Geochemical characterization of the “Chiusicella” saltwork (western Sicily): insights into critical raw materials

Abstract

Saltworks are human-modified ecosystems primarily designed for NaCl production for the food industry, but they also host unique biogeochemical processes still not well known. Environments with intense evaporation, such as salt lakes and saltpans, represent natural settings where solar energy enables the overconcentration of interesting elements. Oceans and seawater, due to their vast quantities of valuable minerals and dissolved ions such as Na+, Ca2+, Mg2+, K+, Li+, Sr2+, Br- and B-, have become a focus of research to address the depletion of high-grade ores[1]. Mining seawater is a debated issue, as it depends on the quantitative abundance of dissolved ions, which in turn affects the energy cost of extraction methodologies and, consequently, their sustainability. Several studies have demonstrated that the precipitation of authigenic minerals involves trace metals and that the brines in each pond of a saltwork, as well as the residual NaCl-depleted solutions, known as “bittern”, could represent secondary resource supplies[2]. This study investigates the mineralogical and chemical characterization of sediments and brines from four ponds of the “Chiusicella” saltwork in Trapani-Paceco (western Sicily, Italy). To evaluate possible accumulations of critical elements, either in precipitates or in solution, the samples were analyzed using X-ray fluorescence (XRF), X-ray diffraction (XRD), ICP-MS, and SEM-EDS. The results underline some elements of interest from both a quantitative and geochemical behaviour perspective, namely Li, B, Sr, Mg, and Br. This research highlights the potential recovery of these elements as insoluble phases using bioremediation technologies such as microbial-induced carbonate precipitation (MICP)[3], or via absorption mechanisms in zeolites and clays minerals[4], leading to the recovery of critical raw materials (CRMs) from alternative supply sources, within the circular economy model, without invasive and environmentally harmful practices[5].