High temperature chlorination reaction of a pyrochlore mineral
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the minerals containing niobium, m a x i m u m concentrations of niobium are usually found in columbite and pyrochlore species. The u s u a l composition of pyrochlores belonging t o the cubic system s e r i e s and containing niobium is : (Na, Ca)~ (Nb, Ti, Ta)2 ((3, OH, F)7. Chemical breakdown of pyrochlore has been studied by a number of authors. Examples of such processes are given by HF dissolution of pyrochlore followed by liquid-liquid extraction. Also Stambaugh 1 has described a process in which high p u r i t y Nb20~ is obtained by chemical breakdown of pyrochlore using concentrated H2SO4. Recently, I. G. Worsley and J. B. Jaillet 2 have obtained NbzO5 by reaction of pyrochlore with concentrated hydrochloric acid, with an appreciable yield at about 150°C. The present paper is concerned with the investigation of the reaction of gaseous chlorine with a pyrochlore m i n e r a l at high temperature. The pyrochlore investigated here originates from the St-Honor6 (PQ) deposit. Chemical analysis of this pyrochlore suggests the approximate formula: (Nao.73, Cao.~5, Ao.32) (Nbl.a2, Ti~l~, Bo.o3) (O6.25, Fo.75), after water elimination. Significant minor constituents here defined as A are e s s e n tially rare e a r t h metals and Sr, while B is essentially F e and Zr. As a result, this m i n e r a l can be considered as having the approximate composition of a niobotitanate of calcium and sodium w i t h fluorine and other elements in substitution. The p u r p o s e of the present study is to investigate the oxides, oxyfluorides, oxychlorides, chlorides and other compounds resulting from the reaction of chlorine with pyrochlore at the temperatures in the r a n g e 1000°C to 1800°C.
r e a c t o r is connected to an erlenmeyer f l a s k whose temperature is cold enough so as t o allow condensation of most of the vapor products issuing from the reaction zone in the s i l i c a tube. The sample temperature was measured by m e a n s of a Leeds and Northrup optical pyrometer, having art effective wavelength of 650 nm while the temperature was adjusted at the required value by m e a n s of the rheostat controlling the electrical current through the c h r o m e l resistance surrounding the s i l i c a tube. P r i o r t o an experiment, the pyrochlore sample was heated at about 700°C under a helium s t r e a m for 15 min, for the p u r p o s e of water elimination. Then, the temperature was r a i s e d t o the required value and.dry chlorine was introduced at a rate of 20 10-6 m3/min while the helium flow was stopped. In this way, the chlorination reaction could be c a r r i e d out under chlorine atmospheric pressure for various reaction t i m e s (respectively 5, 10, 15 and 20 min). After each run, the reaction residue was weighed while residue and vapor condensates, found in the g l a s s f l a s k and on the cooler parts of the s i l i c a tube walls, were analyzed by m e a n s of X - r a y powder diffraction.
B) Pyrochlore Chlorination at 1400 t o 1800°C Chlorine reaction with pyrochlore at 1400 and 1800°C was c a r
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