The Effect Of Calcination On The Stability Of FeAsO 4 And The Distribution Of Arsenic In The Distribution Of FeAsO 4

Ferric arsenate (FeAsO4) has a high content of arsenic, and its stability has a close relationship with the mobilization of As(V). However, less attention has been paid to its stability during the reductive dissolution. In this study, the stability of amorphous FeAsO4 and the calcinated FeAsO4 during the reductive dissolution by ascorbic acidunder acidic and pH neutral conditions was investigated. By means of TGA-DTA, XRD,FT-IR and TEM analyses, structural changes of FeAsO4 under different temperatures were compared. In addition, distribution mechanisms of As(V) between FeAsO4 and Fe oxides was investigated, and the effects of pH and speciation of Fe oxides on distribution behaviors of As(V) on FeOx were discussed.During the reductive dissolution, releasing kinetics of As(V) from FeAsO4 and the calcinated FeAsO4 were carried out. Our results suggested that the released As(V) and its releasing rate were still high when the calcination temperature was lower than 500℃, whereas the mobilization of As(V) was significantly prevented when the calcination temperature was above 550℃. The TGA-DTA, XRD and FT-IR analyses further suggested that recrystallization of FeAsO4 to a new crystalline FeAsO4(I) above 550℃ improved the stability of FeAsO4, whereas only dehydration/dehydroxylation of FeAsO4 occurred when the calcination temperature was below 500℃.In addition, distribution of As(V) between FeAsO4 and Ferrihydrite/Goethite/Hematite under different pHs was also investigated in a Donnan reactor. Our results suggested that Ferrihydrite showed a high affinity to As(V), and the removal percentages of As(V) are 97.53%,95.48% and 66.24% at pH 4.5,7.0 and 9.0, respectively. Under similar experimental conditions, the respective removal percentages of As(V) were 73.91%,37.12% and 15.12% in Goethite system and were 39.45%,7.60% and 12.95% in Hematite system. Addition of Fe(Ⅱ) into the Hematite chamber improved the removal of As(V). When 700 mg L-1 Fe(Ⅱ) was added into the Hematite chamber,96.96% and 95.46% As(V) could be effectively removed at pH 4.5 and 7.0, respectively. However, at pH 9.0, As(V) removal was not affected by the addition of Fe(Ⅱ).The significance of this study is to reveal the calcination temperature on the stability of FeAsO4 during the reductive dissolution and elucidate distribution mechanisms of As(V) between FeAsO4 and Fe oxides for better understanding arsenic mobilization among Fe solid samples. This study provides an efficient method to improve the stability of FeAsO4 and control the mobilization of arsenic in aqueous environments.