EP0135457A1 - Pretreatment of ores having an argillaceous gangue by alkali humidifying and thermal treatment - Google Patents

Abstract

Pretreatment under atmospheric pressure by alkaline wetting and thermal treatment of ground ores, the gangue of which consists of clay compounds which form a stable plastic suspension, and containing at least one metallic element which is recoverable by hydrometallurgy, for ease of separation of the liquid and solid phases, a) the ore, the granulometry of which is at most equal to the mesh for freeing the metallic element to be recovered is treated with at least 4 kg, expressed as OH<->, of alkaline agent per tonne of clay contained in the ore, b) the ratio of the liquid phase, expressed in cubic metres, to the solid phase, expressed in tonnes is at most equal to 1, c) pretreatment temperature is selected from the range of from 15 DEG C to 450 DEG C.

Description

The invention relates to a process for pretreatment at atmospheric pressure or close to atmospheric pressure, by alkaline wetting and heat treatment of ground ores whose gangue contains clay compounds capable of forming a stable plastic suspension in the presence of water and containing at ' minus one metallic element recoverable by hydrometallurgy.

By the expression "pretreatment", the applicant intends to define a treatment prior to a hydrometallurgical recovery action allowing the extraction of the recoverable element (s) from the ore, the pretreatment having the aim of subsequently imparting to the solid phase, in the presence of a liquid phase, an ability to separate the two phases present.

By the expression "recoverable metallic element", the applicant also intends to define all the metallic elements present in at least one of the minerals constituting the clay ore, capable of being extracted therefrom with a view to their valorization by hydrometallurgy.

It has long been known to those skilled in the art that clay compounds, forming the gangue of certain ores (which it would be desirable to exploit), have a real propensity to swell, then disintegrate, and finally disperse in the form of fine crystals and small agglomerates in contact with an aqueous phase. This phenomenon makes it very difficult to practice hydrometallurgical treatments for upgrading said ores since the suspension obtained becomes unfit for separation of the liquid and solid phases, both by filtration and by decantation or can be in a state of high viscosity due to swelling. clays.

The clay compounds capable of forming a plastic suspension in contact with water, and frequently present in the abovementioned ores with clayey matrix, can belong to the groups formed by kaolinites, such as for example kaolinite, dickite, halloysity, disordered kaolinites, serpentines; the group of micas, such as for example muscovite, biotite and paragonite, pyrophyllite and talc, illites and glauconite; the group of montmorillonites, such as, for example, beidellite, stevensite, saponite, and hectorite; the vermiculites group; the group of interstratified clays whose unitary structure is a combination of the preceding groups; the group of fibrous clays, such as for example attapulgite (palygorskite), sepiolite. These clay-matrix minerals may also contain other compounds such as, for example, quartz, calcite (CaC0 ₃ ), dolomite, gypsum, limonite (Fe0 (HO) nH ₂ 0) and other oxides and hydroxides. metallic.

Numerous hydrometallurgical processes for the alkaline treatment of ores with little or no clayey matrix are well known to those skilled in the art, as well as their difficult transposition to ores with frankly clayey properties.

According to a first type of process, and for example in the case of uranium ores, it is known to carry out alkaline treatments, possibly oxidizing, of said ores, by means of an aqueous solution of sodium carbonate and / or bicarbonate.

If the alkaline treatment is oxidizing, it is generally carried out in the presence of free oxygen blown into the hot reaction medium in order to allow the oxidation of uranium, and its solubilization, but also to ensure the oxidation of sulfides d 'impurities, and organic matter present in the ore.

This is how the literature on the subject has described operating methods according to this first type of process for the performing alkaline oxidizing treatments. (The Extractive Metallurgy of Uranium, by Robert C. Merritt, published by Colorado School of Mines Research Institute, 1971 edition, page 83 and following).

According to a first operating method, a uranium-bearing ore, preferably with a high carbonate content, is treated with a liquor containing 40 to 50 g / 1 of Na ₂ C0 ₃ and 10 to 20 g / 1 of NaHC0 ₃ in the presence of oxygen or of air blown into the reaction medium. The conditions of the treatment which is carried out in an autoclave, are in a range of temperatures between 95 ° C and 120 ° C, total prevailing pressure in the enclosure between 2 and 6.5 bars, with durations d 'attack which can vary between 4 and 20 hours.

According to a second mode, the same uranium-bearing ore with a high carbonate content is treated with the same liquor, containing 40 to 50 g / 1 of Na ₂ C0 ₃ and 10 to 20 g / 1 of NaHCO ₃ , in the presence of oxygen or of air blown into the reaction medium. However, the conditions of the treatment which is carried out in a "Pachuca" are different: the temperature is between 75 ° C to -80 ° C, while the injection pressure of air or oxygen in the reaction medium is in the range of 2 to 3 bars, for an attack time of 96 hours.

According to another mode, described in USP 3,036,881, the uranium ore containing hexavalent uranium is treated for approximately 6 hours, in the presence of oxygen, with a liquor containing from 4.2 g / 1 to 70 g / 1 sodium bicarbonate and 40 g / 1 to 100 g / 1 sodium carbonate, this treatment being carried out in the presence of an oxidation catalyst at a temperature of about 80 ° C to 90 ° C.

Such procedures, which have proved to be interesting for the treatment of certain uranium ores, are difficult to apply when it comes to carrying out the treatment of ores whose gangue is formed inter alia of clay compounds, because the application of such a process to an ore with a clay matrix leads, of course, to a correct solubilization of the metal to be recovered but also to obtaining a suspension resulting from the treatment of which it is practically impossible to ensure the separation of the liquid and solid phases, whatever the amount of flocculant added, due to its infiltrable and even indecisable nature.

Those skilled in the art, however, have found a way to overcome this drawback by practicing, before the actual treatment, a prior calcination of the clay-gangue ore. (The Extractive Metallurgy of Uranium by Robert C. Merritt, pages 55 and 56, paragraph "Roasting to improve physical characteristics").

Such a means has certainly proved interesting in certain cases, but it has often appeared that not only calcination could make the recoverable element refractory to the subsequent enhancing action of the treatment, but also that it was very expensive. both in investment and in energy.

According to another type of process, which has been described in the specialized literature, the ore is subjected to an alkaline treatment at a higher temperature by means of a much more concentrated solution of bicarbonate and sodium carbonate, possibly in an oxidizing medium.

Thus, in the case of a beryllium, vanadium, molybdenum or tungsten ore, American patent US 3,429,693 proposes a process for treating this ore by means of an aqueous solution containing in practice at least 100 g / 1, and up to more than 500 g / 1 trona (natural compound of Na ₂ CO ₃ , NaHCO ₃ , 2H ₂ O). to achieve a good dissolution yield, and at a temperature between 60 ° C and 250 ° C for a time comprised in practice between 90 minutes and 240 minutes. Such a procedure, which has proved to be advantageous for the treatment of certain ores containing molybdenum, vanadium, beryllium or tungsten, is not applicable to an ore with a clay matrix because, in the absence of a prior calcination at around 900 ° C. of this clay ore, as mentioned in Example 7 of said patent, it leads to the obtaining of a suspension at plastic character, resulting from the treatment, of which it is practically not possible to carry out the separation of the liquid and solid phases, whatever the amount of flocculant used.

According to a last type of alkaline process, it is recommended to use an activated carbon to extract from a clay pulp (suspension) the metal element to be valorized beforehand dissolved.

This is how an alkaline process for upgrading a clay gold ore is described in the review "Les Techniques: Industrie Minérale", published in November 1982, concerning "the study days of the Mines and Metallurgy sections" by Ollivier , Thomassin, and Winter. This process consists of treating the ore with an aqueous solution of sodium cyanide having the property of dissolving the gold. As the separation operations after attack of the liquid and solid phases by filtration or decantation lead either to too long decantation times, or to excessive filtration surfaces, resulting in both cases of investment costs and operating high, the gold suspension resulting from the cyanide attack is treated with activated carbon. This traps the dissolved gold by a process comparable to an ion exchange, the gold charcoal being separated from the sterile gangue by sieving thanks to the size of the grains of coal deliberately different from that of the grains of the gangue.

Although the latter process is an attractive means of avoiding the difficult separation between the clay and liquid phases, it appears that the consumption of activated carbon leads to a high operating cost which, in certain cases, becomes dissuasive.

However, numerous hydrometallurgical processes for the acid treatment of clay-gang ores are also well known to those skilled in the art, as is their difficult transposition to minerals with a frankly clay-like gangue.

According to a first method of acid treatment of an ore with a clay matrix, described in "The Extractive Metallurgy of Uranium" by Robert C. Merritt, pages 466 and 467, the clay ore is first subjected to a calcination between about 315 ° C and 425 ° C, then to the actual acid treatment, in order to obtain a suspension the phases of which can be separable. But such calcination prior to treatment can make the element recoverable, refractory to the solubilizing action of acids.

According to another process for the acid treatment of an ore with a clay matrix in order to dissolve the metal to be recovered, described in the review "Les Techniques Industrie Minérale", study days, 1982, from the Mines and Metallurgy sections of Angel and Teissié , pages 563 to 569, the clay mineral is first treated with the acid agent at pH 1.5 in a suspension that is not very concentrated in dry matter (65 g / l), then the suspension containing the solubilized metal to be recovered is put in contact with ion exchange resins, which fix the metal to be recovered, finally the metalliferous resins are separated by elutriation thanks to a difference in particle size.

Such a means nevertheless has certain drawbacks which can be significant, such as the consequent volumes of dilute suspensions to be conveyed, or else the high cost of the resin due to the renewal due to wear and the high initial investment for carrying out the filling of the ion exchange columns.

Therefore, due to the aforementioned drawbacks, the applicant, continuing its research, has found and perfected a process for the pretreatment of ores with a clay matrix, not comprising prior calcination, which annihilates the propensity of the compounds clay to swell, disintegrate and disperse in the form of fine crystals and small agglomerates in contact with an aqueous phase and makes it easy to apply known hydrometallurgical upgrading treatments to these ores, since the suspension resulting from the application of said treatments is made suitable for easy separation of the liquid and solid phases, in the same way as for ores with a non-argillous or at most weakly argillous matrix, both by filtration and by decantation.

• a) le minerai dont la granulométrie est au plus égale à la maille de libération de l'élément métallique à valoriser est mis en contact intime avec au moins 4 kg exprimés en OH d'au moins un agent alcalin par tonne d'argile contenue dans le minerai,
• b) le milieu humecté l'est d'une manière telle que, en prenant en compte la quantité d'eau totale présente dans le milieu après humectage, le rapport de la phase liquide exprimée en mètre cube à la phase solide exprimée en tonne est toujours au plus égal à 1,
• c) le milieu humecté est soumis à une température de prétraitement choisie dans l'intervale de 15°C à 450°C.

The pretreatment process according to the invention, which is carried out at atmospheric pressure or close to atmospheric pressure, consisting of an alkaline wetting and a heat treatment of the crushed ore, the gangue of which comprises clay compounds capable of forming a stable plastic suspension in the presence of water and containing at least one metallic element recoverable by hydrometallurgy, is characterized in that, with the aim of allowing easy subsequent separations of the liquid and solid phases:

• a) the ore whose particle size is at most equal to the mesh of release of the metallic element to be valorized is brought into intimate contact with at least 4 kg expressed as OH of at least one alkaline agent per ton of clay contained in the ore,
• b) the moistened medium is so so that, taking into account the total amount of water present in the medium after moistening, the ratio of the liquid phase expressed in cubic meters to the solid phase expressed in tonnes is always at most equal to 1,
• c) the moistened medium is subjected to a pre-treatment temperature chosen in the interval from 15 ° C to 450 ° C.

As has already been expressed, ores whose gangue is formed at least in part from clay compounds are difficult to recover by conventional hydrometallurgical treatments, acid or alkaline, because the suspension resulting from such treatments becomes incapable of separation of the liquid and solid, both by filtration and by decantation, as soon as it becomes plastic and stable in contact with water.

Such clay gangue ores can thus be condemned not to be exploited, even though they are rich in elements to be valued, or else are exploited by means of specific complex and costly treatments.

The method according to the invention pursues the aim of restoring to those skilled in the art minerals with a clay matrix containing at least one metallic element to be recovered, reputed to be difficult to exploit by conventional acid or alkaline treatments, due to the physical consequences previously mentioned, this process consisting in subjecting said ores to a simple and inexpensive alkaline pretreatment preceding the hydrometallurgical upgrading treatments, by means of which the suspension, resulting from said upgrading treatments, becomes suitable for easy separation of the liquid and solid phases by filtration and / or decantation.

First of all, as is well known to those skilled in the art, the ore at the time of contacting with the alkaline pretreatment agent must have a particle size corresponding at most to the mesh of release of the or recoverable metallic elements.

When the ore does not naturally have such a particle size, it is subjected to a grinding operation, preferably carried out in the absence of any addition of aqueous phase.

As soon as the ore has the granulometry corresponding at most to the mesh of liberation of the metallic element or elements to be valued, the flow of solid particles must be carried out with a fluidity close to that of dry silica sand.

However, it may happen that the ore has such a quantity of water before grinding, that the solid particles after grinding have tend to create agglomerates or granules that prevent the proper flow of these particles _f. In this case, the ore is subjected to drying prior to grinding or is simultaneously ground and dried in such a way that the solid particles resulting therefrom have a flow capacity equivalent to that of dry silica sand.

The alkaline pretreatment agent according to the invention can be introduced in a solid form or in the form of an aqueous solution.

When the alkaline agent is introduced in the aqueous form, it may come from a preparation by dissolving the hydroxide in natural or possibly brackish water or else by dissolving in a recycling liquor, for example from a treatment hydrometallurgical, located downstream of the pretreatment according to the invention, said liquor possibly containing chemical compounds as diverse as for example _NaCl , Na ₂ SO ₄ , Na ₂ C0 ₃ , NaV0 ₃ , NaCN.

This agent is such that when it comes into contact with water, it releases OH ions. This alkaline agent can be chosen from the group formed by alkali or assimilated, and / or alkaline-earth hydroxides, and preferably from sodium and potassium and ammonium hydroxides, as well as calcium hydroxide.

Depending on the nature of the ore, the alkaline agent can consist of a single hydroxide, such as sodium hydroxide or by the mixture of at least two hydroxides, such as, for example, sodium and calcium hydroxides.

Similarly, depending on the nature of the ore, the quantity of the alkaline agent brought into intimate contact with the ore to carry out the alkaline wetting is at least 4 kg expressed as OH per tonne of clay contained in the ore. . More generally, the quantity of the alkaline agent expressed as OH can be chosen in the range of 4 to 100 kg per tonne of clay contained in the ore, and preferential It can also be chosen in the range of 10 to 90 kg per tonne of clay contained in the ore.

As soon as the ore has the granulometry corresponding at most to the mesh of liberation of the recoverable metallic element or elements, it is brought into intimate contact with the alkaline agent, thus forming the pretreatment medium which has the appearance of 'A phase moistened by said agent whose physical state can vary from solid to pasty depending on whether the alkaline agent is introduced in the solid form or in the form of an aqueous solution.

However, according to an arrangement which has proved to be interesting, the intimate contact of the ore with a clay matrix with the alkaline agent can also be carried out by introduction of said agent before or during the grinding operation.

When the alkaline agent is in the solid form, it can be introduced with the ore into the grinding zone, the wetting taking place at least partially in said zone.

When the alkaline agent is in the liquid form, it can also be introduced dropwise or by fine spraying into the grinding zone, by partial moistening of the ore both before its introduction into said zone, and during grinding himself. Although it has been previously expressed that the grinding operation should preferably be carried out without adding an aqueous phase, said introduction of the alkaline agent into the grinding zone can be carried out as soon as the alkaline solution is sufficiently concentrated and desirably not too far from saturation.

Simultaneously with the introduction of the alkaline agent, it may prove useful to subject the mixture to kneading favoring the good distribution of the alkaline agent within the ore.

By considering not only the water which can be introduced when the alkaline agent is used in the form of an aqueous solution, but especially the water initially present in the ore, that is to say taking into account the amount of total water present in the medium after moistening, the ratio of the liquid phase expressed in cubic meters to the solid phase expressed in tonnes of ore (L / S) is always at most equal to 1, is generally between 0, 05 and 0.99.

In practice, the L / S ratio of the liquid phase present, expressed in cubic meters, to the solid phase, expressed in tonnes of ore, is all the higher as the clay content of the ore subjected to the pretreatment is itself high, so as to obtain a moist, neither fluid nor sticky dough.

The moistened medium is then subjected to a pre-treatment temperature chosen in the interval from 15 ° C to 450 ° C.

The duration of the pretreatment is generally short and is not a parameter to be controlled by the process according to the invention, it being understood that the pretreatment time is as much shorter as the temperature is chosen in the high values of the corresponding interval .

• a) le minerai dont la granulométrie est au plus égale à la maille de libération de l'élément métallique à valoriser est mis en contact intime avec au moins 4 kg exprimés en OH d'au moins un agent alcalin par tonne d'argile contenue dans le minerai.,
• b) le milieu humecté est soumis à l'élimination de l'eau libérable.présente jusqu'à l'obtention d'un rapport phase liquide exprimée en mètre cube et phase solide exprimée en tonne de minerai (L/S en m3/t) au plus égal à 0,2, enfin,
• c) le milieu humecté ainsi traité est porté à une température minimale de prétraitement d'au moins 105°C.

According to a first variant, the pretreatment method according to the invention, which is carried out at atmospheric pressure, consisting of an alkaline wetting and a rise in temperature of the crushed ore, the gangue of which comprises clay compounds capable of forming a stable plastic suspension in the presence of water and containing at least one metallic element recoverable by hydrometallurgy, can be carried out according to the following stages:

• a) the ore whose particle size is at most equal to the mesh of release of the metallic element to be valorized is brought into intimate contact with at least 4 kg expressed as OH of at least one agent alkaline per ton of clay contained in the ore.,
• b) the moistened medium is subjected to the elimination of releasable water. present until a liquid phase ratio expressed in cubic meters and solid phase expressed in tonnes of ore (L / S in m3 / t) ) at most equal to 0.2, finally,
• c) the moistened medium thus treated is brought to a minimum pre-treatment temperature of at least 105 ° C.

In this first variant and according to the nature of the ore, the quantity of the alkaline agent brought into intimate contact with the ore to carry out the alkaline wetting, is at least 4 kg expressed as OH per tonne of clay contained in the ore. More generally, the quantity of the alkaline agent expressed as OH can be chosen in the range from 4 to 45 kg per tonne of clay contained in the ore, and preferably can be chosen in the range from 10 to 40 kg per tonne of clay contained in the ore.

Likewise, considering not only the water which can be introduced when the alkaline agent is used in the form of an aqueous solution, but especially the water initially present in the ore, that is to say by taking taking into account the amount of total water present in the medium after moistening, the ratio of the liquid phase expressed in cubic meters to the solid phase expressed in tonnes of ore (L / S) is generally between 0.2 and 0.99 and is preferably between 0.2 and 0.8.

As soon as the ore is in intimate contact with the alkaline agent, the moistened medium is subjected to the elimination of the releasable water present in said medium by at least one known means, such as for example evaporation, until upon obtaining a phase report liquid present expressed in cubic meters at the solid phase expressed in tonnes of ore (L / S) at most equal to 0.2 and preferably at most equal to 0.15.

The moistened medium thus depleted in water is then brought to the pretreatment temperature of at least 105 ° C. This temperature at which the pretreatment is carried out is therefore defined as the minimum pretreatment temperature. This temperature can be chosen, in general, in the range from 105 ° C to 450 ° C, and can preferably be chosen in the range from 110 ° C to 200 ° C, depending on the nature of the clay matrix of the ore.

The duration of the pretreatment is generally short, it being understood that the pretreatment time is shorter the higher the temperature is chosen in the corresponding range.

• - une première période dite d'élimination de l'eau présente dans le milieu humecté, permettant de ramener le rapport L/S en m3/t à une valeur au plus égale à 0,2.
• - une deuxième période correspondant au traitement thermique proprement dit, au cours de laquelle le milieu humecté, débarassé de l'eau libérable jusqu'au rapport L/S en m3/t au plus égal à 0,2, est porté à la température minimale d'au moins 105°C. Cette durée est généralement choisie entre l'instantané et au plus 120 minutes, la prolongation au-delà de ce temps de séjour à la température choisie n'améliorant plus l'aptitude à la séparation ultérieure des phases liquide et solide.

This pretreatment time breaks down. in two periods:

• a first so-called elimination period of the water present in the moist environment, making it possible to reduce the L / S ratio in m3 / t to a value at most equal to 0.2.
• - a second period corresponding to the heat treatment proper, during which the moistened environment, rid of releasable water up to the L / S ratio in m3 / t at most equal to 0.2, is brought to the minimum temperature at least 105 ° C. This duration is generally chosen between the instantaneous and at most 120 minutes, the extension beyond this residence time at the chosen temperature no longer improving the ability to subsequently separate the liquid and solid phases.

• a) le minerai dont la granulométrie est au plus égale à la maille de libération de l'élément métallique à valoriser est mis en contact intime avec au moins 4 kg exprimés en OH d'au moins un agent alcalin par tonne d'argile contenue dans le minerai, par l'intermédiaire d'une phase aqueuse présente en une quantité telle que le rapport L/S de la phase liquide exprimée en mètre cube à la phase solide exprimée en tonne de minerai sec soit au plus égale à 0,6.
• b) le minerai ainsi humecté est soumis à une température de prétraitement d'au plus 105°C pendant un temps d'au moins trente minutes.

According to a second variant, the pretreatment method according to the invention, which is carried out at atmospheric pressure or close to atmospheric pressure, consisting of an alkaline wetting and maintaining the temperature of the crushed ore, the gangue of which comprises clay compounds capable of to form a suspension plastic stable in the presence of water and containing at least one metallic element recoverable by hydrometallurgy, can be produced according to the following stages:

• a) the ore whose particle size is at most equal to the mesh of release of the metallic element to be valorized is brought into intimate contact with at least 4 kg expressed as OH of at least one alkaline agent per ton of clay contained in the ore, via an aqueous phase present in an amount such that the L / S ratio of the liquid phase expressed in cubic meters to the solid phase expressed in tonnes of dry ore is at most equal to 0.6.
• b) the ore thus moistened is subjected to a pre-treatment temperature of at most 105 ° C for a time of at least thirty minutes.

In this second variant and, depending on the nature of the ore, the quantity of the alkaline agent brought into intimate contact with the ore to carry out the alkaline wetting is at least 4 kg expressed as OH per tonne of clay contained in the ore. More generally, the quantity of the alkaline agent expressed as, OH can be chosen in the range from 4 to 100 kg per tonne of clay contained in the ore, and preferably can be chosen in the range from 10 to 90 kg. per ton of clay contained in the ore.

Likewise, considering not only the water which can be introduced when the alkaline agent is used in the form of an aqueous solution, but especially the water initially present in the ore, that is to say by taking taking into account the total amount of water present in the medium after moistening, the ratio of the liquid phase expressed in cubic meters to the solid phase expressed in tonnes of ore (L / S) is always at most equal to 0.6, is generally between 0.05 and 0.5 and is preferably between 0.10 and 0; 40.

In practice, the L / S ratio of the liquid phase present, expressed in cubic meters, to the solid phase, expressed in tonnes of ore, is all the more high as the clay content of the ore subjected to the pretreatment is itself higher, so as to obtain a moist paste, neither fluid nor sticky.

As soon as the ore is in intimate contact with the alkaline agent, the moistened medium is then subjected to the pretreatment temperature of at most 105 ° C. This temperature can be chosen, in general, in the wide range from 15 ° C to 100 ° C, and can preferably be chosen in the range from 30 ° C to 90 ° C, depending on the nature of the clay matrix of the ore .

The duration of the pretreatment is generally greater than 30 minutes, but: is not a parameter to be controlled of the process according to the invention, it being understood that the pretreatment time is all the longer as the temperature is chosen in the low values of the corresponding interval.

According to a particular arrangement of the method according to the invention, it may be advantageous to carry out the pretreatment in a redox and / or complexing medium using known suitable agents.

During the pretreatment period according to the invention, the medium moistened with the alkaline agent can be subjected to minimal mechanical stirring.

Thanks to the pretreatment method according to the invention, the disintegration process of the clays, which occurs in the presence of an aqueous phase, is inhibited in an almost irreversible manner allowing subsequent treatment to be carried out at the appropriate time. upgrading, such as for example an acid or alkaline attack in a reactor of pretreated clay-gangue ore, which can without inconvenience include stirring, storage, transfer and separation steps.

In addition, the pretreatment method according to the invention does not subsequently cause limitation of the solubilization yields of the metallic element to be recovered, whatever the type of practical treatment, acid or alkaline, at low temperature.

Finally, in order to facilitate the separation of the liquid and solid phases of the suspension resulting from the pretreatment of the ore according to the invention, it is desirable to introduce a flocculating agent in dilute aqueous solution, generally of a concentration at most equal to one gram per liter, in quantities not exceeding 500 grams per tonne of ore, but always suited to the desired results.

The advantages of the method according to the invention will be more perceptible thanks to the examples given by way of illustration.

EXAMPLE 1

This example illustrates the behavior of the clay matrix of a urano-vanadiferous ore when the latter is suspended in an aqueous, neutral or alkaline phase, cold or hot, without having been subjected to the pretreatment according to the invention.

To do this, a clay uranium ore was used having, after drying, the following composition in% by weight:

Dry ore containing in% by weight. :

The clays consisted mainly of illite and kaolinite.

A first test was carried out in the following manner 100 g of this dry ore, ground and passing through a sieve of 500 microns, were placed in a cylindrical reactor of 500 milliliters of total capacity, with 300 g of water introduced with a gradually with stirring, forming a suspension. The mixture obtained had, cold as hot (90 ° C), the appearance of a gelatinous paste, which after 24 hours of rest had shown no ability to decant.

Consequently, it proved to be impossible to carry out a separation by filtration or decantation of the liquid and solid phases present in the mixture, since the clay matrix had swelled very quickly in contact with water, making the application of a hydrometallurgical process impracticable ore recovery.

Six other tests were then carried out by replacing the water in the medium with aqueous, alkaline or acid solutions, generally used in hydrometallurgy of ores.

The compositions of the various solutions used, as well as the appearance of the suspensions resulting from the treatments were collected in the following table I:

Thus, the observation of these results reveals the inability to separate the liquid and solid phases of a suspension resulting from conventional hydrometallurgical treatments, applied to an ore with a clay matrix, the water promoting in any case the swelling of said gangue in the absence of the pretreatment according to the invention.

EXAMPLE 2

This example illustrates the beneficial influence, on the separation of the liquid and solid phases, of the pretreatment according to the invention of an ore with argillaceous gangue by means of an alkaline agent and more particularly the. various quantities of said agent which can be used, in the form of an aqueous solution, during the moistening of the ore, before heating the ore, before heating the mixture.

To do this, the same urano-vanadiferous ore with a clay gangue was pretreated as in Example 1, according to the first variant of the invention, 100 g of this ore (test No. 8), ground and passing through a sieve. 500 microns, were placed in the presence of an amount of sodium hydroxide equivalent to 50 kg per tonne of ore, but in solution in an amount of water such that the ratio of the liquid phase expressed in cubic meters to the phase solid expressed in tonnes has the value of 0.2.

The pretreatment time, which was 1 hour, was counted from the moment when said L / S ratio fell below 0.2 m3 / tonne.

In order to verify the effectiveness of the pretreatment according to the invention, that is to say to ensure that the clay matrix of the ore has indeed been stabilized in a physical state conducive to subsequent easy separation of the liquid and solid phases, the four pretreated samples were subjected to a degradation test. This test consisted in introducing each sample of pretreated ore into a cylindrical-hemispherical stainless steel reactor with water according to a ratio of the liquid phases expressed in cubic meters and solid expressed in tonnes equal to 3.

A permanent injection of excess CO ₂ gas at the base of each reactor allowed rapid carbonation of the medium.

Each reactor, with a capacity of 1 liter, was fitted with a vertical axis turbine, comprising 3 vertical blades, rotating at 375 revolutions per minute.

The reaction medium was kept at the temperature of 90 ° C for one hour, all these operations being carried out with vigorous stirring.

At the end of this time, the reactor was immersed in cold water in order to cause rapid cooling of the suspension. After cooling to the temperature of 60 ° C., the suspension thus pretreated was subjected to a separation test which consisted in passing the suspension over a Büchner filter by practicing a vacuum of 500 millimeters of mercury, and thus measuring the separation speed. of the liquid phase in cubic meter. hour meter ^-2 .

Before passing the suspension over the filter, it was added by means of a flocculating agent, at the rate of 20 m 3 of a 0.5 g solution of Floerger FA10, prepared from an aqueous solution. 2.5 g / 1.

The filtration rates have been recorded in Table II below.

This table reveals, first of all, by comparison with the results of Example 1, the excellent filterability of the clay ore after it has been subjected to the pretreatment according to the invention. In addition, this table confirms that the value of the L / S ratio in m3 / t of wetting of the clay-gangue ore can be chosen indifferently in the range 0.2 to 0.99, while retaining an excellent ability to filtration.

EXAMPLE 3

This example demonstrates the minimum quantity of the alkaline agent, expressed in kilograms of OH per tonne of clay present in the ore which it is necessary to use to successfully carry out the pretreatment according to the invention.

For this purpose, eight tests were carried out with the same ore as in Example 1 within the same cylindrical reactor of 500 milliliters of total capacity.

For each of these tests (tests 12 to 19), 100 g of this crushed ore and passing through a 500 micron sieve were placed in the presence of increasing amounts of sodium hydroxide, dissolved in an amount of water such that the ratio of the liquid phase expressed in cubic meters to the solid phase expressed in tonnes has the value of 0.3 for each test.

These quantities of sodium hydroxide, expressed in kilograms of OH, represented in the moistening medium, 0 - 2 - 4 - 10 - 15 - 30 - 45 and 85 kilograms of OH per tonne of clay present: in the ore.

All these samples (tests 12 to 19) were then dehydrated according to the first variant of the invention by evaporation until a value of the L / S ratio in m3 / t less than 0.2 (close to 0.15), in an electric oven intended for pretreatment and heated to 130 ° C. The temperature at the heart of the sample remained very close to 100 ° C, during evaporation, then rose rapidly to 130 ° C as soon as the L / S ratio in m3 / t became less than 0.2 .

The pretreatment time, which was 1 hour and 15 minutes, was counted from the moment when said L / S ratio became less than 0.2 m3 / tonne.

In order to verify the effectiveness of the pretreatment according to the invention, that is, to ensure that the clay matrix of the ore has been stabilized in. a physical state conducive to subsequent easy separation of the liquid and solid phases, the eight pretreated samples were subjected to a degradation test. This test consisted in introducing each sample of pretreated ore into a cylindrical-hemispherical stainless steel reactor with water, according to a ratio of the liquid phases expressed in cubic meters and solid expressed in tonnes equal to 3.

A permanent injection of excess C0 ₂ gas at the base of each reactor allowed rapid carbonation of the medium.

Each reactor, with a capacity of 1 liter, was fitted with a vertical axis turbine, comprising 3 vertical blades, rotating at 375 revolutions per minute.

The reaction medium was kept at the temperature of 90 ° C for one hour, all these operations being carried out with vigorous stirring.

At the end of this time, the reactor was immersed in cold water in order to cause rapid suspension cooling. After cooling to the temperature of 60 ° C., the suspension thus pretreated was subjected to a separation test which consisted in passing the suspension over a Büchner filter by practicing a vacuum of 500 millimeters of mercury, and thus measuring the speed -1 -2 separation of the liquid phase in cubic meter. Hour meter.

Prior to the passage of the suspension over the filter, it was added by means of a flocculating agent, at the rate of 20 cm ³ of a 0.5 gl solution of Floeger FA10, prepared from a solution 2.5 gl aqueous

The operating conditions and the filtration rates were recorded in Table III below:

Thus, this table reveals that it is necessary to use a minimum of 4 kg of alkaline agent expressed as OH per tonne of clay so that the effectiveness of the pretreatment can be observed, and that the ore with a clay matrix acquires the ability to separate the liquid and solid phases which are the subject of the invention.

EXAMPLE 4

In this example, it was verified that the pretreatment according to the invention could be carried out at any temperature in the range from 105 ° C to 450 ° C, according to the first variant of the invention.

To do this, we carried out with the same ore as in Example 1, seven tests in the same cylindrical reactor of 500 milliliters of total capacity.

For each of these tests (tests 20 to 26), 100 g of this ground ore, and passing through a 500 micron sieve, were placed in the presence of a quantity of sodium hydroxide equivalent to 50 kg per tonne of ore, dissolved in an amount of water such that the ratio of the liquid phase expressed in cubic meters to the solid phase expressed in tonnes has the value of 0.3.

The pretreatment temperatures were chosen at 105, 110, 130, 150, 180, 250 and 450 ° C.

Each sample underwent the same preprocessing and efficiency verification protocols (degradation test) as in Example 3.

The main operating conditions as well as the values of the filtration rates obtained are summarized in Table IV below.

This table confirms the excellent results obtained by the application of a process according to the invention when the pretreatment is carried out at a temperature of at least 105 ° C.

EXAMPLE 5

In this example, it has been verified that the alkaline agent used in the pretreatment according to the invention could be either sodium hydroxide, potassium hydroxide or a mixture of the two.

For this purpose, three tests were carried out with the same ore as in Example 1 within the same cylindrical reactor of 500 milliliters of total capacity.

For each of. tests (tests 27 to 29), 100 g of this crushed ore and passing through a 500 micron sieve, were placed in the presence of a quantity of sodium hydroxide, potassium and the mixture of the two hydroxides, equivalent to 30 kg of OH per tonne of ore, dissolved in an amount of water such that the ratio of the liquid phase expressed in cubic meters to the solid phase expressed in tonnes has the value of 0.3.

Each sample underwent the same preprocessing and efficiency verification protocols (degradation test) as in Example 3.

The results obtained after degradation and filtration tests are summarized in Table V below.

Thus, it appears that the nature of the alkali hydroxide does not matter and that the pretreatment is carried out correctly, whether one is in the presence of NaOH, of KOH or of their mixture.

EXAMPLE 6

This example illustrates the beneficial influence on the separation of the liquid and solid phases of the pretreatment according to the invention of another uraniferous ore with clay gangue by means of an alkaline agent.

To do this, a clay uranium ore was used having, after drying, the following composition in% by weight:

This dry ore containing in% by weight:

Clays were mainly made up of smectites, attapulgite and sepiolite.

Two tests, 30 and 31, were carried out using this ore, one having only undergone the only degradation test (test 30), the other having successively undergone the pretreatment according to the invention and then the degradation, according to the pretreatment and / or degradation protocols described in example 3 of test 17.

Ces résultats confirment l'intérêt du prétraitement selon l'invention sur un minerai uranifère différent de celui utilisé dans les exemples précédents.The results are reported in Table VI below:

These results confirm the advantage of the pretreatment according to the invention on a uranium ore different from that used in the previous examples.

EXAMPLE 7

This example relates to and illustrates the pretreatment according to the method of the invention of a urano-molybdenum ore with relatively little clay matrix.

For this, use was made of an ore which had the following dry composition, expressed in% by weight:

On this ore, a percentage of clay close to 10% by weight has been determined.

Two tests, 32 and 33, were carried out using this ore, using the. general conditions below with regard to the pretreatment part.

A first sample of 100 g (test 33) of this dry and ground ore, passing to. sieve of 500 microns, was intimately mixed with 300 g of an aqueous sodium solution containing 1 g of NaOH (i.e. 42.5 kg of OH per ton of clay), the solid thus moistened was placed in an oven brought to 130 ° C. After 60 minutes, the L / S ratio in m3 / T of this product had become less than 0.2 and the heat treatment was continued for another 1 hour.

In order to verify the effectiveness of the pretreatment thus carried out, the product obtained was taken up in water and carbonated in a stirred reactor, then subjected to a filtration test according to the protocol of Example 3.

On the other hand, another 100 g sample (test 32) was taken of the same ore on which no pretreatment was carried out and which was immediately subjected to the same degradation test in aqueous phase as previously, but by incorporating 1 g of NaOH into the water of the carbonation reactor.

The two filtration tests, one on the suspension of the pretreated ore, and the other on the suspension of the non-pretreated ore, were carried out subsequently on the same Buchner filter according to the protocol described in Example 3.

Ainsi, il apparaît que le procédé de l'invention permet également d'améliorer la filtrabilité d'un minerai urano-molybdénifère peu argileux.The corresponding results are shown in Table VII below:

Thus, it appears that the process of the invention also makes it possible to improve the filterability of a low-clay urano-molybdenum ore.

EXAMPLE 8

This example illustrates the beneficial influence on the separation of the liquid and solid phases of the pretreatment according to the invention on a weakly clayey laterite, using an alkaline agent.

This laterite, containing nickel and cobalt, contained 30% of clay (kaolinite) and was known for its inability to decantation as to filtration once suspended in water.

This laterite had, after drying, the following composition in% by weight:

On this ore, a percentage of clay close to 30% by weight (kaolinite) has been determined.

Two tests (34 and 35) were carried out starting from 100 g of this ore for each test using the general conditions described in Example 7, both for the pretreatment according to the invention and for the degradation test.

Test 34 corresponds to the only degradation test.

Test 35 relates to the application of the pretreatment according to the invention followed by the degradation test.

The results concerning the filtration tests are recorded in Table VIII below.

Thus, it appears that the filtration performance of the laterite ore has been greatly improved by the application of the pretreatment according to the invention.

EXAMPLE 9

This example illustrates the application of the process according to the invention to a gold ore with a clay gangue.

This ore, after drying, had the following composition in% by weight:

On this ore, a percentage of clay close to 54% by weight has been determined, essentially consisting of kaolinite and chlorite.

Two tests (36 and 37) were carried out using this ore.

As in Example 6, a first fraction of 100 g of this ore (test 37) was treated according to the invention, then underwent aqueous recovery in a carbonation reactor, this latter operation constituting the degradation test, while 'a second fraction of 100 g (test 36) of the same gold ore underwent the only degradation test in the same highly agitated reactor.

During these operations, all the operating conditions were identical to those of Example 6, except, the amount of NaOH added to the ore or used in the degradation test, namely 4 g of NaOH, which corresponds to 31 kg of OH per tonne of clay present in the gold ore.

Table IX shows the results of the two filtration tests carried out at the end of the above-mentioned respective degradation tests.

These results confirm that the process according to the invention applies to all kinds of clay ores, regardless of the nature of the metal to be recovered.

EXAMPLE 10

This example illustrates the application of the method according to the invention to a vanadiferous ore with a highly bentonite gangue (95% bentonite).

This ore, after drying, had the following composition expressed in% by weight:

Two 100 g samples (tests 38 and 39) ground passing through a 500 micron sieve were treated as the two samples of Example 6. The first test (test 39) underwent the pretreatment then the degradation test, the second (test 38) only the degradation test.

The results of these two tests are shown in the table below.

The pretreatment according to the invention makes it possible to make a practically pure clay filterable, which, in the absence of said pretreatment could not have been indebted for a hydrometallurgical treatment, such as an acid or alkaline attack.

EXAMPLE 11

This example illustrates the beneficial influence on the separation of the phases. liquid and solid, of the pretreatment according to the invention of an ore with a clay matrix using an alkaline agent and more particularly the various quantities of said agent which can be used, in the form of an aqueous solution, during moistening the ore, prior to heating the mixture to the temperature used for the tests.

To do this, the same urano-vanadiferous ore with a clay gangue was pretreated as in Example 1, according to the second variant of the invention. 100 g of this ore (test No. 40), ground and passing through a 500 micron sieve, was placed in the presence of an amount of sodium hydroxide equivalent to 50 kg per tonne of ore, dissolved in an amount of water such that the ratio of the liquid phase expressed in cubic meters to the solid phase expressed in tonnes has the value of 0.10. This quantity of sodium hydroxide, expressed as OH, represented in the moistening medium 30 kg of OH equivalent per tonne of clay contained in the ore.

Four other tests (tests 41, 42, 43 and 44) corresponding to samples of 100 g of the same ore, were carried out by treating said ore with the same amount of sodium hydroxide, but with volumes of water different in such a way that the L / S ratio in m3 / T takes values 0.17 - 0.30 - 0.45 and 0.6.

The five samples were then placed in an oven for pretreatment and heated to 50 ° C. The pre-treatment time was 3 hours.

In order to verify the effectiveness of the pretreatment according to the invention, that is to say to ensure that the clay matrix of the mineral has indeed been stabilized in a physical state conducive to subsequent easy separation of the liquid and solid phases, the five pre samples treated were subjected to a degradation test. This test consisted in introducing each sample of pretreated ore into a cylindrical-hemispherical stainless steel reactor with water according to a ratio of the liquid phases expressed in cubic meters and solid expressed in tonnes equal to 3.

A permanent injection of excess C0 ₂ gas at the base of each reactor allowed rapid carbonation of the medium.

Each reactor, with a capacity of 1 liter, was fitted with a vertical axis turbine, comprising 3 vertical blades, rotating at 375 revolutions per minute.

The reaction medium was kept at the temperature of 90 ° C for one hour, all these operations being carried out with vigorous stirring.

At the end of this time, the reactor was immersed in cold water in order to cause rapid cooling of the suspension. After cooling to a temperature of 60 ° C., the suspension thus pretreated was subjected to a separation test which consisted in passing the suspension over a Büchner filter by practicing a vacuum of 500 millimeters of mercury, and thus measuring the speed of separation of the liquid phase in cubic meters. hour ^-1. meter ^-2 .

Before passing the suspension over the filter, it was added by means of a flocculating agent, at the rate of 20 m 3 of a 0.5 gl solution of Floeger FA10, prepared from an aqueous solution. 2.5 gl

The filtration rates have been recorded in the table below.

This table reveals, first of all, by comparison with the results of Example 1, the good ability to filter the clay ore after it has been subjected to the pretreatment of the second variant according to the invention. In addition, this table confirms for this particular ore that the value of the L / S ratio in m3 / T of wetting of the ore with clay matrix can be chosen indifferently in the range 0.1 to 0.4, while retaining a good filtration ability.

EXAMPLE 12

This example highlights, by making use of the second variant, the minimum quantity of the alkaline agent, expressed in kilograms of OH- per tonne of clay present in the ore which it is necessary to use in order to carry out successfully the pretreatment according to the invention.

For this purpose, six tests were carried out with the same ore as in Example 1.

For each of these tests (tests 45 to 50), 100 g of this crushed ore passing through a 500 micron sieve were placed in the presence of increasing amounts of sodium hydroxide, dissolved in an amount of water such that the ratio of the liquid phase expressed in cubic meters at the solid phase expressed in tonnes has the value of 0.3 for each test.

These quantities of sodium hydroxide, expressed in kilograms of OH, represented in the moistening medium, 0 - 4 - 10 - 20 - 40 and 85 kilograms of OH ^- per ton of clay present in the ore.

All these samples (tests 45 to 50) were then placed in an oven intended for pretreatment and heated to 50 ° C.

The pretreatment time was 3 hours.

In order to verify the effectiveness of the pretreatment according to the invention, that is to say to ensure that the clay matrix of the ore has indeed been stabilized in a physical state conducive to subsequent easy separation of the liquid and solid phases, the six pretreated samples were subjected to a degradation test. This test consists in introducing each sample of pretreated ore into a cylindrical-hemispherical stainless steel reactor with water, according to a ratio of the liquid phases expressed in cubic meters and solid expressed in tonnes equal to 3.

A permanent injection of excess C0 ₂ gas at the base of each reactor allowed rapid carbonation of the medium.

Each reactor, with a capacity of 1 liter, was fitted with a vertical axis turbine, comprising 3 vertical blades, rotating at 375 revolutions per minute.

The reaction medium was kept at the temperature of 90 ° C for one hour, all these operations being carried out with vigorous stirring.

At the end of this time, the reactor was immersed in cold water in order to cause rapid cooling of the suspension. After cooling to the temperature of 60 ° C, the suspension thus pre treated was subjected to a separation test which consisted in passing the suspensions on a Büchner filter by practicing a vacuum of 500 millimeters of mercury, and thus measuring the speed of separation of the liquid phase in cubic meters. hour ^-1. meter ^-2 .

Before the suspension was passed over the filter, it was added by means of a flocculating agent, at the rate of 20 cm 3 of a 0.5 g / l solution of Floeger FA10, prepared from a 2.5 g / l aqueous solution.

The operating conditions and the filtration rates were recorded in Table XII below.

Thus, this table reveals that it is necessary to use a minimum of 4 kg of alkaline agent expressed as OH per tonne of clay so that the effectiveness of the pretreatment can be observed, and that the ore with a clay matrix acquires the ability to separate the liquid and solid phases which are the subject of the invention.

EXAMPLE 13

In this example, it has been verified that the pretreatment according to the invention could be carried out at any temperature in the range from 25 ° C to 100 ° C, when use is made of the second variant according to the invention .

To do this, seven tests were carried out with the same ore as in Example 1.

For each of these tests (tests 51 to 57), 100 g of this crushed ore, and passing through a 500 micron sieve, were placed in the presence of a quantity of sodium hydroxide equivalent to 60 kg per tonne of ore, dissolved in an amount of water such that the ratio of the liquid phase expressed in cubic meters to the solid phase expressed in tonnes has the value of 0.3.

The pretreatment temperatures were chosen at 25, 30, 50, 60, 80 and 100 ° C.

Each sample underwent the same preprocessing and efficiency verification protocols (degradation test) as in Example 12.

Ce tableau confirme les excellents résultats acquis par l'application du procédé selon l'invention quand le prétraitement est effectué à une température choisie entre 25°C et 100°C pour ce minerai particulier.The main operating conditions as well as the values of the filtration rates obtained are summarized in Table XIII below.

This table confirms the excellent results obtained by the application of the method according to the invention when the pretreatment is carried out at a temperature chosen between 25 ° C and 100 ° C for this particular ore.

EXAMPLE 14

In this example, it has been verified that the alkaline agent used in the pretreatment according to the invention could be indifferently sodium hydroxide, potassium hydroxide, ammonium hydroxide, calcium hydroxide -or a mixture-

For this purpose, five tests were carried out with the same ore as in Example 1.

For each of the tests (tests 58 to 62) 100 g of this crushed ore and passing through a 500 micron sieve were placed in the presence of an amount of alkaline agent equivalent to 40 kg of OH per tonne of ore, dissolved or suspended in the case of Ca (OH) ₂ in an amount of water such that the ratio of the liquid phase expressed in cubic meters to the solid phase expressed in tonnes has the value of 0.3.

Each sample underwent the same preprocessing and efficiency verification protocols (degradation test) as in Example 3.

The results obtained after degradation and filtration tests are summarized in Table XIV below.

Thus, it appears that the nature of the alkaline agent does not matter and that the pretreatment is carried out correctly, whether one is in the presence of NaOH, KOH, NH ₄ (OH), Ca (OH) ₂ , or a mixture of Ca (OH) ₂ and NaOH.

EXAMPLE 15

This example illustrates the beneficial influence on the separation of the liquid and solid phases of the pretreatment according to the invention of another uraniferous ore with clay gangue by means of an alkaline agent, by use of the second variant.

To do this, a clay uranium ore was used having, after drying, the following composition in% by weight:.

This dry ore containing in% by weight:

The clays consisted mainly of smectite, atta-. pulgite and sepiolite.

Two tests, Nos. 63 and 64, were carried out from this ore, one having only undergone the only degradation test (test No. 63), the other having successively undergone the pretreatment according to the invention then the degradation test, according to the pretreatment and / or degradation protocols described in test No. 49 of Example 12.

The results are reported in Table XV below.

These results confirm the advantage of the pretreatment according to the invention on a uranium ore different from that used in the previous examples.

EXAMPLE 16

This example relates to and illustrates, allegedly according to the method of the invention, a urano-molybdeniferous ore with relatively little clay matrix by use of the second variant.

For this, use was made of an ore which had the following dry composition, expressed in% by weight:

On this ore, a percentage of clay close to 10% by weight has been determined.

Two tests, n ° 65 and 66, were carried out from this ore, using the general conditions below with regard to the pretreatment part.

Le solide ainsi humecté a été placé dans une étuve portée à 50°C pendant 180 minutes.A first sample of 100 g (test No. 66) of this dry and ground ore, passing through a 500 micron sieve, was intimately mixed with 15 g of an aqueous sodium recycling solution containing 1 g of NaOH (i.e. 42, 5 kg of OH per ton of clay), having the following composition in% by weight:

The solid thus moistened was placed in an oven brought to 50 ° C. for 180 minutes.

In order to verify the effectiveness of the pretreatment thus carried out, the product obtained was taken up in water and carbonated in a stirred reactor, then subjected to a filtration test according to the protocol of Example 12.

On the other hand, another 100 g sample (test no. 65) was taken of the same ore on which no pretreatment was carried out and which was immediately subjected to the same degradation test in aqueous phase as previously. , but by incorporating 1 g of NaOH into the water of the carbonation reactor.

The two filtration tests, one on the suspension of the pretreated ore, and the other on the suspension of the non-pretreated ore, were carried out subsequently on the same Büchner filter according to the protocol described in Example 12.

The corresponding results are shown in Table XVI below.

Thus, it appears that the process of the invention also makes it possible to improve the filterability of a low-clay urano-molybdenum ore.

EXAMPLE 17

This example illustrates the beneficial influence on the separation of the liquid and solid phases of the pretreatment according to the invention on a slightly clayey laterite, by means of an alkaline agent, by application of the second variant.

This laterite, containing nickel and cobalt, contained 30% of clay (kaolinite) and was known for its inability to decantation as to filtration once suspended in water.

This laterite had, after drying, the following composition in% by weight:

On this ore, a percentage of clay close to 30% by weight (kaolinite) has been determined.

Two tests, Nos. 67 and 68 were carried out starting from 100 g of this ore for each test, using the general conditions described in Example 16, both for the pretreatment according to the invention and for the degradation test .

Test No. 67 corresponds to the only degradation test.

Test No. 68 relates to the application of the pretreatment according to the invention, followed by the degradation test.

The results concerning the filtration tests are reported in Table XVII below.

Thus, it appears that the filtration performance of the laterite ore has been greatly improved by the application of the pretreatment according to the invention.

EXAMPLE 18

This example illustrates the application of the process according to the invention to a gold ore with a clay gangue.

This ore, after drying, had the following composition in% by weight:

On this ore, a percentage of clay close to 54% by weight has been determined, essentially consisting of kaolinite and chlorite.

Two tests, Nos. 69 and 70, were carried out using this ore.

As in Example 15, a first fraction of 100 g of this ore (test No. 70) was treated according to the invention, then underwent aqueous recovery in a carbonation reactor, this latter operation constituting the degradation test, while a second fraction of 100 g (test no. 69) of the same gold ore underwent the only degradation test in the same highly agitated reactor.

During these operations, all the operating conditions were identical to those of Example 15, except, the amount of NaOH added to the ore or used in the degradation test, namely 4 g of NaOH, which corresponds to 31 kg of OH per tonne of clay present in the gold ore.

Table XVIII indicates the results of the two filtration tests carried out at the end of the respective abovementioned degradation tests.

These results confirm that the process according to the invention applies to all kinds: of clay ores, regardless of the nature of the metal to be recovered.

EXAMPLE 19

• V₂O₅ 0,142
• _Si0₂ 50,1 (dont quartz 0,8 %)
• Al₂O₃ 17,0
• MgO 4,2
• CaO 2,3
• ^K ₂ ⁰ 5,5
• eau de liaison 20,7
• et divers

This example illustrates the application of the method according to the invention to a vanadiferous ore with a highly bentonite gangue (95% bentonite).

• V ₂ O ₅ 0.142
• _S i0 ₂ 50.1 (of which quartz 0.8%)
• Al ₂ O ₃ 17.0
• MgO 4.2
• CaO 2.3
• ^K ₂ ⁰ 5.5
• binding water 20.7
• and various

Five samples of 100 g (tests n ° 71 to 75), ground, passing through a sieve of 500 microns were treated like the two samples of example 15, but with different L / S ratios for tests n ° 72 to 75.

Tests No. 72 to 75 underwent the pretreatment and then the degradation test, while test No. 71 underwent only the degradation test.

Le prétraitement selon l'invention, permet en adaptant le rapport L/S selon la nature et la quantité de l'argile, de rendre filtrable un minéral même constitué d'argile pratiquement pure, et qui, en l'absence dudit prétraitement n'aurait pu être redevable d'un traitement hydrométallurgique, telle qu'une attaque acide ou alcaline.The results of these five tests are shown in Table XIX below.

The pretreatment according to the invention makes it possible, by adapting the L / S ratio according to the nature and the quantity of the clay, to make filterable a mineral even consisting of practically pure clay, and which, in the absence of said pretreatment does not could have been indebted for hydrometallurgical treatment, such as an acid or alkaline attack.

Claims (20)

1 - Process for pretreatment at atmospheric pressure by alkaline wetting and heat treatment of crushed ores, the gangue of which comprises clay compounds capable of forming a stable plastic suspension in the presence of water and containing at least one metallic element recoverable by hydrometallurgy, characterized in that that, in order to allow easy subsequent separation of the liquid and solid phases. a) the ore whose particle size is at most equal to the mesh of release of the metallic element to be valorized is brought into intimate contact with at least 4 kg expressed as OH of at least one alkaline agent per ton of clay contained in the ore, b) the moistened medium is so so that, taking into account the total amount of water present in the medium after moistening, the ratio of the liquid phase expressed in cubic meters to the solid phase expressed in tonnes, is always at most equal to 1, c) the moistened medium is subjected to a pre-treatment temperature chosen in the range from 15 ° C to 450 ° C. 2 - Process for pretreatment at atmospheric pressure or close to atmospheric pressure of clay-gang ores by alkaline wetting and heat treatment, according to claim 1, characterized in that the alkaline agent is preferably chosen from the group consisting of hydroxide sodium, potassium hydroxide, ammonium hydroxide, calcium hydroxide. 3 - Process for pretreatment at atmospheric pressure or close to atmospheric pressure of clay-gang ores by alkaline wetting and heat treatment, according to claims 1 or 2, characterized in that the alkaline agent consists of the mixture of minus 2 alkaline agents. 4 - Process for pretreatment at atmospheric pressure or close to atmospheric pressure of clay-gang ores by alkaline wetting and heat treatment according to any one of claims 1 to 3, characterized in that the alkaline agent is introduced in a solid form . 5 - Process for pretreatment at atmospheric pressure or close to atmospheric pressure of clayey ores by alkaline wetting and heat treatment, according to any one of claims 1 to 3, characterized in that the alkaline agent is introduced in the form of an aqueous solution, possibly saline, or of recycling. 6 - Process for pretreatment at atmospheric pressure or close to atmospheric pressure of clay-gang ores by alkaline wetting and heat treatment according to any one of claims 1 to 5, characterized in that the amount of the alkaline agent expressed as OH put in intimate contact with the ore to carry out the wetting is chosen in the interval from 4 to 100 kg of OH per tonne of clay contained in the ore and preferably from 10 to 90 kg per tonne of clay contained in the ore . 7 - Process for pretreatment at atmospheric pressure or close to atmospheric pressure of ores with a clay matrix by alkaline hnmectage and heat treatment according to any one of claims 1 to 6, characterized in that, taking into account all of the water present in the moistening medium after contacting the ore with the alkaline agent, the ratio of the liquid phase expressed in cubic meters to the solid phase expressed in tonnes of the ore is generally between 0.05 and 0.99. 8 - Process for pretreatment at atmospheric pressure or close to atmospheric pressure of clay-gang ores by alkaline wetting and heat treatment according to any one of claims 1 to 7, characterized in that: a) the ore whose particle size is at most equal to the mesh of release of the metallic element to be valorized is brought into intimate contact with at least 4 kg expressed as OH- of at least one alkaline agent per ton of clay contained in the ore, b) the moistened medium is subjected to the elimination of the releasable water present until a liquid phase ratio expressed in cubic meters and solid phase expressed in tonnes of ore are obtained (L / S in m3 / T) , at most equal to 0.2, finally, c) the moistened medium thus treated is brought to a minimum pre-treatment temperature of at least 105 ° C. 9 - Process for pretreatment at atmospheric pressure or close to atmospheric pressure of clay-gang ores by alkaline wetting and heat treatment, according to claim ⁸ , characterized in that the quantity of the alkaline agent expressed as OH brought into intimate contact with the ore to carry out moistening is chosen in the range from 4 to 45 kg OH per tonne of clay contained in the ore, and preferably from 10 to 40 kg of OH ^- per tonne of clay contained in the ore. 10- Process for pretreatment at atmospheric pressure or close to atmospheric pressure of clay-gang ores by alkaline wetting and heat treatment, according to any one of claims 8 and 9, characterized in that, taking into account all of the water present in the moistening medium after contacting the ore with the alkaline agent, the ratio of the liquid phase expressed in cubic meters to the solid phade expressed in tonnes of the ore is generally between 0.2 and 0 , 99, and preferably between 0.2 and 0.8. 11- Process for pretreatment at atmospheric pressure or close to atmospheric pressure of ores with a clay matrix by alkaline wetting and heat treatment, according to any one of claims 8 to 10, characterized in that the moistened medium is subjected to elimination releasable water present until a liquid phase ratio expressed in cubic meters to the solid phase expressed in tonnes of ore at most equal to 0.2 and preferably at most equal to 0.15 is obtained. 12- A method of pretreatment at atmospheric pressure or close to atmospheric pressure of clayey ores by alkaline wetting and heat treatment, according to any one of claims 8 to 11, characterized in that the moistened medium, whose liquid phase ratio expressed in cubic meters to the solid phase expressed in tonnes of ore has been fixed at most equal to 0.2, is brought to a temperature chosen in the range of 105 ° C to 450 ° C and, preferably in the range of 110 ° C to 200 ° C. 13- Process for pretreatment at atmospheric pressure or close to the atmospheric pressure of clay-gang ores, by alkaline wetting and heat treatment according to any one of claims 1 to 5, characterized in that: a) the ore whose particle size is at most equal to the mesh of release of the metallic element to be valorized is brought into intimate contact with at least 4 kg expressed as OH of at least one alkaline agent per ton of clay contained in the ore, via an aqueous phase present in an amount such that the L / S ratio of the liquid phase expressed in cubic meters to the solid phase expressed in tonnes of dry ore is at most equal to 0.6. b) the ore thus moistened is subjected to a pretreatment temperature of at most 105 ° C for a time of at least 30 minutes. 14 - Process for pretreatment at atmospheric pressure or close to atmospheric pressure of ores with a clay matrix by alkaline wetting and heat treatment, according to claim 13, characterized in that the quantity of the alkaline agent expressed as OH brought into intimate contact with the ore to carry out the wetting is chosen in the range from 4 to 100 kg of OH per tonne of clay contained in the ore, and preferably from 10 to 90 kg of OH per tonne of clay contained in the ore . 15- A method of pretreatment at atmospheric pressure or close to atmospheric pressure of clayey ores by alkaline wetting and heat treatment, according to any one of claims 13 and 14, characterized in that, taking into account all of water present in the moistening medium after the ore has been brought into contact with the alkaline agent, the ratio of the liquid phase expressed in cubic meters to the solid phase expressed in tonnes of the ore is generally between 0.05 and 0.5, and preferably between 0.1 and 0.4. 16- A method of pretreatment at atmospheric pressure or close to atmospheric pressure of clayey ores by alkaline wetting and heat treatment, according to any one of claims 13 to 15, characterized in that the moistened medium is brought to a selected temperature in the range of 15 ° C to 100 ° C, and preferably in the range of 30 ° C to 90 ° C. 17- A method of pretreatment at atmospheric pressure or close to atmospheric pressure of ores with a clay matrix by alkaline wetting and heat treatment, according to any one of claims 1 to 16, characterized in that the ore is subjected to drying prior to putting it in the mesh of liberation of the metallic element or elements to be valued. 18- A method of pretreatment at atmospheric pressure or close to atmospheric pressure of clayey ores by alkaline wetting and heat treatment, according to any one of claims 1 to 17, characterized in that the ore is subjected to drying simultaneously with putting it in the mesh of liberation of the metallic element or elements to be valued. 19- A method of pretreatment at atmospheric pressure or close to atmospheric pressure of ores with a clay matrix by alkaline wetting and heat treatment, according to any one of claims 1 to 18, characterized in that the knitting of the or metal elements to be recovered are made by grinding without adding water. 20- A method of pretreatment at atmospheric pressure or close to atmospheric pressure of clayey ores by alkaline wetting and heat treatment, according to any one of claims 1 to 19, characterized in that a known agent for oxidizing reduction and / or complexing agent is introduced into the pretreatment medium.