Recovering of Disposed Nickel–Titanium Rotary Endodontic Files via Sulphuric Acid Leaching Treatments

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Nickel - titanium based alloys are widely used as a root canal files in dental canal treatment in endodontics. According to the Turkish Ministry of Health, approximately, two million root canal treatments were applied yearly in Turkey. Ni-Ti rotary files have been used for 80 % of these endodontic root canal treatments. Rotary files contain 55-60 wt.% nickel and 40-45 wt.% titanium. Ni-Ti endodontic files can be recovered by hydrometallurgy, which is an economical way, instead of treating them as medical waste. The aim of this study is to provide economical hydrometallurgical recycling of metallic wastes that cannot be recovered by direct melting. Nickel and titanium based endodontic rotary files were recovered via using different leaching techniques in high corrosive environments such as dissolution in concentrated acid, baking in sulfuric acid and hydrothermal treatment in concentrated sulfuric acid. The acid concentration, temperature and time parameters were optimized for concentrated sulfuric acid leaching in autoclave. The acid baking method is a simple system more efficient than the pure dissolution in acid. At the end of the hydroxide structures dehydration, TiO2 (anatase) and NiO powders were obtained. Moreover, under pressure within non-stirring autoclave the rotary file is completely dissolved with a cost-effective two-step process. Thus, an efficient recycling process has been created for waste Ni-Ti alloy tooth files.