含ヒ素殿物の焼成と溶出試験
1980 年 96 巻 1111 号 p. 629-635
詳細
1980 年 96 巻 1111 号 p. 629-635
The fundamental study was carried out in order to clarify the behavior of arsenic on the calcination of precipitate produced by the removal of arsenic as ferric or calcium arsenate from aqueous solution, and the relationship between the condition of calcination and the redissolution of arsenic was discussed. The results obtained are as follows.
(1) Ferric arsenate precipitate from aqueous solution contained As (III) was amorphous state, but the X-ray diffraction patterns of the calcined precipitates showed the formation of α-Fe2O3 at 600°C and FeAsO4 and Fe4As2O11 at 800°C in air. 90% of arsenic in the precipitate vaporized above 600°C in Ar gas stream.
(2) The calcined As (V)-bearing precipitate indicated amorphous state up to 600°C and ferric arsenates at 800°C in air and Ar gas stream, but these compounds decomposed at 1000°C.
(3) The precipitate obtained as calcium arsenate from aqueous solution contained As (III) was Ca3 (AsO3) 2 and that from As (V) solution was Ca3 (AsO4) 2.
(4) When the precipitate of As (III)/Ca molar ratio=1/1 was calcined above 700°C in air, Ca3 (As04) 2, Ca5As4O15 and Ca2As2O7 were formed, and that of As (III)/Ca molar ratios=1/5, 1/10 showed the compounds of Ca3 (AsO4) 2 and Ca5As4O15 above 500°C in air.
(5) The calcined precipitate of As (V)/Ca molar ratio=1/1 formed the compounds of Ca3 (AsO4) 2 and Ca5As4O15 and that of As (V)/Ca molar ratios=1/5, 1/10 formed Ca3 (AsO4) 2 independent of atmosphere and calcination temperature.
(6) In the redissolution tests of arsenic from the calcined precipitate of ferric arsenate, it was indicated that the arsenic redissolution was suppressed by the crystallization of the precipitate caused by the calcination from 700 to 800°C. However the calcined precipitate of calcium arsenate dissolved the larger amount of arsenic than that of the ferric arsenate.
