BRPI0706851A2 - method for recovering nickel and cobalt from bleach solutions in the presence of iron and / or chromium - Google Patents

Abstract

METHOD FOR RECOVERING NICKEL AND COBALT OF LEATHER SOLUTIONS IN THE PRESENCE OF IRON EIOU CHROME, as it is a method (10) for the recovery of nickel and cobalt from bleach solutions in the presence of iron and / or chromium, the method comprising the steps of: i) adding a reducer (13) to a bleach solution containing nickel, cobalt and iron, such that any iron present as ferric sulphate is reduced to ferrous sulphate, and / or any hexavalent chromium is reduced to trivalent chromium; ii) neutralization (14) of at least part of the free acid by the addition of a neutralizing agent; iii) supplementary addition of the reducing agent (15) to ensure that all iron present remains in ferrous form and / or any chromium remains in trivalent form; iv) heating the solution before the mixed precipitation of sulfides; v) adding a mixture of sulfide granules (21) and hydrogen sulfide (22) to cause precipitation (20) of nickel and cobalt in the form of a mixed sulfide (24); and vi) maintain this mixture in the presence of hydrogen sulfide (22) for the required residence time to effect the complete precipitation of the mixed sulfide product (24).

Description

"METHOD FOR RECOVERY OF NICKEL AND COBALT OF BLEACH SOLUTIONS IN THE PRESENCE OF IRON AND / OR CHROME"

Technical Field

The present invention relates to a method for nickel appreciation. Particularly, the present invention consists of a hydrometallurgical method for preferential precipitation of nickel and decobalt sulfides from solutions containing iron and / or chromium. More particularly, the method is intended to substantially prevent the formation of sulfide scales during the precipitation process.

Background of the Invention

Nickel and cobalt are typically recovered from bleach solutions by placing saturated liquids in contact with a suitable total reducer such as hydrogen sulfide. Iron and chromium are known to co-precipitate as sulfides under conventional hydrogen sulfide precipitation conditions. Co-precipitations of this type are undesirable due to the detrimental effects on product quality and the demand required in the sulphide mixed product reduction process.

In metallurgical circuits incorporating acid leaching of high pressure nickel yachts, iron is most often rejected as a ferric oxyhydroxide (typically as a geotite) and as a hematite product. In some situations iron is also rejected as a jejar product.

Unfortunately, the rejection of iron as ferric oxyhydroxide results in a significant co-precipitation of valuable nickel ecobalt products. This results either in metallurgical losses or requires the reprocessing of iron waste to recover valuable nickel and cobalt.

Hematite is the most acceptable iron product for intermediate storage or disposal due to its high thermodynamic stability, high density (4.9 to 5.3 g / cm3), high iron content (60% - 70%) and its low adsorption of water and base metals.

However, the rejection of iron as a haematitan product High pressure acid leaching processes used for deniquite yachts requires the use of temperatures in the order of 250 ° C and order pressures of 45 Bar. The process, by its very nature, It involves expensive equipment that is expensive to maintain and has associated high operational costs.

The rejection of iron as jarosite, while resulting in lower nickel and cobalt losses due to better separation coefficients, is a costly process as it typically requires the use of an appropriate cation (such as ammonia) in conjunction with high temperatures and pressures.

In addition to the losses of nickel and cobalt associated with the formation of ferric oxyhydroxide and ferric hydroxide, the major problems of these processes are the lower filtration rates, the de-settling characteristics of the denser and the flow density characteristics achievable by the densifier. Ferric hydroxide in particular, and to a lesser extent ferric oxyhydroxide, tend to have an open structure. This results in the incorporation of large quantities of base metals during sedimentation. The solids produced also have a low density and the low flow densities of the condenser impact the processing equipment and also the waste volume that needs to be disposed of.

International Patent Application PCT / AU2003 / 001037 (WO 2004/016816) discloses a process for preferential appreciation of nickel and cobalt from iron-containing solutions by the addition of a reductant to reduce ferric ions in ferrous ions.

This reaction generates acid which must be neutralized prior to the addition of granular particles in the presence of additional reducing agents to precipitate nickel and cobalt. However, in this process the peeling effect can typically occur, which adversely affects both precipitation kinetics and recovery of nickel and cobalt sulfide products.

The present method therefore aims to undoubtedly overcome the scaling problem, while at the same time provides the advantage that the incidence of iron sulfide co-precipitation is low, or at least provides a usable alternative to the prior art methods.

The prior discussion of the foundations of the art is merely intended to facilitate understanding of the present invention. It should be understood that the discussion is not an acknowledgment or admission that any of the referenced materials were common knowledge in Australia at the priority date of application.

By this specification, unless the context otherwise requires, the word "comprises" or variations such as "understanding" or "comprising" shall be construed as containing the inclusion of said integer or group of integers, but not excluding any other integer or group of integers. In addition, reference to "degranulated surface area" or variations thereof should be understood to be based on the assumption that the granulate particles are perfect spheres with D50 particle diameter.

Description of the Invention

According to the present invention there is provided a method for recovering nickel and cobalt from bleach solutions in the presence of iron and / or chromium, the method comprising the steps of:

(i) adding a reductant to a solution containing bleach, nickel, cobalt and iron such that any iron present as sulfatoferric is reduced to ferrous sulfate, and / or any hexavalent chromium to be reduced to trivalent chromium;

(ii) neutralizing at least a portion of the free acid through the addition of a neutralizing agent;

(iii) further addition of the reducing agent to ensure that all iron present remains in ferrous form and / or any chromopermance in trivalent form;

(iv) heating the solution prior to mixed sulfide precipitation;

(v) adding a mixture of hydrogen sulfide and sulfide granules to precipitate nickel and cobalt into a mixed sulfide; and (vi) maintain this mixture in the presence of hydrogen sulfide for the residence time required to effect complete precipitation of the mixed sulfide product.

Preferably, the reductant of steps (i) and (iii) comprises one or more hydrogen sulfide, sodium hydrogen sulfide, or sulfur dioxide.

After neutralization, the free acid concentration is preferably within the range of 0.5 g / l and 3.5 g / l.

The neutralizing agent of step (ii) may comprise one or more of limestone, lime and calcrete.

The reduction in step (i) preferably occurs at a temperature below about 100 ° C and at ambient pressure.

Preferably, the resulting sulphate concentration of the solution resulting from step (iii) is less than approximately 1 g / l.

Preferably, the oxidation potential of the resulting solution in steps (i) to (vi) is maintained at approximately 300 mV to 400mV (measured against a reference Pt-Ag / AgCl electrode) to ensure no ferrous sulfate oxidation to ferric sulfate occurs.

Preferably, the temperature of the solution is in the range of from about 80 ° C to 120 ° C when the sulphide granules are added.

Even more preferably, the concentration of granules in the solution is in the range of from about 10 g / l to 100 g / l and the total area of the granulate surface is approximately 1 m2 / l to 10 m2 / l.

The hydrogen sulfide overpressure in step (v) and step (vi) is preferably maintained at approximately 100 kPa to 400 kPa for the purpose of producing the mixed sulfide.

Preferably, the residence time of step (vi) is approximately between 0.25 and 4 hours and is used to ensure complete precipitation of the mixed sulfide. Most preferably, the dwell time is approximately 0.5 to 1.5 hours.

The concentration of nickel in the bleach solution is preferably in the range of from about 1 g / l to 50 g / l, and of cobalton in the range of from about 0.1 g / l to 10 g / l.

Most preferably, the nickel concentration is in the range of from about 1 g / l to 10 g / l in a deniquel Iaterite solution, or from about 10 g / l to 50 g / l in a deniquel sulfide solution. Cobalt concentrations are preferably in the range of from about 0.1 g / L to 2 g / L, and from about 2 g / L to 10 g / L, respectively.

The iron concentration in the bleach solution is preferably in the range of approximately 0.5 g / l to 15 g / l.

Brief Description of the Drawings

The present invention will now be described, by way of example only, with reference to a preferred embodiment and the accompanying drawing, in which:

Figure 1 is a diagrammatic representation of a flowchart illustrating a method for precipitation of nickel and cobalt from bleach solutions in the presence of iron according to the present invention.

Best Mode (s) of Implementation of the Invention

Figure 1 illustrates a hydrometallurgical method 10 for the precipitation of nickel and cobalt from saturated iron-containing bleach solutions obtained by acid leaching of a high pressure denaterel yaterite ore. Nickel concentration is in the range 0.1 g / La 2 g / L. The iron concentration in the bleach solution is in the range of approximately 0.5 g / l to 15 g / l.

Method 10 of the present invention comprises transferring said saturated bleach solution to a pre-reduction step 12 wherein hydrogen sulfide gas 13 is sprayed through the solution at a temperature of 100 ° C. Iron present as ferric sulfate (Fe2 (SO4) 3) is reduced to ferrous sulfate (FeSO4) such that the resulting ferric concentration is less than 1 g / l.

The solution of this pre-reduction circuit 12 is then subjected to neutralization 14 using a calcrete slurry to reduce the free acid (FA) concentration of approximately 0.5 to 3.5 g / L. It should be understood that if the oxidation potential of the uncontrolled solution, so ferric can be formed during neutralization 14. Consequently, after neutralization 14 a hydrogen sulfide gas stream is again passed through the solution of the pre-reduction circuit12 in an additional reduction step 16, to ensure that the deoxidation potential is within the approximate range of 300 to 400 mV (Pt-Ag / AgCI reference electrode), for example from 350 to 380 mV.

Preheating step 18 raises the temperature of the reduction step 16 from approximately 80 to 120 ° C in the preparation for a subsequent precipitation step 20. A degranulated mixture of sulfide 21 in the range of 10 g to 100 g / l is introduced into the solution. of the introduction of hydrogen sulfide gas 22. The total degranulated surface area is approximately 1 m2 / L to 10 m2 / L. Hydrogen sulfide gas 22 is introduced with an overpressure of 100 to 400 kPa to precipitate a sulfide mixture product 24. This process is maintained for a residence time of approximately 0.25 to 4 hours, for example 0.5 and 1 hours. , 5 hours, to effectively complete the conversion to the sulfide blending product 24.

The preheat step 18 allows the precipitate step 20 to occur within acceptable commercial parameters by increasing the kinetics of the precipitation reactions, and also allows the dissolved H2S to be expelled.

Neutralization can also be performed using lime, lime stone, ammonia or caustic.

The precipitated sulfide mixture contains nickel in the range 50 to 55%, cobalt in the range 3 to 5% and iron in the range 1 to 3% wt / wt.

The method of the present invention will now be described with reference to an example which is to be understood as non-limiting.

Example 1 - Scaling Reduction

Two transfer solutions containing high iron levels are treated by pre-reduction with H2S gas and then passed through a neutralization circuit to reduce residual free acid concentration to 1.4 g / L using calcrete slurry. The composition of the transfer solutions is detailed in Table 1 below:

Table 1: Composition of the Mixed Sulfide Transfer Solution.

<table> table see original document page 8 </column> </row> <table>

Solution 1 proceeded directly to the precipitation of mixed sulfides, while Solution 2 Eh was first reduced to 350 - 380 mV (Pt-Ag / AgCI reference electrode) using H2S to ensure that all iron in iron form was converted to ferrous prior to heating of the solution in preparation for disulfide precipitation.

Another test was employed with Solution 2, in which a larger amount of mixed sulfide granules was added. See Table 2 below.

The results of flaking during appreciation of each solution are given in Table 2. It is perfectly clear that the flaking growth rate is significantly reduced when the second reduction step is incorporated into the flowchart. The effect is enhanced by an additional addition of granules in the solution.

Table 2: Effect on Scaling Growth with the Second Step of Granulation Reduction and Addition.

<table> table see original document page 8 </column> </row> <table> Solution 2 3.07 0.3

It is considered that the method of the present invention may be applied for recovering nickel and cobalt from nickel disulfide bleach solutions. In such circumstances it is typical for the saturated bleach solution to have a nickel concentration in the range of about 10 g / l to 50 g / l, a concentration of cobalt in the range of about 2 g / l to 10 g / l. Again, iron concentration is typically in the range of approximately 0.5 to 15g / L.

It should be understood that the method of the present invention is equally applicable to chromium containing bleach solutions.

Modifications and variations such as those apparent to those skilled in the art are considered to be within the scope of the present invention.

Claims (13)

1. METHOD FOR RECOVERING NICKEL ECOBALT FROM IRON AND / OUCROME LIGHT SOLUTIONS, characterized by the steps of: (i) adding a reducer to a solution containing bleach, cobalt and iron in such a way that any iron present as sulfatoferric is reduced to ferrous sulfate, and / or any hexavalent chromium to be reduced to trivalent chromium: (ii) neutralization of at least a part of the free acid through the addition of a neutralizing agent, (iii) further addition of the agent reducer to ensure that all iron present remains in ferrous form and / or any color remains in trivalent form (iv) heating of the solution prior to mixed sulfide precipitation, (v) addition of a mixture of hydrogen sulfide and sulfide granules to cause precipitation of nickel and cobalt into a mixed sulfide; and (vi) maintain this mixture in the presence of hydrogen sulfide for the residence time required to effect complete precipitation of the mixed sulfide product. Method according to claim 1, characterized in that the reductant of steps (i) and (iii) comprises one or more of hydrogen sulfide, sodium hydrogen sulfide, or sulfur dioxide. Method according to claim 1 or 2, characterized in that the free acid concentration is preferably within the range of 0.5 g / l and 3.5 g / l after neutralization. Method according to any one of claims 1 to 3, characterized in that the neutralizing agent of step (ii) may comprise one or more limestone, lime and calcret. Method according to any one of the preceding claims, characterized in that the reduction in step (i) occurs at a temperature below about 100 ° C and at ambient pressure. Method according to any one of the preceding claims, characterized in that the ferric desulphate concentration of the solution resulting from step (iii) is less than 1 g / l. Method according to any of the preceding claims, characterized in that the deoxidation potential of the resulting solution in steps (i) to (vi) is maintained at approximately 300 mV to 400 mV (measured against a Pt-Ag / AgCI electrode). of reference). Method according to any one of the preceding claims, characterized in that the temperature of the solution is in the range of about 80 ° C to 120 ° C when sulphide granules are added. Method according to any of the preceding claims, characterized in that the degranulated concentration of sulphide in the solution is in the range of approximately 10 g / l to -100 g / l such that the total surface area of pellets are approximately 1 m2 / L to 10 m2 / L. Method according to any one of the preceding claims, characterized in that the hydrogen sulfide overpressure in step (v) and step (vi) is maintained between approximately 100 kPa and 400 kPa. Method according to any one of the preceding claims, characterized in that the time remaining in step (vi) is between 0.25 and 4 hours. Method according to any one of the preceding claims, characterized in that the concentration of nickel and cobalt in the bleach solution is in the approximate range of 1 g / L to -50 g / L and in the approximate range of 0.1. g / La 10 g / l, respectively for a nickel ionite solution, or within the range of 10 g / l to 50 g / l and 2 g / l to 10 g / l, respectively, for a nickel sulfide solution. Method according to any of the preceding claims, characterized in that the iron concentration in the bleach solution is in the approximate range from 0.5 g / L to 15 g / L.