Abstract
The influence of ultrasound and microwaves on extraction of copper, nickel, and cobalt from manganese deep-sea nodules by reductive ammoniacal leaching in the presence of ammonium thiosulfate as a reducing agent was studied. The ultrasonic ammoniacal leaching provides higher metals extraction, while the effect of microwaves on the metals extraction under the studied leaching conditions is insignificant. In general, increasing leaching temperature increases significantly extraction of the metals of interest. At high temperatures, extraction efficiencies of copper, nickel, and cobalt decrease over longer leaching duration as a result of decomposition of the metals amino-complexes and reverse precipitation of metals. However, during the ultrasonic leaching at a temperature of 85 °C, the extraction of nickel remains almost unchanged over longer leaching durations and does not follow the decreasing course, observed in the extraction of copper and cobalt. The finding suggests that nickel can be selectively extracted from the nodules by the ultrasonic leaching. The maximal extraction efficiency of copper, nickel, and cobalt was 83%, 71%, and 32%, respectively, when the reductive ultrasonic ammoniacal leaching was carried out at 85 °C for 90 min. In the presence of microwaves, the maximal extraction efficiency of copper, nickel, and cobalt was 67%, 48%, and 8%, respectively, when the reductive ultrasonic ammoniacal leaching was carried out at the output power of 60 W for 210 min.
Highlights
Polymetallic deep-sea nodules are a promising raw material for recovering non-ferrous metals, especially copper, nickel, cobalt, and manganese
The results show that ultrasound can be a vital method for metal extraction in the future, to minimize energy consumption and optimize control over chemical reactions [24]
During ammoniacal leaching at 85 ◦ C, the leaching process was faster (Table 4, Figure 3)
Summary
Polymetallic deep-sea nodules are a promising raw material for recovering non-ferrous metals, especially copper, nickel, cobalt, and manganese. The metal coatings around the nodule core have a concentrically layered, radially dendritic, massive, or combined macrostructure. Two different zones are inside the casing, the dendritic zone is a result of the diagenetic mobilization of the metals from the sediment, and the concentric zone is formed by the precipitation of hydroxides from the seawater [3]. Nodules are made of a mixture of oxides (manganese oxides, goethite, and opal), clay minerals, and a small number of other minerals—apatite, barite, celestite, and so on. The composition of manganese minerals varies according to the depth of occurrence; birnessite occurred until the depth of 3000 m, with todorokite and vernadite occurring deeper. Manganese nodules contain 12.29–33.98% of manganese, 1.62–15.75% of iron, 0.097–1.080%
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