Extraction method

Abstract

The present invention refers to a method for the extraction of at least one metal from a low-silicate source material comprising said at least one metal, said method comprising: a) contacting said low-silicate source material with an acidic solvent comprising methanesulphonic acid (MSA) to form a first extraction mixture; b) maintaining the first extraction mixture at a temperature of between 1 and 160°C for a period of between 1 second and 24 hours; c) separating the first extraction mixture into a first solid fraction and a first liquid fraction; and d) recovering at least a first metal from the first liquid fraction; wherein said low-silicate source material comprises no more than 9% by weight silicate, measured as silica (SiO2).

Description

[0001] 95.177.174638 / 01 - 1 -

[0002] Extraction Method

[0003] Field of the Invention

[0004] The present invention relates to methods for extracting valuable and / or desirable materials from waste. In particular, the invention relates to methods for recovering metals from the waste material generated by industrial processes. Such waste material may be, for example, dust from electric arc furnaces with a low-silicate content.

[0005] Background to the Invention

[0006] Smelting and / or refining of metals typically generates large quantities of solid waste, including hazardous particulate material. An example of the solid waste material is dust generated from electric arc furnace processes, which are commonly used in the recycling of steel to produce new iron and steel products. This solid waste, usually contains metals, such as zinc, iron, lead and cadmium. These may have been the target metal of the original process, or may have been present as impurities in the metal, ore or other starting material. Such metals may be of significant value and / or may represent an environmental hazard if left unprocessed.

[0007] Generally, dust from electric arc furnaces (EAF dust I EAFD) is considered to be a hazardous waste material and poses significant health and environmental risks. It is desirable to recover metals from the EAF dust, which may be hazardous or which may be useful for various applications. For example, cadmium is a toxic material, particularly in its powdered form, and it is desirable to extract this material and dispose of it appropriately. Alternatively, metals like zinc may be valuable and present less of an environmental hazard. As a result, there is both an economic and environmental need to process low-silicate materials such as EAFD to extract desirable metals.

[0008] Typically, the process for recovering metals from EAFD involves direct reduction or smelting. However, such processes often consume large amounts of energy, and operate at temperatures higher than 1000°C, such as 1200 to 1500°C. The95.177.174638 / 01 -2 -

[0009] recovery of metals can be poor additionally from direct reduction and smelting processes. There remains therefore the need for a process for the recovery of metals from low-silicate waste material, such as EAF dust, which is economically viable and has a reduced carbon footprint (e.g. processes which require less energy).

[0010] In view of the above, it would be an evident benefit to provide a new method for the extraction of metals and / or minerals from low-silicate source materials such as EAFD. It would be a particular advantage if the method allowed for efficient processing, recycling of chemical processing materials and / or generation of valuable industrial material products. It would be a further advantage if the process could utilise mild conditions (e.g. without requiring high pressures and / or temperatures) and / or readily available, biodegradable and / or easily handled reagents in order to minimise the risk, cost and / or environmental impact of the process.

[0011] Brief Description of the Invention

[0012] Viewed from one aspect, the present invention refers to a method for the extraction of at least one metal from a low-silicate source material comprising said at least one metal, said method comprising:

[0013] a) contacting said low-silicate source material with an acidic solvent comprising methanesulphonic acid (MSA) to form a first extraction mixture;

[0014] b) maintaining the first extraction mixture at a temperature of between 1 and 160°C for a period of between 1 second and 24 hours;

[0015] c) separating the first extraction mixture into a first solid fraction and a first liquid fraction; and

[0016] d) recovering at least a first metal from the first liquid fraction;

[0017] wherein said low-silicate source material comprises no more than 9% by weight silicate, measured as silica (SiCh).

[0018] In a preferred embodiment, the low-silicate source material is a solid waste material, such as a product or by-product from an industrial process (e.g. dust from an electric arc furnace, quench dust and / or any other material formed during a smelting process).95.177.174638 / 01 - 3 -

[0019] In a preferred embodiment, the at least one metal comprises zinc (Zn) and / or cadmium (Cd).

[0020] Viewed from an alternative aspect, the present invention refers to an apparatus for the extraction of at least one metal from a source material comprising said at least one metal, said apparatus being configured:

[0021] i) to accept a solid low-silicate source material into a first vessel;

[0022] ii) to accept an acidic solvent comprising methanesulphonic acid into said first vessel to generate a first extraction mixture;

[0023] iii) to maintain said first extraction mixture in said first vessel at a temperature of between 1 and 120°C for a period of between 1 second and 24 hours; iv) to separate said first extraction mixture into a first solid fraction and a first liquid fraction; and

[0024] v) to recover at least a first metal from said first liquid fraction.

[0025] In a preferred embodiment, the apparatus is additionally configured to:

[0026] vi) regenerate at least a part of the MSA by addition of a mineral acid and recycle the thus-regenerated MSA to part ii).

[0027] Brief Description of Figures

[0028] Figure 1 is a flow diagram for the process of the present invention. Here “MSA Leach” is the first extraction mixture, which subsequently is separated into a first solid fraction and a first liquid fraction. At least one metal is recovered from the first liquid fraction, and preferably the regeneration of MSA occurs following the recovery of at least one metal.

[0029] Figure 2 is a flow diagram for the process of the present invention, wherein the at least one metal comprises zinc and cadmium. In this embodiment, cadmium is recovered from the first liquid fraction followed by the recovery of zinc from the same. Unwanted components are also precipitated from the first liquid fraction prior to the precipitation of cadmium. MSA is subsequently regenerated from the first liquid fraction which has been depleted of zinc (Zn barren solution). A further acidic95.177.174638 / 01 - 4 -

[0030] leach is additionally used to form a second extraction mixture (sulfuric acid leach) to enable further precipitation of cadmium resulting in a zinc-rich final filtrate.

[0031] Figure 3 is a flow diagram for the process of the present invention, wherein the at least one metal comprises zinc and cadmium. In this embodiment, zinc is recovered from the first liquid fraction. Unwanted components are also precipitated from the first liquid fraction prior to the precipitation of zinc. A further acidic leach is subsequently used to form a second extraction mixture (sulfuric acid leach) to enable precipitation of cadmium resulting in a zinc rich final filtrate.

[0032] Figure 4 is a graphical representation of the % extraction of metals (i.e. Zn, Cu and Si) against the residence time for bench scale leach tests. The leach here was undertaken over a residency time of 4 hours using MSA at 95°C. The leach was periodically sampled to generate the extraction rate curves illustrated in Figure 4.

[0033] Figure 5 is a graphical representation of the % extraction of metals (i.e. Zn, Cu and Si) against the residence time for bench scale leach tests, similar to Figure 4 except wherein here the leach was undertaken over a residency time of 2 hours using an acid mix of 4.4 parts MSA to 1 part sulfuric acid at 90 °C.

[0034] Figure 6 is an image of the extraction mixture (Figure 6a) and solid precipitate which has been subsequently separated from the extraction mixture (Figure 6b) for a cadmium precipitation test using zinc powder (see Example 2).

[0035] Figure 7 is an image of the solid precipitate (Figure 7a) which has been separated from an extraction mixture (Figure 7b) to leave a filtrate (Figure 7c) for the precipitation of a zinc-containing solid using a three-stage precipitation test with Na2S on the first liquid fraction after unwanted components have been removed (see Example 3).

[0036] Figure 8 is an image of the solid precipitate (Figure 8a) and the final filtrate (Figure 8b) for the precipitation of a zinc-containing solid using a three-stage precipitation test with Na2S on the first liquid fraction following on from the precipitation of cadmium from the same (see Example 3).95.177.174638 / 01 - 5 -

[0037] Figure 9 is an image of the second extraction mixture (Figure 9a) wherein the zinc-containing solid fraction is leached in sulfuric acid. The solid precipitate (Figure 9b) can be separated to leave a filtrate (Figure 9c). In this case, cadmium has been recovered from the first liquid fraction in a prior step (see Example 4).

[0038] Figure 10 is an image of the second extraction mixture (Figure 10a) wherein the zinc-containing solid fraction is leached in sulfuric acid and zinc dust has been subsequently added. The solid precipitate (Figure 9b) can be separated to leave a filtrate (Figure 9c). In this case, no cadmium has been recovered from the first liquid fraction in a prior step (see Example 4).

[0039] Detailed Description of the Invention

[0040] The present invention relates to methods for extracting at least one metal from a solid industrial waste material. In particular, the solid industrial waste material is a low-silicate source material. Preferably, the low-silicate source material (also referred to as “source material” herein) is a product (such as a by-product) from an industrial reaction, e.g. the dust from an electric arc furnace; quench dust; or any other material created during, for example, a smelting process. In certain cases, the low-silicate source material is a hazardous material.

[0041] The solid industrial waste material, by definition, does not include natural minerals or resources (e.g. ores).

[0042] The method of the present invention provides for extraction of at least one metal from a low-silicate source material comprising said at least one metal. Metals which are relevant for extraction in the present context may be any metal which is of commercial use / value and / or presents an environmental hazard. Typical metals in low silicate materials which may be extracted by the method of the present invention in various embodiments include lead (Pb), zinc (Zn), cadmium (Cd), chromium (Cr), aluminium (Al), gallium (Ga), iron (Fe), tin (Sn), antimony (Sb), copper (Cu), silver (Ag), gold (Au), arsenic (As), tantalum (Ta), titanium (Ti), niobium (Nb) rare earth metals and any combination thereof. Each metal may be extracted separately or several metals may be extracted together either for95.177.174638 / 01 - 6 -

[0043] combined use or for further separation. For example, Cu, Ag and Au may be extracted together for further processing and / or separation.

[0044] Generally, the “at least one metal” referred to herein will be a desired metal or metal-containing product. This may be desirable from a commercial point of view or desirable in that it is desired to remove the metal from waste materials for environmental reasons. Preferred examples of the “at least one metal” for extraction include Cd, Ag, Pb and Zn, especially Zn. In a preferred embodiment, the source material comprises at least 1 wt% zinc. The source material preferably comprises 5% or more by weight of Zn, such as 10 wt% or more, 15 wt% or more or 20 wt% or more. Preferred ranges for the zinc content of the source material is 5 to 75 wt%, such as 10 to 60 wt% or 15 to 50 wt%, especially 20 to 35 wt%.

[0045] In one embodiment, the source material comprises cadmium, preferably cadmium and zinc. These elements are preferably present at an amount indicated in any compatible embodiment herein.

[0046] In one preferred embodiment, the method of the invention will comprise extraction of at least Cd and Zn. It is preferred that such metals are separated individually and not mixed with a significant amount of other metals. The extracted metals, salts, oxides etc will be of sufficient purity to be of commercial value, preferably of the purity necessary for optimal marketability. Suitable purity will depend upon the metal extracted and the target market and may, for example, be at least 40%. This is described in greater detail herein below.

[0047] Certain metals and / or non-metals may be extracted as waste or by-product material and thus need not be separated with any specific level of purity. Silica and / or silicates may be a waste product of the present methods, as may be aluminium salts and / or iron salts and / or lead salts (e.g. lead oxides).

[0048] Alternatively, the silica and / or silicates may be a useful by-product of the present methods. For example, silica and / or silicates are particularly useful as an additive in the cement industry. Typically, silica and / or silicates which are used as an additive in the cement industry are used in the form of a gel or powder. Lead and iron oxides are also useful in various applications and may be processed further.95.177.174638 / 01 - 7 -

[0049] The term “unwanted components” as referred to herein, may therefore refer to byproducts of the reaction (especially non-metal by-products), although these may be useful for certain applications.

[0050] Iron may be recovered as a desired product (e.g. at concentrations acceptable for steelmaking, especially for primary metal smelters). Alternatively, or in addition, iron may be present in such levels and oxidation states that some iron is lost with the waste materials without significant detriment to the process. Iron may thus be a desired product, a waste product or both.

[0051] The methods of the present invention include step a) of contacting a source material with an acidic solvent comprising methanesulphonic acid (MSA) to form a first extraction mixture. Such contacting will typically take place in a first vessel. In certain cases, prior to contacting the low-silicate source material with an acidic solvent comprising MSA, the low-silicate source material will be washed with water to remove elements such as fluorine or chlorine which could be detrimental to downstream processes such as electrowinning / electroplating.

[0052] Therefore, in certain embodiments, step a) may comprise the following two stages: a-1) washing the low-silicate source material with water; and

[0053] a-2) contacting said washed low-silicate source material with an acidic solvent comprising methanesulphonic acid (MSA) to form a first extraction mixture.

[0054] The low-silicate source material will typically be washed with water in a preextraction vessel, and the washed low-silicate source material will then be transferred to the first vessel.

[0055] Prior to contact with the acidic solvent, the low-silicate source material may be in any form but will preferably be in the form of solid particles. Such particles may be or any appropriate size that allows the metals to be taken up into solution.

[0056] Generally, this will be by exposure of the metals at the surface of the particles and thus the desired size may depend on the nature of the source material being treated, the metals to be extracted and the size of the grains of metal or metal compounds in the source material. In some cases, the material is in the form of solid particles wherein the weight average particle size is 200 pm or less (e.g. 0.05 to 100 pm), such as 50 pm or less, especially 25 pm or less, 10 pm or less, 2 pm or95.177.174638 / 01 - 8 -

[0057] less, preferably 1 pm or less. The “particle size” as used herein is the average size of the largest dimension, where technically meaningful. The weight average particle size may be measured by any suitable technique in the art, such as sieve analysis, microscopy or light scattering techniques such as laser diffraction or dynamic light scattering.

[0058] A preferred low-silicate source material is a product from an industrial reaction / process, e.g. a waste material or by-product. The low-silicate source material may be a product from a smelting process. A particularly preferred low-silicate source material is dust, especially an electric arc furnace dust or a quench dust. Dust as described herein refers to a solid particle where the average size in the largest dimension is as specified herein (such as 200 pm or less, or 25 pm, or 1 pm or less).

[0059] In a preferred embodiment, the low-silicate source matter is not an electronic waste product. Electronic waste products, in the context of the present application refers to any electronic devices or components which form part of an electronic system, such as batteries, semiconductors, electronic components, interconnects and / or circuit boards. In one particular embodiment, the low-silicate source matter does not comprise batteries or battery components. In a further embodiment, the low-silicate source matter does not comprise electronic circuit boards (with or without components attached thereto).

[0060] Suitable particles may be formed by physical treatment of the source material, which itself may be a solid of any physical size and shape. Alternatively, the source material may be in the form of solid particles without any physical treatment. The solid particles for use in any of the method of the invention may be, for example, a weight average of 0.1 pm to 1 cm in largest dimension, such as 50 pm to 5 mm. In one embodiment the solid particles for use in any method of the invention have a weighted size average of 0.1 pm to 2 mm (e.g. 0.1 pm to 50 pm), 0.5 pm to 1 mm,1 pm to 500 pm. It is especially preferred if the weighted average particles size of the solid particles for use in any method of the invention is in the range of 0.05 to 10 pm, such as 0.1 to 0.9 pm or 0.5 to 1 pm, preferably 0.6 to 0.8 pm. Any suitable method, such as grinding, crushing, milling, etc., may be used to reduce larger pieces of source material to an appropriate size. Separation methods such as95.177.174638 / 01 - 9 -

[0061] screening and / or cyclonic separation may be used to separate material of a desired (small) size from larger remaining particles, which may then be re-sized (e.g. reground and re-screened). Where the material is finely divided dust, such material may be aggregated into larger particles, rather than ground into smaller particles, in order to reduce the hazard of airborne material.

[0062] The acidic solution is contacted with the low-silicate source material in any suitable amount. Generally, around 10 to 600g of source material will be used per litre of acidic solution. This may be 10 to 200 g / L or 15 to 150 g / L. In an alternative embodiment, 200 to 600 g / L, such as 300 to 550 or 350 to 500 g / L may be suitable.

[0063] The first extraction mixture may be maintained at an elevated temperature, optionally with agitation, in order to promote extraction of certain metals (e.g. metals other than lead) into the solution phase. In step b) the extraction material may be maintained at a temperature of 1 to 160°C, such as 1 to 120°C, preferably 20 to 160°C, preferably 20 to 120°C. This will preferably be above around 50°C, preferably above around 80°C (e.g. 80°C to 100°C) more preferably above around 90°C (e.g. 90 to 100°C). Where appropriate, pressurised reaction vessels may be used to allow temperatures to be elevated above the temperature at which the reaction mixture would boil at atmospheric pressure. In an alternative embodiment, all steps described herein may be conducted at or around atmospheric pressure (e.g. 1±0.1 Atm).

[0064] The contact time in step b) will be sufficient for a desired proportion of the at least one metal to be extracted from the source material and may depend upon the temperature and the material particle size. Suitable contact times may be 1 second to 24 hours, preferably 10 minutes to 24 hours, preferably 1 to 12 hours or 30 minutes to 6 hours, such as 1 to 5 hours, 2 to 4 hours or 3 to 5 hours. The residence / contact times indicated herein for any step or embodiment may be the average residence times for material undergoing that step. This applies particularly for continuous process implementations where actual residence times for any particular particle or sample may be variable and / or difficult to determine.

[0065] In a preferred embodiment, step b) will involve a continuous leaching process. A continuous process (or continuous leach) generally is used to generate a sufficient95.177.174638 / 01 - 10 -

[0066] bulk quality of the first extraction mixture. The continuous leach typically involves the transfer of the first extraction mixture through a cascade series of reaction vessels which are pre-heated to the desired temperature.

[0067] In some preferred embodiments, during step a) and / or b) the pH of the first extraction mixture and / or acidic solvent remains constant, or varies within less than 10%, such as less than 5%, preferably less than 1%. For example, in some cases it is preferred that no pH modifier is added to the acidic solvent and / or first extraction mixture in step a) and / or b).

[0068] Separation of the first extraction mixture into a first solid fraction and a first liquid fraction at step c) may be by any suitable solid / liquid separation method. Filtration through suitable screens and / or filters is one suitable embodiment, as are methods such as thickeners or cyclonic separation. Combinations of methods can evidently be used. Similar methods may be used for any solid / liquid separation step described herein.

[0069] Step d), relating to the extraction (e.g. recovery) of at least a first metal from the first liquid fraction may take the form of many individual steps, some of which are described herein, with many also being known to those of skill in the art.

[0070] The first liquid fraction, as referred to herein, may alternatively be referred to as the leach filtrate (or first leach filtrate). Typically, the first liquid fraction may comprise metals such as zinc, cadmium and iron.

[0071] Typically, step d) comprises adjusting the pH of the solution through the addition of one or more salts (e.g. soluble salts) or reagents. It is generally preferred that the pH of the solution is increased. Typically, the addition of acidic salts and acidic reagents is avoided at this step. Basic and / or neutral salts and reagents are thus preferred. Generally accepted salts and reagents may be selected from sulphide reagents (e.g. Na2S, K2S, H2S), wherein Na2S is especially preferred.

[0072] For the extraction of some metals, the addition of metal salts such as alkali metal or alkaline earth metals salts is preferred. Examples of suitable alkali or alkaline earth metal salts are calcium carbonate, sodium hydroxide, calcium hydroxide, potassium95.177.174638 / 01 - 11 -

[0073] hydroxide, and especially calcium carbonate and / or calcium hydroxide. Calcium salts are desirable, as described herein, because this can result in generation of valuable calcium sulphate (gypsum) during the regeneration step (see below).

[0074] For the extraction of some metals, step d) may involve a redox reaction, such as an oxidation reaction or a reduction reaction. Therefore, step d) may comprise the addition of an oxidising agent and / or a reducing agent, particularly a reducing agent. In certain cases, the oxidising and / or reducing agent may be in the form of elemental metal particles, such as zinc dust. The use of zinc dust in step d) is typically preferred when the at least one metal includes cadmium.

[0075] In certain cases, it is preferred that steps a) to d) do not involve electrolysis (e.g. do not include electrolysis for the extraction of at least a first metal from a low-silicate source material). The steps a) to d) generally involve solubilisation and precipitation techniques. In a preferred embodiment, the recovery of the first metal does not include any electrolysis step. In one embodiment, no electrolysis is utilised in any step of the present method. In an alternative embodiment, the present invention may utilise electrolysis for recovery of zinc, e.g. through electrowinning.

[0076] The nature of the low-silicate source material is described herein below but will typically contain less than 10% (e.g. 0% to 10%) by weight of silicate, measured as silica (SiCh). The low-silicate source material of the invention generally comprises 9 wt% or less of silicate, preferably 7 wt% or less, especially 5.0 wt% or less.

[0077] The low-silicate source material is preferably EAFD comprising zinc (5-35%), lead (0.2-3%), sulphur (0.1-2%), carbon (1-9%), and silica (2-9%). Inclusions of manganese, calcium, magnesium may fluctuate within 1-5%; while traces of nickel, chromium, copper, titanium, aluminium preferably do not exceed 1%.

[0078] In some cases, the low-silicate source material comprises 50 wt% or less of zinc, such as 40 wt% or less, such as 10 to 50 wt% or 15 to 40 wt%.95.177.174638 / 01 - 12 -

[0079] Typically, the source material comprises less than 50 wt% lead, such as less than 40 wt%, especially less than 35 wt%. In some cases, the lead content of the source material is less than 10 wt%, such as less than 5 wt%, or less than 3 wt%.

[0080] The low-silicate source material may also contain iron. In one embodiment, the source material may also be rich in iron. The low-silicate source material may contain 10 to 50% or 20 to 50% by weight of iron. In one embodiment, there may be a high level of iron, such as 30 to 42% or 35 to 40% by weight of iron (measured as elemental iron). In an alternative embodiment, there may be a lower amount of iron, such as 10 to 34% or 15 to 28% by weight of iron (measured as elemental iron).

[0081] In some embodiments it is preferred that the source material is free from, or substantially free from indium (In) and / or tin (Sn). It may be preferred that the source material comprises less than 10 wt% In and / or Sn, such as less than 5 wt%, less than 1 wt% or less than 0.5 wt%. In one embodiment, the combined level of In and Sn is less than 10 wt%, such as less than 5 wt%, less than 1 wt% or less than 0.5 wt%

[0082] In some embodiments it is preferred that the source material is free from, or substantially free from lithium (Li) and / or cobalt (Co) and / or nickel (Ni). It may be preferred that the source material comprises less than 10 wt% Li and / or Co and / or Ni, such as less than 5 wt%, less than 1 wt% or less than 0.5 wt%. In one embodiment, the combined level of Li, Co and Ni is less than 10 wt%, such as less than 5 wt%, less than 1 wt% or less than 0.5 wt%

[0083] The acidic solution used in all of the various embodiments of the present invention comprises methanesulphonic acid (MSA). Suitable levels of MSA in the acidic solution will generally be around 50 to 500 g / L, preferably around 65 to 200 g / L, such as 80 to 150 g / L. A level of around 90 to 120g / L has been found to work effectively. The acid solvent used in all various embodiments of the present invention typically has a strength in the range of 0.5 to 75 wt%, preferably 5 to 50 wt%, especially 10 to 25 wt%.95.177.174638 / 01 - 13 -

[0084] The total amount of acid present in the acidic solution may be made up from a mixture of MSA and sulphuric acid. Alternatively, the acidic solution may consist of MSA. In certain cases, the acidic solution may comprise acetic acid and / or ammonium acetate mixed with MSA. In one embodiment, the total weight of acid in the acidic solution may thus be around 60 to 500 g / L, preferably around 80 to 200 g / L, such as 100 to 150 g / L. In various embodiments, the total amount of acid may be 80 to 300g / L, 120 to 200g / L, 150 to 25 g / L, 100 to 140g / L or 80 to 170 g / L.

[0085] It is generally preferred that the acidic solution comprises both methanesulphonic acid (MSA) and sulphuric acid (H2SO4). This may be at any suitable ratio by weight (including those described herein), such as between 15:1 to 1:15 or 10:1 and 1:10 MSA to sulphuric acid (e.g. 10:1 to 1:1 or 5:1 to 2:1 MSA to sulphuric acid). It is generally preferred if the amount of MSA is greater than the amount of sulphuric acid, for MSA / sulphuric acid mixture. This may avoid certain issues with, for example, gelling (e.g. gelling of silicates).

[0086] It is preferred if the pH of the first extraction mixture is in the range of 0.1 to 5, such as 0.2 to 3, preferably 0.5 to 2.0, especially 1.4 to 1.6.

[0087] In some preferred embodiments, during step a) and / or b) the pH of the first extraction mixture and / or acidic solvent remains constant, or varies within less than 10%, such as less than 5%, preferably less than 1%. For example, in some cases it is preferred that no pH modifier is added to the acidic solvent and / or first extraction mixture in step a) and / or b).

[0088] The methanesulphonic acid used in the acidic solution (e.g. in step a)) of the present invention may be gradually neutralised during the separation steps leading to the recovery of at least one metal from the first liquid fraction. In one embodiment, the MSA may be regenerated and thus re-used following such extraction steps. The methods of the present invention may thus include:

[0089] z) regenerating the methanesulphonic acid following extraction of at least a first metal.95.177.174638 / 01 - 14 -

[0090] Such regeneration will typically be by means of adding a strong acid component such as a mineral acid. In one embodiment, the MSA is regenerated by addition of sulphuric acid, such as at least a 1 :1 mole ratio of sulphuric acid. The regenerated MSA may then form at least one component of the acidic solution to be used in future iterations of step a). By such a method, the MSA is recycled, reducing waste and reducing the cost of the process and of the resulting waste-handling. It is preferable that at least 50% (e.g. 50 to 99%) by weight of the MSA may be regenerated and recycled to step a). This will preferably be at least 60% or at least 70%, more preferably at least 75% (e.g. at least 80%).

[0091] In certain cases when the acidic solution comprises both MSA and H2SO4, MSA may be regenerated by the further addition of sulphuric acid. When MSA is regenerated from a solution comprising both MSA and H2SO4, a further addition of H2SO4 is added so the ratio of MSA / H2SO4, in the acid solution is an appropriate ratio (e.g. as described herein such as 1:1).

[0092] The method for the extraction of at least one metal from a low-silicate source material may therefore be a cyclic method in which at least a part of the MSA is regenerated, wherein the regenerated MSA is returned to step a) of the process as described herein and may be contacted with a further portion of source material. The amount of MSA regenerated may be, for example 10 to 90% of the MSA added at step a), such as 20 to 80% or 30 to 70%.

[0093] Regeneration of the MSA is typically carried out using sulphuric acid. This is advantageous for several reasons. Firstly, it is a stronger acid than MSA and thus allows regeneration of the MSA. It is also readily available with established handling methods etc. Additionally, the use of sulphuric acid for acid regeneration has a considerable advantage where at least one calcium salt is used in one or more pH control steps during the process (see also below). This is because the use of acidification with sulphuric acid results in precipitation of at least some of the calcium out of the regeneration solution in the form of insoluble calcium sulphate, which can be removed by any appropriate solid / liquid separation method (e.g. filtering, cyclonic separation etc). Calcium sulphate (also known as gypsum) is a valuable product for use in plaster and plaster products such as plasterboard (drywall). In one embodiment, hydrated calcium sulphate of at least 90% purity95.177.174638 / 01 - 15 -

[0094] (e.g. 90 to 99.9% purity) is generated at the regeneration step and separated from the regenerated methanesulphonic acid solution.

[0095] A suitable amount of sulphuric acid may be present in the acidic solution by using excess sulphuric acid when regenerating the MSA. Thus, the regeneration step z) may utilise a 10 to 100% excess of sulphuric acid, and typically 20 to 50% excess. In one embodiment, an amount of 10 to 80g / L of sulphuric acid is added at the regeneration step, preferably 30 to 50g / L. In one embodiment, around 10 to 50% of the total weight of acid in the acidic solution is added as sulphuric acid in the regeneration step. This may be, for example 25 to 40% or 30 to 38% of the total acidity. Thus, for example, where the desired total weight of acid is 120g / L, around 30 to 48g / L or sulphuric acid may be added at the regeneration step, amounting to 25 to 40% of the total.

[0096] In one embodiment, the low-silicate source material comprises lead.

[0097] Correspondingly, the at least one metal may comprise lead (Pb). Lead may be present in the source material at an amount of 0 to 20% by weight, such as 0.1 to 10% or 1 to 5% by weight (measured as elemental Pb). An example lead content may be 0.1 to 3% by weight.

[0098] In some cases, lead may be extracted from the first solid fraction. In order to recover lead from the first solid fraction, this may be treated by any appropriate method. Suitable methods include the steps of:

[0099] t) contacting the first solid fraction with an aqueous solution whereby to give an aqueous extraction mixture comprising dissolved lead;

[0100] u) separating said aqueous extraction mixture into a lead-depleted solid fraction and a lead-containing liquid fraction; and

[0101] v) precipitating lead sulphide from said lead-containing liquid fraction.

[0102] The aqueous solution may be any effective solution, but will preferably be a salt solution, such as a solution of NaCI (brine). Suitable concentrations of brine may be around 75 to 300 g / L, preferably around 100 to 200g / L such as 130 to 170 g / L. Step t) may be carried out at any effective temperature but generally a temperature of 20 to 40’C may be used. The amount of aqueous solution may be any effective amount but will typically be around 1 to 500 g of solid per litre of aqueous solution.95.177.174638 / 01 - 16 -

[0103] This may vary depending upon the scale and the equipment used and so may be, for example, 1 to 20 g / L for lower concentrations or 100 to 500 g / L for large scale production.

[0104] The separation of the second extraction mixture (step u)) may be by any appropriate method, such as those described herein or known in the art.

[0105] The precipitation of lead sulphide in step v) may be under any appropriate conditions. A typical method may include addition of a gaseous sulphide (e.g. H2S) or a soluble sulphide such as Na2S or K2S. Addition of sodium sulphide is preferred. The sulphide may be added in any effective amount but will generally be added until the pH of the second liquid fraction reaches pH 6 to 8, preferably pH 6.5 to 7.5 (e.g. 6.9 to 7.1).

[0106] In one embodiment, at least 70% (e.g. 70 to 99%) of the lead present in the high-silicate slag material is recovered in the lead extraction steps (e.g. steps t) u) and v)). This will preferably be at least 75% or at least 80% by weight.

[0107] In one embodiment, the amount of lead in the lead salts (e.g. PbS) recovered in the lead extraction steps (e.g. steps t), u) and v)) will be at least 40% or at least 50% (e.g. 40 to 90% or 50 to 90%) based on elemental lead content. This will preferably be at least 60% or at least 65%, more preferably at least 70%.

[0108] In one embodiment, copper (Cu) may be recovered from the first solid fraction. Such extraction methods are known in the art and any suitable method may be used. Suitable methods include acid, Fe2(SC>4)3 or H2O2 leaching methods for copper.

[0109] In one embodiment, the at least one metal may comprise zinc (Zn). Zinc is a widely used metal across various applications, such as batteries, anti-corrosion agents, dietary supplements and catalysts. Zinc will typically be recovered from the first liquid fraction, optionally following a clean-up step (see below). Zinc will generally be recovered by precipitation from the first liquid fraction (or from the cleaned-up liquid fraction) by:

[0110] g) precipitation of at least one zinc salt from the first liquid fraction; and95.177.174638 / 01 - 17 -

[0111] h) separation of said precipitated zinc salt from the first liquid fraction to give a zinc-containing solid fraction and a zinc-depleted liquid fraction.

[0112] Since precipitation and separation may not recover all of the zinc from the liquid fraction, the zinc-depleted liquid fraction may be re-extracted for zinc and steps g) and h) repeated as necessary. Thus the process may include:

[0113] i) returning said zinc-depleted liquid fraction to steps g) and h) at least one additional time (e.g. 1 to 7 times, preferably 4 to 6 times or ca. 5 times) to increase the amount of precipitated zinc salt and to generate a zinc-barren solution.

[0114] In an alternative embodiment, steps g) and h) may represent electrowinning and separation steps to remove zinc from the liquid fraction (which may evidently be repeated as needed). In one embodiment, separation of zinc from the first liquid fraction is the only electrolysis step in the method.

[0115] Therefore, step d) of the method, that is recovering at least a first metal from the first liquid fraction, may include steps g), h) and optionally i) when the at least one metal is zinc.

[0116] Typically 1-4 repetitions (to give 2-5 total occurrences) of steps g) and h) may be employed. A total of 5 zinc precipitation and separation steps (g) and h)) are preferred.

[0117] Zinc precipitation may be brought about by any appropriate means. In particular, addition of a reagent or soluble salt which generates an insoluble (or sparingly soluble) zinc salt may be used. Typical reagents include sulphides such as H2S, Na2S or K2S. Na2S is preferred.

[0118] Typically, the precipitation of at least one zinc-containing salt from the first liquid fraction involves two stages: g-1) the addition of an acid solution to the first liquid fraction (especially if the pH of this first liquid fraction was previously increased (e.g. in step e))); followed by g-2) the addition of a soluble salt or reagent. Generally, it is preferred if g-2) is repeated at least once.95.177.174638 / 01 - 18 -

[0119] The acid solution in step g-1) preferably comprises MSA. Step g-1) typically comprises the addition of MSA to achieve a pH of around 2.0. MSA which is suitable for step g-1) is that described for any aspect reported herein. Typically, step g-1) involves the addition of an aqueous solution of MSA, such as at a concentration in the range of 1-20% (w / w) MSA, such as 1-10% (w / w), especially 2-5% (w / w). In certain cases, step g-1) may involve the addition of neat MSA or MSA at concentrations of 70%, or lower. The contact time for step g-1) is not particularly limited, but may be in the range of 1 second to 24 hours, such as 1 minute to 6 hours. Typically, the contact time for step g-i) is in the range of 5 mins to 1 hour, especially 10 to 30 minutes. The contact time as referred to herein for any aspect of the invention is the time in which the reagents are mixed prior to commencing the next stage in the method.

[0120] Step g-2) typically comprises the addition of a metal salt, such as Na2S to achieve a pH of around 4.0. In a preferred embodiment, a metal salt of concentration in the range of 1 to 20% (w / w) is added, such as in the range of 4 to 15% (w / w). In a particularly preferred embodiment, in step g-2) a metal salt (e.g. Na2S) is added at a concentration of 1 to 20% (w / w) and then step g-2) is repeated, for example as step g-3). In some cases when step g-2) is repeated, then a second addition of metal salt in step g-3) is at a higher concentration than the initial amount in step g-2). The contact time for step g-2) is not particularly limited, but may be in the range of 1 second to 24 hours, such as 1 second to 6 hours. Typically, the contact time for step g-2) is in the range of 5 mins to 1 hour, especially 15 to 45 minutes.

[0121] The zinc-depleted liquid fraction (or zinc barren fraction) as described in relation to any aspect herein may be used in step z), i.e. to regenerate the MSA following the extraction of at least a first metal. The (w / w) concentration of the MSA in step g-1) and the concentration of metal salt in step g-2) refers to the concentration with respect to the first liquid fraction or the reaction mixture.

[0122] The purity of the zinc salt(s) recovered may be in the range 25 to 67% or 25 to 70% by weight of elemental zinc (ZnS will be up to 67% zinc while ZnO and mixtures may be higher). This will preferably be at least 30% by weight zinc or at least 40% (e.g. around 40 to 60%) by weight elemental zinc content. More preferably at least 45%.95.177.174638 / 01 - 19 -

[0123] Where zinc is extracted by electrowinning, this may be in the form of metallic zinc and thus may be of higher purity (e.g. 70 to 100% or 85 to 95%).

[0124] It will be preferable that the zinc extract does not contain large amounts of contaminant metals. In one example embodiment, the zinc salt(s) recovered contain no more than 7% by weight of lead (e.g. 0 to 5% or 0 to 3% or 2 to 5%). In a further embodiment, the zinc salt(s) recovered contain no more than 18% by weight of iron (e.g. 0 to 15% or 5 to 15%). In a further embodiment, the zinc salt(s) recovered contain no more than 3% by weight of copper (e.g. 0 to 3% or 0.5 to 2% or 0.2 to 2%). In a further embodiment, the zinc salt(s) recovered contain no more than 2500ppm by weight of cadmium (e.g. 0 to 2000ppm or 0 to 1000ppm or 100 to 2000ppm). Other materials may be present in small quantities, such as silver (e.g.

[0125] 20-50 g / t) or gold (e.g.2-5g / t). These levels are disclosed herein with respect to the zinc product but all such levels may be appropriate with other products indicated herein, where technically viable.

[0126] In one embodiment, at least 50% (e.g. 50 to 95%) of the zinc present in the low-silicate source material is recovered at the zinc extraction stage (e.g. steps h), i) and optionally k)). This will preferably be at least 60% or at least 65%.

[0127] In certain cases, the zinc-containing solid fraction from step h) may be further purified from other contaminate metals, such as cadmium. The method for the extraction of at least one metal from a low-silicate source material comprising said at least one metal, may additionally comprise the following steps when the metal is zinc:

[0128] j) contacting the zinc-containing solid fraction with a second acid solution to form a second extraction mixture;

[0129] k) precipitating at least one cadmium-containing solid from the second extraction mixture; and

[0130] l) separating the cadmium-containing solid from the second extraction mixture to give a cadmium-containing solid fraction and a second liquid fraction.

[0131] Therefore, the method as described in any aspect herein may further comprise steps j), k) and I) when the at least one metal includes zinc and / or cadmium.95.177.174638 / 01 - 20 -

[0132] The second acid solution may comprise or consist of sulfuric acid. In a preferred embodiment the second acid solution comprises an aqueous solution of sulfuric acid. The concentration of the sulfuric acid is preferably in the range of 5 to 50% (w / w), such as 5 to 20% (w / w), especially 7 to 12% (w / w). The concentration (w / w) referred to here is the concentration of the sulfuric acid with respect to the second extraction mixture. The contact time for step j) is not particularly limited and may be in the range of 1 second to 24 hours. Generally, the contact time is 1 hour or more, such as 1 to 12 hours, such as 5 to 1-0 hours or 6 to 8 hours. The temperature for step j) is not particularly limited, and may be in the range of 1 to 120°C, such as 20 to 100°C. Generally, it is preferred if the temperature for step j) is 50°C or greater, such as 80°C or greater, e.g. 85 to 95°C.

[0133] Step k) preferably comprises the addition of an oxidising and / or reducing agent to precipitate the cadmium-containing solid from the second extraction mixture. In a preferred embodiment, the oxidising and / or reducing agent is a metal, such as zinc dust. When the oxidising or reducing agent is added to the second extraction mixture, preferably the temperature is lowered to 50°C or less such as 20 to 40°C or 25 to 35°C. In step k) the contact time is not particularly limited, but preferably is 5 minutes or more, such as 15 to 45 minutes. For step I), the separation method may be any separation method referred to herein for any aspect of the invention.

[0134] The zinc may be extracted from the second liquid fraction by any suitable method, including those discussed herein for extracting zinc in any compatible embodiment. The zinc so-extracted will preferably have a purity in line with the purities discussed herein for zinc in any compatible embodiment. It is generally preferred is zinc is extracted from the second liquid fraction through electrowinning / electroplating.

[0135] In one embodiment, separation of zinc from the first and / or second liquid fraction is the only electrolysis step in the method. In one embodiment, separation of zinc from the second liquid fraction is the only electrolysis step in the method.

[0136] At any stage in the process, particularly after separation of the first solid fraction from the first liquid fraction, liquid components may be subject to a “clean-up” step. This will preferably be before recovery of any of the “at least one metal” which is desired to be extracted from the liquid component. For example, this may take95.177.174638 / 01 - 21 -

[0137] place after the separation step c) but before metal recovery step d) (which may itself be recovery of zinc by steps g) and h) and optionally steps i) to I)).

[0138] A clean-up step may be carried out by:

[0139] e) precipitation of unwanted components from said first liquid fraction by means of increasing pH; and

[0140] f) separation of solid unwanted components precipitated in step e) from said first liquid fraction.

[0141] Unwanted components in this context will typically include silicon compounds such as silica / silicates and may include aluminium salts. Although iron salts and / or lead salts may also be precipitated to a certain extent in step e), these are typically not unwanted materials. However, it may not be desirable and / or practical to avoid precipitation of a certain amount of iron and / or lead during the clean-up step.

[0142] In a preferred embodiment, 50 to 99.99% of the silicon and / or aluminium is removed by clean-up steps e) and f). This will preferably be at least 95%, at least 98% or at least 99%. Such steps may evidently be repeated if necessary or desirable.

[0143] In one preferred embodiment, the pH is adjusted during at least one step by means of a calcium salt. Suitable calcium salts include quick lime (calcium oxide), slaked lime (calcium hydroxide) and / or calcium carbonate.

[0144] The means of increasing pH in step e) typically involves the addition of one or more salt or reagent as described herein. In some cases, the means of increasing pH involves the addition of a salt, such as an alkaline earth metal salt, especially a calcium salt. Such calcium salts include quick lime (calcium oxide), slaked lime (calcium hydroxide) and / or calcium carbonate. It is especially preferred if the calcium salt is calcium carbonate. The concentration of the one or more salt or reagent is preferably in the range of 5 to 50% (w / w), such as 5 to 20% (w / w), especially 7 to 12% (w / w). The concentration (w / w) of the one or more salt or reagent here refers to the concentration with respect to the first liquid fraction or the reaction mixture.95.177.174638 / 01 - 22 -

[0145] The pH is usually increased to a value of 2.0 to 6.0, such as 3.0 to 5.0, e.g. around 4.5. In certain embodiments, step e) is repeated. In certain embodiments therefore, step e) comprises step e-1) the addition of one or more salt or reagent to the first liquid fraction to obtain a solution with a pH of 2.5 to 4.0; and step e-2) the addition of one or more salt of reagent to the first liquid fraction to obtain a solution with a pH of 4.1 to 5.0.

[0146] The temperature is not particularly limited for step e), but typically is in the range of 1 to 120°C, such as 20 to 100°C. It is preferred if the temperature is in the range of 15 to 60°C, such as 20 to 35°C. The contact time for step e) is not particularly limited, but may be in the range of 1 second to 24 hours. Generally, the contact time is 15 minutes, such as 30 minutes to 3 hours or 1-2 hours.

[0147] As mentioned above, although iron salts such as iron oxides may be precipitated from step e) as an unwanted component, they are typically quite useful compounds and thus are not general considered to be unwanted materials. Therefore, the at least one metal in the method across all aspects of the invention may comprise iron.

[0148] The extraction of iron can be achieved effectively through the addition of an oxidising agent such as hydrogen peroxide (H2O2) to the first liquid fraction.

[0149] Alternatively, the first liquid fraction may be aerated to enable the extraction of iron oxide. Aeration as defined herein for any aspect of the invention refers to passing compressed air through the solution.

[0150] In certain cases, the unwanted components which precipitate from the first liquid fraction by means of increasing pH can be washed. In a further embodiment, the clean-up step may comprise the following additional steps:

[0151] q) contacting the solid unwanted components from step f) with a washing solution;

[0152] r) separating the solid unwanted component from step q) and the washing solution; and

[0153] s) combining the washing solution from step r) with the first liquid fraction from step f).95.177.174638 / 01 - 23 -

[0154] The contact time for step q) is not particularly limited, but may be in the range of 1 second to 24 hours. Generally, the contact time is 15 minutes, such as 30 minutes to 3 hours, such as 1-2 hours. It is also preferred if the solution is oxidised.

[0155] The washing solution is not particularly limited, but preferably comprises water. In a preferred embodiment, the washing solution consists of water, e.g. deionised water. In the various methods of the present invention, the pH, especially of the various liquid components, is adjusted at various stages. In one preferred embodiment, the pH is adjusted during at least one step by means of a calcium salt. Suitable calcium salts include quick lime (calcium oxide), slaked lime (calcium hydroxide) and / or calcium carbonate. Alternatively, the pH may be lowered through the addition of an acidic salt or reagent. For example, the pH can be adjusted during at least one stage by means of an acidic reagent such as sulfuric acid and / or MSA.

[0156] In certain cases, where the at least one metal comprises iron, iron may be precipitated from the first liquid fraction. The precipitation of iron preferably follows the precipitation of zinc. As mentioned earlier, the extraction may be achieved through oxidation. Without being bound by theory, it is believed that different oxidation states of iron may precipitate under different conditions.

[0157] In one embodiment, where the at least one metal comprises iron, the method of the present invention may comprise the following steps:

[0158] w) neutralising the zinc-depleted liquid fraction to a pH of around 6 to 8 whereby to precipitate any remaining iron; and

[0159] x) separating the precipitated iron from said zinc-depleted liquid fraction.

[0160] Therefore, in a certain embodiment, where the at least one metal comprises iron and zinc, the method of the present invention may comprise the following steps: g) precipitating at least one zinc salt from the first liquid fraction;

[0161] h) separating said precipitated zinc salt from the first liquid fraction to give a zinc-containing solid fraction and a zinc-depleted liquid fraction;

[0162] i) optionally returning said zinc-depleted liquid fraction to steps g) and h) at least one additional time (e.g. 1 to 7 times, preferably 5 times) to increase the amount of precipitated zinc salt and to generate a zinc-barren solution;95.177.174638 / 01 - 24 -

[0163] w) neutralising the zinc-depleted liquid fraction to a pH of around 6 to 8 whereby to precipitate any remaining iron; and

[0164] x) separating the precipitated iron from said zinc-depleted liquid fraction.

[0165] In a preferred embodiment, the pH is adjusted during at least one step by means of a calcium salt. Suitable calcium salts include quick lime (calcium oxide), slaked lime (calcium hydroxide) and / or calcium carbonate.

[0166] In one embodiment, pH is adjusted at step e) and / or step w). The pH is preferably adjusted by means of at least one calcium salt. Preferably pH will be adjusted at step w) by means of addition of calcium hydroxide and adjusted at step e) by means of addition of calcium carbonate.

[0167] In one embodiment, the at least one metal may comprise cadmium (Cd). It is desirable to recover and isolate Cd from the source material, since cadmium is a toxic metal, particularly in the powdered form where it can burn and release toxic fumes.

[0168] In certain cases, cadmium will be recovered from the first liquid fraction. Cadmium will generally be recovered by precipitation from the first liquid fraction (or from the cleaned-up first liquid fraction as described above). Such method may comprise: m) precipitation of a cadmium-containing solid from the first liquid fraction; and n) separation of said cadmium-containing solid from the first liquid fraction to give a cadmium-containing solid fraction and a cadmium-depleted liquid fraction.

[0169] Step m) preferably comprises the addition of an oxidising and / or reducing agent to precipitate the cadmium-containing solid from the first liquid fraction. In a preferred embodiment, the oxidising and / or reducing agent is a metal, such as zinc dust.

[0170] Alternatively or additionally, cadmium may be recovered from the zinc-containing solid fraction, wherein the method further comprises steps j) to I) as described herein. Cadmium removal may be undertaken prior to zinc recovery, wherein the cadmium may be removed from the first liquid fraction. Alternatively, or additionally, cadmium may be removed from the zinc-containing solid fraction.95.177.174638 / 01 - 25 -

[0171] One embodiment of the present invention may include recovery of at least Zn (and preferably Cd) from a low-silicate source material by a cyclic method comprising use of an acidic solvent comprising MSA (and preferably also comprising H2SO4). Such a method may comprise:

[0172] a) contacting said low-silicate source material with an acidic solvent comprising methanesulphonic acid (MSA) to form a first extraction mixture;

[0173] b) maintaining the first extraction mixture at a temperature of between 1 to 120°C, preferably 20 and 120°C for a period of between 1 second to 24 hours, preferably 10 minutes and 24 hours;

[0174] c) separating the first extraction mixture into a first solid fraction and a first liquid fraction;

[0175] d) recovering at least a first metal from the first liquid fraction; and

[0176] z) regenerating the methanesulphonic acid following extraction of at least a first metal.

[0177] In this and in all methods of the present invention step d) may optionally comprise: e) precipitation of unwanted components from said first liquid fraction by means of increasing pH;

[0178] f) separation of unwanted components precipitated in step e) from said first liquid fraction;

[0179] g) precipitation of at least one zinc-containing salt from the first liquid fraction; h) separation of said precipitated zinc-containing salt from the first liquid fraction to give a zinc-containing solid fraction and a zinc-depleted liquid fraction;

[0180] i) returning said zinc-depleted liquid fraction to steps g) and h) at least one additional time (e.g. 1 to 7 times, preferably 4-6 times) to increase the amount of precipitated zinc-containing salt and to generate a zinc-barren solution;

[0181] j) contacting the zinc-containing solid fraction with a second acid solution to form a second extraction mixture;

[0182] k) precipitation of a cadmium-containing solid from the second extraction mixture; and

[0183] l) separation of said cadmium-containing solid from said second extraction mixture to give a cadmium-containing solid fraction and a second liquid fraction.95.177.174638 / 01 - 26 -

[0184] In a yet further embodiment, step d) may optionally comprise, preferably in the following order:

[0185] e) precipitation of unwanted components from said first liquid fraction by means of increasing pH;

[0186] f) separation of unwanted components precipitated in step e) from said first liquid fraction;

[0187] m) precipitation of a cadmium-containing solid from said first liquid fraction; n) separation of said cadmium-containing solid from said first liquid fraction; o) precipitation of a zinc-containing solid from said first liquid fraction;

[0188] p) separation of the zinc-containing solid from said first liquid fraction.

[0189] j) contacting the zinc-containing solid fraction with a second acid solution to form a second extraction mixture;

[0190] k) precipitation cadmium-containing solid from the second extraction mixture;

[0191] and

[0192] l) separation of said at least one cadmium-containing solid from said second extraction mixture.

[0193] Viewed from a further aspect, the present invention refers to an apparatus for the extraction of at least one metal, said apparatus being configured to carry out the method of any preceding claim.

[0194] The apparatus of the present invention includes various features which embody the key contributions of the present invention. In general, the apparatus has features configured:

[0195] i) to accept a solid low-silicate source material into a first vessel;

[0196] ii) to accept an acidic solvent comprising methanesulphonic acid into said first vessel to generate a first extraction mixture;

[0197] iii) to maintain said first extraction mixture in said first vessel at a temperature of between 1 to 120°C, preferably 20 and 120°C for a period of between 1 second to 24 hours, preferably 10 minutes and 24 hours;

[0198] iv) to separate said first extraction mixture into a first solid fraction and a first liquid fraction; and

[0199] v) to recover at least a first metal from said first liquid fraction.95.177.174638 / 01 - 27 -

[0200] Part i) may be achieved any appropriate feed mechanism such as a conveyor, pump, screw-feeder or batch feeding process. The solid low-silicate source material may be in any suitable form, such as a dry powdered solid or a slurry. Generally, the low-silicate source material is in the form of dry powder, such as electric arc furnace dust (EAF dust). The apparatus may thus contain a low-silicate source material such as EAF dust.

[0201] Part ii) may be achieved by any appropriate liquid-feeding process adapted to handle strong acids, such as a suitably refractory pipeline (e.g. of glass or stainless steel).

[0202] Part iii) may be achieved by use of any suitable refractory first vessel, such as a glass, ceramic or stainless-steel lined vessel equipped with heating and optionally (and preferably) agitation means.

[0203] Part iv) may be achieved with any appropriate separation means such as filtration, settling and / or cyclonic separation equipment adapted to accept the strong acidic solution. Such means may be formed of a refractory material such as glass or stainless steel.

[0204] Part v) may be achieved, for example, by configuring the apparatus to pass the first liquid fraction from part iv) on to a second vessel configured to extract zinc from said first liquid fraction by means of precipitation as an insoluble zinc salt and / or to extract cadmium from said first liquid fraction by means of precipitation. Such apparatus may be configured for pH adjustment and separation steps as described herein including optional re-extraction by repeating appropriate steps by recycling of materials. The second vessel may, in some configurations, be the same physical vessel as the first vessel.

[0205] The apparatus may be additionally configured to:

[0206] vi) regenerate at least a part of the MSA by addition of a mineral acid and recycle the thus-regenerated MSA to part ii)

[0207] The apparatus may be additionally configured to accept a low-silicate source material and water into a pre-extraction vessel.95.177.174638 / 01 - 28 -

[0208] Such regeneration may take place in a fourth vessel configured to accept addition of a mineral acid such as sulphuric acid. The vessel may be configured for regeneration of MSA as described in any embodiment herein. The vessel may be configured to separate a solid such as gypsum generated during the recycling step (as described herein). The fourth vessel may, in some configurations, be the same physical vessel as the first and / or second vessels.

[0209] In use, the apparatus of the invention will, in some embodiments, be configured such that the first vessel contains an acidic solvent such as those described herein (e.g. a mixture of MSA and sulphuric acid) and contains particles of a low-silicate source material (as described herein in any embodiment). The particles of source material may be such that least 50% of particles pass through a screen of aperture size 500 .m or any appropriate size, such as those sizes described herein.

[0210] Definitions

[0211] As used herein, the term “material” or “source material” is used to indicate any solid (e.g. stony and / or glassy) waste, dross, or scoria, generated from an industrial process, such as the smelting or refining of at least one metal. The term “low-silicate source material” is used to indicate that 9% by weight of the material or less is silica / silicate (measured as silica (SiCh) content). Typical amounts of silica / silicate in the low-silicate source material will be 0.1 to 9% by weight, preferably 0.5 to 7% or 1 to 5% by weight.

[0212] The “metals” extracted by the methods of the present invention may be any metal, particularly those which are valuable and / or present an environmental hazard. For the avoidance of doubt, silicon is not a metal and therefore extraction of silicon and / or silica / silicate (SiOx) is not extraction of a metal for the purposes of the present invention. Silcon and / or silica / silicate as referred to herein is an unwanted component. The term “metal” or “metals” includes both elemental metal(s) in addition to metal ions (e.g. in the form of metal salt(s) and / or solution(s)). Where an amount (e.g. content) of a metal element is indicated herein, that is typically measured as elemental metal, unless indicated otherwise.95.177.174638 / 01 - 29 -

[0213] Although aluminium is a metal, in one embodiment, aluminium is not a metal which is desirable for extraction. Thus, in one embodiment, the “at least one metal” to be extracted by the methods of the present invention may be at least one metal excluding aluminium. Thus, although aluminium may in fact be recovered, this may form part of the waste stream from the process and / or may not be in a commercially useful form.

[0214] As used herein, the term “substantially”, as well as terms “about”, “approximately”, “around” and similar terms indicate that the value specified is close to the value indicated and / or is appropriate to achieve the described result. Typically, such values may vary by ±20% of their stated value, preferably ±10% or ±5%, such as ±1%. Evidently, the stated value will be a preferred embodiment.

[0215] Times, temperatures and other conditions specified herein for various steps and embodiments may be absolute measured conditions, or may be average conditions to which a particular mixture is subjected. In particular, where continuous processes are used, contact or residency times may be averages. Similarly, in both batch and continuous processes, contact periods at specified temperatures may be those periods spent at the target temperature or may be periods during which the average temperature is in the target range, allowing for time heating and / or cooling the mixture and / or the physical and / or chemical effects on temperature caused by adding reagents (e.g. exothermic reactions).

[0216] Percentages are given by weight unless indicated otherwise. Where the percentage content of a metal is given, this is the content calculated as the elemental metal, unless otherwise stated. Content of silicate(s) will typically be calculated as SiC>2 unless otherwise stated.

[0217] For percentages of any component which are given w / w, this refers to the w / w with respect to the extraction / reaction mixture unless stated otherwise.

[0218] Where method steps are provided herein, the order of the steps may preferably be the order described in the text and / or set out in the figures and flow-diagrams herein. However, many process steps can be conducted simultaneously or sequentially in any order. The order of method steps provided herein may therefore95.177.174638 / 01 - 30 -

[0219] be simultaneous or sequential in any order. The skilled worker will readily ascertain the order in which appropriate steps should be conducted in order to achieve the desired result.

[0220] Examples

[0221] Materials

[0222] The electric arc furnace dust (EAFD) used in the following examples has been taken from legal stockpiles at the Celsa operation, Cardiff in July 2023.

[0223] The reagents used, or potentially used in the process include

[0224] • Sulphuric Acid

[0225] • MSA

[0226] • Sodium Hydroxide

[0227] • Ferric Sulphate

[0228] • Sodium Sulphide

[0229] • Limestone

[0230] • Lime

[0231] • Thiosulphate

[0232] • Zinc dust

[0233] • Resin

[0234] Example 1 - bench scale agitated leach tests

[0235] All bench scale leach tests were undertaken in 2 litre beakers and agitated and heated by magnetic stirrer hotplates. Tests were performed at elevated temperatures of between 80 to 95°C and undertaken with 800ml of liquid with a solids content of 50g / l.

[0236] In the initial investigative work, Test 1, the leach was undertaken using MSA at 95°C over a residence time of 4 hours. The leach was periodically sampled to generate extraction rate curves, the findings of which are shown in Figure 4 .

[0237] • Both zinc and copper responded very favourably to leaching with MSA with extractions of >90% being obtained;

[0238] • The rate of extraction for both zinc and copper were high with rapid extractions being obtained within the first 15 minutes of the leach. Extraction95.177.174638 / 01 - 31 -

[0239] rates plateaued after 30 minutes of leaching, with minimal extractions being achieved thereafter;

[0240] • Silica was shown to leach with some 80% being extracted in the first 15 minutes of the test. Interesting the silica extraction was shown to gradually decrease with time, perhaps a function of precipitation or metallurgical accounting discrepancies; and

[0241] • Some 87% of the feed sample was digested during the leach.

[0242] Two additional tests were undertaken using an acid mixture of 4.4 parts MSA to 1 part sulphuric acid. The purpose of the sulphuric acid addition was to replicate a flowsheet where sulphuric acid will likely report back to the primary leach as apart of regenerating MSA from spent solution streams. The tests were undertaken at 90°C (Test 2) and 80°C (Test 3) to investigate the effect of temperature. Given that the previous test had shown rapid extraction rates, it was decided to perform these tests with a shorter residence time of 2 hours.

[0243] The results for Test 2, are shown in Figure 5.

[0244] • The MSA- H2SO4 leach tests responded equally as favourably to extraction compared to Test 1 where just MSA was used;

[0245] • Extractions of >96% were achieved for both zinc and copper in Test 2 and 3, with silica extractions of some 70% being obtained;

[0246] • The extraction rate for Test 3 were slightly slower compared Test 2 due to the test being undertaken at a lower temperature; and

[0247] • Tests 2 and 3 had sample digestion rates of 90% and 87% respectively. In further work, scoping tests were undertaken where different lixiviants were investigated in order to evaluate their performance in extraction. The tests were performed at a solids content of 10-11% w / w (some 100g / l solids) with varying lixiviant strengths. Tests performed at 80-90°C for a residence time of 2 hours. A summary of the test results are shown in Table 1.95.177.174638 / 01 - 32 -

[0248]

[0249] • Acetic and sulphuric acid proved to be effective in extracting zinc and copper, with acetic acid giving a high degree of selectivity over silica. Ammonium acetate was also shown to selectively extract zinc and copper over silica but 5 overall extractions were lower in comparison;

[0250] • The extractions rates were less superior compared to tests performed with MSA and MSA-H2SO4, especially considering that those tests were undertaken using significantly lower acid strengths;

[0251] • Cadmium extraction rates were high in all tests performed with extractions of 10 75.5 to 89.9% being obtained; and

[0252] Example 2 - precipitation of cadmium from the first liquid fraction

[0253] From a 1 litre leachate of a 50 g / L solids content (EAF dust) in MSA / H2SO4 (4.4:1

[0254] 15 w / w) unwanted components (e.g. silica) were precipitated using CaCCh. Half of the filtrate was then used for the precipitation of cadmium, once the solid unwanted95.177.174638 / 01 - 33 -

[0255] components had been separated. To the filtrate (577.7 g), 1 g of zinc powder was added. Figure 6 shows the solution during the cadmium precipitation test (a)) and the cadmium-containing solid precipitate when separated (b)).

[0256] Example 3 - precipitation of zinc from the first liquid fraction

[0257] Zinc can be precipitated from either the filtrate generated from the silica precipitation or from the cadmium precipitation (Example 2), when separated from the solid residue. For either case, the conditions are as summarised in Table 2, wherein 5 cycles were undertaken.

[0258] Table 2: conditions forZn precipitation

[0259] Three stage ZnS Precipitation Test Conditions

[0260]

[0261] Figure 7a) shows the ZnS precipitate when the test in Table 2 was carried out on the filtrate following the precipitate of unwanted components (e.g. silica) from Example 2.. Figure 7b) shows the filtrate from the same when the three stage ZnS precipitation test is carried out. Figure 7c) shows the final filtrate, once the precipitate (Figure 7a) has been separated from the liquid fraction. Figure 8a) and b) respectively show the precipitate and filtrate when the three stage ZnS precipitation test is carried out on the filtrate following the precipitation of cadmium (Example 2) and the zinc-containing solid precipitate has been separated from the filtrate.

[0262] Example 4 - cadmium removal from the zinc-containing solid

[0263] The zinc precipitates generated from Stage 3 of Example 3 were then leached with 10% w / w sulphuric acid for 7 hours at 80-90°C to form a second extraction mixture. Aeration was including during leach stages.

[0264] For the sample where cadmium has been precipitated from the first liquid fraction (e.g. Figure 8), Figure 9a) visually shows the second extraction mixture, comprising95.177.174638 / 01 - 34 -

[0265] a solution of zinc-containing solid precipitate (9.39 g) which has been leached in sulfuric acid (213 g). In this case, no additional zinc dust is added at this stage.

[0266] The pH of the leachate is in the range of 0.5 to 0.7. Figure 9b) and c) respectively show the precipitate from the second extraction mixture and the second liquid fraction once the precipitate has been separated. The final weight of the second filtrate was 11.7 g and the weight (dry) of the cadmium-containing solid was 11.9 g.

[0267] The below Table 3 summarises the composition of the cadmium-containing solid fraction as shown in Figure 9b) and the second liquid fraction as shown in Figure 9c).

[0268] Table 3

[0269]

[0270] For the sample where no cadmium has previously been precipitated from the first liquid fraction (e.g. Figure 7), Figure 10a) visually shows the second extraction mixture comprising a solution of the zinc-containing sold precipitate (10.2 g) which has been leached in sulfuric acid (206 g) followed by the subsequent addition of zinc dust (0.5 g). For the addition of zinc dust, the temperature of the second extraction mixture was lowered to 30°C and the resulting mixture was allowed to stir for 30 minutes after the zinc dust addition. Figure 10b) and c) respectively show the precipitate from the second extraction mixture and the second liquid fraction once the precipitate has been separated. The final weight of the second filtrate was 10.5 g and the weight (dry) of the cadmium-containing solid was 10.6 g. The below Table 4 summarises the composition of the cadmium-containing solid fraction as shown in Figure 10b) and the second liquid fraction as shown in Figure 10c).95.177.174638 / 01 - 35 -

[0271] Table 4

[0272]

Claims

- 36 -Claims1. A method for the extraction of at least one metal from a low-silicate source material comprising said at least one metal, said method comprising:a) contacting said low-silicate source material with an acidic solvent comprising methanesulphonic acid (MSA) to form a first extraction mixture;b) maintaining the first extraction mixture at a temperature of between 1 and 160°C for a period of between 1 second and 24 hours;c) separating the first extraction mixture into a first solid fraction and a first liquid fraction; andd) recovering at least a first metal from the first liquid fraction;wherein said low-silicate source material comprises no more than 9% by weight silicate, measured as silica (SiCh).

2. The method of claim 1 wherein step d) comprises adjusting the pH of the first liquid fraction, preferably increasing the pH, through the addition of one or more salts or reagents, preferably one or more basic salts or reagents.

3. The method of claim 2 wherein the one or more salts or reagents is selected from a list comprising: sulphide reagents (e.g. H2S, K2S, Na2S, preferably Na2S); metal salts, such as alkali or alkaline earth metal salts (e.g. CaCCh and / or Ca(OH)2); or elemental metal particles (e.g. Zn dust).

4. The method of any preceding claim wherein in step b) the temperature is in the range 1 to 120°C, such as 20 to 120°C and / or the period is in the range of 10 minutes and 24 hours.

5. The method of any preceding claim wherein the source material is a solid waste material.

6. The method of any preceding claim wherein the source material comprises at least 1 wt% of zinc (e.g. 5 to 35 wt%).- 37 -7. The method of any preceding claim wherein the source material is a product (e.g. by-product) from an industrial process, such as dust from an electric arc furnace, quench dust and / or other material formed during a smelting process.

8. The method of any preceding claim wherein the source material has an average particle size of 10 pm or less, preferably 2 pm or less such as 0.5 to 1 pm, preferably 0.6 to 0.8 pm.

9. The method of any preceding claim comprising the step:z) regenerating the methanesulphonic acid following extraction of at least a first metal.

10. The method of any preceding claim wherein at least a part of the methanesulphonic acid is regenerated by means of addition of sulphuric acid (H2SO4).

11. The method of any preceding claim wherein the acidic solvent comprises both methanesulphonic acid and sulphuric acid.

12. The method of claim 11 wherein the acidic solvent comprises methanesulphonic acid and sulphuric acid at a ratio of 1:1 to 5:1 by weight.

13. The method of any preceding claim wherein the at least one metal comprises zinc (Zn) and the method additionally comprises:g) precipitation of at least one zinc salt from the first liquid fraction;h) separation of said precipitated zinc salt from the first liquid fraction to give a zinc-containing solid fraction and a zinc-depleted liquid fraction; and optionally i) returning said zinc-depleted liquid fraction to steps g) and h) at least one additional time (e.g. 1 to 7 times, preferably 5 times) to increase the amount of precipitated zinc salt and to generate a zinc-barren solution.

14. The method of any preceding claim wherein the at least one metal comprises cadmium (Cd) and the method further comprises:m) precipitation of a cadmium-containing solid from said first liquid fraction; andn) separation of said precipitated cadmium-containing solid from said first liquid fraction to give a cadmium-containing solid fraction and a cadmium-depleted liquid fraction.

15. The method of any of claim 13, wherein the at least one metal comprises zinc and cadmium and the method further comprises:j) contacting the zinc-containing solid fraction with a second acid solution to for a second extraction mixture;k) precipitation of at least one cadmium-containing solid from the second extraction mixture; andl) separation of the precipitated cadmium-containing solid from the second extraction mixture to give a cadmium-containing solid fraction and a cadmium-depleted liquid fraction.

16. The method of claim 14 or 15 wherein the cadmium is separated from the first liquid fraction or the second extraction mixture by means of reduction of the cadmium.

17. The method of any preceding claim comprising:e) precipitation of unwanted components from said first liquid fraction by means of increasing pH; andf) separation of components precipitated in step e) from said first liquid fraction; wherein steps e) and f) preferably take place before steps g), h), and / or j), k), I) and / or m) and n) (where present).

18. The method of claim 17 wherein the unwanted components comprise silicon / silica and / or aluminium and / or lead and / or iron.

19. The method of claim 17 or claim 18 wherein increasing pH is carried out by addition of a calcium salt such as calcium carbonate, preferably in two stages.

20. A method for extraction of at least Cd and Zn from a low-silicate source material by a cyclic method comprising use of an acidic solvent comprising MSA (and preferably also comprising H2SO4), such a method comprising:a) contacting said low-silicate source material with an acidic solvent comprising methanesulphonic acid (MSA) to form a first extraction mixture;b) maintaining the first extraction mixture at a temperature of between 1 and 120°C for a period of between 1 second and 24 hours;c) separating the first extraction mixture into a first solid fraction and a first liquid fraction;d) recovering at least a first metal (e.g. zinc) from the first liquid fraction; andz) regenerating the methanesulphonic acid following extraction of at least a first metal;wherein step d) optionally comprises one or more of steps e) to n):e) precipitation of unwanted components from said first liquid fraction by means of increasing pH;f) separation of components precipitated in step e) from said first liquid fraction;g) precipitation of at least one zinc salt from the first liquid fraction;h) separation of said precipitated zinc salt from the first liquid fraction to give a zinc-containing solid fraction and a zinc-depleted liquid fraction;i) returning said zinc-depleted liquid fraction to steps g) and h) at least one additional time (e.g. 1 to 7 times, preferably 5 times) to increase the amount of precipitated zinc salt and to generate a zinc-barren solution before regenerating said MSA at step z);j) contacting the zinc-containing solid fraction with a second acid solution to form a second extraction mixture;k) precipitation of at least one cadmium-containing solid from the second extraction mixture;l) separation of the precipitated cadmium-containing solid from the second extraction mixture to give a cadmium-containing solid fraction and a cadmium-depleted liquid fraction;m) precipitation of at least one cadmium-containing solid from said first liquid fraction; andn) separation of said cadmium-containing solid from said first liquid fraction.

21. An apparatus for extraction of at least one metal from a source material comprising said at least one metal, said apparatus being configured:i) to accept a solid low-silicate source material into a first vessel;ii) to accept an acidic solvent comprising methanesulphonic acid into said first vessel to generate a first extraction mixture;iii) to maintain said first extraction mixture in said first vessel at a temperature of between 1 and 120°C for a period of between 1 second and 24 hours; iv) to separate said first extraction mixture into a first solid fraction and a first liquid fraction; andv) to recover at least a first metal from said first liquid fraction.

22. The apparatus of claim 21 configured to pass the first liquid fraction from part iv) on to a second vessel configured to extract zinc from said first liquid fraction by means of precipitation as an insoluble zinc salt.

23. The apparatus of any of claims 21 or 22 being additionally configured to: vi) regenerate at least a part of the MSA by addition of a mineral acid and recycle the thus-regenerated MSA to part ii).

24. An apparatus for extraction of at least one metal from a low-silicate source material comprising said at least one metal, said apparatus comprising a first vessel and being configured to carry out the method of any preceding claim.

25. The apparatus of any of claims 21 to 24 wherein the first vessel contains a mixture of MSA and sulphuric acid and particles of said low-silicate source material having a weight average particle size of 1 .m or smaller.

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