Environmental pollution caused by fluorine emissions during H2SO4 roasting of bastnaesite processing in China is becoming of increasing concern. Because of this, processes have been developed to prevent the emission of fluorine. A first method revolves around only leaching the carbonate REE while leaving the REE fluorides in the residue. This is achieved by thermally activating the ore (400 °C for 3 h) and then leaching it with HCl. Thermal activation enables leaching of the carbonates at conditions in which the fluorides are unaffected. The reported leaching efficiency of this process is 94.6% for the carbonates and 0.07% for the fluorides. A different method involves progress in the air-roasting process mentioned in Section 2.1. This process had already been proven ineffective in leaching the fluoride components, but the oxidation of Ce+III to Ce+IV prevented Ce from being leached together with the other REE and led to purification issues. The addition of thiourea offered a solution to this problem. Thiourea prevents the oxidation of Ce, keeping it trivalent after roasting and thus allowing it to be leached with HCl together with other REE. This allowed for the recovery of Ce and the nonfluoride bonded REE. These methods are not optimal because not all REEs present in the bastnaesite are being extracted, which leads to a less efficient process. However, considering the abundance of REEs in China, the Chinese REE industry can consider this loss in efficiency an acceptable tradeoff for reducing the environmental impact of the REE extraction processes.