WO2003006695A1

WO2003006695A1 - Hydrometallurgy method for leaching oxidised ores and metal recovery

Info

Publication number: WO2003006695A1
Application number: PCT/MA2002/000001
Authority: WO
Inventors: Mohamed Bakkar
Original assignee: Mohamed Bakkar
Priority date: 2001-07-10
Filing date: 2002-05-03
Publication date: 2003-01-23
Also published as: MA25367A1; WO2003006695B1

Abstract

The invention concerns a hydrometallurgy method comprising, in a first step, leaching oxidised ore with an aqueous solution inert with respect to the acid or basic gangue, containing amine and/or ammonium carboxylate(s) and/or carbonate(s), selected on the basis of their complexing power with respect to the metals being treated, in particular copper, iron, zinc, cadmium, nickel, cobalt, manganese, silver and/or gold and/or any other transition metal of the periodic table of chemical elements, the metal(s) being brought to the adapted degree of oxidation by air or oxygen injection, and, in a second step, precipitating the metal salts by standard methods, the metal-depleted solution being reusable, after regeneration if required, with the usual equipment in the fields of hydrometallurgy and chemical engineering.

Description

HYDROMETALLURGY PROCESS FOR LEACHING OXIDIZED ORES AND RECOVERING METALS

The present invention relates to a process for the hydrometallurgy of leaching and recovery of metals contained in oxidized ores, their flotation concentrates, the ash from roasting of sulphides or metallic waste, using a solution containing fixed salts. amines and / or ammonia and carboxylic and / or carbonic acids.

The metals are copper, zinc, cadmium, nickel, cobalt, silver, gold, manganese iron and other transition metals from the periodic table of chemical elements.

The materials to be treated contain metal oxides, their carbonates, silicates and / or other weak acid salts.

It is known that the hydrometallurgy of oxidized ores mainly implements the leaching of ores by acids or bases. In such processes, gangue interferes in the metal dissolution reaction and increases the consumption of reagents. Thus, the presence of a basic gangue (carbonates and others) leads to an overconsumption of the acid used. Likewise, an acid gangue (silicates or others) causes losses of reagents when the leaching is carried out using a base.

The ammonia process is based on the formation of complexes of this product with oxidized metals, which eliminates the parasitic reactions of the gangue, whether acid or basic. However, the volatility of the ammonia complicates the installation installations in order to reduce the losses of reagent. It hinders the use of gases such as air, if it is necessary to oxidize the metals during the leaching step, hydrogen, sulfur dioxide or carbon monoxide during the precipitation step of the solubilized metals. In addition, the step of recovering leached metals requires the evaporation of the ammonia and its recycling in order to avoid the use of significant excess of reagents to neutralize the large excess of ammonia required by the leaching step. , which translates into a high expenditure on fuel.

Finally, cyanidation is used mainly in the processing of gold and silver ores and involves the formation of complexes of these metals with cyanide. In addition to the toxic nature of the reagent used, cyanidation takes place in a basic medium (pH 1 1 to 12) in order to limit the hydrolysis of cyanide, which limits the use of acid gas (carbon dioxide or sulfurous) for the precipitation of dissolved metals. In addition, the high stability of the complexes requires severe pressure and temperature conditions for precipitation by hydrogen.

The present invention is a hydrometallurgy process which uses an aqueous solution containing neutral and thermally stable carboxylate and / or carbonate salts of amines and / or ammonium, selected according to their complexing force by relation to the metal or metals to be recovered They are not very volatile by entrainment by gas streams and have little or no affinity with the gangue, whether acid or basic These salts form a homologous series of salts of generic formula R-CO2 H -R ', the amine can be primary, secondary or tertiary

Ammonia carbonate, the first element in this homologous reagent series, is excluded from the scope of the present invention, this product being thermally unstable, decomposable by gas streams and giving a solution with a high pH.

The solution of carboxylates is characterized by a moderate pH, of the order of pH 7. Its low acidity and its low basicity make that its behavior is neutral with respect to basic or acid gangues. It is also not very aggressive compared to certain materials, in particular concrete and in this case it eliminates the use of antacid coatings Its buffering effect compared to bases and acids allows the absorption of significant quantities of acid gases for the precipitation of dissolved metals

The present invention consists of a hydrometallurgy process comprising two main steps, a leaching followed by precipitation, the solution being recycled by adjusting its solvent power. Many operating parameters allow the optimization of the implementation of the process. depending on the nature of the raw material treated, the economic conditions of the site and the chemical form of the metal or metals recovered.

J_ Leaching

Dissolution is a reaction of formation of complexes between the components of the reactants of the solution and the metal (or metals) contained in the solid phase. It's a- slow reaction limited by diffusion of reagents into the solid and reaction products into the solution.

In practice, it depends on the particle size of the solid, the concentration of the solution, the temperature, the contact time and the power of the stirring.

The metal or metals which are the subject of the treatment are optionally brought to the appropriate oxidation degrees, in particular by the injection of air or oxygen for the dissolution of the metals in metallic form or of refractory lower oxides and in this case the leaching depends dissolved oxygen content and / or pressure

In accordance with chemical engineering and hydrometallurgical practices, leaching can be carried out in a single reactor or in a multi-stage reactor system for rational exhaustion of the raw material and rational enrichment of the solution

The reactor (or reactors), their equipment and their instrumentation are those usually used in hydrometallurgy or in chemical engineering for solid-liquid contacts and. possibly solid-gas

2_ Precipitation

The rich solution resulting from the leaching step (leaching) lends itself to conventional techniques for recovering metals such as solvent extraction, electrolysis, precipitation by hydrogen or hydrogen sulfide and case hardening.

The rich solution, having a moderate pH (of the order of 7) and containing unstable metal complexes, makes it possible to implement precipitation methods more specific to the process which is the subject of the present invention.

a) precipitation with carbon dioxide

In the present process, the dissolution of carbonates from metals by the formation of complexes under conditions close to equilibrium obeys the "law of mass action". As a result, the injection of carbon dioxide under moderate pressure shifts the equilibrium towards the formation and precipitation of neutral carbonates or basic carbonates of the metal (metals) of the hxiviat

b) precipitation with sulfur dioxide

The sulfur dioxide is soluble in the solution used in the present process and destroys the leaching complexes by formation, according to the operating conditions, of insoluble sulfites, insoluble lower oxides and / or mixed salts combining oxides, sulfites and / or sulphates

In the case of precipitation with carbon dioxide or sulfur dioxide, the precipitate can be calcined and the recovered gas can be recycled for further precipitation

3_ Recycling the poor solution

The precipitation step regenerates a poor metal solution which is recycled to the leaching step. The dissolution power of this solution can be adjusted, if necessary, by eliminating the excess of reagents used in the solution. precipitation step Ventilation is sufficient after precipitation with carbon dioxide and an excess of sulfur dioxide is eliminated by contact with calcareous sand, crushed limestone or lime

Another possibility of increasing the leaching power of the recycled solution is to limit the precipitation rate, thus reducing the excess of precipitation reagents

4 Process optimization

The dimensioning of a leaching and precipitation installation implementing the present invention depends on several parameters which make the present invention a flexible (versatile) process, adaptable to different economic conditions of the site of the industrial unit.

Laboratory tests make it possible in particular to select the carboxylates and / or carbonates of amines and / or ammonium most suited to the raw material, the energy requirements for crushing and grinding, the concentration of the leaching solution, the power of the stirring, the temperature and the leaching time, the rate of in _j ection of air or oxygen, selection of a precipitating gas (CO2, SO2, H2, or H 2 S) or any other recovery method (case hardening, solvent extraction, electrolysis), calcination temperature, etc., with the aim of optimizing the economic constraints of the implementation of the process

5 Example case of oxidized copper ores

Oxidized copper ores are the result of more or less pronounced natural degradation (alteration) of sulfur deposits They mainly contain malachite, azuπte and cupπte, accompanied by associated metals such as iron and precious metals

One of the carboxylates selected under the present invention for the treatment of copper is ammonium acetate.

In the case of a very weathered ore, composed essentially of malachite in a very porous ferruginous and carbonated gangue, the leaching is rapid from ambient temperature with release of carbon dioxide, without crushing or grinding It is accelerated as soon as the temperature increases, for example under the effect of the sun

A less altered, mixed ore (malachite, azuπte, cupπte), in a silico-magnesian gangue not very permeable requires crushing and grinding. The slow dissolution of copper is accelerated by the rise in temperature, without reaching boiling. The azuπte is more difficult to treat than malachite, the extraction of the cupπte and silver is improved by the injection of air or oxygen.

In the case of a mixed ore of oxides and sulphides which are normally difficult to float, the direct leaching of the ore or a bulk flotation concentrate by the present process makes it possible to separate the oxides which are dissolved in the oxides , sulphides which remain in the leaching residue and are completely freed from the gangue and can therefore be easily treated subsequently by flotation, gravimetry and other enrichment methods The xiviat brought into direct contact with sulfur dioxide gives rise quickly to a precipitate of copper compounds whose composition depends on several parameters (temperature, gas flow, acetate and metal concentrations, agitation, etc.), the combinations of copper oxides (cuprous, cuivπque) and sulfur oxides (sulfites, sulfates) being complex and diverse

The silver and gold accompanying the copper is recovered during the precipitation stage, a fractional precipitation, in particular by recontacting the precipitate with the rich solution resulting from leaching, making it possible to enrich the content of the piecipiter in precious metals.

The rapid absorption of large quantities of sulfur dioxide by the ammonium acetate solution is a variant in addition to the quantity of carboxylate solution used in the hiviviation-precipitation cycle as described above, another quantity of the solution is used in an absorption-precipitation loop The solution from the absorption column allows easy use of sulfur dioxide by reducing the risks associated with the handling of this gas. It reacts quickly with hxiviat, adjusting the flow rates of the mixture allows control of the quantity of metals to be precipitated

Before recycling the lean solution to a new leaching stage, its complexing power is adjusted by adding acetate to compensate for the losses in reagent and, when necessary, by passing over a filter of calcareous sand or by adding lime, to reduce excess sulfite ions and sulfates

The precipitate, washed and dried, is calcined at a temperature varying between 200 ° C and 600 ° C, depending on the chemical nature of the precipitate and the gas recovered (carbon dioxide or sulfur dioxide) is recycled to the precipitation stage

Claims

Hydrometallurgy process for the recovery of metals contained in oxidized ores, their concentrates, the roasting ash of sulphides and the recovered metals consisting in the implementation of a solution of carboxylates and / or carbonates of amines and / or ammonium for leaching and precipitation of salts of these metals

Process characterized in that the metal (s) extιaιt (s) by the said solution can be the transition metals of the periodic classification of the chemical elements, in particular copper, nickel, zinc, cadmium, chromium, cobalt, silver, gold, manganese, the metals being in the form of oxides, carbonates, silicates or salts of other weak acids.

Process characterized in that the carboxylates and / or carbonates of said solution are selected according to their complexing power with respect to the metals which are the subject of recovery, the metals possibly being brought to the appropriate degree of oxidation, in particular by injection air or oxygen

Proceeds caracteπse by the possibility of precipitating the metals, their hydroxides or their salts from the said solution, without significant alteration of the hexivating power of the recycled solution, by carbon monoxide, sulfur dioxide, hydrogen under pressure , hydrogen sulfide or other recovery methods such as carburizing, electrolysis or solvent extraction

Process characterized in that the leaching solution, of neutral or weakly acidic or weakly basic pH is, inert with respect to acidic or basic gangues and with respect to concrete and other equipment manufacturing materials

Process according to the preceding claims, consisting in particular of recovering oxidized copper ores, roasting ash from sulphides or recovered copper by leaching with ammonium acetate and recovering copper and associated metals, in particular by precipitation by hydrogen, carbon dioxide, sulfur gas