Analyses of Pyrolysis Products of Phosphophylllte

Abstract

Phosphophyllite, Zn,Fe(P0t)4H20, was heat-treated in nitrogen gas and in air, and the chemical states of its pyrolysis products were studied by Mössbauer spectrometry, X-ray dif∗ fractometry, thermogravimetry, and differential thermal analysis. The formation of mono- and dihydrate of zinc-iron phosphate in the temperature range from 168°C to 277°C was proposed by thermogravimetric data and their Mössbauer parameters (LS.=1.13mm/s,Q. S.=2.04mm/s; I.S. = l. 18mm/s, Q. S. = 2.57 mm/s). In nitrogen gas, the dehydration process of phosphophyllite was concluded as follows; Ifigr 227T2 Zn,FeCP04),.4H,0. ZntFe(P0,),-2HA Zn^eCPO^-HìO r-(Zn, Fe)8(P04), In air, the phosphophyllite decomposed to the a-form of anhydrous zinc phosphate, the anhydrous iron(m) phosphate, and the other paramagnetic iron(Ql) compounds above 322°C, resulting in the oxidation of irom(ll) to iron(H) ion. The reduction of iron(M) to iron (II) ion proceeded by the pyrolysis above 695°C, favoring the formation of the T-form of anhydrous zinc-iron phosphate. The pyrolysis process of phosphophyllite was concluded as follows; 172T! ZntFeCPOOt^H'O ZnäFe(POJs-2HA Zn,Fe(P04)”∗H,0 32213 ‘’ -” -Znt(PO∗)i, FeP04) paramagnetic iron(m) compounds 69SC -∗ T-(Zn, Fe)j(P04)i> amorphous iron (E) compounds,