BRPI0707373A2 - improved base metal recovery process from pile leaching - Google Patents

Abstract

BASE METAL RECOVERY PROCESS IMPROVED FROM STACK LEASTING. A process for recovering base metals from an oxide ore, comprising the steps of: e) forming at least one pile (40) of the oxide ore containing the base metals to be recovered; f) irrigating at least one pile (40) of oxide ore with a leaching solution (42) comprising sulfuric acid; g) collect the resulting rich leach solution (44.50) from the irrigated pile (40); and treating the rich leach solution (44.50) with a reducing gas stream to create a treated rich leach solution for the recovery of required base metals. The process is applicable for the treatment of laterite ores and the conversion from iron to iron ferrous, with sulfuric acid regeneration in the process, has benefits in terms of enhanced process efficiency and reduced operating costs.

Description

"BASE METAL RECOVERY PROCESS FROM BATTERY LIXIVIATION"

FIELD OF INVENTION

The present invention relates to a process for improving the recovery of base metals using stack leaching. The process concerns particularly, but not exclusively, the recovery of nickel and cobalt from laterite ores.

BACKGROUND FOR THE INVENTION

Nickel is typically extracted from its oxide ores by the use of both pyrometallurgical and hydrometallurgical methods. Pyrometallurgical methods involve the casting of ores for the production of nickel metal and casting for the production of ferronickel. Hydrometallurgical methods include the Caron method of ammonia leaching and the Free-port Sulfur method of sulfuric acid pressure leaching. In Australia, nickel is extracted from its oxide ores using both the Caron process hydrometallurgical methods and the pressure leaching process.

Unfortunately, most of these conventional methods are energy and capital intensive and are not suitable for low grade nickel ores such as nickel terites. Therefore, cost-effective exploration of low grade ecobalt nickel oxide ores in Australia and internationally requires the development of new methods at a much higher energy cost than existing methods.

Pile leaching is a conventional hydrometallurgical method of economically extracting low grade ores and has been successfully used to recover metals such as copper, gold and nickel. Usually it involves forming crude ore piles and introducing leach solution such as sulfuric acid on top of the pile to percolate below the pile. Effluent is drained from the base of the pile and passed to a recovery machinery where metals are recovered. One problem that prevents the leaching of nickel and ecobalt stack containing laterite ores is the substantial clay component of these ores. Most clays have a detrimental effect on the percolation of the leach solution through the ore as the clay components of the ore ore may swell and close gaps leading to the channeling of the leach solution.

In a prior invention of an associated company of the present applicant described in the provisional application of Australia 2005904274. The contents of which are incorporated herein by reference, the associated company reported the separation of laterite ore into a fine fraction and a coarse fraction before leaching. in stack. The coarse fraction has a high percentage of clay material and is treated with an agglomeration step before being formed into a pile for heap leaching. Agglomeration treatment aids in overcoming problems associated with the presence of clay particles.

In the case of stack leaching of Nickel Iaterites, the iron that is leached in the solution is typically present in the form of more than 80% ferric sulfate. The invention previously disclosed in Australian Interim Patent Application 2005904274 for Stack Leach Nickel Yachts describes the need to add hydrogen sulfide to reduce ferric sulfate to ferrous sulfate in the rich leach solution.

The addition of hydrogen sulfide has several disadvantages including that: (a) the reagent is expensive to produce, (b) the reagent may be hazardous to handle, and (c) the addition of hydrogen sulfide results in elemental sulfur formation. which forms sulfur particles and sulfur scale, and needs to be removed from the process, as provided by the formula:

Fe2 (SO4) 3 + H2S -> 2FeS04 + H2SO4 + S

The present invention aims to alleviate or at least partially alleviate one or more of the difficulties associated with the prior art.

References to the prior art in this specification are provided for illustrative purposes only and should not be taken as an admission that such prior art is part of general common knowledge in Australia or elsewhere.

SUMMARY OF THE INVENTION

The present invention provides a process for the recovery of base metals from an oxide ore, comprising the steps of:

(a) form at least one pile of oxide ore containing the base metals to be recovered;

b) irrigating at least one pile of oxide ore with a leaching solution comprising sulfuric acid;

c) collecting the rich leach solution resulting from the irrigated pile; and

d) treating the rich leach solution with a reducing gas stream to create a rich leach solution treated for the recovery of required base metals.

Preferably the reducing gas stream comprises sulfur dioxide.

Preferably the reducing gas stream comprises a mixture of sulfur dioxide and oxygen. Preferably sulfur dioxide and oxygen are in the ratio of about 1: 1.

More preferably, the reducing gas stream comprises a mixture of sulfur dioxide, oxygen and an inert gas such as nitrogen.

More preferably, the rich leach solution is treated with the reducing gas stream in the presence of activated carbon or a similar adsorbent. Typically, the activated carbon is added to the rich leach solution prior to treatment of the solution with the reducing gas. The activated carbon preferably is in the form of granular activated carbon. The granular activated carbon is preferably 6 χ 12 mesh size. The rich leaching solution can be contacted with activated carbon in an absorption column - operated in continuous gas mode - or a slurry reactor.

The leach solution or leach used to irrigate at least one stack may include additional components for sulfuric acid. For example, the leachate may include sulfur dioxide or a salt from which sulfur dioxide may be derived, such as a metabisulphite salt.

The process may further comprise a beneficiation step which is used prior to step a) to separate the ore into a substantially coarse fraction and a substantially fine fraction. The thin fraction is usually the small fraction of the aperture sieve of about 2 mm; or alternatively it may be the small fraction of the 1 mm fence sieve. The coarse ore fraction is usually the largest refuse in the screen. At least one pile is preferably formed from the coarse ore fraction. The coarse deminer fraction is preferably agglomerated before forming the pile. The agglomeration preferably comprises wetting the ore to a moisture content of about 20% to 30%. The agglomeration generally also comprises wetting with a solution containing sulfuric acids and curing for about 1 to 20 days prior to irrigation of the pile. The sulfuric acid content of the wetting agent may range from 01 wt% to 100 wt% (concentrated sulfuric acid).

The leach solution applied to the stack may be a recirculated process solution such as a countercurrent decanting surplus solution from a pressure leach step. The countercurrent decanting surplus solution preferably contains dilute sulfuric acid in the range of 10 to 50 g / l. This solution can also be used at the wetting stage.

Preferably, the oxide ore is a yaterite ore containing nickel, cobalt and iron. Typically, iron in the ore is present as ferric sulfate, and the reducing gas is applied at a concentration to convert at least a portion of the ferrous sulfate to ferrous sulfate. Preferably, the reducing gas is applied at a concentration to convert all ferric sulfate to ferrous sulfate.

Preferably, the flow of the gas stream to the rich leach solution is adjusted so that the treated rich leach solution has a concentration of less than 2 g / l ferric sulfate.

The treated rich leach solution is preferably passed to a neutralization step prior to a base metal recovery step. In relation to this last stage, hydrogen sulfide is generally used to form metal sulfides in the metal recovery step that is conducted through selective nickel and cobalt precipitation.

The addition of reducing gas to the rich leaching solution is believed to assist in the decomposition of ferric sulfate to ferrous sulfate. It is also believed that treatment of the rich leaching solution with the reducing gas stream in the presence of activated carbon further improves reaction kinetics for ferric sulfate to ferrous sulfate conversion. Utilization of reducing gas is considered to be improved with the addition of activated carbon which can act as a catalyst. Activated carbon can also usefully remove intermediate iron species that may interfere with the leaching / base metal recovery steps.

Thus, undesirable ferric ions can be removed from the rich leach solution while sulfuric acid is produced in the reduction reaction. Therefore, the reduction reaction had the benefit of removing ferric ions while generating sulfuric acid required in the leaching process in a useful regeneration step. Another benefit of the reduction reaction is that by removing ferric ions from the rich leach solution the amount of hydrogen sulphide required in the metal recovery step is reduced since hydrogen sulphide is not required for ferric ion reduction.

The present invention further comprises a process for recovering base metals from an oxide ore, the process comprising the steps of:

(a) form at least a first pile of oxide ore;

b) irrigating the first pile of the oxide ore with a leach solution comprising sulfuric acid;

c) collecting the first rich leach solution resulting from the first irrigated pile;

d) passing at least a portion of the first rich leach solution as an intermediate leach solution to a second oxide ore stack, the intermediate leach solution having been treated with a reducing gas mixture before being released to the second cell; and

e) collecting the second rich leach solution resulting from the second required base metal recovery pile.

Preferably, the reducing gas stream comprises sulfur dioxide.

Preferably, the reducing gas stream comprises a mixture of sulfur dioxide and oxygen. Preferably sulfur dioxide and oxygen are in the ratio of about 1: 1.

More preferably, the reducing gas stream comprises a mixture of sulfur dioxide, oxygen and nitrogen.

More preferably, the intermediate leach solution is treated with the reducing gas stream in the presence of activated carbon or a similar adsorbent. Typically, activated carbon is added to the intermediate leach solution before treating the solution with the reducing gas. The activated carbon is preferably in the form of granular activated carbon. The granular activated carbon is preferably the size of 6 χ 12 meshes. The leach solution applied to the first stack may be a processor-circulated solution such as a countercurrent overflow decantation solution of a pressure leach step. The excess countercurrent decanting solution preferably contains dilute sulfuric acid in the range of 10 to 60 g / l. The countercurrent de-overflow solution is typically combined with the release intermediate leaching solution for the second stack, the combined solution containing sulfuric acid in the range of 20 to 60 g / l.

Preferably the oxide ore is a nickel, cobalt and iron containing yaterite ore. Typically, iron in the ore is present as ferric sulfate, and the reducing gas is applied at a concentration to convert at least a portion of the ferrous sulfate to ferrous sulfate. Preferably the reducing gas is applied at a concentration to convert all ferric sulfate to ferrous sulfate.

Throughout the descriptive report, unless the context requires otherwise, the word "understand" or variations such as "comprise" or "comprising" shall be understood to include the inclusion of an established integer or group of numbers. -integers but not excluding any other integer or group of integers. Likewise the word "preferably" or variations such as "preferred" will be understood to imply that an established integer or group of integers is desirable but not essential to the work of the invention.

BRIEF DESCRIPTION OF DRAWINGS

The nature of the invention will be better understood from the following detailed description of various specific embodiments of the invention provided by way of example only with reference to the accompanying drawing in which:

Figure 1 is a flow diagram of a process for recovering nickel and cobalt from Iaterite ores according to the embodiments of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 shows a flow diagram of a process 10 for recovering nickel and cobalt from oxide ores in the form of laterite ores.

Process 10 includes a stream of mine laterite ore 12 which is fed to a beneficiation machinery having a crushing stage 14 and a grinding stage 16. Process water 18 is added to the grinding stage 16 at about 90 ° C.

The machinery further comprises a sieving circuit 20 used for two-stage sieving of the grinding stage product 16. The sieves used in the sieving circuit 20 are a 5 mm primary sieve and a 1.75 mm secondary sieve. The coarse ore fraction discarded in the screening process and referred to as ground "waste" is passed from the screening circuit 20 to an aglomeration step 22. The waste comprises a significant amount of the laterite ore carbyle component.

Agglomeration step 22 comprises adjusting the moisture content of the coarse deminer fraction to between about 20% and 30%. The agglomeration step may further comprise applying concentrated sulfuric acid during agglomeration in the range of about 10 kg to 300 kg of acid per tonne of coarse ore, followed by curing for about 1 to 20 days prior to irrigation.

The small sieve material from the milling step 16 is passed to a pressure acid leaching step 26. A sulfuric acid leaching agent is used to extract nickel and cobalt from the fine ore fraction in solution at elevated temperatures and pressure; producing a leaching slurry comprising liquid components and solid waste. The leaching slurry is passed to a liquid / solid separation step, for example a countercurrent settling ("CCD") step 28. The solid overflowing to the CCD step 28 is passed to residue 30. Between 0 and 100% of the separated or clarified liquid from the CCD step 28 is passed through a reservoir 31 to a neutralization step 32, and a nickel and cobalt recovery step 34. Calcret, a limestone-like limestone material, is used. in neutralization step 32 to neutralize the liquid to between about 0 and 3 g / l free acid. Hydrogen sulfide is used in the nickel and cobalt recovery step 34 to generate a mixed sulfide product 36 suitable for further recovery operations. Sterile liquid 38 from recovery step 34 is returned to CCD step 28.

The agglomerated coarse ore fraction 20 of agglomeration step 22 is stacked in a first stack 40 and a leach solution 42 is applied to the top of stack 40, referred to as irrigation. Leach solution 42 consists of a surplus CCD 42 solution taken from reservoir 32. Leach solution 42 contains diluidone sulfuric acid in the range of about 10 to 50 g / l, and usually between about 20 to 50 g / l. The leach solution is at elevated temperature, usually in the range of about 30 ° C to 60 ° C. The leach solution 42 is allowed to percolate below the stack 40 so as to leach nickel and co-balance to from ore; in particular from the clay component of the ore.

A rich leach solution in the form of an intermediate leach solution44 is collected from the base of the first stack 40 in a first collection tank 46. A reducing gas mixture stream in the form of a sulfur dioxide stream 54 is passed through. in leach solution 44. The treated rich leach solution 56 is then applied to a second pile 48.

In a preferred form of the invention, activated carbon is added to or contacted with the rich leach solution mixture 44 and the reducing gas mixture. This step may be conducted using the adsorption / absorption column (s) or reservoir reactor (s). The activated carbon is added in the range of about 5 g / l to 500 g / l.

By treating the rich leach solution 44 with sulfur dioxide, the ferric sulfate in this solution is reduced to ferrous sulfate generating sulfuric acid in the reaction (regeneration) step as follows:

Fe2 (SO4) 3 + SO2 + 2H20 2FeS04 + 2H2SO4

This is a beneficial step as ferric ions are removed, and 2 mo of sulfuric acids are generated for each mol of converted ferric sulfate. The generation of sulfuric acid in the reaction means that less sulfuric acid needed to be added to the bleaching process contributing to savings in production costs. In addition, less hydrogen sulphide is required as a precipitant in the base metal recovery stage with consecutive reduction in cost and risk.

The reducing gas stream may also be a mixture of different gases, for example a mixture of sulfur dioxide, nitrogen and oxygen. Choosing an appropriate mix will often depend on the availability of existing machinery equipment, and using existing gas equipment would usually provide the advantage of additional cost savings. For example, a reducing gas stream containing a mixture of sulfur dioxide, oxygen and nitrogen may be produced by taking a drain current from an existing sulfur burning acid machinery, or alternatively a dedicated sulfur burning machinery may be installed. . Controls over the composition of the mixture may also allow control over the degree of reduction of ferric ions to ferrous ions in the process.

The introduction of the reducing gas mixture into the rich leach solution allows the sulfuric acid concentration to be adjusted as required by simply adjusting the sulfur dioxide flow. For example, leach solution 56 applied to battery 48 is adjusted to between about 20 g / l and 60 g / l sulfuric acid by regulating the addition of sulfur dioxide and resulting conversion of ferric sulfate to ferrous sulfate. .

The second stack 48 is again formed from the agglomerated coarse step ore fraction 22. One purpose of providing multiple stacks 30 is to neutralize the free acid inlet below the range of about 0 to 20 g / l and preferably below about from 0 to 10 g / l. This assists in reducing neutralization costs in the neutralization step 32.

The final rich leach solution 50 is collected from a base of pile 48 in tank52. The rich leach solution 50 is returned to the existing process circuit via the reservoir 31 as shown in Figure 1. As an alternative to the addition of the stream in step 54, or in addition to step 54, a reducing gas stream 58 may be added. -to the final rich leach solution 50 to reduce the concentration of ferric ions. This avoids the need for the use of hydrogen sulfide to reduce ferric ions. The Stack-leached rich leach solution 44 typically contains between about 3 g / l and 5 g / l nickel in the solution and also about 1 g / l. 25 g / l iron, mainly in the form of ferric sulphate. Ferric sulfate is typically reduced to less than 2 g / l with the addition of a gas mixture containing sulfur dioxide, oxygen and nitrogen.

As an alternative to passing the rich leach solution 50 to the reservoir 31, the leach solution 50 can be passed to neutralization step 32 and then to base metal recovery step 34. A reducing gas stream 60 is added. to the process line immediately prior to neutralization step 32 (in addition to streams 56 and 58) to remove ferric ions immediately prior to neutralization.

In recovery step 34, nickel and cobalt are recovered by treating the hydrogen sulfide gas leach solution 50 at a partial pressure between about 160 kPa and 400 kPa at a temperature between about 80 ° C and 120 ° C. ° C. The dwell time is between about 15 and 90 minutes. The precipitated mixed sulfide product contains from about 50 to 55% nickel and from about 3 to 5% cobalt. Since the ferric sulfate mass has already been reduced, the need for hydrogen sulfide for the reduction of ferric ions is significantly reduced thereby improving the efficiency of the metal recovery process.

Sterile liquid 38 from recovery step 34 may be used to wash the trap or once the batteries are depleted as a significant leach solution stock that may remain contained therein. Sterile liquid 38 is passed to step CCD 28 before being transported to the batteries.

The process 10 of the invention may be varied according to operational needs. For example, more than two batteries may be used. Reducing chain 60 may take the place of chains 56 and / or 58 described above.

The effect of reducing the electrical potential (Eh) in recirculating solutions by adding the reducing gas stream is that some minerals such as mineralasbolane-containing manganese, which contain both cobalt and nickel, would be rapidly leached. These miners, under typical heap leaching conditions, would be slow to leach due to the high oxidation potential of the heap leach solution.

In Examples 1 and 2 shown below, the results of the reduction in ferric ion concentrations of rich leach solutions having been treated with reducing gas mixtures according to the invention are provided.

EXAMPLE 1

A first rich leach solution containing high levels of iron in the form of ferric sulfate was treated with pure SO2 gas to reduce ferric sulfate to ferrous sulfate.

The composition of feed solutions is presented in Table 1 below: Table 1: Rich Leach Solution Composition 1.

<table> table see original document page 10 </column> </row> <table>

Solution 1 was contacted with 100% SO 2 and this reduced the Eh of Solution 1 from 506 mV to 422 mV (Pt-Ag / AgCl reference electrode) as iron in the ferric sulphate-converted ferric form. In addition, the free acid concentration increased from 19.2g / l to 45.9 g / l as ferric sulfate was converted to ferrous sulfate, as by the following reaction regenerating sulfuric acid.

Fe2 (SO4) 3 + SO2 + 2H20 2FeS04 + 2H2SO4

The composition of the resulting rich leach solution is shown in Table 2 below:

Table 2: Composition of Rich Treated Leach Solution 1.

<table> table see original document page 10 </column> </row> <table>

EXAMPLE 2

A second rich leach solution containing high iron levels in the ferric desulfate form was treated with a gas mixture of O2, N2 and SO2 to reduce the sulfatoferric to ferrous sulfate. The composition of the feed solutions is given in the

Table 3 below:

<table> table see original document page 10 </column> </row> <table>

Table 3: Rich Leach Solution Composition 2.

<table> table see original document page 10 </column> </row> <table> Solution 2 was contacted with 4% O2, 79% N2 and 17% SO2 and this reduced Solution 1's Eh by 504 mV at 490 mV (Pt-Ag / AgCl reference electrode) as the ferric form ferrone was converted to ferrous sulfate. In addition, the free acid concentration increased from 40.3 g / l to 44.9 g / l as ferric sulfate was converted to ferrous sulfate, as by the following reaction.

Fe2 (SO4) 3 + SO2 + 2H20 -> 2FeSO4 + 2H2SO4

The composition of the resulting rich leach solution is shown in Table 4 below:

Table 4: Composition of Rich Treated Leach Solution 2.

<table> table see original document page 0 </column> </row> <table>

The effect of reducing the electric potential (Eh) in recirculating solutions by applying the reducing gas SO2 is that some minerals, such as asbolane, which contain both tantocobalt and nickel, would be rapidly leached. These minerals, under typical heap leaching conditions, would be slow to leach due to the high oxidation potential of the heap leach solution.

The use of a reducing gas containing sulfur dioxide, oxygen and nitrogen instead of hydrogen sulfide overcomes the disadvantages associated with the use of hydrogen sulfide. The reducing gas stream of the invention is significantly less expensive to produce, and the associated safety and health risks are lower.

In addition, the addition of sulfur dioxide to reduce ferric sulfate to ferrous sulfate results in the formation of sulfuric acid which can be used in the stack leaching process, advantageously avoiding the formation of elemental sulfur.

In Example 3 shown below, activated carbon was added to a third rich leach solution which was then treated with a sulfur dioxide reducing gas mixture according to the invention. The effect of the presence of activated carbon on the reduction of ferrous to ferrous ions in the rich leach solution was measured as summarized in Table 6.

EXAMPLE 3

A third rich leach solution containing high iron levels in the form of ferric sulfate was treated with pure SO2 gas to reduce ferric sulfate to ferrous sulfate. The composition of the third leach solution is presented in Table 5. Table 5: Rich Leaching 3.

<table> table see original document page 12 </column> </row> <table>

Leach solution 3 was contacted with 100% SO2 in two identical tests. In the first test, no activated carbon was added to the third leach solution and in the second test activated carbon was added to the leach solution. The activated carbon used was Haycarb (trademark) grade YAG of a 6 χ 12 mesh granular shape.

The comparison of the two tests is shown below in Table 6 which summarizes the conversion to ferric sulfate for each of the first and second tests.

Table 6: Ferric sulfate concentrations after test 1 and test 2 measured in rich leaching solution (mg / L concentrations)

<table> table see original document page 12 </column> </row> <table>

Now that preferred embodiments of the base metal recovery process have been described in detail, it will be apparent that the process provides several advantages over the prior art, including the following:

i) Sulfuric acid is generated in the gas reduction step of this invention by reducing the amount of sulfuric acid that must be directly contributed to the process, and lowering overall production costs.

ii) Less hydrogen sulfide is required in the overall recovery process due to the conversion of ferric ions to ferrous ions by the reducing gas stream of the invention. The reducing gas stream is cheaper to produce and has fewer associated health and safety risks than hydrogen sulfide,

iii) The introduction of the reducing gas mixture into the leach solution allows the concentration of sulfuric acid (and ferric ion concentration) to be easily adjusted as required simply by adjusting the flow and concentration of the gas mixture.

iv) The introduction of activated carbon into the rich leach solution along with the addition of the reducing gas mixture improves the process of conversion of ferric ion to ferrous ion thereby contributing to a reduction in overall operating costs.

It would be readily apparent to those skilled in the relevant art that various modifications and improvements may be made to the preceding embodiments, in addition to those already described, without departing from the basic inventive concepts of the present invention. For example, in the described embodiments only two stacks are shown. However, three or four batteries may be used and the intermediate leach solution released to each battery may be treated with the reducing gas stream prior to release to each successive battery. In addition, while embodiments describe the use of granular activated carbon, other forms of activated carbon such as pellets and powder may also be used. Therefore, it will be appreciated that the scope of the invention is not limited to the specific embodiments described.

Claims (24)

Process for the recovery of base metals from an oxide ore, characterized in that it comprises the steps of: a) forming at least one pile of oxide ore containing the base metals to be recovered; at least one oxide ore heap with a leaching solution comprising sulfuric acid c) collecting the rich leaching solution resulting from the irrigated heap; wherein said rich leach solution is treated with a reducing gas stream to create a rich treated leach solution for recovery of required base metals. Process according to Claim 1, characterized in that the rich leach solution is treated with the reducing gas stream in the presence of a catalyst. Process according to Claim 2, characterized in that the catalyst is activated carbon, preferably granular activated carbon. Process according to Claim 2 or 3, characterized in that the catalyst is added to the rich leach solution before treatment of the solution with the reducing gas. Process according to any one of the preceding claims, characterized in that the reducing gas stream comprises sulfur dioxide. Process according to Claim 5, characterized in that the reducing gas stream comprises a mixture of sulfur dioxide and an oxidant. Process according to Claim 6, characterized in that the oxidizer is oxygen. Process according to any one of claims 4 to 7, characterized in that the reducing gas stream comprises a mixture of sulfur dioxide, oxidant and an inert gas. Process according to Claim 8, characterized in that said inert gas is nitrogen. Process according to any of the preceding claims, characterized in that it further comprises an ore beneficiation step prior to step (a). Process according to Claim 10, characterized in that the ore is separated into a substantially coarse fraction and a substantially fine fraction. A process according to claim 10 or 11, characterized in that said at least one pile is formed from the coarse fraction of beneficiated ore. A process according to claim 11 or 12, characterized in that the coarse ore fraction is agglomerated before forming the pile. Process according to Claim 13, characterized in that the agglomeration comprises wetting the ore to a moisture content of about 20 to 30% by weight. Process according to Claim 14, characterized in that the agglomeration comprises wetting with a sulfuric acid-containing solution. Process according to Claim 15, characterized in that the agglomeration comprises curing for about 1 to 20 days prior to irrigation of the pellet. Process according to any one of the preceding claims, characterized in that the battery is irrigated with a recirculated process solution. Process according to any one of the preceding Claims, characterized in that the oxide ore is an Iaterite ore containing nickel, cobalt and iron. A process according to claim 17 or 18, characterized in that the rich leach solution contains iron in the ferric form and the reducing gas is applied in a concentration to convert at least a portion of the ferric iron. to ferrous, regenerating sulfuric acid to irrigate said at least one pile. Process according to Claim 19, characterized in that the reducing gas is applied in one concentration to convert all ferrous iron ferrous iron. Process according to Claim 19 or 20, characterized in that the flow of the reducing gas stream is adjusted so that the treated leaching solution has a concentration of less than 2 g / l sulfate. ferric. Process according to any of the preceding claims, characterized in that the treated rich leach solution is passed to a neutralization step prior to a base metal recovery step. Process according to any one of the preceding claims, characterized in that it comprises the steps of: (a) forming at least one first oxide ore pile; (b) irrigating the first oxide ore pile with a single leaching solution. comprising sulfuric acid c) collecting the first rich leach solution resulting from the first irrigated pile d) passing at least a portion of the first rich leach solution as an intermediate leach solution to a second oxide ore pile, the leach solution intermediate having been treated with a reducing gas mixture before being released to the second stack; ee) collecting the second rich leach solution resulting from the second pile for recovering required base metals. Process according to any one of claims 1 to 23, characterized in that the reducing gas stream is a drainage stream of a sulfur burning machinery.