solving the problem of pollution is an effective way of environment management
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Leaching of Rare Earth Elements
Sebastiaan Peelman, ... Yongxiang Yang, in Rare Earths Industry, 2016
4.1 Progress in Bastnaesite Leaching
Environmental pollution caused by fluorine emissions during H2SO4 roasting of bastnaesite processing in China is becoming of increasing concern (Bian et al., 2011). 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 (Bian et al., 2011).
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 (Yörükoğlu et al., 2003) 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.
Another, more efficient process involves the mechanochemical activation of bastnaesite by milling it with NaOH powder (Zhang and Saito, 1998). In this process, the bastnaesite concentrate is milled together with NaOH powder, followed by washing with water to remove the Na compounds and then leaching with HCl. These steps are performed at room temperature and can lead to a leaching efficiency of around 90%. This process generates no emissions, and the F is bonded with Na as NaF. Ball milling is energy intensive, however, and the process takes several hours.
Sebastiaan Peelman, ... Yongxiang Yang, in Rare Earths Industry, 2016
4.1 Progress in Bastnaesite Leaching
Environmental pollution caused by fluorine emissions during H2SO4 roasting of bastnaesite processing in China is becoming of increasing concern (Bian et al., 2011). 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 (Bian et al., 2011).
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 (Yörükoğlu et al., 2003) 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.
Another, more efficient process involves the mechanochemical activation of bastnaesite by milling it with NaOH powder (Zhang and Saito, 1998). In this process, the bastnaesite concentrate is milled together with NaOH powder, followed by washing with water to remove the Na compounds and then leaching with HCl. These steps are performed at room temperature and can lead to a leaching efficiency of around 90%. This process generates no emissions, and the F is bonded with Na as NaF. Ball milling is energy intensive, however, and the process takes several hours.
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pawan please mark me as brainlist
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yes because when we solve the problem then it becomes a way of environment management
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