AU2011257249A1 - Cementation cell for the extraction of metals from a solution - Google Patents

Abstract

Cementation room comprising at least one cementation cell provided in order to carry out a cementation of at least one first metal in at least one first aqueous phase in contact with at least one second metal in the solid state comprising: a vessel; a basket at least partially submerged in said reaction medium; a supply of said at least one first aqueous phase; at least one pneumatic supply of said at least one second metal; passing through said vessel; and an outlet of at least one second aqueous phase depleted in said at least one first metal and enriched in said at least one second metal.

Description

CEMENTATION CELL FOR THE EXTRACTION OF METALS FROM A SOLUTION 5 The invention relates to a cementation room comprising one or more cementation cells, provided for carrying out cementation in solution in at least one first aqueous phase in contact with at least one second metal, as well as to a cementation method. In extractive metallurgy of non-ferrous metals, certain metals are elaborated as by 0 products of the metallurgical treatment of the main metal in the ore (see DE 32311624, US 3655175, RU 2344185 or BE 898504). This is the case of cobalt which is generally extracted as a by-product of metallurgy of copper and of nickel via a hydrometallurgical route. Certain cobalt minerals have the drawback of requiring a reducing agent for the leaching of ores containing copper-cobalt during their 5 hydrometallurgical treatment, while copper is leached under oxidizing conditions. Therefore it proves to be interesting to develop novel technologies for not only reclaiming copper but also cobalt and trace amounts of uranium, silver and gold from copper-cobalt containing ores in an economically more cost-effective way. It also '0 proves to be interesting to develop novel technologies for extracting metal cobalt and the salts and oxides of cobalt with high purity, since they are more precious than cobalt carbonate and hydroxide salts presently marketed on the global market. Patent US 3,902,896 shows the cementation of several metals like nickel, copper, gold, silver !5 and platinum. Unfortunately, this document does not either disclose or tackle the possibility of cementing cobalt since cobalt is used as a cementing metal. Further it is a great consumer of energy and suggests the addition of thiosulfate so that cementation does not end prematurely. Document US 3,930,846 discloses precipitation of copper by iron. 10 The invention therefore intends to provide a cementation method as well as a cementation room in which elementary metals of very high purity may be applied.

2 Presently, this is only feasible by means of electrolysis. Unfortunately, such a method like electrolysis is highly energy-consuming like present hydrometallurgical methods. In several African countries with mining potential, an blatant electric power deficit 5 unfortunately subsists, which hinders development of the metallurgical industry and consequently makes present methods unusable in a reliable way. This is also the case of the Democratic Republic of Congo, in particular in the copper-cobalt-rich province of KATANGA where the development of hydrometallurgical plants based on copper and cobalt electrolysis comes up against the lack of electric power in the 0 region. The corporations for producing and distributing electric power are often confronted with enormous financial and technical difficulties and are unable to meet this demand for electric power within a reasonably short delay. Consequently, it proves to be interesting to develop novel technologies which are 5 less electrical energy-consuming than conventional extraction methods with solvents and electrolysis methods on mining sites. The present invention therefore relates to a hydrometallurgical method for cementation of metals, including cobalt, less energy-consuming than the methods of .0 the present state of the art, which may be applied industrially. For this purpose, the invention therefore provides a cementation room provided for carrying out cementation of at least one first metal in at least one first aqueous phase in contact with at least one second metal in the solid state, said at least one !5 cementation cell comprising: - a vessel laid out for containing a reaction medium; - a basket laid out so as to be submerged at least partly in the reaction medium; - a supply of said at least one aqueous phase containing said at least one first 30 metal, for supplying said at least one first aqueous phase to the basket; - at least one pneumatic supply of at least one second metal, passing through the vessel so that said at least one pneumatic supply of at least one second metal 3 being laid also as to put said at least one first metal in contact with said at least one second metal supplied pneumatically; and - an outlet of at least one second aqueous phase substantially depleted in said at least one first metal and enriched in said at least one second metal, connected to 5 the vessel. As this may be seen, the present invention therefore relates to a cementation room which may operate in a continuous mode, resulting in elementary metals and derivatives of metals with very high purity, while being clearly less energy-consuming, 0 which, unlike electrolysis, sets into play the internal energy of chemical reactions. Therefore it is no longer necessary to provide external electricity on the production site for maintaining the hydrometallurgical conversions. In conventional methods, since it is known that during cementation, the solution has 5 to be stirred for good kinetics reaction , cumbersome mechanical stirring means are applied, which makes the unloading of the cementation vessels tedious and not very flexible. In the reaction vessel of the cementation room according to the invention, the second metal more electronegative than the first metal (for example copper) is supplied into the cell by pneumatic conveyance, which is used at the same time as a o carrier for stirring the solution in the cell. In this way, the reaction vessel (also sometimes called a cementation cell) is particularly well stirred and this in a compact way and the contact between the first metal to be cemented and the second more electronegative metal than the first metal is optimum. From this, the result is therefore optimum use of the internal reaction energy which then occurs for cementation. 5 By pneumatic conveyance of said first metal is meant a metal present in a carrier gas in the form of powder, flakes, chips, granules, cable pieces, rods, ... Advantageously, the cementation room is designed so as to comprise n cementation 0 cells, wherein an nth cementation cell comprising an nth basket is in series with an (n-1)th cementation cell so that the (n-1)th outlet of a (n-1)th aqueous phase substantially depleted in said at least one first metal and enriched in said at least one second metal of the (n-1)th cementation cell is connected to the nth supply of the 4 (n-1 )th aqueous phase for supplying the (n-1 )th aqueous phase to the nth basket of the nth cementation cell. With this cascade circuit of cementation cells in the cementation room, very great 5 operating flexibility is obtained when it looks like a conventional electro-winning (EW) room and then includes universal portions. Additionally, the cementation room is unloaded for 24 hours a day and therefore has greater productivity than conventional EW rooms. As this may be seen, the cementation room therefore comprising n cells has operational fluidity at least equal to that of an electrolysis room for ensuring an 0 economically competitive productivity level since the outlet of the (n-1 )th cell or reaction vessel is connected to the inlet of the next one, the nth cell or reaction vessel. Advantageously, said at least one pneumatic supply is secured to said vessel and 5 not to said basket while communicating with said basket. Said at least one pneumatic supply is preferably connected to at least one diffuser, the diffuser being secured to the vessel and engaged in through-orifices provided in the bottom of the basket. This arrangement gives the possibility of setting into place and of freely removing the 0 basket from the vessel by sliding it along the diffusers through apertures made in the bottom of the basket and dimensioned for this purpose. The pneumatic stirring according to the invention therefore allows optimum stirring for the distribution of the gas by means of diffusers in the reaction vessel of the device 5 according to the invention. Further, the contact between the first metal and the second metal is also further improved by the presence of a diffuser which distributes over the height and over the surface when they are present in a larger number, the second metal conveyed by said gas. Carrier gas is therefore used at the same time as a carrier for stirring the solution. 0 Further, the supply of said second metal is applied by a set (the diffuser is secured to the vessel) and controlled device which does not perturb the unloading of the vessels. The second more electronegative metal than the first metal is therefore 5 preferably supplied in the vessels through the bottom, as a counter-current relatively to the solution which will be supplied from the top. In another advantageous embodiment according to the invention, one or more 5 baskets comprise at least one attachment means reciprocal to another attachment means laid out on a bridge crane laid out for removing from the top, said basket of said vessel. Thus, the basket of cells is therefore easy to recover. In an alternative, the basket includes a surface of at least one first metal in the solid 0 state for initiating cementation of at least one first metal to be cemented by the growth of the crystals of said at least one first metal to be cemented on said surface of at least one first metal in the solid state. In an advantageous embodiment according to the invention, said at least one second 5 metal in the solid state is pneumatically supplied in a flow of nitrogen gas, instead of and in place of air, which avoids oxidation of the powder of said second metal. In an advantageous embodiment according to the invention, said at least one pneumatic supply is connected to a tank of at least one second metal communicating with a worm screw 0 for metering at least one second metal and to a gas supply, the gas supply being laid out so as to bring at least one gas, for example nitrogen gas, to the pneumatic supply where at least one second metal is metered by the worm screw. Also, in a cementation room comprising n cementation cells, said at least one pneumatic 5 supply of the nth vessel is connected, preferably in parallel, to the pneumatic supply of the (n I)th vessel, each pneumatic supply being connected to a tank of at least one second metal, and communicates with a worm screw for metering at least one second metal, and to a gas supply, the gas supply being laid out so as to bring at least one gas, for example nitrogen gas, to the pneumatic supply where said at least one second metal is metered by the worm screws. Each 0 cell is therefore preferably fed independently of the others at calculated doses and identically controlled for each cell.

6 In an alternative, each cementation cell of the cascade may actually be adjusted to the gas flow rate and to the pneumatic supply of said at least one second metal, thereby allowing optical recovery of said at least one first metal from the aqueous phases increasingly depleted in said at least one first metal in the cascade. 5 The advantage of this cementation room is therefore that it is designed for recovering an abundance of metals, i.e. for carrying out cementation of at least one first metal which is a transition metal from the periodic classification of chemical elements, notably copper, nickel, cobalt in metal form. 0 In an advantageous embodiment according to the invention, said at least one second metal is a metal from the group consisting of aluminium, aluminium nitride, magnesium, iron, zinc. 5 The selection of at least one second metal is determined by the potential difference between the first metal/second metal pair and by the desirable magnitude of the cement crystals. As an example, aluminium will preferably be used for the reasons mentioned later on, as well as for its low density which makes it a second metal of choice in a pneumatic supply. 0 In an advantageous embodiment of the invention, said at least one second metal is in the form of fine particles. In this way, certain fine particles of second metal coated with a first metal to be cemented, having cemented, may pass through the basket and will be driven by the aqueous phase flow into the next cell where they are used 5 as first seeds. Advantageously, the cost of said at least one second metal is balanced by recovering said at least one second metal, for example aluminium by precipitation of the solutions in the form of AI(OH) 3 and partly in the form of

AI(OH)SO

4 , which may be marketed as alumina (A1 2 0 3 ) after calcination. The aluminium is available in most mining regions and this proximity facilitates the return 0 transport of the alumina to the export ports.

7 The outlet of said at least one second aqueous phase advantageously comprises a lateral edge allowing an overflow of said at least one second aqueous phase substantially depleted in said at least one first metal. 5 In an advantageous embodiment according to the invention, one or more cementation cells comprise a surface of at least one second metal, for example one or more copper sheets, for initiating crystallization, for example for initiating copper crystallization during the copper cementation on Al. Preferably, this surface, for example this copper sheet, is provided in one or more baskets for facilitating 0 cementation at said one or more baskets. Therefore, it may be seen that the cementation room is equipped in order to provide productivity on an industrial scale, as large as possible, because of the synergistic function of the supply of said at least one first aqueous phase and of the pneumatic 5 supply, as well as by the permanent flow of the first aqueous phase having set at least one first metal to be cemented, and the exit of the second aqueous phase depleted in said at least one first metal to be cemented. The fluidity of the cementation room is therefore attained. 0 Other embodiments of the cementation room according to the invention are mentioned in the examples, the detailed description and the appended claims. The present invention also relates to a method for cementing at least one first metal in at least one first aqueous phase in contact with at least one second metal in the 5 solid state, the method comprising: - supplying said at least one aqueous phase containing said at least one first metal in at least one first aqueous phase in a vessel; - contacting at least one first metal with said at least one second metal 0 pneumatically brought into the vessel; continuous cementation by the putting of n vessels in series, the nth of which is supplied with the (n-1)th aqueous phase depleted in said at least one first metal and 8 enriched in said at least one second solubilized metal leaving the (n-1)th vessel of at least one first metal by consuming the internal chemical energy of the cementation reaction in the presence of at least one second metal in the solid state, followed by depletion of said at least one aqueous phase in said at least one first metal and by 5 enrichment of at least one aqueous phase in said at least one second solubilized metal; and - recovery of at least one first cemented metal as a solid. 0 With the method according to the invention, it is therefore possible to operate in a region which has an electric energy deficit, as mentioned above. In order to deposit the metal according to the invention, the internal chemical energy of the reactions is used and not the external energy provided by a transformer/rectifier like in the conventional SX/EW method. Further, the method according to the invention gives 5 the possibility of bypassing both SX/EW steps and of replacing them with a single step for precipitation of copper as very pure crystals. Indeed it is possible to attain a purity of 99.9% of Cu. With the same treatment, the solution is totally depleted in copper: a final content of less than a 100 mg/. 0 With the method of the invention, it is therefore advantageously possible to treat via a hydrometallurgical route, copper and cobalt oxidized or sulfurized concentrates or ores for producing by cementation of both of these metals in the form of pure cements. Nickel, when it is present in the ore, has a valuable content, may also be produced by cementation. Finally, trace amounts of uranium may be precipitated. 5 The advantage of this method is therefore recovering an abundance of metals, i.e. at least one first metal selected from a transition metal of the periodic classification of chemical elements, notably copper, nickel, cobalt, silver, gold, manganese, platinum in the metal or oxide form, or as an acid salt. 0 Finally it is possible to reach an inexpensive and cost-effective recovery of valuable metals such as copper and cobalt as compared with conventional techniques. Further, this is the first time that an industrial application of cementation of metals 9 such as cobalt and nickel is carried out as a continuous process on aqueous phases on an industrial scale. In an advantageous embodiment according to the invention, said at least one first 5 metal in at least one aqueous phase stems from a preliminary leaching step. The cementation method preferably also comprises a step for initiating cementation of at least one first metal by growing crystals of at least one first metal on a surface of at least one first metal in the solid state. 0 In an advantageous embodiment according to the invention, the cementation method uses at least one second metal, being a metal from the group consisting in aluminium, aluminium nitride, magnesium, iron, zinc. 5 In an advantageous embodiment according to the invention, said at least one second metal in the solid state is pneumatically supplied in a flow of nitrogen gas, instead of and in place of air, which avoids oxidation of the aluminium powder. The selection of at least one second metal is determined by the potential difference 0 between the first metal/second metal pair and by the desirable magnitude of the cement crystals. The price of copper has considerably increased these last few years so that it is economically possible to use Al for cementing Cu instead of and in place of iron, with as an advantage, the establishment of a very high potential difference between the pairs: 5 AE*cu/A = 0.34V -(-1.67V) = 2.01V This potential difference is of the same order of magnitude as the industrial voltage on the terminals of the copper electrolysis cell: UA/c = 1.9 to 2.2 V. Such a potential difference gives 0 the possibility of collecting the copper cement in the form of giant crystals, of depleting the cemented aqueous phase (final concentration of the solution < 100 mg/l of copper), which corresponds to purification for copper by SX, and of ensuring very fast cementation kinetics 10 in the sulfate medium. Indeed, the cementation occurs on a short-circuited battery cell. AE* being widely greater than 0.36 V, the cementation current is in the area of the limiting Cu diffusion current. The cementation kinetics are then controlled by diffusion and not by the electrochemical reaction. The reaction is quasi-spontaneous. The growth of the crystals occurs 5 on the first seeds, a conducting solid phase. In order to deposit the metal, the chemical energy internal to the reactions and not the external energy provided by a transformer/rectifier are therefore used. Technically in the method according to the invention, copper is deposited by cementation on 0 powdered aluminium according to the reaction: 3Cu** + 2A1 0 = 3Cu* + 2A 3 * 3CuSO4(aq) + 2Alcs) = 3CuS) + Al2(SO4)3(aq)

AG

0 z 98 = 278.73 kcal 5 Moreover, as copper is very electropositive as compared with the other elements present in the solution, it precipitates alone without any possible contamination. The low Al stoichiometric excess is consumed by the secondary reactions such as the Fe2+/Fe3+ pair and the acid attack. In order to avoid simultaneous precipitation of 0 aluminium hydroxide [AI(OH) 3 ], the pH of the solution will advantageously be controlled to pH = 2 - 2.5. It is thus possible to obtain a copper cement with a titer of 99.9% Cu after intensive washing for removing the impregnating sulfate solution. Cementation by iron or zinc leads to a very fine powdery cement which easily 5 oxidizes in air and is polluted with iron or zinc, the potential difference between the pairs being relatively low so as to lead to a cement in the form of giant crystals. Moreover, the depletion of the solution is not always very extensive. The other advantage and not the very least, is the difference in the valences and 0 molecular masses between Al and Cu which leads to low consumption of Al per ton of Cu. Indeed, the theoretical consumption of Al per cemented copper ton is: 2 x 27/3 x 63.55 = 0.283 T of Al per T of Cu.

II From an economical profitability point of view, this aspect of the question is one of the fundamental criteria in the selection of Al as a metal for cementation of copper among other metals. 5 Other embodiments of the cementation method according to the invention are indicated in the appended claims. The present invention also relates to a use of a hydrometallurgical reactor according 0 to the invention for enhancing the value of a (either oxidized or sulfurized) metal ore, its concentrate or its ash from sulfide roasting. Other embodiments of the use of a hydrometallurgical reactor according to the invention are indicated in the appended claims. 5 Other characteristics, details and advantages of the invention will become apparent from the description given hereafter, in a non-limiting way and with reference to the appended drawings and examples. o Fig. 1 is a graph illustrating a cementation room according to the invention. Fig. 2A is a graph illustrating a cementation cell according to the invention. Fig. 2B is a schematic sectional view of a cementation cell according to the invention. 5 Fig. 3 is an assembly plan illustrating two cementation cells connected in series according to the invention. Fig. 4 is a graph illustrating a diffuser according to the invention. 0 Fig. 5 is a cementation diagram applied in the cementation room according to the invention. In the figures, identical or similar elements bear the same references.

12 By the term of "metal ore" is meant in the sense of the invention, polymetal ores, inter alia comprising those of the Shinkolobwe type or the deposits of Swampo, Kasompi, or Musonoi, polymetal ores low in uranium, and copper-cobalt containing ores as inter alia from the 5 Katanga belt, characterized by the presence of trace amounts of uranium. By the term of "metal ore", is also meant in the sense of the invention oxidized ores, often occurring at the surface of the deposit and sulfurized ores occurring in depth instead. This metal ore may be an ore which comprises U, Cu, Co, Ni in the presence of trace amounts of noble metals such as Au, Ag and platinoids. 0 Fig. 1 therefore illustrates a cementation room 100 comprising at least one or more cementation cells 300 intended for carrying out cementation of at least one first metal in at least one first aqueous phase in contact with at least one second metal. 5 As this may be seen in Fig. 1, the cells 300 may be arranged as a cascade in rows in the cementation room 100, so that the upper cell feeds the lower following cell. The aqueous phase containing one or more metals to be cemented may be stored in a tank 102 from which the first cell 300 is fed. 0 The cementation room 100 includes a network 104 for distributing the second cementation metal in a gas flow, for example Al powder in a flow of nitrogen gas. The second cementation metal may be stored for example in a tank 105. Each cell 300 is then equipped with a pneumatic supply for pneumatically metering this second cementation metal in the reaction medium for carrying out cementation, for example copper cementation. An adequate dosage 5 of powder Al may be carried out in each cell by flow rate regulators, for example worm screws 106. The powdered Al is therefore blown into one or more cells 300 by blowing 107 gas, for example a flow of nitrogen gas. Additionally, the cementation room 100 may comprise a bridge crane 101 designed 0 for removing the baskets from the cells, for example the baskets filled with one or more cements. In a particular embodiment of the invention, a column of four cells is unloaded at a time. Thus, 6 unloading cycles may be obtained per cell and per day.

13 The cementation room 100 may further comprise elements for treating the final products of the cementation method. Thus, a depletion tank 108 may be provided for containing the last aqueous phase. The obtained cement may in turn be washed in a station 109 for rinsing cements, before being displaced towards storage by a 5 conveyance means 110. In order to recover the fines of the cements, for example from the last aqueous phase, a pump 111 may facilitate conveyance towards a filtration means. The cementation room 100 may further comprise a working floor 112 between the 0 rows. As the cementation room is designed for operating on an industrial scale, its dimensions are suitable for this treatment of large volumes of liquids. In a particular embodiment of the invention, the dimensions shown in Table 1 are contemplated: 5 Table 1. Making the room available (MAD) 90% Rate of use of MAD 90% Productive working time 80% Average load per basket 1T Average loading/unloading cycle per basket 4 h Maximum height of the cascade row (4 cells) 7 m Height of the hall lom 0 In another particular embodiment of the invention, the cementation room is configured in four halls each with sixteen cells, arranged in columns and rows in cascade, 4 x 4. Each hall is equipped with a bridge crane (± 7.5T). The room is thus equipped with 64 cementation cells, which, with an average load of one ton per 14 basket and 6 cycles per day may produce up to 112,128 tons. The daily average production is therefore 307.2 tons. For example, for a first aqueous phase with a titer of 40 g/l of Cu, the flow rate of the 5 aqueous phase per row is 25 m 3 /h. Unlike the conventional EW room, the unloading of a cementation room may take place 24 hours a day. The total surface area of the room may thus be established to 65 m x 25 m = 1,625 M 2 . It may be noted that the same room may produce twice its capacity, i.e. 200,000 tons 0 of copper per year, if the solution is enriched to 50 g/l of Cu and if the flow rate of the solutions is increased to 35 m 3 /h. This is only possible in a cementation room and not in EW. As this may be seen in Figs. 2A, 2B and 3, the cementation cell 200 comprises a 5 vessel 201 laid out for containing a reaction medium 202. Depending on the reactions to be applied in the vessel 201, the latter may be in glass fibre, in stainless steel, or electrically insulated from the aqueous phase such as in carbon steel, optionally protected by an anti-acid resin coating, as well as all the 0 mobile and static parts which are present therein. In a particular embodiment according to the invention, the vessel 201 is fed by a supply 203 from the top and emptied through an outlet 204 through the bottom. The vessel 201 may also be supplied from the top and emptied from the top. 5 In another advantageous embodiment according to the invention, the cementation cell 200 comprises a basket 205 laid out so as to be at least partly submerged in the reaction medium. The basket 205 is laid out so as to receive said at least one pneumatic supply 206, for example through apertures in the bottom of the basket 0 207. The basket 205 may be perforated with fine holes 208, for example from 2 mm to 3 mm in order to let through the giant copper crystals. The basket 205 may be laid on foundations 209, for example fixed foundations inside the vessel.

15 The cementation room 100 is preferably equipped with an installation for distributing the aqueous phases over the different rows. The register valves at the inlet 212 and at the outlet 213 of each cell 200 control the flow rate of the solutions in order to maintain the level constant in each vessel 201. This level is flush with the basket 205 5 while maintaining the safety guard at the vessel 201. In the case of total blocking of the basket by the cements, the latter may thus overflow over the lateral edges 203, 204, 212, 213 of the basket in the vessel, without losing the solutions out of the circuit of the cells. 0 The basket 205 includes a surface 210 of at least one first metal for initiating cementation of the metal to be cemented by growing crystals of the metal to be cemented on the first metal sheet. For example a more or less rough copper sheet 210 may be placed in the bottom of the basket 205 on four legs so as not to hinder circulation of the solution. 5 The basket 205 has dimensions such that it does not touch the bottom and the walls of the vessel 201 for allowing the aqueous phase to circulate through the basket. The aqueous phase supplied from the top through an orifice 203 made in a wall of the vessel, may totally overflow into the basket and may be collected in the bottom of the vessel through the outlet 0 204 after having crossed the basket. The thereby collected solution feeds the next cell. The basket may be provided with handles 211 which may be hooked up by the crosspiece of a bridge crane 101 (see Fig. 1) in order to set it into place or to evacuate it from the vessel 201. The cementation cell 200 further comprises a supply 203 of said aqueous phase 5 containing said at least one first metal in solution, for supplying said at least one first aqueous phase into the basket. The cementation cell 200 comprises at least one pneumatic supply 206 of at least one second metal, connected to the basket 205 and passing through the vessel 201 10 in such a way that the pneumatic supply 206 is secured to the vessel and not to the basket while ending up in the basket. The pneumatic supply also comprises a diffuser explained in more detail in Fig. 4. Each cementation cell of the cascade may further 16 be adjusted as regards the gas flow rate and at the pneumatic supply of said at least one second metal by a flow rate regulating means 212, 213. The cementation cells will be dimensioned in such a way that the handling of the 5 baskets is not too tedious and cumbersome. The crossing rate of the solution through the basket should be relatively low so as not to carry away out of the basket the seed nuclei before their growth. Thus the cells will have the following outer dimensions shown in Table 2. 0 Table 2. Vessel Basket Length 1.95 m 1.45 m Width 1.70 m 1.20 m Height 1.35 m 1.00 m Wall thickness 0.10 m 0.05 m Useful volume 1.41 m 3 As this may be seen in Fig. 4, the pneumatic supply includes at least one diffuser 400 which includes an anti-return valve 402 and a leak-proof cap 403 rotating around the 5 diffuser and pierced with excentered holes. The conduits 401 for supply of aluminium powder in the cell 200 cross the vessel through leak-proof passages and release the aluminium powder and the stirring gas at half height in the basket. These conduits, 4 per basket, are arranged at the four corners of the basket, a little set back from the walls of the latter. The basket is itself provided with the four holes 207 through which 0 the conduits pass freely. These diffuser conduits 400 (or aluminium powder disperser 400) are therefore secured to the vessel and not to the basket. With this arrangement, it is possible to set into place and to freely remove the basket from the vessel by sliding it along the diffuser-conduits through holes 207 made in the bottom of the basket and dimensioned for this purpose. 5 17 The invention also relates to a cementation method which is preferably integrated into a treatment method particularly suitable for ores from the Democratic Republic of Congo. The method will therefore be described while being integrated into the overall method for treating copper-cobalt containing ore, being aware that the latter may of 5 course be applied separately or in another overall method for treating ore depending on the needs. The ore rich in copper and cobalt is therefore first of all subject to oxidation leaching for the copper and reduction leaching for the cobalt 601 from which the aqueous phase containing the copper is separated from the pulp in order to carry out in a subsequent step 602 a cementation of copper on aluminium. The 0 aqueous phase containing the copper also contains iron, manganese, cobalt and magnesium. After clarification of the solution from the oxidation leaching, the copper is produced by cementation on the aluminium powder in the cementation room according to the 5 invention, according to the reaction: 3Cu 2 + + 2Al* = 3Cu* + 2A1 3 . 3 CUSO4(aq)+ 2Al (s) 3Cu*(s) + AI2(SO4)3(aq) AGreact 2 9 8 = 278.73 kcal 0 AE~react 29 8 = 2.014 V This potential difference of the same order of magnitude as the industrial voltage on the terminals of the EW copper cell (UAc = 1.9 - 2.2V) therefore allows, as mentioned earlier, the copper cement to be collected in the form of giant crystals, the 5 cemented solution to be depleted (final concentration of the solution < 100 mg/I). This corresponds to purification for copper by SX and insures very fast cementation kinetics in a sulfuric medium. Consequently, during cementation of the copper 602, the copper present in a first 0 state of oxidation (+1, +2) passes into the second state of oxidation (0) upon contact with the second more electronegative metal (for example aluminium) and precipitates.

18 As copper is very electropositive as compared with the other elements present in the solution, it precipitates alone without any possible contamination. The small aluminium excess is consumed by the parasitic reactions such as the Fe 2 +/Fe3+ pair 5 and acid attack. In order to avoid the simultaneous precipitation of AI(OH) 3 , the pH of the solution is maintained to pH = 2 - 2.5. A copper cement with a titer of 99.9% Cu may thereby be obtained after extensive washing for removing the impregnating sulfate solution. O The metered aluminium powder is fed into the cell by pneumatic conveyance with nitrogen gas which is used at the same time as a carrier for stirring the solution in the cell. For safety reasons (inflammability of powdered aluminium), it is possible to make use 5 of aluminium nitride (AIN) as a powder instead and in place of the aluminium but, in this case, AE* is lowered to AE* = 1.285 V. The copper cements will be melted in order to be cast into ingots. The solid copper is therefore recovered while the aqueous phase is further treated 0 subsequently for precipitating and removing impurities such as iron and manganese by oxidation with a mixture of air and of SO 2 in a suitable reactor. The iron and the manganese are recovered as a solid oxide or hydroxide while the aqueous phase is further treated for recovering aluminium in step 604. This step 5 comprises neutralization of the aqueous phase with a base in order to precipitate aluminium hydroxide, recover it and then calcine it in order to form alumina. The aqueous phase may then be treated for recovering cobalt, either by precipitation 605, or by cementation 610. 0 The aqueous phase is then subject to oxidation, for example with an air/SO 2 gas mixture which produces cobalt oxide C020 3 from the Co(OH) 3 obtained from the 19 cobalt sulfate initially present in the aqueous phase. The pH of the aqueous phase is advantageously comprised between 5 and 6, after neutralization by adding a basic solution or suspension, for example by adding milk of magnesia in order not to pollute the precipitate. Generally, the nickel present in the aqueous phase in trace amounts 5 will not be oxidized before cobalt. If the aqueous phase contains more nickel, a preliminary purification step will have to be added in order to remove the nickel. The salt C020 3 is recovered by decantation, filtration, washing on a filter press and is then calcined and conditioned for its recovery. 0 The aqueous phase substantially depleted in cobalt is rich in magnesium. Magnesium salts at a high concentration are generally harmful to the environment. This aqueous phase is therefore treated by adding a basic solution or suspension, for example by adding limestone or lime milk which allows precipitation of Mg(OH) 2 at a 5 pH preferably > 10 (606). The solid Mg(OH) 2 present in the state of oxidation of +2 is recovered and may be reused as a neutralizer in the basic solution/suspension. Otherwise Mg(OH) 2 is separately or simultaneously discarded with the leaching wastes. 0 The aqueous phase depleted in magnesium may then be subsequently treated in order to re-pulp the solid waste or the ore in the leaching step 601. Otherwise, the aqueous phase may again be treated with view to recovering uranium when it is present (607). 5 If the aqueous phase from the step for precipitation of the aluminium 604 is treated in order to recover cobalt by cementation 610, optionally with addition of a basic solution/suspension, for example milk of magnesia, in order to promote the kinetics of the reaction. 0 The thereby cemented cobalt (optionally together with aluminium and magnesium) is thus recovered and the aqueous phase is then optionally treated in order to precipitate aluminium hydroxide 611 in the presence of a base before treating residual waters in step 608.

20 Cobalt hydroxide precipitated in step 605 may again be leached in a sulfuric medium and in the presence of SO 2 . S02 appears in the case of re-leaching precipitates of pure oxides Co 2 0 3 .xH 2 0, as a non-polluting reducing agent for the solution, in the 5 absence of the oxidation-reduction pair Fe2+/Fe3+, re-leaching of cobalt oxides is accomplished according to the reactions: 2[Co(OH) 3 s + [SO2](aq) + [H2SO4]aq = 2[COSO4]aq + 4[H 2 0] 0 2[CoOOH], + [SO2](aq) + [H2SO4]aq = 2 [COSO4]aq + 2[H 2 0] [CO30 4 ]s + [SO2](aq) + 2 [H2SO4]aq = 3 [COSO4]aq + 2[H 2 0] [C0203]s + [S 0 2](aq) + [H2SO4]aq = 2 [COSO4]aq + [H 2 0] 5 The re-leached cobalt from step 609 may after being cemented 610 be used for obtaining metal cobalt with very high purity. The residual waters are then also treated 608 and neutralized with limestone (filler) 0 and lime milk in order to precipitate Mg(OH) 2 at pH > 10. After decantation and filtration, the clear waters may be recycled into the process. After solid/liquid separation, the solids, if they are not reused as a neutralizer in another step of the method, are discarded separately or at the same time as the leaching wastes. 5 Of course, the present invention is by no means limited to the embodiments described above and many modifications may be provided thereto without departing from the scope of the appended claims.

Claims (12)

1. A cementation room comprising at least one cementation cell provided for carrying out cementation of at least one first metal in at least one first aqueous 5 phase upon contact with at least one second metal in the solid state, said at least one cementation cell comprising: - a vessel laid out for containing a reaction medium; - a basket laid out for being at least partly submerged in said reaction medium; - a supply of said at least one first aqueous phase containing said at least one 0 first metal, for supplying said at least one first aqueous phase to said basket; - at least one pneumatic supply of said at least one second metal, passing through said vessel so that said at least one pneumatic supply of said at least one second metal is laid out for putting said at least one first metal in contact with said at least one second metal supplied pneumatically; and 5 - an outlet of at least one second aqueous phase substantially depleted in said at least one first metal and enriched in said at least one second metal, connected to said vessel.

2. The cementation room according to claim 1 comprising n cementation cells 0 wherein an nth cementation cell comprises an nth basket is in series with an (n-1)th cementation cell so that the (n-1)th outlet of an (n-1)th aqueous phase substantially depleted in said at least one first metal and enriched in said at least one second metal of said (n-1)" cementation cell is connected to the nth supply of the (n-1)1h aqueous phase for supplying said (n-1)th aqueous phase to said nth basket of said 5 nth cementation cell.

3. The cementation room according to claim 1 or 2, wherein said at least one pneumatic supply is secured to said vessel and not to said basket while communicating with said basket. 10

4. The cementation room according to any of claims 1 to 3, wherein said at least one pneumatic supply is connected to a tank of said at least one second metal communicating with a worm screw for metering said at least one second metal; 22 and to a gas supply, said gas supply being laid out in order to bring said gas to the pneumatic supply wherein said at least one second metal is metered by said worm screw. 5 5. The cementation room according to any of claims 1 to 4, wherein said at least one pneumatic supply is connected to at least one diffuser, said diffuser being secured to said vessel and engaged into through-orifices provided in the bottom of the basket. 0 6. The cementation room according to any of claims 2 to 5, wherein said at least one pneumatic supply of the nth vessel is connected, preferably in parallel, to the pneumatic supply of the (n-1)th vessel, each pneumatic supply is connected to a tank of said at least one second metal and communicates with a worm screw for metering said at least one second metal and to a nitrogen gas supply laid out for 5 bringing nitrogen gas to the pneumatic supply, wherein said at least one second metal is metered by said worm screw.

7. The cementation room according to any of claims 1 to 6, wherein said at least one first metal is a transition metal from the periodic classification of chemical 0 elements, notably copper, nickel, cobalt, silver, gold, manganese, platinum as an oxide or an acid salt.

8. The cementation room according to any of claims 1 to 7, wherein said at least one second metal is a metal selected from the group consisting of aluminium, 5 aluminium nitride, magnesium, iron, zinc.

9. The cementation room according to any of claims 1 to 8, wherein said gas is nitrogen. 0 1O.The cementation room according to any of claims 1 to 9, wherein at least one surface of at least one first metal in the solid state is present in a reaction vessel. 23

11. The cementation room according to any of claims 1 to 10, wherein said basket comprises at least one attachment means reciprocal to another attachment means laid out on a bridge crane laid out for removing from the top, said basket of said vessel. 5

12.A method for cementation of at least one first metal in at least one first aqueous phase in contact with at least one second metal in the solid state, said method comprising: - supplying said at least one aqueous phase containing said at least one first 0 metal in at least one first aqueous phase in a vessel; - putting said at least one first metal in contact with said at least one second metal pneumatically brought into said vessel; - continuous cementation by putting into series n vessels, the nth of which is supplied with said (n-l)th aqueous phase depleted in said at least one first 5 metal and enriched in said at least one second solubilized metal leaving the (n-l)th vessel of said at least one first metal by consuming the internal chemical energy of the cementation reaction in the presence of said at least one second metal in the solid state followed by depletion of said at least one aqueous phase in said at least one first metal and by enrichment of said at 0 least one aqueous phase in said at least one second solubilized metal; and - recovering said at least one first cemented metal in solid form.

13.The cementation method according to claim 12 wherein said at least one first metal is a transition metal from the periodic classification of chemical elements, 5 notably copper, nickel, cobalt, silver, gold, manganese, platinum as an oxide or an acid salt.

14.The cementation method according to claim 12 or 13, wherein said at least one second metal is a metal from the group consisting of aluminium, aluminium 0 nitride, magnesium, iron, zinc. 24

15.The cementation method according to any of claims 12 to 14, wherein said at least one first metal in at least one aqueous phase stems from a preliminary leaching step. 5 16.The cementation method according to any of claims 12 to 15, wherein said at least one second metal in the solid state is pneumatically supplied in a nitrogen gas flow.