FI93973C - Method for preventing the formation of jarosite and ammonium- and alkali-based double salts in liquid-liquid extraction of acidic leaching processes - Google Patents

Description

93973

METHOD FOR PREVENTING THE FORMATION OF JAROSITE AND AMMONIUM AND ALKALINE-BASED DOUBLE SALTS IN THE LIQUID LIQUIDATION OF ACID DISSOLUTION PROCESSES

The invention relates to a process for preventing the formation of jarosite and ammonium- and alkali-based double salts in liquid-liquid extraction of acidic leaching processes, by means of which the precious metals are separated from one another. In the process, the organic extraction solution is neutralized with ammonium or alkali salts before the separation of precious metals to improve the extraction result. In the pre-extraction after neutralization, the extractant is brought into mixing contact with an aqueous solution containing a metal which, in this pre-extraction, replaces the ammonium or alkali ions contained in the extraction solution. Thus, ko. the ions leave the extraction circuit before the actual precious metals are separated by extraction.

Iron processing is an important component in the processing of non-metallic concentrates or ores. Especially in dissolution processes or in cases where the treatment is based on combining dissolution and smelting, the behavior of the iron is particularly important. The properties of iron include that in the trivalent valence state it forms basic double salts with the composition D [Fe 3 (SO 4) 2 (OH) 6]. In these so-called the jarosite compounds D have an alkali metal such as sodium or potassium, or it may also be ammonium.

Jarosite compounds consist of acidic solutions containing trivalent iron and ammonium, sodium or potassium. Jarosite is mainly formed in the pH range of 0.5 to 5.0. Raising the temperature promotes this formation. Jarosite is easily formed in the range of 60 to 220 ° C. The higher the temperature, the lower the pH at which jarosite is formed.

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In zinc processes based on leaching, it is common to use jarosite formation to remove iron from zinc-containing solutions. Our invention, in turn, is directed to processes in which it is desired to avoid the formation of jarosite or other ammonium or alkali double salts. Such a process is, for example, a process for the manufacture of nickel, cobalt or copper. The raw material may be an ore, concentrate or an intermediate obtained from the smelting of a concentrate or other similar metalliferous substance.

It is a process with processing steps at elevated temperatures. These include atmospheric or pressurized dissolution steps above 0.5 ° C containing 0.5 to 85% iron. These process steps also include the removal of iron from the process solutions obtained from these dissolution steps when the process uses general hydrolysis at elevated temperature (60-220 ° C).

In the above cases, the formation of jarosite cannot be avoided if the there is a need to add ammonium or alkaline substances in the process. These include ammonia or lye for pH adjustment. These, in turn, are needed to facilitate solution purification, which operates at a higher pH than leaching and iron removal. For example, the nickel process mainly involves the removal of zinc, copper and cobalt. Similarly, ammonium double salts such as ammonium nickel sulfate can cause crystallization problems.

In the past, the formation of jarosite and double salts could be better allowed. However, stricter environmental requirements are one of the factors currently imposing restrictions. When ammonia is used for the neutralization, the formation of ammonium jarosite causes nitrogen emissions in the form of NOx evolution, for example in a process of the type shown in Scheme 1. Under the process conditions used, jarosite formation cannot be prevented during the dissolution and iron removal steps. In this case, the metal sulfate obtained as a dissolution residue is jarosite-containing.

This jarosite decomposes, consuming energy, in the next processing step, which in the above case is smelting. Thus, the formation of jarosite impairs the cost-effectiveness of the process. Similarly, iron smelting consumes energy in smelting treatment, although on the other hand smelting treatment binds iron to inert slag in an excellent way, while eliminating the problems associated with storing fine iron precipitate. Alkali metals, on the other hand, have traditionally been undesirable substances in smelting.

Our invention relates to a process in liquid-liquid extraction to avoid the formation of jarosite or ammonium- and alkali-based double salts by preventing ammonium, sodium or potassium from entering the solution circuit, even if ammonium or lye is used to enhance solution purification. The extraction solution from the extraction process cycle is neutralized with ammonium or alkali salt, but the the entry of ions into the actual extraction circuit, where the precious metals are separated from each other, is prevented by using a pre-extraction step in which ammonium or alkali ions are extracted into the aqueous solution and replaced in the extraction solution by the so-called välitysionilla. It is essential that at least one of the precious metals to be separated by liquid-liquid extraction extracts more strongly than the transfer ion. Once the ammonium and alkali ions have been removed from the solution, it is possible to use an elevated temperature to enhance the dissolution and melt as a natural further processing step to recover some of the metal to be separated and to enhance the nature protection. The essential features of the invention appear from the appended claims.

The invention is also illustrated by the accompanying figures, in which Figure 1 is a flow diagram of a preferred embodiment of the invention, and Figure 2 shows the extraction of certain metals as a function of pH with a particular extractant.

Using our method also achieves some important process engineering advantages. When a neutral salt such as ammonium sodium or potassium sulfate does not accumulate in the solution circuit, the solubility of nickel sulfate, for example, increases. This can be used to increase the capacity of the reduction and electrolysis steps involved in the process. Advantages also include facilitation of thickening, filtration and electrolysis. The high metal content also improves the quality of the metal produced. It is also important not to have to prepare for the separate removal of the neutral salt from the actual process solutions, for example by crystallization.

According to our invention, the process consisting of smelting, dissolution and recovery of two different precious metals, which could be described by the letters A and B, by reduction and / or electrolysis, is accompanied by further characteristic extraction process steps supplemented by crystallization. The method also uses metal C as an aid, which does not necessarily have to be a precious metal. From the recovery of the precious metal B, such as from reduction, a C-containing solution is passed to the pre-extraction, the C content of which is always increased by an amount corresponding to the losses. The neutralizing agent used is substance D, which is an ammonium, sodium or potassium salt. Pre-extraction is followed by mixing contact with the extraction solution neutralized with neutralizing agent D. The extraction solution is generally kerosene-based and contains an extraction agent which, according to its extraction equilibria, preferably extracts metal A in the next extraction separation, to which a solution containing A, B and C is introduced from the iron removal. The aqueous solution is preferably a sulfate solution.

In the pre-extraction, the extraction solution containing D substances encounters the C- and D-containing solution from the reduction. An ion exchange reaction takes place, according to which C is extracted into the extraction solution, while at the same time exchanging all D from the extraction solution into the aqueous phase, which is led out of the pre-extraction. This is led to the separation of the D-salt, such as crystallization. The extraction solution containing C-metal is passed to the actual extraction separation with an aqueous solution containing precious metals A and B, whereby a similar ion exchange takes place between C and A. C transitions back to the aqueous phase and returns via B recovery to pre-extraction for a new extraction solution cycle. Thus, C acts as a kind of mediator ion by first displacing D from the extraction solution in the pre-extraction but by returning itself to the aqueous solution in the extraction separation. Thus, C is not substantially consumed in the process except for small amounts with D and A, and this wear can be treated with a small addition before pre-extraction. A is removed from the extraction solution by acid extraction and passed from the further process to its own recovery circuit.

Our method is not tied to any specific metals or extraction solutions. Essentially, the extraction equilibrium favors the extraction of the A metal over the B and C metals. It is preferred, but not necessary, that C be extracted more strongly than B, thereby promoting the selective extraction of A over B. The metals are extracted mainly by cation exchange with extraction agents that need the addition of a neutralizing agent to promote the extraction reaction. Such extractants include di- (alkyl) -phosphoric acids, mono-alkyl esters of alkylphosphonic acid, as well as di- (alkyl) -phosphinic acids and organic carboxylic acids, generally of the C-10 type, as well as numerous other acidic organic extractant compounds.

Next, a typical processing method within the scope of our invention for producing pure nickel and recovering cobalt in solution purification of that process will be described. The process is also described using the flow chart in Figure 1. However, our method can also be applied to other metals, as shown by the above and the accompanying examples.

In this example, metal A is cobalt and metal B is nickel. C is preferably magnesium and D is ammonia. Said nickel separation process preferably operates in connection with nickel and copper smelting processes, in which case the leaching target may be a sulphide nickel concentrate and / or a stone produced in the smelting process. The copper sulfide-containing material formed as a leach residue is preferably further processed in copper smelting to recover copper and any precious metals.

According to our method, the magnesium-containing solution separated from the hydrogen reduction of nickel is passed to the pre-extraction, to which also. a pre-neutralized extraction solution with ammonia is passed. This preferably consists of di- (alkyl) -phosphinic acid dissolved in kerosene. It is further preferred that said phosphinic acid is di- (2,4,4-trimethyl-pentyl) -phosphinic acid which, due to its extraction properties, is capable of separating cobalt and nickel.

In pre-extraction, almost all of the magnesium is transferred to the extraction solution, which releases an equivalent amount of ammonium back into the aqueous solution. This aqueous solution is then passed to crystallize ammonium sulfate. This procedure avoids the release of 7 93973 ammonia from the nickel solution circuit to promote extraction. At the same time, the so-called from the crystallization of the neutral salt in the actual main process stream itself.

Next, the extraction solution in the form of magnesium is passed to an extraction separation, where contact between it and the aqueous solution of cobalt-containing nickel takes place. As can be seen from the extraction curves in Figure 2, cobalt extracts more strongly than Cyanex 272® than magnesium. This extraction solution is a technical product of di- (2,4,4-trimethyl-pentyl) -phosphinic acid. Thus, cobalt displaces magnesium from the extraction solution with the result that a cobalt-purified nickel solution and a cobalt-enriched extraction solution are obtained. For the recovery of cobalt, the next step is the treatment of the extraction solution with acid and the further treatment of that back-extraction solution.

Magnesium, on the other hand, does not interfere with the recovery of nickel in the subsequent electrolysis and / or reduction, but remains in solution and can be extracted therefrom again in the pre-extraction during the next process cycle. The method according to the invention of using magnesium as a transfer ion for cobalt extraction successfully prevents the entry of ammonium into the process cycle. However, the use of ammonium is necessary because cobalt extraction would be severely interrupted without the use of ammonia to intensify the extraction.

In the example above, metal A may also be a metal to be removed other than cobalt. The requirement is that A extracts more strongly than magnesium. Thus, according to our method, it is also possible to remove metals such as zinc, manganese, cadmium, copper, iron, vanadium, molybdenum and uranium. In addition to cobalt or another metal belonging to said group, another or more other metals belonging to said group may also be removed simultaneously.

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In turn, in all of the above cases, the precious metal B may be cobalt instead of nickel, or B may be a solution mixture of nickel and cobalt. In this case, less ammonia and correspondingly the magnesium extraction solution are used, whereby the pH of the extraction separation is adjusted precisely by the amount of the magnesium extraction solution. The extraction separation then operates at a pH at which the metal (s) to be extracted or extractors are able to fill the ion exchange sites of the extraction solution, but not cobalt. As with nickel, cobalt can be electrolysed or reduced from magnesium-containing solutions.

Similarly, our method can be used to purify a whole range of solutions containing B and C metals. This is technically and economically feasible in cases where B and C represent metals that can be separated from each other by known methods. Care must also be taken to ensure that the A metals removed in the extraction separation are extracted more strongly than the B and C metals, i.e. at a lower pH. B can also extract more strongly than C. In order to achieve the desired extraction separation, the amount of extraction solution in which C is extracted is adjusted, which in turn makes the pH of the extraction separation suitable for the metal separation in question.

The following are some examples of other metal solutions that can be treated by the process of our invention. When handling zinc-, copper-, and cobalt-containing feedstocks, it is also difficult to combine acid leaching and the use of ammonia as a neutralizing agent due to the limited solubility of ammonium and cobalt-containing double salts. In this exemplary case, zinc represents the A metal. In contrast, the B metal can be either copper and C, respectively

9 93973 may be copper. The solution is affected by the relative amounts of metals and other further processing. As above, A may also represent other metals that extract more strongly than B and C, such as iron and indium.

Similarly, other metal groups such as zinc, manganese and copper can be distinguished. A in this case is zinc and / or iron. Manganese is either B or C, which may also be copper.

Our method is not limited to di- (alkyl) -phosphine-type extractants, which, however, are advantageous for the separation of cobalt from nickel due to their separation sharpness. In addition, monoalkyl esters of alkylphosphonic acid and di- (alkyl) -phosphoric acids, to which the metals are also extracted, can be used in the following order: U022 +> Fe3 +> Zn2 +> Mn2 +> Cu2 +> Cd2 +>

Co2 +> Mg2 +> Ni2 +. Calcium does not show uniform behavior, but acts on an extractant-specific basis. This must be taken into account when grouping metals into categories A, B and C based on their extraction behavior for the use of our method.

Carboxylic acids, usually C-10 acids, are one of the extractants. the group used in the extraction. When forming groups according to the invention from metals, the following extraction order must be taken into account: Fe3 +> U022 +> Sn2 +> Hg2 +> Cu2 +> Zn2 +> Pb2 +> Cd2 +> Ni2 +> Co2 +> Fe2 +> Mn2 +> Ca2 +> Mg2 +.

Other ion exchange based extractants can also be used for metal separation based on our method. Chelating agents 93973, such as oximes, are particularly relevant in so far as they require neutralization. Neutralization usually occurs when the concentration of the metal to be extracted in the extraction solution is high.

Claims (15)

A method for preventing the formation of jarosite and ammonium- and alkali-based double salts in liquid-liquid extraction as part of acid leaching processes, by means of which the precious metals are selectively separated, characterized in that the organic extraction solution is neutralized by ammonium or liquid extraction before the actual separation of precious metals , after which the extraction solution is passed to a pre-extraction, where the extractant is contacted with an aqueous solution containing a metal as a transfer ion which in this pre-extraction step replaces the ammonium or alkali ions contained in the extraction solution, preventing the formation of ammonium and alkali-based double salts in the actual extraction; can be derived from the actual extraction contact with an aqueous solution containing precious metals. • Process according to Claim 1, characterized in that the ammonium or alkali ions are removed from the aqueous solution after pre-extraction. Process according to Claim 1, characterized in that at least one of the precious metals to be separated by liquid-liquid extraction is extracted more strongly than the transfer ion. A method according to claims 1 and 3, characterized in that -. n e t t u that in the actual extraction the more strongly extractable precious metal replaces the transfer ion in the extraction solution, whereby the transfer ion is transferred back to the aqueous solution. and 93975 Process according to Claim 1, characterized in that both the at least one precious metal and the transfer ion are extracted more strongly than the other precious metals. Process according to Claim 1, characterized in that the extraction or the subsequent solution treatments take place at an elevated temperature, from 60 to 220 ° C. 7. A method according to claim 1, characterized in that the mediating ion is magnesium. Process according to Claim 1, characterized in that the precious metals to be separated are cobalt and nickel. Process according to Claims 1 and 3, characterized in that the metal which is more strongly extracted in the actual extraction is cobalt. Process according to Claim 1, characterized in that the extractant is di- (alkyl) -phosphinic acid. Process according to Claim 10, characterized in that the extractant is di- (2,4,4-trimethyl-pentyl) -phosphinic acid. 11,93973 Process according to Claim 1, characterized in that the extractant is a monoalkyl ester of an alkylphosphonic acid. 93973 Process according to Claim 1, characterized in that the extractant is di- (alkyl) -phosphoric acid. Process according to Claim 1, characterized in that the metal which is more strongly extracted in the actual extraction is one of the metals zinc, manganese, cadmium, copper, iron, vanadium, molybdenum or uranium. Process according to Claims 1 and 14, characterized in that the less extractable metal is copper or manganese. «93973