Ultrasound-assisted extraction of rare-earth elements from carbonatite rocks

In view of the increasing demand for rare-earth elements (REE) in many areas of high technology, alternative methods for the extraction of these elements have been developed. In this work, a process based on the use of ultrasound for the extraction of REE from carbonatite (an igneous rock) is proposed to avoid the use of concentrated reagents, high temperature and excessive extraction time. In this pioneer work for REE extraction from carbonatite rocks in a preliminary investigation, ultrasonic baths, cup horn systems or ultrasound probes operating at different frequencies and power were evaluated. In addition, the power released to the extraction medium and the ultrasound amplitude were also investigated and the temperature and carbonatite mass/volume of extraction solution ratio were optimized to 70 °C and 20 mg/mL, respectively. Better extraction efficiencies (82%) were obtained employing an ultrasound probe operating at 20 kHz for 15 min, ultrasound amplitude of 40% (692 W dm⁻³) and using a diluted extraction solution (3% v/v HNO₃ + 2% v/v HCl). It is important to mention that high extraction efficiency was obtained even using a diluted acid mixture and relatively low temperature in comparison to conventional extraction methods for REE. A comparison of results with those obtained by mechanical stirring (500 rpm) using the same conditions (time, temperature and extraction solution) was carried out, showing that the use of ultrasound increased the extraction efficiency up to 35%. Therefore, the proposed ultrasound-assisted procedure can be considered as a suitable alternative for high efficiency extraction of REE from carbonatite rocks.     

白云鄂博富稀土碳酸岩的地球化学特征

重点解剖了一条距白云鄂博ＲＥＥ－Ｎｂ－Ｆｅ矿床东矿,ＮＥ方向３ｋｍ并切割白云鄂博群Ｈ１及Ｈ２岩性段的细料方解石碳解岩岩墙的岩石地球化学特征。结果表明：碳酸岩的稀土元素含量变化大,最高可达２０％（质量分数）、已构成稀土富矿石、碳酸岩的轻稀土元素高度富集,轻、重稀土元素之间发生地极度分馏,但无铕异常显示。形成这种岩石地球化学特征的可能机制为．：碳酸岩浆直接来源于岩石圈富集地幔的代程度部分熔融作用,残留