Comparative Study of HCl Leaching with and without Microwave Pretreatment for Rare Earth Recovery from Vietnamese Bastnaesite Concentrate

Rare earth elements (REEs) are essential components in modern technologies, including electric vehicles, wind turbines, and consumer electronics. As global demand for REEs continues to grow, there is an urgent need for efficient and diversified extraction methods that minimize reliance on harsh chemicals and high energy input. To this end, this study compares two approaches for REE recovery from Vietnamese bastnaesite concentrate: (1) direct HCl leaching, and (2) microwave-assisted NaOH roasting followed by HCl leaching. These methods were systematically evaluated in terms of leaching efficiency and reagent consumption. Direct HCl leaching was carried out at 25–90 ℃, 2–12 M acid concentration, a liquid-to-solid ratio of 10 mL/g, and 500 rpm. We obtained a maximum REE recovery of 72.41% under 12 M HCl at 90 ℃ for 8 h. In contrast, the microwave-assisted roasting was conducted at 700 W and a NaOH-to-concentrate ratio of 0.1–1:1 (w/w) for 90 s, followed by HCl leaching under the conditions of 2–12 M HCl, 90 ℃, a liquid-to-solid ratio of 10 mL/g, and 500 rpm. Using this method, we achieved 91.86% leaching efficiency with 3 M HCl and 99.38% with 4 M HCl at a 0.2:1 (w/w) NaOH-to-concentrate ratio. These results support ongoing efforts to develop more robust and environmentally responsible REE extraction strategies, contributing to a secure and regionally diversified supply chain.