Alumina-supported nickel catalyst is an important catalyst in
various petrochemical industrial processes [1]. After a certain period,
depending on the operating conditions, destructive effects
such as coking, poisoning, sintering and contamination would
decrease its catalytic activity [2]. Deactivated catalysts undergo
regeneration for several times; however, the number of regeneration
cycles is limited since the process effectively removes the coke
and not the deposited heavy metals. Therefore, after several regeneration
cycles, accumulation of heavy metals deactivate the catalyst
to a level that its regeneration is not financially favorable
and it should be discharged and replaced by fresh catalyst [3,4].
Release of hazardous heavy metal content of the spent catalysts
to the environment has raised serious concerns during the last decades
leading to strict legislations on handling and disposal of this
kind of wastes [5]. Recently, extensive studies have been conducted
to establish possible environmental friendly treatments
for recycling of the spent catalysts [6]