5.06 A novel Circular Approach to Recover Critical Raw Materials and Energy from Spent Seawater Brines (CARMEn) 

technological progress and the increasing human living standards have been causing a growing exploitation of Earth’s non-renewable resources. The linear approach of productive processes has raised a considerably concern pushing towards novel circular approaches. Seawater brines and bitterns are by-products of desalination industry and natural sea salt production processes (an ancient process implemented in Italy since the Phoenician and Roman times in Sicily, Apulia, Sardinia). Seawater contains many elements belonging to the Critical Raw Materials (CRMs) list published by the European Union. CRMs are materials declared crucial for the European Union strategic industrial and society autonomy. CRMs concentration considerably increase in the seawater brines and bitterns. In this context, the exploitation of seawater brines and bitterns through novel circular approaches represents a crucial opportunity to satisfy CRMs EU demand in view of achieving the 2030 EU Green Deal goals. The proposed project introduces a novel circular approach aiming at recovering critical raw materials and energy from spent seawater bitterns and recovering CO2. Magnesium, currently listed among the 30 EU CRMs, in the form of Mg(OH)2 is targeted. Innovative membrane-based technologies will be adopted for:

• the pre-treatment of brines (POLITO_2),
• the production of reactants (UNIPA), such as sodium hydroxide or hydrochloric acid,
• the post treatment of brines (POLITO_2) and
• the production of sustainable electric energy (UNIPA).

The process implements:

1. an innovative patented multiple plug flow crystallizer (UNIPA) for the recovery of highly pure Mg(OH)2 and Ca(OH)2, and
2. a new technology, recently patented, for heavy metals stabilisation, based on the use of waste products (UNIBS) able to sequester carbon dioxide.

The process will also lead to environmental benefits by tackling the environmental impact of brine disposals and reducing CO2. For the proposed circular approach, a purposely developed modelling and optimization of the manufacturing and de-manufacturing circular process (POLITO_1) will be carried out through the definition of targets, models, and practices for energetic, economic and environmental sustainability. Below a graphical representation of the proposed circular chain of integrated processes is reported.