studies (Angelopoulos et al., 2013 [1]). Having already accomplished the production of various expanded perlite grades for many varying applications,the entire state space of product quality against key manipulated variables has also been explored, and ideal experimental condition ranges for process operation have also been identified (Angelopoulos et al., 2013 [2]). Response Surface Methodologies (RSM) have an long track record of contribution to substantial improvements in many advanced chemical and material processing technologies. Their fundamental principle is the systematic exploration and statistical correlation of input (conditional) and output (response) variables with respect to interactions (if any) of the former and their combined effect (if any) on the latter – thus on end product quality. This paper focuses on using parametric sensitivity analysis results from the published furnace dynamic model as well as original experimental furnace results towards extracting a new three-dimensional RSM model which achieves an accurate correlation of both pivotal experimental variables (furnace temperature, air flowrate) with their combined effect on a known end-product quality metric (grain expansion factor): optimal condition ranges can thus be derived via bivariate quadratic polynomial fits for any plant and any raw perlite feed composition.

Expanded perlite has outstanding thermal and acoustic insulating properties and is widely used in the manufacturing and construction industries. The conventional perlite expansion method has certain disadvantages which affect the quality of expanded perlite products, thus limiting their performance and range of applications. A new perlite expansion process has been designed and a vertical electrical furnace for perlite expansion has been constructed in our laboratory in order to overcome these drawbacks, enabling precise control of experimental conditions in order to prescribe the temperature profile and residence time within the new heating chamber. A novel dynamic model for perlite grain expansion has been developed and validated so as to study and optimize the new furnace operation. Perlite ore origin, size distribution and water content are key parameters affecting expanded perlite quality. Moreover, air feed flow rate and temperature, as well as the imposed wall temperature distribution along the heating chamber are experimentally known to have a profound, measurable effect on grain residence time and expansion. A detailed sensitivity analysis has been performed so as to quantitatively understand the effect and relative importance of all foregoing operational parameters on macroscopic furnace operation (perlite particle velocity and temperature evolution) as well as on inaccessible microscopic characteristics (internal steam bubble pressure and size). Perlite grain radius and expansion ratio are probed in detail as a function of time, and furnace operation can be tuned vs. feed variation toward optimal product quality. Particle critical characteristics along trajectories as well as final particle size plots are presented; also, optimal furnace operating condition ranges are determined for variable initial size and water content.

Expanded perlite has outstanding thermal and acoustic insulating properties and is widely used in the manufacturing and construction industries. The conventional perlite expansion method suffers disadvantages which affect the quality of expanded perlite products, thus limiting their performance and range of applications. A new perlite expansion process has been designed and a vertical electrical furnace for perlite expansion has been constructed in our laboratory in order to overcome these drawbacks, enabling precise control of experimental conditions, so as to prescribe the temperature profile and residence time in the heating chamber. Perlite ore origin, size distribution and water content are critical parameters affecting expanded perlite quality; air feed flow rate and temperature, as well as the imposed wall temperature distribution along the chamber are also experimentally known to have a profound, measurable effect on perlite grain residence time and expansion. A detailed sensitivity analysis has been performed in order to quantitatively understand the effect and relative importance of all these operational parameters on macroscopic furnace operation (perlite particle velocity and temperature evolution) and inaccessible microscopic characteristics (internal steam bubble pressure and size), based on a new dynamic model for perlite grain expansion we have developed towards furnace optimization [1].

Expanded perlite has outstanding thermal and acoustic insulating properties and is widely used in the manufacturing and construction industries. The conventional perlite expansion method suffers disadvantages which affect the quality of expanded perlite products, thus limiting their performance and range of applications. A new perlite expansion process has been designed and a vertical electrical furnace for perlite expansion has been constructed in our laboratory to overcome these drawbacks: the new design enables precise control of experimental conditions, so as to prescribe the temperature profile and residence time in the heating chamber. Expanded perlite can thus be produced with various quality specifications for a range of different applications. A mathematical model for perlite grain expansion has been developed, aimed at the detailed investigation and optimization of perlite expansion in the new furnace. The dynamic model consists of ordinary differential equations for both air and particle heat and momentum balances, probing the air temperature distribution as well as the particle velocity, temperature and size along its trajectory in the heating chamber. The effect of raw material physical properties as well as operational parameters on product quality is investigated and discussed.