WO2013030741A2

WO2013030741A2 - Method for recovering technical-grade molybdenum from diluted acid leacing solutions (pls) that have a high arsenic concentration and originate from metallurgical waste

Info

Publication number: WO2013030741A2
Application number: PCT/IB2012/054308
Authority: WO
Inventors: Felipe Andrés LAGNO SÁNCHEZ; Ricardo Fernando SEPÚLVEDA LETELIER; Marcelo Gustavo ACUÑA GOYCOLEA
Original assignee: Ecometales Limited
Priority date: 2011-08-26
Filing date: 2012-08-24
Publication date: 2013-03-07
Also published as: WO2013030741A3

Abstract

The invention relates to a method for recovering technical-grade molybdenum from diluted acid leaching solutions (PLS) that have a high arsenic concentration, said method comprises the following steps consisting in: (a) bringing a pre-filtered acid leaching solution (PLS), originating from the leaching of smelter dust, into contact with an anionic ion-exchange resin; (b) washing the loaded resin with water; (c) extracting the molybdenum from the ion-exchange resin with an alkaline ammonium regenerant solution at a pH value of between 8 and 12, in order to form ammonium molybdenum in solution; (d) washing the unloaded resin with water; (e) adding iron and/or magnesium salts to the recovered ammoniacal solution, in order to obtain a precipitate which is transferred to the arsenic abatement step and a solution containing ammonium molybdate in solution; (f) adding sulphuric acid to the arsenic-free ammoniacal solution in order to precipitate the moylbdenum in the form of ammonium molybdate in an acid environment at a pH value of between 1.5 and 4; (g) separating the precipitate formed by filtering the molybdate and re-circulating the solution obtained with the initial PLS solution; (h) calcining the separated precipitate in order to obtain ammonia and molybdenum trioxide; and (i) recovering the released ammonia for its subsequent use in the method as a recirculated regenerant solution.

Description

PROCESS FOR THE RECOVERY OF MOLIBDEN TECHNICAL GRADE FROM DILUATED ACID SOLUTIONS OF LIXIVIATION (PLS), HIGHLY CONCENTRATED IN ARSENIC, FROM RESIDUES

METALLURGICAL

DESCRIPTIVE MEMORY

The present invention discloses a process for obtaining technical grade molybdenum trioxide from dilute acid leaching solutions (PLS) with a high concentration of arsenic, antimony or bismuth. Said solution is obtained through the leaching of metallurgical residues with high concentration of these impurities such as smelting powders.

More specifically, the present invention discloses a process for recovering molybdenum by ion exchange, through which molybdenum is separated from other metals also present in said solution by using ion exchange resins and controlled precipitation of As, Sb and Bi with magnesium or iron salts, followed by a precipitation of ammonium molybdate which is subsequently calcined to obtain technical grade molybdenum trioxide.

BACKGROUND OF THE INVENTION

A mining process or method is the sum of methods by which, from a deposit, metals and / or metal compounds of commercial purity and quality are obtained, in a cost-effective manner and with an acceptable environmental impact.

In the known leaching process, one or more mineral values contained in an ore or concentrate are dissolved, generally using an aqueous solution of the leaching agent. The term can also be extended to include the dissolution of secondary materials such as scrap, waste and scrap.

Leaching produces an aqueous solution rich in the extracted valuable metal ions (PLS) from which it must be possible to separate this metal and recover it with a high level of purity. In addition, a solid or gravel residue is produced which, ideally, has a sufficiently low content in the leached mineral values as to be discarded to a dump or tranque.

If the solid leaching residue is impregnated with salts or precipitates that may eventually release toxic agents once exposed to the environment, before being discarded, the residue must be properly treated in order to achieve the elimination or stabilization of the potential contaminating compounds. In some cases, leaching may have a different objective than the one stated above. For example when a concentrate is leached to selectively remove certain impurities, and thus increase the quality of the concentrate (for example the removal of copper from molybdenite concentrates).

In the processes of purification and enrichment of solutions, the leaching processes are not necessarily selective and, consequently, leaching solutions are produced that contain, in addition to the metal of interest, a varied range of impurities. This added to the fact that the concentration of the metal of interest may not be very high, makes it impossible to directly recover the metal of interest from the leaching solution, so that these solutions must be previously treated through purification and enrichment stages. Purification eliminates impurities, selectively isolating valuable elements. The enrichment of the solutions is also particularly beneficial for reducing the volumes of solution to be treated in the subsequent stages of metal recovery. This helps to reduce investment costs and increase recovery efficiency.

In the present invention, a process for recovering molybdenum in the form of molybdenum trioxide from dilute acidic solutions of leaching of metallurgical residues, with high arsenic, antimony or bismuth content, is disclosed. The object of the present invention is to recover molybdenum by ion exchange contained in leaching solutions diluted in molybdenum but which nevertheless contain a high concentration of arsenic, among others, in order to obtain a molybdenum product efficiently and economically profitably. In the prior art there are documents that disclose molybdenum recovery through ion exchange Such is the case of US Patent 4,891,067, which discloses a process for the selective separation of molybdenum present, in an acid solution having a pH of 2 and containing molybdenum and at least one of the elements within the group formed by Uranium, iron, arsenic, phosphorus, silicon and vanadium. Said process comprises contacting the acid solution with a stationary phase consisting of a resin with an active group of the oxime type and eluting said stationary phase with an alkaline solution to recover molybdenum. US 4,596,701 discloses a process for the purification of molybdenum trioxide, specifically discloses a method for the preparation of ammonium molybdate comprising contacting said concentrate with an aqueous solution of sulfuric acid, ammonium, sulfate and ammonium persulfate. to solubilize at least 2% of the molybdenum values of said concentrate.

There is also the Chilean patent application CL N ² 3137-2005 that discloses a process for the extraction of molybdenum and copper contained in solidified slags from fusion processes of copper concentrates. This document does not interfere with the present patent application since the slag does not contain arsenic, thus treating a different technical problem than the one addressed in the present patent application. None of the aforementioned processes interfere with the present application since said prior art documents show processes with different operating variables and therefore do not result in the benefits obtained with the present invention, which, as disclosed herein. Patent application, consist in the recovery of Mo0 ₃ technical grade efficiently and profitably from a high arsenic leaching solution. Through the present invention it is possible to obtain molybdenum trioxide with a technical grade, that is with a molybdenum content of over 58%, and with a content of non-standard metals, such as, As, Sb and Bi in values below 0, one %. DESCRIPTION OF THE INVENTION

The process of the present invention discloses the recovery of molybdenum by means of ion exchange, followed by an increase in the concentration of molybdenum in the regenerant, precipitation of impurities, precipitation of molybdenum, then drying and calcining to obtain the final product of molybdenum trioxide grade technician, as shown in Figure 1.

More specifically the present invention discloses a process for recovering about 70% or more specifically about 90% of the molybdenum present in the PLS as Mo0 ₃ technical grade. Specifically, the invention consists in the selective recovery of molybdenum, in the form of Mo0 ₃ , from the PLS solution generated from the leaching of smelting powders.

The present invention develops a molybdenum recovery process via ion exchange. The process was validated on a pilot scale and the fundamental aspects of the process, validation stages and the methodology of industrial scaling as disclosed in the present invention, demonstrate a novel and inventive height process. The ion exchange process consists of two stages that are repeated in ion exchange cycles: loading and regeneration of the resin; each followed by water wash stages. The resin loading process consisted of capturing the molybdenum ion in the form of molybdate from the acid leaching solution, while the resin regeneration process consisted of the re-extraction or discharge of the molybdate ion by an alkaline regenerating solution. The equations corresponding to the process are shown below:

Resin Loading Stage:

H ₂ Mo0 ₄ + 2 R-OH → R2-Mo0 ₄ + 2 H ₂ 0

Resin Regeneration Stage:

R ₂ -Mo0 ₄ + 2 NH ₄ OH → 2R-OH + (NH ₄ ) ₂ Mo0 ₄

Where R represents the ion exchange resin. The resin used in this process is of the weak base anionic type or weak / strong base anionic type, presenting functional groups selected from secondary, tertiary amines, tertiary / quaternary amines and polyamines.

Molybdenum extraction with ion exchange resins is carried out by contacting the PLS solution containing Mo with an anionic resin. This contact can be carried out discontinuously, adding the resin to the solution and stirring, or continuously using columns.

The extraction of Mo via ion exchange is highly selective for Mo, the solutions obtained by the leaching of metallurgical residues or foundry powders have elements and impurities that are co-extracted during the ion exchange process, in particular As, Sb and Bi are partially extracted during ion exchange and report in the charged regenerating solution, so it is necessary to send the charged solution to the impurity removal stage (see Figure 2).

Subsequently, the Mo loaded in the resin must be discharged by contacting the charged resin with an alkaline solution of ammonium hydroxide, where a Mo-laden solution contaminated in As, Sb or Bi is obtained which is partially co-extracted with the Mo The removal of these impurities can be carried out by precipitation with a magnesium or iron salt where a solid product is obtained that must be treated for a subsequent disposal and obtain a regenerating solution loaded in Mo and virtually free of impurities (Fig. 2 ). The chemical reactions using magnesium sulfate for arsenic, antimony and bismuth precipitations are:

3MgS0 ₄ + H ₃ As0 ₄ → Mg ₃ (As0 ₄ ) ₂ (s) + H ₂ S0 ₄

MgS0 ₄ + 2HSb0 ₂ → Mg (Sb0 ₂ ) ₂ (s) + H ₂ S0 ₄

MgS0 ₄ + 2HBi0 ₂ → Mg (Bi0 ₂ ) ₂ (s) + H ₂ S0 ₄ After the removal of As, Sb and Bi, there is a regenerating solution loaded free of impurities, which is then sent to the precipitation stage Mo (Fig. 2) through the addition of sulfuric acid, Mo precipitates as an ammonium molybdate with an efficiency greater than 70%, according to the following reaction: 8 (NH ₄ ) ₃ Mo0 ₄ + 6H ₂ S0 ₄ → (NH ₄ ) ₄ Mo ₈ 0 ₂₆ + 6 (NH ₄ ) ₂ S0 ₄ + 6H ₂ 0,

The last stage to obtain molybdenum tritoxide is the calcination stage, where the ammonium molybdate precipitate is subjected to controlled heating from 20 to 700 ° C. The temperature profile used (Figure 3) that allows obtaining in the calcination stage of the present invention considers: one . - Heating from 20 to 260 ° C and maintenance for approximately 20 minutes to 2 hours, for hydration water removal.

2. - Heating from 260 to 370 ° C and maintenance for approximately 20 minutes to 2 hours, for water and ammonia removal.

3.- Heating from 370 to 500 ° C and maintenance for approximately 20 minutes to 2 hours, to remove As as arsenic oxide.

4.- Heating from 500 to 700 ° C and maintenance for approximately 20 minutes to 2 hours, for decomposition and desorption of sulfur and arsenic. In summary, by means of the present invention it is possible to produce molybdenum trioxide with impurities, such as As, Sb and Bi with values less than 0.1%. More in detail the present invention has the following correlative steps:

one . - Contact the acidic leaching solution (PLS) previously filtered with a pH of less than 1, 6, with an anionic type ion exchange resin. As for example those indicated in Table 1.

2. - Wash the post-load resin with water to avoid possible precipitation of solids of elements that are dissolved in the PLS due to their acidity (such as iron) that could precipitate on contact with the regenerant due to the basic pH of the solution. ammonium hydroxide

3. - Extract the molybdenum from the ion exchange resin with alkaline solution of ammonium hydroxide in a concentration range of about 5 g / L to 150 g / L, reaching a pH of about 8 to 12, more preferably between 8.5 and 9.5, in the form of ammonium molybdate in solution.

4. - Wash the post discharge resin with water, step similar to step 2. 5.- Add a magnesium or iron salt, such as magnesium sulfate, magnesium chloride or ferric sulfate, to the solution obtained in step 3, to obtain a pulp with a precipitate of arsenic and other impurities, which is separated into 2 lines: the obtained ammonia solution containing the Mo passes to the molybdenum precipitation stage and the solid obtained is taken to a stage of despondency and external arrangement to the process of the present invention. 6. - Add H ₂ S0 ₄ to the ammonia solution obtained in step 5 to precipitate molybdenum in the form of ammonium molybdate ((NhU ^ MosC ^ e) in an acidic environment between pH 1, 5 and 4, more preferably at pH 3.3 and in a temperature range between 50 ² C and 90 ² C more preferably at 70 ² C.

7. - Separate the precipitate from step 6, by filtration of the molybdate and the solution obtained is recycled to mix with the initial PLS solution.

8. - Calcinate on a ramp or floor temperature between 20 to 700 ° C the filtrate of step 7 to molybdenum trioxide (Mo0 ₃ ) technical grade. At this stage, traces of sulfur, arsenic and ammonium are removed, so that the product meets the requirements of the market for technical grade molybdenum trioxide.

9. - Additionally recover the ammonia released in the calcination stage 8 in a condenser and / or gas scrubber, for its subsequent return to the process as a regenerant.

For the process of the present invention, weak anionic ion exchange resins (WBA) and weak / strong mixtures (WBA / SBA) were tested. By way of example and without limiting the invention, the resins indicated in Table 1 were worked on. After a large number of batch and column tests, the results indicated in Table 2 are obtained.

Table 1 . Specifications of the resins used for batch and column tests.

Appearance Size Group Capacity

Resin Type Base Structure

cia (μιτι) Functional (eq./L)

A 170 / Spherical Macroporous Amine 1, 3 (base

Free WBA 875 +/- 125

4675 (pearls) PES / DVB comoleia libre)

A SBA / Spherical Macroporous Amina 3.8 (base

Chloride 800 to 1300

100 Mo WBA (beads) PES / DVB tertiary CI-)

Macroporous Amina

SBA / Spherical 1, 3 (base

Free 64 MP 590 +/- 50 PES / tertiary DVB /

WBA (pearls) free) Quaternary

Spherical Macroporous Amine 1, 7 (base

MP 62 WBA Free 470 +/- 60

(pearls) PES / DVB tertiary free)

Spherical 3.4 (base

A 365 WBA Free> 400 Acrylate Gel / DBV Polyamine

(pearls) free) Table 2. Results obtained for column tests.

As shown in Table 2, all resins have an acceptable percentage of affinity for Mo, highlighting resins MP64, MP62 and A100Mo. However, resins A170 / 4675 and MP62 stand out in the capacity of Mo re-extraction from the resin.

The variables considered relevant for obtaining a product with less impurities were those reflected in Table 3. Table 3. Operation variables analyzed for impurity precipitation and Mo.

level

Variable

Low High

Mo concentration in the charged regenerating solution * 5,000 mg / L = 10,000 mg / L pH of the feed solution at precipitation of As = 8.5 = 9.5

Temp. of the feed solution to precipitation from As Ambiente 60 ^a C

Residence time for As precipitation 30 min 120 min

As concentration in the precipitation feed of

2,500 mg / L = 8,000 mg / L As

Sb concentration in the precipitation feed of

39 mg / L = 150 mg / L Sb

Concentration of Bi in the feed at precipitation of Bi 29.2 mg / L = 64.9 mg / L pH of the feed solution at precipitation of Mo = 7.3 = 8.5 pH of the residual precipitation solution of Mo (at 70

= 2.8 = 3.3 BC)

Residence time for precipitation of Mo 30 min 120 min APPLICATION EXAMPLE

330 L of PLS solution was contacted with 6 L of a Lanxess® MP-62 resin (by way of example and without limiting the invention). The resin was placed in a static column that allowed the passage of PLS solution at a flow of 4.5 L / h, after this period a "refining" or Mo-free solution was obtained, as shown in Table 4 .

Subsequently, 12 L of water was passed at a flow of 4.5 L / h to wash the resin. After washing, the resin was regenerated, extracting the captured Mo, passing an alkaline solution of ammonium hydroxide (50 g / L of NH ₄ OH) through the column. This procedure was carried out during 47 loading / unloading cycles, using 330 L of fresh PLS solution in each cycle. The regenerating solution was not renewed since its concentration is increased after each cycle; maintaining a pH close to 9. Table 4. Concentrations of PLS solutions before and after Mo extraction

The charged regenerating solution was fed to a 5 L impurity precipitation reactor, contacting it with 215.8 g magnesium sulfate (5% above the stoichiometric value). The pulp was allowed to react for 120 min. The solid was filtered and washed to be disposed. The results obtained showed a high efficiency of impurity precipitation, obtaining a solution with only 41 mg / L of As and with concentrations of Sb and Bi under 10 mg / L. There was no co-precipitation of Mo.

Then the treated solution or clean solution was charged to the Mo precipitation reactor, where it was heated to 60 ² C. In this condition sulfuric acid was added bringing the solution to pH 3.3.

For this condition a Mo precipitation of 70% was obtained. Solid that was filtered and washed with water in a ratio of 3 water to 1 solid by weight. From the previous procedure a solid was obtained with the concentrations indicated in Table 5. Table 5. Ammonium molybdate concentrations.

This solid was subsequently calcined in an electric oven for 3.5 h, reaching a temperature of 650 ² C. The concentration results for the product are shown in Table 6.

Table 6. Concentrations of elements in the molybdenum trioxide produced.

By the present invention the final molybdenum product exceeds conventional commercial concentration standards. The purity obtained is compatible with the conventional market of technical grade molybdenum trioxide.

Claims

1 .- Process for the recovery of technical grade molybdenum from diluted acid leaching solutions (PLS), highly concentrated in arsenic, from metallurgical waste, CHARACTERIZED because it comprises the stages of:

a.- contacting a previously filtered acid leaching solution (PLS) from the leaching of the smelting powders with an anionic ion exchange resin;

b.- wash the resin loaded in step (a) with water;

c- extracting the molybdenum from the ion exchange resin with an alkaline regenerating solution of ammonium at a pH value between 8 and 12, to form ammonium molybdate in solution; This solution is conveniently recirculated to adjust the molybdenum concentration;

d.- wash the resin discharged in step (c) with water;

e.- add magnesium and / or iron salts to the ammonia solution recovered in step (c), to obtain a precipitate of Mg ₃ (As0) 2 and / or FeAs0 which is taken to the arsenic abatement stage, and a solution containing the ammonium molybdate in solution;

f.- add sulfuric acid to the ammonia solution obtained in step (e), free of arsenic, to precipitate molybdenum in the form of ammonium molybdate ((NhU ^ MosC ^ e) in acidic environment at a pH value between 1, 5 and 4;

g.- separating the precipitate formed in step (f), by filtration of the molybdate and recirculating the solution obtained to the initial solution of PLS;

h.- calcinate the precipitate separated in step (g) to obtain molybdenum trioxide (Mo0 ₃ ), and ammonia; Y

i.- recover the ammonia released in step (h) for its subsequent return to the process as a recirculated regenerating solution.

2. Process for the recovery of technical grade molybdenum according to claim 1, CHARACTERIZED because the ion exchange resin used is selected from weak base or weak / strong base type resins, presenting functional groups selected from tertiary amines, amines tertiary / quaternary and polyamines.

3. - Process for the recovery of technical grade molybdenum according to claim 2, CHARACTERIZED because the ion exchange resin is preferably selected from resins A170 / 4675, MP64, MP62, A100 Mo or A 365.

4. - Process for the recovery of technical grade molybdenum according to claim 1, CHARACTERIZED because in step (e) magnesium sulfate is preferably used.

5. - Process for the recovery of technical grade molybdenum according to claim 1, CHARACTERIZED because the ammonia regenerating solution used in step (c) has a pH value between 8.5 and 9.5.

6. Process for the recovery of technical grade molybdenum according to claim 1, CHARACTERIZED because the calcining step (h) is carried out by means of temperature floors.

7. - Process for the recovery of technical grade molybdenum according to claim 6, CHARACTERIZED because the calcining step (h) is carried out between 20 and 700 ° C.

8. - Process for the recovery of molybdenum technical grade according to claim 1, CHARACTERIZED because the recovery of the ammonia released in step (i) is carried out in a condenser.

9. - Process for the recovery of technical grade molybdenum according to claim 1, CHARACTERIZED because the recovery of the ammonia released in step (i) is carried out in a gas scrubber.