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Combinations of p-toluenesulfonic acid monohydrate with different hydrogen-bond acceptors (i.e., choline chloride, tetraethylammonium chloride, tetrabutylammonium chloride, betaine hydrochloride, β-alanine, tetrabutylphosphonium chloride, ethylammonium chloride, methyltriphenylphosphonium bromide, and benzyltriphenylphosphonium chloride) were tested for deep-eutectic solvent (DES) formation. Only p-toluenesulfonic acid monohydrate:choline chloride, p-toluenesulfonic acid monohydrate:tetrabutylammonium chloride, and p-toluenesulfonic acid monohydrate:tetrabutylphosphonium chloride at a 1:1 molar ratio remained liquid at room temperature. The obtained deep-eutectic solvents were characterized by determining their density and viscosity as function of temperature, and their thermal operational window (i.e., decomposition temperature and melting point/glass transition temperature). Moreover, IR spectroscopy was used to elucidate the formation of hydrogen bonds. The solubility of different metal oxides in the DES p-toluenesulfonic acid monohydrate:choline chloride was experimentally determined. The effect of the hydrogen-bond donor:hydrogen-bond acceptor molar ratio (2:1, 1:1, and 1:2) on the metal oxide solubility was explored. A comparison was made with metal oxide solubilities in other choline chloride-based DESs and in acidic aqueous solutions.

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Plasma processing of materials is a technology now also employed in the management of municipal solid wastes, often mixed with industrial residues. The specifics depend per case, but typically the process delivers energy, in the form of a gas or heat, a metal-rich fraction as well as a slag. The slag, containing mainly Si-, Fe-, Ca-and Al-oxides, is almost completely amorphous after rapid cooling and thus could possibly be used as precursor in the synthesis of inorganic polymers (IP). The latter is explored in the present work. Slag resembling the composition of refuse-derived fuel ash was mixed with various Na-silicate activating solutions, and the effect of SiO 2 /Na 2 O as well as H 2 O/Na 2 O molar ratio on the synthesis and mechanical properties of the prepared IP was investigated. It was found that for SiO 2 / Na 2 O molar ratios of 1.2 and H 2 O/Na 2 O molar ratio of 30.8, the mechanical strength of casted IP reached almost 90 MPa after 90 days. Further decrease in the SiO 2 /Na 2 O ratio, accompanied by decrease in the H 2 O/Na 2 O ratio, increased the early strength and the released reaction heat, but had no effect on the late strength. In addition to that, crack formation was pronounced. The increase of the concentration of activating solution, by means of reducing the water content level, i.e. H 2 O/Na 2 O, resulted in an increase of the released reaction heat as well as an increase of the mechanical strength, up to 112 MPa at 90 days. The above results are relevant to a range of metallurgical slags and other vitreous by-products and contribute towards more high added-value applications.