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

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/O2, a partial dearsenization of Ni11As8 occurs, giving Ni5As2, between 580 and 650 °C. Ni5As2 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.