Contents lists available at ScienceDirect Hydrometallurgy journal homepage: www.elsevier.com/locate/hydromet Recovery of dimethylglyoxime (DMG) from Ni-DMG complexes Meenakshi Rath, Laxmi Priya Behera, Barsha Dash ⁎ , Abdul Rauf Sheik, Kali Sanjay CSIR-Institute of Minerals and Materials Technology, Bhubaneswar 751013, India ARTICLE INFO Keywords: Dimethylglyoxime (DMG) Nickel-DMG Recovery ABSTRACT Dimethylglyoxime (DMG) is an analytical reagent used to precipitate Ni from its aqueous solution. The process is very efficient for Ni recovery in terms of selectivity and completeness but hardly adopted industrially. The reason is attributed to the loss of the reagent when calcined. The paper outlines extraction of DMG from Ni-DMG complex by sulphuric acid treatment in two methods i.e. leaching and dissolution-recrystallization. In leaching the Ni-DMG is just treated with sulphuric acid and DMG is recovered. In the second case the Ni-DMG complex is completely dissolved in sulphuric acid and recrystallized through refrigeration. 1. Introduction Selective extraction of metal of interest is no doubt an area of common interest. There are some methods for high selectivity of metals like Ni, Co etc. Precipitation of dimethyl glyoxime complex of nickel is one such example. This method is implied for separation of cobalt and nickel (Schuster, 1930). Nickel was separated from iron and steel containing cobalt and copper (Claassen, 1966; Nechamkin, 1981), high pure thorium compound (Chan and Tam, 1969), cadmium containing electrolyte (Ya Ben'yash et al., 1974), through Ni-dimethylglyoxime complex formation. Even if Ni is present in trace is also removed by this complexation process such as Ni removal from alkali halide (Blank et al., 1961), waste sludge (Brooks, 1985) or in micro amount (Masatada, 1979). But this type of process is never adopted industrially irrespective of its high selectivity towards nickel. The reason is due to the zero recovery of DMG after calcination. This makes the process cost higher. Lots of trials are going on to recover nickel from Ni-DMG through wet chemical methods. The methods may include treatment of Ni-DMG with perfluorinated alcohol (Echtek, 1994), non-oxidising acids (Anon and Mond Nickel Co Ltd, 1953), hydrochloric acid, sul- phuric acid or nitric acid (Dzliev and Alkatsev, 1971; Zhong, 2011; John et al., 2011). Recently extraction of nickel from Ni-DMG has been studied by ionic liquid (Fitzpatrick and C-Tech Innovation Limited, 2013). Extraction of Ni has been given emphasis on all the paper dealing with dissociation of Ni-DMG. But in this paper the recovery of DMG is studied through acid treatment of Ni-DMG. 2. Experimental 2.1. Materials Dimethyl glyoxime (Spectrochem), Ni(NO 3 ) 2 (Rankem), Ammonia (Fischer Scientific), Ethyl alcohol (Spectrochem-Spectrosol), H 2 SO 4 (Fischer Scientific). 2.2. Method Nickel-DMG complex was prepared by using the standard analytical method (Vogel). The acid treatment is of two types. 1. Leaching, 2. Dissolution-recrystallization. 2.2.1. Leaching To a 100 mL solution of sulphuric acid Ni-DMG was added. It was shaked with hand in a closed bottle at ambient temperature to ensure proper mixing (Otherwise Ni-DMG floats on solution with improper contact with acid). Then it was filtered. The residue was washed and dried. The amount of acid, pulp density, temperature and time were varied so as to fix an optimum condition. 2.2.2. Dissolution-recrystallization To 100 mL of sulphuric acid solution Ni-DMG was added at 80 °C and stirred for 1 h where all the material should be dissolved. After dissolution the liquor is kept in refrigeration unit to maintain 5 °C for 24 h where a white precipitate was obtained. 2.2.3. Characterization Nickel present in the liquor was analyzed by Atomic Absorption https://doi.org/10.1016/j.hydromet.2018.01.014 Received 23 October 2017; Received in revised form 16 January 2018; Accepted 20 January 2018 ⁎ Corresponding author. E-mail address: barshadash@immt.res.in (B. Dash). Hydrometallurgy 176 (2018) 229–234 Available online 31 January 2018 0304-386X/ © 2018 Elsevier B.V. All rights reserved. T