Acid leaching process of a ferronickel slag

Abstract

Acid leaching process of a ferronickel slag This presentation relates to a process for extracting magnesium or magnesium compounds from a ferronickel slag feed comprising magnesium and silica compounds, the process comprising: a grinding step to reduce the particle size distribution of the ferronickel slag feed;and an acid leaching step after the grinding step, comprising: leaching the ferronickel slag load from the grinding step into a vessel with hydrochloric acid at a concentration of 5 to 15 wt% HCl to form a leached slurry, controlling the hydrochloric acid concentration during leaching by adding additional hydrochloric acid to the vessel to maintain the hydrochloric acid concentration at 5 to 15 wt% HCl, and obtaining a leached slurry from the vessel, wherein the leached slurry comprises a liquid portion and a solid residue, and wherein the liquid portion comprises magnesium chloride. Figure 3.;

Description

Title of the invention: Acid leaching process for ferronickel slag technical field

[0001] The present description relates to an improved acid leaching process for extracting valuable elements, metals, or metallic compounds from a slag feedstock. More specifically, embodiments of the present description relate to a process based on improved acid leaching for extracting magnesium from ferrous slags or ferrous alloy slags, such as ferronickel slag. Previous technique

[0002] Slags and similar by-products from smelting processes typically include a number of materials with potential utility or value, dispersed throughout the slag composition (e.g., magnesium, calcium, aluminum, rare earth metals, etc.). However, in conventional industrial processes, all or part of these materials may not be extracted before the slag is discarded due to technical difficulties, high reagent usage, time requirements, and / or low process yields for recovering these materials, making extraction technically and commercially unviable.

[0003] This is evident, for example, in the processing of laterite ores to produce ferronickel, which produces a slag (namely, "ferronickel slag") having no or limited commercial utility, which is typically accumulated as a waste product. In principle, magnesium can be recovered from such slags by leaching with an acid and purifying the resulting solution to obtain a magnesium-bearing product. For example, Mubarok, MZ, and A. Yudiarto. "Synthesis of magnesium oxide from ferronickel smelting slag through hydrochloric acid leaching-precipitation and calcination." Energy Technology 2017: Carbon Dioxide Management and Other Technologies.Springer International Publishing, 2017, describe a maximum magnesium extraction of 97% from a ferronickel slag by grinding the particles down to less than 200 mesh (i.e., a particle size less than 74 pm) and leaching with a highly concentrated acid (HCl 8 M, about 25 wt% HCl) at 80°C for 24 hours, and with a liquid / solids ratio of 40 / 1. However, every other experiment by Mubarok resulted in a significantly lower magnesium extraction, namely less than . at 80%, which would not be commercially viable for an industrial-scale production process.

[0004] In addition, Mubarok reported that extending the leaching step to 48 hours resulted in the precipitation of gelatinous silica and a reduction in magnesium extraction, and, at lower liquid / solid ratios, the viscosity of the solution was higher; the extraction of Mg was lower; and the susceptibility to the formation of gelatinous silica increased.

[0005] The formation of silica gels is well known in the field of hydrometallurgy. For example, Queneau, P., and Berthold, C., “Silica in Hydrometallurgy: An Overview,” Canadian Metallurgical Quarterly, 25:3, 201-209, 1986, describe the following: “In acidic solutions, silica concentrations exceeding the equilibrium solubility of monomeric silica [Si(OH)₄][... are encountered. These high levels of silica result from polymerization [...] Aging results in the formation of amorphous silica, in the form of a colloid, a precipitate, or a gel. The colloidal particles are so small that they do not settle. A silica gel forms when these particles aggregate in a way that incorporates most, if not all, of the water [...]The formation of a gel or a precipitate, as the case may be, depends on the degree of supersaturation in silica, the availability of silica surface area on which fresh silica can be deposited, the temperature, the pH, and the ionic strength.

[0006] The formation of a gel is very disadvantageous during acid leaching, particularly in an industrial-scale manufacturing context.

[0007] Prasetyo, Agus Budi, et al. "Magnesium Extraction of Ferronickel Slag Waste Processed by Alkali Fusion and Hydrochloric Acid Leaching." Journal of Mining and Metallurgy, Section B: Metallurgy 57.2 (2021): 225-233 describe the difficulty of separating a silica gel formed from a leached solution to obtain valuable Mg compounds. To prevent the formation of silica gels, Prasetyo teaches the addition of an alkaline fusion pretreatment step to reduce the amount of silica in the slag before leaching and thus reduce the amount of silica available to form a silica gel.However, the pretreatment step proposed by Prasetyo involves pretreating the ferronickel slag with a 1:1 addition of sodium carbonate and a reaction at a high temperature of 1000°C for 60 minutes to transform the silica-bound phases within the slag (e.g., magnesium silicates) into sodium silicates, which could then be removed by washing with water. These conditions are unsuitable for an industrial-scale manufacturing process. The alkaline melting pretreatment step also has the disadvantage of requiring additional equipment and considerable capital investment to calcine all of the ground slag. 1000°C. Other disadvantages of this approach are the considerable increase in overall carbon dioxide emissions released by sodium carbonate, as well as the need to find suitable uses or disposal methods for the sodium silicate solution.

[0008] It is important to note that the Mubarok and Prasetyo processes for extracting magnesium from ferronickel slag have not been implemented on a large or commercial scale. This is likely due to significant commercial barriers, including one or more of the following: the high cost of reagents (e.g., concentrated hydrochloric acid, magnesium oxide, ammonium hydroxide, and sodium carbonate); the need to dispose of the leaching residue (which represents about 60% by weight of the slag feed); low magnesium extraction yields without a significant leaching time (e.g., about 24 hours); or problems associated with the formation of gelatinous silica inhibiting the operation of the downstream leaching and purification steps.

[0009] An industrial-scale manufacturing process is needed that allows the extraction of valuable components, for example magnesium, from a low-value slag, such as ferronickel slag, without prohibitive consumption of reagents. An industrial-scale manufacturing process is also needed to extract valuable components such as magnesium from ferronickel slag without the formation of silica gels.

[0010] Any reference to or discussion of any document, regulatory act, or piece of knowledge in this disclosure is incorporated solely for the purpose of providing context for the present invention. It is not suggested or asserted that any such material or any combination thereof was, at the priority date, part of the general common knowledge, or was known to be relevant to attempting to solve any problem to which this disclosure relates. Summary of the invention

[0011] In a first aspect, the present disclosure provides a process for extracting magnesium or magnesium compounds from a ferronickel slag feed comprising magnesium and silica compounds, the process comprising: a grinding step to reduce the particle size distribution of the ferronickel slag feed; and an acid leaching step after the grinding step, comprising: leaching the ferronickel slag feed from the grinding step in a container with hydrochloric acid at a concentration of 5 to 15 wt% HCl to form a leached slurry, controlling the concentration of hydrochloric acid during leaching by adding additional hydrochloric acid to the container to maintain the hydrochloric acid concentration at 5 to 15% by weight of HCl, and obtaining a leached slurry from the container, in which the leached slurry comprises a liquid part and a solid residue, and in which the liquid part comprises magnesium chloride.

[0012] In one or more embodiments, the acid leaching step occurs successively, that is, immediately after the grinding step. In one or more embodiments, there is no intermediate treatment step between the grinding step and the acid leaching step. In one or more embodiments, there is no intermediate treatment or pretreatment step between the grinding step and the acid leaching step to react the slag feed. In one or more embodiments, the slag feed is not treated with a fluoride compound, such as ammonium fluoride (NH4F), sodium fluoride (NaF), or hexafluorosilicic acid (also called fluorosilicic acid, H2SiF6), before or during the acid leaching step.The absence of such a treatment step is beneficial for reducing the number of reagents required for the extraction of magnesium or magnesium compounds and for reducing any waste by-products. In one or more embodiments, the composition of the slag feedstock is maintained between the grinding step and the acid leaching step.

[0013] In one or more embodiments, the slag load is transported directly from the grinding stage to the leaching vessel. In other embodiments, the transport of the slag load from the grinding stage to the vessel includes storing the slag load for a certain period of time.

[0014] In one or more embodiments, the acid leaching step essentially consists of: transporting the slag load directly from the grinding step to a container containing an acid to leach the slag load and extract a leached slurry from the container.

[0015] In one or more embodiments, controlling the hydrochloric acid concentration during leaching includes adding additional hydrochloric acid in one or more batch additions of HCl or by continuous feeding of HCl. In one or more embodiments, the additional HCl is recycled from a downstream acid recovery step.

[0016] In one or more embodiments, the ferronickel slag charge further contains one or more of aluminium, calcium, chlorine, chromium, potassium, nickel, sulfur, or any combination thereof.

[0017] In one or more embodiments, the ferronickel slag charge contains one or more of ferrosilite (FeSiO3), fayalite (Fe2SiO4), clinoenstatite (MgSiO3) and fosterite (Mg2SiO4), and other complex iron materials.

[0018] In one or more embodiments, the ferronickel slag charge further contains Al2O3, Cr2O3, or one of their combinations.

[0019] In one embodiment, the ferronickel slag feed is produced from the smelting of nickel laterite.

[0020] In one embodiment, the ferronickel slag charge comprises silica at concentrations of approximately 15 to 90% by weight.

[0021] In one embodiment, the ferronickel slag charge comprises silica at concentrations of approximately 20 to 50% by weight.

[0022] In one embodiment, the ferronickel slag charge comprises silica at concentrations of approximately 25% by weight.

[0023] In some embodiments, the slag charge comprises silica at concentrations of about 15% by weight, 20% by weight, 25% by weight, 30% by weight, 35% by weight, 40% by weight, 45% by weight, 50% by weight, 55% by weight, 60% by weight, 65% by weight, 70% by weight, 75% by weight, 80% by weight, 85% by weight, or 90% by weight, or any range between these values.

[0024] In one embodiment, the solid residue comprises amorphous silica.

[0025] In one embodiment, the solid residue comprises amorphous silica at a concentration of approximately 20 to 90% by weight.

[0026] In one embodiment, the solid residue comprises amorphous silica at a concentration of approximately 30 to 60% by weight.

[0027] In some embodiments, the solid residue comprises amorphous silica at a concentration of approximately 30 to 50% by weight.

[0028] In some embodiments, the solid residue comprises about 20% by weight, 25% by weight, 30% by weight, 35% by weight, 40% by weight, 45% by weight, 50% by weight, 55% by weight, 60% by weight, 65% by weight, 70% by weight, 75% by weight, 80% by weight, 85% by weight, or 90% by weight of amorphous silica, or any range between these values.

[0029] In one embodiment, in the acid leaching step, the control of the hydrochloric acid concentration during leaching maintains the hydrochloric acid concentration at 8 to 12 wt% of HCl.

[0030] In one embodiment, in the acid leaching step, the control of the hydrochloric acid concentration during leaching maintains the hydrochloric acid concentration at approximately 10% by weight of HCl.

[0031] In one or more embodiments, the concentration of HCl in hydrochloric acid varies during the acid leaching step.

[0032] In one embodiment, at least part of the additional hydrochloric acid is recycled hydrochloric acid from a downstream manufacturing step.

[0033] In one embodiment, the recycled hydrochloric acid has a higher HCl concentration than the hydrochloric acid in the container.

[0034] In one embodiment, during the acid leaching step, the slag feed passes through multiple containers with hydrochloric acid to leach the slag feed.

[0035] In one embodiment, the concentration of HCl in each container is controlled independently.

[0036] In one embodiment, during the acid leaching step, the slag load has a total residence time for leaching of between 0.5 and 12 hours in the container(s).

[0037] In one embodiment, the total residence time for leaching is between 0.5 and 8 hours or between 0.5 and 6 hours in the container(s).

[0038] In one embodiment, the total residence time for leaching is approximately 8 hours in the container or containers.

[0039] In some embodiments, the total residence time for leaching is approximately 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, or any range between these values.

[0040] In one embodiment, in the acid leaching step, the leaching of the ferronickel slag feedstock with hydrochloric acid is carried out at a temperature between approximately 50 and 100°C.

[0041] In some embodiments, the acid leaching step is controlled at a maximum temperature of about 80°C.

[0042] In one embodiment, in the acid leaching step, the leaching of the ferronickel slag feedstock with hydrochloric acid is carried out at a temperature of about 80°C.

[0043] In some embodiments, in the acid leaching step, the leaching of the ferronickel slag feedstock with hydrochloric acid is carried out at a temperature of about 50°C, about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, or any range between these values.

[0044] In one embodiment, in the acid leaching step, the leaching of the ferronickel slag feedstock with hydrochloric acid is carried out at an initial liquid / solid ratio of 10 mL / g to 20 mL / g.

[0045] In some embodiments, in the acid leaching step, the leaching of the ferronickel slag feedstock with hydrochloric acid is carried out at an initial liquid / solid ratio of about 10 mL / g, about 15 mL / g, or about 20 mL / g.

[0046] In one embodiment, during the grinding step, the slag charge is ground to a particle size P98 of no more than 100 micrometers.

[0047] In one embodiment, during the grinding step, the slag charge is ground to a P98 particle size of approximately 75 micrometers.

[0048] In some embodiments, during the grinding step, the slag charge is ground to a P98 particle size of about 50 micrometers, about 55 micrometers, about 60 micrometers, about 65 micrometers, about 70 micrometers, about 75 micrometers, about 80 micrometers, about 85 micrometers, about 90 micrometers, about 95 micrometers, or about 100 micrometers.

[0049] In one embodiment, the container or containers are sealed under negative pressure.

[0050] In one or more embodiments, the acid leaching step is a continuous leaching process.

[0051] In one or more embodiments, the slag feed and hydrochloric acid are supplied to at least one container by co-current flow.

[0052] In one or more embodiments, the slag feed and hydrochloric acid are supplied to at least one container by counter-current flow.

[0053] In one or more embodiments, the process further comprises a residue thickening step, in which the leached slurry is thickened and separated into an overflow stream and an underflow stream, in which the underflow stream comprises practically all of the solid residue.

[0054] In one or more embodiments, the process further comprises an iron removal step, in which the overflow stream is treated with oxygen and an alkaline reagent so that the acids inside the overflow stream are neutralized and a mixture of an iron precipitate stream and a magnesium chloride product stream is produced, in which the iron precipitate is separated from the magnesium chloride product stream.

[0055] In one or more embodiments, an iron precipitate seed material is added to the overflow stream to seed the formation of the iron precipitate stream.

[0056] In one or more embodiments, the iron precipitate seed material comprises recycled material from a downstream step.

[0057] In one or more embodiments, the alkali reagent comprises a calcium-containing ore and / or a calcined product.

[0058] In one or more embodiments, the alkaline reagent comprises limestone and / or quicklime.

[0059] In one or more embodiments, the alkali reagent comprises a magnesium-containing ore.

[0060] In one or more embodiments, the magnesium-containing ore comprises magnesite and / or dolomite.

[0061] In one or more embodiments, the alkali reagent comprises magnesium oxide.

[0062] In one or more embodiments, the alkaline reagent comprises recycled magnesium oxide from a downstream step.

[0063] In one or more embodiments, the process further comprises a roasting step, in which the produced magnesium chloride stream is heated to produce a magnesium oxide product and an acid by-product.

[0064] In one or more embodiments, the magnesium chloride stream produced has a residence time for heating in the roasting step of up to 2 hours at approximately 700°C.

[0065] In one or more embodiments, the magnesium chloride stream produced has a residence time for heating in the roasting step of about 2 hours at about 700°C.

[0066] In one or more embodiments, the produced magnesium chloride stream is heated in a spray roasting oven.

[0067] In one or more embodiments, the produced magnesium chloride stream is heated in a fluidized bed roasting furnace.

[0068] In one or more embodiments, at least part of the magnesium oxide produced is recycled to the iron removal step.

[0069] In one or more embodiments, the process further includes an acid regeneration step, in which at least a portion of the by-product acid is absorbed into water to produce recycled hydrochloric acid.

[0070] In one or more embodiments, the process further comprises a residue thickening step, in which the leached slurry is separated into an overflow stream and an underflow stream, in which the underflow stream comprises practically all of the solid residue; an iron removal step, in which the overflow stream is treated so that the acids are neutralized within the overflow stream and so that an iron precipitate is separated from a produced magnesium chloride stream; a roasting step, in which the produced magnesium chloride stream is heated to produce a produced magnesium oxide and an acid by-product; and an acid regeneration step, in which at least a portion of the acid by-product is absorbed into water to produce regenerated hydrochloric acid.

[0071] In one or more embodiments, the by-product acid is gaseous hydrogen chloride.

[0072] In one embodiment, the acid regeneration step includes washing the by-product acid in a Venturi washer with the produced magnesium chloride stream before the produced magnesium chloride stream is delivered to the roasting step.

[0073] In one embodiment, the regenerated hydrochloric acid is recycled to the acid leaching step.

[0074] In a second aspect, the present presentation makes available a leached slurry produced by the process according to the first aspect.

[0075] In another aspect, the present exposition makes available a produced magnesium oxide, which is produced by the process according to the first aspect.

[0076] In another aspect, the present disclosure makes available a recycled acid produced by the process according to the first aspect.

[0077] In another aspect, the present disclosure makes available a system for extracting one or more metals or metallic compounds from a slag feed, comprising: a grinding step to reduce the particle size distribution of the slag feed; and an acid leaching step after the grinding step to receive the slag feed from the grinding step and leach the slag feed with hydrochloric acid to form a leached slurry, wherein the slag feed comprises magnesium and silica compounds, the hydrochloric acid has a concentration of between 5 and 20 wt% HCl, and the leached slurry comprises a liquid portion and a solid residue, wherein the liquid portion comprises magnesium chloride.

[0078] In one or more embodiments, the system further includes a residue thickening step, in which the leached slurry is thickened and separated into an overflow stream and an underflow stream, in which the underflow stream comprises practically all of the solid residue.

[0079] In one or more embodiments, the process further comprises an iron removal step, in which the overflow stream is treated with oxygen and an alkaline reagent to neutralize the acids inside the overflow stream and to produce a mixture of an iron precipitate stream and a magnesium chloride product stream, in which the iron precipitate is separated from the magnesium chloride product stream.

[0080] In one or more embodiments, the system further comprises a roasting step, in which the produced magnesium chloride stream is heated to produce a magnesium oxide product and an acid by-product.

[0081] In one or more embodiments, the system further includes an acid regeneration step, in which at least a portion of the by-product acid is absorbed into water to produce recycled hydrochloric acid.

[0082] Other features and advantages of the present exposition will become evident from the detailed description that follows. Brief description of the drawings

[0083] Various preferred embodiments of the present exposition will now be described, by way of example only, with reference to the accompanying figures, in which:

[0084] [Fig. 1] illustrates a particle size distribution of a sample of ferronickel slag used during a laboratory test;

[0085] [Fig.2] illustrates the extraction of magnesium over time from a sample of ferronickel slag during laboratory-scale acid leaching according to the invention;

[0086] [Fig.2a] illustrates the extraction of metal (in the liquor) over time from the HY7547 sample during laboratory-scale acid leaching;

[0087] [Fig.2b] illustrates the extraction of metal (in the liquor) over time from the HY7548 sample during laboratory-scale acid leaching;

[0088] [Fig.2c] illustrates the extraction of metal (in the liquor) over time from the HY7549 sample during laboratory-scale acid leaching;

[0089] [Fig.2d] illustrates the extraction of metal (in the liquor) over time from sample HY8595 during laboratory-scale acid leaching;

[0090] [Fig.2e] illustrates the extraction of metal (in the liquor) over time from the HY8215 sample during laboratory-scale acid leaching;

[0091] [Fig.2f] illustrates the extraction of metal (in the liquor) over time from sample HY8070 during laboratory-scale acid leaching;

[0092] [Fig.2g] illustrates the extraction of metal (in the liquor) over time from the HY8071 sample during laboratory-scale acid leaching;

[0093] [Fig. 2h] illustrates the extraction of metal (in the liquor) over time from sample HY8072 during laboratory-scale acid leaching; and

[0094] [Fig.3] illustrates a block flowchart of an industrial recovery process comprising an extraction process according to the invention. Detailed description

[0095] The present invention relates to a process for extracting one or more elements, metals, or metallic compounds, for example magnesium, from a slag feedstock, such as ferronickel slag. In preferred embodiments, the process can be carried out on an industrial scale using recycled reagents, such as hydrochloric acid.

[0096] During research on processes for extracting magnesium from slag, it was surprisingly found that low concentrations of hydrochloric acid (e.g., concentrations of about 20 wt% HCl or less) could efficiently leach magnesium from ferronickel slag in high yields (e.g., 90% or more) while also avoiding the formation of silica gels without a high-temperature pretreatment step to convert the silica-bound phases within the slag into sodium silicates. This discovery was contrary to the general idea in this field, according to which HCl concentrations above the azeotropic concentration of HCl, about 20 wt%, typically 32 wt% HCl, or the use of a pretreatment step, are necessary for leaching magnesium from slag without the formation of silica gels.

[0097] Since there is currently no or limited commercial use of ferronickel slags, the applicant believes that the potential use of relatively low concentrations of hydrochloric acid should allow for the commercially viable conversion of ferronickel slag (and similar refractory slags) into useful products, without the need for pretreatment reagents prior to leaching to alter the composition of the feedstock. Examples

[0098] Laboratory tests

[0099] A mass of ferronickel smelting slag was received in the form of a fragmented solid with an estimated particle size (Pioo) of 3.5 mm. Analysis of the slag indicated a composition comprising: Analyte % by weight Analyte % by weight Al 1.44 Mg 19.1 Ca 0.32 Na 0.048 Cl <0.01 Ni 0.08 Cr 0.82 S 0.03 Fe 8.66 Si 24.4 K 0.02 - -

[0100] The minerals identified in the slag included ferrierite (FeSiO3) and clinoenstatite (MgSiO3). The other minerals were not identified by XRD, and it is understood that the remaining elements existed in an amorphous (non-crystalline) phase within the slag mass.

[0101] Ferronickel slag was ground to a P98 particle size of 75 µm for all the laboratory experiments detailed below. The particle size distribution of the slag is illustrated in [Fig. 1].

[0102] The inventors believe that a smaller particle size can result in a higher reaction rate and thus faster extraction of valuable elements, metals, or metallic compounds from the slag during the leaching step. However, a higher reaction rate could also disperse a critical mass of silica in solution, which may have the potential to supersaturation the silica and lead to the formation of gelatinous silica (depending further on additional factors such as temperature, instantaneous acid strength, etc.). Therefore, in practice, it may be advisable to control the conditions and the amount of silica in solution to avoid the formation of gelatinous silica.In one embodiment, the control of conditions includes the control of grinding conditions, for example, to obtain a desired particle size in order to control the amount of silica in solution and thus control or minimize the formation of gelatinous silica.

[0103] Laboratory-scale acid leaching (load = 100 g)

[0104] Samples containing between 5 and 32 wt% of HCl were prepared (with HCl concentrated and deionized water) and introduced into a sealed baffled vessel under stirring to establish an initial HCl solution for the acid leaching test. A condenser was connected to the vessel to minimize the effects of evaporation. The HCl solution was preheated to the target temperature (see Table 1 below) using a thermocouple-controlled hot plate, after which 100 g of ground ferronickel slag were added to the vessel to initiate magnesium leaching from the slag.

[0105] Aliquots of the resulting slurry were removed at predetermined time intervals and analyzed for chemical composition determination over time. After a predetermined leaching period, the final solution was also analyzed for chemical composition, including Mg concentration. The final (solid) residues were washed with water, dried, and then analyzed in a similar manner. The percentage of Mg extracted was then calculated for each sample.

[0106] The samples of the invention contained initial HCl concentrations of 5%, 10%, 15%, 20%, and 25% (w / w) HCl. Since the acid was consumed during the leaching process, the acid concentration was maintained during leaching by adding 32% HCl as needed. Those skilled in the art will appreciate that this acid concentration can be maintained by using any hydrochloric acid having a weight percentage of HCl higher than the target HCl concentration by adding a suitable amount of acid to achieve the target HCl concentration.

[0107] These samples of the invention were compared to three control samples with an initial concentration of 32 wt% HCl and without the addition of HCl during leaching. These control sample conditions use an HCl concentration that is higher than the azeotropic concentration of HCl.

[0108] A summary of the results is presented in Table 1 below:

[0109] [Table 1] - Laboratory-scale acid leaching results Test No. Conc. Initial HCl concentration (% wt) Initial liquid / solid ratio (mL / g) Leaching time (min) P-CO₂ temperature Mg in solution (g / L) Residual Mg concentration (%) Mg extraction (%) Final free acid concentration (% wt HCl) HY7 547 (control) 32 40 1440 80 4.64 1.52 93.68 27.8 HY7 548 (control) 32 20 1440 80 9.71 1.48 92.2 28.0 HY7 549 (control) 32 20 360 95 9.08 1.56 92 24.2 HY8 595 5 20 480 80 8.22 3.27 87.62 5.15 HY8 215 10 20 480 80 8.32 1.93 92.81 9.34 HY8 070 15 10 480 80 12.9 1.58 93.32 14.82 HY8 071 20 10 480 80 11.3 1.48 93.21 19.1 HY8 072 25 10 480 80 7.18 1.8 93.39 24.7

[0110] As is evident from the differences between the initial concentration of HCl and the final concentration of free acid in the three control samples, the HCl was consumed to drive the acid leaching reaction.

[0111] Another comparison of magnesium extraction over time for the five acid leachates maintained at 5%, 10%, 15%, 20% and 25% (w / w) HCl is illustrated in [Fig.2], the metal extraction (in the liquor) over time for each of the above samples being shown in Figures 2a-2h.

[0112] These tests confirm that a leaching HCl concentration maintained between 10 and 25 wt% HCl for 8 hours can achieve Mg extraction comparable to that obtained by the control samples using an initial HCl concentration of 32%. Advantageously, by maintaining the HCl concentration within this range, there will always be a sufficient mass of acid to drive the leaching reactions.

[0113] The Mg extraction data also indicate little or no benefit from either leaching for more than approximately 4-8 hours (provided there is a sufficient mass of HCl, approximately 10%, or more acid to drive the leaching reactions), or from increasing the temperature from 80°C to 95°C. Advantageously, none of the samples of the invention formed a silica gel-like substance during the duration of the experiment.

[0114] Furthermore, as shown in Figures 2a, 2b, 2c, 2g and 2h, a negligible concentration of silica gel in the liquor was found throughout the experiment for the samples with the higher acid concentration. It is thought that, in these samples, the leached silica precipitates immediately out of the leaching liquor.

[0115] However, as shown in Figures 2d, 2e and 2f, the samples with lower acid concentration exhibit an early increase in silica concentration in the liquor, which decreased over time, indicating that the rate of silica precipitation was lower with the samples with lower acid concentration.

[0116] Magnesium purification

[0117] A PLS (enriched leaching solution) composite was prepared by mixing the leaching solutions of control samples HY7547, HY7548, and HY7549. An assay of the PLS composite indicated a composition comprising: Analyte Concentration Analyte Concentration Al 334 mg / L Mg 7.648 mg / L Ca 110 mg / L Na 18 mg / L Cl 327.300 mg / L Ni 83 mg / L Cr 360 mg / LS 30 mg / L Fe 3.519 mg / L Si 3.0 mg / LK 10 mg / L HCl 357 g / L

[0118] 5 litres of the PLS composite were added to a sealed baffled container under Agitation to concentrate the dissolved metals and to release as much water and hydrochloric acid as possible, with the results shown below: Test NO Initial HCL (g / D Initial Mg (g / D Final HCl (g / D Final Mg (g / D Loss in vol. (%)) HCl evaporation % (%) HY7 829 357 7.65 86.8 68.2 90.4 97.7

[0119] 500 mL of the resulting evaporated PLS composite were then subjected to a 3-hour precipitation to remove iron and other impurities from the solution, using magnesia (MgO), by preheating the solution to 95°C and adding magnesia in small quantities to reach a target pH of 1.5 at the end of the 3-hour period, with the results shown below: Test No. Dose of MgO (g / gFe) Fe in initial solution (mg / L) Fe in final solution (mg / L) Mass of precipitate (%) Fe in precipitate (%) Fe extraction (%) HY7 830 3.2 31780 6 9.3 26.2 99.98

[0120] The purified PLS composite liquor thus obtained was then transferred to a beaker and heated to its boiling point (approximately 100°C) and allowed to evaporate for up to 6 hours. The solution was then allowed to cool to produce a crystalline solid, which was transferred to a nitrogen-purged muffle furnace at 700°C for 6 hours, and then allowed to cool.

[0121] It was calculated that the resulting calcinate achieved a Mg recovery of 95.4% from the initial control samples (assuming that all the magnesium was present as MgO). In addition, the test achieved a chloride evaporation of 99.1% in the form of hydrogen chloride vapor.

[0122] Stability of the leachate with respect to gelation

[0123] Before carrying out the experiments, the inventors thought that leaching slags with low concentrations of hydrochloric acid would increase the content of dissolved silica (due to increased solubility at lower HCl concentrations) and thus increase the risk that the silica particles would aggregate over time in a gelled form (i.e., as gelatinous silica) rather than precipitate rapidly out of the solution and be easier to separate.

[0124] However, since no silica gel formed during the laboratory experiment, the inventors surprisingly found that relatively low concentrations of acid could be used to leach ferronickel slag without forming gelatinous silica and without compromising metal extraction by actively controlling the weight percentage of HCl to a low target concentration, by adding additional hydrochloric acid when the HCl is consumed during the leaching step. This can be seen in Figures 2d, 2e, and 2f, with a controlled hydrochloric acid concentration of 5 to 15 wt% of HCl.

[0125] The inventors currently theorize that, by supplying sufficient acid for leaching, however at a low concentration, the simultaneous dissolution and reprecipitation rates of silica can be controlled to avoid a high level of silica supersaturation, and thus to reduce the risk of gelation.

[0126] Other advantages of maintaining a low concentration of hydrochloric acid during the leaching step include the following: (i) fewer downstream reagents are required to neutralize the acid for further processing, thereby reducing manufacturing costs and environmental impact; (ii) because the solubility of silica does not change during the leaching step (since the pH is controlled by the addition of additional hydrochloric acid), the leaching rate and aggregation / precipitation mechanisms can be more easily predicted so as to control any undesirable formation of silica gel (e.g., by controlling the amount of silica in solution).

[0127] The use of a relatively low concentration of hydrochloric acid, of about 5 to 15% by weight, also provides a commercial advantage in that a downstream acid regeneration step can be used to recycle the hydrochloric acid back to the leaching step. This is particularly useful given that hydrochloric acid regeneration is typically limited to a maximum of 20% by weight of HCl in industrial processes, and more commonly at most 18% by weight of HCl. Any acid regeneration exceeding these values ​​would require specialized equipment and uneconomical operating parameters, increasing the complexity of the circulation scheme and reducing commercial viability.

[0128] It is also possible that silica gels may form after the leaching step, as the leachate solution is progressively separated from the residual solids by thickening and filtration steps.

[0129] Therefore, experimental tests were carried out to determine the gelling stability of a leachate obtained by leaching with a low HCl concentration of 5% (corresponding to test No. HY8595 above). This 5% HCl concentration was selected for the gelling stability tests because it is believed that this lower acid concentration is more likely to develop a gelatinous silica product.

[0130] Test 1: 5% HCl, no acid added, 6 hours at 80°C

[0131] 100 g of ferronickel slag were leached with 2043 g of hydrochloric acid at 5 % in a 4-liter beaker. The mixture was stirred using a suspended stirrer operating at 500 rpm, with the temperature maintained at 80°C for 6 hours using a hot plate. No additional acid was added during the test.

[0132] 50 mL samples were extracted from the slurry at 1, 2, 4, and 6 hours and tested for gel formation by vacuum filtration using a Buchner funnel with Whatman #42 ash-free filter paper and three washes with deionized water. No gel formation was observed for any of these samples.

[0133] After the 6-hour leaching period, the suspended agitator and hot plate were switched off, and the resulting slurry was left to stand at ambient conditions for 24 hours. After 24 hours, the slurry was tested for gel formation using a method similar to that detailed above, with no gel formation observed.

[0134] The filtrate samples obtained were subjected to a chemical analysis of their elemental composition, and the results are detailed in Table 2 below.

[0135] [Table 2] - Chemical analysis of Test 1 samples Test No. Cl- (g / L) Al (mg / L) Ca (mg / L) Cr (mg / L) Fe (mg / L) K (mg / L) Mg (mg / L) Na (mg / L) Ni (mg / L) S (mg / L) Si (mg / L) Filtrate - 1 hour 53 280 88 150 1800 5 4000 10 17 2 2600 Filtrate - 2 hours 53 310 100 170 2000 5 4400 9 23 1 2700 Filtrate - 4 hours 55 340 100 190 2200 6 4900 10 28 1 2900 Filtrate - 6 hours 59 360 100 210 2400 5 5400 10 30 1 3000 Filtrate-30 hours 50 380 100 240 2500 6 5700 10 32 1 3100

[0136] Comparing the results for "Filtrate - 6 hours" and "Filtrate - 30 hours", it is evident that there was only a minor change in the overall level of Si in solution after 24 hours of rest following leaching. This supports the conclusion that no silica gel formation occurred during this time.

[0137] Test 2: 5% HCl, addition of acid, 6 hours at 80°C

[0138] 100 g of ferronickel slag were leached with 2043 g of hydrochloric acid at 5% in a 4-liter beaker. The slurry had a liquid-to-solid ratio of 20:1 and contained 4.7% w / w solids. The slurry was stirred using a suspended stirrer operating at 500 rpm, with the temperature maintained at 80°C for 6 hours using a hot plate.

[0139] Additional 32% HCl was added during leaching at 5 minutes (94 g of 32% HCl), 15 minutes (94 g of 32% HCl), 60 minutes (50 g of 32% HCl) and 120 minutes (50 g of 32% HCl) to maintain the acid concentration at approximately 5% HCl.

[0140] After the 6-hour leaching period, the suspended agitator and hot plate were switched off and the resulting slurry was left to stand and cool overnight for 12 hours under ambient conditions.

[0141] The resulting slurry was tested for gel formation by vacuum filtration using a Buchner funnel with Whatman #542 hardened ash-free filter paper having a diameter of 185 mm. Filtration of the slurry took approximately 3 minutes. No gel formation was observed. A sample of the filtrate obtained was subjected to from a chemical analysis of its elemental composition, with the detailed results under the heading "Acid Leaching Solution" in Table 3 below.

[0142] Test 3: Removal of iron and impurities in Test 2

[0143] To further determine whether the silica dissolved in the filtrate would impact a step of downstream purification, removal of iron or other impurities, the 1650 mL of the filtrate obtained were separated in a 4 litre beaker and stirred using a suspended stirrer at 250 rpm, the temperature being maintained at 90°C for 5 hours using a hot plate.

[0144] The solution was sprayed with 2 L / min of oxygen for the initial 1 hour and 15 minutes, and then with 1 L / min of oxygen for the remaining time to form visible bubbles on the surface of the solution. 19 g of hematite were added to the solution to seed the precipitation.

[0145] A sodium hydroxide solution (10% NaOH; Merck Chemical, Analar grade) was added at intervals to the slurry to gradually increase the pH from a pH of about 1, at a rate of 1 pH unit per hour up to a pH of about 4 at the end of the three hours.

[0146] After the 5-hour period, the suspended agitator and the hot plate were switched off.

[0147] The remaining slurry (approximately 2700 mL) was filtered using a Buchner funnel with Whatman 541 hardened ashless filter paper with a diameter of 185 mm. Filtration of the slurry took approximately 2 minutes. A sample of the resulting filtrate was subjected to chemical analysis for its elemental composition, with the results detailed under the heading "Purified Acid Leaching Solution" in Table 3 below. After the test was carried out, the inventors noted that it is possible that the addition of hematite to the solution before at least partial neutralization of the solution with a sodium hydroxide solution may have resulted in the dissolution of some of the hematite before it could be seeded with the precipitation. It is therefore thought that the addition of hematite with or after the sodium hydroxide would improve the precipitation of iron and other impurities.

[0148] Test 4: Synthetic Si-free leaching solution from Test 2

[0149] A synthetic leaching solution was prepared from analytical grade reagents at concentrations based on the "acid leaching solution" of Test 2 above, except that no silica was added to the synthetic leaching solution to help determine whether the presence of silica affected the purification step.

[0150] 1650 mL of the synthetic leaching solution were added to a beaker of 4 litres. The solution was stirred using a suspended stirrer at 250 rpm, the temperature being maintained at 90°C for 4 hours using a hot plate.

[0151] NaOH was added to the slurry to first raise the pH to approximately 1, then 23 g of hematite were added to the solution to seed the precipitation. After a period of 4 hours, the suspended stirrer and the hot plate were switched off.

[0152] The remaining slurry (approximately 1700 mL) was filtered using a Buchner funnel with Whatman 541 hardened ashless filter paper having a diameter of 185 mm, and the residue was washed with deionized water. Filtration of the slurry took approximately 3 minutes. A sample of the filtrate obtained was subjected to chemical analysis for its elemental composition, with the detailed results under the heading "Purified Synthetic Leaching Solution" in Table 3 below.

[0153] The solid-liquid separation results of both Tests 3 and 4 are presented in Table 4 below.

[0154] [Table 3] - Chemical analysis of Test 2-4 samples Sample No. Cl (g / L) Mg (g / L) Al (mg / L) Ca (mg / L) Cr (mg / L) Fe (mg / L) K (mg / L) Na (mg / L) Ni (mg / L) S (mg / L) Si (mg / L) Acid leaching solution 83 8.2 370 95 405 3745 20 16 85 10 1858 Purified acid leaching solution 64 3.3 <10 64 <10 <10 125 354 00 11 <10 37 Purified synthetic leaching solution 59 3.5 7 <0.5 14 <0.3 1 75 310 00 <0.5 3 5

[0155] [Table 4] - Solid-liquid separation results of Test 3-4 samples Sample No. Iron Removal (%) Filtration Time (min) Purified Acid Leaching Solution 99.7 2 Purified Synthetic Leaching Solution 99.9 3

[0156] In the samples from both Tests 3 and 4, the removal of iron was indeed complete. At the elevated temperature and with a pH in the range of 2 to 4, a large proportion of the silica and aluminum also precipitated. The strong Sodium concentrations were obtained by using a 10% NaOH solution for pH adjustment. Filtration times were comparable.

[0157] Industrial valorization of a ferronickel slag

[0158] Based on the positive results of laboratory tests, the applicant has designed an industrial process for upgrading ferronickel slag to produce a commercially available magnesium oxide (MgO) powder product. A block flow diagram of this process is shown in [Fig. 3] and is summarized below. It is believed that the process can be applied in a similar manner to the extraction of magnesium from any other suitable magnesium-rich slag feedstock.

[0159] Based on a computer model of the heat-mass balance, it is estimated that 6.5 tonnes (dry) of a typical ferronickel slag, obtained from a nickel laterite smelting, would be required to produce 1 tonne of metallic magnesium. However, the magnesium recovery may vary depending, for example, on the composition of the original slag, or on the specific operating parameters used in implementing the process.

[0160] 1. Slag storage

[0161] Ferronickel slag (FNS), for example from a nickel laterite smelter, can be delivered to the processing site and stored until ready for recovery. Preferably, the slag should have a composition comprising large amounts (e.g., 15 wt% or more) of magnesium compounds, such as magnesium silicates (e.g., MgSiO3, Mg2SO4). Such slags should also typically contain large amounts of iron silicates (e.g., FeSiO3). Smaller amounts (e.g., < 5 wt%) of metal oxides (e.g., Al2O3, Cr2O3) and other minor compounds (e.g., aluminum, calcium, chlorine, chromium, potassium, nickel, and / or sulfur compounds) may also be present.

[0162] 2. Grinding of slag

[0163] The particle size of the FNS can be reduced by any conventional process, for example by fragmentation in a wet ball mill, to reduce the slag particles to a size suitable for acid leaching. Laboratory tests have reduced the particle size distribution to a P98 value of 75 µm. However, alternative particle size distributions (for example, smaller or larger) can also be used with the downstream acid leaching step 3, depending on the required leaching kinetics, in particular to avoid silica gelation conditions, and the available equipment. For example, alternative particle size distributions could include a P98 value of 50 µm, a P98 value of 100 µm, or a P95 value of 75 µm.

[0164] If necessary, the fragmented slag particles can be dried after fragmentation during this step, for example by means of a vacuum belt or other conventional drying or filtration equipment. The advantage of this would be to avoid any unnecessary dilution of the acid in the subsequent acid leaching step.

[0165] 3. Acid leaching

[0166] After the slag grinding step 2, the fragmented NSF is transported from the grinding step into a leaching vessel for slag leaching. Preferably, the slag is transported directly from the grinding step into the leaching vessel. However, in other envisaged implementations, the transport step may include temporary storage of the slag for a certain period of time.

[0167] The FNS is leached with hydrochloric acid at a target concentration of approximately 5 to 20 wt% HCl for 0.5 to 12 hours to produce a leached slurry comprising a liquid portion and a solid residue. During this leaching step, magnesium is extracted from the FNS and dissolved in the liquid portion as magnesium chloride. As demonstrated by laboratory testing, the applicant found that the use of relatively low acid concentrations did not result in the formation of gelatinous silica, and therefore the solid residue (now rich in precipitated silica) can still be separated from the liquid portion by conventional solid-liquid separation processes.

[0168] Preferably, the majority of the HCl used in the leaching step can be recycled from a downstream step (for example, as illustrated in acid regeneration step 11). If necessary, this recycling stream can be supplemented with a makeup HCl stream to achieve the target concentration of the feed HCl.

[0169] In a preferred embodiment envisaged, the leaching step will be carried out with a hydrochloric acid solution maintained at a concentration in the range of 8 to 12 wt% HCl, for approximately 6 hours. Advantageously, the consumed HCl can be supplemented with acid regenerated using conventional industrial techniques, thereby avoiding the use of higher concentrations of HCl (e.g., corresponding to or exceeding the azeotropic concentration of approximately 20 wt%) which would require specialized technologies that can be difficult or costly to regenerate (e.g., requiring extractive rectification technology or double-pressure technology).

[0170] Due to the corrosive nature of the reagents and products, the equipment and piping (including for relevant downstream steps) should be constructed of corrosion-resistant materials, such as fiber-reinforced plastic (FRP), or other plastics or metals coated with corrosion / abrasion-resistant plating. Furthermore, the Any gases produced should be purged for scrubbing before release into the atmosphere.

[0171] Depending on the available equipment and the volume of NSF to be leached, various leaching conditions can be selected to optimize the leaching step, including the following:

[0172] the selected concentration of HCl is maintained during the leaching process (for example by adding more HCl to the container as it is consumed);

[0173] leaching can take place in one or more leaching containers;

[0174] the concentration of HCl in each leaching container can be controlled independently;

[0175] the leaching process, which is an exothermic reaction, can be controlled at a temperature between about 50 and 100°C, or at a maximum temperature of about 80°C, or at an average temperature of about 80°C;

[0176] the leaching container(s) can be sealed under negative pressure;

[0177] The leaching step may be a batch process, or may be a process continuous; and / or

[0178] the FNS and the acid are delivered to at least one leaching vessel by co-current flow, and / or to at least one leaching vessel by counter-current flow.

[0179] 4. Thickening of the leaching residue

[0180] After leaching, the resulting slurry is pumped from the (final) leaching tank into a thickener where, possibly with the aid of a flocculant, the first solids / liquid separation stage takes place. In the modeled example, the hot acid slurry was settled to approximately 35% by weight of solids.

[0181] The overflow solution, containing magnesium chloride, is extracted and forms a feed solution for further processing. The underflow, comprising silica, is optionally further filtered in a silica filtration step.

[0182] 5. Filtration of silica

[0183] The sub-pour slurry stream from the thickening step can be further separated for the extraction of any residual magnesium chloride in the bulk silica.

[0184] This can be accomplished by any suitable filtration device, such as a plate and frame filter press equipped with a membrane pressing stage for drying and washing the solids, to recover a leachate containing magnesium chloride and unreacted acid. This leachate can be added to the overflow for further treatment. The filtered solids, consisting mainly of amorphous silica, are separated for further processing, sale, or disposal.

[0185] In the modeled example, 6.5 tonnes of initial slag produced 4 tonnes of amorphous (dry) silica.

[0186] 6. Iron removal

[0187] The overflow solution and the filter leachate can be treated with oxygen and an alkaline reagent, such as magnesium oxide, to oxidize ferrous iron to its ferric form, neutralize any unreacted acid, and separate the iron into ferric compounds by precipitation as the pH increases. This can be carried out in one or more tanks. The tanks can be sprayed with oxygen to ensure uniform oxygen distribution and minimize oxygen consumption.

[0188] As shown in [Fig. 3], magnesium oxide can be recycled from a downstream step to reduce the input of new reagent required into the system and to improve the overall process yield. This can be done through direct recycling after roasting step 10 (as illustrated), or the magnesium oxide can be crushed first to improve its dispersibility and reactivity.

[0189] In addition, an iron "seeding" material can be supplied from a downstream step (e.g., iron thickening or iron calcination) to promote the formation of large iron precipitate particles. Preferably, the iron removal step is carried out in the pH range of 1 to 4. Even better, the iron removal step is carried out at a temperature close to 100°C. Such conditions can promote the iron precipitate being mainly in the form of hematite and akaganeite, which can be more easily separated from the liquor (e.g., compared to ferric hydroxide).

[0190] 7. Thickening of iron

[0191] The resulting precipitate slurry is intended to be pumped from the final iron removal tank into a thickener where, optionally with the addition of flocculant, the slurry can be decanted to produce a sub-pour slurry. The modeled example indicates that a slurry having approximately 40 wt% / w solids should be obtainable.

[0192] Part of the thickener underflow can be recycled to the first iron removal tank to act as a seeding material for precipitation. The remainder of the underflow slurry is pumped for further filtration.

[0193] The overflow from the thickener, containing the magnesium, is pumped to a roasting stage 10.

[0194] 8. Iron filtration

[0195] The sub-flow slurry can be further separated for the extraction of any residual magnesium by means of suitable filtering devices, such as a filter A plate and frame press equipped with a membrane pressing device. The filtrate can be combined with the thickener overflow and the filter cake, which is then passed to iron calcination stage 9.

[0196] 9. Calcination of iron

[0197] The discharged filter cake (having a modeled moisture content of approximately 25%) is delivered by a conveyor for drying and calcination. This can be carried out, for example, in a rotary kiln with a residence time of approximately 2 hours at a temperature of approximately 700°C, in order to complete the oxidation of the non-hematite constituents (such as akaganeite and ferric hydroxide) to hematite and to eliminate virtually all of the remaining chloride content.

[0198] In the modeled example, 6.8 tonnes of initial slag produced 0.65 tonnes of hematite produced.

[0199] 10. Grilling

[0200] Streams containing magnesium chloride (including the overflow from iron thickening step 7 and the filtrate from filtration step 8) can be heated in a suitable apparatus (e.g. a spray roaster or fluidized bed roaster) so that the magnesium chloride is converted into solid magnesium oxide and hydrogen chloride vapor.

[0201] Based on the modeled example, a solution concentration of approximately 25 wt% of MgCl2 can be obtained as feedstock to the roasting stage, which can be roasted at 700°C to obtain MgO(s) and HCl(g). As noted above, 6.8 tonnes of initial slag were modeled to produce approximately 3 tonnes of magnesium oxide, which can be further purified downstream to approximately 1 tonne of metallic magnesium.

[0202] Part of the magnesium oxide produced can be recycled to iron removal stage 6, while the remaining magnesium oxide can be transported downstream for storage and / or sale and / or use as a commercial product.

[0203] 11. Acid regeneration

[0204] Advantageously, the hydrogen chloride vapor produced during roasting step 10 can be absorbed in water and the regenerated hydrochloric acid can be recycled to acid leaching step 3 to reduce reagent costs associated with the recovery process.

[0205] This can be achieved in any conventional gas absorption equipment, including venturi scrubbers, packed columns, and cap columns.

[0206] In the designed model, the acid vapor is first scrubbed with the magnesium chloride stream entering roasting stage 10, in order to improve the utilization of overall heat of the process, and the cooled gas is then counter-currently contacted with water in one or more gas absorption stages.

[0207] Although this constitutes an economically viable process for recovering hydrochloric acid, the inventors have found that the maximum strength of the acid regenerated in this process is limited to at most 20% by weight of HCl, and more likely to at most 18% by weight of HCl. However, through laboratory experiments, the inventors have found that this concentration of HCl could be advantageously used in the leaching of ferronickel slag.

[0208] 12. Gas scrubbing

[0209] In light of the temperatures and the use of hydrochloric acid, ideally all reaction tanks and vessels will be sealed under slightly negative pressure, and the resulting gaseous effluents will be purged via additional gas scrubbing stages such as packed columns. Depending on emission limits, the final scrubbing liquid may be either water or an alkaline solution. Sodium hydroxide and / or sodium thiosulfate may be added to the water in this step to complete the removal of HCl from the exhaust gases and to destroy any traces of chlorine gas that may have been generated in side reactions in the roaster.

[0210] Aspects of the present exposition are further illustrated by reference to the following non-limiting embodiments.

[0211] 1. A process for extracting magnesium or magnesium compounds from of a ferronickel slag charge comprising magnesium and silica compounds, the process comprising:

[0212] a grinding step to reduce the particle size distribution of the ferronickel slag feed; and

[0213] an acid leaching step after the grinding step, comprising:

[0214] leaching of the ferronickel slag load from the grinding stage in a container with hydrochloric acid at a concentration of 5 to 15% by weight of HCl to form a leached slurry,

[0215] controlling the concentration of hydrochloric acid during leaching by adding additional hydrochloric acid to the container to maintain the hydrochloric acid concentration at 5 to 15% by weight of HCl, and

[0216] obtaining a leached slurry from the container,

[0217] wherein the leached slurry comprises a liquid part and a solid residue, and wherein the liquid part comprises magnesium chloride.

[0218] 2. The process according to point 1, in which the control of the acid concentration hydrochloric acid during leaching includes the addition of hydrochloric acid additional in one or more batch additions of HCl or by a continuous supply of HCl.

[0219] 3. The process according to point 1 or point 2, wherein the slag charge of ferronickel also contains one or more of aluminium, calcium, chlorine, chromium, potassium, nickel, sulfur, or any combination thereof.

[0220] 4. The method according to any one of points 1 to 3, wherein the charge of Ferronickel slag contains one or more of the following: ferrosilite (FeSiO3), fayalite (Fe2SiO4), clinoenstatite (MgSiO3), fosterite (Mg2SiO4), and other complex iron materials.

[0221] 5. The process according to any one of points 1 to 4, in which the slag charge ferronickel contains Al2O3, Cr2O3, or one of their combinations.

[0222] 6. The process according to any one of points 1 to 5, in which the slag charge Ferronickel is produced from the smelting of nickel laterite.

[0223] 7. The process according to any one of points 1 to 6, in which the slag charge ferronickel comprises silica at concentrations of approximately 15 to 90% by weight.

[0224] 8. The process according to point 7, in which the ferronickel slag charge includes silica at concentrations of approximately 20 to 50% by weight.

[0225] 9. The process according to point 8, in which the ferronickel slag charge includes silica at concentrations of approximately 25% by weight.

[0226] 10. The process according to any one of points 1 to 9, in which the solid residue includes amorphous silica.

[0227] 11. The process according to point 10, wherein the solid residue comprises silica amorphous at a concentration of approximately 20 to 90% by weight.

[0228] 12. The process according to point 10 or 11, wherein the solid residue comprises amorphous silica at a concentration of approximately 30 to 60% by weight.

[0229] 13. The process according to any one of points 1 to 12, wherein, in the step In acid leaching, control of the hydrochloric acid concentration during leaching maintains the hydrochloric acid concentration at 8 to 12% by weight of HCl.

[0230] 14. The method according to any one of points 1 to 13, wherein, in the step In acid leaching, control of the hydrochloric acid concentration during leaching maintains the hydrochloric acid concentration between approximately 8% by weight and 12% by weight, or approximately 10% by weight of HCl.

[0231] 15. The process according to any one of points 1 to 14, wherein at least one part of the additional hydrochloric acid is recycled hydrochloric acid from a downstream manufacturing step.

[0232] 16. The process according to point 15, in which the recycled hydrochloric acid has a concentration of HCl greater than that of hydrochloric acid in the container.

[0233] 17. The process according to any one of points 1 to 16, in which, during the step In acid leaching, the slag load passes through multiple containers with hydrochloric acid to leach the slag load.

[0234] 18. The process according to point 17, wherein the concentration of HCl in each The container is controlled independently.

[0235] 19. The process according to any one of points 1 to 18, in which, during the step For acid leaching, the slag load has a total residence time for leaching of between 0.5 and 12 hours in the container(s).

[0236] 20. The process according to point 19, in which the total residence time for the Leaching takes between 0.5 and 8 hours in the container(s).

[0237] 21. The process according to point 19 or 20, in which the total residence time for the Leaching takes approximately 8 hours in the container(s).

[0238] 22. The process according to any one of points 1 to 21, wherein, in the step Acid leaching, the leaching of the ferronickel slag load with hydrochloric acid is carried out at a temperature between approximately 50 and 100°C.

[0239] 23. The process according to point 22, wherein, in the acid leaching step, the leaching of the ferronickel slag load with hydrochloric acid is carried out at a temperature of approximately 80°C.

[0240] 24. The method according to any one of points 1 to 23, wherein, in the step For acid leaching, the leaching of the ferronickel slag feedstock with hydrochloric acid is carried out at an initial liquid / solid ratio of 10 mL / g to 20 mL / g.

[0241] 25. The method according to any one of points 1 to 24, in which, during the step During grinding, the slag charge is ground to a P98 particle size of no more than 100 micrometers.

[0242] 26. The method according to any one of points 1 to 24, in which, during the step During grinding, the slag charge is ground to a P98 particle size of approximately 75 micrometers.

[0243] 27. The process according to any one of points 1 to 26, in which the containers are sealed under negative pressure.

[0244] 28. The process according to any one of points 1 to 27, further comprising:

[0245] a residue thickening step, in which the leached slurry is separated into an overflow stream and an underflow stream, in which the underflow stream comprises practically all of the solid residue;

[0246] an iron removal step, in which the overflow stream is treated so that the acids are neutralized within the overflow stream and so that an iron precipitate is separated from a stream of magnesium chloride produced;

[0247] a roasting step, in which the stream of magnesium chloride produced is heated to produce a magnesium oxide product and an acid by-product; and

[0248] an acid regeneration step, in which at least a portion of the by-product acid is absorbed into water to produce regenerated hydrochloric acid.

[0249] 29. The process according to point 28, in which the acid regeneration step includes washing the by-product acid in a Venturi washer with the produced magnesium chloride stream before the produced magnesium chloride stream is delivered to the roasting stage.

[0250] 30. The process according to point 28 or 29, in which the regenerated hydrochloric acid is recycled as additional hydrochloric acid in the acid leaching step.

[0251] 31. A leached slurry produced by the process of any one of points 1 to 27.

[0252] 32. A recycled acid produced by the process of any one of points 28 to 30.

[0253] In this application, adjectives such as left and right, up and down, hot and cold, first and second, and the like, may be used to distinguish one element or action from another without necessarily requiring or implying any such order or true relationship. Where the context permits, a reference to a component, integer, or step (or the like) should not be taken to be limited to a single such component, integer, or step, but could rather represent one or more such components, integers, or steps.

[0254] In this application, the terms "includes", "comprising", "includes", "including" or similar terms are intended to signify non-exclusive inclusion, so that a process, system or apparatus which includes a list of elements does not include only those elements, but may well include other unlisted elements.

[0255] In the present application, the expression "consisting essentially of" is intended to be considered in a non-exhaustive manner, so that a process, system or apparatus which essentially consists of a list of elements may include one or more elements in minor proportions, which are not included in the list of elements.

[0256] In this application, the expression "consisting of" means consisting solely of.

[0257] In this application, "virtually all" means "all or almost all" to take into account accidental impurities (e.g. less than 5% total impurities in a process stream).

[0258] In this application, the term "approximately" indicates that the stated value may vary within a margin of error foreseen by a person skilled in the art, rather than imposing a precise value. Typical margins of error are ±10% or ±5%. Therefore, for example, the expression "approximately 10" indicates that minor variations above and below 10, such as 9.9 and 10.1, are included.

[0259] In this application, when a range is specified, the outer limits of that range are included. For example, a range of 20 to 50 includes both 20 and 50 as well as the values ​​in between.

[0260] The above description concerning embodiments of this exposition is given for descriptive purposes to persons with ordinary knowledge of the technique concerned. It is not intended to be exhaustive or to limit the exposition to a single embodiment. As mentioned above, many alternatives and variants to this exposition will become obvious to a person skilled in the art from the teaching above. Therefore, although some alternative embodiments have been discussed specifically, other embodiments will become obvious or will be readily developed by persons with ordinary knowledge of the technique. This exposition is intended to encompass all the modifications, alternatives, and variants that have been discussed here, and other embodiments that fall within the spirit and scope of the above description.

Claims

Demands

1. A process for extracting magnesium or magnesium compounds from a ferronickel slag feed comprising magnesium and silica compounds, the process comprising: a grinding step to reduce the particle size distribution of the ferronickel slag feed;and an acid leaching step after the grinding step, comprising: leaching the ferronickel slag load from the grinding step into a vessel with hydrochloric acid at a concentration of 5 to 15 wt% HCl to form a leached slurry, controlling the hydrochloric acid concentration during leaching by adding additional hydrochloric acid to the vessel to maintain the hydrochloric acid concentration at 5 to 15 wt% HCl, and obtaining a leached slurry from the vessel, wherein the leached slurry comprises a liquid portion and a solid residue, and wherein the liquid portion comprises magnesium chloride.

2. A method according to claim 1, wherein the control of the hydrochloric acid concentration during leaching includes the addition of additional hydrochloric acid in one or more batch additions of HCl or by continuous feeding of HCl.

3. A process according to claim 1 or claim 2, wherein the ferronickel slag charge further contains one or more of aluminium, calcium, chlorine, chromium, potassium, nickel, sulfur, ferrosilite (FeSiO3), fayalite (Fe2SiO4), clinoenstatite (MgSiO3), fosterite (Mg2SiO4), other iron complex materials, Al2O3, Cr2O3, or any combination thereof.

4. A process according to any one of claims 1 to 3, wherein the ferronickel slag feedstock is produced from the smelting of nickel laterite.

5. A method according to any one of claims 1 to 4, wherein the ferronickel slag charge comprises silica at concentrations of about 15 to 90% by weight, preferably about 20 to 50% by weight, better still about 25% by weight.

6. A process according to any one of claims 1 to 5, wherein the solid residue comprises amorphous silica, preferably at a concentration of about 20 to 90 wt%, better still at a concentration of about 30 to 60 wt%.

7. A method according to any one of claims 1 to 6, wherein, in the acid leaching step, the control of the hydrochloric acid concentration during leaching maintains the hydrochloric acid concentration at 8 to 12 wt% of HCl, preferably at about 10 wt% of HCl.

8. A process according to any one of claims 1 to 7, wherein at least a portion of the additional hydrochloric acid is recycled hydrochloric acid from a downstream manufacturing step.

9. A process according to claim 8, wherein the recycled hydrochloric acid has an HCl concentration greater than that of the hydrochloric acid in the container.

10. A method according to any one of claims 1 to 9, wherein, during the acid leaching step, the slag feed passes through multiple containers with hydrochloric acid to leach the slag feed.

11. A method according to claim 10, wherein the concentration of HCl in each container is controlled independently.

12. A method according to any one of claims 1 to 11, wherein, during the acid leaching step, the slag charge has a total residence time for leaching of between 0.5 and 12 hours in the container(s), preferably between 0.5 and 8 hours in the container(s), better still about 8 hours in the container(s).

13. A process according to any one of claims 1 to 12, wherein, in the acid leaching step, the leaching of the ferronickel slag feedstock with hydrochloric acid is carried out at a temperature between about 50 and 100°C, preferably at a temperature of about 80°C.

14. A method according to any one of claims 1 to 13, wherein, in the acid leaching step, the leaching of the feedstock of ferronickel slag with hydrochloric acid is carried out at an initial liquid / solid ratio of 10 mL / g to 20 mL / g.

15. A method according to any one of claims 1 to 14, wherein, during the grinding step, the slag feed is ground to a P98 particle size of no more than 100 micrometers, preferably to a P98 particle size of about 75 micrometers.

16. A method according to any one of claims 1 to 15, wherein the container or containers are sealed under negative pressure.

17. A process according to any one of claims 1 to 16, further comprising: a residue thickening step, wherein the leached slurry is separated into an overflow stream and an underflow stream, wherein the underflow stream comprises practically all of the solid residue; an iron removal step, wherein the overflow stream is treated so that the acids are neutralized within the overflow stream and so that an iron precipitate is separated from a produced magnesium chloride stream; a roasting step, wherein the produced magnesium chloride stream is heated to produce a produced magnesium oxide and a by-product acid; and an acid regeneration step, wherein at least a portion of the by-product acid is absorbed into water to produce regenerated hydrochloric acid.

18. A method according to claim 17, wherein the acid regeneration step includes washing the by-product acid in a Venturi washer with the produced magnesium chloride stream before the produced magnesium chloride stream is delivered to the roasting step.

19. A process according to claim 17 or 18, wherein the regenerated hydrochloric acid is recycled as additional hydrochloric acid in the acid leaching step.

20. Leached slurry produced by the process according to any one of claims 1 to 16.

21. Recycled acid produced by the process according to any one of claims 17 to 19.

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