WO2010022481A1

WO2010022481A1 - Electrochemical method for nickel and cobalt extraction from oxide ores

Info

Publication number: WO2010022481A1
Application number: PCT/BG2008/000013
Authority: WO
Inventors: Stoian Borissov Mitov; Bozhidar Stoyanov Mashev
Original assignee: Stoian Borissov Mitov; Bozhidar Stoyanov Mashev
Priority date: 2008-08-28
Filing date: 2008-08-28
Publication date: 2010-03-04

Abstract

The method for extraction of nickel and cobalt from oxide ores comprises the steps of: pulp of ore and sulphuric acid solution is subjected to treatment in the cathode compartment of an electrolytic cell maintaining oxidation reduction potential at 200 to 300 mV which provides the reduction Of Fe³⁺ from the Fe₂O_3, contained in the ore, to Fe²⁺, thus iron, nickel and cobalt passing into the said sulphuric acid solution; the pulp, treated in the cathode compartment, is fed to the electrolytic cell anode compartment wherein Fe²⁺ oxidizes to Fe³⁺; the pulp is withdrawn from the anode compartment and ammonia is added to the pulp in order to precipitate iron and to neutralize the free sulphuric acid; the liquor obtained is separated from the solid residue; nickel and cobalt are extracted from said liquor.

Description

ELECTROCHEMICAL METHOD FOR NICKEL AND COBALT EXTRACTION FROM OXIDE ORES

TECHNICAL FIEDL

The present invention relates to a method for nickel and cobalt extraction from oxide ores and more specifically to a hydrometallurgical method for nickel and cobalt extraction from oxide ores which contain nontronitic serpentinites, chlorite, magnetite, hematite, goethite, and jarosite wherein the main nickel content in the ore substitutes the bivalent iron in the said minerals.

BACKGROUND OF THE INVENTION

U.S. Patent 6,379,637 describes an atmospheric acid leaching method for extraction nickel and cobalt from highly serpentinized saprolitic fractions of nickel laterite deposits that are generally too low in nickel and cobalt, comprising the steps of: pulping a finely ground highly serpentinized saprolite ore with water to produce a pulped ore with a density of between 15 % and 33 % solids; heating said pulp ore; adding sulphuric acid to the heated pulped ore at atmospheric pressure in an amount of at least about 80 % by weight of the ore; agitating the mixture for an effective period of time, whereby metal oxides are leached from the heated pulped ore mixed with sulphuric acid to produce a hot leach pulp; separating said hot leach pulp into liquid and solids, wherein said liquid contains sulphates of said metals; neutralizing said liquid with limestone to precipitate dissolved iron contained therein; and recovering an intermediate product containing nickel and cobalt from said liquid.

U.S. Patent 4,410,498 describes a method for extraction of nickel and cobalt from serpentinic laterite ores by leaching the ore with an aqueous solution of sulphuric acid while adding to the solution a reducing agent to maintain the redox potential of the solution at a value between 200 and 400 millivolts, measured against the saturated calomel electrode.

K.R. Patent Publication No. 890002035 B discloses a method for extraction of nickel from the low quality laterite ore by leaching electrochemically in the electrolysis cell with a separator between cathode chamber and anode chamber. Nickel is recovered from 0.01-10.0 mol sulphuric acid solution with blowing the sulfurous acid gas. Anode chamber consists of 0.01-10.0 mol sulphuric acid solution including source ore powder under 10 mesh.

A disadvantage of the known methods is the low extraction degree of nickel and cobalt while treating low-grade oxide ores, containing the said metals, and more specifically while treating nontronitic serpentinites wherein the main nickel content in the ore substitutes the bivalent iron in the present minerals.

SUMMARY OF THE INVENTION

An object of the present invention is a hydrometallurgical method for nickel and cobalt extraction from oxide ores which provides high-degree extraction of nickel and cobalt from low-grade ores with low content of the said metals.

According to the present invention, the method for nickel and cobalt extraction from oxide ores comprises the steps of: pulp of ore and sulphuric acid solution with concentration of 50 to 250 g/1 is subjected to treatment in the cathode compartment of an electrolytic cell at a temperature of 55⁰C to 85⁰C maintaining oxidation-reduction potential at 200 to 300 mV which provides the reduction of Fe³⁺ from the Fe₂O₃, contained in the ore, to Fe²⁺, thus the contained iron, nickel and cobalt passing to the said sulphuric acid solution; the pulp, treated in the cathode compartment, is fed to the electrolytic cell anode compartment wherein Fe²⁺ oxidizes to Fe³⁺; the pulp is withdrawn from the anode compartment of the electrolytic cell and ammonia is added to the pulp in order to precipitate iron and to neutralize the free sulphuric acid; the neutralized liquor obtained is separated from the solid residue; and nickel and cobalt are extracted from said neutralized liquor.

In one embodiment of the present invention, the cathode compartment is fed with a portion of pulp, comprising a mixture of sulphuric acid solution and ore, and the anode compartment is fed with a portion of pulp which has been already treated in the cathode compartment, and having the electrolytic cell operating, both processes, the process of Fe³⁺ to Fe²⁺ reduction in the cathode compartment, and the process of Fe³⁺ to Fe²⁺ oxidation in the anode compartment, take place simultaneously. In another embodiment of the present invention, the anode compartment is separated from the cathode compartment in the electrolytic cell by a diaphragm. In an alternative embodiment of the present invention, the anode and the cathode compartments are separated by an impenetrable separator, the electric circuit being closed via a salt bridge.

The advantages of the method for nickel and cobalt leaching from oxide ores, and more specifically from nontronitic serpentinites, reveal in the following: during the treatment of pulp of ore and sulphuric acid solution in the cathode compartment of the electrowinning cell under conditions providing reduction of Fe³⁺ from the contained in the ore Fe₂O₃ to Fe ⁺, the structure of the crystal lattice of the magnetite and the other iron and magnesium minerals is destroyed which enhances the penetration of sulphuric acid solution into the minerals, leads to accelerated desorption of nickel and cobalt from those minerals, and to dissolution of nickel and cobalt in the sulphuric acid solution. As a result, nickel and cobalt extraction grade in the sulphuric acid solution is increased. The subsequent pulp treatment in the anode compartment of the electrowinning cell, wherein Fe²⁺ oxidizes to Fe³⁺, ensures more complete process of hydrolysis of the ferric ions, and respectively greater iron recovery from the solution at lower pH values which from the other hand reduces the probability in occurrence of partial nickel hydrolysis.

DETAILED DESCRIPTION OF THE INVENTION

Treated ochre nontronitic serpentinite with a general formula of (Na,K,Ca)Fe₂[(Si, Al)₄O₁₀] (OH)₂nH₂O contains 36.68% Fe₃O₄ and 35.84% SiO₂, low concentration of Mg₀ - 6.26%, and low concentration of precious components: Ni -

0.712 %, and Co - 0.034% which substitute the iron in the mineral structure. The average Fe content is 29.6%.

The ore is subjected to grinding and water in a solid to liquid ratio = 4:1 is fed to fraction of -0.080 mm. The mixture is pulped, and sulphuric acid is added to the resultant pulp up to concentration in the range of 50 to 250 g/1.

The treatment of pulp takes place in an electrolytic cell with a cathode of lead or of stainless steel or of titanium or of base metal with platinum coating.

In an embodiment of the invention, the anode compartment and the cathode compartment are separated by a filter fabric diaphragm. The pulp of oxide ore and sulphuric acid solution with concentration of the sulphuric acid between 50 and 250 g/1 is fed into the cathode compartment of the electrolytic cell, and is treated at atmospheric pressure for 2 to 4 hours at temperature of 55-85⁰C, at continuous agitating and maintenance of 200 to 300 mV oxidation-reduction potential which provides reduction of Fe³⁺ from the contained in the ore Fe₂O₃ to Fe²⁺. The anode and the cathode current density is between 200 and 600 A/m², and the cell voltage is between 4 and 7.5 V. The crystal lattice structure of the magnetite and the other iron and magnesium minerals is destroyed during the electrochemical reduction of Fe³⁺ to Fe²⁺. As a result, the process of dissolution of nickel and cobalt in the sulphuric acid solution is enhanced, and the extraction grade of those metals is increased. Iron passes into the sulphuric acid solution.

There is no necessity of special regulation of the water levels to prevent from water interpenetration from one chamber into the other when using diaphragm for separation of the cathode compartment from the anode compartment.

In an alternative embodiment of the present invention, an electrolytic cell is used wherein the anode compartment and the cathode compartment are separated by an impenetrable separator, and the electric circuit is closed via a salt bridge. The treatment of the pulp of oxide ore and sulphuric acid solution with concentration of 50 to 250 g/1 takes place in the cathode compartment of an electrolytic cell for 2 to 4 hours at temperature of 55 to 85 C, the pulp being continuously agitated, and the oxidation-reduction potential being maintained at 200 to 300 mV thus providing reduction of Fe³⁺ from the contained in the ore Fe₂O₃ to Fe²⁺. The anode and the cathode current density is 10 to 20 A/m , and the cell voltage is between 10 and 20 V. Under such treatment in the cathode compartment of the electrolytic cell, Fe³⁺ is reduced to Fe²⁺. As a result iron, nickel, and cobalt are solubilized. The pulp, treated in the cathode compartment, is conveyed to the anode compartment of the electrolytic cell wherein Fe²⁺ oxidizes to Fe³⁺.

In both alternative embodiments of the present invention, nickel and cobalt dissolution process takes place in a reduction medium, created in the cathode compartment of an electrolytic cell by maintaining of an oxidation-reduction potential in the range of 200-300 mV, and the anode compartment is filled with a portion of pulp which has been already treated in the cathode compartment of the electrolytic cell. In the beginning of the process when the first portion of pulp of sulphuric acid solution and oxide ore is treated in the cathode compartment of the electrolytic cell, the anode compartment is fed with sulphuric acid solution with the same sulphuric acid concentration as it is in the cathode compartment. Thereafter, the anode compartment and the cathode compartment are fed simultaneously with pulp: the portion of pulp which has been already treated in the cathode compartment is conveyed to the anode compartment, and the cathode compartment is fed with a new portion of pulp. Both processes, the dissolution and the oxidation, take place simultaneously in the same electrolytic cell. Thus, the electrolytic cell operates in a mode in which the process of pulp treatment in the cathode compartment, which process is used for the reduction of Fe³⁺ to Fe²⁺ and for nickel and cobalt dissolution, takes place simultaneously with the process of oxidation of Fe ⁺ to Fe³⁺ in the anode compartment which is fed with a portion of pulp, being already treated in the cathode space. Thus, in passing of solution from a compartment to the other, dilution of solutions is prevented. The pulp, withdrawn from the anode compartment, is heated to a temperature of 75-85⁰C, and ammonia is added in an amount, stoichiometric to the iron content. As a result, the main amount of iron is precipitated, and the free sulphuric acid is neutralized.

Upon separation of the liquid from the solid phase, the iron content in the resultant liquor is up to 2-3 g/1. Nickel and cobalt are recovered from the liquor using conventional methods such as extraction, liquid extraction, precipitation, and crystallization.

The degree of nickel extraction is 90 - 92 %, and of cobalt is 80-86 % in the treatment of very low-grade nickel- and cobalt-bearing oxide ores. The method in accordance with the present invention is explained by the following non-limiting examples. Example 1.

The method in accordance with the present invention is used for processing of oxide nickel-bearing ore which contains nontronitic serpentinites, chlorite, and magnetite. The ore contents: 0.74% nickel, 35-38% iron, 0.051 % cobalt, 1.95 % magnesium, and 1.29 % aluminium. The nickel is not presented by natural minerals, and it substitutes the bivalent iron in the specified minerals. The ore is subjected to grinding and water in a solid to liquid ratio = 4:1 is fed to fraction of -0.080 mm. Upon pulping sulphuric acid is added to concentration of 250 g/1.

The treatment of pulp takes place in an electrolytic cell with a stainless steel cathode and lead anode which are of the same surface. The anode compartment is separated from the cathode compartment by a filter fabric diaphragm.

A portion of pulp is fed to the cathode compartment of the electrolytic cell, and the anode compartment is fed with a portion of pulp, already treated in the cathode compartment. The treatment of both portions of pulp is carried out simultaneously for 4 hours at 60 C temperature, and at continuous agitation. The cathode and the anode current densities are 400 A/m , and the cell voltage is 7.5 V. Under these conditions a reduction medium is created in the cathode compartment of an electrolytic cell, and an oxidation-reduction potential in the range of 200-300 mV is maintained. As a result,

Fe³⁺ reduces to Fe²⁺ under the action of the electric current, and iron, nickel, and cobalt are solubilized. Simultaneously Fe²⁺ oxidizes to Fe³⁺ in the anode compartment which is charged with a portion of pulp already treated in the cathode compartment.

Upon completion of the above processes, the said portion of pulp is withdrawn from the anode compartment out of the electrolytic cell, the treated in the cathode compartment portion of pulp is pumped to the anode compartment, and the cathode compartment is charged with a new portion of pulp of ore and sulphuric acid solution.

The results of a chemical analysis exhibit the following: upon filtration the catholyte contains nickel, 1.2 g/1; iron, 24 g/1; the solid residue contains nickel 0.15 % and iron 13.5 %. Upon filtration the anolyte contains nickel, 1.15 g/1 and iron, 23 g/1; the solid residue contains nickel 0.15 % and iron 14.2 %. This data shows that the pulp composition is not changed in the anode compartment and that just oxidation of the dissolved iron occurs.

Energy consumption is 11600 kW h per ton of nickel.

Precipitation of the dissolved iron is carried out after pulp withdrawal from the anode compartment of the electrolytic cell. The pulp is heated to a temperature of 80⁰C, and 25 % ammonia solution is fed for precipitation of the dissolved iron and neutralization of the free sulphuric acid. Upon separation of the liquid from the solid phase by filtration, the resultant liquor contains nickel 1.05 g/1, cobalt 0.1 g/1, iron 2.7 g/1, magnesium 0.480 g/1, and aluminium 0.081 g/1. The solid residue contains nickel 0.116 % and cobalt 0.0076 %.

The degree of nickel extraction is 92 %, and of cobalt is 85%.

Mass loss relative to the original ore mass is in the range between 30 to 60%. The liquor is subjected to three-stage extraction using LIX84-I. The pH is priorly adjusted to 2.8-3.2. The concentrated extractant is regenerated in two stages with a solution of sulphuric acid.

Example 2.

The method in accordance with the present invention is used for processing of oxide nickel-bearing ore which contains nontronitic serpentinites, chlorite, and magnetite. The content of nickel is 0.74%, of iron 35-38%, of cobalt 0.051 %, of magnesium 1.95 %, and of aluminium 1.29 %. The nickel is not presented by natural minerals, and it substitutes the bivalent iron in the specified minerals.

The ore is subjected to grinding and water in a solid to liquid ratio = 4:1 is fed to fraction of -0.080 mm. Upon pulping sulphuric acid is added to concentration of 250 g/1.

The treatment of pulp takes place in an electrolytic cell with lead cathode and lead anode which are of the same surface. The cathode compartment is separated from the anode compartment by an impermeable diaphragm, and the current connection is effected via a high resistance liquid salt bridge.

A portion of pulp is fed to the cathode compartment of the electrolytic cell, and the anode compartment is fed with a portion of pulp, already treated in the cathode compartment. The treatment of both portions of pulp is carried out simultaneously for 4 hours at 60⁰C temperature, and at continuous agitation. The cathode and the anode current densities are 16 A/m² and the cell voltage is 19 V. Under these conditions a reduction medium is created in the cathode compartment of an electrolytic cell, and an oxidation-reduction potential in the range of 250-270 mV is maintained. As a result, Fe³⁺ reduces to Fe²⁺ under the action of the electric current, and iron, nickel, and cobalt are solubilized. Simultaneously Fe²⁺ oxidizes to Fe³⁺ in the anode compartment which is charged with a portion of pulp already treated in the cathode compartment. Upon completion of the above processes, the said portion of pulp is withdrawn from the anode compartment out of the electrolytic cell, the treated in the cathode compartment portion of pulp is pumped to the anode compartment, and the cathode compartment is charged with a new portion of pulp of ore and sulphuric acid solution.

Energy consumption is 7600 kW h per ton of nickel.

The withdrawn from the anode compartment pulp is heated to a temperature of 80⁰C, and 25 % ammonia solution is added to it. Upon filtration the resultant liquor contains nickel 0.98 g/1, cobalt 0.1 g/1, iron 2.5 g/1, magnesium 0.300 g/1, and aluminium 0.05 g/1.

The degree of nickel extraction is 87 %, and of cobalt is 81%.

The liquor is subjected to three-stage extraction using LIX84-I for nickel and cobalt recovery, pH being priorly adjusted to 2.8-3.2. The concentrated extractant is regenerated in two stages with a solution of sulphuric acid.

Example 3.

The method in accordance with the invention is used for processing of oxide nickel-bearing ore which contains nontronitic serpentinites, chlorite, and magnetite. The content of nickel is 0.74%, of iron 35-38%, of cobalt 0.051 %, of magnesium 1.95

%, and of aluminium 1.29 %. The nickel is not presented by natural minerals, and it substitutes the bivalent iron in the specified minerals.

The ore is subjected to grinding and water in a solid to liquid ratio = 4:1 is fed to fraction of -0.080 mm. Upon pulping sulphuric acid is added to concentration of 150 g/1.

The electrolytic cell used is equipped with lead cathode and lead anode which are of the same surface. The cathode compartment is separated from the anode compartment by an impermeable diaphragm, and the current connection is effected via a high resistance liquid salt bridge. A portion of pulp is fed to the cathode compartment of the electrolytic cell, and the anode compartment is fed with a portion of pulp, already treated in the cathode compartment. The treatment of both portions of pulp is carried out simultaneously for 4 hours at 60⁰C temperature, and at continuous agitation. The cathode and the anode current densities are 4 A/m² and the cell voltage is 10.2 V. Under these conditions a reduction medium is created in the cathode compartment of an electrolytic cell, and oxidation-reduction potential in the range of 220 to 250 mV is maintained. As a result, Fe³⁺ reduces to Fe²⁺, and iron, nickel, and cobalt are solubilized. Simultaneously Fe²⁺ oxidizes to Fe³⁺ in the anode compartment which is charged with a portion of pulp already treated in the cathode compartment. Upon completion of the above processes, the said portion of pulp is withdrawn from the anode compartment out of the electrolytic cell, the treated in the cathode compartment portion of pulp is pumped to the anode compartment, and the cathode compartment is charged with a new portion of pulp of ore and sulphuric acid solution.

Energy consumption in this Example is 1940 kW h per ton of nickel.

The results of a chemical analysis exhibit the following: upon filtration the catholyte contains nickel 1.2 g/1 and iron 23 g/1; the solid residue contains nickel 0.06 % and iron 17.5 %. Upon filtration the anolyte contains nickel 1.2 g/1 and iron 23 g/1; the solid residue contains nickel 0.06 % and iron 17.6 %. This data shows that the pulp composition is not changed in the anode compartment and that just oxidation of the dissolved iron occurs.

The withdrawn from the anode compartment pulp is heated to temperature of 80⁰C, and 25 % ammonia solution is added to it. Upon filtration the resultant liquor contains nickel 1.14 g/1, iron 2.8 g/1, magnesium 0.390 g/1, and cobalt 0.1 g/1.

The degree of nickel extraction is 96 %, and of cobalt is 86%.

The liquor is subjected to three-stage extraction using LIX84-I for nickel and cobalt recovery under the conditions described in Example 1. While using salt bridge the energy consumption is very low. Furthermore, the chambers obtain higher working volume due to the lack of diaphragm which enhances the process of pulp agitation in the chambers.

Claims

1. A method for nickel and cobalt extraction from oxide ores, characterized in that said method comprises the steps of: pulp of ore and sulphuric acid solution with concentration of 50 to 250 g/1 is subjected to treatment in the cathode compartment of an electrolytic cell at a temperature of 55⁰C to 85⁰C maintaining oxidation-reduction potential at 200 to 300 mV which provides the reduction of Fe³⁺ from the Fe₂O₃, contained in the ore, to Fe²⁺, thus the contained iron, nickel and cobalt passing to the said sulphuric acid solution; the pulp, treated in the cathode compartment, is fed to the electrolytic cell anode compartment wherein Fe²⁺ oxidizes to Fe³⁺; the pulp is withdrawn from the anode compartment of the electrolytic cell and ammonia is added to the pulp in order to precipitate iron and to neutralize the free sulphuric acid; the liquor obtained is separated from the solid residue; and nickel and cobalt are extracted from said liquor.

2. A method according to claim 1, characterized in that the cathode compartment is fed with a portion of pulp, comprising a mixture of sulphuric acid solution and ore, and the anode compartment is fed with a portion of pulp which has been already treated in the cathode compartment, and having the electrolytic cell operating, both processes, the process of Fe³⁺ to Fe²⁺ reduction in the cathode compartment, and the process of Fe to Fe oxidation in the anode compartment, take place simultaneously.

3. A method according to claims 1 and 2, characterized in that the anode compartment and the cathode compartment of the electrolytic cell are separated by a diaphragm.

4. A method according to claims 1 and 2, characterized in that the anode compartment and the cathode compartment of the electrolytic cell are separated by an impenetrable separator, and the electric circuit is closed via a salt bridge.