AU667539B2

AU667539B2 - Method for preventing the formation of jarosite and ammonium and alkali based double salts in solvent extraction circuits connected to acidic leaching processes

Info

Publication number: AU667539B2
Application number: AU41267/93A
Authority: AU
Inventors: Stig-Erik Hultholm; Bror Goran Nyman
Original assignee: Outokumpu Harjavalta Metals Oy
Current assignee: Boliden Harjavalta Oy
Priority date: 1992-06-18
Filing date: 1993-06-16
Publication date: 1996-03-28
Anticipated expiration: 2013-06-16
Also published as: DE4320314A1; JP3386516B2; NO932223L; JPH0770656A; NO300429B1; AU4126793A; ZA934326B; NO932223D0; FI922842A; FI93973C; CA2098638A1; CA2098638C; FI93973B; DE4320314C2; ZW7693A1; FI922842A0

Description

k4-* i~~tC~ 667539

AUSTRALIA

Patents Act 1990 .4 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): OUTOKUMPU HAR3AVALTA METALS OY Invention Title: METHOD FOR PREVENTING THE FORMATION OF wAROSITE AND AMMONIUM AND ALKALI BASED DOUBLE SALTS IN SOLVENT EXTRACTION CIRCUITS CONNECTED TO ACIDIC LEACHING

PROCESSES

The followiD.no statement is a full description of thic invention, including the best method of performing it known to me/us: 1A METHOD FOR PREVENTING THE FORMATION OF JAROSITE AND AMMONIUM AND ALKALI BASED DOUBLE SALTS IN SOLVENT EXTRACTION CIRCUITS CONNECTED TO ACIDIC LEACHING PROCESSES The invention relates to a method for preventing the formation of jarosite and ammonium and alkali based double salts in the solvent extraction of acidic leaching processes, whereby valuable metals are separated.

In a preferred method the organic leaching solution is neutralised by ammonium or alkali salts prior to the separation of valuable metals in order to improve the extraction recovery. In a pre-extraction step after neutralisation, the extractant is contacted with an aqueous solution containing a metal which in this pre-extraction replaces the ammonium or alkali ions contained in the 15 extraction solution. Thus the said ions are removed from 0" the solvent used for extraction prior to the separation of valuable metals in the main solvent extraction stages.

The treatment of iron is an important factor when processing metallurgical concentrates and ores. In 20 leaching processes and cases where the treatment is based Son the combination of leaching and smelting, the behaviour of iron is extremely important. One of the characteristics of iron is that in a trivalent state it forms alkali double salts, with a composition D[Fe 3

(SO

4 2

(OH)

6 In these socalled jarosite compounds, D is an alkali metal such as natrium or potassium, or it may also be ammonium.

Jarosite compounds are formed from acidic solutions containing trivalent iron and ammonium, sodium or potassium. Jarosite is mainly formed within the pH region 0.5 5.0. An increase in temperature supports this formation. Jarosite is readily formed in the region 60 V' -tatth~Mhy~k</ieV 1t426m I w I~h \T "y 2 220 0 C. The higher the temperature, the lower the pH where jarosite is formed.

In leaching-based zinc processes it is normal to utilize the jarosite formation in removing iron from zinc-bearing solutions. The present invention in turn relates to processes where the formation of jarosite c~r other ammonium or alkali double salt shoul.d be avoided. One of these processes is the production process of nickel, cobalt or copper. The raw material can be an ore, a concentrate or an ointermediate product obtained frtm the smelting of a a concentrate or other similar metal bearing riterial.

The process in question includes processing steps carried out at temperatures above ambient. These steps are atmospheric or pressurized leaching steps taking place at a,:,:over 600 C and containing 0. 5 85 iron, Within the scope of the said process steps, there is also the removal of iron from process solutions obtained from the said leaching aa 20 steps, when the applied method is a normal hydrolysis carried out in a temperature range (60 220 0

C)

in the above mentioned cases, the formation of jarosite 0 cannot be avoided, if the process in question requires an addition of ammonium or alkali bearing materials, Such materials are for instance ammonium or sodium needed in the adjustment of th6 p11 value. They are also need~ed in intensifying solution cleaning which takes place at a higher.

pH1 value than leaching and iron removal, For example in the nickel process, the question is mainly of removing zinc, copper and cobalt. Tn casea Ihike this ammonium double salts, such as ammonium nickol sulfate, which cause problems in ceystallitation, can be formed, 3- Earlier the creation of Jarosite and double salts was not as problematic as today. The increased demands for environmental protection represent a factor which nowadays restricts the said processes. When using ammonia for neutralisation, the creation of ammonium jarosite causes nitrogen emissions, in the form of NO, development, for instance in a process of the type illustrated in figure 1.

Xn the process conditions used, the formation of Jarosite cannot be prevented in the leaching and iron removal steps.

The inevitable result is that the leach residue contains jarosite, in these cases.

The said Jarosite is decomposed, consuming energy, in the next further processing step, which in the said case is smelting. Thus the formation of jarosite lowers the cost efficiency. Xn similar fashion, the iron precipitate consumes energy in the smelting treatment, although on the other hand, the smelting I.reatment binds the iron to the inert slag to an excellent degree, at the same time eliminating the problems connected to the storage of finely divided iron precipitates. Alkali metals in turn are traditionally non-desirable materials in smelting.

Xn accordance with the present invention there is provided a method for preventing the formation of jarosite and ammonium and alkali based double salts in a solvent extraction process belonging as a process step to acidic leaching whereby valuable metals are selectively separated, characterised in that prior to valuable metal separation by said solvent extraction procesi: an organic extraction solution is neutralised by means of ammonium or alkali salts, whereaf ter the extraction solution is subjected to pre-extraction where resulting extractant is placed in contact with an aqueous solution containing a metal as an exchange ion, which metal in this pro-extraction step replaces the ammonium or alkali ions continued in the ft 2 I kl. I -4 extraction solution so that the formation of ammonium and alkali based double salts in a leach process solution of a leaching process of said solvent extraction process is prevented, and said extraction solution can be conducted to said solvent extraction process with the aqueous solution containing valuable metals from said leaching process.

in a preferred example the access of ammonium, sodium or potassium to solution circulation, even if amimonium or sodium is used for boosting the solution cleaning is prevented. In this example the extraction solution obtained from the circulation of the extraction process is neut):alised by an ammonium or alkali salt, but the access of the said ions into the main extraction circuit, where the valuable metals are separated, is prevented by using a is pre-extraction step, where the ammonium or alkali ions are transferred inzo an aqueous solution, and they are replaced in the extraction solution by a so-called exchange iou. it is essential that of the valuable metals to be separated in the solvent extraction atep; at least one of which is extracted more intensively than the exchange ion. When the .2 ammonium and alkali ions are removed from the solution, a higher temperature can be used for intensifying the leaching. Smelting can then be applied as a natural further processing atep for recovering one of the metals to be separated and for improving environmnental protection.

The essential novel features of the invention are apparent from the appended patent claims.

The invention is illustrated with reference to the appended drawings, where: Vigure I is a flowchart of an example of a preferred embodiment of the invention, and F~iue 2 illustrates the extraction of some metald do a to i -4Afunction of the pH value with a fixed extractant.

When using the preferred example of the embodiment of the invention, certain process technical advantages are also achieved. When a neutral salt, such as ammonium, sodium or potassium sulfate, is not accumulated in the solution circulation, the solubility of for instance nickel sulfate is increased. This can be utilised for raising the capacity of the reduction and electrolysis steps included in the process. Among other advantages, let us point out that thickening, filtering and electrolysis all become easier. A high metal content also improves the quality of the metal produced. Another specific advantage is that it is not necessary to introduce a separate removal of neutral salt from the main process solutions, for instance by 15 crystallization.

According to the preferred example, a process including smelting steps, leaching and recoveries of two valuable metals, referred to as A and B, by means of reduction and/or taisfdf*e t aB st electrolysis is further complemented by characteristic extraction process steps complemented with crystallization.

Another metal C also is utilized in the process, which metal does not necessarily have to be a valuable metal.

From the recovery of valuable metal B, for instance from the reduction, there is conducted a C-bearing solution to the pre-extraction, and the C-content of the said solution is continuously increased to a degree that compensates the losses. The employed neutralizing agent is a substance D, which is ammonium, sodium or potassium salt. In the pre-extraction, there follows a mixing contact with the extraction solution neutralized with the neutralizing agent D. Generally the extraction solution is kerosene-based and contains an extractant which, according to its extraction equilibriums, has a preference to extracting metal A in the next extraction separation, whereto a solution containing A, B and C is conducted from the iron removal step. The employed aqueous solution is advantageously a sulfate solution.

In the pro-extraction, the extraction solution containing substances D meets a C and D bearing solution coming from reduction. An ion exchange reaction takes place, and according to the said reaction C is extracted into the extraction solution, at the same time exchanging all D out of the extraction solution to an aqueous phase, which is directed out of pro-extraction. This is conducted to the separation of D-salt, such as crystallization. The extraction solution containing metal C is conducted to the main extraction separation together with an aqueous solution containing the valuable metals A and 8, so that an ion exchange takes place between C and A. C is transferred back to the aqueous phase and returns, via the recovery of R, to pro-extraction for a now cycle of solvent extraction, Thus C serves as a typo of exchang# iont first it displaces D from the extraction solution in pro-extraction, but then it goes back to the aqueous solut:,on in the extraction separation itself. Thus C is not essentially consumed in the process, apart from small quantities along with D and A, and this consumption can be compensated with a small addition prior to the pre- extraction. Metal A is again removed from the extraction solutioi. by extracting with acid, and conducted to its own recovery ciroul.t.

Owmethod is not bound to any special metals or extraction solutions. The essential point is that the extraction equilibrium favours the extraction of metal A with respect to metals B and C. It is advantageous but not necessary that C is extracted more intensively than B, so that it helps the selective extraction of A in relation to B. The metals are extracted mainly according to the cation exchange with such extractants that need a neutralizer addition in order to boost the extraction reaction. Such extractants are di- (alkyl)-phosphoric acids, monoalkyl 20 esters of alkyl phosphonic acid and di-(alkyl)-phosphinic acids and organic carboxylic acids,. gonorally of the type as well as a large number of other acidic organic extractant compounds.

The following description is a typical processing method e' for producing pure nickel and for recovering cobalt in connection with the solution cleaning of the said process. The process is further explained with reference to the flowchart of figure 1. However, 64hi method can be applied to other metals, too, as is apparent from the above 4-4~n and the examples given below.

In this example, metal A is cobalt and metal B is nickel. C is advantageously magnesium and D ammonia. The said nickel 3$ separation process is advantageously arranged in connection I -il.i -~X with nickel and copper smelting processes, where the leaching object may be a sulfidic nickel concentrate and/or matte produced in a smelting process. The copper sulfide bearing material formed as leaching residue is advantageously further processed in copper smelting for recovering copper and possible precious metals.

According to the method, of- t-h=nnl-onr, the magnesiumbearing solution, separated in hydrogen rduction, is conducted to the pre-extraction where also is supplied an extraction solution which is pronoutralized with ammonia.

This is advantageously composed of di-(alkyl)-phosphinic acid, which is dissolved into kerosene. It is also advantageous that the said phosphinic acid is a di-(2,4,4trimethyl-penthyl)-phosphini adic, which according to itd extraction properties is capable of separating cobalt and nickel.

In the pro-oxtraction, nearly all magnesium is transferred S 20 to the extraction solution, which returns an equivalent quantity of ammonium to the aqueous solution. Next the said aqueous solution is conducted to the crystallization of ammonia sulfate. This procedure ensures that ammonium, which is beneficial to the extraction, is not emitted to the nickel solution circulation. Also the crystallization of the so- called neutral salt is avoided in the main process flow proper.

Neat the extraction solution, in magnesium form, is conducted to the extraction separation, where it is contacted with an aqueous solution of cobalt-boaring nickel. As is seen from the extraction curves of figure 2, the cobalt is extracted more intensively than magnesium with Cyanex 272*. The said extraction solution is a technical di-(2,4,4-brimethyl- penthyl)-phospinie acid i' r i i -I product. Thus cobalt displaces magnesium from the extraction solution; as a result there is obtained a nickel solution cleared of cobalt and an extraction solution concentrated with respect to cobalt. For the recovery of cobalt, the next step is the treatment of the extraction solution with acid and further treatment of the said re-extraction solution.

As to magnesium, it does not disturb the nickel recovery in the successive electrolysis and/or reduction, but remains in the solution and can again be extracted therefrom in the pro-extraoqiqn during the next process cycle. The method o sium as an exchange ion for cobalt extraction successively prevents the access of magnesium to o' 15 the process circulation. However, the use of magnesium is necessary, because the cobalt extraction would be seriously oincomplete without the use of ammonia for boosting the extraction.

20 In the above described example, metal A can also be some other removable metal than cobalt. A general requirement is that A is extracted more intensively than magnesium. In the method,,h9-4i4nvenoni- it is thus possible also to remove such metals as zinc, manganese, cadmium, copper, iron, vanadium, molybdenum and uranium. Apart from cobalt or some 1 thor metal of the said group, there can simultaneuosly be removed another or several other metals of the same group.

in all of the above described caaes, the vaJuable metal B in turn can be cobalt instead of nickel, or B can be a solution mixture of nickel and cobalt. Than the amount of employed ammonia and respectively of the extraction solution in magnesium form are smaller, do that the pH value of the extraction separation in adjusted exactly with the quantity 31 of the extraction solution in magnesium form. Then the

I

9 extraction separation succeeds with a pHl whore the metal or metals to be extracted are capable of taking the ion exchange places of the extraction solution, whereas cobalt is not. In similar fashion as with nickel, cobalt can be electrolyzed or reduced from magnesium bearing solutions.

The method -lhdnvn-n can be applied in a corresponding fashion for cleaning a number of solutions containing metals B and C. This is technically efficient.

and economical in oases where 13 and C represent metals which can be separated with known methods. Attention must also be paid 4" that the metals A, to be removed in extraction separation, are extracted more intensively than the metals B and C, i.e. at a pH lower than these. B can also be extractea more intensively than C. In order to achieve the dosirod extraction separation, the extent of the extraction solution whore C is exotracted is adjusted, so that the pH of the extraction separation is suitable for the said metal separation.

Next there are given some examples of other metal solutions that can be treated according to th'o mehd -oa4 -venion~ When treating zinc, copper and cobalt bearing raw materials, it is also difficult to combine acidic leaching and the use of ammonia as the neutralizing agent, owing to the limited solubility of double salts containing ammonila and cobalt. in the example in question, zinc represents metal A. On the other hand, metal B can be copper, and respectively C can also be copper. The decisive factors are the relative proportions of the metals and other further processing, As above, A can also represent other metals that are extracted more intensively than B and C, such as iron and indium.

K

Other metal groups, such as zinc, manganese and copper, can be separated in corresponding fashion. In this case A is zinc and/or iron. Manganese is either B or C, and C can also be copper.

The method e- -=he=i&enhon is not restricted to extractants of the di-(alkyl)-phosphine type, which because of their separation sharpness are in any case advantageous when separating cobalt from n.'ckel. In addition to this, there can be employed monoalkyl esters of alkyl phosponic acid and di- (alkyl)-phosphoric acids, whereto metals also are extracted in the following order: U02+ Fe 3 Zn 2 Mn" Cu' Cd 2 Co 2 Mg 2 Ni Calcium does not show consistent behaviour, but behaves according to the extractant in question. This must be taken into account when grouping metals into the categories A, B and C according to their extraction behaviour in order to apply the method of the invention.

S 20 Carboxylic acids, generally C-10 acids, form a group of extractants that is used in extraction. When arranging metals into groups according to 'he invention, the following extraction order must be takn into account: Foe 3 S> UO' Sn" Hg'^ Cu 2 Zn Pba+ Cd N 2 Co 2 FFo p Mn Ca Mg 2 Other extractants behaving on the ion exchange basis can also be used in the metal separation based on the method,e.

Mn i on tor The most important of those are kelatine-formers such as oximes, as far as they need neutralization. Usually neutralization is applied when the metal to be extracted has a high cot .ant in the leach solution, I

Claims

1. A method for preventing the formation of jarosite and ammonium and alkali based double salts in a solvent extraction process belonging as a process step to acidic leaching whereby valuable metals are selectively separated, characterised in that prior to valuable metal separation by said solvent extraction process an organic extraction solution is neutralised by means of ammonium or alkali salts, whereafter the extraction solution is subjected to pro-extraction where resulting extractant is placed in contact with an aqueous solution containing a metal as an exchange ion, which metal in this pre-extraction step replaces the ammonium or ulkali ions continued in the extraction solution so that the formation of ammonium and alkali based double salts in a leach process solution of a leaching process of said solvent extraction process is prevented, and said extraction solution can be conducted to said solvent extraction process with the aqueous solution containing valuable metals f.om said leaching process. S 20

2. A method according to claim 1, further characterised in that ammonium or alkali ions are removed from the aqueous solution after it has been processed by pre-extraction.

3. A method according to claim 1, further characterised in that among the valuable metals to be separated by solvent extraction, at least one is extracted more intensively than the exchange ion.

4. A method according to any one of claim 3, further characterised in that in said solvent extraction process, the more intensively extracted valuable metal replaces the exchange ion in the extraction solution, so that the exchange ion is transferred back to the aqueous solution. L: 1 i. II- i Ii;- i.

LI I I I -12- A method according to claim 1, further characterised in that at least one valuable metal and said exchange ion are both extracted more intensively than other valuable metals.

6. A method according to claim 1, further characterised in that the extraction or the leaching treatments carried out thereafter take place at a raised temperature, 60 2200 C.

7. A method according to claim 1, further characterised in that the exchange ion is magnesium,

8. A method according to claim 1, further characterised in that the valuable metals to be separated are cobalt and nickel.

9. A method according to claim 3, further 15 characterised in that in said solvent extraction process, the most intensively extracted metal is cobalt. S'

10. A method according to claim 1, further characterised in that the extractant is a di-(alkyl)- phosphinic acid.

11. A method according to claim 1, further characterised in that the extractant is a di-(2,4,4- trimethyl-penthyl)-phosphinic acid.

12. A method according to claim 1, further characterised in that the extractant is a mono-alkyl ester of alkylphosphonic acid.

13. A method accordingly to claim 1, further characterised in that the extractant is a di-(alkyl)- phosporic acid. .i 13

14. A method according to claim 1, further charactersed in that the most intensively extracted metal in said solvent extraction process is one of the metals zinc, manganese, cadmium., copper, iron, vanadium, molybdenum or uranium.

A method according to anyone of clai-s 1 and 14, further characterised in that the least inten, ily extracted metal is oopper or manganese.

16. A method as claimed in anyone of the preceding claims and substantially as herein described with reference to the accompanying drawings. DATED THIS 1ST DAY OF FEBRUARY 1996 OUTO RJAVALTA METALS OY %o by its Patent Attorneys: 15 GRIFFITH HACK CO Fellows Institute of Patent Attorneys of Australia S M~WaNy4t2~93 (57) ABSTRACT The invention relates to a method for preventing the formation of jarosite and ammonium and alkali based double salts in the solvent extraction of acidic extraction processes, by means of which method different valuable metals are separated from each other. In the said method, the organic extraction solution is neutralized by ammonium or alkali salts prior to the separation of valuable metals in order to improve the extraction riasult. In a pre-extraction step after the neutralization, the extraction agent is contacted with an aqueous solution containing a metal which in this pro-extraction replaces tho ammonium or alkali ions contained in the extraction solution. Thus the said ions are removed from the extraction circuit prior to tho separation of the valuable nWetals proper, carried out by extraction. e 3*43 3 .4 3,