Dearsenization of nickel-based catalysts: Thermal behaviour of nickel arsenide in oxygen and in air

Abstract The arsenic present in the spent Ni-catalysts of petroleum industries is supposed to form arsenides. It must be removed for the catalysts regeneration or for recycling nickel. In air or Ar/O 2 , a partial dearsenization of Ni 11 As 8 occurs, giving Ni 5 As 2 , between 580 and 650 °C. Ni 5 As 2 forms AsO (g) and a NiO layer that blocks the arsenic elimination (passivation layer). The reaction mechanism is complex, dearsenization being governed by the surface oxidation of arsenic, and oxidation being rate-limited by the Ni outward diffusion. This work shows that the industrial process of regeneration does not eliminate arsenides, but only the physisorbed arsenic.