The effect of NaOH for the recovery of elemental mercury from simulated mixture wastes and waste sludge from an industrial process using a thermal desorption process

•The target waste is contaminated by high content of mercury (Hg).•A thermal desorption and condensation process were applied to recover elemental Hg.•Hg was hard to be recovered due to the contents of S, Cl and As in the waste.•Recovery rate has increased by adding NaOH into waste sludge.•Moreover, elemental Hg was recovered by reactions of NaOH with interfering agents.