Degradation of polychlorinated naphthalene by mechanochemical treatment

•We investigate the feasibility of degradation of polychlorinated naphthalene (PCN) by mechanochemical (MC) treatment with CaO.•We confirm the yield of chloride ions and the degradation products after the MC treatment.•100% PCN degradation is achieved after 1 h milling while chloride ions are recovered completely after 3 h milling.•PCN degradation progresses via dechlorination, resulting in the transformation of PCNs into low-molecular substances. Polychlorinated naphthalene (PCN) is a hazardous compound that is listed as a new persistent organic pollutants candidate by the United Nations Environment Program. The production, import and use of PCNs are prohibited by the Chemical Substances Control Law in Japan. PCN was milled with calcium oxide as an additive to investigate the feasibility of its degradation by mechanochemical treatment. The milling process cleaved the C–C and C–Cl bonds by the mechanically induced solid-state reaction. Gas chromatography/mass spectrometry analysis confirmed that the PCN was decomposed after 1h milling. The yield of chloride ions reached 100% after 3h milling. This indicates that all PCN was broken down into inorganic compounds after milling, thereby maintaining the chlorine mass balance through the reaction. This experiment, for the first time, exhibited the effectiveness of mechanochemical treatment as a PCN degradation method.