ABSTRACT:

The ammonia-ammonium carbonate leaching of roast-reduced polymetallic nodules analysing 1.175% copper, 1.625% nickel and 0.116% cobalt was carried out in lock cycle mode. The steady state composition was analysing 2.40 g/L copper, 3.41 g/L nickel and 0.163 g/L cobalt with leach recoveries of 93.95%, 96.53% and 64.65%, respectively. The iron and manganese contents of the steady state leach liquor were found to be 0.002 g/L and 0.008 g/L, respectively. The leach liquor was subjected to solvent extraction for the separation of copper, nickel and cobalt using LIX 84 in kerosene. It was observed that three stages were sufficient for co-extraction of copper and nickel leaving cobalt in the raffinate. The loaded organic phase after ammonia scrubbing was selectively stripped with spent electrolytes of nickel and copper and subsequently electrowon to produce copper and nickel of 99.94% and 99.8% purity, respectively. Cobalt was recovered as cobalt cake from the raffinate by ammonia stripping. The overall leach-solvent extraction recoveries obtained for copper, nickel and cobalt are found to be 93.9%, 94.23% and 62.50%, respectively.

INTRODUCTION

As the kinetics of direct leaching of valuable metal oxides present in the Ocean nodules are generally slow, reducing the metal oxides either to metallic or to their lower oxide states is a common practice before leaching. During reduction roasting the valuable metals get released from the crystal lattices of manganese and iron oxides and get reduced either to their metallic states or to their lower oxide forms. Though, LIX 64N has been reported to be an excellent solvent for the separation of these metals, in this study LIX 84, a 5-nonyl 2-hydroxy acetophenoneoxime, was used to treat the ammoniacal solution of roasted nodule obtained from the leaching circuit. The results of ammonia leaching, metal separation and recovery (SX-EW) are described in this communication.

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