Treatment of lead furnace slag

Abstract

This invention relates to the recovery of metals from lead-containing metallurgical slag. A method is described for separating and recovering metals, particularly Pb, Cu, and Ni, from slag by using a combination of sulfur and hydrogen instead of a carbon source. Replacing carbon with sulfur and hydrogen significantly reduces the carbon footprint of the method. The target metal is selectively fed into the matte phase, alloy, lead block, or retained in the slag phase, thereby allowing for more efficient refining.

Description

[0001] introduction

[0002] The field of this invention is the recovery of metals from lead-containing metallurgical slag.

[0003] When extracting metals from ores or secondary feedstocks containing copper and lead, the first step is typically a smelting operation, producing copper matte and lead-containing slag. While the majority of the valuable metals are deposited in the matte, a significant portion is deposited in the slag. This slag may contain 10% by weight or more lead, as well as metals such as copper, iron, and zinc. Further processing is required to recover these valuable metals, especially copper and zinc.

[0004] Therefore, slag is usually subjected to reducing conditions in blast furnaces or electric arc furnaces to produce metal alloys containing valuable metals and clean slag.

[0005] The required reduction conditions are typically achieved by adding carbon, carbohydrates, or hydrocarbons into the furnace, often in the form of coke, or as liquid or gaseous fuels. The redox reaction leads to the formation of CO, which ultimately produces CO2. Capturing CO2 from the furnace exhaust is particularly difficult because the technology is still under development for metallurgical processes. Therefore, CO2 ultimately enters the atmosphere, which is undesirable given its recognized greenhouse effect.

[0006] Such methods are described, for example, by Vanparys et al. (PbZn 2020: The 9th International Symposium on Lead and Zinc Processing. Minerals, Metals and Materials Series. Springer, Cham.).

[0007] One possible alternative to adding carbon-based materials is to use sulfur (S) or sulfur compounds.

[0008] CN116024438A describes introducing a sulfur-containing sulfiding agent in the form of gypsum, pyrite, or nickel sulfide ore into molten nickel-rich slag to obtain low-nickel matte, etc.

[0009] Tian et al. (Synergistic recovery of copper, lead and zinc via sulfurization-reduction method from copper smelting slag; Transactions of Nonferrous Metals Society of China 33, 3847-3859, 2023) described the recovery of Cu, Pb and Zn from copper smelting slag using pyrite and coke to form slag, matte and gas phase. Coke was used to reduce high-valence Fe3O4 to low-valence FeO oxides.

[0010] CN113046550 describes the reduction of metals in lean electric arc furnace slag using a mixture of pyrite, raw coal, and nickel / copper concentrate. The only reducing agent is coke.

[0011] CN113862489 describes a multi-stage method in a reduction furnace, divided into two sections: a pre-reduction section and a deep reduction section. The pre-reduction method for lead concentrate uses metal sulfides, such as zinc sulfide, iron sulfide, and copper sulfide, or mixtures of metal sulfides and sulfur, to produce liquid metallic lead, high-concentration sulfur dioxide gas, and lead-poor slag. At the end of the pre-reduction stage, the liquid lead and residual slag are separated. The residual slag, containing a small amount of unreduced lead, proceeds to the deep reduction stage, illustrated in several examples using methane or water gas.

[0012] Yuan et al. (Powder Technology 230, 63–66, 2012) taught the addition of sulfur to PbO. Intense co-milling of the mixture at low temperatures resulted in the partial conversion of Pb to PbS. The sulfides could then be separated using flotation. This process can be applied to lead-containing waste, such as glass, where lead exists in the form of oxides.

[0013] Han et al. (Selective Sulfidation of Lead Smelter Slag with Sulfur; MetalMater Trans B 47, 344–354, 2016) demonstrated the sulfidation roasting of slag containing 0.5 to 5% Pb, some Zn, and Fe. Sulfur was used instead of the more conventional pyrite to avoid Fe as an impurity. Carbon was added to suppress SO2 formation. This led to the formation of CO and CO2. The initial roasting temperature was limited to about 400 °C to remain below the boiling point of sulfur. The final roasting temperature could be applied up to 1200 °C while the bulk material remained solid. The higher roasting temperature favored crystal growth and enabled more efficient ZnS separation by flotation in subsequent process steps.

[0014] Another possible alternative to adding carbon, carbohydrates, or hydrocarbons is based on using hydrogen (H2).

[0015] US2022389538A1 describes the recovery of copper from secondary feedstocks, where hydrogen is used as a combustor to generate heat, rather than as a chemical reducing agent.

[0016] Rukini et al. (Lead Recovery From PbO Using Hydrogen as a Reducing Agent; Metal Mater Trans B 54, 996-1016, 2023) described the addition of hydrogen to pure PbO pellets at temperatures ranging from 350 to 800 °C, resulting in the formation of metallic lead droplets on the PbO surface. Hydrogen alone was used as the reducing agent.

[0017] WO2008014538A1 describes a method for reducing lead in slag to metallic lead by injecting a sulfide material using a top-blown submerged lance under reducing conditions. The sulfide material can be concentrate, sulfide slag, pyrite, or a combination thereof. If the fuel used in this method is solid (such as fine-particle coal), it can be entrained in a carrier gas, or it can be a suitable hydrocarbon gas or liquid.

[0018] It appears that most known pyrometallurgical processes use carbon, carbohydrates, or hydrocarbons to achieve reducing conditions that produce clean slag (depleted of heavy metals). This inevitably leads to the formation of CO2.

[0019] The object of this invention is to provide an alternative for separating and recovering metals, particularly Pb, Cu and Ni, from slag by using a combination of sulfur and hydrogen instead of a carbon source.

[0020] Replacing carbon with sulfur and hydrogen sources results in the formation of SO2 and H2O, respectively, instead of CO2. H2O is a harmless gas that can be emitted directly, while SO2 is relatively easy to capture. SO2 can be converted to SO3, and then to sulfuric acid using standard industrial processes. Sulfuric acid is a widely used reactant, for example, in fertilizer production. SO2 can also be converted to sulfur when the concentration in the exhaust gas is sufficiently high. Environmentally friendly processes have been developed, such as using the CaS-SO2 reaction (Environ. Sci. Technol. 2002, 36, 13, 3020–3024). In this way, the direct effect of the present invention is to achieve decarbonization in industrial recycling processes.

[0021] This new method leads to the formation of so-called matte, a sulfide phase formed from metal sulfides, along with so-called alloys, which are mixtures of two or more elements, at least one of which is a metal, and lead blocks, which are also alloys but contain a majority weight percentage of Pb. This allows for better separation of Cu, Pb, and Fe in different phases and eliminates the use of conventional carbon-based reduction and the resulting CO2 formation.

[0022] The first aspect describes a method for removing Pb and Cu from metallurgical slag, comprising the following steps:

[0023] Provide smelting furnaces;

[0024] Provide metallurgical slag containing more than 10% by weight of Pb, and also containing Cu and Fe;

[0025] The molar amounts of Pb, Cu, Fe, Ni and Zn in the slag were determined;

[0026] The slag is smelted or slag already in molten form is provided to obtain molten slag in the furnace;

[0027] Provide a certain amount of sulfur (S) and hydrogen (H2), wherein the sum of (S) divided by the stoichiometric molar amounts of Pb, Cu, Fe, Ni and Zn in the slag and (H2) divided by the stoichiometric molar amounts of Pb, Cu and Ni in the slag corresponds to a stoichiometric excess of at least 110% and at most 400%.

[0028] The aforementioned amounts of sulfur and H2 are added to the molten slag to obtain a slag phase containing depleted Pb and Cu, a matte phase, an alloy phase, lead blocks, SO2-containing tail gas, and flue dust in a molten bath; and,

[0029] Separate the slag phase, the matte phase, the alloy, and the lead block.

[0030] This metallurgical slag typically originates from industrial smelting and refining operations. The most abundant metal in this type of slag is phosphorus (Pb), with a content commonly ranging from 10% to 50%.

[0031] In this type of metallurgical slag, a Pb content exceeding 50% is uncommon because it reduces the efficiency of upstream processes. A Pb content below 10% results in excessively high slag viscosity, necessitating additional flux.

[0032] On the other hand, the metallurgical slag contains 10 to 50% by weight of Pb, or 10 to 40%, or 20 to 40%.

[0033] The metallurgical slag according to the invention is typically derived from other industrial processes in which most of the valuable copper has been removed. Therefore, on the other hand, this metallurgical slag contains 1 to 15% by weight of Cu. Even processes specifically designed for copper removal usually leave some residual copper in the slag. The presence of at least 1% Cu makes a dedicated copper separation step economically worthwhile.

[0034] In addition to Pb, Cu, and Fe, other metals such as Ni, As, Bi, Sb, Sn, and Zn may also be present in this metallurgical slag. Therefore, on the other hand, this metallurgical slag also contains one or more of Ni, As, Bi, Sb, Sn, and Zn. Their respective weight percentages are typically much lower than the Pb content mentioned above. Except for Ni, Fe, and Zn, all other elements are considered minor impurities with little or no impact on the method of this invention. The metallurgical slag used at the beginning of the method may be referred to as the "starting slag."

[0035] In the starting slag, Fe is typically present in an amount of at least 4% by weight and at most 20% by weight. More common contents are 4% to 15%, or even 4% to 10%. Fe is generally considered a non-critical element and can be classified as either the slag phase (usually in its oxide form) or the matte phase (usually in the form of FeS). An iron content exceeding 20% ​​is less preferred because it reduces the efficiency of upstream recovery processes.

[0036] Ni may be present in the starting slag at a rate of at least 0.2% by weight and at most 10% by weight.

[0037] Zn can be present in the starting slag at a level of at least 2% by weight and at most 15% by weight. More common contents are 2% to 10%, or even 2% to 7%. High Zn contents are less desirable because Zn not only forms sulfides, but also volatilizes from the slag and settles in the flue gas, where it can cause undesirable downstream condensation.

[0038] Therefore, on the other hand, the metallurgical slag also contains one or more of Ni and Zn.

[0039] The key to this method is the reaction of metals (especially Pb) in the initial slag with sulfur to form sulfides. For certain selected metals, the relevant stoichiometric sulfidation reactions are as follows:

[0040] 2 PbO + 3 S → 2 PbS + SO2

[0041] 2 Cu₂O + 3 S → 2 Cu₂S + SO₂

[0042] 2 Fe2O3 + 7 S → 4 FeS + 3 SO2

[0043] 2 NiO + 3 S → 2 NiS + SO2

[0044] 2 ZnO + 3 S → 2 ZnS + SO2

[0045] It has been found that, according to the present invention, the stoichiometry of sulfur (X) s Use the following equation to calculate:

[0046] (X s ) = 1.5 (Pb) + 0.75 (Cu) + 1.5 (Ni) + 0.75 (Zn) + 0.875 (Fe)

[0047] Where (Pb), (Cu), (Ni), (Zn) and (Fe) represent the molar amounts of Pb, Cu, Ni, Zn and Fe present in the initial slag, respectively.

[0048] It is known that Pb, Cu, Ni, Zn, and Fe react with sulfur to form sulfides, which typically belong to the matte phase. If Fe and Zn are present in significant amounts, this should be taken into account when estimating the amount of sulfur to be added to the starting slag. Generally, under the chosen conditions, they do not completely transform, and the metals are partially retained in the slag as their oxide phases. It has been observed that in this method, adding sulfur corresponding to approximately 50% of the stoichiometry of these two metals is sufficient.

[0049] Although As, Bi, Sb and / or Sn can also react with sulfur, they are considered minor impurities in this type of slag and have very limited or no effect on the total stoichiometry required for the entire process.

[0050] Hydrogen typically reduces metal oxides in the initial slag to metallic phases, such as alloy phases or lead block phases. For certain metals, the relevant stoichiometric reduction reactions are:

[0051] PbO + H2 → Pb + H2O

[0052] Cu₂O + H₂ → 2 Cu + H₂O

[0053] NiO + H2 → Ni + H2O

[0054] It has been found that, according to the present invention, the stoichiometry of hydrogen (X) H2 The following equation can be used to calculate: (X) H2 ) = (Pb) +0.5 (Cu) + (Ni)

[0055] Where (Pb), (Cu) and (Ni) represent the molar amounts of Pb, Cu and Ni present in the initial slag, respectively.

[0056] It is known that oxides of Pb, Cu, and Ni react with hydrogen to form metals, which are usually classified as alloys or bulk lead phases.

[0057] Fe (usually present in slag as oxides) reacts with hydrogen at a low rate, having a very limited or no effect on the overall stoichiometry of the process.

[0058] The key to this method is the reaction of metal oxides in the initial slag with both sulfur and hydrogen to form metal sulfides and metals, respectively, thereby improving the separation of different metals in different phases. Typically, under selected conditions, Cu preferentially enters the matte phase as Cu₂S, while Pb tends to enter the alloy or lead block phase as metallic Pb.

[0059] On the other hand, the amounts of sulfur (S) and hydrogen (H2) are calculated according to the following equation:

[0060] (S) = A (X s ), where 0.05 < A < 1.0;

[0061] (H2) = B (X H2 ), where 0.2 < B < 3.5; and,

[0062] 1.1 < (A + B) < 4; and,

[0063] Where (X) s ) and (X H2 () represents the stoichiometric molar amounts of sulfur and hydrogen, based on:

[0064] (X s ) = 1.5 (Pb) + 0.75 (Cu) + 1.5 (Ni) + 0.75 (Zn) + 0.875 (Fe);

[0065] (X H2 ) = (Pb) + 0.5 (Cu) + (Ni); and,

[0066] Where (Pb), (Cu), (Ni), (Zn) and (Fe) are the molar amounts of the metals Pb, Cu, Ni, Fe and Zn in the slag.

[0067] In addition to the metals mentioned above, metallurgical slags also contain slagging agents. Typical slagging agents are silicon dioxide (SiO2), aluminum oxide (Al2O3), calcium oxide (CaO), or magnesium oxide (MgO). In the metallurgical slags of this invention, such slagging agents are generally found within the following ranges:

[0068] 10 to 50% by weight of silicon dioxide;

[0069] 0 to 20% by weight of alumina;

[0070] 5 to 60% by weight of calcium oxide; and,

[0071] 0 to 10% by weight of magnesium oxide.

[0072] The metallurgical slag according to the invention may contain a total of 25 to 60% by weight, preferably 25 to 40% of a slag-forming agent combination. Slag containing 25 to 40% slag-forming agent allows for appropriate reaction with sulfur or hydrogen and facilitates phase separation between the slag, alloy, lead block, and matte phases. Reducing the slag-forming agent dosage to below 25% will result in excessive metal concentration, while increasing the slag-forming agent dosage to more than 60%, or even more than 70%, will result in overall dilution of the composition, making metal recovery uneconomical.

[0073] Metallurgical slag typically contains a fairly complex mixture of slag-forming agents and metals (usually in the form of oxides). In addition, other impurities such as P₂O₅, Na₂O, or BaO may be present, depending largely on the differences in the feed materials used to produce the slag and / or the process conditions employed.

[0074] On the other hand, other materials containing Pb, Cu, and / or Ni may be added to the furnace together with the metallurgical slag according to the first aspect. In determining the amount of sulfur and hydrogen used in this method, their respective amounts should be considered similarly.

[0075] Sulfur refers to elemental sulfur as well as sulfur combined with any chemical element other than sulfur itself. The former includes octasulfur (S8), which is a major industrial form of elemental sulfur. The latter includes metal sulfides, such as iron sulfide, zinc sulfide, copper sulfide, nickel sulfide, lead sulfide, pyrite, and chalcopyrite.

[0076] The contents of different metals in lead-containing slag were determined in advance using known analytical methods. Based on this, the stoichiometric amounts of sulfur and hydrogen can be easily derived from the aforementioned sulfidation and reduction reactions, respectively.

[0077] The kinetics of the reaction between sulfur and metal oxides in the molten initial slag are finite. The kinetics depend particularly on temperature and the degree of mixing between the introduced sulfur and the metal oxides in the molten slag. Some sulfur may leave the molten slag unreacted, forming SO2 with any air present in the gas purge loop above or further downstream of the molten bath.

[0078] The kinetics of the reaction between hydrogen and metal oxides in the molten initial slag are finite. The high buoyancy of hydrogen in the molten slag bath will result in some hydrogen remaining unreacted due to short reaction time or insufficient mixing between the gas and the molten slag.

[0079] The sum of A and B should represent a stoichiometric excess, such as 110% or more, 120% or more, 130% or more, or 140% or more. "A" or "B" refers to the formula mentioned above used to determine the amount of sulfur and hydrogen.

[0080] Preferably, the sum of A + B is limited to a maximum of 400%, more preferably a maximum of 380%, more preferably a maximum of 360%, and most preferably a maximum of 340%. In industrial practice, due to the cost of sulfur and hydrogen themselves and to avoid a larger exhaust gas flow, it is recommended to limit the excess amount of sulfur and hydrogen added to the slag.

[0081] The current embodiments have only been carried out on a laboratory scale, not under industrial conditions. Optimization of preferred industrial conditions is underway to save sulfur and / or hydrogen, and thus reduce costs.

[0082] Therefore, the preferred range for the sum of A and B is 120% to 200%.

[0083] On the other hand, A is between 5% and 100%, preferably between 10% and 90%, and more preferably between 10% and 80%.

[0084] On the other hand, B is between 20% and 350%, preferably between 40% and 300%, and more preferably between 50% and 300%.

[0085] When both phases are liquid, the separation of the alloy and matte phase from the slag phase is typically achieved through selective discharge. The separation of the lead block from the alloy can proceed sequentially at decreasing temperatures, where the lead block remains liquid but the alloy has solidified. This gradual solidification occurs at approximately 800 °C.

[0086] On the other hand, the furnace is an electric furnace. Using electricity as a heat source reduces or eliminates the need for carbon-based fuels. Assuming the use of green electricity, the carbon footprint can therefore be kept very low.

[0087] On the other hand, the furnace is either a bath furnace or a horizontal converter. A bath furnace can be a top-blown submerged lance (TSL) furnace. These types of furnaces are particularly suitable for injecting sulfur and hydrogen, optionally using a carrier gas.

[0088] On the other hand, no carbon-based fuel or carbon-based reducing agent is added to the furnace.

[0089] Adding carbon-based fuels or carbon-based reducing agents to the furnace is preferable to avoid. This leads to CO2 formation, which is undesirable when aiming for decarbonization in industrial recycling processes. Furthermore, CO2 is not only more difficult to capture than SO2, but it also makes SO2 recovery and reuse more difficult due to the dilution of the latter.

[0090] Therefore, avoiding carbon-based fuels or carbon-based reducing agents has significant advantages, reducing the overall carbon footprint of the method, especially in industrial plants.

[0091] Fuel refers to any material that burns to provide the heat required for a high-temperature process, rather than participating in the reaction itself.

[0092] Typically, in pyrometallurgical systems, the oxygen partial pressure (pO2) affects the oxidation state and thermodynamic stability of the metal, slag, and gas phase. In this method, pO2 is preferably above 10. -14 Up to 10 -8 Within the range, more preferably within 10 -12 Up to 10 -9 Within the range.

[0093] It is preferable to avoid injecting large amounts of oxygen-containing gases (such as air) into the molten bath, as this would cause sulfur and hydrogen to react directly with oxygen, rather than with metal oxides in the slag. Furthermore, this would generate a significantly larger amount of exhaust gas that would require treatment.

[0094] Excess sulfur or hydrogen that does not need to react with the metals (metal oxides) in the slag can be used as a heat source in this method.

[0095] Non-reactive gases such as nitrogen can be injected into the slag. The effect is that more volatile species, such as PbS and ZnS, can be disposed of in the flue dust rather than in the matte or alloying phase. This effect can be desirable or undesirable depending on the downstream refining processes available for recovering these elements from the flue dust. To enrich more Pb in the flue dust, a gas flow rate, such as nitrogen, is applied at 0.1 to 5 Nm³ per kilogram of Pb.

[0096] Therefore, on the other hand, during or after the step of adding sulfur and hydrogen to the molten slag, non-reactive gases are injected into the molten bath. This increases the amount of Pb in the flue gas. Depending on the flow rate, even most of the Pb can be enriched in the flue gas.

[0097] Any amount of Pb that is classified as part of the soot will reduce the amount of Pb that can be classified as matte, alloys, or lead block phases.

[0098] A low operating temperature near the slag melting point is preferred to limit the degradation of refractory materials in the furnace as much as possible. Preferably, the operating temperature is selected to avoid slag overheating far above its melting point. Typically, the furnace operating temperature is between 1150 and 1450°C, preferably between 1180 and 1230°C.

[0099] On the other hand, sulfur (S) is provided in the form of liquid elemental sulfur. One advantage of using liquid sulfur is the mature technology for handling and transporting it in industrial environments. Liquid sulfur can be directly injected into molten slag, positively impacting process kinetics.

[0100] On the other hand, sulfur is injected through one or more spray guns or vents.

[0101] A lance is understood as a tubular device that is immersed in the molten bath from above. A tuyer is understood as a tubular device that passes through the furnace wall or bottom, is located below or above the molten bath surface, and is equipped with means for injecting gas, liquid, or solid into the molten bath. This also includes porous plugs or similar structures.

[0102] One disadvantage of adding solid sulfur, whether elemental sulfur or sulfur compounds, such as in particulate form, is the generation of sulfur dust during operation. Sulfur dust poses a potential explosion hazard. Furthermore, it can lead to operational difficulties, such as blockages in conveyor systems.

[0103] A possible solution to these problems is to use solid pellets or briquettes containing sulfur. The advantage is that granulated sulfur can be added to the furnace from the top, for example via an overhead belt conveyor, optionally along with other feed materials or flux, while avoiding the aforementioned dust generation.

[0104] Therefore, on the other hand, the sulfur added to the molten slag is in the form of sulfur-containing solid pellets or briquettes.

[0105] In a preferred embodiment, sulfur is mixed with solid metallurgical slag having the same or similar composition as the first aspect, and then pressed. Pressing increases the relative density of the pellets and improves the mixing of sulfur with the metals in the furnace bath. This enhances the overall reactivity of sulfur with those metals, making the method more efficient.

[0106] Therefore, on the other hand, sulfur-containing solid pellets also contain solid slag.

[0107] On the other hand, the solid slag used to manufacture pellets has the same composition as the metallurgical slag described in the first aspect.

[0108] The ratio of sulfur to slag in the mixture has been tested at 4:1, 3:1, 2:1, 1:1, and 1:2. A ratio of 2:1 is preferred.

[0109] On the other hand, the ratio of sulfur to slag in the pellets is 4:1 to 1:2, preferably 3:1 to 1:1, and more preferably 2.5:1 to 1.5:1.

[0110] On the other hand, gaseous hydrogen is added to the molten bath through one or more spray guns or tuyeres via immersion injection.

[0111] Using a gas (such as hydrogen or an increased amount of carrier gas) instead of a solid or liquid in this method may result in an increase in the amount of smoke and dust.

[0112] On the other hand, a method is described in which, during the step of adding the same amount of sulfur and H2, it is simultaneously added. This triggers the direct formation of the desired liquid-phase matte, alloy, and lead block.

[0113] On the other hand, hydrogen is added first, followed by sulfur.

[0114] On the other hand, sulfur is added first, followed by hydrogen.

[0115] The order of addition of hydrogen and sulfur has little effect on the product phase, as long as no material is irreversibly removed from the melt bath, for example by transferring (significant) amounts of Pb or Zn (in the form of PbS or ZnS) into the flue, or by removing (completely or partially) one or more product phases, for example by discharge.

[0116] In the context of this invention, it is preferable to add sulfur and hydrogen simultaneously. In the setting where sulfur is added first, more Pb and / or Zn may leave the melt bath in the form of volatile sulfides, especially when using a relatively large amount of sulfur. This typically does not occur in the setting where hydrogen is added first, and is therefore also preferred.

[0117] All liquid phases should preferably be kept together until they are allowed to react with both sulfur and hydrogen.

[0118] The residual Pb in the slag after the addition of sulfur and hydrogen may be due to insufficient sulfur and hydrogen addition, poor reaction behavior of Pb with sulfur and hydrogen in the molten slag, unfavorable reaction kinetics, and / or inadequate decantation during the step of separating the slag from any other gaining phase. The latter will result in the presence of Pb-containing matte or alloy droplets in the final / depleted slag, thus the total Pb content in the slag will still be higher than expected, despite successful conversion to PbS or Pb.

[0119] On the other hand, the slag phase of depleted Pb and Cu contains less than 6% by weight of Pb, preferably less than 3%.

[0120] Technically, the slag can be further purified to achieve a lower Pb content. However, this requires additional refining operations, which are currently uneconomical.

[0121] On the other hand, the slag phase depleted of Pb and Cu contains less than 0.5% by weight of Cu.

[0122] Such a low copper value indicates that this valuable metal is transferred almost quantitatively to one of the other liquid phases, such as the matte phase, from which it can be more easily refined and recovered.

[0123] In another aspect, the method of the present invention also includes the step of converting SO2 in the SO2-containing tail gas into H2SO4. Modern industrial plants are typically equipped with conversion units for the production of sulfuric acid. H2SO4 can be used, for example, for value-added processing or in acid leaching operations.

[0124] In another aspect, the method of the present invention also includes the step of recovering metals from the matte phase, the alloy, and / or the lead block. Forming three liquid phases is highly advantageous as a means of enriching Pb in the lead block, Cu in the matte phase, and Ni in the alloy.

[0125] Therefore, the target metal is selectively fed into the matte phase, alloy, lead block, or retained in the slag phase, thereby allowing for more efficient refining.

[0126] Downstream refining processes for matte phases, alloys, and lead blocks are known and can be combined with the scheme of this invention.

[0127] One possibility for refining matte is to subject it to an oxidation process, such as a blowing process. Another, especially for low-grade matte, is to subject it to copper smelting. These processes produce high-grade matte or metallic phase, which can then be processed in a conventional manner, generating SO2, which can be captured and / or treated as described above.

[0128] Other refining methods are also possible, such as leaching or flotation. Similarly, SO2 generated from the matte phase containing PbS and Cu2S obtained from further refining can be recovered and converted into H2SO4.

[0129] Downstream refining of lead ingots is a conventional lead refining process that involves the sequential removal and / or value-added utilization of impurity elements. These can be a combination of pyrometallurgical and hydrometallurgical processes. When the percentage of lead in the lead ingot is high, the refining of the lead ingot is simplified, illustrating the advantages of pre-removing Ni by forming an alloying phase and removing Cu by forming a matte phase in the upstream smelting process.

[0130] Downstream refining of the alloy phase can be carried out through hydrometallurgical and / or pyrometallurgical refining steps.

[0131] The fumes can also be processed through a hydrometallurgical processing unit or recycled as feed, thereby recovering the metal that escapes from the molten bath or during feeding.

[0132] Further definitions of some terms in the context of non-ferrous metal pyrometallurgy:

[0133] Slag: Slag is a byproduct formed during the smelting process. It typically contains a mixture of metal oxides and silica, but may also contain metal sulfides and elemental metals. Slag is generally less dense than the metal being extracted, allowing it to be separated and removed from the molten metal, for example, by discharge.

[0134] Mat: Mat is a molten mixture of metal sulfides produced during the smelting process. It is typically an intermediate product when extracting metals (such as copper). Mat contains the desired metal (or multiple metals) in sulfide form, which is subsequently converted to a purer form through further processing.

[0135] Alloy: An alloy is a mixture of two or more elements, at least one of which is a metal. In pyrometallurgy, alloys are typically formed during the smelting process when different metals are combined.

[0136] Ingot: An ingot refers to a block of precious metal, usually gold or silver, cast into bars or ingots. In pyrometallurgy, ingots are the product obtained after a refining process to remove impurities from the metal. Lead ingots are a specific type of ingot.

[0137] The “major part” of an element refers to at least 50% by weight, preferably 80%, of the amount of that element entering the method.

[0138] The following examples illustrate the present invention.

[0139] Example

[0140] When the embodiment mentions "(X)" s ) "(X H2 When “A” or “B” is used, it refers to the formula used to determine the amount of sulfur and hydrogen.

[0141] Example 1

[0142] 2000 g of starting slag with the composition shown in Table 1 is provided. The stoichiometric molar amount (X) of this starting slag is... s ) and (X H2 The initial slag contained 9.6 mol S (308 g sulfur) and 3.8 mol H2 (7.6 g hydrogen). 1.9 mol S (A = 0.2) and 7 mol H2 (B = 1.84) were added to the initial slag, resulting in a total A + B of 2.04. Pellets containing both initial slag and elemental sulfur were prepared. The sulfur-to-slag ratio in this mixture was 2:1. To achieve this, 30 g of initial slag was ground and sieved to an average particle size of less than 2 mm. The initial slag was mixed with elemental sulfur to prepare a briquetting mixture. Pellets were then formed from this mixture.

[0143] A 1.5-liter alumina crucible containing 1970 g of starting slag was placed in an induction furnace and heated to 1250 °C at 650 °C / h under a nitrogen atmosphere. Sulfur pellets were then added. H2 was blown into the slag at a flow rate of 60 L / h. Periodic sampling was performed to monitor the Pb% content in the slag. At the end of the process, 1191 g of final slag, 108 g of matte, 88 g of alloy, and 265 g of lead blocks were obtained. Periodic sampling was performed to monitor the evolution of the slag composition. This was necessary to determine the endpoint of the method. Six intermediate samples, totaling 150.9 g, were collected during the experiment. For a laboratory-scale method using only 2000 g of starting slag, the sample size resulted in significant metal loss. These losses would not occur on an industrial scale. In this embodiment, dust was not captured. The dust will primarily contain Pb, Zn, and S. The composition of each phase is shown in Table 1. Only selected metals are listed in Table 1. The alloy typically also contains varying amounts of As, Sb, and Sn. All other metals are considered minor impurities with little or no effect on the method of this invention. The composition of the slag is typically not 100% total because the metals are present in their oxidized forms and the oxygen content is not included in the calculation.

[0144] Table 1: Mass and Composition of Slag, Mat, Alloys and Lead Blocks

[0145]

[0146] Conclusion: This example demonstrates that the final Pb content in the slag is 2.6% after the addition of 1.9 mol S and 7 mol H2. In addition to the slag and matte, alloys and lead blocks are formed due to the presence of H2 as a reducing agent. Of the Pb present in the initial slag, 5.6% remained in the slag phase, 5.1% transferred to the matte phase, 2.7% to the alloy phase, and 43.5% to the lead block phase. 69% of the Cu present in the initial slag transferred to the matte, and 56% of the Ni present in the initial slag transferred to the alloy. The remaining Pb, Cu, and Ni can be found in periodic samples and flue dust.

[0147] Example 2

[0148] 2000 g of starting slag with the composition shown in Table 2 is provided. The stoichiometric molar amount (X) of this starting slag is... s ) and (X H2 The initial slag contains 9.6 mol S (308 g sulfur) and 3.6 mol H2 (7.2 g hydrogen). 7.5 mol S (A = 0.78) and 9.5 mol H2 (B = 2.62) are added to the initial slag, resulting in a total of 3.4 mol A + B.

[0149] Pelletizing was prepared by combining starting slag and elemental sulfur in a 2:1 sulfur-to-slag ratio. To achieve this, 120 g of starting slag was ground and sieved to an average particle size of less than 2 mm. The starting slag was then mixed with elemental sulfur to prepare a briquetting mixture. This mixture was then pressed into pellets.

[0150] A 1.5-liter alumina crucible containing 1880 g of starting slag was placed in an induction furnace and heated to 1250 °C at 650 °C / h under a nitrogen atmosphere. Sulfur pellets were then added. H2 was blown into the slag at a flow rate of 60 l / h. Periodic sampling was performed to monitor the Pb% content in the slag. At the end of the process, 1077 g of final slag, 60 g of matte, 81 g of alloy, and 425 g of lead ingots were obtained. Periodic sampling was performed to monitor the evolution of the slag composition. This was necessary to determine the endpoint of the method. Seven intermediate samples, totaling 152.8 g, were collected during the experiment. For a laboratory-scale method using only 2000 g of starting slag, the sample size resulted in significant metal loss. These losses would not occur on an industrial scale. In this embodiment, dust was not captured. The dust will primarily contain Pb, Zn, and S. The composition of each phase is shown in Table 2. Only selected metals are listed in Table 2. The alloy typically also contains varying amounts of As, Sb, and Sn. The composition of the slag is usually not 100% total because the metals exist in their oxidized forms, and oxygen content is not included in the calculations. All other metals are considered minor impurities with little or no effect on the method of this invention.

[0151] Table 2: Mass and Composition of Slag, Matte, Alloys and Lead Blocks

[0152]

[0153] Conclusion: This example demonstrates that the Pb content in the final slag is 1.9% after the addition of 7.5 mol S and 9.5 mol H2. In addition to the slag and matte, alloys and lead blocks are formed due to the presence of H2 as a reducing agent. 3.7% of the Pb present in the initial slag remains in the slag phase, 2% is transferred to the matte phase, 2.8% to the alloy phase, and 68% to the lead block phase. 35% of the Ni present in the initial slag is transferred to the alloy phase, only 3.6% is found in the final slag, and 1.6% is in the matte. Cu present in the initial slag is transferred almost equally to the matte, alloy, and lead blocks. Increased H2 addition may lead to a favorable transfer of Cu to the alloy and lead block phases. The remaining Pb, Cu, and Ni can be found in periodic samples and flue dust.

[0154] Example 3

[0155] Provide 2000 g of starting slag with the composition shown in Table 3. The stoichiometric molar amount (X) of this starting slag... s ) and (XH2 The initial slag contains 9.6 mol S (308 g sulfur) and 4.3 mol H2 (8.6 g hydrogen). 3.7 mol S (A = 0.39) (in the form of pyrite) and 9.5 mol H2 (B = 2.21) are added to the initial slag, bringing the total sum of A and B to 2.6.

[0156] Pellets containing both starting slag and pyrite were prepared. The ratio of pyrite to slag in the mixture was 2:1. For this purpose, 120 g of starting slag was ground and sieved to an average particle size of less than 2 mm. The starting slag and pyrite were mixed to prepare a briquetted mixture. This mixture was then pressed into pellets. A 1.5 L alumina crucible containing 1880 g of starting slag was placed in an induction furnace and heated to 1250 °C at 650 °C / h under a nitrogen atmosphere. Then, pyrite pellets were added. H2 was blown into the slag at a flow rate of 60 L / h. Samples were taken periodically to monitor the Pb% content in the slag.

[0157] Table 3: Quality and Composition of Slag

[0158]

[0159] Conclusion: It can be demonstrated that the following metals are significantly reduced in the slag: Pb from 29.3% to 2.1%, Cu from 5.6% to 0.7%, and Ni from 1.6% to 0.1%. Similarly, matte phase, alloys, and lead blocks are formed, but further detailed analysis was not performed. This suggests that pyrite can potentially replace elemental sulfur in industrial applications. Further experimental work is underway to determine the optimal conditions for such methods on an industrial scale.

[0160] Example 4 (Comparative Example)

[0161] 2000 g of starting slag with the composition shown in Table 4 is provided. The stoichiometric molar amount (X) of this starting slag is... s The initial slag contained 9.6 mol S (308 g sulfur). 24.4 mol S (A = 2.55) was added to the initial slag.

[0162] Pelletizing was prepared by combining starting slag and elemental sulfur in a 2:1 sulfur-to-slag ratio. To achieve this, 390 g of starting slag was ground and sieved to a size less than 2 mm. The starting slag was then mixed with elemental sulfur to prepare a briquetting mixture. This mixture was then pressed into pellets.

[0163] A 1.5-liter alumina crucible containing 1610 g of starting slag was placed in an induction furnace and heated to 1250 °C at 650 °C / h under an argon atmosphere. Sulfur-slag pellets were then added at regular intervals over a 3-hour period. Periodic sampling was performed to monitor the Pb% in the slag. At the end of the process, 1000 g of final slag and 519 g of matte were obtained. The compositions of the two phases are shown in Table 4. Periodic sampling was performed to monitor the evolution of the slag composition. This was necessary to determine the endpoint of the method. Ten intermediate samples, totaling 251.2 g, were collected during the experiment. For a laboratory-scale method using only 2000 g of starting slag, the sample size resulted in significant metal loss. These losses would not occur on an industrial scale. In this embodiment, dust was not captured. The dust will primarily contain Pb, Zn, and S.

[0164] Table 4 lists only the selected metals. All other metals are considered minor impurities with little or no effect on the method of this invention. The composition of the slag is generally not 100% total because the metals exist in their oxidized forms and the oxygen content is not included in the calculation.

[0165] Table 4: Mass and Composition of Slag and Matte

[0166]

[0167] Conclusion: This example demonstrates that the final Pb content in the slag after adding 24.4 mol S was 5.6%. Besides the slag, using S as the sole reducing agent resulted only in matte formation. 10% of the Pb present in the initial slag remained in the slag phase, while 48.2% transferred to the matte phase. The remaining Pb was found in periodic samples (ranging from 27.4 to 5.6 wt.% Pb) and flue dust. 97% of the Cu present in the initial slag transferred to the matte phase. 90% of the Ni present in the initial slag transferred to the matte phase. The remaining Pb, Cu, and Ni were found in periodic samples and flue dust.

[0168] Example 5 (Comparative Example)

[0169] Provide 2000 g of starting slag with the composition shown in Table 5. The stoichiometric molar amount (X) of this starting slag... H2 The initial slag contains 3.7 mol H2 (7.4 g hydrogen). 11 mol H2 (B = 2.99) is added to the initial slag.

[0170] A 1.5-liter alumina crucible containing 2000 g of starting slag was placed in an induction furnace and heated to 1250 °C at 650 °C / h under a nitrogen atmosphere. H₂ was then blown into the slag at a flow rate of 60 L / h. Periodic sampling was performed to monitor the Pb% content in the slag. At the end of the process, 1216 g of final slag, 101 g of alloy, and 285 g of lead ingot were obtained. Periodic sampling was performed to monitor the evolution of the slag composition. This was necessary to determine the endpoint of the method. Seven intermediate samples, totaling 159.2 g, were collected during the experiment. For a laboratory-scale method using only 2000 g of starting slag, the sample size resulted in significant metal loss. These losses would not occur on an industrial scale. In this embodiment, dust was not captured. The dust will primarily contain Pb, Zn, and S. The composition of each phase is shown in Table 5. Only selected metals are listed in Table 5. The alloy typically also contains varying amounts of As, Sb, and Sn. All other metals are considered minor impurities with little or no effect on the method of this invention. The composition of the slag is generally not 100% total because the metals exist in their oxidized forms and the oxygen content is not included in the calculation.

[0171] Table 5: Mass and Composition of Slag, Alloy and Lead Ingots

[0172]

[0173] Conclusion: This example demonstrates that the final Pb content in the slag after adding 11 mol H2 is 2.3%. Apart from the slag, using H2 as the sole reducing agent resulted only in the formation of alloys and lead blocks. Pb was transferred to the alloy and lead block phases. Of the Pb present in the initial slag, 5.2% remained in the slag phase, 4.2% transferred to the alloy phase, and 47% transferred to the lead block phase. 51% of the Cu present in the initial slag transferred to the alloy phase. 54% of the Ni present in the initial slag transferred to the alloy phase. The remaining Pb, Cu, and Ni were found in periodic samples and flue dust.

Claims

1. A method for removing Pb and Cu from metallurgical slag, comprising the following steps: - Provide smelting furnaces; - Provides metallurgical slag containing more than 10% by weight of Pb, and also containing Cu and Fe; - Determine the molar amounts of Pb, Cu, Fe, Ni and Zn in the slag; - Melt the slag or provide slag already in molten form to obtain molten slag in the furnace; - Provide a certain amount of sulfur (S) and hydrogen (H2), wherein the sum of (S) divided by the stoichiometric molar amounts of Pb, Cu, Fe, Ni and Zn in the slag and (H2) divided by the stoichiometric molar amounts of Pb, Cu and Ni in the slag corresponds to a stoichiometric excess of at least 110% and at most 400%. - The aforementioned amounts of sulfur and H2 are added to the molten slag to obtain a slag phase, matte phase, alloy phase, lead block, SO2-containing tail gas, and flue dust comprising depleted Pb and Cu; and, - Separate the slag phase, the matte phase, the alloy, and the lead block.

2. The method according to claim 1, wherein the amounts of sulfur (S) and hydrogen (H2) are calculated according to the following equation: (S) = A (X s ), where 0.05 < A < 1.0; (H2) = B (X H2 ), where 0.2 < B < 3.5; and, 1.1 < (A + B) < 4; and, Where (X) s ) and (X H2 () represents the stoichiometric molar amounts of sulfur and hydrogen, based on: (X s ) = 1.5 (Pb) + 0.75 (Cu) + 1.5 (Ni) + 0.75 (Zn) + 0.875 (Fe); (X H2 ) = (Pb) + 0.5 (Cu) + (Ni); and, Where (Pb), (Cu), (Ni), (Zn) and (Fe) are the molar amounts of the metals Pb, Cu, Ni, Fe and Zn in the slag.

3. The method according to claim 1 or 2, wherein the furnace is an electric furnace.

4. The method according to any one of claims 1 to 3, wherein no carbon-based fuel or carbon-based reducing agent is added to the furnace.

5. The method according to any one of claims 1 to 4, wherein the sulfur added to the molten slag is in the form of sulfur-containing solid pellets.

6. The method of claim 5, wherein the sulfur-containing solid pellets further comprise solid slag.

7. The method according to claim 6, wherein the solid slag has the same composition as the metallurgical slag according to claim 1.

8. The method according to claim 6 or 7, wherein the ratio of sulfur to solid slag is 4:1 to 1:

2.

9. The method according to any one of claims 1 to 8, wherein the slag phase of depleted Pb and Cu contains less than 6% by weight of Pb, preferably less than 3% by weight.

10. The method according to any one of claims 1 to 9, wherein the slag phase depleted of Pb and Cu contains less than 0.5% by weight of Cu.

11. The method according to any one of claims 1 to 10, wherein in the addition step, the amounts of sulfur and H2 are added simultaneously.

12. The method according to any one of claims 1 to 4, wherein sulfur is injected through one or more spray guns or vents.

13. The method according to any one of claims 1 to 12, wherein gaseous hydrogen is added to the molten bath via immersion injection through one or more spray guns or tuyeres.

14. The method according to any one of claims 1 to 13, further comprising the step of converting SO2 from SO2-containing exhaust gas into H2SO4.

15. The method according to any one of claims 1 to 14, further comprising the step of recovering metal from the matte phase, the alloy, and / or the lead block.

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