ELECTRO-DIALYSIS WITH BIPOLAR MEMBRANES FOR A CIRCULAR AND SUSTAINABLE VALORISATION OF WASTE BRINES

In today rapidly evolving and resource-dependent world, the extraction of minerals from waste streams is emerging as a critical solution to meet the growing demands of various industries. Brines, which are highly concentrated saline solutions, are not only by-products of numerous industrial processes but can also be found in natural environments such as salt lakes and underground reservoirs. Rich in essential minerals like lithium, magnesium, potassium, and sodium chloride, these brines are indispensable for applications ranging from energy storage to agriculture and chemical manufacturing. Membrane processes have become pivotal in this extraction, offering efficient, scalable, and sustainable methods for recovering these valuable minerals. Among these processes, Electro-Dialysis with Bipolar Membranes (EDBM) stands out as a groundbreaking advancement in membrane technology. EDBM provides a sustainable and effective approach to producing acids and bases, recovering vital resources, and treating industrial waste streams. With ongoing improvements in membrane materials, stack design, and process integration, EDBM is becoming increasingly viable across a wide range of industrial applications. As global demand for critical minerals continues to increase, the development and optimization of membrane technologies for mineral recovery from brines are of paramount importance. These technologies are not only essential for supporting the transition to a more sustainable and circular economy but also open new pathways for innovation and economic growth in the industrial sector. As industries continue to seek out sustainable and cost-effective solutions, EDBM and related membrane technologies are poised to play a leader role in shaping the future of green chemistry and resource recovery.The research activities presented in the following PhD thesis, has been devoted to the prototyping of the Electro-Dialysis with Bipolar Membranes technology and to the development and testing of innovative strategies to valorise waste brines. The research aims have mainly focused on developing advanced control strategies for the EDBM process, enabling it to store fluctuating energy coming from renewable sources or smart grids in the form of chemical reagents (e.g., acids and bases). By adjusting process variables based on energy availability and utilizing waste saline streams, this approach allowed to promote circular processes as well as sustainable energy utilization.The present PhD thesis is organized in 8 chapter which are summarized as follow:Chapter 1 presents an overview of brine sources, related issue, innovative solutions to recover it through renewable energy-driven process. Moreover, it provides a brief introduction to the Horizon 2020 European projects, Water-Mining and SEArcularMINE, which have proposed innovative treatment chain for brine valorisation.Chapter 2 provides a general introduction to the electro membrane processes, as EDBM belongs to this class of processes. Moreover, an in-depth description of the EDBM process along with its state of the art is presented.Chapter 3 describes the design and construction of an Electro-Dialysis with Bipolar Membranes stack at pilot scale provided by FuMa-Tech, along with the description of the main part composing the hydraulic circuit such as pumps, valves, data acquisition software and hardware.Chapter 4 outlines a comprehensive experimental campaign carried out in Lampedusa Island, as part of the Water-Mining project. In the initial phase, an analysis of the unit performance was performed under various process configurations such as closed-loop, feed and bleed, and fed-batch, while varying the current density applied to the stack. The best configuration was then selected to test the pilot stack with real solutions for a long-run test (60 hours) in order to demonstrate the scalability of the process for industrial applications.Chapter 5 presents unconventional and innovative process schemes for the EDBM process aimed at reducing the environmental impact within treatment chains for the valorisation of waste brines that use acidic and basic solutions, where the presence of salt has no influence on the up/down stream processes. Chapter 6 presents a study of the dynamic behaviour of the EDBM process. A linearized model of the process was derived through the application of step tests to the real process. Subsequently, the design and testing of advanced controllers were presented, aimed at operating the EDBM process under highly transient energy sources, such as solar energy. These controllers successfully adapted to the non-stationary nature of the input energy while maintaining the product quality at the target value.Chapter 7 provides a description of the design and development of a new pilot-scale EDBM stack provided by Water Treatment Solutions (WTS) within the SEArcularMINE project. Additionally, it presents the role of EDBM in the treatment chain and the technological solutions implemented to increase the Technology Readiness Level (TRL) of the technology compared to the FuMa-Tech. Furthermore, a comprehensive comparison between the FuMa-Tech and the WTS EDBM stacks was performed, at three different current densities (i.e. 200, 300 and 400 A m-2). This comparison allowed for the identification of the best technological solution for future industrial-scale implementations of the EDBM technology.Chapter 8 focuses on the testing of a thermal desalination called Mechanical Vapor Compression (MVC). A long-run test, of about 20 hours, was performed using the real waste brine coming from the SEArcularMINE treatment chain. The results show how implementing this technology in synergy with EDBM allows for the elimination of effluent discharge from the EDBM process, recovering industrial-grade NaCl and a concentrated solution rich in trace elements such as Lithium, Rubidium, Caesium, and Strontium, thereby generating a Zero Liquid Discharge process as outlined in the SEArcularMINE treatment chain.