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
  • C22B11/00—Obtaining noble metals
  • C22B11/04—Obtaining noble metals by wet processes
• • 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
• • 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
  • C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
• • 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
  • C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
  • C22B3/06—Extraction of metal compounds from ores or concentrates by wet processes by leaching in inorganic acid solutions, e.g. with acids generated in situ; in inorganic salt solutions other than ammonium salt solutions
  • C22B3/08—Sulfuric acid, other sulfurated acids or salts thereof
• • 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 disclosure relates generally to precious metal recovery from precious metal- containing materials and particularly to gold recovery from gold-containing materials.
• oxide ores may be refractory in nature. They neither yield sufficient gold leaching in a thiosulfate leach system nor are leached as effectively compared to cyanide. Thiosulfate gold extraction from some oxide ores can be minimal. As oxide ores do not contain sulfides (or have very low levels of sulfide), the refractory nature cannot be mitigated in the same manner as for sulfide ores (e.g., by roasting, bio-oxidation or pressure oxidation).
• the disclosure is directed generally to pre- treatment of precious metal-containing materials prior to thiosulfate precious metal leaching.
• a pre -treatment process can include the steps of:
• an oxidant e.g., a molecular oxygen-containing gas
• the precious metal for example, can be gold.
• carbon is removed depends on the particle size of the carbon employed. When coarse carbon is employed, the carbon is typically removed before thiosulfate leaching. When fine carbon is employed, the carbon is typically not removed before thiosulfate leaching.
• Finely sized carbon can be contacted with the precious metal-containing material either separately after grinding of the material or before and/or during grinding. In the latter case, the carbon particles can be coarsely sized but are ground to a fine size distribution similar to a size distribution of the ground precious metal-containing material.
• the precious metal-containing material Prior to leaching in step (c), the precious metal-containing material can be substantially free of contact with thiosulfate.
• the slurried precious metal-containing material, before and during step (a) typically includes less than 0.005, more typically no more than about 0.0025, and even more typically no more than about 0.001 molar thiosulfate. In some applications, no thiosulfate or other lixiviant is contacted with the precious metal-containing material before or during pre-treatment in step (a).
• the precious metal-containing material can be amenable to cyanide leaching (and therefore is not cyanide refractory) but not to thiosulfate leaching (i.e., the material is a thiosulfate refractory precious metal-containing material).
• leaching of precious metals from the precious metal-containing material by cyanide can be more effective than precious metal leaching by thiosulfate.
• the pretreatment process can enhance further precious metal recovery by thiosulfate.
• the precious metal-containing material may or may not be concentrated. Generally, the precious metal is in a matrix that is predominantly one or more oxides. By way of example, the precious metal-containing material can contain more oxides than sulfides.
• the slurry before pretreatment and the pre-treated slurry can each have a pH about pH 3 or higher (and, in some cases, about pH 7 or higher); an oxidation-reduction potential during pretreatment ranging from about 100 to about 600 mV (Ag/AgCl electrode); and/or a rate of contact of a molecular oxygen-containing gas with the slurry during pretreatment of about 0.10 L 0 2 /L slurry/min or higher.
• a weight ratio of the precious metal-bearing material to carbon ranges from about 50: 1 to about 1 :0.01 but the amount of carbon employed in any application can depend on the carbon particle size.
• a weight ratio of the precious metal-bearing material to coarsely sized carbon commonly ranges from about 1 :5 to about 1 :0.01 and more commonly from about 1 :3 to about 1 :0.5.
• a weight ratio of the precious metal-bearing material to finely sized carbon commonly ranges from about 1 : 1 to about 50: 1 and more commonly from about 10: 1 to about 30: 1.
• the pre-treatment process can be carried out under ambient conditions (room temperature and atmospheric pressure) in less than 24 hours. Increasing the process temperature can further improve the gold recovery and/or pretreatment kinetics.
• the carbon is normally removed from the pre-treated slurry by screening, which generally requires about 95% or more, and even more commonly about 98% or more of the carbon to be retained on the screen while about 90% or more and more commonly about 95% or more of the precious metal-containing material passes through the screen.
• the relative mean, median, mode, and Pso particle sizes of the carbon and precious metal- containing material are selected to produce at least these levels of separation.
• the discharge slurry from the pre-treatment process can be directly advanced to thiosulfate leaching.
• the carbon-depleted slurry can be contacted with thiosulfate in the substantial absence of pH adjustment and/or slurry density adjustment.
• a pH of the carbon-depleted slurry is commonly adjusted by no more than about pH 0.1 and the slurry density by no more than about 5%.
• Pre-treating oxide ores in oxygenated water in the presence of activated carbon or other carbon-based materials can improve significantly the gold recovery by thiosulfate leaching.
• the process can have a low operating cost and provide a straightforward pre-treatment method for oxide ores to be followed by thiosulfate leaching of gold. Attrition, due to mixing of the slurry, is commonly the only cause for carbon loss and may be minimized by proper engineering of the agitators and reactors.
• the carbon- based material can be recycled and re-used, thereby decreasing operating costs.
• each of the expressions “at least one of A, B and C”, “at least one of A, B, or C”, “one or more of A, B, and C", “one or more of A, B, or C" and "A, B, and/or C” means A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B and C together.
• each one of A, B, and C in the above expressions refers to an element, such as X, Y, and Z, or class of elements, such as Xi-X n , Yi-Y m , and Zi-Z 0
• the phrase is intended to refer to a single element selected from X, Y, and Z, a combination of elements selected from the same class (e.g., Xi and X 2 ) as well as a combination of elements selected from two or more classes (e.g., Yi and Z 0 ).
• activated carbon is a form of carbon processed to be riddled with small, low-volume pores that increase the surface area available for adsorption or chemical reactions. Activated carbon can be granular, extruded, bead, impregnated, and/or polymer coated.
• carbon includes a carbon-containing organic material, such as one or more of activated carbon (or activated charcoal or activated coal), coal (e.g., peat, lignite, sub -bituminous coal, bituminous coal, steam coal, anthracite, and graphite), brown coal, coke, hard carbon derived from coconut shells or elemental carbon, a calcined resin, and mixtures thereof.
• activated carbon or activated charcoal or activated coal
• coal e.g., peat, lignite, sub -bituminous coal, bituminous coal, steam coal, anthracite, and graphite
• brown coal coke
• hard carbon derived from coconut shells or elemental carbon a calcined resin
• precious metal refers to gold and silver.
• a "thiosulfate refractory" precious metal-containing material is a material in which at least part of the precious metal-containing material is naturally resistant to recovery by thiosulfate leaching.
• the recovery of thiosulfate refractory ores can be increased by pretreatment prior to thiosulfate leaching, or by employing cyanide leaching.
• component or composition levels are in reference to the active portion of that component or composition and are exclusive of impurities, for example, residual solvents or by-products, which may be present in commercially available sources of such components or compositions.
• the phrase from about 2 to about 4 includes the whole number and/or integer ranges from about 2 to about 3, from about 3 to about 4 and each possible range based on real (e.g., irrational and/or rational) numbers, such as from about 2.1 to about 4.9, from about 2.1 to about 3.4, and so on.
• Fig. 1 is a process flow schematic according to an embodiment of the disclosure.
• the present disclosure provides a process for pre -treating precious metal-bearing materials.
• the process can be performed prior to thiosulfate leaching and improve the overall precious metal recovery of thiosulfate refractory precious metal-containing materials.
• the pre -treatment is done by mixing a slurry containing the precious metal- containing material, water, a carbon-based material, and dissolved molecular oxygen (as the oxidizing reagent) for a predetermined residence time.
• the precious metal-bearing material can be an oxide ore, concentrate, tailings, leach residue, calcine, and other precious metal-bearing oxide materials.
• Typical precious metal-bearing oxide ores and concentrates may contain silicates, phosphates, iron oxides, and hydroxides, and relatively low levels of residual sulfides.
• the precious metal-bearing material is mixed, in a stirred tank, vat, or other suitable reactor, with the carbon-based material, such as activated carbon, and water to form the slurry.
• Molecular oxygen is typically contacted by sparging the slurry.
• the molecular oxygen can be supplied by a suitable source, such as air, oxygen-enriched air, or industrially-pure oxygen, with ambient air being preferred.
• the process can be carried out in any water source, whether raw water or relatively clean process water.
• Other suitable reactors, such as pulse columns, can be any reactor able to adequately mix carbon, the slurried precious metal-containing material, and gas.
• Proper reaction conditions can provide relatively high kinetics.
• the pre- treatment process is conducted at atmospheric pressure and temperature, though the use of a higher operating temperature (e.g., typically about 35°C or higher and more typically about 50°C or higher) can provide improved reaction kinetics.
• the pH of the slurry is typically about pH 7 or higher, more typically about pH 8 or higher, and even more typically about pH 9 or higher.
• the oxidation-reduction potential ("ORP") of the slurry is typically greater than about 100 mV and more typically greater than about 200 mV and typically less than about 750 mV and more typically less than about 500 mV (Ag/AgCl electrode).
• the rate of sparging of molecular oxygen through the slurry during pretreatment typically ranges from about 0.05 to about 5 and more typically from about 0.10 to about 2.5 L 0 2 /L slurry/min.
• the residence time of the slurry in the mixing vessel typically ranges from more than about 1 hour to about 24 hours, depending on the temperature, dissolved oxygen concentration in solution, and the ore type.
• the weight ratio of the carbon-based material to the precious metal-bearing material can vary depending on the requirements of the specific ore, the properties of the carbon-based material itself, and the desired level of precious metal recovery. Typically, for coarsely sized carbon the weight ratio of the precious metal-bearing material to the carbon-based material ranges from about 1 :3 to about 1 :0.01 and more typically from about 1 :3 to about 1 :0.1. A more typical weight ratio of the precious metal-containing material to the coarsely sized carbon-based material is about 1 :0.5. Typically, for finely sized carbon the weight ratio of the precious metal-bearing material to the carbon-based material commonly ranges from about 1 : 1 to about 50: 1 and more commonly from about 10: 1 to about 30: 1.
• a more typical weight ratio of the precious metal-containing material to the finely sized carbon-based material is about 20: 1.
• the carbon-based material is generally not consumed in the pre-treatment process and can be recycled and re -used, with make-up for carbon attrition.
• Oxygen gas is commonly the only reagent consumed though any other oxidant, including ozone and a peroxygen compound such as hydrogen peroxide, may be employed.
• the process can be carried out batch- wise or continuously, the latter being preferred.
• the carbon-based material can be separated by a suitable technique from the pre-treated precious metal-bearing material in the pre-treated slurry. Separation is generally done in applications using coarsely sized carbon particles but not finely sized carbon particles. Coarsely sized carbon particle separation may be done using differences in particle size. To make this effective, a considerable particle size difference between the coarsely sized particles of the carbon-based material and the more finely sized particles of the precious metal-containing material is normally required. Regardless of the separation technique employed, the coarsely sized carbon-based material may be recycled many times to the pre-treatment process.
• operations using finely sized carbon particles generally do not separate the carbon particles from the particles of the pre-treated precious metal-containing material. After precious metal recovery, the finely sized carbon particles are sent to tailings along with the precious metal barren material.
• the pre-treated slurry can then be fed directly to the thiosulfate leaching process. No filtration of the slurry before thiosulfate leaching is generally required.
• the pre-treated slurry commonly has pH greater than about pH 3, more commonly greater than about pH 7, and even more commonly greater than about pH 8. In some cases, no pH adjustment is required before the pre-treated slurry is contacted with the thiosulfate lixiviant to commence leaching.
• thiosulfate leaching is generally performed at a pH of between about pH 7.5 and pH 10.
• the method of the present invention is particularly suitable for pre-treatment of gold-bearing oxide ores and concentrates, prior to thiosulfate leaching, to improve the gold recovery of the thiosulfate leaching process.
• Direct thiosulfate leaching of some gold- bearing ores can result in poor gold recovery, and pre-treatment before the leaching process can provide a substantial increase in gold recovery.
• Fig. 1 is an exemplary schematic flow diagram depicting the unit operations of gold-bearing oxide ore pre-treatment prior to thiosulfate leaching.
• the process generally pre-treats the gold-bearing ore with a carbon-based material (e.g., activated carbon) in oxygenated-water, optionally removes the carbon-based material after pre-treatment, and feeds the pre-treated slurry directly to the thiosulfate leaching process. While discussed with reference to gold-bearing oxide ores, the process can be applied to any type of precious metal-bearing material.
• a carbon-based material e.g., activated carbon
• the precious metal-bearing material 100 is mixed, in step 116, with water 104 in the mixer unit (not shown) to form a slurry to be pre-treated.
• the pH can increase during pretreatment.
• the initial pH can be acidic or basic, depending on the application. For example, the initial pH commonly ranges from about pH 3 to about pH 9.
• step 116 fresh and/or recycled carbon-based material 128 and an oxidant 198 (e.g., molecular oxygen/ air or enriched air) are contacted with the slurry in the mixer unit.
• the mixer commonly mixes the various slurry constituents at the ambient temperature and atmospheric pressure in an oxygenated condition.
• the oxidant 108 can be supplied by the use of air, oxygen-enriched air, or pure oxygen and the non-reacted portion of the oxidant gas may be vented as off-gas 112.
• the residence time of the slurry in the mixer unit depends on the material type and can range from about 1 hr to about 24 hrs.
• the carbon-based material is comminuted with the precious metal-bearing material before pretreatment.
• a size distribution of the comminuted precious metal-bearing material can be substantially the same as the size distribution of the comminuted carbon.
• step 124 most, or all, of the coarsely sized carbon-based material is removed from (e.g., screened out of) the pre-treated slurry 120 to form a carbon-based material-depleted slurry 136.
• removing the coarsely sized carbon-based material by screening in the carbon-based material screen unit is particularly effective where there is a considerable size difference between the coarsely sized carbon- based material and other solid phases in the pre-treated slurry 120. Screening can typically remove 95% or more of the coarsely sized carbon from the pre-treated slurry.
• the screened coarsely sized carbon-based material 128 may be directly recycled back to the pre-treatment step 116 and introduced into the mixer unit, typically without requiring further washing or processing. Acid or basic washing can be performed if required or desired.
• the carbon-based material depleted slurry 136 or pre-treated slurry 120 is advanced to precious metal recovery step 140 in which the slurry 136 or 120 is contacted with a thiosulfate lixiviant to leach or dissolve most of the precious metal from the precious metal-bearing material. Dissolved precious metals can be recovered by known techniques, such as resin-in-leach, cementation, precipitation, electrolysis, carbon adsorption, and the like, to form a precious metal product 144.
• the pulp density of solids (including the precious metal-bearing material and carbon-based material) in the mixer unit may be designed to achieve the required solid pulp density for thiosulfate leaching with or without the removal of the carbon-based material 128.
• the carbon-based material-depleted slurry 136 can then be fed directly to thiosulfate leaching, without any filtration or water addition being necessary.
• Table 2 shows the gold recovery by thiosulfate leaching and cyanidation.
• Example 2 The same three oxide ore samples from Example 1 were pre-treated with activated carbon in oxygenated water at atmospheric temperature and pressure for 24 hrs.
• the weight ratio of ore to activated carbon was 2: 1 in all three of the tests.
• Overall solid pulp density (inclusive of ore and activated carbon) of the slurry in the pre-treatment process was about 45%, which resulted, after carbon separation, in solid pulp density of 35% in ore-water slurry.
• the required oxygen gas was supplied by sparging the slurry via industrially-pure oxygen gas with the sparging rate of 0.5 L 0 2 /L slurry/min.
• the oxidation-reduction potential ("ORP") of the slurry during pre-treatment was greater than about lOOmV and less than about 500 mV Ag/AgCl.
• ORP oxidation-reduction potential
• the ORP employed depends on the type of ore and the slurry makeup.
• the activated carbon was screened out from the pre-treated slurry, and the slurries leached with thiosulfate as described in Example 1.
• the gold recovery results of the leaching process are presented below in Table 3:
• Example 2 The same tests of Example 2 were repeated on the same ores, however, no carbon was added to the pre-treatment process (i.e., ore was mixed in oxygenated water). The final gold recovery from the samples was very similar to those of Example 1. In other words, pre-treatment without the carbon-based material has no beneficial effect on gold recovery by thiosulfate leaching.
• Sample B of Example 2 was pre-treated and leached with the identical processes to those of Example 2, except the pre-treatment was conducted for 6 hrs, instead of 24 hrs. Decreasing the pre-treatment duration from 24 hours to 6 hrs decreased the gold recovery from 71.1% to 60.7%.
• oxygen containing gases such as pure oxygen gas, air or oxygen-enriched air
• oxygen containing gases such as pure oxygen gas, air or oxygen-enriched air
• Ore sample A was pretreated in the same manner described in Example 2 with the exception that oxygen was supplied as (i) pure oxygen gas, and (ii) air.
• thiosulfate leaching was performed as described in Example 1. The gold recovery was 86.2% when the pretreatment was performed with oxygen and 81.4% when it performed with air.
• finely sized carbon may be used.
• the carbon can not only be introduced in the pretreatment stage but also added into the grinding stage to grind the precious metal-bearing feed material and carbon together to form a combined precious metal-containing and carbon-containing feed to the pretreatment stage.
• Using fine carbon in this way can reduce the amount of carbon consumed to less than 1 part carbon and 2 parts precious metal-containing feed material.
• the oxidant can be added during grinding or thereafter to effect pretreatment.
• the present disclosure in various aspects, embodiments, and configurations, includes components, methods, processes, systems and/or apparatus substantially as depicted and described herein, including various aspects, embodiments, configurations, subcombinations, and subsets thereof. Those of skill in the art will understand how to make and use the various aspects, aspects, embodiments, and configurations, after understanding the present disclosure.
• the present disclosure in various aspects, embodiments, and configurations, includes providing devices and processes in the absence of items not depicted and/or described herein or in various aspects, embodiments, and configurations hereof, including in the absence of such items as may have been used in previous devices or processes, e.g., for improving performance, achieving ease and ⁇ or reducing cost of implementation.

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