Method and arrangement for treating fine tailings

Abstract

A method for handling fine tailings (1) from mineral treatment processes is disclosed. An arrangement for handling fine tailings (1) from mineral treatment processes is further disclosed.

Description

[0001] METHOD AND ARRANGEMENT FOR TREATING FINE TAILINGS

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a method for handling fine tailings from mineral treatment processes . The present disclosure further relates to an arrangement for handling fine tailings from mineral treatment processes .

[0004] BACKGROUND

[0005] In the field of metallurgy, flotation can be used for separating minerals from gangue by taking advantage of differences in their hydrophobicity . Hydrophobicity differences between valuable minerals and waste gangue are increased through the use of surfactants and wetting agents . The selective separation of the minerals makes processing complex ( that is , mixed) ores economically feasible . The flotation process is used for the separation of a large range of sulfides , carbonates and oxides prior to further refinement .

[0006] Flotation is normally undertaken in several stages to maximi ze the recovery of the target mineral or minerals and the concentration of those minerals in the concentrate . Once the desired material has been separated in the flotation steps , the process generates so called tailings that comprise a mixture of materials such as chemicals , organics , and process water as wel l as metals and minerals in amounts that are too small to be efficiently and economically recovered using conventional methods . The tailings materials are commonly viewed as waste and stored or piled . SUMMARY

[0007] A method for producing handling fine tailings from mineral treatment processes is disclosed . The method may comprise :

[0008] - roasting tailings material in a first roaster having oxidi zing conditions creating a first roaster off-gas comprising dust and a first roaster bed discharge ,

[0009] - separating the first roaster off-gas comprising dust in at least one primary cyclone to form a cyclone overflow and cyclone underflow,

[0010] - roasting the first bed discharge and the cyclone underflow in a second roaster having oxidi zing conditions to form a roasted material flow, and

[0011] - feeding the cyclone overflow into a recovery boiler to form a heat recovery boiler overflow and a heat recovery boiler underflow .

[0012] The method of the present disclosure is characteri zed in that the underflow from the heat recovery boiler i s fed into the second roaster and the roasted material flow from the second roaster is fed into a cooler to form a cooler underflow in the form of calcine and a cooler overflow .

[0013] An arrangement for handling fine tailings from mineral treatment processes is further disclosed . The arrangement may comprise :

[0014] - a first roaster configured to roast the fine tailings from the mineral treatment process to form a first roaster off-gas comprising dust and a first roaster underflow and the roaster is configured to feed the first roaster off-gas comprising dust into a first cyclone and to feed the first roaster underflow into a second roaster,

[0015] - at least one cyclone configured to receive the first roaster off-gas comprising dust and separating it to form a cyclone overflow and a cyclone underflow and the cyclone is configured to feed the cyclone underflow into a second roaster and the cyclone overflow into a heat recovery boiler,

[0016] - a heat recovery boiler configured to receive the primary cyclone overflow and forming a heat recovery boiler overflow and heat recovery boiler underflow and feeding the heat recovery boiler underflow as into a second roaster, a second roaster configured to receive the first roaster underflow and cyclone underflow, and roasting them to form a roasted material flow and feeding it into a cooler, and a cooler configured to receive the roasted material flow and forming a cooler overflow and a cooler underflow in the form of calcine .

[0017] BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawing, which is included to provide a further understanding of the embodiments and constitute a part of this specification, illustrates various embodiments . In the drawings :

[0019] Figs . 1 to 3 present schematic representations of a method or arrangement for handl ing tai lings material from a mineral treatment process according to embodiments of the present disclosure .

[0020] Fig . 4 presents a schematic representation of a method for handling fine tailings from primary flotation treatment arranged to receive underflow from a mineral flotation line and separating them into cleaner underflow of recovered valuable material and cleaner overflow arranged to flow into the first roaster as infeed.

[0021] Fig. 5 presents a schematic representation of a method for handling fine tailings from primary flotation treatment arranged to receive underflow from a mineral flotation line and separating them into cleaner overflow of recovered valuable material and cleaner underflow arranged to flow into the first roaster as in- feed .

[0022] DETAILED DESCRIPTION

[0023] A method for handling fine tailings from mineral treatment processes is disclosed. The method may comprise :

[0024] - roasting tailings material (1) in a first roaster (3) having oxidizing conditions creating a first roaster off-gas comprising dust (5) and a first roaster bed discharge (4) ,

[0025] - separating the first roaster off-gas comprising dust (5) in at least one primary cyclone (6) to form cyclone overflow (7) and cyclone underflow (8) ,

[0026] - roasting the first bed discharge (4) and the cyclone underflow (8) in a second roaster (9) having oxidizing conditions to form a roasted material flow (18) ,

[0027] - feeding the cyclone overflow (7) into a heat recovery boiler (10) to form a heat recovery boiler overflow (12) and a heat recovery boiler underflow (11) , characterized in that the underflow (11) from the heat recovery boiler (10) is fed into the second roaster (9) and the roasted material flow (18) from the second roaster (9) is fed into a cooler (23) to form a cooler underflow in the form of calcine (22) .

[0028] In certain embodiments, the first roaster may be a stationary fluidized bed roaster or a circulating fluidized bed roaster. In certain embodiments, the second roaster may be a stationary fluidized bed roaster. As is known to a person skilled in the art, a stationary fluidized bed roaster may also be called a bubbling fluidized bed roaster, the terms are used synonymously in this description.

[0029] In certain embodiments, off-gas (17) from the second roaster (9) may be separated in a cyclone (19) to form dust (21) that is combined with the calcine (22) and secondary air (28) that may be fed into the upper part of the first roaster (3) , see Fig. 1.

[0030] In certain embodiments, the cooler (23) used to cool the roasted material is a fluid bed cooler or a drum cooler.

[0031] In certain embodiments, e.g. when the cooler (23) is a fluid bed cooler, additional gas and / or air (35) is fed into the cooler together with the roasted material flow (18) . In certain embodiments, the cooler off-gas (24) may be fed into a cyclone (36) and separated to form dust (21) that is combined with the calcine (22) and secondary air (28) that may be fed into the upper part of the first roaster (3) , see Fig. 2.

[0032] In certain embodiments, e.g. when the cooler (23) is a drum cooler, no additional gas and / or air is fed into the cooler together with the roasted material flow (18) .

[0033] In certain embodiments, off-gas (17) from the second roaster (9) is fed into the cooler together with the roasted material flow (18) . In certain embodiments, the cooler off-gas (24) may be fed into a cyclone (36) and separated to form dust (21) that is combined with the calcine (22) and secondary air (28) that may be fed into the upper part of the first roaster (3) , see Fig. 2.

[0034] In certain embodiments, off-gas (17) from the second roaster (9) may be separated in a cyclone (19) to form dust (21) that is combined with the calcine (22) and secondary air (28) that may be fed into the upper part of the first roaster (3) . When the cooler (23) is a fluid bed cooler, additional gas and / or air (35) is fed into the cooler together with the roasted material flow (18) . The cooler off-gas (24) may be fed into a cyclone (36) and separated to form dust (21) that is combined with the calcine (22) and secondary air (28) that may be fed into the upper part of the first roaster ( 3 ) , see Fig . 3.

[0035] In certain embodiments, off-gas (17) from the second roaster (9) may be separated in a cyclone (19) to form dust (21) that is combined with the calcine (22) and secondary air (28) that may be fed into the upper part of the first roaster (3) . The cooler off-gas (24) may be fed into a cyclone (36) and separated to form dust (21) that is combined with the calcine (22) and secondary air (28) that may be fed into the upper part of the first roaster (3) , see Fig. 3.

[0036] In certain embodiments, the tailings material from mineral treatment processes may comprise, e.g., cobalt, nickel, gold, platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, and platinum) , copper, zinc, silver, iron, and / or sulfur. In certain embodiments, the tailings material may comprise materials such as of I2O3, SiCy, FeS, FeS2-

[0037] In certain embodiments, the calcine leaving the cooler may be subjected to further treatments to increase the recovery of valuable materials. In one embodiment, the calcine is subjected to hydrometallurgical treatment such as leaching to extract valuable metals from it for further processing .

[0038] In certain embodiments , the calcine leaving the cooler may be fed into a direct reduction treatment to obtain reduced iron which may be further utili zed in steel production .

[0039] In certain embodiments , the calcine leaving the cooler may be fed into a smelting process to extract valuable metals or alloys .

[0040] As used herein, the term "roasting" refers to the proces s of treating an ore or ore concentrate with very hot roasting gas . As used herein, the term "roasting gas" refers to the gas present in the roaster during the roasting . "Roasting gas" may in certain embodiments be used synonymously with "fluidi zing gas" . In certain embodiments , the roasting gas may be air or other gas mixtures comprising oxygen . In certain embodiments , the roasting gas comprises recycled air or gas recycle from other parts of the method or arrangement .

[0041] In certain embodiments , an ore or ore concentrate comprising sulfur is heated to a high temperature in the presence of an oxygen-containing gas , thereby oxidi zing the sulfur . In certain embodiments , roasting refers to decreasing the sulfur content in solid materials by oxidation of sulfur in the form of sulfides , mainly metal sulfides (e . g . FeS , FeS2 ) , into oxides such as sulfate or sulfite that may be recovered .

[0042] In certain embodiments , roasting gas ( 2 ) is fed into the first and / or second roaster .

[0043] While roasting in a method according to the present disclosure occurs mainly in the roasters , it is obvious to a skilled person that the oxidation reactions of roasting may occur also in other stages or parts of the method . The only pre-requisite for roasting to occur is that a sufficient portion of oxygen is present in the atmosphere and that the temperature is high enough for the oxidation to occur. In certain embodiments, roasting will also happen e.g. in the cyclones before the material has cooled down sufficiently.

[0044] By roasting the tailings material and separating solids from the off-gas of the roasted materials, it is possible to improve the recovery of valuable materials from tailings recovered from various processes such as metallurgical processes. As a nonlimiting example, the recovery of sulfur (e.g. in the form of sulfuric acid) from pyrite material may be improved by roasting the tailings material while simultaneously lowering the amount of sulfur present in the calcine formed in the process. Following collecting the valuable material or desired product from various processes, they leave a tailings fraction that will inevitably also contain some of the valuable material that would normally be discarded as waste.

[0045] As used herein, the terms "tailings material" or "fine tailings" refer to a concentrate of materials formed and recovered as tailings in metallurgical processes. The tailings material comprises sulfur- containing materials also containing metals such as cobalt, nickel, gold, platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, and platinum) , copper, zinc, silver, iron, or any combination thereof. In certain embodiments, the tailings material may be overflow material from a flotation treatment.

[0046] In certain embodiments, tailings material (1) from the flotation has a d50 particle size of 250 pm or less, or 200 pm or less, or 150 pm or less, or 125 pm or less, or 100 pm or less, or 75 pm or less, or 50 pm or less, or 30 pm or less.

[0047] In certain embodiments, tailings material (1) from the flotation has a d50 particle size of 20 pm or more, or 25 pm or more, or 30 pm or more.

[0048] In certain embodiments, tailings material (1) from the flotation has a d50 particle size of 20 - 200 pm, or 20 - 150 pm, or 20 - 125 pm, or 20 - 100 pm, or

[0049] 20 - 75 pm, or 20 - 50 pm, or 20 - 30 pm.

[0050] In certain embodiments, the tailings material may be classified as fine tailings.

[0051] In certain embodiments, very fine tailings material with a d50 particle size of 30 pm or less may be granulated prior to treatment with the method of the present disclosure. In certain embodiments, the d50 particle size of the granulated material is approximately 50 - 250 pm.

[0052] In certain embodiment, the overflow material may comprise, e.g., cobalt, nickel, gold, platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, and platinum) , copper, zinc, silver, iron, and / or sulfur. In certain embodiments, the overflow material may comprise copper, iron, gold, and / or sulfur.

[0053] In one embodiment, at least one roasting is performed in an oxygen-enriched atmosphere. Oxidizing roasting is performed in an atmosphere that comprises oxygen, in general oxidizing roastings are performed in an atmosphere of air, i.e. in an atmosphere comprising approximately 21 % oxygen. If the roasting is performed in an oxygen-enriched atmosphere, the oxidationefficiency is improved. As used herein, "oxygen-enriched atmosphere" refers to an atmosphere that contains more oxygen than air, i.e. more than 21 % oxygen. In certain embodiments, the oxygen-enriched atmosphere consist of a gas mixture comprising 22 % , or 24 % , or 26 % , or 28 % , or 30 % , or 40 % , or 45 % , or 50 % , or 55 % , or up to 60 % oxygen. In certain embodiments, the oxygen- enriched atmosphere consist of a gas mixture comprising

[0054] 21 - 60 %, or 22-50 %, or 24-40 %, or 26-35 %, or 28-30 % oxygen. In one embodiment, the first roaster off-gas comprising dust is separated to form a cyclone overflow and a cyclone underflow by passing it through at least two, at least three, at least four, or at least five consecutive cyclones configured to feed the cyclone offgas from one cyclone into the next cyclone and feeding the cyclone overflow from the final cyclone into the recovery boiler .

[0055] In certain embodiments , the first roaster offgas comprising dust is separated to form a cyclone overflow and a cyclone underflow by passing through two or more primary cyclones arranged parallel to each other . In certain embodiment , the cyclone off-gas from the two or more primary cyclones are combined into one stream of off-gas that is fed into a following cyclone passing it through at least one , at least two , at least three , at least four, or at least five consecutive cyclones configured to feed the cyclone off-gas from one cyclone into the next cyclone and feeding the cyclone overflow from the final cyclone into the recovery boiler .

[0056] In certain embodiments , the first roaster offgas comprising dust is separated to form a cyclone overflow and a cyclone underflow by passing it through at least two , at least three , at least four, or at least five parallel arranged consecutively so in series of at least two , at least three , at least four, or at least five consecutive setups of parallel cyclones configured to feed the cyclone off-gas from one cyclone into the next cyclone and feeding the cyclone overf low from the final cyclone into the recovery boiler .

[0057] In certain embodiments , the first roaster offgas may be separated to form an overflow and an underflow using any suitable de-dusting device .

[0058] In one embodiment , the underflow ( 27 ) from the at least one primary cyclone ( 6 ) may be fed back into the first roaster to increase the retention time of the calcine in the roaster as illustrated in Fig . 2 .

[0059] By using multiple consecutive cyclones configured to feed the cyclone off-gas from one cyclone into the next cyclone more of the dust contained in the gas fed into the first cyclone is entrained, meaning that more of the valuable materials contained in the overflow materials is recovered .

[0060] In one embodiment , the first roaster off-gas comprising dust is separated in a separation process comprising using a multiclone . As used herein, a multiclone refers to a dust collector system comprising multiple smaller cyclones in one device to efficiently separate dust from a gas stream .

[0061] By using a multiclone system comprising multiple cyclones more of the dust contained in the gas fed into the first cyclone is entrained, meaning that more of the valuable materials contained in the overflow materials is recovered .

[0062] In one embodiment , the off-gas formed in the one or more cyclones or multiclone is fed into a dedusting device . By feeding the off-gas from the cyclones and / or multiclone into a de-dusting device , it is possible to recover dust contained in the off-gas .

[0063] In one embodiment , the off-gas ( 28 ) formed in the one or more cyclones , multiclone , and / or de-dusting device is fed into the first roaster . By feeding the off-gas from the cyclones , multiclone , cooler, sealing device , and / or de-dusting device into the first roaster, it is possible to recycle air within the process , thus reducing the requirement for clean air fed into the process as well as reducing the requirement for purification of air before being released into the atmosphere .

[0064] In one embodiment , the sulfur-containing material contained in the heat recovery boiler overflow ( 12 ) is fed into a de-dusting device ( 13 ) to separate remaining dust ( 15 ) from the off-gas ( 14 ) . The dust may be collected, granulated or pelleti zed ( 20 ) , and returned to the first roaster ( 26 ) . By pelleti zing or granulating the sulfur-containing material in the cyclone overflow, the smaller particles can be returned to roasting enabling the recovery of more of the valuable material. In certain embodiments, the dust collected from the de-dusting device may be combined (25) with the calcine (22) .

[0065] In certain embodiments, the off-gas (14) from the de-dusting device is fed into a wet gas cleaning device (16) . In one embodiment, the wet gas cleaning device may be a wet scrubber. In certain embodiments, the wet gas cleaning device may comprise several steps for cleaning said gas.

[0066] In one embodiment, the sulfur-containing material contained in the heat recovery boiler overflow (12) is fed into a hot ESP (electrostatic precipitator) to separate remaining dust (15) from the off-gas (14) . The dust may be collected, granulated or pelletized (20) , and returned to the first roaster (26) . By pelletizing or granulating the sulfur-containing material in the cyclone overflow, the smaller particles can be returned to roasting enabling the recovery of more of the valuable material. In certain embodiments, the dust collected from the hot ESP may be combined (25) with the calcine (22) .

[0067] In one embodiment, sulfur is oxidized in the first and / or second roasting. By roasting the sulfur contained in the tailings material by oxidizing it, it is possible to recover the sulfur and utilize it e.g. for the production of sulfuric acid.

[0068] In one embodiment, the tailings material (1) comprises tailings formed in a primary flotation treatment (30) of underflow material (31) from a mineral flotation line. When the tailings or underflow material exits a mineral flotation line, it will essentially always contain valuable materials to some extent and the valuable materials will generally be discarded as waste as the amounts of valuable material is relatively low and the particle size is relatively small, making the collection of the valuable materials impractical using conventional flotation processes.

[0069] In certain embodiments, the valuable materials contained in the tailings material and recovered using the process of the present disclosure may be cobalt, nickel, gold, platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, and platinum) , copper, zinc, silver, iron, and / or sulfur.

[0070] In one embodiment, the primary flotation treatment arranged to receive underflow (31) from a mineral flotation line as slurry infeed, for the separation of slurry into cleaner underflow of recovered valuable material (33) and cleaner overflow (29) arranged to flow into the first roaster as infeed.

[0071] In one embodiment, the recovered valuable material comprises cobalt, nickel, gold, platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, and platinum) , copper, zinc, silver, iron, and / or sulfur. In one embodiment, the recovered valuable material comprises iron.

[0072] In one embodiment, the primary flotation treatment arranged to receive underflow (31) from a mineral flotation line as slurry infeed, for the separation of slurry into cleaner overflow of recovered valuable material (33) and cleaner underflow (34) arranged to flow into the first roaster as infeed.

[0073] In one embodiment, the recovered valuable material comprises cobalt, nickel, gold, platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, and platinum) , copper, zinc, silver, iron, and / or sulfur which can be oxidized and used e.g. in the production of sulfuric acid. In one embodiment, the recovered valuable material comprises copper. In one embodiment , the amount of water in the tailings material is reduced using a thickener prior to roasting .

[0074] In one embodiment , the amount of water in the tailings material is reduced by filtering prior to roasting .

[0075] In one embodiment , the amount of water in the tailings material is reduced by filtering using a pressure filter prior to roasting .

[0076] In certain embodiments , the tailings material is roasted in a roasting according to the present disclosure ( 32 ) .

[0077] Reducing the amount of water included in the tailings material fed into the roaster will generally improve the energy efficiency as evaporation of water in the roaster consumes significant amounts of energy .

[0078] The method described in the current specification has the added util ity of improving the recovery of valuable materials from the tailings produced in various metallurgical processes . The valuable materials recovered from the process may be metals such as cobalt , nickel , gold, platinum group metals ( ruthenium, rhodium, palladium, osmium, iridium, and platinum) , copper, zinc, silver, iron, and / or sulfur which can be oxidi zed and used e . g . in the production of sulfuric acid . An additional added advantage of the method of the present disclosure is that it increases the amount of sul furic acid that may be recovered from the tailings material by reducing the content of sulfur in the calcine formed in the roasting proces s whi le at the same time producing a calcine with a lowered sulfur content .

[0079] An arrangement for handl ing tail ings material from mineral treatment processes is disclosed . The arrangement may comprise : - a first roaster (3) configured to roast tailings material (1) from a mineral treatment process to form a first roaster off-gas comprising dust (5) and a first roaster underflow (4) and the roaster in configured to feed the first roaster offgas comprising dust (5) into a first cyclone (6) and to feed the first roaster underflow (4) into a second roaster (9) ,

[0080] - at least one primary cyclone (6) configured to receive the first roaster off-gas comprising dust (5) and separating it to form a cyclone overflow (7) and a cyclone underflow (8) and the cyclone is configured to feed the cyclone underflow (8) into a second roaster (9) and the cyclone overflow (7) into a heat recovery boiler (10) ,

[0081] - a heat recovery boiler (10) configured to receive the primary cyclone overflow (7) and forming a heat recovery boiler overflow (12) and heat recovery boiler underflow (11) and feeding the heat recovery boiler underflow (11) into a second roaster (9) ,

[0082] - a second roaster (9) configured to receive the first roaster underflow (4) and cyclone underflow (8) , and roasting them to form a roasted material flow (18) and feeding it into a cooler (23) , and

[0083] - a cooler (23) configured to receive the roasted material flow (18) and forming a cooler underflow in the form of calcine (22) .

[0084] By roasting the tailings material and separating solids from the off-gas of the roasted materials it is possible to improve the recovery of valuable materials from tailings recovered from various processes such as metallurgical processes. Following collecting the valuable material or desired product from various processes, they leave a tailings fraction that will inevitably also contain some of the valuable material that would normally be discarded as waste.

[0085] In certain embodiment, the first roaster may be a stationary fluidized bed roaster or a circulating fluidized bed roaster. In certain embodiments, the second roaster may be a stationary fluidized bed roaster .

[0086] In certain embodiments, roasting gas (2) is fed into the first and / or second roaster.

[0087] In one embodiment, the underflow from the at least one primary cyclone can be arranged to be fed back (27) into the first roaster to increase the retention time of the calcine in the roaster.

[0088] In certain embodiments, off-gas (17) from the second roaster (9) may be separated in a cyclone (19) to form dust (21) that is combined with the calcine (22) and secondary air (28) that may be fed into the upper part of the first roaster (3) .

[0089] In one embodiment, at least one roaster is an oxidizing roaster.

[0090] In one embodiment, all roasters are oxidizing roasters .

[0091] In certain embodiments, the cooler (23) used to cool the roasted material is a fluid bed cooler or a drum cooler.

[0092] In certain embodiments, when the cooler (23) is a fluid bed cooler, additional gas and / or air (35) is fed into the cooler (23) together with the roasted material flow (18) . In certain embodiments, the cooler off-gas (24) may be fed into a cyclone (36) and separated to form dust (21) that is combined with the calcine (22) and secondary air (28) that may be fed into the upper part of the first roaster (3) , see Figs. 2 and 3. In certain embodiments, off-gas (17) from the second roaster (9) is fed into the cooler together with the roasted material flow (18) . In certain embodiments, the cooler off-gas (24) may be fed into a cyclone (36) and separated to form dust (21) that is combined with the calcine (22) and secondary air (28) that may be fed into the upper part of the first roaster (3) , see Fig. 3.

[0093] In certain embodiments, off-gas (17) from the second roaster (9) may be separated in a cyclone (19) to form dust (21) that is combined with the calcine (22) and secondary air (28) that may be fed into the upper part of the first roaster (3) . When the cooler (23) is a fluid bed cooler, additional gas and / or air (35) is fed into the cooler (23) together with the roasted material flow (18) . The cooler off-gas (24) may be fed into a cyclone (36) and separated to form dust (21) that is combined with the calcine (22) and secondary air (28) that may be fed into the upper part of the first roaster ( 3 ) , see Fig . 3.

[0094] In certain embodiments, off-gas (17) from the second roaster (9) may be separated in a cyclone (19) to form dust (21) that is combined with the calcine (22) and secondary air (28) that may be fed into the upper part of the first roaster (3) . , when the cooler (23) is a fluid bed cooler, additional gas and / or air (35) is fed into the cooler together with the roasted material flow (18) . The cooler off-gas (24) may be fed into a cyclone (36) and separated to form dust (21) that is combined with the calcine (22) and secondary air (28) that may be fed into the upper part of the first roaster ( 3 ) , see Fig . 3.

[0095] Roasting the tailings in oxidizing conditions enables recovery of sulfur contained in the tailings. In an oxidizing roaster, sulfur is oxidized to sulfate which may be recovered as sulfuric acid. In one embodiment , the second roaster is part of a fluid bed cooler or a drum cooler .

[0096] In certain embodiments , the off-gas from the second roaster may be separated in a cyclone to form dust that is combined with the calcine and secondary air that may be fed into the upper part of the first roaster .

[0097] In one embodiment , the arrangement comprises at least two , at least three , at least four, or at least five primary cyclones arranged consecutively after each other .

[0098] In one embodiment , the arrangement comprises at least two primary cyclones arranged parallel to each other .

[0099] By using multiple consecutive or parallel cyclones configured to feed the cyclone off-gas from one cyclone into the next cyclone more of the dust contained in the gas fed into the first cyclone is entrained, meaning that more of the valuable materials contained in the overflow materials is recovered .

[0100] In one embodiment , the arrangement comprises a multiclone . As used herein, a "multiclone" refers to a dust collector system comprising multiple smaller cyclones in one device to efficiently separate dust from a gas stream .

[0101] In one embodiment , the sulfur is oxidi zed in the first and / or second roasting . By roasting the sulfur contained in the tai lings material by oxidi zing it , it is possible to recover the sulfur and utili zing it e . g . for the production of sulfuric acid .

[0102] In one embodiment , the arrangement comprises a de-dusting device ( 13 ) arranged to receive the heat recovery boiler overflow ( 12 ) to separate remaining dust ( 15 ) in the recovery boiler overflow from the off-gas ( 14 ) . The dust may be collected, granulated or pelleti zed, and returned to the first roaster . By pelleti zing or granulating the sulfur-containing material in the cyclone overflow, the smaller particles can be returned to roasting enabling the recovery of more of the valuable material. In one embodiment, the de-dusting device may be a hot ESP (electrostatic precipitator) .

[0103] In one embodiment, the arrangement comprises a hot ESP (electrostatic precipitator) arranged to receive the recovery boiler overflow to separate remaining dust in the recovery boiler overflow from the off-gas. The dust may be collected, granulated or pelletized (20) , and returned (26) to the first roaster. By pelletizing or granulating the sulfur-containing material in the cyclone overflow, the smaller particles can be returned to roasting enabling the recovery of more of the valuable material. In certain embodiments, the dust collected from the de-dusting device may be combined (25) with the calcine (22) .

[0104] In certain embodiments, the off-gas (14) from the de-dusting device is fed into a wet gas cleaning device (16) . In one embodiment, the wet gas cleaning device may be a wet scrubber. In certain embodiments, the wet gas cleaning device may comprise several steps for cleaning said gas.

[0105] In one embodiment, the tailings material comprises tailings formed in a primary flotation treatment (30) of underflow material (31) from a mineral flotation line. When the tailings or underflow material exits a mineral flotation line, it will essentially always contain valuable materials to some extent and the valuable materials will generally be discarded as waste as the amounts of valuable material is relatively low and the particle size is relatively small, making the collection of the valuable materials impractical using conventional floatation processes.

[0106] In one embodiment, the primary flotation treatment arranged to receive underflow (31) from a mineral flotation line as slurry infeed, for the separation of slurry into cleaner underflow of recovered valuable material (33) and cleaner overflow (29) arranged to flow into the first roaster as infeed (Fig.4) .

[0107] In one embodiment, the recovered valuable material comprises iron.

[0108] In one embodiment, the primary flotation treatment arranged to receive underflow (31) from a mineral flotation line as slurry infeed, for the separation of slurry into cleaner overflow of recovered valuable material (33) and cleaner underflow (34) arranged to flow into the first roaster as infeed (Fig.5) .

[0109] In certain embodiments, the tailings material is roasted in a roasting according to the present disclosure ( 32 ) .

[0110] In certain embodiments, the valuable materials contained in the tailings material and recovered using the process of the present disclosure may be cobalt, nickel, gold, platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, and platinum) , copper, zinc, silver, and / or iron which may be recovered following further treatment of the calcine, and / or sulfur.

[0111] In one embodiment, the recovered valuable material comprises cobalt, nickel, gold, platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, and platinum) , copper, zinc, silver, and / or iron which may be recovered following further treatment of the calcine, and / or sulfur. In one embodiment, the recovered valuable material comprises copper.

[0112] In one embodiment, the mineral flotation line comprises at least three flotation units. By using at least three flotation units, it is possible to ensure that all valuable materials that can be recovered by flotation have been recovered prior to feeding the tailings into an arrangement according to the present disclosure . In essence , only the very last fines collected after several flotation treatments are collected and fed into an arrangement according to the present disclosure .

[0113] The arrangement described in the current specification has the added util ity of improving the recovery of valuable materials from the tailings produced in various metallurgical processes . The valuable materials recovered from the process may be metals such as cobalt , nickel , gold, platinum group metals ( ruthenium, rhodium, palladium, osmium, iridium, and platinum) , copper, zinc, silver, and / or iron which may be recovered following further treatment of the calcine , and / or sulfur which can be oxidi zed and used e . g . in the production of sulfuric acid .

[0114] EXAMPLES

[0115] Reference will now be made in detail to various embodiments .

[0116] The description below discloses some embodiments in such a detail that a person skilled in the art is able to utili ze the embodiments based on the disclosure . Not all steps or features of the embodiments are discussed in detail , as many of the steps or features will be obvious for the person skilled in the art based on this specification .

[0117] Example

[0118] A flow of approximately 31 . 6 t / h of fine pyrite tailings from a mineral flotation line was fed into a roaster and roasted at approximately 850 ° C . The roaster off-gas was fed into a cyclone to separate the dust contained in the off-gas into a cyclone underflow which was combined with the bed discharge from the first roaster and fed into the second roaster . The cyclone overflow was fed into a heat recovery boiler and separated into a boiler overflow containing gas and fine dust that was fed into a hot ESP and a boiler underflow containing most of the solids that was fed into the second roaster . The dust collected from the hot ESP was granulated and returned to the first roaster while the off-gas from the hot ESP was treated in wet gas cleaning .

[0119] The roasted material collected from the second roaster was fed into a f luid bed cooler from which the cooled calcine was collected .

[0120] Comparative example

[0121] A flow of approximately 31 . 6 t / h of fine pyrite tailings from a mineral flotation line was fed into a roaster and roasted at approximately 850 ° C . The roasted material was fed into a heat recovery boiler from which the off-gas was fed into a hot ES P and the bed discharge into a fluid bed cooler .

[0122] The dust collected from the hot ESP was granulated and returned to the f irst roaster whi le the off-gas from the hot ESP was treated in wet gas cleaning .

[0123] The roasted material collected from fluid bed cooler was collected as a cooled calcine .

[0124] In both examples , the sulfur collected from the off-gas from the hot ESP was converted to sulfuric acid

[0125] The results of the two examples are presented in Table 1 .

[0126]

[0127] As is evident from comparison of the two examples , a method according to the present disclosure produced a calcine containing a lower amount of sul fur and consequently also produced more sulfuric acid . As the amount of sulfur contained in the calcine was lower, the relative content of valuable products , in this case iron, was higher . Simultaneously, the method according to the present disclosure also required less process water as the amount of calcine needed to be cooled was lower than in the comparative example .

[0128] It is obvious to a person skil led in the art that with the advancement of technology, the basic idea may be implemented in various ways . The embodiments are thus not limited to the examples described above ; instead, they may vary within the scope of the claims .

[0129] The embodiments described hereinbefore may be used in any combination with each other . Several of the embodiments may be combined together to form a further embodiment . A method or an arrangement , disclosed herein, may comprise at least one of the embodiments described hereinbefore . It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to 'an' item refers to one or more of those items. The term "comprising" is used in this specification to mean including the feature (s) or act(s) followed thereafter, without excluding the presence of one or more additional features or acts.

Claims

CLAIMS1. A method for handling fine tailings from mineral treatment processes comprising- roasting tailings material (1) in a first roaster (3) having oxidizing conditions creating a first roaster off-gas comprising dust (5) and a first roaster bed discharge (4) ,- separating the first roaster off-gas comprising dust (5) in at least one primary cyclone (6) to form a cyclone overflow (7) and cyclone underflow (8) ,- roasting the first bed discharge (4) and the cyclone underflow (8) in a second roaster (9) having oxidizing conditions to form a roasted material flow (18) ,- feeding the cyclone overflow (7) into a heat recovery boiler (10) to form a heat recovery boiler overflow (12) and a heat recovery boiler underflow (11) , characterized in that the underflow (11) from the heat recovery boiler (10) is fed into the second roaster (9) and the roasted material flow (18) from the second roaster (9) is fed into a cooler (23) to form a cooler underflow in the form of calcine (22) .

2. The method of claim 1, wherein the first roaster is a stationary fluidized bed roaster or a circulating fluidized bed roaster.

3. The method of any of the preceding claims, wherein the second roaster is a stationary fluidized bed roaster .

4. The method of any of the preceding claims, wherein the tailings material (2) has a d50 particle size of 250 pm or less, or 200 pm or less, or 150 pm or less, or 125 pm or less, or 100 pm or less, or 75 pm or less, or 50 pm or less, or 30 pm or less.

5. The method of any of the preceding claims, wherein at least one roasting is performed in an oxygen- enriched atmosphere.

6. The method of any of the preceding claims, wherein the first roaster off-gas comprising dust is separated to form a cyclone overflow and a cyclone underflow by passing it through at least two, at least three, at least four, or at least five consecutive primary cyclones configured to feed the cyclone off-gas from one cyclone into the next cyclone and feeding the cyclone overflow from the final cyclone into the recovery boiler.

7. The method of any one of claims 1 - 5, wherein the first roaster off-gas comprising dust is separated to form a cyclone overflow and a cyclone underflow by passing through two or more primary cyclones arranged parallel to each other.

8. The method of any of the preceding claims, wherein the first roaster off-gas comprising dust is separated in a separation process comprising using a multiclone .

9. The method of any of the preceding claims, wherein the sulfur-containing material contained in the cyclone underflow is granulated and returned (27) to the first roaster.

10. The method of any of the preceding claims, wherein the off-gas formed in the one or more cyclones or multiclone is fed into a de-dusting device.

11. The method of any of the preceding claims, wherein the off-gas formed in the one or more cyclones, multiclone, and / or de-dusting device is fed into the first roaster.

12. The method of any of the preceding claims, wherein sulfur is oxidized in the first and / or second roasting .

13. The method of any of the preceding claims, wherein the heat recovery boiler overflow (12) is fedinto a de-dusting device (13) to separate remaining dust (15) from the off-gas (14) and the dust is collected, granulated or pelletized (20) , and returned (26) to the first roaster (3) .

14. The method of any of the preceding claims, wherein the tailings material (1) comprises tailings formed in a primary flotation treatment (30) of underflow material (31) from a mineral flotation line.

15. The method of claim 14, wherein the primary flotation treatment arranged to receive underflow (31) from a mineral flotation line as slurry infeed, for the separation of slurry into cleaner underflow of recovered valuable material (33) and cleaner overflow (29) arranged to flow into the first roaster as infeed.

16. The method of claim 15, wherein the recovered valuable material comprises iron.

17. The method of claim 14, the primary flotation treatment arranged to receive underflow (31) from a mineral flotation line as slurry infeed, for the separation of slurry into cleaner overflow of recovered valuable material (33) and cleaner underflow (34) arranged to flow into the first roaster as infeed.

18. The method of claim 17, wherein the recovered valuable material comprises copper.

19. The method of any one of claims 14 - 18, wherein the amount of water in the tailings material is reduced using a thickener prior to roasting.

20. The method of any one of claims 14 - 19, wherein the amount of water in the tailings material is reduced by filtering prior to roasting.

21. The method of any one of claims 14 - 20, wherein the amount of water in the tailings material is reduced by filtering using a pressure filter prior to roasting .

22. An arrangement for handling fine tailings from mineral treatment processes comprising- a first roaster (3) configured to roast the fine tailings (1) from the mineral treatment process to form a first roaster off-gas comprising dust (5) and a first roaster underflow (4) and the roaster is configured to feed the first roaster offgas comprising dust (5) into a first cyclone (6) and to feed the first roaster underflow (4) into a second roaster (9) ,- at least one cyclone (6) configured to receive the first roaster off-gas comprising dust (5) and separating it to form a cyclone overflow (7) and a cyclone underflow (8) and the cyclone is configured to feed the cyclone underflow (8) into a second roaster (9) and the cyclone overflow (7) into a heat recovery boiler (10) ,- a heat recovery boiler (10) configured to receive the primary cyclone overflow (7) and forming a heat recovery boiler overflow (12) and heat recovery boiler underflow (11) and feeding the heat recovery boiler underflow (11) into a second roaster (9) ,- a second roaster (9) configured to receive the first roaster underflow (4) and cyclone underflow (8) , and roasting them to form a roasted material flow (18) and feeding it into a cooler (23) , and a cooler (23) configured to receive the roasted material flow (18) and forming a cooler underflow in the form of calcine (22 ) .

23. The arrangement according to claim 22, wherein at least one roaster is an oxidizing roaster.

24. The arrangement according to any one of claims 22 - 23, wherein all roasters are oxidizing roasters .

25. The arrangement according to any one of claims 22 - 24, wherein the first roaster is a stationary fluidized bed roaster or a circulating fluidized bed roaster .

26. The arrangement according to any one of claims 22 - 25, wherein the second roaster is a stationary fluidized bed roaster.

27. The arrangement according to any one of claims 22 - 26, wherein the cooler is a fluid bed cooler or a drum cooler.

28. The arrangement according to any one of claims 22 - 27, wherein the arrangement comprises at least two, at least three, at least four, or at least five cyclones arranged consecutively after each other.

29. The arrangement according to any one of claims 22 - 28, wherein the arrangement comprises at least two primary cyclones arranged parallel to each other .

30. The arrangement according to any one of claims 22 - 29, wherein the arrangement comprises a multiclone .

31. The arrangement according to any one of claims 22 - 30, wherein the sulfur is oxidized in the first and / or second roasting.

32. The arrangement according to any one of claims 22 - 31, wherein the arrangement comprises a dedusting device (13) arranged to receive the heat recovery boiler overflow (12) to separate remaining dust (15) in the recovery boiler overflow from the off-gas (14) .

33. The arrangement according to any one of claims 22 - 32 collected, granulated or pelletized (20) , and returned (26) to the first roaster.

34. The arrangement according to of any one of claims 22 - 33, wherein the tailings material (2) comprises tailings formed in a primary flotation treatment (30) of underflow material (31) from a mineral flotation line.

35. The arrangement according to of any one of claims 22 - 34, wherein the primary flotation treatment arranged to receive underflow (31) from a mineral flotation line as slurry infeed, for the separation of slurry into cleaner underflow of recovered valuable material (33) and cleaner overflow (29) arranged to flow into the first roaster as infeed.

36. The arrangement according to of any one of claims 22 - 35, wherein the recovered valuable material comprises iron.

37. The arrangement according to of any one of claims 22 - 36, the primary flotation treatment arranged to receive underflow (31) from a mineral flotation line as slurry infeed, for the separation of slurry into cleaner overflow of recovered valuable material (33) and cleaner underflow (34) arranged to flow into the first roaster as infeed.

38. The arrangement according to of any one of claims 22 - 37, wherein the recovered valuable material comprises copper.

39. The arrangement according to of any one of claims 22 - 38, wherein the mineral flotation line comprises at least three flotation units.

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