Kinetics of chlorination and microstructural changes of xenotime by carbon tetrachloride

Abstract

Among the rare earth minerals, fluorides, phosphates, and oxides have received attention from the rare earth industry. Traditional methods of decomposition of these minerals, usually alkaline or acid processes, involve several operations. Another possibility to obtain lanthanide chlorides or oxychlorides is reacting the mineral with chlorinating agents, such as gaseous chlorine, hydrogen chloride, thionyl chloride, and carbon tetrachloride, reducing the operation costs and making the process less complicated. In this context, we investigated the decomposition of xenotime using carbon tetrachloride at temperatures from 873 to 1173 K and kinetic and mechanistic studies have been performed. Powder X-ray diffraction, scanning electronic microscopy, energy dispersive X-ray spectrometry, ultra-violet/ visible spectroscopy, and thermal analysis techniques were used in this study. The results showed that the reaction follows the shrinking-unreacted-core model with formation of a product layer (lanthanide oxychloride), confirmed by powder X-ray diffraction. Moreover, microstructural changes of xenotime grains during the chlorination reaction were verified.

Chlorination kinetics of ZnO with Ar-Cl2-O2 gas and the effect of oxychloride formation

“…[1], [11], and [12] and mass balance in the reaction system. Estimated values at each experimental condition are also shown in Table VII.…”

“…On the other hand, partial pressure of ZnOCl could be calculated from the present experimental results by using Gibbs energies of Eqs. [1] and [11]. [8] Calculated partial pressure of ZnOCl is also shown in Table VII at each experimental condition.…”

“…Recovered heavy metal chlorides could be used as raw materials and the chlorinated residue, mainly iron oxide, also could be used as an ironmaking resource. The efficiency of selective chlorination has been investigated for extraction of metals, [9][10][11][12] mutual separation of rare earth elements, [13][14][15][16][17][18] and recovery of metals from spent catalysis, [19,20] polishes, [21] or bottom ash of incinerated municipal waste. [22] Son and Tsukihashi measured vapor pressures of ZnCl 2 between 823 K and 873 K [23,24] and of PbCl 2 between 923 K and 1023 K [25] by the transpiration method in Ar-O 2 stream and reported that vapor pressures decreased with the increase of partial pressure of oxygen.…”

Stability field diagrams for Ln–O–Cl systems

“…Hence, there is general interest in recycling used products containing lanthanide metals and compounds. The conventional process for the extraction of lanthanide elements from oxide ores involves carbochlorination [4], although other chlorinating agents such as HCl and CCl 4 are also being tried [5]. In the conversion of most lanthanide oxides to chlorides, oxychloride phase forms as an intermediate product and controls the kinetics of the reaction, a fact recognized only in the recent literature.…”

The Kinetics of the Chlorination of Yttrium Oxide

“…They found that yttrium oxychloride (YOCl) was produced in an intermediary step during the carbochlorination of the xenotime ore, and then the reaction could be followed by a fast step related to the generation of the yttrium trichloride (YCl 3 ). Augusto et al [5] investigated the kinetics of chlorination and microstructural changes of xenotime by carbon tetrachloride at temperatures from 600°C to 900°C. Their results showed that the reaction follows the shrinkingunreacted-core model with formation of a product layer (YOCl), which is chlorinated to give YCl 3 .…”