Mechanical activation-assisted leaching with saline water or dilute acid for lithium recovery from boron processing plant tailings

Abstract

Lithium (Li) is a soft, silver-white alkali metal that has become an increasingly strategic resource, primarily due to its critical role in lithium-ion batteries used in electric vehicles and renewable energy storage systems. High electrochemical potential, low atomic weight, and high energy density make lithium indispensable for battery technologies. As one of the most electropositive elements on the periodic table, lithium enables the production of high-voltage cells, making it ideal for rechargeable batteries. Due to their light weight, long cycle life, and high energy efficiency, lithium-ion batteries have the potential to reduce dependence on fossil fuel–based systems and significantly lower carbon emissions. In this context, the use of lithium is not only a technological choice but also a strategic solution in terms of environmental sustainability. Due to its high reactivity, lithium is never found in its pure form in nature; instead, it occurs in various mineral and brine deposits. Major lithium-bearing minerals include spodumene, lepidolite, petalite, and zinnwaldite. Additionally, lithium can be recovered from alternative sources such as lithium-rich clay minerals, primarily composed of phyllosilicates with a 2:1-layer structure. These structures exhibit charge imbalances caused by isomorphic substitutions in the tetrahedral and octahedral sheets, making them suitable for cation exchange and chemical reactions. Lithium resources are generally classified into hard rock deposits (pegmatites), lithium-rich brine reservoirs (salt flats), and volcano-sedimentary deposits. While South American countries dominate brine sources, countries like Australia possess significant spodumene reserves. In recent years, the increasing global demand for lithium has fueled interest in alternative sources such as clay minerals and industrial wastes. This growing demand necessitates the evaluation of lower-grade and more complex reserves. In this regard, clay minerals are considered sustainable, economically viable, and accessible alternative sources. In Türkiye, dolomitic clays associated with borate deposits, particularly in the Eskişehir-Kırka region, offer strategic potential for such applications. Lithium production methods vary depending on the source. Lithium recovery from ores typically involves roasting followed by hydrometallurgical processing, while brine-based extraction relies on solar evaporation, precipitation, solvent extraction, and ion exchange. Recently, mechanical activation has emerged as a promising pretreatment technique that enhances surface reactivity and disrupts crystal structures, thereby improving leaching efficiency. In this study, lithium recovery was investigated through both direct acid leaching and mechanical activation–assisted methods. Dolomitic clay waste obtained from the Eskişehir-Kırka Boron Plant was used as the raw material. Mechanical activation was carried out using various high-energy mills, including planetary mills (PM), stirred mills (SM), and vibrating mills (VM). The activated samples were subjected to sulfuric acid leaching under varying acid concentrations, temperatures, and leaching durations. Additionally, a two-stage leaching method combining saltwater leaching and acid leaching (SM Act.-WL+AL) was also evaluated. Experimental results revealed that mechanical activation significantly improved lithium solubility by increasing the surface area and disrupting the crystal structure of the clay minerals. Lithium recovery without any mechanical pretreatment, in the temperature range of 25–80 °C was between 12.17% and 13.17%, with lithium concentrations in solution reaching 21.9–23.7 ppm. However, the addition of 10% NaCl slightly reduced the yield and concentration (22.5 ppm, 12.50%), indicating a minor inhibitory effect of salt on untreated samples. Conversely, mechanical activation effectively mitigated this issue and enhanced lithium dissolution. For example, samples activated with the planetary mill (PM) exhibited significant improvement: 80.5 ppm (44.72%) with no salt, 87.2 ppm (48.44%) with 10% NaCl, and 96.1 ppm (53.39%) with 25% NaCl. Stirred mill (SM) activation achieved to lithium recoveries of 54.11%, 60.72%, and 63.67% for 0%, 10%, and 25% salt additions, respectively. Similarly, vibrating mill (VM)–activated samples showed recoveries of 36.72% (0% salt), 41.00% (10% salt), and 42.06% (25% salt). These findings demonstrate that mechanical activation not only enhances the leaching kinetics by increasing the surface accessibility but also reduces the negative effects of salt presence in the leaching medium. In acid leaching experiments, lithium recovery also increased significantly with acid concentration. For raw (ROM) samples, lithium recovery gradually increased from 22.06% at 0.75 mol/L to 24.56% at 1.00 mol/L, 32.89% at 1.25 mol/L, 91.94% at 1.50 mol/L, and ultimately reached 100.00% at 1.75 mol/L. For mechanically activated samples, the improvements were even more striking. PM-activated materials achieved 70.06% recovery at 0.50 mol/L H₂SO₄, rising to 76.00% at 0.75 mol/L, 84.06% at 1.00 mol/L, and reaching 100.00% at 1.25 mol/L. Similarly, SM-activated samples recorded 72.08%, 80.69%, 88.61%, and 95.56% recoveries at corresponding acid concentrations. VM-activated samples exhibited 62.06% at 0.50 mol/L, 72.44% at 0.75 mol/L, and peaked at 91.67% at 1.00 mol/L, though a slight decline to 64.28% at 1.25 mol/L was observed, possibly due to reprecipitation phenomena or saturation effects. Complementary surface analyses (EDS/EDX) demonstrated significant ion redistribution after activation. Na⁺ ions were enriched on PM-treated surfaces, whereas Ca²⁺ and Mg²⁺ ions became dominant in SM and VM-treated samples. Additionally, FTIR and XRD results confirmed major disruptions in crystal structures, confirming that mechanical activation is a viable pre-treatment to enhance lithium extraction performance from low-grade dolomitic clays. In conclusion, mechanical activation is an effective and applicable method for lithium recovery from low-grade clay minerals and industrial wastes. This study demonstrates that high lithium yields can be achieved through mechanical activation alone, and by using low concentrations of sulfuric acid, recovery can be increased to 100%. This approach not only offers environmental advantages by minimizing chemical use but also represents a cost-effective solution. The type of mill and processing parameters play a decisive role in the degree of crystal structure disruption and leaching efficiency. Moreover, the evaluation of dolomitic clays in regions such as Kırka, which contain borate deposits, offers a strategic opportunity as alternative sources for Türkiye. These findings support the integration of mechanical activation into lithium recovery workflows, particularly from complex or low-grade resources, while also contributing to waste management and aligning with principles of sustainable production.