AU624286B2 - Extraction and recovery of gold - Google Patents
Extraction and recovery of goldInfo
- Publication number
- AU624286B2 AU624286B2 AU73031/91A AU7303191A AU624286B2 AU 624286 B2 AU624286 B2 AU 624286B2 AU 73031/91 A AU73031/91 A AU 73031/91A AU 7303191 A AU7303191 A AU 7303191A AU 624286 B2 AU624286 B2 AU 624286B2
- Authority
- AU
- Australia
- Prior art keywords
- gold
- thiourea
- process according
- leaching
- leach
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Ceased
Links
- 239000010931 gold Substances 0.000 title claims description 62
- 229910052737 gold Inorganic materials 0.000 title claims description 60
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 title claims description 59
- 238000011084 recovery Methods 0.000 title claims description 14
- 238000000605 extraction Methods 0.000 title description 7
- UMGDCJDMYOKAJW-UHFFFAOYSA-N thiourea Chemical compound NC(N)=S UMGDCJDMYOKAJW-UHFFFAOYSA-N 0.000 claims description 98
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Natural products NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 claims description 54
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 claims description 32
- 238000000034 method Methods 0.000 claims description 23
- 239000000463 material Substances 0.000 claims description 11
- 235000006408 oxalic acid Nutrition 0.000 claims description 10
- VTLYFUHAOXGGBS-UHFFFAOYSA-N Fe3+ Chemical compound [Fe+3] VTLYFUHAOXGGBS-UHFFFAOYSA-N 0.000 claims description 6
- 229910001447 ferric ion Inorganic materials 0.000 claims description 6
- KCXVZYZYPLLWCC-UHFFFAOYSA-N EDTA Chemical compound OC(=O)CN(CC(O)=O)CCN(CC(O)=O)CC(O)=O KCXVZYZYPLLWCC-UHFFFAOYSA-N 0.000 claims description 5
- 239000008139 complexing agent Substances 0.000 claims description 5
- 150000003839 salts Chemical class 0.000 claims description 5
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 4
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims description 4
- 239000002253 acid Substances 0.000 claims description 4
- 230000002378 acidificating effect Effects 0.000 claims description 4
- 229910052739 hydrogen Inorganic materials 0.000 claims description 4
- 239000001257 hydrogen Substances 0.000 claims description 4
- 239000000203 mixture Substances 0.000 claims description 3
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 2
- 150000004673 fluoride salts Chemical class 0.000 claims 1
- 150000003013 phosphoric acid derivatives Chemical class 0.000 claims 1
- 150000003567 thiocyanates Chemical class 0.000 claims 1
- 150000003628 tricarboxylic acids Chemical class 0.000 claims 1
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 49
- 238000002386 leaching Methods 0.000 description 24
- 239000000243 solution Substances 0.000 description 19
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 10
- RAHZWNYVWXNFOC-UHFFFAOYSA-N Sulphur dioxide Chemical compound O=S=O RAHZWNYVWXNFOC-UHFFFAOYSA-N 0.000 description 9
- 238000006243 chemical reaction Methods 0.000 description 8
- 239000003153 chemical reaction reagent Substances 0.000 description 8
- 238000004090 dissolution Methods 0.000 description 8
- 230000003647 oxidation Effects 0.000 description 8
- 238000007254 oxidation reaction Methods 0.000 description 8
- 150000001875 compounds Chemical class 0.000 description 7
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 description 6
- 230000000536 complexating effect Effects 0.000 description 6
- 238000010668 complexation reaction Methods 0.000 description 6
- 238000010525 oxidative degradation reaction Methods 0.000 description 6
- 230000001590 oxidative effect Effects 0.000 description 6
- 150000002500 ions Chemical class 0.000 description 5
- -1 cyclic thioureas Chemical class 0.000 description 4
- 239000007800 oxidant agent Substances 0.000 description 4
- XFXPMWWXUTWYJX-UHFFFAOYSA-N Cyanide Chemical compound N#[C-] XFXPMWWXUTWYJX-UHFFFAOYSA-N 0.000 description 3
- PDQAZBWRQCGBEV-UHFFFAOYSA-N Ethylenethiourea Chemical compound S=C1NCCN1 PDQAZBWRQCGBEV-UHFFFAOYSA-N 0.000 description 3
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 3
- 150000001735 carboxylic acids Chemical class 0.000 description 3
- 239000012043 crude product Substances 0.000 description 3
- 238000011065 in-situ storage Methods 0.000 description 3
- 238000002161 passivation Methods 0.000 description 3
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 3
- 239000010970 precious metal Substances 0.000 description 3
- 235000010269 sulphur dioxide Nutrition 0.000 description 3
- RGHNJXZEOKUKBD-SQOUGZDYSA-N D-gluconic acid Chemical compound OC[C@@H](O)[C@@H](O)[C@H](O)[C@@H](O)C(O)=O RGHNJXZEOKUKBD-SQOUGZDYSA-N 0.000 description 2
- PNKUSGQVOMIXLU-UHFFFAOYSA-N Formamidine Chemical compound NC=N PNKUSGQVOMIXLU-UHFFFAOYSA-N 0.000 description 2
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 2
- 229920001732 Lignosulfonate Polymers 0.000 description 2
- 229910019142 PO4 Inorganic materials 0.000 description 2
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- 239000004202 carbamide Substances 0.000 description 2
- GJLUFTKZCBBYMV-UHFFFAOYSA-N carbamimidoylsulfanyl carbamimidothioate Chemical compound NC(=N)SSC(N)=N GJLUFTKZCBBYMV-UHFFFAOYSA-N 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 238000009852 extractive metallurgy Methods 0.000 description 2
- 229940104869 fluorosilicate Drugs 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- NUJOXMJBOLGQSY-UHFFFAOYSA-N manganese dioxide Chemical compound O=[Mn]=O NUJOXMJBOLGQSY-UHFFFAOYSA-N 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 239000010452 phosphate Substances 0.000 description 2
- 229910052700 potassium Inorganic materials 0.000 description 2
- 239000011591 potassium Substances 0.000 description 2
- 238000012827 research and development Methods 0.000 description 2
- 239000004291 sulphur dioxide Substances 0.000 description 2
- NVHNGVXBCWYLFA-UHFFFAOYSA-N 1,3-diazinane-2-thione Chemical compound S=C1NCCCN1 NVHNGVXBCWYLFA-UHFFFAOYSA-N 0.000 description 1
- XZMCDFZZKTWFGF-UHFFFAOYSA-N Cyanamide Chemical compound NC#N XZMCDFZZKTWFGF-UHFFFAOYSA-N 0.000 description 1
- RGHNJXZEOKUKBD-SQOUGZDYSA-M D-gluconate Chemical class OC[C@@H](O)[C@@H](O)[C@H](O)[C@@H](O)C([O-])=O RGHNJXZEOKUKBD-SQOUGZDYSA-M 0.000 description 1
- RGHNJXZEOKUKBD-UHFFFAOYSA-N D-gluconic acid Natural products OCC(O)C(O)C(O)C(O)C(O)=O RGHNJXZEOKUKBD-UHFFFAOYSA-N 0.000 description 1
- FEWJPZIEWOKRBE-JCYAYHJZSA-N Dextrotartaric acid Chemical compound OC(=O)[C@H](O)[C@@H](O)C(O)=O FEWJPZIEWOKRBE-JCYAYHJZSA-N 0.000 description 1
- BWGNESOTFCXPMA-UHFFFAOYSA-N Dihydrogen disulfide Chemical compound SS BWGNESOTFCXPMA-UHFFFAOYSA-N 0.000 description 1
- 241000233866 Fungi Species 0.000 description 1
- ZGDPKXCYFYUNCK-UHFFFAOYSA-M N#C[S-].N#CS.N#CS.N.[Na+] Chemical compound N#C[S-].N#CS.N#CS.N.[Na+] ZGDPKXCYFYUNCK-UHFFFAOYSA-M 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- LSNNMFCWUKXFEE-UHFFFAOYSA-N Sulfurous acid Chemical class OS(O)=O LSNNMFCWUKXFEE-UHFFFAOYSA-N 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- FEWJPZIEWOKRBE-UHFFFAOYSA-N Tartaric acid Natural products [H+].[H+].[O-]C(=O)C(O)C(O)C([O-])=O FEWJPZIEWOKRBE-UHFFFAOYSA-N 0.000 description 1
- 239000003929 acidic solution Substances 0.000 description 1
- 238000013019 agitation Methods 0.000 description 1
- 239000004411 aluminium Substances 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 230000001580 bacterial effect Effects 0.000 description 1
- BVKZGUZCCUSVTD-UHFFFAOYSA-N carbonic acid Chemical class OC(O)=O BVKZGUZCCUSVTD-UHFFFAOYSA-N 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000005341 cation exchange Methods 0.000 description 1
- 239000013522 chelant Substances 0.000 description 1
- 239000003638 chemical reducing agent Substances 0.000 description 1
- 150000001860 citric acid derivatives Chemical class 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- XPPKVPWEQAFLFU-UHFFFAOYSA-J diphosphate(4-) Chemical class [O-]P([O-])(=O)OP([O-])([O-])=O XPPKVPWEQAFLFU-UHFFFAOYSA-J 0.000 description 1
- 229960001484 edetic acid Drugs 0.000 description 1
- 238000005363 electrowinning Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000013213 extrapolation Methods 0.000 description 1
- 239000000174 gluconic acid Substances 0.000 description 1
- 235000012208 gluconic acid Nutrition 0.000 description 1
- 150000002343 gold Chemical class 0.000 description 1
- 239000000383 hazardous chemical Substances 0.000 description 1
- 230000002427 irreversible effect Effects 0.000 description 1
- WABPQHHGFIMREM-UHFFFAOYSA-N lead(0) Chemical compound [Pb] WABPQHHGFIMREM-UHFFFAOYSA-N 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 1
- 244000005700 microbiome Species 0.000 description 1
- 238000005065 mining Methods 0.000 description 1
- 238000006386 neutralization reaction Methods 0.000 description 1
- 238000005325 percolation Methods 0.000 description 1
- 229920005862 polyol Polymers 0.000 description 1
- 150000003077 polyols Chemical class 0.000 description 1
- 239000001205 polyphosphate Chemical class 0.000 description 1
- 235000011176 polyphosphates Nutrition 0.000 description 1
- 238000002203 pretreatment Methods 0.000 description 1
- NIFIFKQPDTWWGU-UHFFFAOYSA-N pyrite Chemical compound [Fe+2].[S-][S-] NIFIFKQPDTWWGU-UHFFFAOYSA-N 0.000 description 1
- 229910052683 pyrite Inorganic materials 0.000 description 1
- 239000011028 pyrite Substances 0.000 description 1
- 230000001172 regenerating effect Effects 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 238000004088 simulation Methods 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 238000000638 solvent extraction Methods 0.000 description 1
- 241000894007 species Species 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- LSNNMFCWUKXFEE-UHFFFAOYSA-L sulfite Chemical class [O-]S([O-])=O LSNNMFCWUKXFEE-UHFFFAOYSA-L 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 239000001117 sulphuric acid Substances 0.000 description 1
- 235000011149 sulphuric acid Nutrition 0.000 description 1
- 239000013589 supplement Substances 0.000 description 1
- 239000011975 tartaric acid Substances 0.000 description 1
- 235000002906 tartaric acid Nutrition 0.000 description 1
- 150000003892 tartrate salts Chemical class 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 150000003585 thioureas Chemical class 0.000 description 1
Classifications
-
- 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
Landscapes
- Treatment Of Liquids With Adsorbents In General (AREA)
- Extraction Or Liquid Replacement (AREA)
Description
EXTRACTION AND RECOVERY OF GOLD
FIELD OF INVENTION;
This invention relates to the extraction and recovery of gold from gold-bearing material. Such material encompasses gold-bearing ores, concentrates, anodic slimes and residues, as well as gold-bearing metallic scrap, and materials previously treated by roasting, bacterial leaching, pressure leaching or other techniques required to liberate the gold from its matrix.
The invention relates to the extraction and recovery of gold from gold-bearing materials, for example those above mentioned, using leaching methods such as continuous or batch stirred-tank agitation, vat leaching, or the in situ techniques such as dump and heap leaching, or the _in situ technique of solution mining.
SUBSTITUTESHEET
Background of the Invention:
At present, the conventional cyanide leach process is used almost universally to extract gold. However, the growing concern over safety and environmental hazards associated with the use of cyanide combined with the limited use of the process for treatment of problematic gold ores (e.g., refractory sulfide ores, carbonaceous ores, ores containing significant amounts of cyanocides) requires development of an economically viable, alternative leach process.
Gold is readily dissolved in acidified solutions containing thiourea, using manganese dioxide, hydrogen peroxide or ferric ions as the oxidant [D.W. Bilston, R.N. Millet and J.T. Woodcock (1987) Proc. Confer. "Research and Development in Extractive Metallurgy" (Aus. I.M.M. Melbourne) pp. 19-28]. However, this gold dissolution process has found little application in the gold industry. The main drawback has been the excessive oxidative degradation of thiourea which occurs in the presence of the above mentioned oxidants. The relevant chemical reactions can be written in two stages involving initial oxidation to formamidine disulfided) , followed by further irreversible decomposition to sulfur, cyanamide and thiourea(2) .
Fe + tu - i(tu)2 2+ + Fe2+ (1)
( u 2 +— sulfinic compound ^ S + CN(NH2 ) + tu ....(2)
where tu = thiourea and (tu)„2+ = formamidine disulfide.
Reaction (1) is much faster than reaction (2) and was considered as the dominant reaction in determining the relative consumption of thiourea. Furthermore, the rapid consumption of thiourea during the leach process is often associated with passivation of gold in the feed material, and hence low gold recoveries. Consequently, in the past, the thiourea leaching process has proved very unattractive in comparison with the universally accepted cyanidation process.
In recent work it has been shown that the use of sulphur dioxide in conjunction with thiourea significantly reduces reagent loss through oxidative degradation (R.G. Schulze (1984) J. Metals 3jS (6) pp. 62-653. However, the lowering of thiourea consumption by using sulphur dioxide has not always been achieved in practice [D.W. Bilston, R.N. Millet and J.T. Woodcock (1987) Proc. Conf. "Research and Development in Extractive Metallurgy" (Aus. I.M.M. Melbourne) pp. 19-28]. The same workers have also patented the use of a substituted thiourea, i.e. ethylene thiourea. This particular derivative is more stable to oxidation and exhibits a far greater resistance to oxidative degradation than thiourea [R.G. Schulze (1983) German Patent 3347165]. However, the cost of ethylene thiourea is too high to be considered as an economic alternative.
Summary of the Invention:
The present invention is based on the discovery that
3+ the oxidative degradation of thiourea by Fe is markedly reduced by the use of chemical reagents which have the ability to complex Fe in acidic solutions.
The invention accordingly provides a process for the hydrometallurgical recovery of gold from gold-bearing material comprising the step of treating gold-bearing material with an acidic lixiviant solution containing thiourea and ferric ions, characterised in that the said solution also includes a complexing agent for ferric ions.
3+ The oxidising power or strength of Fe is reduced to an extent where gold dissolution still occurs at an appreciable rate and the oxidative degradation of thiourea
3+ by Fe is markedly reduced.
1+ Gold in solution as the Au(thiourea) species, in
3+ the presence of Fe and these chemical reagents, can be recovered using known techniques, eg. absorption on activated carbon or resins; cementation with iron or aluminium; electrowon using porous carbon electrodes; reduced using hydrogen; or solvent extracted. Thus the invention extends to methods of extracting and recovering gold from gold-bearing material.
COMPARISON WITH THE PRIOR ART
The present invention differs from the prior art in this field since the essence of the present invention
3+ involves the deliberate complexation of Fe , with the aim
3+ to lower the oxidising power of Fe , which results in a marked reduction in the oxidative loss of thiourea. The essence of other patents in this field is described as follows.
GB 2 152 488 R. Schulze (SKW Trostberg)
Relates to the use of cyclic derivatives of thiourea as complexants for gold. The relevant cyclic thioureas are ethylene thiourea .and propylene thiourea. The cyclic thioureas exhibit greater resistance to oxidative degradation compared to thiourea, whilst still allowing satisfactory gold complexation and gold leaching kinetics.
US 4 561 947 R. Schulze (SKW Trostberg)
Relates to the use of SO , sulfur dioxide; (or other compounds that provide a source of S02, such as sulfites, hydrogen sulfites, pyrosulfites and the like); as a reductant for regenerating oxidised thiourea, (i.e. formamidine disulfide) . In the leach process, SO2 is used in conjunction with thiourea and an oxidant, (ie. usually Fe 3+) , to control the leach potential at a desired value where satisfactory precious metal leaching rates are achieved and thiourea degradation is minimised. In this invention, the leach potential is continuously controlled by the use of SO-, which one would expect to first act by
Δ 3+ reducing a majority of the Fe ion that that is present to Fe ion. The leach potential value will determine the
3+ 2+ extent of the reduction of Fe to Fe . Due to the chemistry of this invention, the predominant oxidant that exists under typical leach conditions is formamidine
3+ disulfide. The complexation of Fe is not an issue in this invention.
GB 2 181 722 R. H. Little
Relates to the use of thiourea in conjunction with urea and potassium lignin sulfonate for the extraction and recovery of precious metals. The role of these compounds in the thiourea leaching reaction is unclear. However, these compounds may effect the recovery of precious metals from thiourea containing solutions by co-adsorbing onto activated carbon and increasing the cation exchange properties of the carbon, and thus increasing the efficiency of the recovery of the precious etal-thiourea complexes using activated carbon. Urea and potassium lignin sulfonate do not form any significant complexes with ferric ions and therefore this invention has no similarities with the present invention.
S. Afr. ZA 85/4463 B. K. Loveday et. al. (Anglo American Corp. of Sth. Afr.)
Relates to in situ recovery of gold from the fines on a footwall and in the fissures and cracks therein by passing a solution capable of solubilising the gold across the footwall. An acid solution containing 0.2-1.0 g/1
3+ thiourea and optionally 0.75 g/1 Fe and 1.3 g/1 Na^SO-^ was applied for leaching of gold. The sprayed on solution was collected in a sump for recirculation. Dissolved gold was recovered by passing the loaded solution through a column of activated carbon. This patent is concerned with a leaching technique rather than any specific novel leaching chemistry.
Detailed Description of the Invention:
In simple terms, to leach gold in the presence of thiourea, a leach potential in excess of 380mV vs. N.H.E. is required. However, a leach potential above 420 mV vs.
N.H.E. will also result in the oxidation of thiourea. The oxidation potential of uncomplexed Fe ion is 770mV vs.
N.H.E.. As expected, both gold and thiourea will oxidise
3+ 3+ m the presence of uncomplexed Fe . By complexing Fe ,
3+ the oxidising potential of Fe can be reduced well below
770 mV vs. N.H.E.. The oxidation of gold still occurs at a satisfactory rate, whilst the oxidative loss of thiourea is markedly reduced. As a practical matter, it is preferred to operate at an oxidising potential between 390 and 500 mV vs. N.H.E.
3+ The complexation of Fe in acid solution, say
3+ pH<7, can be achieved by a number of compounds. The Fe complexing reagents can be added as commercially available salts or they can be synthesised as a crude product,
3+ (typically a mixture of Fe complexing reagents). For example, the crude product could be made chemically; e.g. by oxidation of cellulosic material to form a complex mixture of polyols, hydroxycarboxylic acids and carboxylic
acids which can provide a complexing solution meeting the requirements of this invention, or the crude product can be made biologically; e.g. by using microorganisms such as the fungi Asperqillus niσer to produce carboxylic acids, such as citric acid, that complex Fe 3+
3+ A list of some relevant Fe complexing reagents is given in table 1.
Preferred complexing reagents are compounds which can form ferric complexes having a stability constant of log K greater than 1, and preferably greater than 2.0.
Convenient compilations providing stability constants of many complexing agents for iron are Martell and Calvin, "Chemistry of the Metal Chelate Compounds", U.S. copyright 1952, and "Stability Constants of Metal-Ion Complexes," supplement No. 1, Special Publication No. 25, published by The Chemical Society, U.S. copyright 1971.
The general leach conditions for the "modified" Fe 3+/thiourea gold leaching system (i.e. using complexed Fe 3+) are summarised in Table 2. The range of conditions
3-1- listed in Table 2 covers the use of all the Fe complexants given in Table 1.
3+ A comparison of the rate of reaction between Fe and thiourea in the presence and absence of a Fe 3+ complexant (i.e. 0.05M oxalic acid), is illustrated in Figure 1. These data were generated by reaction of 0.05M
3+ thiourea with 0.01M Fe in 0.1M H S04 at 25°C. A value of 100% relative thiourea consumption was taken as the
3+ point where all of the Fe ion had been reduced to
Fe ion.
It is clear that the reduction in the oxidative strength of Fe 3+ by complexation with oxalic acid has been effective in lowering the consumption of thiourea. However, the complexation of Fe 3+ by oxalic acid, while lowering the consumption of thiourea, does not have any detrimental effect on the gold leaching reaction. This is
SUBSTITUTESHEET
illustrated in Figure 2 where the dissolution of a rotating gold disc electrode was examined. • Figure 2 illustrates the effect of 0.05M oxalic acid and solution age on the dissolution of a gold rotating disc electrode.
3+ The initial leach solution contained 0.005M Fe and 0.05M thiourea (0.1M sulfuric acid background, 25°C). In the absence of oxalic acid, the rate of gold dissolution steadily decreased as the solution age increased.
After 20 hours, the rate of gold dissolution was markedly reduced, (i.e. by approximately 73%) and the gold surface had a dark brown appearance which is indicative of some form of passivation. In contrast, the rate of gold dissolution in the presence of oxalic acid exhibited a far more gradual decrease with increasing solution age. For example, after 960 hours (i.e. 40 days), the rate of gold dissolution had decreased by only 40%. The gold surface also maintained a bright lustrous appearance, showing no evidence of passivation.
The "modified" Fe 3+/thiourea gold leaching system was also applied to a column leach experiment which was aimed at simulating a heap leaching operation of a gold ore. The conditions are summarised below:
General Column Leach Conditions
Ore type Refractory, low grade pyritic ore (ca. 7 kg grading 1.2 pp gold)
Ore pre-treatment A biological "heap leaching" simulation was carried out on the ore packed in the column. A target of ca.>80% pyrite oxidation was set prior to any attempts at gold leaching.
SUBSTITUTESHEET
Gold Leaching The ore was initially leached with a
(at ambient temp) ssuullpphhuurriicc aacciidd ssoolluuttiioonn ccoomntaining oxalate to stabilize the Fe 3+ concentration. Once the Fe 3+ concentration was stabilized, thiourea was added to the leachant solution.
SUBSTITUTESHEET
- 9 -
3+ Gold Leachant Fe ca. 0.005M oxalic acid 0.056M
H2S04 0.100M thiourea 0.065M
Percolation rate ca. 32 ml/hour (average over 32 days)
The column leaching results are summarised in Table 3. A plot of gold extraction (%) vs . the number of days is given in Figure 3. Extrapolation from day no. 27 (i.e. where thiourea addition was ceased), shows that ca. 80% recovery can be expected after ca. 43 days if thiourea addition was continued throughout.
In summary, the results are extremely encouraging with respect to gold recovery, leaching kinetics, and thiourea consumption. This technology also creates new possibilities for treating low grade gold ores which are either inherently acidic or require an acidic pretreatment step such as biological oxidation. The application of alkaline cyanidation under these circumstances is limited due to the need for expensive and most likely ineffective neutralisation, and more than likely high cyanide consumption.
Recovery of gold from the modified acid-thiourea leaching systems was achieved by cementation of gold into iron powder. However other techniques as described by Deschnes (G. Deschnes (1986) C.I.M. Bulletin, 7 pp. 76-83.], such as absorption on carbon, electrowinning, solvent extraction, hydrogen reduction or cementation on lead powder are equally applicable. In a typical experiment, iron powder was added to a solution containing 100 ppm Au(tu) , 0.066M thiourea, 0.1M sulphuric acid and 0.05M oxalic acid. Approximately 90% of the gold in solution was cemented out after 30 minutes.
- 10 -
TABLE 1: RELEVANT ACID-STABLE COMPLEXING AGENTS FOR 3+
Fe WHICH ARE APPLICABLE TO THE "MODIFIED' Fe 3+/THIOUREA GOLD LEACHING SYSTEM
General Type Examples
carboxylic acids oxalic acid and oxalate (di-and tri-) salts, citric acid and citrate salts, tartaric acid and tartrate salts, gluconic acid and gluconate salts.
phosphate based phosphoric acid and phosphate reagents salts, ortho-phosphate salts, pyro-phosphate salts, poly-phosphate salts.
thiocyanate ammonium thiocyanate sodium thiocyanate
fluorides hydrofluoric acid sodium fluoride
fluorosilicate fluorosilicic acid fluorosilicate salts
EDTA ethylene diamine tetra acetic acid, EDTA salts.
- 11
TABLE 2: GENERAL CONDITIONS FOR THE "MODIFIED" FERRIC/THIOUREA GOLD LEACHING SYSTEM
VARIABLE CONDITIONS
Fe 0.0025 to 0.1M
Thiourea 0.005 to 0.4M preferably 0.02 to 0.4M
pH 0.5 to 4.5
Potential 350 to 700 mV vs NHE (Normal Hydrogen Electrode)
3+
Fe complexants 0.01 to 1.0M preferably 0.01 to 0.2M
Temperature 10 to 90° C
- 12 -
TABLE 3: COLUMN LEACH TEST RESULTS USING THE
"MODIFIED" FERRIC-THIOUREA LEACH SYSTEM.
NUMBER OF DAYS %GOLD EXTRACTION
18.0
10 36.1
15 45.7
22 57.9
32 68.7
NB: 1. After 27 days, thiourea addition was stopped 2. % thiourea recovered after 32 days = 98%
It will be clearly understood that the invention in its general aspects is not limited to the specific details referred to hereinabove.
Claims (6)
1. A process for the hydrometallurgical recovery of gold from gold-bearing material comprising the step of treating gold-bearing material with an acidic lixiviant solution containing thiourea and ferric ions, characterised in that the said solution also includes a complexing agent for ferric ions.
2. A process according to claim 1, which the complexing agent is selected from the group consisting of di- and tri-carboxylic acids, phosphoric acid and phosphate salts, thiocyanates, fluorides, fluosilicic acid and fluosilicate salts, EDTA and EDTA salts, and mixtures thereof.
3. A process according to claim 1 or claim 2, in which the treatment is carried out a temperature within the range 10 to 90°C, the lixiviant solution has a pH in the range 0.5 to 4.5, contains 0.0025 to 0.1M Fe , 0.005 to
3+ 0.4M thiourea, and 0.01 to 1.0M Fe complexant, and has a leach potential in the range 350 to 700 V vs Normal
Hydrogen Electrode.
4. A process according to claim 3 in which the leach potential is in the range 390 to 500 mV vs NHE.
5. A process according to any one of the preceding claims in which the complexant forms ferric complexes having a stability constant of log K greater than 1.
6. A process according to claim 5, in which the complexant comprises oxalic acid.
SUBSTITUTESHEET
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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AU73031/91A AU624286B2 (en) | 1990-02-23 | 1991-02-19 | Extraction and recovery of gold |
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
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AUPJ879090 | 1990-02-23 | ||
AUPJ8790 | 1990-02-23 | ||
AU73031/91A AU624286B2 (en) | 1990-02-23 | 1991-02-19 | Extraction and recovery of gold |
Publications (2)
Publication Number | Publication Date |
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AU7303191A AU7303191A (en) | 1991-09-18 |
AU624286B2 true AU624286B2 (en) | 1992-06-04 |
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Application Number | Title | Priority Date | Filing Date |
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AU73031/91A Ceased AU624286B2 (en) | 1990-02-23 | 1991-02-19 | Extraction and recovery of gold |
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AU (1) | AU624286B2 (en) |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
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AP538A (en) * | 1992-06-26 | 1996-09-18 | Intec Pty Ltd | Production of metal from minerals |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4645535A (en) * | 1985-08-15 | 1987-02-24 | Little Roger H | Method for the recovery of precious metals from ores |
US4668289A (en) * | 1985-11-22 | 1987-05-26 | Wisconsin Alumni Research Foundation | Method for reclaiming gold |
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1991
- 1991-02-19 AU AU73031/91A patent/AU624286B2/en not_active Ceased
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4645535A (en) * | 1985-08-15 | 1987-02-24 | Little Roger H | Method for the recovery of precious metals from ores |
US4668289A (en) * | 1985-11-22 | 1987-05-26 | Wisconsin Alumni Research Foundation | Method for reclaiming gold |
Also Published As
Publication number | Publication date |
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AU7303191A (en) | 1991-09-18 |
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