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The use of closed-loop salinity gradient power (SGP) technologies has been recently presented as a viable option to generate power using low-grade heat, by coupling a SGP unit with a thermally-driven regeneration process in a closed loop where artificial solutions can be adopted for the conversion of heat into power. Among these, the closed-loop reverse electrodialysis (RED) process presents a number of advantages such as the direct production of electricity, the extreme flexibility in operating conditions and the recently demonstrated large potentials for industrial scale-up. Ammonium hydrogen carbonate (NH4HCO3) is a salt suitable for such closed-loop RED process thanks to its particular properties. At temperatures above 40–45°C, it decomposes into a gaseous phase containing NH3, CO2 and water. Thus, the use of NH4HCO3 solutions for feeding a RED unit would allow their easy regeneration (after the power generation step) just using low-temperature waste heat in a purposely designed regeneration unit. This work aims at presenting an experimental investigation performed on a RED system fed with NH4HCO3 solutions. Laboratory tests were carried out to find the best conditions for maximizing the power density and process performances of a RED unit by investigating a number of operating parameters such as fluid velocity and feed solutions concentration

Seawater brines, generated either by natural or anthropic processes, often cause significant environmental issues related to their disposal. A clear example is the case of brines from desalination plants, which can have severe environmental impacts on the receiving water body. On the other side, brines can represent a rich and appealing source of raw materials, especially when they are very concentrated, as it happens with bitterns (i.e. exhausted brines) produced in saltworks. In particular, magnesium concentration can reach values up to 30-40 kg/m3 of brine, which is 20-30 times that of typical seawater.\ud An experimental campaign has been carried out in the present work for assessing the potentials for magnesium recovery from concentrated brines. Real brines were collected from the final basins of the saltworks operating in the district of Trapani (Sicily - Italy).\ud Experiments were performed both in a semi-batch and in a continuous 5 litre crystalliser operating by a reactive precipitation process. NaOH solutions were adopted as standard alkaline reactant in order to assess the influence of all operating parameters and reactor configuration on the recovery efficiency and purity of the Mg(OH)2 powder produced.\ud Results have highlighted a very promising strategy for the recovery of Mg from concentrated brines, which could be scaled-up and applied to a number of different scenarios, including existing saltworks and newly designed integrated cycles for Zero Liquid Discharge desalination

The problem of brines disposal has raised great interest towards new strategies for their valorisation through the recovery of minerals or energy. As an example, the spent brine from ion exchange resins regeneration is often discharged into rivers or lakes, thus impacting on the process sustainability. However, such brines can be effectively reconcentrated, after removal of bivalent cations, and reused for the resins regeneration. This work focuses on developing and testing a pilot plant for selective recovery of magnesium and calcium from spent brines exploiting a novel proprietary crystallization unit. This is part of a larger treatment chain for the complete regeneration of the brine, developed within the EU-funded ZERO BRINE project. The pilot crystallizer was tested with the retentate of the nanofiltration unit processing the spent brine from the industrial water production plant of Evides Industriewater B.V. (Rotterdam, The Netherlands).Magnesium and calcium hydroxide were selectively precipitated by adding alkaline solution in two consecutive steps and controlling reaction pH. Performance was assessed in terms of recovery efficiency and purity of produced crystals, observing in most investigated cases a recovery of about 100% and 97% and a purity above 90% and 96%, for magnesium and calcium hydroxide, respectively.

Reverse Electrodialysis in a closed-loop arrangement is a viable way to convert lowgrade heat into electric power. For the first time, the present work experimentally investigates the use of pure saltwater and equimolar two salts-water as feed solutions in a lab-scale RED unit in terms of OCV, stack resistance and corrected power density. The pure salts and the mixture salts to be employed were chosen via a computational analysis. Effect of feed solution velocity and concentration was also investigated. Results concerning the pure saltwater experiments suggest the use of NH4Cl in the concentration range investigated, while higher power density values are expected with the use of LiCl at larger concentrations. As regards the salt binary mixtures, in some cases the measured stack electrical resistance was found lower than both the two values measured for the corresponding pure salts, thus resulting into higher power density values for the mixtures. This surprising experimental evidence suggests that it is possible to increase the power produced by a conventional RED unit by adding an equivalent molar quantity of another suitable salt. Finally, among the mixtures tested, the NH4Cl-LiCl mixture appears as the most promising, thanks to the combination of the favorable properties of these two salts.