Polymetallic Sea Nodules Research Articles

Pathway of Sucrose Oxidation in Manganese (Pyrolusite) Nodule

Polymetallic sea nodules are the potential resources of copper, cobalt, manganese, and nickel. The exploration and exploitation of manganese nodules are necessary to meet the future demands of Mn in the world. This work describes the valuable extraction of Mn through an innovative approach of using sucrose as a reductant. The metal extraction from the nodule leaching was studied in ambient temperature (27 °C) and at an elevated temperature 90 °C with and without agitation. In both cases, 99.9% of Mn was extracted while the extraction time appears to be significantly low (2 h) at 90 °C but it requires a longer time of 24 h at 27 °C. The optimum sucrose concentration selected was 7% (w/w) of nodule for maximum metal extraction. With use of 10% (v/v) H2SO4, 7% (w/w) sucrose at 90 °C, and solid to liquid (S/L) ratio of 1:10 the achieved metal recovery figures were the following: Mn >99%, Ni 98%, Cu 87%, Co 83% in 2 h. The oxidation pathway of sucrose is outlined in this study with the aid of mass spectrometry...

Efficacy of phytoremediation technology in decontaminating the toxic effluent released during recovery of metals from polymetallic sea nodules

Efficacy of phytoremediation using two macrophytes Azolla pinnata and Lemna minor in decontaminating the toxic effluent released during recovery of metals from polymetallic sea nodules was analysed by applying fish bioassay. The economically important fish, L. rohita, was exposed to both, the Azolla-phytoremediated effluent (APE) and Lemna-phytoremediated effluent (LPE) for assessment of metal bioaccumulation (Fe, Mn, Zn, Cu, Pb, Cr and Cd) and alterations in biochemical (proteins, lipids, glycogen, cholesterol, AST (aspartate amino transferase), ALT (alanine amino transferase) and ALP (alkaline phosphatase) composition of various tissues. Accumulation of metals (e.g. Mn, Zn, Cu and Fe) decreased in most of the tissues exposed to both the phytoremediated effluents perhaps due to decontamination of metals by the two macrophytes. The significantly recovered concentrations of different biomolecules included glycogen, lipids, cholesterol and proteins. The activities of three marker enzymes (AST, ALT and ALP) in phytoremediated effluent-exposed fish also decreased due to lowering of the toxicity of the decontaminated effluents achieved by phytoremediation. The improvement in different biomolecules and reduction in metal concentration in the fish tissues were better in APE exposed fish. However, their concentrations in both the phytoremediated effluent-exposed fish failed to reach the levels of control fish. This study points towards the efficacy of phytoremediation in detoxification of metal-contaminated effluents often released following industrial activities.

Biochemical Alteration in the Labeo rohita Tissues Following Exposure to the Effluent Generated during Extraction of Metals from Polymetallic Sea Nodules

Effect of the effluent generated during extraction of precious metals from polymetallic sea nodules have been illustrated by analyzing the biochemical alterations in freshwater fish Labeo rohita. Increase or decrease in the different biomolecules in various tissues (skin, muscles, gills, liver, kidney, and brain) observed was discussed in the light of stress caused by exposures of this effluent. Decrease in concentration of glycogen, total lipids, cholesterol, and total protein in most of the tissues indicate their role in providing the continuous energy requirement under toxic stress in the exposed fish. Reduced DNA and RNA concentration in exposed fish showed effluent toxic effect on DNA synthesis and transcriptional level. With the prolongation of exposure, reduction in activities of aspartate amino transferase, alanine amino transferase, and alkaline phosphatase were observed in all the exposed tissues indicating their cellular degeneration. In conclusion, the sea nodule effluent was found to be very toxic and have negative health impact on the fish.

Metal bioaccumulation in fish Labeo rohita exposed to effluent generated during metals extraction from polymetallic sea nodules

The aim of this study was to investigate the potential impact of effluent released during metals extraction from polymetallic sea nodules at the Pilot Plant at National Metallurgical Laboratory, India, by analysing different metal (Mn, Cu, Zn, Fe, Pb and Cr) concentrations in six tissues (skin, muscles, gills, liver, kidney and brain) of the fish Labeo rohita. Of the six analysed tissues of sea-nodule-effluent-exposed fish, liver accumulated highest concentration of most of the metals (2.91–287.36 mg kg−1) while muscles (2.1–81.14 mg kg−1) lowest. While the concentration of Fe was maximum (60.41–218.7 mg kg−1) in all the tissue systems (except muscles and liver), Pb was minimum (0.8–2.91 mg kg−1). Accumulation of most of the metals in all the tissues was above the safe limits as recommended by Food and Agricultural Organisation that indicate metal’s potential hazardous impact on the fish. High bioaccumulation factors for these metals in the different tissues revealed that metals were extensively bio accumulated and bio concentrated. The time-dependent variation in metal pollution index illustrated increase in gross metal load (p < 0.05) in different tissue components with increase in exposure period. In conclusion, the sea nodule effluent was found to cause adverse health impact on the fish which in turn might also affect the human health when consumed.

Phytoremediation of the Toxic Effluent Generated During Recovery of Precious Metals from Polymetallic Sea Nodules

Recovery of metals from the polymetallic sea nodules at the pilot plant at National Metallurgical Laboratory, Jamshedpur, India has generated a highly toxic effluent. This effluent contains several metals like Mn, Cu, Zn, Fe, Pb, Cr, and Cd that pollute the neighboring water bodies when discharged. Hence detoxification of this effluent was practiced using two plants: Lemna minor and Azolla pinnata for 7 days. During investigation A. pinnata removed 96% of Mn, 97% of Cu, 98% of Zn, 70% of Fe, 96% of Pb, 93% of Cr, 78% of Cd, and was comparatively more effective than L. minor which removed 94% of Mn, 86% of Cu, 62% of Zn, 74% of Fe, 84% of Pb, 63% of Cr, 78% of Cd. During the 7 days of experiment chlorophyll content decreased by 51% and 59% in A. pinnata and L. minor respectively. Based on our findings we can suggest that these two plants have wide range of metal retention potentialities hence can be of routine use for purification of toxic effluents.

Extraction of copper, nickel and cobalt from the leach liquor of manganese-bearing sea nodules using LIX 984N and ACORGA M5640

This paper describes a method, using sulfuric acid and activated charcoal for leaching Polymetallic sea nodules. Resulting leach solutions were examined for the extraction of copper, nickel and cobalt using LIX 984N and ACORGA M5640 in kerosene. After the removal of manganese and iron impurities from the leach liquor, copper and nickel were co-extracted leaving cobalt in the raffinate. The selective stripping of nickel and copper produces solutions rich in these metals, while regenerating the solvent for reuse.

A GENETIC ALGORITHMS BASED MULTI-OBJECTIVE OPTIMIZATION APPROACH APPLIED TO A HYDROMETALLURGICAL CIRCUIT FOR OCEAN NODULES

Several hydrometallurgical processes have been studied for the extraction of metals from lean ores utilizing various flow sheet options. Of particular significance is the grade of the ore being treated, the energy consumed and associated costs, options for byproduct recovery, and the relative price of the products. A process scheme needs to be optimized for simultaneously maximizing metal throughput and minimizing the direct operating costs incurred within constraints set for the operating variables. This leads to a multi-objective optimization problem. The range of input grades for raw material, which a flowsheet can handle, needs to be worked out based on an optimization exercise. A lean manganese-bearing resource such as polymetallic sea nodules has been chosen in this article for the development of an optimization approach based on which the input raw nodules grades are to be treated by a particular flowsheet. Only the chemical consumption costs have been adopted in this article as a measure of direct operating costs. A linear simulation model for the flowsheet has been developed, keeping a set of design parameters constant. The solutions generated by using a sequential modular approach become inputs to an optimization procedure based on a multi-objective genetic algorithm belonging to the differential evolution family. The variables considered in the optimization task are the grade of nodules and reactivity of different species inside the reactor. A nickel equivalent (t/h function) has been suggested as a measure of productivity, as it indirectly enhances the input manganese ore grade through a price ratio effect. This productivity function was maximized with the simultaneous minimization of direct chemical costs. Pareto optimal solutions were generated with grades of nodules and reactivity in the leach reactor as decision variables. The effect of the price ratio on the Pareto optimal solutions was also investigated. The various cases investigated clarifies the methodology for choosing an appropriate ore grade range for a given process flowsheet. Appropriate decisions regarding the nature of raw material to be used for a given flowsheet are then found on the basis of the Pareto optimal solutions.

Multiobjective Optimization of Manganese Recovery from Sea Nodules Using Genetic Algorithms

Treatment of low grade manganese ores is receiving widespread attention due to major use of manganese (85–90%) as ferromanganese alloy in the rapidly growing iron and steel sector and also in other important industrial products like electrolytic manganese dioxide (EMD) used in the energy sector. Manganese bearing polymetallic sea nodules containing less than 40% Mn fall in the category of lean grade ores and besides manganese these nodules are the reserve for other metals like copper, nickel, and cobalt. In this present work, treatment of these polymetallic sea nodules in an acid-based hydrometallurgical route has been proposed using two different schemes, batch and parallel in nature. Both processes have been optimized using multiobjective genetic algorithms.

Studies on the Extraction of Manganese from Sea Nodule Residue as Ferrosilicomanganese

Most of the extraction processes developed for the polymetallic sea nodules concentrated mainly on the recovery of strategically important metals viz. Cu, Ni and Co. The residue generated in such processes is quite high enough to upset the environmental balance for industrial scale operation. The economics of the process too cannot be favourable if manganese in the residue is not recovered. In this study an attempt has been made to utilize this residue, containing appreciable amount of manganese (about 20%) for producing ferrosilicomanganese, an important ferroalloy primarily used for deoxidation in the steel industry, through smelting process. In order to have an alloy of standard grade, the residue is enriched in its manganese content, by blending it with ferromanganese slag. Bench scale studies indicate that it is possible to produce ferrosilicomanganese, of the grade required by the steel industry, by reduction smelting of the sea nodule residue with ferromanganese slag. Metal recovery, however, was less because of metal entrapment.

Removal of zinc from aqueous solutions using sea nodule residue

Sea nodule residue (SNR), a solid waste generated during the processing of polymetallic sea nodules for copper, nickel, and cobalt recovery, has been demonstrated to be an effective adsorbent for removing an inorganic pollutant such as zinc from wastewaters/industrial effluents by adsorption. The technology offers the potential for inexpensive recovery and reuse of a material normally discarded as a solid waste. Metal removal by this adsorbent was compared favorably with those achieved by commercial adsorbents. The adsorption experiments were performed, while varying adsorbent particle size (152–53 μm), adsorbent concentration (0.2–3% (w/v)), initial zinc concentration (75–500 mg l −1), shaking time (0.08–24 h), pH (1–6), and temperature (303–333 K). About 2.0 g of SNR was found to be sufficient to remove 99.8% of 200 mg l −1 zinc from 100 ml aqueous solution in 4 h, and the optimum pH value for maximum adsorption was found to be 5.5. The kinetic curves show very clearly the selectivity of SNR for zinc. The uptake obeys both the Freundlich and the Langmuir isotherms. The applicability of Lagergren kinetic model has also been investigated. Thermodynamic parameters were calculated to understand the nature of adsorption.

Recovery of cobalt, nickel, and copper from sea nodules by their extraction with alkylphosphines

The paper describes a process for the recovery of pure Co(II), Ni(II), and Cu(II) from a hydrochloric acid solution of polymetallic sea nodules. An overnight contact of the nodule powder with 4 M HCl almost quantitatively leaches these metal ions. From the leachate, Co(II) and Cu(II) were recovered by their extraction with Cyanex 923 and Ni(II) by extraction with Cyanex 301. Co(II) and Cu(II) are partitioned in the organic phase as H 2CoCl 4·2 Cyanex 923 and CuCl 2·2 Cyanex 923, whereas Ni(II) is extracted in the form of NiR 2 (HR=Cyanex 301). A solution of 0.001 M H 2SO 4 is used for the stripping of Co(II) and Cu(II) and 5% NH 4Cl in 75% NH 3 for Ni(II). Both extractants are found to be stable toward prolonged contact with HCl and show negligible loss in their extraction capacity even after recycling them for 20 cycles. The partition data have been utilized in developing conditions for the separation of Co(II), Ni(II), and Cu(II) mutually and from other metal ions, namely Ti(IV), Al(III), Fe(III), Mn(II), and Zn(II). The procedure of separation thus developed has been extended for the recovery of around 90% Co(II), Ni(II), and Cu(II) from sea nodules. The purity of the metal ions thus obtained is around 99%.

Ammoniacal leaching of roast reduced deep-sea manganese nodules

The paper describes the reduction-roast ammonia leach process developed at NML for recovery of copper, nickel and cobalt from polymetallic sea nodules. A brief account of the development of a two stage ammoniacal leaching scheme with a prior pre-conditioning step is given. The necessity of monitoring redox potential in the first stage leaching to control cobalt recovery has been emphasized. Based on the two stage leaching scheme, recycle leaching has been carried out to generate leach liquor having suitable composition for the subsequent solvent extraction–electrowinning operation. The average recovery of metals in 16 cycles of leaching has been found to be 92% Cu, 90% Ni and 56% Co.

Hydrochloric Acid Leaching of Sea Nodules with Methanol and Ethanol Addition

A study has been made to investigate the effects of methanol and ethanol additions in dilute hydrochloric acid leaching of polymetallic sea nodules. In the absence of additives, the hydrochloric acid solution in an aqueous medium (2.75 kmol/m3) leaches out only copper and iron in considerable amounts and more than 90% recovery of all the metals are achieved only when a very strong concentration of acid (11 kmol/m3) is used. It has been found that metal recoveries can be considerably improved even in 2.75 kmol/m3 hydrochloric acid solution if an appropriate amount of methanol or ethanol is incorporated with it. The addition of 75 vol% of methanol in the 2.75 kmol/m3 hydrochloric acid system has been found to recover more than 90% of each metal. The requirement of ethanol has been found to be 18.5 vol% to achieve the same degree of recovery of metals in dilute hydrochloric acid solution. The effects of other parameters such as period of leaching and acid concentration on the recovery of metals in the alcoholic hydrochloric acid leaching system have also been studied.

Leaching of roast-reduced polymetallic sea nodules to optimise the recoveries of copper, nickel and cobalt

The reduction-roasting ammoniacal-leaching technology, widely used for the processing of nickel laterites, has been applied for the extraction of copper, nickel and cobalt from polymetallic sea nodules of the Indian Ocean. Results are presented of the various leaching experiments conducted under different conditions to optimise the recoveries of copper, nickel and cobalt. Leaching of the ground roasted product was carried out in ammoniacal ammonium carbonate solution. The effect of preconditioning of the reduced nodules in strong ammoniacal solution prior to leaching was studied. The leaching behaviour of the metals after grinding the roasted product in air, water, leachant and preconditioning solution was carefully examined. Air grinding of the roasted product, preconditioning and leaching was found to give the best recoveries of copper, nickel and cobalt. Cobalt was recovered to a maximum of about 60% in 2 h, but dropped to 40% at the end of 4 h of leaching. Based on these observations, a two-stage leaching scheme (each stage of 2 h duration) was devised to optimise the recoveries of all the three metals, which has yielded copper, nickel and cobalt recoveries of 91%, 94% and 62%, respectively.

Electrowinning of nickel in the processing of polymetallic sea nodules

As the land based reserves for nickel in India are meagre its extraction from sea nodules will assume increasing importance in the coming years. In the processing of polymetallic sea nodules by the reduction roast/ammonia leach/solvent extraction route, the recovery of nickel by electrolysis was considered. This led to the optimization of the parameters for electrowinning of the metal from synthetic solutions. The simulated condition was subsequently applied to win the metal from actual nickel pregnant electrolyte obtained during the treatment of ammoniacal liquor of polymetallic sea nodules using LIX 64N as an extractant. Energy consumption and current efficiency were worked out at current density in the range of 200–300 A/m 2 in these experiments and deposit character of the electrocrystallised nickel was closely observed with the objective of producing metal of acceptable quality.