WO2015086906A1 - Method and process arrangement of separating elemental sulphur - Google Patents

Method and process arrangement of separating elemental sulphur Download PDF

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Publication number
WO2015086906A1
WO2015086906A1 PCT/FI2014/050983 FI2014050983W WO2015086906A1 WO 2015086906 A1 WO2015086906 A1 WO 2015086906A1 FI 2014050983 W FI2014050983 W FI 2014050983W WO 2015086906 A1 WO2015086906 A1 WO 2015086906A1
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Prior art keywords
water soluble
organic solvent
elemental sulphur
soluble organic
leaching
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PCT/FI2014/050983
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French (fr)
Inventor
Pia SINISALO
Tuukka KOTIRANTA
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Outotec (Finland) Oy
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Publication of WO2015086906A1 publication Critical patent/WO2015086906A1/en

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B17/00—Sulfur; Compounds thereof
    • C01B17/02—Preparation of sulfur; Purification
    • C01B17/027—Recovery of sulfur from material containing elemental sulfur, e.g. luxmasses or sulfur containing ores; Purification of the recovered sulfur
    • C01B17/033—Recovery of sulfur from material containing elemental sulfur, e.g. luxmasses or sulfur containing ores; Purification of the recovered sulfur using a liquid extractant
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/11—Removing sulfur, phosphorus or arsenic other than by roasting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/02—Apparatus therefor
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • the present invention relates to a method and process arrangement of separating elemental sulphur. More specifically the present invention relates to a method and process arrangement of separating elemental sulphur from materials originating from hydrometallurgical processes.
  • US patent 3,619,147 discloses a process and apparatus wherein a solvent for dissolving and recovering sulphur from sulphur-bearing ore or concentrate may be continuously recycled and reused without loss.
  • the publication relates to a process for initially leaching a crushed sulphur ore or concen- trate and thereafter passing the resultant slurry to a separator for the separation of the leached residue from the sulphur saturated or rich solvent. Thereafter, water is separated from the sulphur saturated solvent and the solvent is fed into a crystal I izer from which extremely pure elemental sulphur is obtained.
  • the solvent disclosed to be used in the method is tnchloroethylene.
  • US patent 3,762,880 discloses an apparatus for the crystallization and recovery of sulphur from sulphur-pregnant solvent.
  • tnchloroethylene was used for dissolving sulphur.
  • tnchloroethylene is poorly soluble in water.
  • the apparatus disclosed in US 3,762,880 utilises the non- solubility of tnchloroethylene and water for crystallizing the sulphur.
  • US patent 3,063,817 discloses a process for extracting sulphur from material containing elemental sulphur, which comprises treating the sulphur containing material with an aliphatic hydrocarbon solvent having from 7 to 18 carbon atoms.
  • the temperature is maintained between 85°C and 132°C, the solution is separated from the residual solid matter, cooled to a sulphur crystallizing temperature and the sulphur is separated from the cooled solution.
  • aliphatic hydrocarbon solvents are not water soluble.
  • Harlamovs, J.R., Preliminary evaluation of sulphur sulphidic residue separations, Final Report, Cominco Ltd., Research & Development, Trail, B.C. 1991 , 76 p. relates to methods for separating sulphur from leaching residue. However, the method is performed in a temperature above the melting point of sulphur and above the flash point of the solvent used.
  • perchloroethylene is not water soluble, is toxic to aquatic life with long lasting effects and is suspected of causing cancer.
  • An object of the present invention is thus to provide a method and a process arrangement for implementing the method of separating elemental sulphur from starting material containing the same.
  • the objects of the invention are achieved by a method and a process arrangement, which are characterized by what is stated in the independent claims.
  • the preferred embodiments of the invention are disclosed in the dependent claims.
  • the invention is based on the idea of separating elemental sulphur from elemental sulphur -containing starting material by a method, which comprises
  • a leaching step wherein the starting material is contacted with a water soluble organic solvent at a temperature below the flash point of the water soluble organic solvent for leaching the elemental sulphur contained in the starting material into the water soluble organic solvent
  • the water soluble organic solvent used in the leaching step is a compound or a mixture of com- pounds capable of leaching elemental sulphur.
  • the method comprises a first washing step of the leaching residue by a water soluble organic solvent, typically after the first solid-liquid separation step.
  • the first washing step may also be a part of the first solid-liquid separation step.
  • the water solu- ble organic solvent used for the washing of the leaching residue is the same as the water soluble organic solvent used in the leaching step.
  • the water soluble organic solvent is fed after the washing step to be used further in the leaching step.
  • the organic solvent for washing serves also as a make-up feed to the overall method.
  • the elemental sulphur - containing starting material is any suitable material containing elemental sulphur.
  • the starting material originates from metallurgical process, such as hydrometallurgical process. More typically the starting material is hydromet- allurgical residue produced during treatment of sulphide-bearing raw material. More typically the starting material is leaching residue containing elemental sulphur.
  • the temperature is below the flash point of the water soluble organic solvent used in the leaching step.
  • the temperature is in the range of 80 - 140°C. More typically the temperature is in the range of 100 - 130°C, more typically in the range of 105 - 125°C.
  • the water soluble organic solvent containing the elemental sulphur is separated from the leaching residue by any suitable method for solid- liquid separation such as thickening, filtration, centrifuging, or by any combination of previously mentioned methods.
  • the temperature of the water soluble organic solvent containing the elemental sulphur is lowered to a temperature in the range of 10 - 80°C for crystallizing the elemental sulphur.
  • the water soluble organic solvent is separated from the crystallized elemental sulphur by any suitable solid-liquid separation method, such as thickening, filtration, centrifuging, or by any combination of previously mentioned methods. If desired, it is also possible to wash the separated crystallized elemental sulphur with water and according to an embodiment of the invention the method comprises a second washing step after the second solid- liquid separation step.
  • the second washing step may also be a part of the second solid-liquid separation step.
  • the invention also relates to a process arrangement of separating elemental sulphur from a starting material containing elemental sulphur, typically for performing the above method of the present invention, wherein the arrangement comprises
  • a leaching unit adapted for leaching a starting material by contacting it with a water soluble organic solvent at a temperature below the flash point of the water soluble organic solvent for leaching the elemental sulphur contained in the starting material into the water soluble organic solvent
  • a first solid-liquid separation unit adapted for separating the water soluble organic solvent containing the elemental sulphur from a leaching residue
  • a second solid-liquid separation unit adapted for separating the water soluble organic solvent from the crystallized elemental sulphur.
  • the leaching unit is any reactor or series of reactors suitable for leaching.
  • the first solid-liquid separation unit is any unit suitable for solid-liquid separation such as a thickening unit, a filtration unit, a centrifuging unit or any combination of previously mentioned units.
  • the crystallization unit is any unit suitable for crystallization.
  • the second solid-liquid separation unit is any unit suitable for solid-liquid separation such as a thickening unit, a filtration unit, a centrifuging unit or any combination of previously mentioned units.
  • the process arrangement comprises a first washing unit after the first solid-liquid separation unit.
  • the washing unit may also be part of another process unit, for example the washing unit may be realized as part of the solid-liquid separation unit.
  • the process arrange- ment comprises a second washing unit after the second solid-liquid separation unit.
  • the washing unit may also be part of another process unit, for example the washing unit may be realized as part of the solid-liquid separation unit.
  • the water soluble organic solvent used can be characterized as non-toxic, non-carcinogenic, and environmentally friendly.
  • the whole method is also conducted in a temperature below the flash point of the water soluble organic solvent used.
  • the whole method is further performed in atmospheric or slightly elevated pressure (up to 3 bar).
  • Another advantage of the present method is that elemental sulphur can be recovered with high yield and excellent purity.
  • a high yield can be ob- tained with the conditions of the leaching step of the present invention, wherein starting material is fed into the leaching step in an amount, which is not more than from which amount the solvent is able to leach elemental sulphur.
  • the solvent is fairly selective to elemental sulphur and hence elemental sulphur with high purity is obtained.
  • the produced elemental sulphur may also be washed with water or melted in order to remove solvent residues from the product and thus increase the product purity.
  • An advantage of the present method is further that the leaching residue from which the elemental sulphur has been separated can be processed further for recovering valuable metals. Traces of water soluble organic solvent tend not to cause foaming due to water soluble property of the organic solvent during further processing if hydronnetallurgical. This alleviates process control during further metal recovery.
  • a further advantage of an embodiment of the present invention is that the leaching residue does not contain elemental sul- phur or contains only very small unavoidable amounts of elemental sulphur. Elemental sulphur is known to have a remarkable detrimental economic impact on hydronnetallurgical platinum group metals and gold recovery processes. If no further metals are desired to be recovered from the leaching residue, it is also possible to route the elemental sulphur-free leaching residue to land filling.
  • a further advantage of the present method is that the loss of the organic solvent from the process can be avoided in a relatively simple way. It is possible to remove organic solvent from leaching residue and/or crystallized elemental sulphur simply by washing with water and thereafter recovering the organic solvent and recycling it back to the leaching step.
  • a further advantage of an embodiment of the present method is that it is not necessary to dry the starting material before the leaching. This results in decreased amount of process equipment as well as economical savings as there is no need for a drying step or unit before feeding to the leaching step.
  • Figure 1 shows an example embodiment of the present invention
  • Figure 2 shows an example embodiment of the present invention, wherein the optional steam condensing and water/organic solvent separation are presented.
  • the invention relates to a method of separating elemental sulphur from elemental sulphur -containing starting material, which method comprises a leaching step, wherein the starting material is contacted with a water soluble organic solvent at a temperature below the flash point of the organic solvent.
  • the temperature is in the range of 80 - 140°C, more typically in the range of 100 - 130°C, even more typically in the range of 105 - 125°C for leaching the elemental sulphur contained in the starting material into the water soluble organic solvent.
  • the temperature in the leaching step is between the boiling point of water and the flash point of the organic solvent used. This enhances the leaching of elemental sulphur and evaporates the water possibly contained in the starting material.
  • the temperature of the leaching liquor may be maintained above the boiling point of water and below the flash point of the organic, water soluble solvent.
  • the temperature of the leaching liquor By selecting the temperature of the leaching liquor to be above the boiling point of water, it is possible to separate the water contained in the starting material by evaporating it, thus according to an embodiment of the invention the water possibly comprised in the water soluble organic solvent is evaporated already during the leaching step and thereby the leaching liquor is regenerated already during the leaching step. This enhances the leaching of the elemental sulphur into the organic, water soluble solvent, because the wa- ter present in the leaching step typically interferes with the leaching of the elemental sulphur.
  • the leaching is understood to mean both dissolving and/or carrying the elemental sulphur. Typically, when performing the method below the melting point of sulphur the leaching means dissolving. Typically when performing the method above melting point of sulphur, the leaching is meant to comprise carrying the elemental sulphur or both dissolving and carrying the elemental sulphur.
  • the starting material may be any material containing elemental sulphur, from which it is desired to remove the elemental sulphur.
  • the starting material is material obtained from hydrometallurgical process. More typically the starting material is leaching residue.
  • the starting material may be dried before the leaching or the starting material may contain moisture, such as water. In some embodiments, due to the temperature used in the leaching step the water possibly contained in the starting material evaporates in the leaching step. This enables to control the water balance of the method.
  • the elemental sulphur is leached into the organic water soluble solvent.
  • the leaching liquor of the leaching step typically contains organic, water soluble solvent.
  • the leaching liquor may also be a mixture of suitable water soluble organic solvents.
  • water typically evaporates from the starting material. Water evaporation may be enhanced by using any suitable carrier gas, such as nitrogen.
  • the evaporated water may be directed to a condenser and condensed to distillate to be used for example in the washing step later in the process.
  • a further possibility is to treat the water- containing solution obtained from the leaching step by any known method, such as membrane filtration, evaporation or distillation for separating any organic solvent possible present and recycling them back to the process. It is also possible to treat any washing water used in the present method in the same way as the water-containing solution obtained from the leaching step.
  • the leaching is typically performed under atmospheric pressure.
  • the leaching is performed in a pressure between the atmospheric pressure and 3 bar.
  • the leaching step is typically performed in conditions in which as much as possible elemental sulphur is leached to the solvent, however in such conditions that all of the elemental sulphur is leached. If elemental sulphur is not leached it will end up in the leaching residue, which is not desired.
  • the former conditions decrease the size of the streams in the process and hence make the leaching unit, the first solid-liquid separation unit, crystallization unit and the second solid-liquid separation unit smaller.
  • the organic, water soluble solvent is any organic solvent capable of dissolving and/or carrying elemental sulphur. More typically the organic, water soluble solvent is selected from suitable solvents, which are water soluble but not heavily azeotropic with water. The selected solvents have a high flash point, typically at least 10 degrees above the leaching temperature.
  • the solvent of the present invention is able to leach elemental sulphur and can be characterized as non-toxic, non-carcinogenic, and environmentally friendly.
  • organic, water soluble solvent is a compound or mixture of compounds of general formula (I)
  • Ri-(O-C 2-4 -alkylenyl)n-OR 2 (I) wherein Ri is H, Ci -5 -alkyl, or -C(O)-Ci -5 -alkyl,; R 2 is independently H, Ci-5-alkyl, or -C(O)-Ci -5 -alkyl; and n is equal to or greater than 1 , provided that the compound is water soluble.
  • the water soluble solvent is a compound or mixture of compounds of general formula (I), wherein Ri is H or Ci-5-alkyl, in particular H or ethyl; and R 2 is H or Ci -5 -alkyl, in particular H or ethyl.
  • n in the general formula (I) is determined by the solubility of the compound. This depends of the nature of the C 2-4 -alkylene group. For exam- pie, the average number of repeating units (expressed by n in the formula) in the case of polyethylene glycols, i.e. when the C 2-4 - alkylenyl is ethylenyl, can range from 2 to 80. In the case of polypropylene glycols, i.e. when the C 2-5 - alkylenyl is propylenyl, the n value can range from 2 to 60. In the case of poly- butylene glycols, i.e. when the C 2-4 - alkylenyl is butylenyl, the n value can range from 2 to 40. In a preferable example n in the general formula (I) is from 1 to 30.
  • the water soluble solvent is a compound or mixture of compounds of general formula (II) Ri-(OCH 2 CH 2 ) n -OR 2 (l l) wherein Ri is H or Ci -5 -alkyl, preferably H, methyl or ethyl; R 2 is independently H or Ci-5-alkyl, preferably H, methyl or ethyl, and n is an integer from 1 to 20, preferably 1 to 10.
  • Ri is H or Ci -5 -alkyl, in partic- ular methyl or ethyl, R 2 is H, and n is an integer from 1 to 20, preferably 1 to 10.
  • the water soluble organic solvent is selected from a group consisting of ethylene glycol,diethylene glycol, triethylene glycol, polyethylene glycol such as polyethylene glycol having average molecular weight 300, diethylene glycol monomethyl ether, diethy- lene glycol dimethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, triethylene glycol monomethyl ether, triethylene glycol dimethyl ether, triethylene glycol monoethyl ether, triethylene glycol diethyl ether, triethylene glycol monobutyl ether, triethylene glycol dibutyl ether, polyethylene glycol monomethyl ether such as polyethylene glycol monomethyl ether having average molecular weight 350, polyethylene glycol monomethyl ether having average molecular weight 500, polyethylene glycol dimethyl ether, polyethylene glycol monoethyl ether, and polyethylene glycol diethyl ether.
  • polyethylene glycol such as polyethylene glycol having average molecular weight 300, diethylene
  • the water soluble organic solvent is polyethylene glycol monomethyl ether, in particular polyethylene glycol monomethyl ether having average molecular weight 350 or 500.
  • the water solubility of the leaching liquor simplifies the washing of organic solvent from the solid matter, e.g. all solid matter formed in the process, such as leaching residue, remaining after the leaching or the crystallized elemental sulphur.
  • the leaching residue obtained from the present method is elemental sulphur-free, which alleviates recovery of many valuable metals from it.
  • the recovery of valuable metals is also alleviated, as metal concentrations have increased during elemental sulphur separation as elemental sulphur is removed from the solids.
  • the recovery of valuable metals is further alleviated as traces of water soluble organic solvent tend not to cause foaming due to water soluble property of the organic solvent unlike traces of non-volatile and not water soluble organic solvent during further processing if hydrometallur- gical. This alleviates process control during further metal recovery.
  • the leaching liquor used would be organic non-volatile and not water soluble, then for separating the elemental sulphur from the starting material the organic solvent used as the leaching liquor would have to be washed from the solid matters with another organic solvent, such as a short chain hydrocarbon, which hydrocarbon can be further removed by an alcohol and be evaporated from the solid matter.
  • distillation steps would be required for treating the used washing solutions for separating the leaching liquor and the washing liquors from each other to be able to recycle them.
  • the method comprises a first solid-liquid separation step, wherein the water soluble organic solvent containing the elemental sulphur is separated from a leaching residue.
  • the solid-liquid separation may be performed by any suitable method for solid-liquid separation such as thickening, filtration, centri- fuging, or by any combination of previously mentioned methods.
  • the method comprises a first washing step.
  • the first washing step may also be after the first solid- liquid separation step or it may be arranged in connection with the first solid- liquid separation step.
  • the method typically comprises a first washing step, wherein the leaching residue is washed by a water soluble organic solvent.
  • the water soluble organic solvent used for the washing of the leaching residue is the same as the water soluble organic solvent used in the leach- ing step.
  • the leaching residue may be typically further washed with water for removing small amounts of the organic solvent left in the leaching residue.
  • the leaching residue may also be washed with only water.
  • the obtained elemental sulphur -depleted leaching residue may be directed further to known process steps for recovering desired metals, such as zinc, gold, silver and/or platinum group metals.
  • the method of the present invention comprises a crystallization step, wherein elemental sulphur is crystallized.
  • the crystallization is typically performed by lowering the temperature of the water soluble organic solvent containing the elemental sulphur to a temperature of 10 - 80°C.
  • the temperature to which the water soluble organic solvent is cooled is 20 - 60°C.
  • the cooling may be performed by any suitable method for cooling such as using heat exchangers, using cooling water or using any combination of previously mentioned methods.
  • a counter-current heat exchanger may be used, wherein the solution stream from the first solid-liquid separation step to crystallization step is cooled by us- ing the solution stream from the second solid-liquid separation step to the leaching step, which again on its side is warmed up in the heat exchanger.
  • the method further comprises a second solid-liquid separation step, wherein the water soluble organic solvent is separated from the crystallized elemental sulphur.
  • the second solid-liquid separation may be performed by any suitable solid-liquid separation method, such as thickening, filtration, cen- trifuging, or by any combination of previously mentioned methods.
  • the obtained crystallized elemental sulphur may be washed in a second washing step with water for removing small amounts of the organic solvent left in the solids.
  • the second washing step may be either after the second solid-liquid separation step or in connection with the second solid-liquid separation step.
  • the obtained crystallized elemental sulphur may also be melted whereby elemental sulphur and the organic solvent residues form separate phases that can be recovered. It is possible to form briquettes from the produced elemental sulphur.
  • the invention also relates to a process arrangement of separating elemental sulphur from a starting material containing elemental sulphur, typically for performing the above method of the present invention, wherein the arrangement comprises
  • a leaching unit adapted for leaching a starting material by con- tacting it with a water soluble organic solvent at a temperature below flash point of the water soluble organic solvent for leaching the elemental sulphur contained in the starting material into the water soluble organic solvent
  • a first solid-liquid separation unit adapted for separating the water soluble organic solvent containing the elemental sulphur from a leaching resi- due
  • a second solid-liquid separation unit adapted for separating the water soluble organic solvent from the crystallized elemental sulphur.
  • the leaching unit is any reactor or series of reactors suitable for leaching.
  • the leaching unit is series of agitated tanks.
  • the first solid-liquid separation unit is any unit suitable for solid-liquid separation such as a thicken- ing unit, a filtration unit, a centrifuging unit or any combination of previously mentioned units.
  • the crystallization unit is any suitable crystallization unit, such as an agitated tank or series of agitated tanks, and/or crystallizer and/or series of crystallizers.
  • the second solid-liquid separation unit is any unit suitable for solid-liquid separation such as a thickening unit, a filtration unit, a centrifuging unit or any combination of previously mentioned units.
  • the process arrangement comprises a first washing unit after the first solid-liquid separation unit.
  • the washing unit may also be part of another process unit, for example the washing unit may be realized as part of the solid-liquid separation unit.
  • the process arrangement comprises a second washing unit after the second solid-liquid separation unit.
  • the washing unit may also be part of another process unit, for example the washing unit may be realized as part of the solid-liquid separation unit.
  • the process arrangement further comprises a unit for further processing the crystallized, and optionally washed elemental sulphur.
  • the unit for further processing may be for example a melting unit or a briquetting unit.
  • Figure 1 is an example embodiment of the present method, wherein the starting material 1 is fed into a leaching step 2 containing water soluble organic solvent.
  • the leaching step the elemental sulphur contained in the starting material is leached into the organic water soluble solvent and vaporized steam 23 is removed from the leaching step 2.
  • Water soluble organic solvent containing leached elemental sulphur and solid matter 3 is removed from the leaching step 2 and routed to a first solid-liquid separation step 4.
  • the leaching residue 1 1 is separated from the water soluble organic solvent 5.
  • the separated leaching residue 1 1 is washed in a first washing step 14 by an organic water soluble solvent 7 and/or fresh water fed to the first washing step 14 (not shown in the figure).
  • the separated and washed leaching residue 12 is removed from the first washing step 14 and possibly routed to further processing for recovering metals contained in the leaching residue.
  • the water soluble organic solvent containing elemental sulphur is routed to a crystallization step 6, wherein the temperature of the water soluble organic solvent is reduced to be in the range of 10 - 80°C for crystallizing the elemental sulphur.
  • the water soluble organic solvent containing crystallized ele- mental sulphur is routed to a second solid-liquid separation step 8, wherein the crystallized elemental sulphur is removed from the water soluble organic solvent and recovered as crystallized elemental sulphur 15.
  • the separated organic water soluble solvent 17 is recycled back to the leaching step 2.
  • the obtained crystallized elemental sulphur 15 is routed to a washing step 10, wherein the crystallized elemental sulphur is washed with water (not shown in the Figure) and thus washed crystallized sulphur 19 is obtained.
  • the crystallized elemental sulphur 15 or washed crystallized sulphur 19 may be optionally routed to further processing 22 from which an elemental sulphur product 21 , such as briquettes, is obtained.
  • FIG 2 is otherwise equal to Figure 1 , except it shows in more detail the optional circulation of vaporized steam, organic solvent and washing waters in the method.
  • the vaporized steam 23 may be optionally routed to a condenser 16, wherein the vaporized steam is condensed into distillate 9 that may be routed to an optional water-organic solvent separation step 24.
  • the used washing water 32 from the 1 st washing step 14 and the used washing water 26 from the 2 nd washing step 10 are routed to the separation step 24.
  • water and the water soluble organic solvent are separated from each other, typically by membrane filtration or distillation.
  • the ob- tained organic fraction 30 may be routed to the leaching step 2 and the obtained water fraction 28 may be recycled back to the present method.
  • Diethylene glycol was used to separate elemental sulphur from dry hydrometallurgical residue. Leaching was carried out at 105°C in a 10 L reactor for 1 h. Leaching residue was separated from the pregnant solvent and washed with fresh diethylene glycol and then with water in a hot oil jacketed buchner funnel. Elemental sulphur was crystallized by cooling the hot pregnant filtrate to room temperature in a continuously stirred beaker. Crystallized ele- mental sulphur was separated from the raffinate and washed with water in a buchner funnel.
  • Elemental sulphur content was reduced from the original 64% of the starting material to 0.4% of the leaching residue during the treatment. Elemental sulphur purity in crystallized sulphur was 99.8%. The main impurity in crystallized sulphur was carbon originating from the solvent.
  • Polyethylene glycol monomethyl ether having average molecular weight 350 was determined to have elemental sulphur solubility of 26 g/L at 105°C and elemental sulphur solubility of 2 g/L at room temperature. Solubilities were calculated based on masses of solids and on the amount of solvent used in the test.
  • Triethylene glycol was found to dissolve elemental sulphur and wa- ter to evaporate during leaching.
  • the amount of crystallized elemental sulphur recovered was 16 g and the purity of the sulphur was 99.7%.
  • the main impurity in crystallized sulphur was carbon originating from the solvent. Residence time for cooling was 2 h.
  • a continuous leaching and crystallization test for diethylene glycol was made.
  • the test setup contained leaching of hydrometallurgical residue, solid liquid separation and washing of leaching residue, crystallization of elemental sulfur and solid liquid separation and washing of elemental sulfur.
  • Solvent was loaded to or close to the saturation point of elemental sulphur in the leaching stage that operated at 105°C temperature. Solvent was recycled 70 times during the run. The volume of the solvent circulating in the operation was 12 L.
  • FTIR Fourier trans- form infrared spectroscopy

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Abstract

The invention relates to a method of separating elemental sulphur from elemental sulphur-containing starting material, wherein the method comprises a) a leaching step, wherein the starting material is contacted with a water soluble organic solvent at a temperature below the flash point of the water soluble organic solvent for leaching the elemental sulphur contained in the starting material into the water soluble organic solvent, b)a first solid-liquid separation step, wherein the water soluble organic solvent containing the elemental sulphur is separated from a leaching residue, c) a crystallization step, wherein elemental sulphur is crystallized from the water soluble organic solvent; and d) a second solid-liquid separation step, wherein the water soluble organic solvent is separated from the crystallized elemental sulphur. The invention relates also to an apparatus of separating elemental sulphur from elemental sulphur-containing starting material.

Description

METHOD AND PROCESS ARRANGEMENT OF SEPARATING ELEMENTAL SULPHUR
FIELD OF THE INVENTION
The present invention relates to a method and process arrangement of separating elemental sulphur. More specifically the present invention relates to a method and process arrangement of separating elemental sulphur from materials originating from hydrometallurgical processes.
BACKGROUND OF THE INVENTION
The presence of elemental sulphur in materials, especially in mate- rials originating from hydrometallurgical processes, such as leaching residues, is problematic if the materials need to fulfil certain environmental requirements and/or if the materials contain valuable metals such as zinc, gold, silver or platinum group metals that are desired to recover from the materials. It is commonly known that the presence of elemental sulphur interferes at least the re- covery of precious metals such as gold.
US patent 3,619,147 discloses a process and apparatus wherein a solvent for dissolving and recovering sulphur from sulphur-bearing ore or concentrate may be continuously recycled and reused without loss. The publication relates to a process for initially leaching a crushed sulphur ore or concen- trate and thereafter passing the resultant slurry to a separator for the separation of the leached residue from the sulphur saturated or rich solvent. Thereafter, water is separated from the sulphur saturated solvent and the solvent is fed into a crystal I izer from which extremely pure elemental sulphur is obtained. The solvent disclosed to be used in the method is tnchloroethylene. Also other solvents which are vaporizable below the melting point of sulphur may be used. However, tnchloroethylene is poorly soluble in water, is harmful to aquatic life with long lasting effects and may cause cancer. In the process disclosed in US 3,619,147, the solvent is evaporated from the leaching residue and from produced elemental sulphur.
US patent 3,762,880 discloses an apparatus for the crystallization and recovery of sulphur from sulphur-pregnant solvent. Here again tnchloroethylene was used for dissolving sulphur. Again, tnchloroethylene is poorly soluble in water. The apparatus disclosed in US 3,762,880 utilises the non- solubility of tnchloroethylene and water for crystallizing the sulphur. US patent 3,063,817 discloses a process for extracting sulphur from material containing elemental sulphur, which comprises treating the sulphur containing material with an aliphatic hydrocarbon solvent having from 7 to 18 carbon atoms. The temperature is maintained between 85°C and 132°C, the solution is separated from the residual solid matter, cooled to a sulphur crystallizing temperature and the sulphur is separated from the cooled solution. However, aliphatic hydrocarbon solvents are not water soluble.
Herve, B . et al, Sulphur extraction from elemental sulphur-bearing materials. (U.S.) Bureau of Mines, Reno, NV. 1985, 1 1 p., discloses a method of separating sulphur from leaching residue. However, the method is performed in a temperature, above the flash point of the solvent used. Operating above the flash point of the solvent creates many special requirements for the process.
Harlamovs, J.R., Preliminary evaluation of sulphur sulphidic residue separations, Final Report, Cominco Ltd., Research & Development, Trail, B.C. 1991 , 76 p. relates to methods for separating sulphur from leaching residue. However, the method is performed in a temperature above the melting point of sulphur and above the flash point of the solvent used.
Ramalingam, K.V., Thomas, J., Recovery of sulphur. Chemical En- gineering World, Vol. XIV No. 6, p. 43 - 46 discloses a method of separating sulphur with kerosene and steam. However, kerosene is not water soluble.
Sciamanna, S.F., Lynn, S., Sulphur Solubility in Pure and Mixed Organic Solvents. Ind. Eng. Chem. Res., v 27, p. 485- 491 , 1988 discloses sulphur solubility values into organic solvents. However, no method for applying these values is presented.
Harver, F.P. and Wong, M.M., Recovering elemental sulfur from nonferrous minerals: ferric chloride leaching of chalcopyrite concentrate, Bureau of Mines, Report of investigations 7474, January 1971 , 20 p discloses the recovery of elemental sulphur from the leaching residue by using perchloroeth- ylene. However, perchloroethylene is not water soluble, is toxic to aquatic life with long lasting effects and is suspected of causing cancer.
BRIEF DESCRIPTION OF THE INVENTION
An object of the present invention is thus to provide a method and a process arrangement for implementing the method of separating elemental sulphur from starting material containing the same. The objects of the invention are achieved by a method and a process arrangement, which are characterized by what is stated in the independent claims. The preferred embodiments of the invention are disclosed in the dependent claims.
The invention is based on the idea of separating elemental sulphur from elemental sulphur -containing starting material by a method, which comprises
a) a leaching step, wherein the starting material is contacted with a water soluble organic solvent at a temperature below the flash point of the water soluble organic solvent for leaching the elemental sulphur contained in the starting material into the water soluble organic solvent,
b) a first solid-liquid separation step, wherein the water soluble organic solvent containing the elemental sulphur is separated from a leaching residue,
c) a crystallization step, wherein elemental sulphur is crystallized from the water soluble organic solvent; and
d) a second solid-liquid separation step, wherein the water soluble organic solvent is separated from the crystallized elemental sulphur.
According to an embodiment of the invention the water soluble organic solvent used in the leaching step is a compound or a mixture of com- pounds capable of leaching elemental sulphur.
According to an embodiment of the invention the method comprises a first washing step of the leaching residue by a water soluble organic solvent, typically after the first solid-liquid separation step. The first washing step may also be a part of the first solid-liquid separation step. Typically the water solu- ble organic solvent used for the washing of the leaching residue is the same as the water soluble organic solvent used in the leaching step. Typically the water soluble organic solvent is fed after the washing step to be used further in the leaching step. Thus, the organic solvent for washing serves also as a make-up feed to the overall method. By using the water soluble organic solvent in the leaching step after the washing step provides economic advantages. The solvent charged with elemental sulphur is washed from the solid matter in order to avoid the elemental sulphur ending up in the solid matter. Thus, the elemental sulphur content of the solid leaching residue is reduced.
According to an embodiment of the invention the elemental sulphur - containing starting material is any suitable material containing elemental sulphur. Typically the starting material originates from metallurgical process, such as hydrometallurgical process. More typically the starting material is hydromet- allurgical residue produced during treatment of sulphide-bearing raw material. More typically the starting material is leaching residue containing elemental sulphur.
Typically in the leaching step the temperature is below the flash point of the water soluble organic solvent used in the leaching step. According to an embodiment of the invention the temperature is in the range of 80 - 140°C. More typically the temperature is in the range of 100 - 130°C, more typically in the range of 105 - 125°C.
According to an embodiment of the invention in the first solid-liquid separation step the water soluble organic solvent containing the elemental sulphur is separated from the leaching residue by any suitable method for solid- liquid separation such as thickening, filtration, centrifuging, or by any combination of previously mentioned methods.
According to an embodiment of the invention in the crystallization step the temperature of the water soluble organic solvent containing the elemental sulphur is lowered to a temperature in the range of 10 - 80°C for crystallizing the elemental sulphur.
According to an embodiment of the invention in the second solid- liquid separation step the water soluble organic solvent is separated from the crystallized elemental sulphur by any suitable solid-liquid separation method, such as thickening, filtration, centrifuging, or by any combination of previously mentioned methods. If desired, it is also possible to wash the separated crystallized elemental sulphur with water and according to an embodiment of the invention the method comprises a second washing step after the second solid- liquid separation step. The second washing step may also be a part of the second solid-liquid separation step.
According to an aspect, the invention also relates to a process arrangement of separating elemental sulphur from a starting material containing elemental sulphur, typically for performing the above method of the present invention, wherein the arrangement comprises
a) a leaching unit adapted for leaching a starting material by contacting it with a water soluble organic solvent at a temperature below the flash point of the water soluble organic solvent for leaching the elemental sulphur contained in the starting material into the water soluble organic solvent, b) a first solid-liquid separation unit adapted for separating the water soluble organic solvent containing the elemental sulphur from a leaching residue,
c) a crystallization unit adapted for crystallizing elemental sulphur from the water soluble organic solvent, and
d) a second solid-liquid separation unit adapted for separating the water soluble organic solvent from the crystallized elemental sulphur.
According to an embodiment of the invention the leaching unit is any reactor or series of reactors suitable for leaching.
According to an embodiment of the invention the first solid-liquid separation unit is any unit suitable for solid-liquid separation such as a thickening unit, a filtration unit, a centrifuging unit or any combination of previously mentioned units.
According to an embodiment of the invention the crystallization unit is any unit suitable for crystallization.
According to an embodiment of the invention the second solid-liquid separation unit is any unit suitable for solid-liquid separation such as a thickening unit, a filtration unit, a centrifuging unit or any combination of previously mentioned units.
According to an embodiment of the invention the process arrangement comprises a first washing unit after the first solid-liquid separation unit. The washing unit may also be part of another process unit, for example the washing unit may be realized as part of the solid-liquid separation unit.
According to an embodiment of the invention the process arrange- ment comprises a second washing unit after the second solid-liquid separation unit. The washing unit may also be part of another process unit, for example the washing unit may be realized as part of the solid-liquid separation unit.
An advantageous feature of the method and arrangement of the invention is that it has features that alleviate many concerns related to the safety of operating the method. The water soluble organic solvent used can be characterized as non-toxic, non-carcinogenic, and environmentally friendly. The whole method is also conducted in a temperature below the flash point of the water soluble organic solvent used. The whole method is further performed in atmospheric or slightly elevated pressure (up to 3 bar).
Another advantage of the present method is that elemental sulphur can be recovered with high yield and excellent purity. A high yield can be ob- tained with the conditions of the leaching step of the present invention, wherein starting material is fed into the leaching step in an amount, which is not more than from which amount the solvent is able to leach elemental sulphur. The solvent is fairly selective to elemental sulphur and hence elemental sulphur with high purity is obtained. The produced elemental sulphur may also be washed with water or melted in order to remove solvent residues from the product and thus increase the product purity.
An advantage of the present method is further that the leaching residue from which the elemental sulphur has been separated can be processed further for recovering valuable metals. Traces of water soluble organic solvent tend not to cause foaming due to water soluble property of the organic solvent during further processing if hydronnetallurgical. This alleviates process control during further metal recovery. A further advantage of an embodiment of the present invention is that the leaching residue does not contain elemental sul- phur or contains only very small unavoidable amounts of elemental sulphur. Elemental sulphur is known to have a remarkable detrimental economic impact on hydronnetallurgical platinum group metals and gold recovery processes. If no further metals are desired to be recovered from the leaching residue, it is also possible to route the elemental sulphur-free leaching residue to land filling.
A further advantage of the present method is that the loss of the organic solvent from the process can be avoided in a relatively simple way. It is possible to remove organic solvent from leaching residue and/or crystallized elemental sulphur simply by washing with water and thereafter recovering the organic solvent and recycling it back to the leaching step.
A further advantage of an embodiment of the present method is that it is not necessary to dry the starting material before the leaching. This results in decreased amount of process equipment as well as economical savings as there is no need for a drying step or unit before feeding to the leaching step.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following the invention will be described in greater detail by means of preferred embodiments with reference to the attached drawing, in which
Figure 1 shows an example embodiment of the present invention; Figure 2 shows an example embodiment of the present invention, wherein the optional steam condensing and water/organic solvent separation are presented.
DETAILED DESCRIPTION OF THE INVENTION
As presented above, the invention relates to a method of separating elemental sulphur from elemental sulphur -containing starting material, which method comprises a leaching step, wherein the starting material is contacted with a water soluble organic solvent at a temperature below the flash point of the organic solvent. Typically the temperature is in the range of 80 - 140°C, more typically in the range of 100 - 130°C, even more typically in the range of 105 - 125°C for leaching the elemental sulphur contained in the starting material into the water soluble organic solvent. Typically the temperature in the leaching step is between the boiling point of water and the flash point of the organic solvent used. This enhances the leaching of elemental sulphur and evaporates the water possibly contained in the starting material. In an embodiment of the invention the temperature of the leaching liquor may be maintained above the boiling point of water and below the flash point of the organic, water soluble solvent. By selecting the temperature of the leaching liquor to be above the boiling point of water, it is possible to separate the water contained in the starting material by evaporating it, thus according to an embodiment of the invention the water possibly comprised in the water soluble organic solvent is evaporated already during the leaching step and thereby the leaching liquor is regenerated already during the leaching step. This enhances the leaching of the elemental sulphur into the organic, water soluble solvent, because the wa- ter present in the leaching step typically interferes with the leaching of the elemental sulphur. By evaporating the water already in the leaching step the capacity of the organic solvent to leach elemental sulphur is enhanced below the melting point of sulphur and thus the capacity of the needed equipment is decreased. Furthermore, there is no need for a separate regeneration step for treating the organic solution. By using the present method there is no need to dry and homogenize the starting material before feeding to the leaching step.
The leaching is understood to mean both dissolving and/or carrying the elemental sulphur. Typically, when performing the method below the melting point of sulphur the leaching means dissolving. Typically when performing the method above melting point of sulphur, the leaching is meant to comprise carrying the elemental sulphur or both dissolving and carrying the elemental sulphur.
The starting material may be any material containing elemental sulphur, from which it is desired to remove the elemental sulphur. Typically the starting material is material obtained from hydrometallurgical process. More typically the starting material is leaching residue. The starting material may be dried before the leaching or the starting material may contain moisture, such as water. In some embodiments, due to the temperature used in the leaching step the water possibly contained in the starting material evaporates in the leaching step. This enables to control the water balance of the method.
In the leaching step the elemental sulphur is leached into the organic water soluble solvent. The leaching liquor of the leaching step typically contains organic, water soluble solvent. The leaching liquor may also be a mixture of suitable water soluble organic solvents. While the elemental sulphur is leached into the organic, water soluble solvent at the same time water typically evaporates from the starting material. Water evaporation may be enhanced by using any suitable carrier gas, such as nitrogen. The evaporated water may be directed to a condenser and condensed to distillate to be used for example in the washing step later in the process. A further possibility is to treat the water- containing solution obtained from the leaching step by any known method, such as membrane filtration, evaporation or distillation for separating any organic solvent possible present and recycling them back to the process. It is also possible to treat any washing water used in the present method in the same way as the water-containing solution obtained from the leaching step.
The leaching is typically performed under atmospheric pressure.
More typically the leaching is performed in a pressure between the atmospheric pressure and 3 bar.
The leaching step is typically performed in conditions in which as much as possible elemental sulphur is leached to the solvent, however in such conditions that all of the elemental sulphur is leached. If elemental sulphur is not leached it will end up in the leaching residue, which is not desired. The former conditions decrease the size of the streams in the process and hence make the leaching unit, the first solid-liquid separation unit, crystallization unit and the second solid-liquid separation unit smaller.
The organic, water soluble solvent is any organic solvent capable of dissolving and/or carrying elemental sulphur. More typically the organic, water soluble solvent is selected from suitable solvents, which are water soluble but not heavily azeotropic with water. The selected solvents have a high flash point, typically at least 10 degrees above the leaching temperature. The solvent of the present invention is able to leach elemental sulphur and can be characterized as non-toxic, non-carcinogenic, and environmentally friendly.
Typically the organic, water soluble solvent is a compound or mixture of compounds of general formula (I)
Ri-(O-C2-4-alkylenyl)n-OR2 (I) wherein Ri is H, Ci-5-alkyl, or -C(O)-Ci-5-alkyl,; R2 is independently H, Ci-5-alkyl, or -C(O)-Ci-5-alkyl; and n is equal to or greater than 1 , provided that the compound is water soluble.
In a particularly suitable example the water soluble solvent is a compound or mixture of compounds of general formula (I), wherein Ri is H or Ci-5-alkyl, in particular H or ethyl; and R2 is H or Ci-5-alkyl, in particular H or ethyl.
The upper limit for the n value is determined by the solubility of the compound. This depends of the nature of the C2-4-alkylene group. For exam- pie, the average number of repeating units (expressed by n in the formula) in the case of polyethylene glycols, i.e. when the C2-4- alkylenyl is ethylenyl, can range from 2 to 80. In the case of polypropylene glycols, i.e. when the C2-5- alkylenyl is propylenyl, the n value can range from 2 to 60. In the case of poly- butylene glycols, i.e. when the C2-4- alkylenyl is butylenyl, the n value can range from 2 to 40. In a preferable example n in the general formula (I) is from 1 to 30.
In a particular example of the present invention the water soluble solvent is a compound or mixture of compounds of general formula (II) Ri-(OCH2CH2)n-OR2 (l l) wherein Ri is H or Ci-5-alkyl, preferably H, methyl or ethyl; R2 is independently H or Ci-5-alkyl, preferably H, methyl or ethyl, and n is an integer from 1 to 20, preferably 1 to 10. Advantageously Ri is H or Ci-5-alkyl, in partic- ular methyl or ethyl, R2 is H, and n is an integer from 1 to 20, preferably 1 to 10. In a typical example of the present invention the water soluble organic solvent is selected from a group consisting of ethylene glycol,diethylene glycol, triethylene glycol, polyethylene glycol such as polyethylene glycol having average molecular weight 300, diethylene glycol monomethyl ether, diethy- lene glycol dimethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, triethylene glycol monomethyl ether, triethylene glycol dimethyl ether, triethylene glycol monoethyl ether, triethylene glycol diethyl ether, triethylene glycol monobutyl ether, triethylene glycol dibutyl ether, polyethylene glycol monomethyl ether such as polyethylene glycol monomethyl ether having average molecular weight 350, polyethylene glycol monomethyl ether having average molecular weight 500, polyethylene glycol dimethyl ether, polyethylene glycol monoethyl ether, and polyethylene glycol diethyl ether.
Typically the water soluble organic solvent is polyethylene glycol monomethyl ether, in particular polyethylene glycol monomethyl ether having average molecular weight 350 or 500.
It has been found out that by using a water soluble organic solvent instead of non-volatile organic solvent the number of required process steps can be diminished. The water solubility of the leaching liquor simplifies the washing of organic solvent from the solid matter, e.g. all solid matter formed in the process, such as leaching residue, remaining after the leaching or the crystallized elemental sulphur. The leaching residue obtained from the present method is elemental sulphur-free, which alleviates recovery of many valuable metals from it. The recovery of valuable metals is also alleviated, as metal concentrations have increased during elemental sulphur separation as elemental sulphur is removed from the solids. The recovery of valuable metals is further alleviated as traces of water soluble organic solvent tend not to cause foaming due to water soluble property of the organic solvent unlike traces of non-volatile and not water soluble organic solvent during further processing if hydrometallur- gical. This alleviates process control during further metal recovery. Furthermore, if the leaching liquor used would be organic non-volatile and not water soluble, then for separating the elemental sulphur from the starting material the organic solvent used as the leaching liquor would have to be washed from the solid matters with another organic solvent, such as a short chain hydrocarbon, which hydrocarbon can be further removed by an alcohol and be evaporated from the solid matter. Furthermore, distillation steps would be required for treating the used washing solutions for separating the leaching liquor and the washing liquors from each other to be able to recycle them.
The method comprises a first solid-liquid separation step, wherein the water soluble organic solvent containing the elemental sulphur is separated from a leaching residue. The solid-liquid separation may be performed by any suitable method for solid-liquid separation such as thickening, filtration, centri- fuging, or by any combination of previously mentioned methods.
According to an embodiment of the invention the method comprises a first washing step. The first washing step may also be after the first solid- liquid separation step or it may be arranged in connection with the first solid- liquid separation step. The method typically comprises a first washing step, wherein the leaching residue is washed by a water soluble organic solvent. Typically the water soluble organic solvent used for the washing of the leaching residue is the same as the water soluble organic solvent used in the leach- ing step. After washing the leaching residue with the water soluble organic solvent the leaching residue may be typically further washed with water for removing small amounts of the organic solvent left in the leaching residue. The leaching residue may also be washed with only water. By washing the leaching residue with the water soluble organic solvent, or with the water soluble organ- ic solvent and thereafter with water an elemental sulphur -depleted leaching residue containing only unavoidable traces of elemental sulphur, is obtained. Thus, elemental sulphur does not interfere with the recovery of valuable metals in a further processing step.
The obtained elemental sulphur -depleted leaching residue may be directed further to known process steps for recovering desired metals, such as zinc, gold, silver and/or platinum group metals.
After the first solid-liquid separation step the method of the present invention comprises a crystallization step, wherein elemental sulphur is crystallized. The crystallization is typically performed by lowering the temperature of the water soluble organic solvent containing the elemental sulphur to a temperature of 10 - 80°C. Typically the temperature to which the water soluble organic solvent is cooled is 20 - 60°C. The cooling may be performed by any suitable method for cooling such as using heat exchangers, using cooling water or using any combination of previously mentioned methods. For example a counter-current heat exchanger may be used, wherein the solution stream from the first solid-liquid separation step to crystallization step is cooled by us- ing the solution stream from the second solid-liquid separation step to the leaching step, which again on its side is warmed up in the heat exchanger.
The method further comprises a second solid-liquid separation step, wherein the water soluble organic solvent is separated from the crystallized elemental sulphur. The second solid-liquid separation may be performed by any suitable solid-liquid separation method, such as thickening, filtration, cen- trifuging, or by any combination of previously mentioned methods. The obtained crystallized elemental sulphur may be washed in a second washing step with water for removing small amounts of the organic solvent left in the solids. The second washing step may be either after the second solid-liquid separation step or in connection with the second solid-liquid separation step. The obtained crystallized elemental sulphur may also be melted whereby elemental sulphur and the organic solvent residues form separate phases that can be recovered. It is possible to form briquettes from the produced elemental sulphur.
According to an aspect, the invention also relates to a process arrangement of separating elemental sulphur from a starting material containing elemental sulphur, typically for performing the above method of the present invention, wherein the arrangement comprises
a) a leaching unit adapted for leaching a starting material by con- tacting it with a water soluble organic solvent at a temperature below flash point of the water soluble organic solvent for leaching the elemental sulphur contained in the starting material into the water soluble organic solvent,
b) a first solid-liquid separation unit adapted for separating the water soluble organic solvent containing the elemental sulphur from a leaching resi- due,
c) a crystallization unit adapted for crystallizing elemental sulphur from the water soluble organic solvent, and
d) a second solid-liquid separation unit adapted for separating the water soluble organic solvent from the crystallized elemental sulphur.
According to an embodiment of the invention the leaching unit is any reactor or series of reactors suitable for leaching. Typically the leaching unit is series of agitated tanks.
According to an embodiment of the invention the first solid-liquid separation unit is any unit suitable for solid-liquid separation such as a thicken- ing unit, a filtration unit, a centrifuging unit or any combination of previously mentioned units. According to an embodiment of the invention the crystallization unit is any suitable crystallization unit, such as an agitated tank or series of agitated tanks, and/or crystallizer and/or series of crystallizers.
According to an embodiment of the invention the second solid-liquid separation unit is any unit suitable for solid-liquid separation such as a thickening unit, a filtration unit, a centrifuging unit or any combination of previously mentioned units.
According to an embodiment of the invention the process arrangement comprises a first washing unit after the first solid-liquid separation unit. The washing unit may also be part of another process unit, for example the washing unit may be realized as part of the solid-liquid separation unit.
According to an embodiment of the invention the process arrangement comprises a second washing unit after the second solid-liquid separation unit. The washing unit may also be part of another process unit, for example the washing unit may be realized as part of the solid-liquid separation unit.
According to an embodiment of the invention the process arrangement further comprises a unit for further processing the crystallized, and optionally washed elemental sulphur. The unit for further processing may be for example a melting unit or a briquetting unit.
Example embodiments of the invention are presented with reference to the figures. The following reference numbers have been used in the figures:
1 starting material
2 leaching step
3 water soluble organic solvent containing leached ele- mental sulphur and solid matter
4 first solid-liquid separation step
5 water soluble organic solvent containing elemental sulphur
6 crystallization step
7 water soluble organic solvent
8 second solid-liquid separation step
9 distillate
10 second washing step
1 1 leaching residue
12 washed leaching residue 13 water soluble organic solvent containing crystallized elemental sulphur
14 first washing step
15 crystallized elemental sulphur
16 condenser
17 water soluble organic solvent
18 used organic washing solution
19 washed crystallized sulphur
21 elemental sulphur product
22 further processing
23 vaporized steam
24 water/organic solution separation
26 used washing water
28 water fraction
30 organic fraction
32 used washing water
Figure 1 is an example embodiment of the present method, wherein the starting material 1 is fed into a leaching step 2 containing water soluble organic solvent. In the leaching step the elemental sulphur contained in the starting material is leached into the organic water soluble solvent and vaporized steam 23 is removed from the leaching step 2. Water soluble organic solvent containing leached elemental sulphur and solid matter 3 is removed from the leaching step 2 and routed to a first solid-liquid separation step 4. In the first solid-liquid separation step 4 the solid matter, the leaching residue 1 1 is separated from the water soluble organic solvent 5. After the first solid-liquid separation step 4 the separated leaching residue 1 1 is washed in a first washing step 14 by an organic water soluble solvent 7 and/or fresh water fed to the first washing step 14 (not shown in the figure). The separated and washed leaching residue 12 is removed from the first washing step 14 and possibly routed to further processing for recovering metals contained in the leaching residue. From the first solid-liquid separation step 4 the water soluble organic solvent containing elemental sulphur is routed to a crystallization step 6, wherein the temperature of the water soluble organic solvent is reduced to be in the range of 10 - 80°C for crystallizing the elemental sulphur. From the crystallization step 6 the water soluble organic solvent containing crystallized ele- mental sulphur is routed to a second solid-liquid separation step 8, wherein the crystallized elemental sulphur is removed from the water soluble organic solvent and recovered as crystallized elemental sulphur 15. The separated organic water soluble solvent 17 is recycled back to the leaching step 2. Optionally the obtained crystallized elemental sulphur 15 is routed to a washing step 10, wherein the crystallized elemental sulphur is washed with water (not shown in the Figure) and thus washed crystallized sulphur 19 is obtained. The crystallized elemental sulphur 15 or washed crystallized sulphur 19 may be optionally routed to further processing 22 from which an elemental sulphur product 21 , such as briquettes, is obtained.
Figure 2 is otherwise equal to Figure 1 , except it shows in more detail the optional circulation of vaporized steam, organic solvent and washing waters in the method. The vaporized steam 23 may be optionally routed to a condenser 16, wherein the vaporized steam is condensed into distillate 9 that may be routed to an optional water-organic solvent separation step 24. The used washing water 32 from the 1 st washing step 14 and the used washing water 26 from the 2nd washing step 10 are routed to the separation step 24. In the separation step 24 water and the water soluble organic solvent are separated from each other, typically by membrane filtration or distillation. The ob- tained organic fraction 30 may be routed to the leaching step 2 and the obtained water fraction 28 may be recycled back to the present method.
EXAMPLES Example 1 :
Diethylene glycol was used to separate elemental sulphur from dry hydrometallurgical residue. Leaching was carried out at 105°C in a 10 L reactor for 1 h. Leaching residue was separated from the pregnant solvent and washed with fresh diethylene glycol and then with water in a hot oil jacketed buchner funnel. Elemental sulphur was crystallized by cooling the hot pregnant filtrate to room temperature in a continuously stirred beaker. Crystallized ele- mental sulphur was separated from the raffinate and washed with water in a buchner funnel.
Elemental sulphur content was reduced from the original 64% of the starting material to 0.4% of the leaching residue during the treatment. Elemental sulphur purity in crystallized sulphur was 99.8%. The main impurity in crystallized sulphur was carbon originating from the solvent. EXAMPLE 2:
Property of polyethylene glycol monomethyl ether having average molecular weight 350 to leach elemental sulphur was investigated. Pure elemental sulphur was added in small amounts to the solvent at 105°C. Solution was cooled down to room temperature after becoming saturated with elemental sulphur. Crystallized elemental sulphur was separated from the solvent and washed with water in a buchner funnel after cooling. Leaching and cooling was performed in a stirred 100 mL erlenmeyer flask.
Polyethylene glycol monomethyl ether having average molecular weight 350 was determined to have elemental sulphur solubility of 26 g/L at 105°C and elemental sulphur solubility of 2 g/L at room temperature. Solubilities were calculated based on masses of solids and on the amount of solvent used in the test.
EXAMPLE 3:
Water was evaporated while elemental sulphur was leached from hydrometallurgical residue. Dry base of the starting material was 70 g, the amount of water used 105 mL and the amount of triethylene glycol used 3 L. Leaching and water evaporation was performed at 105°C for 1 h. After leaching, solids were separated from the pregnant solvent and washed with water in a hot oil jacketed buchner funnel. Elemental sulphur was crystallized by cooling hot pregnant filtrate to room temperature in a stirred water-jacketed reactor. Crystallized elemental sulphur was separated from the raffinate and washed with water in a buchner funnel.
Triethylene glycol was found to dissolve elemental sulphur and wa- ter to evaporate during leaching. The amount of crystallized elemental sulphur recovered was 16 g and the purity of the sulphur was 99.7%. The main impurity in crystallized sulphur was carbon originating from the solvent. Residence time for cooling was 2 h.
EXAMPLE 4:
A continuous leaching and crystallization test for diethylene glycol was made. The test setup contained leaching of hydrometallurgical residue, solid liquid separation and washing of leaching residue, crystallization of elemental sulfur and solid liquid separation and washing of elemental sulfur. Solvent was loaded to or close to the saturation point of elemental sulphur in the leaching stage that operated at 105°C temperature. Solvent was recycled 70 times during the run. The volume of the solvent circulating in the operation was 12 L.
The solvent stayed unformed during the run based on Fourier trans- form infrared spectroscopy (FTIR) measurements. FTIR graphs of the solvent were identical before and after the continuous operation. Negligible amounts of impurities were analysed from the diethylene glycol after the continuous operation. Zinc was the most soluble impurity and the zinc concentration increased from 1 to 350 mg/L in 70 cycles. No impurity other than zinc was greater than 150 mg/L after 70 cycles. The starting material contained among other things 74% sulphur, 7.3% iron, 3.0% zinc and 0.9% lead.
It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1 . A method of separating elemental sulphur from elemental sulphur -containing starting material, wherein the method comprises
a) a leaching step, wherein the starting material is contacted with a water soluble organic solvent at a temperature below the flash point of the water soluble organic solvent for leaching the elemental sulphur contained in the starting material into the water soluble organic solvent,
b) a first solid-liquid separation step, wherein the water soluble organic solvent containing the elemental sulphur is separated from a leaching residue,
c) a crystallization step, wherein elemental sulphur is crystallized from the water soluble organic solvent; and
d) a second solid-liquid separation step, wherein the water soluble organic solvent is separated from the crystallized elemental sulphur.
2. The method according to claim 1 , wherein the method comprises a first washing step comprising washing the leaching residue by a water soluble organic solvent.
3. The method according to claim 1 or 2, wherein the method comprises a first washing step comprising washing the leaching residue by water.
4. The method according to any one of the preceding claims, wherein the water soluble organic solvent is a compound or a mixture of compounds having the general formula (I)
Ri-(O-C2-4-alkylenyl)n-OR2 (I) wherein Ri is H, Ci-5-alkyl, or -C(O)-Ci-5-alkyl, preferably H or Ci-5- alkyl, more preferably H or ethyl; R2 is independently H, Ci-5-alkyl, or -C(O)-Ci-5- alkyl, preferably H or Ci-5-alkyl, more preferably H or ethyl; and n is equal to or greater than 1 , preferably from 1 to 30, provided that the compound is water soluble.
5. The method according to claim 4, wherein the water soluble solvent is a compound or mixture of compounds of general formula (II)
Ri-(OCH2CH2)n-OR2 (II) wherein Ri is H or Ci-5-alkyl, preferably H, methyl or ethyl; R2 is H or Ci-5-alkyl, preferably H, methyl or ethyl; and n is an integer from 1 to 20, preferably 1 to 10.
6. The method according to any one of the preceding claims, where- in the water soluble organic solvent is selected from a group consisting of ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol such as polyethylene glycol 300, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, triethylene glycol monomethyl ether, triethylene glycol dimethyl ether, triethylene glycol monoethyl ether, triethylene glycol diethyl ether, triethylene glycol monobutyl ether, triethylene glycol dibutyl ether, polyethylene glycol monomethyl ether such as polyethylene glycol monomethyl ether having average molecular weight 350, polyethylene glycol dimethyl ether, polyethylene glycol monoethyl ether, and polyethylene glycol diethyl ether.
7. The method according to any one of the preceding claims, wherein in the leaching step the temperature is in the range of 80 - 140°C, typically 100 - 130°C, more typically 105 - 125°C.
8. The method according to any one of the preceding claims, wherein the water comprised in the water soluble organic solvent in the leaching step is evaporated during the leaching step.
9. The method according to any one of the preceding claims, wherein the first solid-liquid separation step the water soluble organic solvent containing the elemental sulphur is separated from the leaching residue by any suitable solid-liquid separation method such as thickening, filtration, centrifug- ing, or by any combination of the previous.
10. The method according to any one of the preceding claims, wherein in the crystallization step the temperature of the water soluble organic solvent containing the elemental sulphur is lowered to a temperature in a range of 10 - 80°C.
1 1 . The method according to any one of the preceding claims, wherein the second solid-liquid separation step the water soluble organic solvent is separated from the crystallized elemental sulphur by any suitable solid- liquid separation method such as thickening, filtration, centrifuging, or by any combination of the previous.
12. The method according to claim 1 1 , wherein the water soluble organic solvent separated from the crystallized elemental sulphur is recycled back to the leaching step.
13. A process arrangement of separating elemental sulphur from a starting material containing elemental sulphur, wherein the arrangement comprises
a) a leaching unit adapted for leaching a starting material by contacting it with a water soluble organic solvent at a temperature below the flash point of the water soluble organic solvent for leaching the elemental sulphur contained in the starting material into the water soluble organic solvent,
b) a first solid-liquid separation unit adapted for separating the water soluble organic solvent containing the elemental sulphur from a leaching residue,
c) a crystallization unit adapted for crystallizing elemental sulphur from the water soluble organic solvent, and
d) a second solid-liquid separation unit adapted for separating the water soluble organic solvent from the crystallized elemental sulphur.
14. The process arrangement according to claim 13, wherein the leaching unit is an agitated tank or series of agitated tanks.
15. The process arrangement according to claim 13 or 14, wherein the first solid-liquid separation unit comprises a thickening unit, filtration unit, centrifuging unit, or any combination thereof.
16. The process arrangement according to any one of claims 13 to
15 wherein the crystallization unit comprises an agitated tank or series of agi- tated tanks and/or crystallizer or series of crystal I izers.
17. The process arrangement according to any one of claims 13 to
16 wherein the second solid-liquid separation unit is a thickening unit, filtering unit, a centrifuging unit or any combination thereof.
18. The process arrangement according to any one of claims 13 to 17 wherein the process arrangement comprises a first washing unit after the first solid-liquid separation unit or in connection with the first solid-liquid separation unit.
19. The process arrangement according to any one of claims 13 to 18, wherein the process arrangement comprises a second washing unit after the second solid-liquid separation unit or in connection with the second solid- liquid separation unit.
20. The process arrangement according to any one of claims 13 to 19, wherein the process arrangement comprises a unit for further processing the elemental sulphur.
PCT/FI2014/050983 2013-12-12 2014-12-11 Method and process arrangement of separating elemental sulphur WO2015086906A1 (en)

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