Simultaneous leaching of a deep-sea manganese nodule and chalcopyrite in hydrochloric acid
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I. INTRODUCTION
POLYMETALLIC manganese nodules are found on or just beneath the sea floor in parts of all the deep oceans of the world except the Arctic. They contain mainly two intimately mixed metal oxides, namely, manganese dioxide and hydrated iron oxide. Besides, other valuable metals such as Cu, Ni, Co, Zn, Mo, etc., are also present in them in appreciable quantities. The presence of these metal values has prompted the researchers to project these nodules as a future resource of these metals and to concentrate on metallurgical extraction of the same.[1–9] Various processing options have been examined, out of which about six routes have been identified for future potential application. One of these routes is processing of the nodule in the presence of hydrochloric acid,[10,11,12] where the nodule is reduced at 500 ⬚C by HCl to form metal chlorides as per the following reactions: MeO ⫹ 2HCl ⫽ MeCl2 ⫹ H2O
[1]
(where Me stands for Ni and Cu)
II. EXPERIMENTAL
Fe2O3 ⫹ 6HCl ⫽ FeCl3 ⫹ 3H2O
[1a]
MnO2 ⫹ 4HCl ⫽ MnCl2 ⫹ 2H2O ⫹ Cl2
[2]
Co2O3 ⫹ 6HCl ⫽ 2CoCl2 ⫹ 3H2O ⫹ Cl2
[2a]
Most of the iron chloride in this condition (Reaction [1a]) is converted to oxide by pyrohydrolysis. A portion of HCl is also oxidized to produce a Cl2 gas (Eqs. [2] and [2a]), which is reused in the downstream process route. In another process developed by Metallurgie–Hoboken–Overpelt,[13] the nodule is leached in a 4M HCl solution to dissolve almost all the metal values as per the same reactions (Eqs. [1] through [2a]). Metal values are subsequently recovered from the solution following various hydrometallurgical techniques. Incidentally, sulfide minerals of Cu, Ni, and Zn (the metals
N.B. DEVI, Research Associate, M. MADHUCHHANDA, Senior Research Fellow, P.C. RATH, Scientist, K. SRINIVASA RAO, Scientist, and R.K. PARAMGURU, Scientist F and Head, Electrometallurgy Department, are with the Regional Research Laboratory (Council of Scientific & Industrial Research) Bhubaneswar - 751013, Orissa, India. Manuscript submitted November 14, 2000. METALLURGICAL AND MATERIALS TRANSACTIONS B
present in the nodule) are the main source of these metals. The conventional extraction processes for these metals consist of pyro- and/or hydrometallurgical techniques. Recently, some very interesting studies have been reported pertaining to leaching of MnO2-sulfide mineral couples in an acid medium, where (1) galvanic interaction between MnO2-FeS2,[14,15,16] MnO2-ZnS,[16,17,18] and MnO2-CuFeS2;[16,19] (2) the cyclic action of a redox couple between MnO2-FeS2[20,21,22] and MnO2-ZnS;[23,24] and (3) the action of Cl2 generated in the system for MnO2-CuFeS2[25] and MnO2-ZnS[26] couples have been envisaged. In all these cases, the extent of dissolution of MnO2 and sulfide minerals individually was small or negligible, whereas the same in combination was appreciable and also fast. Against this background, leaching of a manganese nodule in the presence of chalcopyrite provides interesting possibilities. This article presents the results of the leaching of a CuFeS2-n
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