Solubilization of cobalt from ocean nodules at neutral pH?a novel bioprocess

Abstract

A marine organism ( Bacillus M1) isolated from Indian Ocean manganese nodules was characterized. The organism grew well in artificial seawater medium, at near neutral pH, 30 degrees C and 0.25 M NaCl, and showed MnO(2)-reducing activity. Growing cultures of Bacillus M1 as well as cell-free spent liquor from fully-grown cultures were employed to extract metals from the nodules. The spent liquor of cultures of the organism could dissolve around 45% cobalt (Co) at a pH of 8.2 in 2 h. Co recovery by this treatment was comparable to that in acidic leaching with 2.5 M hydrochloric acid solutions, and was independent of pulp density (w/v ratio). The amount of Co dissolved was beyond the thermodynamic solubility limit in aqueous solution at a pH of 8.2. It is inferred that the metabolites present in the spent liquor played a pivotal role in complexing the Fe (III) phase, solubilizing Co in the process. Partial characterization of spent liquor by spot tests, UV visible spectroscopy and FTIR spectroscopy, showed the presence of siderophore-like phenolic compound(s) with an attached carboxyl group that might form soluble organic complexes with Fe (III).

Mechanisms for solubilization of cobalt, copper and nickel from Indian Ocean nodules at near neutral pH by a marine isolate

“…Spectral study of the spent growth medium A kinetic study with the spent liquor to observe changes in the UV spectra during the growth of the marine isolate was reported [9]. The spent growth medium of cultures of the isolate had a p K a value in the range 11.5-12.5, suggesting a change in the structure of metabolite(s) present therein.…”

“…Bacillus M1, isolated from Indian Ocean nodules [9] was grown in 250-ml baffled Erlenmeyer flasks at 30°C on a rotary shaker (200 rpm), using sterilized artificial seawater nutrient broth (ASWNB) which had the following components (per liter of distilled water): 28.13 g NaCl, 0.77 g KCl, 1.60 g CaCl 2 AE6H 2 O, 4.8 g MgCl 2 AE6H 2 O, 0.11 g NaHCO 3 , 3.5 g MgCl 2 AE7H 2 O, 5 g peptone and 3 g beef extract.…”

“…Recently, Mukherjee et al [9,10] studied biologically mediated metal extraction from Indian Ocean nodules using a marine isolate, Bacillus M1. The spent growth medium from the cultures of the organism solubilized metals from the nodules at near neutral pH and room temperature.…”

“…The spent growth medium from the cultures of the organism solubilized metals from the nodules at near neutral pH and room temperature. Almost 45% Co and 25% Cu and Ni were obtained in about 4 h at an operating pulp density of 10 g/l [9]. The major objective of our present work was to study the mechanism of Cu, Co and Ni solubilization from the nodules by spent growth medium of cultures of the marine isolate.…”

Exploring process options to enhance metal dissolution in bioleaching of Indian Ocean nodules

“…8 The probable mechanism of metal dissolution by the spent growth medium at near neutral pH has been discussed elsewhere (Mukherjee A, unpublished).…”