AU616967B2

AU616967B2 - Treatment of mixed metal sulfide concentrates

Info

Publication number: AU616967B2
Application number: AU34690/89A
Authority: AU
Inventors: Alan Keith Haines
Original assignee: General Mining Union Corp Ltd
Current assignee: Biomin Technologies SA
Priority date: 1988-05-19
Filing date: 1989-05-11
Publication date: 1991-11-14
Anticipated expiration: 2009-05-11
Also published as: AU3469089A; BR8902300A; FR2631635B1; FR2631635A1; ES2016018A6; GR1001547B; GR890100324A

Description

616967 COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION NAME ADDRESS OF APPLICANT: General Mining Union Corporation Limited 74-78 Marshall Street Johannesburg Transvaal 2001 Republic of South Africa NAME(S) OF INVENTOR(S): Alan Keith HAINES ADDRESS FOR SERVICE: DAVIES COLLISON Patent Attorneys 1 Little Collins Street, Melboume, 3000.

COMPLETE SPECIFICATION FOR THE INVENTION ENTITLED: STreatment of mixed metal sulfide concentrates The following statement is a full description of this invention, including the best method of performing it known to me/us:- 8 i la This invention relates to the treatment of mixed metal sulfide concentrates and particularly to concentrates which are precious metal bearing.

Existing methods known to the applicant for treating such concentrates include a pressure leaching process wherein the concentrate is oxidised under elevated pressure and temperature 1 10 conditions, a biological process wherein the concentrate is oxidised i with air in the presence of autotrophic bacteria, and direct chemical oxidation with chemical agents such as nitric acid, ferric I sulphate and ferric chloride.

The objective with each method is to break down the metal sulfides fr and to reprecipitate the metal in a form which is acceptable to the environment and at the same time to release the precious metal for subsequent recovery by known methods.

The pressure leaching process is effective on all metal sulfides.

VThe most common gold and silver bearing sulfides are pyrite i including marcasite, pyrrhotite and arsenopyrite. Other related minerals contain arsenic, nickel, cobalt, iron, copper and zinc.

Pressure leaching is however expensive for it requires the use of pure oxygen at high pressure which in turn requires the use of expensive plant for its production. Similarly the acidic leach medium at elevated temperatures necessitates the use of expensive corrosion resistant materials.

IBacterial oxidation on the other hand is less expensive to operate and is carried out at lower temperatures and at ambient pressures using air as the source of supply of the oxygen which is required.

These less vigorous leach conditions do not require such expensive equipment.

-2- The metal sulphides exhibit differing readiness to bacterial oxidation. Arsenopyrite for example is attacked relatively rapidly by bacterial oxidation but most other pyrite concentrates are attacked more slowly.

On the other hand pressure oxidation attacks such pyrite concentrates more rapidly and uniformly.

In treating mixed sulphide concentrates the leaching process is therefore usually selected on the basis of the predominant concentrate type. This means that the concentrate which is present in a smaller volume is treated in a manner which, for it, is not necessarily Q° optimal.

o 0 O°o SUMMARY OF THE INVENTION 15 According to one aspect of the invention there is 0oooo es provided a method of treating a mixed concentrate of at least pyrrhotite, arsenopyrite and pyrite, which comprises the steps of firstly subjecting the mixed concentrate to bacterial oxidation whereby substantially 20 all of the pyrrhotite, arsenopyrite and some of the 0 pyrite are oxidized with atmospheric oxygen under ambient conditions, and secondly subjecting the bacterially S ,Oo oxidized mixed concentrate to pressure oxidation whereby substantially all of the pyrite in the concentrate is oxidized.

0, In the first step the more readily oxidized sulphides are oxidized with atmospheric oxygen under ambient conditions while the slower reacting pyrite is Sreacted principally in the strongly oxidizing oxygen-rich conditions of the second step.

If pyrrhotite is present in the mixed concentrate then the pyrrhotite and substantially all of the arsenopyrite are oxidized in the biological step, and the pyrite is left to react in the pressure oxidation step.

According to another aspect of the invention there is provided method of treating a mixed concentrate of 910605,dbdaLO64,34690.res,2 -3arsenopyrite, pyrite and pyrrhotite wherein substantially all pyrrhotite and the arsenopyrite are principally oxidized in a first biological stage in accordance with the following equations and FeAsS 7 02 H 2 0 FeAsO 4

H

2

SO

4 (1) 2 FeS 9 02 1 H 2 SO4 1 Fe 2 (S04)3 1 H 2 0 (2) 4 2 2 2 and thereafter, most of the pyrite is oxidized at elevated temperature under oxygen-rich conditions substantially in accordance with the following equation S 0o o0o together with residual pyrrhotite and arsenopyrite: 2 FeS 2 15 02 H 2 0 Fe 2 (S0 4 3

H

2 S0 4 (3) S15 2 0o90 According to a further aspect of the invention there o* is provided a process for enhancing economical recovery of metals from mineral compositions containing pyrrhotite, arsenopyrite, and pyrite comprising the consecutive steps of: first, subjecting to bacterial oxidation a mineral composition containing at least two metal sulfides that exhibit differing susceptibility to bacterial oxidation so that varying amounts of metal sulfides are oxidized, 25 and second, subsequently leaching any remaining metal sulfides contained in the bacterially oxidized mineral 0 composition with oxygen present at a pressure greater than ambient air pressure to promote oxidation of the remaining metal sulfides.

BRIEF DESCRIPTION OF THE DRAWING The accompanying block diagram schematically represents the process of the invention for treating mixed sulphide concentrates.

910605,dbdat.64,34690.res,3 DESCRIPTION OF PREFERRED EMBODIMENT The concentrate containing pyrrhotite, arsenopyrite and pyrite is passed through a biological oxidation stage and a pressure oxidation stage, in series. In the first stage the pyrrhotite, and a portion of the arsenopyrite are economically treated by bacterial oxidation.

Some of the arsenopyrite remains unreacted while, on the other hand, some of the pyrite reacts in the first stage but to a lesser extent than does the arsenopyrite and the pyrrhotite.

In the second stage the oxygen-rich conditions at elevated temperature are effective in efficiently oxidising the pyrite and any residual pyrrhotite and arsenopyrite.

When the pyrite reacts with oxygen the following simplified equation applies: 2 FeS 2 +15 02 H0 Fe (SO 4 3 H2SO (1) 2 The sulphuric acid which is generated must be neutralised, if the pyrite reacts with oxygen in a bacterial environment, so that ideal conditions for bacterial activity can be maintained. It follows that S 25 if the pyrite is caused to react with oxygen in the pressure 4 oxidation step then it is not necessary to neutralise the sulphuric acid. Consequently the pyrite is more economically treated in the pressure oxidation process.

30 Arsenopyrite also reacts with oxygen to produce sulphuric acid in accordance with the following equation: FeAsS 7 02 H0 FeAsO H 2

SO

4 (2) 2 It is necessary to neutralise the sulphuric acid produced in accordance with equation 2 in the bacterial oxidation process. On th other hand if pyrrhotite is present then sulphuric acid is consumed, as follows: FeS 9 02 1 H 2

SO

4 1 Fe 2 (SO 4 3 1 H 2 0 (3) 4 2 2 2 Thus if pyrrhotite and arsenopyrite are present then the most economical process occurs when the pyrrhotite and arsenopyrite are allowed to react in the biological step and the pyrite is left to react in the pressure oxidation step. In the first step the acid which is generated by the arsenopyrite is partially or wholly consumed in the reaction with pyrrhotite and the need for neutralising the sulphuric acid is therefore at least substantially obviated.

The invention lends itself particularly to the case where an existing pressure oxidation plant must be expanded by providing Iadditional equipment. In such a case it would be advantageous to I 2 precede the pressure oxidation plant with a bacterial oxidation 20 plant, as illustrated in the block diagram. In other words the two plants are run in series as opposed to an alternative approach of operating the two plants in parallel.

',i In the series case only the arsenopyrite and the pyrrhotite are allowed to oxidise in the biological oxidation stage. The reaction i time is reduced to approximately half that required for the parallel case. The series approach is therefore preferable to operating the two stages in parallel, for the biological stage will require about one half of the size of the biological stage in the parallel case.

The gold content of the concentrate is easily recovered by known techniques after the sulfide minerals have been broken down, with the metal content beine precipitated in a more acceptaLle form.

ii

Claims

1. A method of treating a mixed concentrate of at least pyrrhotite, arsenopyrite and pyrite, which comprises the steps of firstly subjecting the mixed concentrate to bacterial oxidation whereby substantially all of the pyrrhotite, arsenopyrite and some of the pyrite are oxidized with atmospheric oxygen under ambient conditions, and secondly subjecting the bacterially 0 oxidized mixed concentrate to pressure oxidation whereby substantially all of the pyrite in the concentrate is oxidized. j|

2. A method of treating a mixed concentrate of S* 15 arsenopyrite, pyrite and pyrrhotite wherein substantially all pyrrhotite and the arsenopyrite are principally oxidized in a first biological stage in accordance with the following equations and FeAsS 7 02 H 2 0 FeAsO 4 H 2 SO 4 (1) 2 FeS 9 02 1 H 2 SO4 1 Fe 2 (S0 4 3 1 H 2 0 (2) 4 2 2 2 and thereafter, most of the pyrite is oxidized at elevated temperature under oxygen-rich conditions substantially in accordance with the following equation together with residual pyrrhotite and arsenopyrite: 2 FeS 2 15 02 H 2 0 Fe 2 (SO 4 3 H2SO 4 (3) 2

3. A process for enhancing economical recovery of metals from mineral compositions containing at least pyrrhotite and arsenopyrite, comprising the consecutive steps of: 910828,dbdatO78,34690.res 1 6 -7- subjecting the mineral composition to bacterial oxidation so that at least the pyrrhotite and the arsenopyrite are at least partially oxidized, and subsequently leaching any remaining metal sulfides contained in the bacterially oxidized mineral composition with oxygen present at a pressure greater than ambient air pressure to promote oxidation of the remaining metal sulfides.

4. A process according to claim 3 further including the Sstep of initiating the second step when substantially all tf C of the pyrrhotite and arsenopyrite contained in the mineral composition have been oxidized in the first step. A process according to claim 3 or 4 further Sincluding the step of ensuring a supply of oxygen to the mineral composition at ambient pressure during the first S step. DATED this 30th day of August, 1991 General Mining Union Corporation Limited By Its Patent Attorneys DAVIES COLLISON 910830,dbdat078,34690.res,7 i