Additionally, there was one well resolved band, peaked at 825-829 [cm.sup.-1], owing to the As-O stretching vibration of the As-O-Fe coordination of the ferric arsenate
(i.e., scorodite) and the surface complex (i.e., protonated Fe[O.sub.2]As(O)(OH) and unprotonated Fe[O.sub.2]As[(O).sup.2.sup.2-] forms) on the precipitates .
The process also frees up both the iron and the arsenic, which then combine to form a compound known as ferric arsenate
. This compound, which has been found by the Environmental Protection Agency to be a benign substance, sinks to the bottom of the vat and can then be safely disposed of.