CA1219132A - Hydrometallurgical arsenopyrite process - Google Patents
Hydrometallurgical arsenopyrite processInfo
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- CA1219132A CA1219132A CA000443728A CA443728A CA1219132A CA 1219132 A CA1219132 A CA 1219132A CA 000443728 A CA000443728 A CA 000443728A CA 443728 A CA443728 A CA 443728A CA 1219132 A CA1219132 A CA 1219132A
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- 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
- C22B11/06—Chloridising
-
- 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
- C22B11/00—Obtaining noble metals
- C22B11/08—Obtaining noble metals by cyaniding
Abstract
HYDROMETALLURGICAL ARSENOPYRITE PROCESS
ABSTRACT
A process for the hydrometallurgical recovery of gold from arsenical pyrite concentrate. The process comprises decomposing the concentrate by using a leach composed of higher valence nitrogen oxides present in acidic solution; subjecting the decomposed product to a solid-liquid separation to produce a residue and a liquid fraction; recovering gold from the residue by conventional means; and precipitating dissolved arsenic, iron and sulphur from the liquid fraction before recycling the liquid fraction in the process.
ABSTRACT
A process for the hydrometallurgical recovery of gold from arsenical pyrite concentrate. The process comprises decomposing the concentrate by using a leach composed of higher valence nitrogen oxides present in acidic solution; subjecting the decomposed product to a solid-liquid separation to produce a residue and a liquid fraction; recovering gold from the residue by conventional means; and precipitating dissolved arsenic, iron and sulphur from the liquid fraction before recycling the liquid fraction in the process.
Description
~219:132 ~YD~OMETALLURGICAL ARSENOPYRITE PROCESS
FIELD OF THE INVENTION
This invention is directed to a novel environ-mentally amicable hydrometallurgical process for therecovery of gold from arsenical pyrite concentrate.
BACKGROUND OF THE INVENTION
The mineral arsenopyrite is known to contain gold which is in solution in the mineral matrix or is present as fine inclusions. This gold is not available for extraction by hydrometallurgical processes which treat only the mineral surfaces, for example, cyanida-tion. The mineral pyrite is often associated with arsenopyrite and may contain in its matrix finely dispersed gold which is difficult to extract. ~rseno-pyrite and pyrite are the main constituents of arsenical pyrite concentrates.
The conventional means of liberating gold rom arsenical pyrite concentrates is to roast the material and then treat the calcine by cyanidation. This process generates environmental pollution problems due to the airborne emission of sulphur and arsenic oxides. The tailings from the calcine cyanidation contain arsenic which is alRo a potential environmental contaminant.
Arsenical pyrite concentrates may also be treated for gold recovery through conventional pyro-metallurgical processes which include copper smelting, 12~g~3,~
lead smelting and zinc roas-ting. These processes also produce potentially harmful airborne arsenic emissions from the treatment of these concentrates. Problems associated with the added arsenic burden in the process flows also arise.
Two hydrometallurgical processes exist which could potentially be used to decompose arsenical pyrite concentrates though they are not specifically used for this purpose. These are the Sill and the Calera pro-cesses which are both used for the treatment of cobaltand arsenic-bearing materials. In the Sill process, the concentrate is solubilized by the action of a caustic substance and oxygen under elevated temperatures and pressures. In the Calera process sulphuric acid and lS oxygen at high temperature and pressure are the active agents. Neither process, as far as is known, is commercially operated at the present time.
SUMMARY OF THE INVENTIO~
The subject invention is directed to an environmentally amicable hydrometallurgical process for decomposing arsenical pyrite concentrates in acidic solution through the action of higher valence nitrogen oxides. The decomposed product can be subjected to a solid-liquid separation to produce a residue and a liquid fraction. The solid residue produced can be readily treated for the recovery of gold by conventional techniques. The active nitrogen oxides can be regener-12~9~3Z
ated by an oxidizing agent. Arsenic, iron and sulphurare precipitated from the solution making it suitable for reuse in the decomposition step.
Arsenopyrite and pyrite are decomposed in acid solutions where the pH is less than 2 by the action of nitrogen oxides where the nitro~en has a valence of 3 or greater. These oxides include nitric acid, nitrous acid and nitrogen dioxide. The nitrogen oxide is present in sufficient quantity in the solution to provide an adequate rate of dissolution. The main products from the decomposition are soluble ferric iron species, soluble arsenate species, soluble sulphate species, elemental sulphur and nitric oxide, as well as nitrogen dioxide. Nitrogen dioxide becomes increasingly abundant as a product in the gas phase as the nitric acid concen-tration increases: see Canadian Patent No. 995,468, Paul B. Queneau et al., August 24, 1976. The minor products are arsenic trioxide and nitrous acid. The gold contained in the concentrate remains in the solid residue which is composed of elemental sulphur and insoluble gangue minerals. Any silver present in the concentrate would also report to the residue.
The introduction of oxygen into the leach, as demonstrated in the Examples herein, permits less than stoichiometric amounts o~ nitric acid to be used. As demonstrated in Examples 7 and 8 herein, it is not necessary to use nitric acid in order to practise the ., ,Jj. ~
~2~3i3~
invention.
The hydrometallurgical process for the recovery of precious metal from an ore or concentrate containing arsenopyrite or pyrite wherein at least some of the precious metal is occluded in the arsenopyrite or pyrite comprises:
(a) forming in a common volume space a gas phase and a liquid slurry comprising the ore or concen-trate as the solid phase and acid and water as the liquid phase of the slurry, (b) effecting in the slurry between the arsenopyrite or pyrite and a higher valence oxidized nitrogen species in ~hich the nitrogen has a valence of at least plus 3 an oxidation-reduction reaction having a standard potential between about 0.90 and about 1.20 volts on the hydrogen scale, thereby solubilizing in the liquid phase the arsenic, iron and sulphur in the arsenopyrite or the iron and sulphur in the pyrite, all as the oxidation products, and producing in the liquid phase nitric oxide (N0) in which the nitrogen has a valence of plus 2, as the reduction product;
(c) releasing at least part of the nitric oxide from the liquid phase into the gas phase;
(d) oxidizing the nitric oxide in the gas phase, in which a significant oxygen partial pressure is maintained by continuous addition of an oxygen containing gas, to form a higher valence oxidized - 3a -12~9~l 3~
nitrogen species in which the nitrogen has a valence of at least plus 3, the total amount of oxygen added being at least in an amount stoichiometrically required for solubilization in the liquid phase of the arsenic, iron and sulphur in the arsenopyrite or the iron and sulphur in the pyrite;
(e~ absorbing the higher valence oxidized nitrogen species into the slurr~ wherein the oxidized nitrogen species become available for the oxidation-reduction reaction of step (b) whereby the nitrogen, inits oxide for~s, functions as a catalyst for the trans-port of oxygen from the gas phase to the oxidation-reduction reactions in the slurry, thereby permitting the total of the oxidized nitrogen species and nitric oxide in the system to be substantially less than a stoichiometric balance required for the oxidation of the arsenic, iron and sulphur;
(f) subjecting the slurry to a solid-liquid separation to produce a solid residue and a liquid fraction; and (g) recovering precious metal from the solid residue.
DRAWING
.
Figure 1 illustrate arsenic concentration as a function of time for three similar experiments with solution composition as a variable.
- 3b -12~913~
DETAILED DESCRIPTION OF THE INVENTION
The decomposition of arsenopyrite and pyrite by nitric acid occurs according to the following reactions.
Fe AsS + 23/3 HNO3 = Fe(NO3)3 + H3 As04 (1) + H2SO4 + 4/3 H2O + 14/3 NO
FeAsS + 17/3 HNO3 = Fe(~O3)3 + H3AsO4 (2) + S + 4/3 H2O ~ 8/3 NO
FeS2 + 8 HNO3 = Fe(NO3)3 + 2H2SO4 `(3) + 2H~O + 5NO
15 FeS2 + 5 HNO3 = Fe(NO3)3 + 2S + 2H2O ~ NO (4) In the reaction with arsenopyrite, it has been found that 60-90% of the mineral's sulphur is converted to soluble sulphate species. In the reaction with 20 pyrite, the degree of conversion is 80-100%.
The gold in the decomposition residue may be readily extracted by conventional techniques such as cyanidation, following leaching of the residue with sodium hydroxide to dissolve sulfur prior to cyanida-tion, or treatment with oxidizing chloride lixiviants,such as aqua regia. Silver may also be extracted by these techniques.
, lZ~9~32 It is important that the decomposition solution does not contaln significant quantities of species which complex gold, for example, chloride ions.
These would put the gold into solution and a separate 5 additional process step would have to be included to extract it.
The active nitrogen oxides are required only to decompose the minerals in the concentrate. The nitrogen oxide should ~e present in sufficient concen-tration in the solution to provide an adequate rate ofdissolution. Any suitable acid may be used to form the soluble ferric iron species. An adequate rate of dissolution is about 10 to 30 minutes.
In the reaction detailed below, nitrogen dioxide is the decomposition agent for arsenopyrite with sulphuric acid present.
FeAsS + 4N02 = 1/2 Fe2 (S04)3 + H3 As04 (5) + 3/2 H2S4 + S + 4N0 In the reaction detailed below, the sulphuric acid is formed from the decomposition of pyrite.
FeS2 + 15/2 N02 = 1/2 Fe2 (S04)3 (6) + 1/2 H20 + 1/2 H2S04 + 15/2 N0 In the preceding reactions, the active nitrogen oxides are r~duced to nitric oxide which may then be regenerated by an oxidant. A useful oxidant is oxygen which reacts with nitric oxide in the presence of ~Z19132 water to form nitrogen dioxide, nitrous acid and nitric acid as shown in the reactions set forth below.
N0 + 1/2 2 - N02 N0 + N02 + H20 = 2HN02 3HN2 = HN3 + H20 + 2N0 10 The regeneration of nitric oxide to the higher valence states may be done concurrently with the Aecom-position.
Nitrous oxide is formed by the decomposition of nitric oxide according to the side reaction shown below.
3N0 N20 + N02 When the regeneration step is carried out with oxygen concurrently with the decomposition reactions, the overall stoichiometry of arsenopyrite reacting with nitric acid and oxygen to produce sulphuric acid as the sulphur product is illustrated by the reaction below.
FeAsS + 3.502 = Fe(N03)3 + H3 As04 + 3EIN03 + H20 + H2S4 5ince the active nitrogen oxides can be regenerated during the decomposition step, the quantity ~;~1913~
of these oxides present at any time may be quite small.
The criterion is that there must be sufficient acid present in solution to form the soluble ferric iron species. It must be emphasized -that it is the nitrogen oxides rather than oxygen that are the active decomposi-tion agent. The presence of nitrogen oxides with sulphuric acid differentiates the decomposition step described above from the Calera process.
An important feature of decomposition using nitrogen oxides is the high speed of reaction. If a solution which is three molar in nitric acid is reacted with fine arsenical pyrite flotation concentrate, it has been found that the reaction is complete within ten minutes. This is significantly faster than rates claimed by other processes at similar conditions.
Figure l shows the arsenic concentration as a function of time for three similar experiments in which the only variable is the composition of the solution.
The three compositions are 3 M acid as HN03; 2.5 M
acid as H~S04; 0.5 M acid as HN03; and 3.0 M acid as H2S04. The other conditions are given on Figure l. It is apparent from the data that the presence of nitric acid greatly speeds the rate of reaction.
The decomposition and regeneration steps are both exothermic. When a solution which is three molar in nitric acid is reacted with fine arsenical pyrite 3~Z:~L9:132 concentrate at 15~ solids without oxygen present for regeneration, the temperature increase of the slurry is 40C. With oxygen present for regeneration, the temperature increase is 130C. Since the rates of the decomposition and regeneration reactions increase with temperature the overall reactions appear to accelerate as they proceed. It is possible that controlled cooling may be required to prevent the melting of elemental sulphur and to prevent the precipitation of salts.
The decomposition step proceeds at any temperature above ambient. However, on a practical basis, the reaction is carried out at temperatures of between 80 and 120C. It is important that sufficient acid be present to form the soluble ferric iron species.
Without this acid, compounds will precipitate from solution. If oxygen is used for regeneration, any oxygen pressure above ambient is adequate. Agitation increases the speed of the reactions and improves the quality of the final sulphur-bearing residue.
The decomposition leach can be carried out over a wide range of solid-liquid ratios. Increasing the ratio of solids to liquids provides economic bene-fits, but the upper limit of this ratio is reached when the solubility limit of dissolved species is reached.
When the decomposition reactions are complete, a solid-liquld separation is carried out to produce a residue containing all the gold and a clarified solution which is recycled in the process.
To enable the solution to be reused for the decomposition step, the soluble arsenic, iron and sulphur must be removed from solution.
Arsenic in the pentavalent state as ferric arsenate is removed from solution with ferric iron. The following reaction shows the formation of ferric arsenate from ferric nitrate and arsenate.
FelN03)3 + H3As04 = 3HN03 + FeAsO4 (12) - + x H20 XH20 Ferric arsenate is produced virtually quan-titatively from an equimolar solution of ferric nitrate and arsenic acid at all temperatures above ambient.
However, the rate of precipitation can be controlled by temperature. At room temperature, complete precipita-tion requires several months; at 100C precipitation requires one to two hours; and at 200C precipitation occurs in less than one hour.
Ferric arsenate can be precipitated rapidly at low temperatures by the neutralization of the acid in the solution. At 25C the solubility of ferric arsenate between pH 3 and pH 7 is very low. The solids produced at low temperature tend to be colloidal and dificult to filter. The solids can contain ferric hydroxide which also tends to be colloidal.
12~L9132 The presence of sulphate in solution raises the solubility of ferric arsenate. A solution which is 1 M in ferric nitrate and arsenic acid is stable at room temperature in the presence of 0.5 M H2S04. At higher temperatures, the effect oE sulphate is less pronounced.
A calcium-bearing neutralizing agent, such as calcium oxide or calcium carbonate, can be used to neutralize excess acid in solution and to remove sulphate in order to improve ferric arsenate precipita-tion.
A small portion of the extracted arsenic is present as arsenite and thus arsenic trioxide can preci-pitate when the filtered decomposition solution is cooled.
If insufficient arsenate or ferric is present in solution to bring about complete precipitation of the appropriate species, then arsenate or ferric compounds may be added to the solution.
Sulphate is removed from solution by the addition of calcium-bearing materials to form calcium sulphate. The reaction between calcium carbonate and sulphuric acid is as follows.
CaC03 + H2S04 = CaS04 + C2 + H20 (13) 1;~'1 9~32 There are two forms of calcium sulphate which may be formed. Gypsum ~CaS04 2H20) has a low solubility which is virtually unaffected by temperature.
In a 1 M solution of ferric nitrate and arsenic acid, the solubility of CaS04 2H2O is approximately 0.1 M. Anhydrite (CaS04) forms at temperatures above 60C (although the crossover point from gypsum may be as high as 110C due to supersaturation). The solubility of anhydrite drops rapidly with temperature. Solubility data for anhydrite in water gives a solubility of 0.02 M
at 60C and .0015 M at 160C.
Ferric iron is removed from solution by the formation of insoluble iron compounds.
When a ferric iron solution is slowly neutral-ized at low temperatures, ferric hydroxide (Fe(OH)3)is formed. This material may be undesirable as it is colloidal and very difficult to filter. As the temper-ature is raised to 100C, the precipitate is transformed to goethite, a more crystalline ferric iron compound, and as the temperature is raised further to 130C, hematite (Fe203~ is produced. The exact nature of the precipitate is dependent on neutralization history and the duration at temperature.
Higher acid concentrations are permitted for a given iron rejection as the temperature is raised.
In the production of hematite, a residual iron concentration of 5 g/l can be achieved in the presence of 60 g/l H2SO4 at 150C. At 200C, the same residual can be achieved in the presence of 90 g/l H2S04 .
With sulphate in solution, various basic sulphate salts are stable. In the range o temperature and solution compositions expected in the iron precipitation stage, hydronium jarosite ((H3O)Fe3(SO4~2(OH)6) and fibroferrite (Fe~OH)(SO4)~ are expected to form. Hydronium 1^ jarosite is the most significant below 150C.
Fibrorerrite is most significant above 150C.
Other forms of jarosite may be formed by the addition of alkali salts where the alkali metal or radical is NH4, Na, K, Ag or Pb. Jarosites are typically formed at 90 to 150C at a pH of 1.0 to 1.5.
The reaction below shows the formation of ammonium jarosite.
3/2 Fe2 (SO4)3 = (NH4) Fe3 (SO4)2 (OH)6 (14) + 6 H2O + ~H3 + 5/2 H2S4 The exact nature of ferric-sulphate compounds precipitated is difficult to specify as many different species are possible and the factors which govern their formation are complex.
Various trace elements such as bismuth or tellurium may be present in the concentrate being :~LZ~3~' treated. ~hile some of these trace elements will report to the leach residue or waste precipitation residues, some may build up in solution and have to be bled-off.
When trace elements are present in sufficient concentration, their recovery may be warranted.
The operations described can be combined to create processes which will ef~ectively decompose arsenical pyrite concentrates of varying compositions producing a residue which can be treated for gold recovery and a solution from which the soluble arsenic, iron and sulphur species can be removed. This solution can then be reused in the decomposition step.
With a concentrate that is primarily arseno-pyrite one possible process is a decomposition step with a recycled nitric acid solution using oxygen for regeneration, followed by a solids-liquid separation.
The solids go to gold recovery, while calcium carbonate is added to the liquid and C02 is evolved. The solution is then heated to a high temperature at which ferric arsenate and calcium sulphate co-precipitate.
Another solids-liquid separation provides liquid for re-use in the decomposition, with nitric acid and water being added to account for losses.
Another possible process for a concentrate that is primarily arsenopyrite is a decomposition step with recycled nitric acid solution containing soluble calcium, using oxygen for regeneration. After leaching, ~Z1~13~
the solution is cooled to precipitate calcium sulphate and a solid-liquid separation is made. The liquid is heated to precipitate ferric arsenate and another solid-liquid separation is made to give a solution to which calcium carbonate is added before reuse.
With a concentrate that contains si~nificant quantities of pyrite, one possible process is a decom-position step with a recycled solution, nitric oxide gas and oxygen being used for regeneration. This is followed by another decomposition step without oxy~en to convert all the nitrogen oxides to nitric oxide, which is bled off. A solid-liquid separation produces a residue for gold treatment. Calcium carbonate is added to the liquid which is then heated to a high temperature to precipitate ferric arsenate, calcium sulphate and hematite. Another solids-liquid separation provides liquid for decomposition.
Other processes within the scheme of the invention can be proposed from the steps described. Some processes are illustrated in the following examples.
Example 1 A test was done to demonstrate the decomposition of an arsenical pyrite concentrate containing a large fraction of arsenopyrite (44.7% As, 31.7% Fe, 17.3% ~, 7.34 oz/ton Au). This example demonstrates the basic decomposition step with a nitric 1:~1913Z
acid solution. The following conditions and results were noted.
HNO3 concentration 4 N
Temperature 80C
Pulp density 8~
Arsenic extraction 100%
Iron extraction100 Sulphur extraction 68~
The decomposition was rapid and complete.
Example 2 A series of tests were run to demonstrate the decomposition of an arsenopyrite concentrate (as in Example 1) using a nitric acid solution and oxygen to regenerate the active nitrogen oxides.
The conditions and results from a typical test in this series are shown below.
HNO3 concentration 3 Temperature 80C
Oxygen Pressure200 psig Pulp density15% solids by weight Arsenic extraction 100%
Iron extraction96%
Sulphur extraction 84~
The use of oxygen permits the pulp density to be raised with respect to the nitric acid concentration.
lZ19~32 Example 3 In another test under conditions similar to those shown above, it was found that 99% of the gold in the concentrate reported to the decomposition residue.
Example 4 The residue from another test conducted under conditions similar to those outlined in Examples 1 and 2 was treated with an aqua regia solution composed of 2 parts HCl, 1 part HNO3 and 3 parts H2O at 60C. The gold extraction was 98% based on the initial concentrate.
Example 5 Another residue prepared along the lines of Examples l and 2 was treated with an alkaline cyanide solution. The gold extraction was 86% based on the initial concentrate. Cyanide use was heavy due to the formation of thiocyanate from the reaction of sulphur and cyanide.
Example 6 A test was done to demonstrate the decomposition of an arsenical pyrite concentrate containing a lar~e fraction of pyrite (4.9% As, 36.9 Fe, 36.2% S~. A nitric acid solution was used with oxygen to regenerate the active nitrogen oxides.
HN03 concentration 3 N
Temperature 80C
Oxygen pressure 200 psig ~Z~9132 Pulp density 16~
Arsenic extraction 99%
Iron extraction 98~
Sulphur extraction 95%
5The decomposition of this material was observed to be rapid and complete.
Example 7 A test was conducted to demonstrate the decomposition of a pyrite-rich concentrate (as in Example 2) using a ferric nitrate and sulphuric acid solution. This example simulates a decomposition using the product solution from Example 6.
Initial Fe(NO3)3 1 M
Initial H2SO4 2.5 M
Temperature 80C
Pulp density 6%
Total pressure 0 psig As extraction 99%
Fe extraction 100%
S extraction 99%
Example 8 A test was performed to demonstrate the decomposition of an arsenopyrite concentrate (as in Example 1) using nitric oxide gas. Oxygen was added to regenerate the active nitrogen oxides. The nitric oxide gas was produced by the reaction of arsenopyrite with nitric acid as in Example 1.
12~9~.32 HNO3 concentration 0 N
Temperature 80C
Pulp density 8%
As extraction lO0~
Fe extraction 100%
S extraction 60%
A pyrite-rich concentrate can be reacted in a similar manner.
Example 9 A test was done to demonstrate the precipita-tion of ferric arsenate by raising the solution temperature. No sulphate was present in the solution.
Fe(N03)3 concentration1 M
As concentration 1 M
Temperature 200C
Fe removal 97%
As removal 98%
Similar results were obtained at 150C.
Example 10 A series of tests were conducted to demonstrate the effect of neutralization and sulphate removal on the precipitation of ferri~ arsenate. To remove sulphate, calcium carbonate was added to the solution and the evolved C02 was released.
As concentration l M1 M
Fe concentration 1 M1 M
S042- concentration 0.5 M 0.5 M
~219~ 2 CaCO3 added 0.5 M
Temperature 200C200C
As removal 66% 98%
Fe removal 72% 96~
S042- removal 5% 59%
_xample 11 A series of tests were performed to demon-strate an entire process which would treat an arsenical pyrite concentrate containing a large fraction o arsenopyrite (as in Example 1).
The decomposition step was the same as or Example 2 using a nitric acid solution and oxygen for regeneration.
HNO3 concentration 3 N
Temperature 80C
Oxygen pressure 200 psig Pulp density 16 As extraction 96 Fe extraction 99 S extraction 82~
After filtration, calcium carbonate was added to the solution, the CO2 evolved was released and the mixture was heated as in Example 10. The removal figures shown are relative to the starting solution.
As concentration 0.9 M
Fe2 concentration 0.9 M
S042~ concentration 0.7 M
1;2~9:~'32 CaCO3 added 0.7 M
Temperature 200C
As removal 98%
Fe removal 96~
S S removal 76%
The solution was then used for a second decomposition step with arsenopyrite concentrate. The extraction figures are relative to the added concentrate.
Temperature 80C
Oxygen pressure220 psig Pulp density 16%
As extraction 97~
Fe extraction 97%
S extraction 60 Example 12 A series of tests were done to demonstrate an entire process which would treat an arsenical pyrite concentrate containing a large fraction of arsenopyrite ~as in Example 1).
The decomposition step was carried out with a nitric acid and calcium nitrate solution. After decomposition, the slurry was cooled to reduce the solubility of calcium sulphate.
Ca concentration 1 M
HN03 concentration3 N
Decomposition temperature 80C
~2~L9~3~
Oxygen pressure200 psig Precipitation temperature 20C
Pulp density 16%
As extraction 86%
Fe extraction 100~
S extraction 22%
After filtration, the solution was heated to precipitate ferric arsenic.
As concentration 0.8 M
Fe concentration 0.9 M
S042- concentration 0.1 M
Temperature 200C
As removal 81%
Fe removal 81%
S042- removal 34%
After filtration, calcium carbonate was added to the solution and the CO2 evolved was released. ~le solution was then used in a second decomposition stage similar to the first.
CaCO3 added 1.3 M
Decomposition temperature 80C
Oxygen pressure200 psig Precipitation temperature 20C
Pulp density 16%
As extraction 94~
Fe extraction 94%
*S extraction ~ -5%
~2~9~3;~
*In the second decomposition step, more sulphate was removed than was produced by the decomposition.
Example 13 A series of tests were run to demonstrate an entire process which would treat an arsenical pyrite concen-trate containing a large fraction of pyrite (as in Example 6).
The decomposition step was as Example 6 using nitric acid solution and oxygen for regeneration.
HNO3 concentration 3 N
Temperature 80C
Oxygen pressure200 psig Pulp density 12~
As extraction 100%
Fe extraction 93%
S extraction 97%
A second decomposition step was conducted as in Example 7 using the filtrate from above. Oxygen was not used.
Temperature 80C
Pulp density 12~
Total pressure 0 psig As extraction 100%
Fe extraction 90 S extraction 87%
Calcium carbonate was added to the filtrate obtained from the previous step and C2 was evolved.
12~9132 The solution was then heated to precipitate a mixture of ferric arsenate, basic iron compounds and calcium sulphate.
CaC03 added 1.2 M
Temperature 200 DC
As removal 97%
Fe removal 82%
S042- removal 77~
After filtration, the solution from the precipitation stage could be reused by the addition of nitrogen oxides, for example, the addition of nitric acid or the addition of nitric oxide and oxygen.
As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.
FIELD OF THE INVENTION
This invention is directed to a novel environ-mentally amicable hydrometallurgical process for therecovery of gold from arsenical pyrite concentrate.
BACKGROUND OF THE INVENTION
The mineral arsenopyrite is known to contain gold which is in solution in the mineral matrix or is present as fine inclusions. This gold is not available for extraction by hydrometallurgical processes which treat only the mineral surfaces, for example, cyanida-tion. The mineral pyrite is often associated with arsenopyrite and may contain in its matrix finely dispersed gold which is difficult to extract. ~rseno-pyrite and pyrite are the main constituents of arsenical pyrite concentrates.
The conventional means of liberating gold rom arsenical pyrite concentrates is to roast the material and then treat the calcine by cyanidation. This process generates environmental pollution problems due to the airborne emission of sulphur and arsenic oxides. The tailings from the calcine cyanidation contain arsenic which is alRo a potential environmental contaminant.
Arsenical pyrite concentrates may also be treated for gold recovery through conventional pyro-metallurgical processes which include copper smelting, 12~g~3,~
lead smelting and zinc roas-ting. These processes also produce potentially harmful airborne arsenic emissions from the treatment of these concentrates. Problems associated with the added arsenic burden in the process flows also arise.
Two hydrometallurgical processes exist which could potentially be used to decompose arsenical pyrite concentrates though they are not specifically used for this purpose. These are the Sill and the Calera pro-cesses which are both used for the treatment of cobaltand arsenic-bearing materials. In the Sill process, the concentrate is solubilized by the action of a caustic substance and oxygen under elevated temperatures and pressures. In the Calera process sulphuric acid and lS oxygen at high temperature and pressure are the active agents. Neither process, as far as is known, is commercially operated at the present time.
SUMMARY OF THE INVENTIO~
The subject invention is directed to an environmentally amicable hydrometallurgical process for decomposing arsenical pyrite concentrates in acidic solution through the action of higher valence nitrogen oxides. The decomposed product can be subjected to a solid-liquid separation to produce a residue and a liquid fraction. The solid residue produced can be readily treated for the recovery of gold by conventional techniques. The active nitrogen oxides can be regener-12~9~3Z
ated by an oxidizing agent. Arsenic, iron and sulphurare precipitated from the solution making it suitable for reuse in the decomposition step.
Arsenopyrite and pyrite are decomposed in acid solutions where the pH is less than 2 by the action of nitrogen oxides where the nitro~en has a valence of 3 or greater. These oxides include nitric acid, nitrous acid and nitrogen dioxide. The nitrogen oxide is present in sufficient quantity in the solution to provide an adequate rate of dissolution. The main products from the decomposition are soluble ferric iron species, soluble arsenate species, soluble sulphate species, elemental sulphur and nitric oxide, as well as nitrogen dioxide. Nitrogen dioxide becomes increasingly abundant as a product in the gas phase as the nitric acid concen-tration increases: see Canadian Patent No. 995,468, Paul B. Queneau et al., August 24, 1976. The minor products are arsenic trioxide and nitrous acid. The gold contained in the concentrate remains in the solid residue which is composed of elemental sulphur and insoluble gangue minerals. Any silver present in the concentrate would also report to the residue.
The introduction of oxygen into the leach, as demonstrated in the Examples herein, permits less than stoichiometric amounts o~ nitric acid to be used. As demonstrated in Examples 7 and 8 herein, it is not necessary to use nitric acid in order to practise the ., ,Jj. ~
~2~3i3~
invention.
The hydrometallurgical process for the recovery of precious metal from an ore or concentrate containing arsenopyrite or pyrite wherein at least some of the precious metal is occluded in the arsenopyrite or pyrite comprises:
(a) forming in a common volume space a gas phase and a liquid slurry comprising the ore or concen-trate as the solid phase and acid and water as the liquid phase of the slurry, (b) effecting in the slurry between the arsenopyrite or pyrite and a higher valence oxidized nitrogen species in ~hich the nitrogen has a valence of at least plus 3 an oxidation-reduction reaction having a standard potential between about 0.90 and about 1.20 volts on the hydrogen scale, thereby solubilizing in the liquid phase the arsenic, iron and sulphur in the arsenopyrite or the iron and sulphur in the pyrite, all as the oxidation products, and producing in the liquid phase nitric oxide (N0) in which the nitrogen has a valence of plus 2, as the reduction product;
(c) releasing at least part of the nitric oxide from the liquid phase into the gas phase;
(d) oxidizing the nitric oxide in the gas phase, in which a significant oxygen partial pressure is maintained by continuous addition of an oxygen containing gas, to form a higher valence oxidized - 3a -12~9~l 3~
nitrogen species in which the nitrogen has a valence of at least plus 3, the total amount of oxygen added being at least in an amount stoichiometrically required for solubilization in the liquid phase of the arsenic, iron and sulphur in the arsenopyrite or the iron and sulphur in the pyrite;
(e~ absorbing the higher valence oxidized nitrogen species into the slurr~ wherein the oxidized nitrogen species become available for the oxidation-reduction reaction of step (b) whereby the nitrogen, inits oxide for~s, functions as a catalyst for the trans-port of oxygen from the gas phase to the oxidation-reduction reactions in the slurry, thereby permitting the total of the oxidized nitrogen species and nitric oxide in the system to be substantially less than a stoichiometric balance required for the oxidation of the arsenic, iron and sulphur;
(f) subjecting the slurry to a solid-liquid separation to produce a solid residue and a liquid fraction; and (g) recovering precious metal from the solid residue.
DRAWING
.
Figure 1 illustrate arsenic concentration as a function of time for three similar experiments with solution composition as a variable.
- 3b -12~913~
DETAILED DESCRIPTION OF THE INVENTION
The decomposition of arsenopyrite and pyrite by nitric acid occurs according to the following reactions.
Fe AsS + 23/3 HNO3 = Fe(NO3)3 + H3 As04 (1) + H2SO4 + 4/3 H2O + 14/3 NO
FeAsS + 17/3 HNO3 = Fe(~O3)3 + H3AsO4 (2) + S + 4/3 H2O ~ 8/3 NO
FeS2 + 8 HNO3 = Fe(NO3)3 + 2H2SO4 `(3) + 2H~O + 5NO
15 FeS2 + 5 HNO3 = Fe(NO3)3 + 2S + 2H2O ~ NO (4) In the reaction with arsenopyrite, it has been found that 60-90% of the mineral's sulphur is converted to soluble sulphate species. In the reaction with 20 pyrite, the degree of conversion is 80-100%.
The gold in the decomposition residue may be readily extracted by conventional techniques such as cyanidation, following leaching of the residue with sodium hydroxide to dissolve sulfur prior to cyanida-tion, or treatment with oxidizing chloride lixiviants,such as aqua regia. Silver may also be extracted by these techniques.
, lZ~9~32 It is important that the decomposition solution does not contaln significant quantities of species which complex gold, for example, chloride ions.
These would put the gold into solution and a separate 5 additional process step would have to be included to extract it.
The active nitrogen oxides are required only to decompose the minerals in the concentrate. The nitrogen oxide should ~e present in sufficient concen-tration in the solution to provide an adequate rate ofdissolution. Any suitable acid may be used to form the soluble ferric iron species. An adequate rate of dissolution is about 10 to 30 minutes.
In the reaction detailed below, nitrogen dioxide is the decomposition agent for arsenopyrite with sulphuric acid present.
FeAsS + 4N02 = 1/2 Fe2 (S04)3 + H3 As04 (5) + 3/2 H2S4 + S + 4N0 In the reaction detailed below, the sulphuric acid is formed from the decomposition of pyrite.
FeS2 + 15/2 N02 = 1/2 Fe2 (S04)3 (6) + 1/2 H20 + 1/2 H2S04 + 15/2 N0 In the preceding reactions, the active nitrogen oxides are r~duced to nitric oxide which may then be regenerated by an oxidant. A useful oxidant is oxygen which reacts with nitric oxide in the presence of ~Z19132 water to form nitrogen dioxide, nitrous acid and nitric acid as shown in the reactions set forth below.
N0 + 1/2 2 - N02 N0 + N02 + H20 = 2HN02 3HN2 = HN3 + H20 + 2N0 10 The regeneration of nitric oxide to the higher valence states may be done concurrently with the Aecom-position.
Nitrous oxide is formed by the decomposition of nitric oxide according to the side reaction shown below.
3N0 N20 + N02 When the regeneration step is carried out with oxygen concurrently with the decomposition reactions, the overall stoichiometry of arsenopyrite reacting with nitric acid and oxygen to produce sulphuric acid as the sulphur product is illustrated by the reaction below.
FeAsS + 3.502 = Fe(N03)3 + H3 As04 + 3EIN03 + H20 + H2S4 5ince the active nitrogen oxides can be regenerated during the decomposition step, the quantity ~;~1913~
of these oxides present at any time may be quite small.
The criterion is that there must be sufficient acid present in solution to form the soluble ferric iron species. It must be emphasized -that it is the nitrogen oxides rather than oxygen that are the active decomposi-tion agent. The presence of nitrogen oxides with sulphuric acid differentiates the decomposition step described above from the Calera process.
An important feature of decomposition using nitrogen oxides is the high speed of reaction. If a solution which is three molar in nitric acid is reacted with fine arsenical pyrite flotation concentrate, it has been found that the reaction is complete within ten minutes. This is significantly faster than rates claimed by other processes at similar conditions.
Figure l shows the arsenic concentration as a function of time for three similar experiments in which the only variable is the composition of the solution.
The three compositions are 3 M acid as HN03; 2.5 M
acid as H~S04; 0.5 M acid as HN03; and 3.0 M acid as H2S04. The other conditions are given on Figure l. It is apparent from the data that the presence of nitric acid greatly speeds the rate of reaction.
The decomposition and regeneration steps are both exothermic. When a solution which is three molar in nitric acid is reacted with fine arsenical pyrite 3~Z:~L9:132 concentrate at 15~ solids without oxygen present for regeneration, the temperature increase of the slurry is 40C. With oxygen present for regeneration, the temperature increase is 130C. Since the rates of the decomposition and regeneration reactions increase with temperature the overall reactions appear to accelerate as they proceed. It is possible that controlled cooling may be required to prevent the melting of elemental sulphur and to prevent the precipitation of salts.
The decomposition step proceeds at any temperature above ambient. However, on a practical basis, the reaction is carried out at temperatures of between 80 and 120C. It is important that sufficient acid be present to form the soluble ferric iron species.
Without this acid, compounds will precipitate from solution. If oxygen is used for regeneration, any oxygen pressure above ambient is adequate. Agitation increases the speed of the reactions and improves the quality of the final sulphur-bearing residue.
The decomposition leach can be carried out over a wide range of solid-liquid ratios. Increasing the ratio of solids to liquids provides economic bene-fits, but the upper limit of this ratio is reached when the solubility limit of dissolved species is reached.
When the decomposition reactions are complete, a solid-liquld separation is carried out to produce a residue containing all the gold and a clarified solution which is recycled in the process.
To enable the solution to be reused for the decomposition step, the soluble arsenic, iron and sulphur must be removed from solution.
Arsenic in the pentavalent state as ferric arsenate is removed from solution with ferric iron. The following reaction shows the formation of ferric arsenate from ferric nitrate and arsenate.
FelN03)3 + H3As04 = 3HN03 + FeAsO4 (12) - + x H20 XH20 Ferric arsenate is produced virtually quan-titatively from an equimolar solution of ferric nitrate and arsenic acid at all temperatures above ambient.
However, the rate of precipitation can be controlled by temperature. At room temperature, complete precipita-tion requires several months; at 100C precipitation requires one to two hours; and at 200C precipitation occurs in less than one hour.
Ferric arsenate can be precipitated rapidly at low temperatures by the neutralization of the acid in the solution. At 25C the solubility of ferric arsenate between pH 3 and pH 7 is very low. The solids produced at low temperature tend to be colloidal and dificult to filter. The solids can contain ferric hydroxide which also tends to be colloidal.
12~L9132 The presence of sulphate in solution raises the solubility of ferric arsenate. A solution which is 1 M in ferric nitrate and arsenic acid is stable at room temperature in the presence of 0.5 M H2S04. At higher temperatures, the effect oE sulphate is less pronounced.
A calcium-bearing neutralizing agent, such as calcium oxide or calcium carbonate, can be used to neutralize excess acid in solution and to remove sulphate in order to improve ferric arsenate precipita-tion.
A small portion of the extracted arsenic is present as arsenite and thus arsenic trioxide can preci-pitate when the filtered decomposition solution is cooled.
If insufficient arsenate or ferric is present in solution to bring about complete precipitation of the appropriate species, then arsenate or ferric compounds may be added to the solution.
Sulphate is removed from solution by the addition of calcium-bearing materials to form calcium sulphate. The reaction between calcium carbonate and sulphuric acid is as follows.
CaC03 + H2S04 = CaS04 + C2 + H20 (13) 1;~'1 9~32 There are two forms of calcium sulphate which may be formed. Gypsum ~CaS04 2H20) has a low solubility which is virtually unaffected by temperature.
In a 1 M solution of ferric nitrate and arsenic acid, the solubility of CaS04 2H2O is approximately 0.1 M. Anhydrite (CaS04) forms at temperatures above 60C (although the crossover point from gypsum may be as high as 110C due to supersaturation). The solubility of anhydrite drops rapidly with temperature. Solubility data for anhydrite in water gives a solubility of 0.02 M
at 60C and .0015 M at 160C.
Ferric iron is removed from solution by the formation of insoluble iron compounds.
When a ferric iron solution is slowly neutral-ized at low temperatures, ferric hydroxide (Fe(OH)3)is formed. This material may be undesirable as it is colloidal and very difficult to filter. As the temper-ature is raised to 100C, the precipitate is transformed to goethite, a more crystalline ferric iron compound, and as the temperature is raised further to 130C, hematite (Fe203~ is produced. The exact nature of the precipitate is dependent on neutralization history and the duration at temperature.
Higher acid concentrations are permitted for a given iron rejection as the temperature is raised.
In the production of hematite, a residual iron concentration of 5 g/l can be achieved in the presence of 60 g/l H2SO4 at 150C. At 200C, the same residual can be achieved in the presence of 90 g/l H2S04 .
With sulphate in solution, various basic sulphate salts are stable. In the range o temperature and solution compositions expected in the iron precipitation stage, hydronium jarosite ((H3O)Fe3(SO4~2(OH)6) and fibroferrite (Fe~OH)(SO4)~ are expected to form. Hydronium 1^ jarosite is the most significant below 150C.
Fibrorerrite is most significant above 150C.
Other forms of jarosite may be formed by the addition of alkali salts where the alkali metal or radical is NH4, Na, K, Ag or Pb. Jarosites are typically formed at 90 to 150C at a pH of 1.0 to 1.5.
The reaction below shows the formation of ammonium jarosite.
3/2 Fe2 (SO4)3 = (NH4) Fe3 (SO4)2 (OH)6 (14) + 6 H2O + ~H3 + 5/2 H2S4 The exact nature of ferric-sulphate compounds precipitated is difficult to specify as many different species are possible and the factors which govern their formation are complex.
Various trace elements such as bismuth or tellurium may be present in the concentrate being :~LZ~3~' treated. ~hile some of these trace elements will report to the leach residue or waste precipitation residues, some may build up in solution and have to be bled-off.
When trace elements are present in sufficient concentration, their recovery may be warranted.
The operations described can be combined to create processes which will ef~ectively decompose arsenical pyrite concentrates of varying compositions producing a residue which can be treated for gold recovery and a solution from which the soluble arsenic, iron and sulphur species can be removed. This solution can then be reused in the decomposition step.
With a concentrate that is primarily arseno-pyrite one possible process is a decomposition step with a recycled nitric acid solution using oxygen for regeneration, followed by a solids-liquid separation.
The solids go to gold recovery, while calcium carbonate is added to the liquid and C02 is evolved. The solution is then heated to a high temperature at which ferric arsenate and calcium sulphate co-precipitate.
Another solids-liquid separation provides liquid for re-use in the decomposition, with nitric acid and water being added to account for losses.
Another possible process for a concentrate that is primarily arsenopyrite is a decomposition step with recycled nitric acid solution containing soluble calcium, using oxygen for regeneration. After leaching, ~Z1~13~
the solution is cooled to precipitate calcium sulphate and a solid-liquid separation is made. The liquid is heated to precipitate ferric arsenate and another solid-liquid separation is made to give a solution to which calcium carbonate is added before reuse.
With a concentrate that contains si~nificant quantities of pyrite, one possible process is a decom-position step with a recycled solution, nitric oxide gas and oxygen being used for regeneration. This is followed by another decomposition step without oxy~en to convert all the nitrogen oxides to nitric oxide, which is bled off. A solid-liquid separation produces a residue for gold treatment. Calcium carbonate is added to the liquid which is then heated to a high temperature to precipitate ferric arsenate, calcium sulphate and hematite. Another solids-liquid separation provides liquid for decomposition.
Other processes within the scheme of the invention can be proposed from the steps described. Some processes are illustrated in the following examples.
Example 1 A test was done to demonstrate the decomposition of an arsenical pyrite concentrate containing a large fraction of arsenopyrite (44.7% As, 31.7% Fe, 17.3% ~, 7.34 oz/ton Au). This example demonstrates the basic decomposition step with a nitric 1:~1913Z
acid solution. The following conditions and results were noted.
HNO3 concentration 4 N
Temperature 80C
Pulp density 8~
Arsenic extraction 100%
Iron extraction100 Sulphur extraction 68~
The decomposition was rapid and complete.
Example 2 A series of tests were run to demonstrate the decomposition of an arsenopyrite concentrate (as in Example 1) using a nitric acid solution and oxygen to regenerate the active nitrogen oxides.
The conditions and results from a typical test in this series are shown below.
HNO3 concentration 3 Temperature 80C
Oxygen Pressure200 psig Pulp density15% solids by weight Arsenic extraction 100%
Iron extraction96%
Sulphur extraction 84~
The use of oxygen permits the pulp density to be raised with respect to the nitric acid concentration.
lZ19~32 Example 3 In another test under conditions similar to those shown above, it was found that 99% of the gold in the concentrate reported to the decomposition residue.
Example 4 The residue from another test conducted under conditions similar to those outlined in Examples 1 and 2 was treated with an aqua regia solution composed of 2 parts HCl, 1 part HNO3 and 3 parts H2O at 60C. The gold extraction was 98% based on the initial concentrate.
Example 5 Another residue prepared along the lines of Examples l and 2 was treated with an alkaline cyanide solution. The gold extraction was 86% based on the initial concentrate. Cyanide use was heavy due to the formation of thiocyanate from the reaction of sulphur and cyanide.
Example 6 A test was done to demonstrate the decomposition of an arsenical pyrite concentrate containing a lar~e fraction of pyrite (4.9% As, 36.9 Fe, 36.2% S~. A nitric acid solution was used with oxygen to regenerate the active nitrogen oxides.
HN03 concentration 3 N
Temperature 80C
Oxygen pressure 200 psig ~Z~9132 Pulp density 16~
Arsenic extraction 99%
Iron extraction 98~
Sulphur extraction 95%
5The decomposition of this material was observed to be rapid and complete.
Example 7 A test was conducted to demonstrate the decomposition of a pyrite-rich concentrate (as in Example 2) using a ferric nitrate and sulphuric acid solution. This example simulates a decomposition using the product solution from Example 6.
Initial Fe(NO3)3 1 M
Initial H2SO4 2.5 M
Temperature 80C
Pulp density 6%
Total pressure 0 psig As extraction 99%
Fe extraction 100%
S extraction 99%
Example 8 A test was performed to demonstrate the decomposition of an arsenopyrite concentrate (as in Example 1) using nitric oxide gas. Oxygen was added to regenerate the active nitrogen oxides. The nitric oxide gas was produced by the reaction of arsenopyrite with nitric acid as in Example 1.
12~9~.32 HNO3 concentration 0 N
Temperature 80C
Pulp density 8%
As extraction lO0~
Fe extraction 100%
S extraction 60%
A pyrite-rich concentrate can be reacted in a similar manner.
Example 9 A test was done to demonstrate the precipita-tion of ferric arsenate by raising the solution temperature. No sulphate was present in the solution.
Fe(N03)3 concentration1 M
As concentration 1 M
Temperature 200C
Fe removal 97%
As removal 98%
Similar results were obtained at 150C.
Example 10 A series of tests were conducted to demonstrate the effect of neutralization and sulphate removal on the precipitation of ferri~ arsenate. To remove sulphate, calcium carbonate was added to the solution and the evolved C02 was released.
As concentration l M1 M
Fe concentration 1 M1 M
S042- concentration 0.5 M 0.5 M
~219~ 2 CaCO3 added 0.5 M
Temperature 200C200C
As removal 66% 98%
Fe removal 72% 96~
S042- removal 5% 59%
_xample 11 A series of tests were performed to demon-strate an entire process which would treat an arsenical pyrite concentrate containing a large fraction o arsenopyrite (as in Example 1).
The decomposition step was the same as or Example 2 using a nitric acid solution and oxygen for regeneration.
HNO3 concentration 3 N
Temperature 80C
Oxygen pressure 200 psig Pulp density 16 As extraction 96 Fe extraction 99 S extraction 82~
After filtration, calcium carbonate was added to the solution, the CO2 evolved was released and the mixture was heated as in Example 10. The removal figures shown are relative to the starting solution.
As concentration 0.9 M
Fe2 concentration 0.9 M
S042~ concentration 0.7 M
1;2~9:~'32 CaCO3 added 0.7 M
Temperature 200C
As removal 98%
Fe removal 96~
S S removal 76%
The solution was then used for a second decomposition step with arsenopyrite concentrate. The extraction figures are relative to the added concentrate.
Temperature 80C
Oxygen pressure220 psig Pulp density 16%
As extraction 97~
Fe extraction 97%
S extraction 60 Example 12 A series of tests were done to demonstrate an entire process which would treat an arsenical pyrite concentrate containing a large fraction of arsenopyrite ~as in Example 1).
The decomposition step was carried out with a nitric acid and calcium nitrate solution. After decomposition, the slurry was cooled to reduce the solubility of calcium sulphate.
Ca concentration 1 M
HN03 concentration3 N
Decomposition temperature 80C
~2~L9~3~
Oxygen pressure200 psig Precipitation temperature 20C
Pulp density 16%
As extraction 86%
Fe extraction 100~
S extraction 22%
After filtration, the solution was heated to precipitate ferric arsenic.
As concentration 0.8 M
Fe concentration 0.9 M
S042- concentration 0.1 M
Temperature 200C
As removal 81%
Fe removal 81%
S042- removal 34%
After filtration, calcium carbonate was added to the solution and the CO2 evolved was released. ~le solution was then used in a second decomposition stage similar to the first.
CaCO3 added 1.3 M
Decomposition temperature 80C
Oxygen pressure200 psig Precipitation temperature 20C
Pulp density 16%
As extraction 94~
Fe extraction 94%
*S extraction ~ -5%
~2~9~3;~
*In the second decomposition step, more sulphate was removed than was produced by the decomposition.
Example 13 A series of tests were run to demonstrate an entire process which would treat an arsenical pyrite concen-trate containing a large fraction of pyrite (as in Example 6).
The decomposition step was as Example 6 using nitric acid solution and oxygen for regeneration.
HNO3 concentration 3 N
Temperature 80C
Oxygen pressure200 psig Pulp density 12~
As extraction 100%
Fe extraction 93%
S extraction 97%
A second decomposition step was conducted as in Example 7 using the filtrate from above. Oxygen was not used.
Temperature 80C
Pulp density 12~
Total pressure 0 psig As extraction 100%
Fe extraction 90 S extraction 87%
Calcium carbonate was added to the filtrate obtained from the previous step and C2 was evolved.
12~9132 The solution was then heated to precipitate a mixture of ferric arsenate, basic iron compounds and calcium sulphate.
CaC03 added 1.2 M
Temperature 200 DC
As removal 97%
Fe removal 82%
S042- removal 77~
After filtration, the solution from the precipitation stage could be reused by the addition of nitrogen oxides, for example, the addition of nitric acid or the addition of nitric oxide and oxygen.
As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.
Claims (40)
1. A hydrometallurgical process for the recovery of gold from arsenical pyrite concentrate, comprising leach decomposing the concentrate by using a leach composed of higher valence nitrogen oxides in which the nitrogen has a valence of at least plus 3, present in acidic solution, and concurrently regenerat-ing the higher valence nitrogen oxides using oxygen;
subjecting the decomposed product to a solid-liquid separation to produce a residue and a liquid fraction;
recovering gold from the residue by conventional means; and precipitating dissolved arsenic, iron and sulphur from the liquid fraction before recycling the liquid fraction in the process.
subjecting the decomposed product to a solid-liquid separation to produce a residue and a liquid fraction;
recovering gold from the residue by conventional means; and precipitating dissolved arsenic, iron and sulphur from the liquid fraction before recycling the liquid fraction in the process.
2. A process as defined in Claim 1 wherein the valence of the nitrogen of the nitrogen oxide is 3 or greater.
3. A process as defined in Claim 1 wherein the source of the nitrogen oxide is a substance selected from the group consisting of nitric acid, nitrous acid and nitrogen dioxide.
4. A process as defined in Claim 1 wherein the decomposition leach is conducted at a slurry temperature between 60°C and 120°C.
5. A process as defined in Claim 1 wherein the decomposition leach contains nitric acid.
6. A process as defined in Claim 1 wherein the decomposition leach is conducted at a pH of less than about 2.
7. A process as defined in Claim 1, 2 or 3 wherein the nitrogen oxide is present in sufficient concentration in the solution to provide an relatively rapid rate of dissolution.
8. A process as defined in Claim 4, 5 or 6 wherein the nitrogen oxide is present in sufficient concentration in the solution to provide an adequate rate of dissolution.
9. A process as defined in Claim 1 wherein arsenic and iron are removed from the separated liquid fraction \
by elevating the temperature thereof to precipitate ferric arsenate.
by elevating the temperature thereof to precipitate ferric arsenate.
10. A process as defined in Claim 1 wherein iron insoluble iron compounds caused by the combined action of neutralization and temperature elevation of the fraction.
11. A process as defined in Claim l wherein sulphate is removed from the liquid fraction by the addition of calcium bearing materials to form calcium sulphate.
12. A process as defined in Claim 1 wherein gold is recovered from the solid residue by utilizing a cyanidation process.
13. A process as defined in Claim 1 wherein gold is recovered from the solid residue by treating the residue with an oxidizing chloride lixiviant.
14. A process as defined in Claim 11 wherein the calcium bearing material is selected from the group consisting of calcium oxide and calcium carbonate.
15. A process as defined in Claim 9 or 10 wherein the temperature of the liquid fraction is elevated to a temperature between about 100°C and about 200°C.
16. A process as defined in Claim 1 wherein the nitrogen oxide is present in sufficient concentration in - -the solution that dissolution occurs in a time of less than about 30 minutes.
17. A process as defined in Claim 1, wherein the nitrogen oxide is present in sufficient concentration in the solution that dissolution occurs in a time of about 10 minutes.
18. A hydrometallurgical process for the recovery of gold from a primarily arsenical pyrite concentrate comprising:
leach decomposing the concentrate by using a leach composed of recycled nitric acid solution which has been regenerated by the use of oxygen;
subjecting the decomposed product to a solid-liquid separation to produce a residue and a liquid fraction;
recovering gold from the residue;
adding calcium carbonate to the liquid fraction; and elevating the temperature of the liquid fraction thereby precipitating ferric arsenate and calcium sulphate from the liquid fraction before recycling and oxygen regenerating the liquid fraction in the process.
leach decomposing the concentrate by using a leach composed of recycled nitric acid solution which has been regenerated by the use of oxygen;
subjecting the decomposed product to a solid-liquid separation to produce a residue and a liquid fraction;
recovering gold from the residue;
adding calcium carbonate to the liquid fraction; and elevating the temperature of the liquid fraction thereby precipitating ferric arsenate and calcium sulphate from the liquid fraction before recycling and oxygen regenerating the liquid fraction in the process.
19. A hydrometallurgical process for the recovery of gold from a primarily arsenical pyrite concentrate comprising:
leach decomposing the concentrate by using a leach composed of recycled nitric acid solution containing soluble calcium, whereby the solution has been regenerated by the use of oxygen;
cooling the solution to precipitate calcium sulphate;
subjecting the resultant product to a solid-liquid separation to produce a residue and a liquid fraction;
recovering gold from the residue;
elevating the temperature of the liquid fraction to precipitate ferric arsenate;
subjecting the resultant liquid fraction to a solid-liquid separation to produce a residue and a liquid fraction; and adding calcium carbonate to the resulting liquid fraction before recycling and oxygen regenerating the liquid fraction in the process.
leach decomposing the concentrate by using a leach composed of recycled nitric acid solution containing soluble calcium, whereby the solution has been regenerated by the use of oxygen;
cooling the solution to precipitate calcium sulphate;
subjecting the resultant product to a solid-liquid separation to produce a residue and a liquid fraction;
recovering gold from the residue;
elevating the temperature of the liquid fraction to precipitate ferric arsenate;
subjecting the resultant liquid fraction to a solid-liquid separation to produce a residue and a liquid fraction; and adding calcium carbonate to the resulting liquid fraction before recycling and oxygen regenerating the liquid fraction in the process.
20. A hydrometallurgical process for the recovery of gold from an arsenical pyrite-pyrite concentrate comprising:
leach decomposing the concentrate by using a leach composed of higher valence nitrogen oxides present in acidic solution, whereby nitric oxide gas and oxygen have been used for regeneration of the leach solution;
subjecting the decomposed concentrate to a second leach decomposing step using a leach composed of higher valence nitrogen oxides present in acidic solution whereby the solution has been regenerated using nitric oxide gas in the absence of oxygen to thereby convert all the nitrogen oxides to nitric oxides;
bleeding off the nitric oxides;
subjecting the decomposed concentrate to a solid-liquid separation to produce a residue and a liquid fraction;
recovering gold from the residue;
adding calcium carbonate to the liquid fraction; and elevating the temperature of the liquid fraction to precipitate ferric arsenate, calcium sulphate and hematite from the liquid fraction before recycling and oxygen regenerating the liquid fraction in the process.
leach decomposing the concentrate by using a leach composed of higher valence nitrogen oxides present in acidic solution, whereby nitric oxide gas and oxygen have been used for regeneration of the leach solution;
subjecting the decomposed concentrate to a second leach decomposing step using a leach composed of higher valence nitrogen oxides present in acidic solution whereby the solution has been regenerated using nitric oxide gas in the absence of oxygen to thereby convert all the nitrogen oxides to nitric oxides;
bleeding off the nitric oxides;
subjecting the decomposed concentrate to a solid-liquid separation to produce a residue and a liquid fraction;
recovering gold from the residue;
adding calcium carbonate to the liquid fraction; and elevating the temperature of the liquid fraction to precipitate ferric arsenate, calcium sulphate and hematite from the liquid fraction before recycling and oxygen regenerating the liquid fraction in the process.
21. A hydrometallurgical process for the recovery of precious metal from an ore or concentrate containing arsenopyrite or pyrite wherein precious metal is occluded in arsenopyrite or pyrite, which process comprises:
(a) forming in a common volume space a gas phase comparing air and water vapour and a liquid slurry comprising the ore or concentrate as the solid phase and acid and water as the liquid phase of the slurry;
(b) effecting in the slurry between the arsenopyrite or pyrite and an oxidized nitrogen species in which the nitrogen has a valence of at least plus 3 an oxidation-reduction reaction having a standard potential between about 0.90 and about 1.20 volts on the hydrogen scale, thereby solubilizing in the liquid phase the arsenic, iron and sulphur in the arsenopyrite, or the iron and sulphur in the pyrite, all as the oxidation products, and producing in the liquid phase nitric oxide in which the nitrogen has a valence of plus 2, as the reduction product;
(c) releasing nitric oxide from the liquid phase into the gas phase;
(d) oxidizing the nitric oxide in the gas phase, in which an oxygen partial pressure above the ambient oxygen partial pressure in air is maintained by continuous addition of an oxygen containing gas, to form an oxidized nitrogen species in which the nitrogen has a valence of at least plus 3, the total amount of oxygen added being at least in an amount stoichiometrically required for solubilization in the liquid phase of the arsenic, iron and sulphur in the arsenopyrite or the iron and sulphur in the pyrite;
(e) absorbing the oxidized nitrogen species into the slurry wherein the oxidized nitrogen species become available for the oxidation-reduction reaction of step (b) whereby the nitrogen, in its oxide forms, functions as a catalyst for the transport of oxygen from the gas phase to the oxidation-reduction reactions in the slurry, thereby permitting the total of the oxidized nitrogen species and nitric oxide in the system to be less than a stoichiometric balance required for the oxidation of the arsenic, iron and sulphur;
(f) subjecting the slurry to a solid-liquid separation to produce a solid residue and a liquid fraction; and (g) recovering precious metal from the solid residue.
(a) forming in a common volume space a gas phase comparing air and water vapour and a liquid slurry comprising the ore or concentrate as the solid phase and acid and water as the liquid phase of the slurry;
(b) effecting in the slurry between the arsenopyrite or pyrite and an oxidized nitrogen species in which the nitrogen has a valence of at least plus 3 an oxidation-reduction reaction having a standard potential between about 0.90 and about 1.20 volts on the hydrogen scale, thereby solubilizing in the liquid phase the arsenic, iron and sulphur in the arsenopyrite, or the iron and sulphur in the pyrite, all as the oxidation products, and producing in the liquid phase nitric oxide in which the nitrogen has a valence of plus 2, as the reduction product;
(c) releasing nitric oxide from the liquid phase into the gas phase;
(d) oxidizing the nitric oxide in the gas phase, in which an oxygen partial pressure above the ambient oxygen partial pressure in air is maintained by continuous addition of an oxygen containing gas, to form an oxidized nitrogen species in which the nitrogen has a valence of at least plus 3, the total amount of oxygen added being at least in an amount stoichiometrically required for solubilization in the liquid phase of the arsenic, iron and sulphur in the arsenopyrite or the iron and sulphur in the pyrite;
(e) absorbing the oxidized nitrogen species into the slurry wherein the oxidized nitrogen species become available for the oxidation-reduction reaction of step (b) whereby the nitrogen, in its oxide forms, functions as a catalyst for the transport of oxygen from the gas phase to the oxidation-reduction reactions in the slurry, thereby permitting the total of the oxidized nitrogen species and nitric oxide in the system to be less than a stoichiometric balance required for the oxidation of the arsenic, iron and sulphur;
(f) subjecting the slurry to a solid-liquid separation to produce a solid residue and a liquid fraction; and (g) recovering precious metal from the solid residue.
22. A process as defined in claim 21 wherein the oxidation-reduction reaction has a standard potential of at least 0.94 and less than about 1.0 volts on the hydrogen scale.
23. A process as defined in claim 22 wherein the nitrogen in the oxidized nitrogen species has a valence of +3 or +4.
24. A process as defined in claim 22 wherein at least about 90% by weight of the arsenic and iron in arsenopyrite or the iron in the pyrite is solubilized and about 60 - 90% by weight of the sulphur in the arsenopyrite or pyrite is solubilized.
25. A process as defined in claim 24 wherein the process is initiated by the addition to the common volume space of an oxidized nitrogen species of a valence of at least +2.
26. A process as defined in claim 25 wherein the oxidized nitrogen species is added to the gas phase as NO, NO2 or N2O4.
27. A process as defined in claim 25 wherein the oxidized nitrogen species is added to the liquid phase as HNO3, NaNO3, KNO3, NaNO2, Fe(NO3)3, NH4NO3, Ca(NO3)2 or Mg(NO3)2.
28. A process as defined in claim 24 wherein the liquid fraction is recycled to the liquid phase in the process.
29. A process as defined in claim 24 wherein the solubilized iron, arsenic and sulphur are precipitated from the liquid fraction and the precipitated iron, arsenic and sulphur are removed from the process and the liquid fraction is recycled to the liquid phase in the process.
30. A process as defined in claim 29 wherein the liquid fraction is recycled to the liquid phase and the liquid fraction contains the oxidized nitrogen species required to initiate and maintain the process.
31. A process as defined in claim 24 wherein steps (a) to (e) are conducted within a residence time of about 2 minutes to about 60 minutes.
32. A process as defined in claim 24 wherein the oxidation-reduction reaction is conducted at a temperature of about 60°C to about 180°C.
33. A process as defined in claim 24 wherein the oxidation-reduction reaction is conducted at a pH of less than about 3.
34. A process as defined in claim 24 wherein the oxidation-reduction reaction is conducted at a pH of less than about 1 or at about 1.
35. A process as defined in claim 24 wherein the oxidized nitrogen species concentration is between about 0.25 M and about 4.0 M.
36. A process as defined in claim 24 wherein the oxidized nitrogen species concentration is between about 0.5 M and about 3.0 M.
37. A process as defined in claim 29 wherein solubilized iron, arsenic or sulfur is precipitated as jarosite and ferric arsenate from the liquid fraction by raising the temperature of the liquid fraction to a temperature of about 100°C and removing precipitated solids from the liquid fraction before recycling the liquid fraction to the liquid phase.
38. A process as defined in claim 29 wherein solubilized iron, arsenic or sulfur is precipitated as jarosite, ferric arsenate and calcuim sulfate from the liquid fraction by neutralizing acid generated by pyrite oxidation, and removing precipitated solids from the liquid fraction before recycling the liquid fraction to the liquid phase.
39. A process as defined in claim 29 wherein a calcium bearing substance or a barium bearing substance is used to remove solubilized sulphur from the liquid fraction, ferric arsenate is added as a nucleating agent, and the liquid fraction is heated to precipitate ferric arsenate.
40. A process as defined in claim 39 wherein the liquid fraction is heated to about 100°C.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US45884683A | 1983-01-18 | 1983-01-18 | |
| US458,846 | 1983-01-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1219132A true CA1219132A (en) | 1987-03-17 |
Family
ID=23822319
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000443728A Expired CA1219132A (en) | 1983-01-18 | 1983-12-20 | Hydrometallurgical arsenopyrite process |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0119685B1 (en) |
| AU (1) | AU566135B2 (en) |
| CA (1) | CA1219132A (en) |
| DE (1) | DE3473163D1 (en) |
| ZA (1) | ZA84153B (en) |
Families Citing this family (18)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3534224A1 (en) * | 1985-09-23 | 1987-04-02 | Gock Eberhard Priv Doz Prof Dr | METHOD FOR THE WET-CHEMICAL EXTRACTION OF PRECIOUS METALS FROM CARBON-CONTAINING ARSENOPYRITE CONCENTRATES |
| AU582961B2 (en) * | 1986-05-29 | 1989-04-13 | Sasox Processing Pty Ltd | Improved hydrometallurgical arsenopyriteprocess |
| EP0272060A3 (en) * | 1986-12-18 | 1990-08-01 | Electrolytic Zinc Company Of Australasia Limited | Hydrometallurgical recovery of metals and elemental sulphur from metallic sulphides |
| AU650802B2 (en) * | 1991-10-25 | 1994-06-30 | Sasox Processing Pty. Limited | Extraction or recovery of metal values |
| ZA928157B (en) * | 1991-10-25 | 1993-06-09 | Sasox Processing Pty Ltd | Extraction or recovery of metal values. |
| CA2154560C (en) * | 1993-01-27 | 2004-11-02 | Robert N. O'brien | Hydrometallurgical recovery of metals from complex ores |
| CA2196981C (en) * | 1994-08-15 | 2004-11-23 | R & O Mining Processing Ltd. | Hydrometallurgical conversion of zinc sulfide to sulfate from zinc sulfide containing ores and concentrates |
| RU2114196C1 (en) * | 1995-09-19 | 1998-06-27 | Клиблей Генри Хадыевич | Method of hydrometallurgical recovery of rare metals from technologically persistent raw material |
| US8168847B2 (en) | 2009-04-01 | 2012-05-01 | Earth Renewal Group, Llc | Aqueous phase oxidation process |
| US7915474B2 (en) | 2009-04-01 | 2011-03-29 | Earth Renewal Group, Llc | Aqueous phase oxidation process |
| US8481800B2 (en) | 2009-04-01 | 2013-07-09 | Earth Renewal Group, Llc | Aqueous phase oxidation process |
| US8115047B2 (en) | 2009-04-01 | 2012-02-14 | Earth Renewal Group, Llc | Aqueous phase oxidation process |
| US9272936B2 (en) | 2009-04-01 | 2016-03-01 | Earth Renewal Group, Llc | Waste treatment process |
| US7951988B2 (en) | 2009-04-01 | 2011-05-31 | Earth Renewal Group, Llc | Aqueous phase oxidation process |
| CN104263961B (en) * | 2014-09-23 | 2016-03-30 | 铜仁市万山区盛和矿业有限责任公司 | A kind of method extracting gold from pyrite |
| CN104263962B (en) * | 2014-09-23 | 2016-08-17 | 铜仁市万山区盛和矿业有限责任公司 | A kind of method extracting gold from magnetic iron ore |
| CN104263963B (en) * | 2014-09-23 | 2016-08-24 | 铜仁市万山区盛和矿业有限责任公司 | A kind of method extracting gold from arsenical pyrite |
| RU2657254C1 (en) * | 2017-07-21 | 2018-06-09 | Федеральное государственное унитарное предприятие "Горно-химический комбинат" (ФГУП "ГХК") | Method of gold recovery from solid silver-containing sulfide ores of concentrates and of secondary raw materials |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE744120C (en) * | 1938-01-25 | 1944-01-10 | Dr Aurel Bognar | Process for the processing of ores or other mining and mining products |
| FR1058809A (en) * | 1951-01-19 | 1954-03-19 | Chemical Construction Corp | Improvements in the recovery of the precious metal content of ores containing arsenic and their concentrates |
| US2805936A (en) * | 1954-08-16 | 1957-09-10 | Felix A Schaufelberger | Leaching of arsenide ores |
| US2805940A (en) * | 1954-08-20 | 1957-09-10 | Bennedsen Hans Oluf | Process for extracting cobalt and nickel from their ores |
| US2951741A (en) * | 1955-08-05 | 1960-09-06 | Metallurg Resources Inc | Process for treating complex ores |
| US3793429A (en) * | 1972-02-18 | 1974-02-19 | Kennecott Copper Corp | Nitric acid process for recovering metal values from sulfide ore materials containing iron sulfides |
-
1983
- 1983-12-20 CA CA000443728A patent/CA1219132A/en not_active Expired
-
1984
- 1984-01-09 ZA ZA84153A patent/ZA84153B/en unknown
- 1984-01-16 AU AU23515/84A patent/AU566135B2/en not_active Ceased
- 1984-01-18 DE DE8484300292T patent/DE3473163D1/en not_active Expired
- 1984-01-18 EP EP84300292A patent/EP0119685B1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| AU2351584A (en) | 1984-07-19 |
| EP0119685A1 (en) | 1984-09-26 |
| EP0119685B1 (en) | 1988-08-03 |
| ZA84153B (en) | 1985-04-24 |
| DE3473163D1 (en) | 1988-09-08 |
| AU566135B2 (en) | 1987-10-08 |
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