Pressure acid leaching of seabed polymetallic nodules — An update

Seabed polymetallic nodules, which contain significant quantities of metals key to electrification such as nickel (Ni), cobalt (Co), copper (Cu) and manganese (Mn) can be processed using several different metallurgical processing options, including direct smelting and subsequent hydrometallurgical refining of the copper/nickel matte; ammoniacal leaching (gas reduction or Cuprion); and acid leaching (often reductive). Many of these approaches suffer from reduced cobalt extraction, difficult physical performance, or overall circuit complexity in general, leading to increased risk to the overall project. SGS has considered the pressure acid leaching of nodules for further investigation, as publicly shared data on this processing route stem from the 1970s and 1980s, and are not always easily accessible. This article details the series of tests conducted and provides updated results obtained — high Ni/Co/Cu recovery with limited manganese/iron (Mn/Fe) — as well as comments on the potential treatment options on the product solution and residue. Background Polymetallic manganese nodules are a noteworthy potential feed source for cobalt, nickel, copper and manganese occurring in the deep ocean — for example, in the Pacific Ocean between Mexico and Hawaii. Other oceans contain nodules as well, though their metal contents differ according to their location. Table 1 shows the general composition of nodules from the Clarion Clipperton Zone (CCZ) in the Pacific Ocean, which contains significant quantities of nickel, cobalt, copper, manganese and various critical metals.An evaluation of the average nodule composition reveals that a significant percentage (66 percent) of the contained value is associated with nickel, cobalt and copper while 34 percent of the contained value is associated with manganese, if it is assumed to be recovered as high-purity manganese sulfate monohydrate (HPMSM), which contains 32 percent Mn and is worth about $2,000/t. However, it is not practical to assume that all manganese contained in a nodule processing operation will advance to HPMSM. According to AMC Consultants (2021), The Metals Co. proposes a nodule processing capacity of 6.4 Mt/a — if all contained manganese is processed into HPMSM, that would equate to 70 to 75 production trains at 65,000 t/a of HPMSM, which far outweighs the market demand for HPMSM. Based on its feasibility study, Element 25 Ltd. (2023) proposes to construct two such production trains each at 65,000 t/a of HPMSM for a total of 130,000 t/a. Therefore, it may be more realistic to use a manganese ore price (assumed at $130/t of ore at 32 percent Mn). Using this assumption, 97 percent of the potential revenue from nodules is associated with copper, nickel and cobalt, and only 3 percent with manganese (though hybrid approaches targeting multiple Mn products could also be considered). Should all four metals be dissolved in a simple sulfuric acid leach, it can also be calculated that manganese contributes to 92 percent of the sulfuric acid demand. Downstream treatment of the resulting leach liquors to separate manganese from copper/nickel/cobalt will further contribute to overall processing costs. Clearly, a key challenge in processing polymetallic nodules relates to the behavior of manganese, and that processes with an inherent selectivity of nickel/copper/cobalt against manganese are of economic interest. Onshore processing of polymetallic nodules Much attention has been paid to the mining aspects of the nodules and potential environmental impacts. However, little attention has been paid to the onshore processing of nodules. Similar questions exist as in traditional “terrestrial” mining projects, such as: (1) What is the capital expenditure (capex) and operating expenditure (opex) of the processing plant? (2) What is the metallurgical performance (recovery, product grade, and reagent consumption)? (3) What is the “operability” of the selected flowsheet, and how robust is the flowsheet for circuit upsets and changing feed compositions? (4) What are the environmental impacts of the processing plants and produced residues? An overview of various processing techniques had been previously detailed by Dames and Moore (1977), Dreisinger (2018) and Verbaan (2022) and can be briefly summarized as follows: Ammoniacal systems, such as: Cuprion process. Gas reduction and ammoniacal leaching. Sulfate systems, such as: Smelting and hydrometallurgical processing of matte. High-pressure acid leaching (HPAL). Reducing-acid (H2SO4/SO2) leaching. Other hydrometallurgical routes based on chloride and nitrate chemistries. The Cuprion process, as described by Agarwal et al. (1979), Szabo (1976) and Barner et al. (1979) and recently piloted at SGS Canada (Dreisinger et al., 2022), offers selectivity against manganese dissolution but suffers from depressed cobalt extraction at elevated leach liquor concentrations. In this flowsheet, manganese does not report to the primary leach solution and instead remains in the leach residue as MnCO3. Some, all or none of this residue may be further processed into EMM (electrolytic manganese metal) or HPMSM, which will obviously contribute to reagent requirements. Metal recoveries using the Cuprion process were measured during the operation of the SGS pilot plant at approximately 90 to 95 percent copper and 97 to 100 percent nickel, with decreasing cobalt recoveries with time. Cobalt extractions never stabilized, and continuously decreased from approximately 95 percent at the outset of the campaign –— when cobalt levels in the pregnant leach solution (PLS) were very low — to around 85 percent after five days as cobalt tenors in the PLS increased due to PLS recycling. Seaborn et al. (2020) reported cobalt extractions as low as 30 percent at 2 g/L Co in the PLS, and Haynes et al. (1985) reported Cuprion recoveries of 90 percent for copper and nickel and 50 percent for cobalt.According to AMC Consultants (2021), The Metals Co. intends to use a combined pyro/hydrometallurgical flowsheet. Nodules are mixed with reductant (coal), flux (silica) and residues from the hydrometallurgical refinery before feeding to a rotary kiln at about 900 °C. The calcine discharge is smelted at 1,450 °C in electric arc furnaces to produce a metal alloy and a Mn silicate stream (sold into the manganese industry, predominately the steelmaking industry). The molten alloy is further processed in Peirce-Smith convertors at 1,300 °C, where it is mixed with sulfur to produce a NiCuCo matte. Expected recoveries into the matte are 94.6 percent Ni, 86.5 percent Cu and 77.4 percent Co. The matte is further treated using a two-stage atmospheric/pressure oxidation leach process and sequential purification to ultimately produce copper cathode, cobalt sulfate and nickel sulfate. The overall process has been described by Von Schroeter et al. (2020), Boulby et al. (2022) and Verbaan (2022) and has been tested at SGS Canada. Global Sea Mineral Resources, a subsidiary of Belgian dredging company DEME, patented a reductive acid leach process (Daniels, 2021). It contracted SGS in 2021 to confirm and optimize that flowsheet. The process is described by Alvarenga et al. (2022), and a high-level overview was presented at the DeepSea Mining Summit in 2022 (Verbaan, 2022). The process is based on single-step reductive leaching using sulfuric acid (H2SO4) and sulfur dioxide (SO2), which effectively recovers all of the nickel, copper, cobalt and manganese into a leach solution. Copper is precipitated from the leach solution as copper sulfide, nickel and cobalt are recovered as a mixed sulfide precipitate (MSP), and crude manganese sulfate is crystallized at elevated temperatures and subsequently pyrolyzed to produce an iron-manganese oxide. SO2 contained in the offgas is recovered and processed into sulfuric acid for recycling. Reported leach extractions were high at 99 percent NiCoMn and 98 percent Cu. Metal precipitation efficiencies were also high at approximately greater than 99 percent Cu and greater than 99 percent NiCo into MSP. However, the novel manganese sulfate crystallization step (including the hot filtration step) and associated thermal decomposition was identified as a challenging unit operation requiring further development. High-pressure acid leaching HPAL is applied in the recovery of nickel and cobalt from high-iron lateritic ores (limonite), generally containing 1.0 to 1.2 percent nickel and 0.10 to 2 percent cobalt. Typical process conditions include operating temperatures of 240 to 260 °C, residence time of one hour, and acid dosages of 250 to 400 kg/t. HPAL was considered in past publications from the 1970s and 1980s for the treatment of nodules, but not pursued for various reasons. Han and Fuerstenau (1975) considered the pressure acid leaching of nodules at 200 °C, 0.26 t/t acid addition and 690 kPa oxygen overpressure, reporting recoveries of 90 percent Ni, 91 percent Cu, 44 percent Co and 6 percent Mn. Anand et al. (1988) investigated HPAL processing at 150 °C under an oxygen partial pressure of 550 kPa and reported metal recoveries of more than 90 percent for Ni and Cu, 88 percent Co and 28 percent Mn. Seaborn et al. (2020) commented on HPAL testing conducted on polymetallic nodules, which led to high (94 to 99 percent) recoveries of nickel, copper, cobalt and manganese. Haynes et al. (1985) considered HPAL processing of nodules at 245 °C, with a residence time of 1.5 hours and acid addition of 0.4 t/t, reporting recoveries of 98 percent Ni, 95 percent Cu, 92 percent Co and only 5 percent Mn.The variability in manganese behavior across several studies is significant and may be due to different feed samples used or process conditions applied. Relevant literature on HPAL processing of manganese nodules is sparse and relatively old, and yet it appears to show promising performance. The literature also showed significant variable behavior of manganese, encouraging us to reconsider HPAL processing. Based on the apparent potential of manganese rejection, high recoveries of nickel/copper/cobalt, and the mature state of HPAL technology (and associated lower technical risks), SGS initiated a small internal research and development program consisting of a single series of tests investigating HPAL processing of an available nodule sample. Preliminary results of this work have been published elsewhere by Verbaan and Johnson (2024) and Verbaan (2024). This article includes an update to the earlier presented work. HPAL testwork Feed source. The nodules used in the study were sourced from the Pacific Ocean, with the average nodules composition from such deposits given in Table 1, though the range for impurity elements such as iron can be large depending on the exact location of nodule harvesting. Prior to using the nodules in the testwork, they were crushed, dried at low temperature and then pulverized to 100 percent passing 75 µm. Experimental. The testwork was conducted using 2-L Parr titanium autoclave vessels equipped with dual impellers and temperature control (via external electrically powered heating mantles and internal cooling coils). Reagents were of laboratory grade, with 96 percent sulfuric acid provided by Fisher Scientific and 99 percent oxygen supplied by Messer. In the majority of the tests, the nodules were pulped in water to the target solids density before adding the acid to the pulp and then heating to the target temperature after pressure testing. One test was performed where acid was not added until the nodules slurry had reached temperature, injecting the acid at pressure. HPAL test conditions and key results The first HPAL test conditions were inspired by previous testwork (Anand et al., 1988) that used nodules collected from the Indian Ocean and applied relatively low temperatures to the leaching process (130 to 170 °C), along with 380 to 550 kg/t acid addition in the presence of oxygen (550 kPa partial/overpressure) for four hours at 5 percent solids. Additional tests were conducted with varying acid addition, as detailed in Table 2a, increasing from 500 kg/t to 800 kg/t. Figure 1: Average composition of seabed nodules from Paciﬁc deposits (Dames and Moore, 1977). Figure 1a presents the calculated extractions from the first three tests conducted at the same temperature, overpressure and pulp density, only varying the acid addition. While reduced iron and manganese leaching was accomplished, key metal extractions were incomplete, with 75 percent Ni or less, 20 percent Co or less and 80 percent Cu or less recovered to the leach solution. As more acid was added, extractions did increase, but such high acid additions were uneconomical based on the nodule grades.The second set of tests aimed to investigate leaching conditions without the use of oxygen, under the hypothesis that the oxidation, while helpful in preventing Fe/Mn leaching, was negatively impacting cobalt leaching (and Ni/Cu as well, potentially). As outlined in Table 2b, these tests were conducted under natural steam pressure and increased both the temperature and the pulp density. The acid addition in test 6 was reduced from 800 kg/t to 650 kg/t in order to remain near the final leach solution acidity of test 5, accounting for the change in pulp density. Including test 3 for comparison, Fig. 1b shows the calculated extractions for the tests that did not use oxygen. Test 4 resulted in 93 percent Ni, 69 percent Co and 94 percent Cu extraction, a significant improvement over test 3, while manganese extraction remained limited (5 percent). Iron extraction rose (27 percent versus less than 10 percent previously), as was expected based on the lack of additional oxidation to promote its reprecipitation. Further improvement was seen in test 5 after increasing the temperature from 150 °C to 225 °C, yielding extractions of 99 percent Ni, 97 percent Co, 99 percent Cu, 19 percent Fe and 10 percent Mn, with the higher temperature promoting increased hydrolysis of iron. Increasing the pulp density further and adjusting the acid addition in test 6 resulted in a decrease in extractions, with 88 percent Ni, 84 percent Co, 84 percent Cu, 16 percent Fe and 8 percent Mn. The final two tests — tests 7 and 8 — made further reductions in the acid addition as well as comparing acid addition methods, investigating whether pretreating the pulp with acid before/during heat-up of the autoclave was falsely improving the extractions (as a pseudo two-stage leach in principle). The test conditions are summarized in Table 2c and show similar levels of acidity in solution and overall acid consumption. Figure 1c shows that the results for acid pretreating and acid injection were essentially the same, with 98 to 99 percent Ni, 92 to 93 percent Co, 94 percent Cu, 9 to 10 percent Fe, and 6 to 7 percent Mn extraction. Test 7 offered better extractions at a lower acid addition compared to test 6 for reasons unknown, which may be a result of an anomalous condition within test 6 that impacted the leach performance, though it was not physically noticeable/quantifiable. HPAL overall findings Table 3 summarizes the calculated metal extractions/deportment to solution achieved in all eight HPAL tests, including the key metals illustrated in Figs. 1a-c. Elements such as magnesium were relatively easily leached in all tests, while others (Cr) were present in small quantities and showed larger variation from test to test, regardless of conditions. In addition to the increased pulp density in later tests helping to reduce the overall acid addition (while maintaining similar levels of free acidity and extractions) it also helped to increase the concentration of the key metals in solution (Table 4, along with the typical residue concentration) as would be expected.The tenors at the lowest pulp density (5 percent) were impacted by the reduced leach performance under oxygen overpressure, but there is a large increase in the nickel, cobalt and copper concentrations in subsequent tests, while the levels of iron and aluminum in solution are not as strongly influenced. This improves the relative ratios of Ni/Co/Cu in solution with Fe/Al prior to downstream impurity removal. The sodium (Na) present in solution is assumed to be from the nodules themselves, due to residual dried salt water entrained in the nodules after harvesting. The HPAL residues remained enriched in Mn, with silicon (Si) as the next most prevalent element. The increased leaching of Ni/Co/Cu under conditions without oxygen resulted in very low levels of those metals in the residue (less than 0.1 percent each). Figure 2: Figure 2: Figure 2: Summary of mineral mass (weight percent) for the feed and HPAL residue. The testwork demonstrated the ability of conventional pressure acid leaching to selectively recover nickel, cobalt and copper from seabed nodules, with only limited coextractions of iron, aluminum and manganese, leaving up to 90 percent in the leach residue. The residue at 30 to 35 percent Mn is of higher grade than many manganese deposits and could be considered for further processing to recover the manganese, either using a reductive leach or through pyrometallurgical means. The process as tested has not been optimized and significant opportunities exist to reduce acid addition via variations in operating temperature and feed pulp density. Nevertheless, the process conditions are in essence quite comparable to (but less aggressive than) HPAL conditions used in the nickel laterite industry. To confirm the amenability of the HPAL residue to reductive leaching, a single test was conducted using sulfur dioxide gas as the reductant, sparging in a reactor at 10 percent solids maintained at 80 °C or higher, using residue from HPAL test 8 as feed. Gas was injected until the pulp reached 200 mV ORP (Ag/AgCl reference electrode) before turning off the gas flow and holding the reactor for one hour. Nearly quantitative leaching of Mn was achieved (leaving 0.43 percent Mn in the residue), along with 85 percent Fe, 13 percent Al and the balance of the remaining Ni/Co/Cu that was not leached in the HPAL test. The residue contained 24.4 percent Si, 2.6 percent Fe and 6.8 percent Al as major components. Mineralogical characterization of feed and HPAL residue The feed and HPAL residue samples were investigated with chemical analyses and TIMA-X to provide a mineralogical perspective to the metallurgical testwork results. The feed was stage-crushed to a P80 of approximately 40 μm, and the residue was analyzed as produced. TIMA-X is an acronym for TESCAN Integrated Mineral Analyzer, which is one of the newest automated scanning electron microscopy (ASEM) instruments on the market. It is based on four energy dispersive X-ray (EDX) silicon drift detectors (SDD) attached to a TESCAN MIRA (field-emission gun – FEG) platform, which also includes backscattered electron (BSE) and secondary electron (SE) detectors. The TIMA system uses both the EDX and BSE signals to identify minerals at each measurement point (or each homogenous segment of a grain, depending upon the analysis mode), and it is optimized to deal with rapidly acquired low-count spectra. These EDX (and BSE) spectra (and BSE data) are compared to entries in a mineral library on a first-match principle to identify the mineral phase, where this mineral library is based on theoretical mineral/phase composition or created by the user based on BSE, X-ray spectral windows counts and/or ratios. Figure 3: Clockwise BSE, pseudo color image, and X-ray maps of Mn, S and Cu and corresponding spectrum from the feed. Chemical characterization. The chemical composition of the feed and HPAL leach residue streams is given in Table 5, showing the decrease (from feed to residue) of well-leached elements such as nickel, cobalt and copper, along with an increase of elements that do not leach significantly such as iron, aluminum and manganese. Mineral abundance. Figure 2 illustrates a summary of the mineral weight percent distribution in the two samples. The compounds are fine-grained and characterized by crypto to microcrystalline intergrowths yielding mixed chemical analyses, and do not conform to common rock-forming minerals. Therefore, they have been described based on their elemental composition. For example, Mn-(high Si) oxides consist of Mn oxides intergrown with Mn silicates. Both samples consist of Mn-(high Si) oxides, Fe-(Mn) silicates, Mn(Si,S) oxides, Mn-(Cu,Ni) oxides and other minerals in lower quantities (approximately less than 2 percent). A notable difference is the presence of significant levels of Mn-(Cu,Ni) oxides in the feed material (approximately 19 percent) and the low level (2 percent) in the HPAL leach residue, indicative of efficient leaching. This coincides with the increase in Mn-(Si,S) oxides from 2.83 percent in the feed to 13.7 percent in the leach residue. Examples of the occurrence and chemistry of Mn-(Cu,Ni) particles from the TIMA-X are shown in Fig. 3 from the feed and Fig. 4 from the HPAL residue. They illustrate the BSE microscope images, the pseudo color images of the particles and X-ray maps of Mn, S, Si, Ni and Cu, and the corresponding spectrum of the minerals. A semiquantitative analysis yields 40.7 percent Mn, 2.4 percent Ni, 1.7 percent Cu and 0.6 percent Co, and minor other elements. Figure 4: Clockwise BSE, pseudo color image, and X-ray maps of Mn, S and Cu and corresponding spectrum from the HPAL residue. Grain size. The P80 of selected minerals is given in Table 6. The P80 of Mn-(Cu,Ni) ranges from 39 to 26 μm in the feed and HPAL residue, respectively, and that of Mn-(high Si)-Ox from 31 to 150 μm. The term “particle” refers to both liberated and middling particles, monomineralic and polymineralic. The P80 of the particle ranges from approximately 39 μm in the feed to 151 μm in the HPAL residue. Exposure of Mn-(Cu,Ni) oxides. The exposure (exposed surface percent) of Mn-(Cu,Ni) is summarized into well-exposed particles (80 percent exposure or more), which ranges from 19 to 24 percent, poorly exposed (less than 30 percent exposure) ranging from 20 to 35 percent, and moderately exposed (30 percent exposure or more, but less than 80 percent) ranging from 61 to 41 percent in the feed and HPAL residue, respectively (Fig. 5). It is of interest to note that despite the relatively high levels of poorly exposed Cu/Ni-bearing manganese oxides, leach extraction for copper, nickel and cobalt were still high. This is indicative that either the acid solution was able to penetrate into poorly exposed areas, or that the mineral structure of the Cu-Ni-bearing manganese oxides was destroyed and reprecipitated as a barren manganese oxide. Flowsheet options The leach liquor compositions shown in Table 4 of approximately 4 g/L Cu, 5 g/L Ni, 0.8 g/L Co, 8 g/L Mn and 2.5 g/L Fe are amenable for conventional metal recovery options: Excess acid can be neutralized via conventional limestone neutralization. Other means of consuming the excess acid (such as counter-current leaching) should be considered. Copper can be recovered selectively via either solvent extraction-electrowinning (SX-EW) or sulfide precipitation. Impurities (such as Fe, Cr, Al) can be removed via precipitation (possibly in a two-stage configuration) using lime or limestone. Manganese can be recovered selectively via SX (with D2EHPA). Cobalt and nickel can be recovered together as a mixed hydroxide precipitate (MHP) or MSP product, or separately via SX (with Cyanex 272, Versatic 10). While final effluent treatment is dependent on the metal recovery processes selected, it is expected to include production of sodium or ammonium sulfate if SX is included. Finally, it is worth pointing out that if a production capacity of 60,000 t/a of nickel is selected, and manganese extraction of 5 percent is assumed, this would lead to 225 kt/a of HPMSM, or around 1.75 times the planned production by Element 25. Considering the increased usage of manganese in lithium-ion battery chemistries, this provides a more realistic production scenario than processing all manganese into HPMSM. Figure 5: Summary of exposure (mass percent) of Mn-(Cu,Ni) calculated for the feed and HPAL leach residue. Valid concerns exist around the handling or final outcome of the Mn-rich leach residue, as well as potential waste products such as gypsum (produced by limestone neutralization) and crystallized sodium or ammonium sulfate salts. However, many of these issues are no different than those encountered in current black mass recycling projects and other terrestrial mining operations (such as lithium conversion plants). Conclusions Preliminary testwork has shown that selective recovery of nickel (more than 98 percent), copper (94 percent) and cobalt (92 percent) against manganese (6 to 7 percent), iron (10 percent) and aluminum (10 percent) is feasible using conventional HPAL technology. While the HPAL processing of nodules was considered in the 1970s and 1980s, little accessible data were available and at times conflicting observations or results were published. We believe that HPAL processing deserves further investigation, with potential benefits of higher extractions of nickel, copper and cobalt than published competing technologies while also providing the ability to valorize some of the manganese. n References Dames and Moore, E.I.C. Corporation (1977) Description of Manganese Nodule Processing Activities for Environmental Studies. Vol. III. Processing Systems Technical Analysis. U.S. Dep. Commerce – NOAA, Oce of Marine Minerals.AMC Consultants Pty Ltd. (2021) Technical Report Summary: Initial Assessment of the NORI property, Clarion-Clipperton Zone for Deep Green Metals Inc.Element 25 Limited (2023) Feasibility Study Battery grade high purity manganese processing facility, https://www.element25.com.au/site/pdf/d53d05d9 - 3 bc 8 - 4 da 9 - b 671 - 56 d 960 c 3 bb 28 / HPMSM-Feasibility-Study-Delivers-Outstanding-Economics.pdf, last accessed 2024/04/04.Dreisinger D. (2018) International Seabed Authority. https:// www. i sa. org. jm/ wp- content/ uploads/2022/12/UKSR-1.pdf, last accessed 2024/04/04.Verbaan N (2022) “On shore processing of polymetallic nodules,” Presentation provided to Deep Sea Mining Summit.Agarwal JC, Barner HE, Beecher N, Davies DS, Kust RN (1979) Kennecott Process for Recovery of Copper, Nickel, Cobalt and Molybdenum from Ocean Nodules. Society of Mining Engineer 31 No 12: 1704–1707.Szabo LJ. (1976) Recovery of Metal Values from Manganese Deep Sea Nodules Using Ammoniacal Cuprous Leach Solutions. U.S. Patent 3,983,017.Barner HE, Kust RN, Cox RP (1976) Elevated pressure operation in the Cuprion Process. US Patent 3,988,416.Dreisinger D, Verbaan N, Canizares M (2022) The demonstration of the Cuprion Process for recovery of nickel, cobalt, copper and manganese from seabed nodules. 61st Conference of Metallurgists, COM2022, https://doi.org/10.1007/978-3-031-17425-4_86.Haynes BW, Law SL, Barron DC, Kramer GW, Maeda R, Magyar MJ (1985) Laboratory Processing and Characterization of Waste Materials from Manganese Nodules. USBM Report of Investigation 8938.Seaborn C, Smit H and Halkyard J (2020) Harvesting nodules from the seabed surface and extracting cobalt nickel copper and manganese. ALTA 2020, Perth.Von Schroeter H, Sutherland A, Donald J (2020) Deep-sea nodules: lower impact processing to enable the green transition. 59th Conference of Metallurgists, COM2020, Processing of Critical Materials Symposium, ISBN: 978-1-926872-47-6.Boulby MN, Canaguier V, Donald JR (2022) Using polymetallic nodules to innovate manganese markets: A new manganese feed for SiMn Alloy produc- tion. 61st Conference of Metallurgists, COM2022, https://doi.org/10.1007/978-3-031-17425-4_108.Boulby MN, Bradley K, Donald JR (2024) Production of battery grade sulfates from deep-sea polymetallic nodules. 63rd Conference of Metallurgists, COM2024.Daniels, M (2021) Process for the recovery of metals from oxidic ores. WIPO. Patent number WO2021/028201A1.Alvarenga RAF, Preat N, Duhayon C, Dewulf J (2022) Prospective life cycle assessment of metal commodities obtained from deep-sea polymetallic nodules, Journal of Cleaner Production 330. https:// doi.org/10.1016/j.jclepro.2021.129884.Han KN, Fuerstenau DW (1975) Acid leaching of ocean manganese nodules at ele- vated temperatures. International. Journal of Mineral Processing 2: 163–171. https://doi. org/10.1016/0301-7516(75)90019-8.Anand S, Das SC, Das RP, Jena PK (1988) Leaching of manganese nodules at elevated temperature and pressure in the presence of oxygen. Hydrometallurgy 20 No 2: 155–168. https://doi.org/10.1016/0304-386X(88)90049-7.Verbaan N and Johnson M (2024). “Revisiting Pressure Acid Leaching of Seabed Polymetallic Nodules”. 63rd Conference of Metallurgists, COM2024.Verbaan N (2024) “On shore processing of polyme- tallic nodules: Revisiting Pressure Acid leaching. The importance of piloting during development of critical minerals projects to avoid delay plant ramp-ups,” Presentation provided to Deep Sea Mining Summit. November 2024, Miami.

Pressure acid leaching of seabed polymetallic nodules — An update

Authored by: Niels Verbaan, Mike Johnson and Tassos Grammatikopoulos

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