Classifications

• • 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
  • C22B23/00—Obtaining nickel or cobalt
  • C22B23/04—Obtaining nickel or cobalt by wet processes
  • C22B23/0407—Leaching processes
  • C22B23/0415—Leaching processes with acids or salt solutions except ammonium salts solutions
  • C22B23/0438—Nitric acids or salts thereof

Definitions

• the present invention relates to a method for the recovery of nickel, other base metals, and precious metals from nickel bearing ores and concentrates, and sulphide metallurgical wastes, using nitric acid, and relates particularly, though not exclusively, to such a method for the recovery of nickel and other metals from nickel laterite ores and concentrates.
• Nickel resources in the world occur principally as either nickel sulphide or nickel laterite (oxide) deposits.
• the chemistry of the two ores is quite different resulting in quite different extraction and treatment processes required in each case.
• Nickel sulphide ores are typically easier to process, with techniques of conventional mining, smelting and refining being used to extract the nickel and other metals, usually referred to as pyrometallurgy.
• Nickel laterite ores typically require more rigorous hydrometallurgical extraction techniques such as high pressure acid leaching (HPAL). Due to the easier processing of nickel sulphide ores, historically most nickel production has been derived from sulphide ores.
• nickel sulphide tailings some of these nickel sulphide tailings also include other metals such as precious metals and platinum group metals (PGMs). It is therefore also desirable to find a recovery process for these precious metals and PGMs, in particular in view of the high value of some of these metals.
• PGMs platinum group metals
• Prior art acid extraction processes for nickel have principally used sulphuric acid.
• international application PCT/US2008/005608 by Drinkard Metalox, Inc. describes an improved method for processing nickel laterite ores using nitric acid as the solvent. This disclosure describes the leaching of laterite ores at temperatures above about 70°C and higher.
• the present invention was developed with a view to providing a two stage acid leach process for the recovery of nickel and other metals from nickel bearing laterite and sulphide ores using nitric acid as the solvent, and subsequently adding sulphide ore or tailings to improve the economics of metal recovery.
• a method for the recovery of nickel and other metals from nickel bearing laterite ore, sulphide ore, oxide ore or concentrate, and nickel sulphide ore or nickel sulphide metallurgical waste comprising the steps of: in a first stage leach: i) adding nitric acid to the nickel bearing laterite ore, sulphide ore, oxide ore or concentrate to form a slurry; and,
• the method also includes the step of grinding of the ore, concentrate or nickel sulphide metallurgical waste prior to the nitric acid addition step.
• the ore, concentrate or nickel sulphide metallurgical waste is ground to a particle size of less than 150 microns.
• the 1 sf stage slurry comprises more than about 50% w/w solids. More preferably the 1 st stage slurry comprises about 50% w/w solids in barren liquor recovered from a precipitation step.
• the nitric acid is of a concentration between about 1 and 90%. More typically the concentration of the nitric acid is about 70%. Barren liquor or water may be added in the nitric acid addition step to form the slurry. Preferably the concentration of the nitric acid after water addition is around 20-50%, and more typically about 30-40%.
• the 1 st stage treatment step involves agitation carried out for about 1 to 3 hours.
• the temperature of the slurry during the 1 st stage treatment step is heated to between 60°C to 100°C. More preferably the temperature of the slurry during the 1 st stage treatment step is increased to about 90°C.
• barren liquor from a precipitation step or water is also added during the nickel sulphide metallurgical waste addition step to promote hydrolysis during the 2 nd stage leaching.
• the temperature of the slurry increases during the 2 nd stage treatment step.
• the temperature of the slurry as it enters the 2 nd stage treatment step is in the range of about 85°C to 100°C. More typically the temperature in the 2 nd stage treatment step commences at a temperature of about 90°C, and increases during agitation to about 95°C.
• the 2 nd stage treatment releases metals, such as gold, nickel and cobalt, from the nickel sulphide metallurgical waste into solution.
• the 2 nd stage treated slurry is separated into a pregnant solution and an insoluble residue in a solid/liquid separation step as part of the step of recovering nickel and other metals from the 2 nd stage treated slurry.
• the pregnant solution is subjected to further treatment to recover the metals in solution.
• the pregnant solution is treated to extract the nickel, base metals and precious metals in metallic form.
• the pregnant solution is treated to precipitate the nickel, the high value base metals and the precious metals as sulphides, hydroxides or carbonates.
• the pregnant solution is further treated by the addition of Na 2 S, NaHS and H 2 S to form a cobalt-nickel mixed sulphide precipitate ("MSP").
• MSP cobalt-nickel mixed sulphide precipitate
• the step of recovering nickel and other metals from the 2 nd stage treated slurry includes a step of heating the treated slurry to increase the pH to form the pregnant solution and the insoluble residue, the insoluble residue containing precipitated iron and other base metals.
• the heating step is preferably carried out at about 80°C to 100°C.
• the heating step is carried out for about 30 minutes to 3 hours.
• the pH of the solution rises to between 1 and 2 during the heating step so that iron and other low value base metals, such as aluminium and chromium are precipitated as the insoluble residue.
• the pregnant solution typically also comprises other high value base metals in addition to nickel such as cobalt and copper, as well as some precious metals and PGMs, for example gold and platinum.
• the nickel sulphide metallurgical waste is nickel sulphide tailings.
• the nickel sulphide tailings comprise less than 10% nickel. More typically the nickel sulphide tailings comprise about 0.2 to 1.0% nickel, and more typically about 0.5% nickel.
• the method may further comprise a nitric acid recycle step in which NOx gases formed during one or more of the steps of the method are removed and converted into recycled nitric acid for further use in the method.
• NOx gases or recycled nitric acid may be collected and used for other purposes.
• NOx gases formed during the agitation step may be removed and converted into nitric acid.
• Figure 1 is a schematic flow diagram of a preferred method for the recovery of nickel and other metals in accordance with the present invention
• Figure 2 is a graphical representation of test data showing the recovery of nickel and cobalt, iron an aluminium during a 2 nd stage leaching.
• a preferred embodiment of a method 10 for the recovery of nickel and other metals from nickel bearing laterite ore, sulphide ore, oxide ore or concentrate, and nickel sulphide tailings is illustrated in schematic form in Figure 1.
• the method 10 preferably involves the step of grinding 12 the nickel bearing laterite ore, oxide ore or concentrate 14 prior to the 1 st stage of the acid leach process.
• the nickel bearing laterite ore or concentrate 14 is ground to a particle size of less than 150 microns.
• the 1 st stage acid leach process comprises the step of adding nitric acid 16 to the ore or concentrate 14 to form a 1 st stage leach slurry 18.
• the slurry 18 comprises more than about 50% w/w solids. More preferably the slurry 18 comprises about 50% w/w solids in barren liquor recovered from a precipitation step.
• the nitric acid 16 is of a concentration between about 1 and 90%. More typically the concentration of the nitric acid is about 70%. Barren liquor or water 17 may also be added to the ore or concentrate 14 to form the 1 st stage leach slurry 18.
• the concentration of the nitric acid after water addition is around 40-70%, and more typically about 50-60%.
• the nitric acid is of a concentration less than 1 tonne nitric acid to 1 tonne ore.
• the nitric acid is of a concentration in the range of about 0.6 - 0.8 tonne nitric acid to 1 tonne of tailings. Typically greater than 30% nickel extraction is achieved using nitric acid in the 1 st stage leach. The acid can be added to the ore quickly during this stage as the oxide ore is quite benign.
• the 1 st stage leach process then involves agitating the slurry 18 in a 1 st stage treatment step 20 to allow at least partial oxidation of the nickel bearing laterite (oxide) ore or oxide concentrate to form a 1 st stage treated slurry 22.
• the agitation during the 1 st stage treatment step takes place for between 2 to 3 hours. More typically the slurry is agitated for about 150 minutes. Typically the temperature of the slurry during the 1 st stage treatment step is heated to between 60°C to 100°C. More preferably the temperature of the slurry during the 1 st stage treatment step is increased to about 90°C.
• a nickel sulphide ore or disseminated nickel bearing sulphide ore may also be used in the 1 st stage leach process. If sulphide ore is used as the primary leach up to 90% recovery of the nickel can be achieved.
• the 1 st stage treated slurry 22 is then subject to a 2 nd stage leach process.
• the 2 nd stage leach process comprises adding nickel sulphide or sulphide tailings 24 to the 1 st stage treated slurry 22 to form a 2 nd stage leach slurry 26.
• the nickel sulphide tailings 24 typically comprise less than 10% nickel. More typically the nickel sulphide tailings 24 comprise about 0.2 to 1.0% nickel, and more, typically about 0.5% nickel.
• barren liquor from a precipitation step or water is also added during the nickel sulphide tailings addition step to promote hydrolysis during the 2 nd stage leaching.
• the 2 nd stage leach process further comprises treating the slurry in a 2 nd stage treatment step 28 to form a 2 nd stage treated slurry 30.
• the 2 nd stage treatment step 28 comprises adjusting the pH of the 2 nd stage leach slurry 26 to maximise the concentration of free acid.
• the 2 nd stage treatment step also comprises agitating the slurry.
• the agitation takes place for 1 to 3 hours. More preferably the agitation in the 2 nd stage treatment step 28 takes place for about 2 hours.
• the temperature of the slurry as it enters the 2 nd stage treatment step 28 is in the range of about 85°C to 100°C.
• the temperature in the 2 nd stage treatment step 28 commences at a temperature of about 90°C, and increases during agitation to about 95°C, due to the heat generated in the reaction of sulphides (sulphide tailings) with nitric acid.
• the 2 nd stage treatment step releases metals, such as gold, nickel and cobalt, from the 2 nd stage treated slurry 30 into solution at step 32.
• metals such as gold, nickel and cobalt
• Advantageously adjusting the pH of the 2 nd stage leach slurry 26 during the 2 nd stage treatment step 28 comprises incrementally adding nickel sulphide tailings 24 to the slurry 26. Addition of the nickel sulphide tailings has to be performed in small increments due to the high reactivity of the sulphide. Preferably the pH is adjusted to > 1 by the incremental addition of nickel sulphide tailings 24.
• This has the further advantage of obviating the need for adding a neutralant to precipitate iron and other low value base metals, such as aluminium and chromium, as well as releasing free acid.
• the iron cannot precipitate in the 1 st stage leach due to the high level of nitric acid required to leach nickel laterite or oxide ore. This is another significant benefit of the two stage leach process.
• the method comprises the step of recovering nickel and other metals in solution 32 from the 2 nd stage treated slurry 30.
• the treated slurry 30 is separated into a pregnant nickel solution 36 and an insoluble residue 38 in a solid/liquid separation step 34.
• the pregnant nickel solution 36 typically also comprises other high value base metals in addition to nickel such as cobalt and copper, as well as some precious metals, for example gold.
• the present invention also may provide a way of recovering precious metals and PGMs such as gold and platinum, in particular from nickel tailings.
• the step of recovering nickel and other metals from the 2 nd stage treated slurry also comprises further treatment 40 of the pregnant nickel solution 36 to precipitate the nickel, the high value base metals and the precious metals as sulphides, hydroxides or carbonates.
• a cobalt-nickel mixed sulphide precipitate (“MSP") 42 and free nitric acid are formed, and the sulphides are then insoluble in the resultant nitric acid.
• MSP cobalt-nickel mixed sulphide precipitate
• the insoluble MSP is then sent to market after thickening and filtration at step 44.
• the spent barren liquor from the step of recovering nickel and other metals from the 2 nd stage treated slurry with the free nitric acid is recycled to the 1 st and 2 nd stage leaching circuits to recover more acid, as shown in Figure 1.
• the method may further comprise a nitric acid recycle step in which NOx gases formed during one or more of the steps of the method, such as the agitation step or the heating step, are removed and converted into recycled nitric acid for further use in the method.
• the NOx gases or recycled nitric acid may be collected and used for other purposes.
• a sample of nickel oxide ore was treated according to the method of the invention as follows.
• Figure 2 provides a graphical summary of the % extraction of nickel and cobalt, as well as iron and aluminium, during the 2 nd stage leach.
• the process is suitable for treating all forms of nickel oxide and sulphide ores, oxide and sulphide concentrates and sulphide wastes, and has particular application to nickel bearing laterite
• the two stage acid leach process means that previously uneconomic leaching of oxide ores can be successfully accomplished, using sulphide metallurgical waste (such as nickel sulphide tailings) in the 2 nd stage leach.
• sulphide metallurgical waste such as nickel sulphide tailings
• the invention also provides for a relatively easy way to extract such PGMs simultaneously with the extraction of nickel, allowing the PGMs to be extracted using appropriate techniques.

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Citations (14)

• 2013
  • 2013-09-18 AU AU2013325098A patent/AU2013325098B2/en active Active
  • 2013-09-18 WO PCT/AU2013/001066 patent/WO2014047672A1/fr not_active Ceased

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