An extensive experimental campaign on Li recovery from relatively dilute LiCl solutions (i.e., Li⁺ ∼ 4000 ppm) is presented to identify the best operating conditions for a Li₂CO₃ crystallization unit. Lithium is currently mainly produced via solar evaporation, purification, and precipitation from highly concentrated Li brines located in a few world areas. The process requires large surfaces and long times (18-24 months) to concentrate Li⁺ up to 20,000 ppm. The present work investigates two separation routes to extract Li⁺ from synthetic solutions, mimicking those obtained from low-content Li⁺ sources through selective Li⁺ separation and further concentration steps: (i) addition of Na₂CO₃ solution and (ii) addition of NaOH solution + CO₂ insufflation. A Li recovery up to 80% and purities up to 99% at 80 °C and with high-ionic strength solutions was achieved employing NaOH solution + CO₂ insufflation and an ethanol washing step.

The continuous depletion of minerals caused by land mining and the increase in their demand have pushed the development of novel sustainable technological processes for mineral recovery from unconventional sources. In this context, magnesium (Mg) has gained considerable attention for its peculiar properties and high relevance of its compounds, such as magnesium hydroxide, Mg(OH)₂. In the present work, the influence of several operating conditions on the Mg(OH)₂ precipitation process was thoroughly investigated by adopting a novel multiple feed-plug flow reactor. The influence of (i) initial Mg²⁺ concentrations in the feed stream; (ii) brine and alkaline flow rates; and (iii) the product recycling strategy (seeded crystallization) was considered. The results marked the possibility of improving sedimentation and filterability properties of Mg(OH)₂ suspensions by adopting the recycling strategy to overcome industrial issues associated with the production of Mg(OH)₂ suspensions using NaOH solutions.

Magnesium hydroxide, Mg(OH)₂, is an inorganic compound extensively employed in several industrial sectors. Nowadays, it is mostly produced from magnesium-rich minerals. Nevertheless, magnesium-rich solutions, such as natural and industrial brines, could prove to be a great treasure. In this work, synthetic magnesium chloride and sodium hydroxide (NaOH) solutions were used to recover Mg(OH)₂ by reactive crystallization. A detailed experimental campaign was conducted aiming at producing grown Mg(OH)₂ hexagonal platelets. Experiments were carried out in a stirred tank crystallizer operated in single- and double-feed configurations. In the single-feed configuration, globular and nanoflakes primary particles were obtained, as always reported in the literature when NaOH is used as a precipitant. However, these products are not complying with flame-retardant applications that require large hexagonal Mg(OH)₂ platelets. This work suggests an effective precipitation strategy to favor crystal growth while, at the same time, limiting the nucleation mechanism. The double-feed configuration allowed the synthesis of grown Mg(OH)₂ hexagonal platelets. The influence of reactant flow rates, reactant concentrations, and reaction temperature was analyzed. Scanning electron microscopy (SEM) pictures were also taken to investigate the morphology of Mg(OH)₂ crystals. The proposed precipitation strategy paves the road to satisfy flame-retardant market requirements.

Magnesium is a critical raw material and its recovery as Mg(OH)₂ from saltwork brines can be realized via precipitation. The effective design, optimization, and scale-up of such a process require the development of a computational model accounting for the effect of fluid dynamics, homogeneous and heterogeneous nucleation, molecular growth, and aggregation. The unknown kinetics parameters are inferred and validated in this work by using experimental data produced with a T_2mm-mixer and a T_3mm-mixer, guaranteeing fast and efficient mixing. The flow field in the T-mixers is fully characterized by using the k-ε turbulence model implemented in the computational fluid dynamics (CFD) code OpenFOAM. The model is based on a simplified plug flow reactor model, instructed by detailed CFD simulations. It incorporates Bromley's activity coefficient correction and a micro-mixing model for the calculation of the supersaturation ratio. The population balance equation is solved by exploiting the quadrature method of moments, and mass balances are used for updating the reactive ions concentrations, accounting for the precipitated solid. To avoid unphysical results, global constrained optimization is used for kinetics parameters identification, exploiting experimentally measured particle size distribution (PSD). The inferred kinetics set is validated by comparing PSDs at different operative conditions both in the T_2mm-mixer and the T_3mm-mixer. The developed computational model, including the kinetics parameters estimated for the first time in this work, will be used for the design of a prototype for the industrial precipitation of Mg(OH)₂ from saltwork brines in an industrial environment.

Magnesium has been listed among the 30 critical raw materials by the European Union. In recent years, many green and sustainable alternative Mg²⁺ sources have been sought to satisfy the EU’s demand and to avoid mineral ore consumption. In this context, saltwork bitterns, the by-products of solar sea salt production, have attracted much attention thanks to their high Mg²⁺ concentrations (up to 80 g/L) and low Ca²⁺ and bicarbonate contents (95% (w/w). This work presents a comprehensive experimental effort of reactive precipitation tests with NaOH solutions at stoichiometric and over-stoichiometric concentrations to: (i) assess the technical feasibility of Mg²⁺ recovery from real bitterns collected in saltworks of the Trapani district (Italy) and, (ii) for the first time, conduct an extensive purity investigation of the precipitated magnesium hydroxide powders as brucite. This experimental investigation demonstrates the possibility of extracting highly valuable compounds from saltwork bittern waste, embracing the water valorization and resource recovery approach.