AU2012225185A1 - Metal separation method - Google Patents

Abstract

The invention relates to a metal separation method, comprising the following steps: introducing the metal to be separated together with a liquid into a reactor; adding process gas that reacts with the metal to be separated and blending same, recovering the metal to be separated, wherein the blending of the liquid and process gas is carried out after the "surface-gassing" operation and the gas is introduced via at least one gas inlet above the maximum fill level of the reactor and is discharged via at least one gas outlet above the maximum fill level of the reactor; the liquid is introduced via at least one liquid inlet and is drained off via at least one liquid outlet, the discharge preferably being effected via the base of the reactor; the liquid is stirred by a stirrer; wherein a homogeneous stirring-in of the process gas is rendered possible by at least one flow disturbance means interacting with the stirrer.

Description

Metal separation method The present invention relates to a metal separation method. 5 The purification and recovery of metals are in many respects important for various industrial materials cycles. By way of introduction, the hydrometallurgical purification and recovery of metal, especially using technical gases or pressurized gassing systems, will be described referring to the example of gold. lo Since antiquity, gold has been a precious metal highly in demand, used for various applications. Known processes for the exploitation of gold, for example, include gold washing, the amalgamation process, cyanidation or the anode mud process. In addition, the reprocessing of recycled gold- and metal-containing products is gaining an increasing importance for the recovery of gold, but also for recovery and 15 separation processes for other metals. In the course of gold washing, gold-containing sand is slurried with water. As gold is heavier than the sand surrounding it, it settles faster on the bottom andr may thus be separated. ?0 Cyanidation is applied in case of larger deposits which allow for an industrial exploitation. As gold dissolves as a complex compound in an oxygen-containing sodium cyanide solution (sodium salt of hydrocyanic acid HCN), the metal-containing sands are ground until they have the fineness of dust, piled up, and treated with the .5 extraction solution in a free-flowing process with free admission of air. In the course of this process, the smallest metal particles are dissolved first, as they have a relatively large reaction surface. The precious metal is then found chemically bound in the highly toxic percolation water. After filtration and precipitation using zinc dust, the precious metal is obtained as a brown slurry which, after washing and drying, o yields crude gold by way of reduction. 1 The anode mud process recovers gold from anode muds forming in the course of refining of other metals, mainly of copper. During electrolysis, the precious gold is neither oxidized nor dissolved; it accumulates beneath the anode. 5 The purification (refining) may also be achieved by different processes. Known processes include the Miller process, the Wohlwill electrolysis, solvent extraction, and chemical refining (see, for example Ullmann (1989), Encyclopedia of Industrial Chemistry, vol. A12, pp. 510-512). 10 The Miller process passes a chlorine gas stream through melted impure gold in order to remove the contaminants in the form of chlorides, which then escape in the form of gases or precipitate in the form of salts. The Wohlwill electrolysis uses an anode of contaminated gold, a cathode of pure 15 gold, and an electrolyte of tetrachloroauric acid. After applying a voltage, highly purified gold is deposited on the cathode. Solvent extraction may extract tetrachloroauric acid from an aqueous solution, using organic solvents, such as ethers and esters. A complete separation of contaminants 20 is not possible, however. Chemical refining separates contaminants, such as silver, by dissolving silver using nitric acid (nitric acid separation) or sulfuric acid (affination). Relatively pure gold may be obtained by dissolving crude gold in hydrochloric acid containing an oxidant. Gold 25 may then be reduced and precipitated using pxalic acid or sUlfur dioxide. Precipitation and separation normally have to be carried out repeatedly, in order to achieve an acceptable degree of purity and especially fine gold quality (99.99 or 99.999 % by weight, for example). 30 The precipitation of gold from a tetrachloroauric acid solution, using S02, is carried out according to the following reaction equation (I): 2 3 SO 2 +.2 H(AuCl 4 ) + 6 H20 2 Au + 3 H2SO 4 + 8 HCI (1) According to the state of the art, gold is separated from an aqueous gold solution as follows: 5 a) by precipitation, using FeSO 4 , Na 2

S

2 0 5 , FeCI2, or oxalic acid, for example; b) by introducing SO 2 gas into the aqueous gold solution. Compared to other ways of precipitation, the process according to b) has the significant advantage that gold may be precipitated selectively from the gold solution. o Usually, forced (pressure) gassing systems are used for gassing reactors. A disadvantage of forced (pressure) gassing systems which have been used so far is that the gas introducing body (lancet, gassing ring, for example) for introducing SO 2 gas into the system which looms into the gold solution may become clogged by the gold which spontaneously precipitates when contacted with the S021 gas; that a 5 hollow shaft stirrer, which may also be used for introducing the SO 2 gas into the system, may become clogged or covered by gold on the inside (difficult to clean); that the gold may precipitate in the gas feeding tubes and/or in the gas circulation tubes, so that they become covered by gold or clogged; that diaphragms of the gas circulation pumps may become covered by gold and may show signs of wear after a o relatively short period of time, requiring expensive wearing parts to be preventively replaced due to working safety considerations, in order to prevent the leakage of toxic process gases, for example, etc. The above practical problems in connection with forced (pressure) gassing do not S only occur in the case of the recovery of gold, but also, in a similarlform, in the course of the following processes: the dissolution of gold, the dissolution of silver, the dissolution of lithium carbonate, the dissolution of metals from the platinum group, and the dissolution and precipitation of other metals. D The object of the invention is to provide a process for separating metals which does not have the disadvantages of forced (pressure) gassing. 3 According to the invention, this is achieved by mixing of liquid and process gas according to the "surface effect gassing" (also referred to as surfacee gassing") method and the reactor comprising: - at least one gas inlet and at least one gas outlet, said at least one gas ihlet and said 5 at least one gas outlet being located above the maximum filling level of the reactor; - at least one liquid inlet and at least one liquid outlet, the latter being preferably located at the bottom of the reactor, - a stirrer, - at least one flow interrupting means (baffle) which, together with the Itirrer, allows L0 for the process gas to be stirred in homogeneously. The process steps are carried out by mixing of liquid and process gas according to the "surface effect gassing" method (also referred to as "surface gassing" method) and by 5 - introducing gas via at least one gas inlet above the maximum filling level of the reactor and discharging the gas via at least on gas outlet above the maximum filling level of the reactor; - introducing the liquid via at least on liquid inlet and discharging the liquid via at least one liquid outlet, wherein the discharging is preferably effected via the bottom of the 0 reactor; - stirring the liquid with a stirrer; - wherein a homogeneous stirring in of the process gas is allowed via at least one flow interrupting means (baffle) in combination with the stirrer. 5 The process gas is introduced according to the "surface effect gassing" Method (also referred to as "surface gassing" method) above the liquid level within th reactor (i.e. above the maximum filling level of the reactor which is not exceeded by the liquid). This has the significant advantage that the metal to be separated reacts with the process gas reacting with the metal to be separated in the liquid, instead of 0 immediately at the introduction site, when the process gas is introduced. This arrangement makes sure that the process gas feeding tube will not become clogged. 4 Arranging at least one flow interrupting means (baffle) within the reactor, in combination with the stirrer, allows for the process gas to be stirred in homogeneously. This arrangement homogeneously distributes the gas in the liquid, without creating a higher concentration of said gas anywhere in the liquid. Using 5 conventional stirrers and conventional reactors with or without conventional flow interrupting means (baffle), the gas is stirred in at the stirring axis, usually creating a spout (vortex effect); the stirred-in gas is only sparely distributed to the other areas of the liquid. Disposing at least one flow interrupting means (baffle), which is a surface effect flow interrupting means (surface effect baffle), in the reactor, interrupts the 10 liquid flow, so that gas from the surface (reactor headspace) is spread to the overall liquid. The co-rotation of the liquid and the stirrer is interrupted, and the surface effect flow interrupting means (surface effect baffle) additionally creates a so called "retaining dam effect". This creates a homogeneous distribution of the gas within the liquid, already at a low RPM value. One or several stirring blades may be fixed to the 15 stirrer, said blades also serving the purpose of improving the stirring in of-the gas. This process also entails a so called "surface gassing". "Surface effect gassing" is, thus, defined as the introduction of the gas via the liquid surface, the liquid being stirred in that way that the liquid only forms a small, ?0 eccentrical spout or, in the case of the "up-pumping system" described below, a spout close to the wall, and is still moved sufficiently by the combined action of the stirrer and the flow interrupting means (baffle) that the gas above the liquid is stirred into the liquid. "Forced (pressure) gassing" is just the opposite; in this case, the gas is introduced directly into the liquid. '5 This method of surface effect gassing constitutes a central element of the invention. In the case of forced (pressure) gassing systems, the gas is introduced into the liquid in a pressurized state. Typically, plunge pipes, feeding pipes or gassing rings, from 0 which the gas exits beneath the liquid surface, are used for such systems. The required gas pressure results from the desired amount of gas to be introduced as well as from the necessity to overcome the liquid's hydrostatic pressure at the point 5 of introduction. The choice of the gas introduction system depend on several parameters, including, for example, their implementability in a partic iar materials system, mountability, proneness to clogging, etc. The choice of the stirrilbg system, of course, also has an influence on the choice of the gas introduction system. 5 Self-aspirating systems use fluidic effects for introducing gas, which is present above the liquid surface, into the liquid. The hollow shaft stirrer, for example, works based on the principle of self-aspiration. Due to the negative pressure, forming at the tips of the stirring blades during the rotation of the stirrer (Bernoulli effect), gas is sucked 10 through the hollow stirrer shaft, which is open towards the gas space, and exits near the end of the stirring blades. When choosing the appropriate design of the stirrer and selecting the optimum RPM for the stirrer, this method may achieve the introduction of a good amount of gas. L5 Another form of self-aspiring gassing consists in the so called "self/vortex-gassing" method. This method substantially uses the effect of the formation of $pouts during stirring, in order to suck in gas via the liquid surface in the liquid. Mounting parts, such as conventional flow interrupting means (baffles), commonly counteract the formation of spouts, If sufficiently high energy is supplied to the stirrer, an appropriate 0 spout may be produced, with or without conventional flow interrupting means (baffles). As for gassing using a hollow shaft stirrer, self/vortex-gassing also requires the stirrer to have a sufficient, relatively high number of RPM in order to introduce a significant amount of gas into the fluid. The amounts of gas which may be introduced into a liquid by means of self/vortex-gassing are strongly limited and often not 5 sufficiently high for technical applications. A further development of the method of self-aspiring gassing consists in gassing via the liquid's surface, which is referred to as "surface gassing" or "Ourface effect gassing". 0 A surface effect gassing system consists of a surface effect flow interripting means (surface effect baffle) and an optimized single-stage or multi-stage (depending on the 6 reactor size) stirrer. The flow interrupting means (surface effect baffle) is a mounting part which is mounted close to the liquid surface and has the form of a specifically shaped "paddle", for example, the form of an "L" turned upside down. The "paddle" (for example, shorter leg of the upside-down "L") is oriented in direction of the stirrer's 5 shaft and, this way, substantially forms a wide flow interrupting means (baffle) which, however, does not extend too far into the liquid in the (eccentric) spout area and, thus, almost exclusively impacts the liquid surface. The flow interrupting means (surface effect baffle) may be located completely beneath the liquid level, but also partially above and partially below it. 10 The functioning principle of the surface effect gassing technology may easily be illustrated as follows: in addition to axial and radial flows, the stirring element rotating in the vessel also creates a substantial tangential flow. In conventional devices, this tangential flow is responsible for the formation of a central spout (vortex). The flow .5 interrupting means (baffle) influences the formation and the location of the spout: While the spout rotates substantially around the stirrer's shaft in conventional stirring vessels and, thus, has hardly any influence on the introduction of gas into the liquid, the surface effect flow interrupting means (surface effect baffle) prevents the central spout from being formed. Instead, an area with substantial rotational flow is created 0 at the back of the "paddle", said rotational flow forming a spout in the liquid (vortex effect). This vortex is formed eccentrically in the stirring vessel and ends in the area of the blades of the upper stirring element (dispersion level). This eccentrical spout sucks down large amounts of gas from the surface into the liquid. 5 In addition, the "paddle" has the effect of a "retaining dam" which is partially overflown by the liquid. The same way as at a dam in flowing waters, an area forms behind the surface effect flow interrupting means (surface effect baffle) where high amounts of gas are introduced into the liquid (dam effect). The combination of the two effects, the formation of an eccentrical spout (vortex effect) and the "dam effect", 0 results in the introduction of a high amount of gas via the liquid surface Into the liquid, contrary to the previously described self/vortex-gassing (which is merely based on the (central) vortex effect). 7 It is possible to arrange the system of stirrer/flow interrupting means (baffle) in a way that the axial movement of the liquid around the stirring axis is a downward movement or an upward movement. In conventional systems, the liquid moves 5 downwards along the stirring axis and upwards along the wall. If the liquid moves upwards along the stirring axis and downwards along the wall, the system is referred to as an "up-pumping system". In this case, the gas is sucked in along the wall or by means of surface effect flow interrupting means (surface effect baffle) exercising their influence close to the wall. It is possible to use both methods in the present invention. 10 In one embodiment of the invention, the at least one flow interrupting means (baffle) may be mounted to the reactor wall or secured by means of a reactor connecting piece (reactor nozzle) or extend downwards form the reactor lid. This is the most efficient way to prevent the liquid from rotating together with the stirrer and, thus, L5 contributes to a homogeneous distribution of the gas within the liquid. This flow interrupting means (baffles) may be made of materials suitable for the process (with view to chemical resistance, surface, etc.), such as tantalum, titanium, stainless steel, but preferably of industrial enamel. The flow interrupting means (baffles) preferably do not comprise any dead volume or are, at most, low in dead volume, 0 in another embodiment of the invention, the metal to be separated may be precipitated as metal or metal salt from a solution containing the metal to be separated. This has the advantage that the gas feeding tube cannot clog or become covered, as the gas is introduced via the liquid surface and, thus, can react with the 5 metal to be separated only within the liquid. In a further embodiment, the metal to be separated can be dissolved out of a mixture containing said metal to be separated. In such an embodiment, the metal in solution is dispersed and contacted with the process gas by means of surface effect gassing, o which leads to its dissolution. The metal is dissolved homogeneously In the overall liquid, overcoming the previous disadvantage of the locally limited dissolution at the feeding site of the process gas. Moreover, any insoluble components or particles 8 cannot clog or cover the gas feeding tube or affect the feeding site of the process gas in any other way. If the metal to be separated cannot be dispersed (for example, due to its particle size, density) and is, for example, settled on the bottom of the reactor, surface effect gassing pushes a sufficient amount of process gas to the metal surface 5 on the reactor's bottom. In one embodiment of the invention, gold may be precipitated, the process comprising the following steps: (i) introducing an aqueous gold solution into the reactor, the reactor comprising: 0 - at least one gas inlet and at least one gas outlet, said at least one gas Inlet and said at least one gas outlet being located above the maximum filling level of the reactor; - at least one liquid inlet and at least one liquid outlet, the latter being preferably located at the bottom of the reactor, - a stirrer, 5 - at least one flow interrupting means (baffle) which, together with the $tirrer, allows for the process gas to be stirred in homogeneously; (ii) sealing the reactor, (iii) exchanging the gas in the headspace by a process gas which comprises SO 2 , (iv) stirring the mixture, resulting in a self-aspirated gassing of the mixture according 0 to the method of surface effect gassing, (v) adding additional process gas, if need be, (vi) completing the conversion, if SO 2 is no longer consumed, (vii) cooling/warming to room temperature, (viii) recovering the gold. 5 The process comprises the following steps: (i) introducing an aqueous gold solution into the reactor via at least one liquid inlet, (ii) sealing the reactor, (iii) exchanging the gas in the headspace by a process gas which comprises SO 2 , o wherein the gas is introduced via at least one gas inlet above the maximum filling level of the reactor and discharged via at least on gas outlet above t e maximum filling level of the reactor, (iv) stirring the mixture, resulting in a self-aspirated gassing of the mixture according to the method of surface effect gassing, wherein a homogeneous stirring in of the process gas is allowed via at least one flow interrupting means (baffle) in combination with the stirrer, 5 (v) adding additional process gas, if need be, (vi) completing the conversion, if SO 2 is no longer consumed, (vii) cooling/warming to room temperature, (viii) recovering the gold. .0 In this process, gold may be recovered. Gold is selectively precipitated using SO 2 . Room temperature is herein defined as about 25 *C. The process gas preferably consists of SO 2 of industrial grade. If only a small part, for example only about 30 %, of the headspace of the reactor is replaced with process gas, this, in principle, does not influence the process, the time/yield curves may become significantly reduced, 5 however. In another embodiment of the invention, the aqueous gold solution may be an aqueous solution of H[AuCl 4 ]. It is relatively easy to obtain a tetrachloropuric solution using gold and mixtures of gold and other metals, for example, by dissolving gold in 0 HCI and C1 2 or in aqua regia. In one embodiment of the invention, the process may be carried out at a temperature from -10 to +120 *C. The precipitation reaction of gold is an exothermic reaction. The temperature is regulated by means of a temperature regulator which is connected to 5 the reactor and capable of heating and cooling the reactor. A temperature ranging from -10 to +120 *C has proved advantageous. In another embodiment of the invention, the process may be carried out at a temperature from 40 to 90 *C. A better conversion can be achieved in this range of 0 temperatures. 10 In one embodiment of the invention, the pressure may be regulated to 0.05 to 6 bar by supplying process gas or by letting off excess pressure. The reaction according to reaction scheme (1) consumes SO 2 , which means that the overall pressure is reduced, as the HCI which is produced dissolves in water. The changes in pressure 5 are regulated to be limited to a range of 0.05 to 6 bar by supplying additional process gas or by letting off excess pressure. The reaction proceeds at acceptable speed with these pressures. In another embodiment, the pressure may be regulated to a range from 0.5 to 4 bar 0 by supplying process gas or by letting off excess pressure. It is easier to control the pressure at these levels, and the reaction's degree of completeness is higher. In another embodiment of the invention, the stirring rate may amount to 10 to 800 RPM, depending on the reactor size. At these stirring rates, the process gas is stirred 5 homogeneously into the liquid, in order to allow a fast reaction within the liquid. The stirring rate is adapted according to reactor size, the liquid's viscosity and its solid content. In a further embodiment of the invention, the stirring rate may amount to 100 to 300 0 RPM, depending on the reactor size. At this rotational speed, the process gas is excellently stirred into the liquid. In one embodiment of the invention, it is possible to recover the precious metals remaining in the supernatant after step (viii), such as metals from the platinum group, 5 like platinum, palladium, rhodium, iridium, and ruthenium, possibly contained in the hydrochloric solution in addition to gold. This can be achieved by the following steps: - Step 1: oxidizing with C1 2 , reducing of lr(IV), precipitating with NH 4 CI, wherein

(NH

4 )2PtCI 6 is obtained as precipitate, which can be reduced to platinum e.g. with H 2 or by tempering, wherein Pd(ll), Rh(lll), Ir(Ill), Ru(IllI) remain in solution; - Step 2: oxidizing of Ir(Ill), wherein (NH 4

)

2 lrCle is obtained as precipitate, which can be reduced to iridium e.g. with H 2 or by tempering, wherein Pd(ll), Rh(lll), Ru(lll) remain in solution; 11 - Step 3: oxidizing with Cl 2 , precipitating with NH 4 CI, wherein (NH 4 )2PdQIe is obtained as precipitate, which can be reduced to palladium e.g. with H 2 or by tempering, wherein Rh(IllI), Ru(IV) remain in solution; - Step 4: crystallizing, wherein (NH 4

)

2 RhC 6 is obtained as a crystallizate, which can 5 be reduced to rhodium e.g. with H 2 , wherein Ru(IV) remains in solution; - Step 5: removing of NH 4 *, oxidizing distillation, wherein RuO 4 is obtained as distillation product. In one embodiment of the invention, the gold may be recovered by filtration. The gold .0 is slurried by stirring the suspension already in the precipitation rector, so that it may be released from the reactor and filtered. In one embodiment of the invention, the aqueous gold solution may have a gold content of 5 to 450 g/l. At these gold concentrations, it is possible to achieve good 5 results and minimal supernatant volumes (and as a consequence waste water volumes). In another embodiment of the invention, the aqueous gold solution may have a gold content of 150 to 400 g/l. These gold contents can be handled easily. 0 In one embodiment of the invention, the separated gold may have a purity of > 99,99 %. This degree of purity is sufficiently high, so that it is not necessary to carry out further purification before selling the gold, and the precipitated gold may be processed immediately after a washing step using de-ionized water; it may, for 5 example, be dried, melted, and cast into the desired gold product form. In one embodiment of the invention, the supernatant resulting from the gold precipitation may have a residual gold content of < 5 ppm; if the process is appropriately controlled, the residual gold content may decrease to < 2: ppm or to < o 0.6 ppm. This low residual gold content allows for a high gold yield and, thus, a high metal yield, which is important for precious metal refineries, and an economic operation of the refineries. 12 In one embodiment of the invention, the aqueous gold solution may be obtained as follows before step (i): a) by dissolving gold using C1 2 in HCI and/or HBr; or 5 b) by dissolving gold in aqua regia and, subsequently, removing the nitrate; or c) by dissolving gold electrochemically. Dissolving gold using C1 2 in HCI and/or HBr directly yields a tetrachloroauric solution which may be directly used in the reactor. Any silver which may be present 10 precipitates in the form of insoluble AgCl. Dissolving gold in aqua regia also yields tetrachloroauric solution but before precipitating gold from auric acids, the nitrate portions (HN0 3 ), which cannot be avoided in the aqua regia process, have to be destroyed. The nitrate portions are 15 removed by boiling under HCI excess, for example. Depending on the starting material, the electrochemical dissolution of gold may also yield a sufficiently pure gold solution. 20 In one embodiment of the invention, Li 2 COa may be dissolved using CO 2 as process gas. This yields a highly pure, low sodium Li 2

CO

3 , which may either be used directly or processed to obtain Li. In one embodiment of the invention, gold may be dissolved using HCI and/or HBr and ?5 Cl 2 as process gas. This way, it is possible to obtain a highly pure gold solution. In one embodiment of the invention, silver may be dissolved using HNO 3 and 02 as process gas. This yields a nitrate solution which is rich in silver and from which silver electrolyte, fine silver or highly pure silver nitrate may be obtained by means of 0 known chemical processes. 13 In another embodiment of the invention, metals from the platinum group (Pt, Pd, Jr, Rh, Ru, Os) may be dissolved using HCI and/or HBr and C12 as process gas. This way, it is possible to achieve a fast and almost complete dissolution of metals from the platinum group. The resulting solution may then be used for purifying or refine 5 said platinum group metals by precipitation. Another aspect of the present invention relates to a device for use in one of the above mentioned processes, the device comprising: - at least one gas inlet and at least one gas outlet, said at least one gas inlet and said 0 at least one gas outlet being located above the maximum filling level of the reactor; - at least one liquid inlet and at least one liquid outlet, the latter being preferably located at the bottom of the reactor, - a stirrer, - at least one flow interrupting means (baffle) which, together with the stirrer, allows 5 for the process gas to be stirred in homogeneously. All above mentioned advantages are achievable with this device. In this device, the at least one flow interrupting means (baffle) may be mounted to the 0 reactor wall or secured by means of a reactor connecting piece (reactor nozzle) or extend downwards form the reactor lid. Another aspect of the present invention relates to the use of an above mentioned device in a metal separation process. 5 Another aspect of the present invention relates to the use of an above mentioned device in an above mentioned process. Description of the drawing 0 Figure 1 shows a flow chart of the recovery of gold, the numerals referring to: 14 1A: Facultative pre-refining of gold Any primary gold, for example having a gold content of 75 % by weigh , may be pre refined by means of a separation using nitric acid: 5 In nitric acid separation, the primary gold-dore is first "diluted" to a gold content of about 20 to 25 % by weight by alloying silver in a melting furnace and cast in the form of granules. Dore is used herein to refer to batch or a mixture of precious metals which does not correspond to an explicit, standard alloy, such as 14 carat gold, or the term dore represents a partially refined precious metal alloy, such as gold-dore LO standing for partially refined gold having a gold content of 90 % by weight after a first and/or second purification step, the balance being, for example, silver and/or non ferrous metals and/or metals from the platinum group. The resulting pre-refined silver/gold alloy is dissolved in nitric acid, the insoluble gold residue is filtered off and subsequently dissolved using, for example, hydrochloric acid (HCI/C 2 ) or aqua regla L.5 (HCI/HNO 3 ). Eventually, fine gold is precipitated from the thus obtained gold solution (Ullmanns Enzyklopsdie der technischen Chemie, Vol. 12, (1979)). By means of a specific, closed silver dissolving apparatus, the above silver/gold alloy (gold content of about 20 to 25 % by weight) may be dissolved in the system o HN0 3 /0 2 applying the surface effect gassing method and under pressure, under normal operating conditions, practically without causing any emissions of nitrous oxides. This way, a gold content appropriate for the subsequent process step 11 is obtained in the gold residue. The supernatant, a nitrate solution rich in silver, may be used in silver refinery, for example as a silver electrolyte. 5 The specific silver dissolving apparatus is also referred to ,,Dissolvomat Ag" and may, amongst other things, also be used for the production of nitrate solutions rich in silver for the recovery of silver. 0 1 B: Gold dissolving apparatus 15 Gold dore having a gold content of ;98 % by weight is dissolved, for example using HCI/Cl 2 . The pressurized gassing process is carried out in the form of a "surface effect gassing" method. The destruction of nitrates, as in the aqua regla process, is not necessary on principle. This gold dissolving apparatus is also referred to as 5 "Dissolvomat Au". 2: Filtration unit AgCI is filtered off. The filtration may take place in a single or in multiple steps. 10 3: Gold solution tank Tank providing gold solution, free from any solids and free from any nitrates. 15 4: Gold precipitation apparatus Selective precipitation of gold from the solution using SO 2 . The pressurized gassing process is carried out in the form of a "surface effect gassing" method. This gold precipitation apparatus is also referred to as "Aureomat". 20 5: Filtration unit The thus obtained gold is filtered off. The filtration may be carried out in a single or in several steps. 25 EXAMPLES Example 1 Recovering gold from a tetrachloroauric acid solution by means of a reactor which is 30 referred to as "Aureomat". 16 A reactor equipped with a stirrer, a temperature controller, two gas inlets (SO 2 , N 2 ), one gas outlet, two liquid inlets (H[AuCl 4 ], de-ionized water), one liquid outlet, a pressure measuring device and a flow meter for liquids and gases, and flow interrupting means (baffles) having a nominal volume of 440 I is filled with 360 to 440 5 I of an aqueous gold solution. It is also possible to use a smaller reactor; a reactor having a nominal volume of 275 I may, for example, be filled with 225 to 275 I of an aqueous gold solution. The reactor size may be scaled, a range from 15 to 800 I having proved advantageous, but the reactor size may be scaled according to the desired starting quantity. The gold is present in the form of tetrachloroauric acid. The 0 reactor is sealed, and the gas in the headspace is almost completely replaced by process gas, or the headspace is filled with process gas. The process gas is introduced via the gas inlet. The process gas preferably consists of S02 of industrial grade. If only a small part, for example only about 30 %, of the headspace of the reactor is replaced with process gas, this, in principle, does not Influence the 5 process, the time/yield curves may become significantly reduced, however. The gas inlet is situated above the filling level of the reactor. Stirring is started, and the mixture is stirred at 200 RPM; the process is usually initiated at room temperature and during the heating and/or cooling times. The gold is precipitated according to the reaction equation (I). The S02 is consumed by the reaction with tetrachloroauric acid, 0 which leads to a decrease in pressure. The pressure in the reactor amounts to approx. 1.5 bar. Additional process gas is added in appropriate amounts, until no S02 consumption is detectable any more. During normal operation of the precipitation process, the system remains sealed - a discharge of process gas is not carried out. If no SO 2 is consumed any more, the reactor is cooled or heated to room 5 temperature, and only after that, possible excess or negative pressure is let off at the safety washer. The gas outlet is also situated above the filling level of the reactor. N 2 is used for purging, until any residual amounts of process gas in the headspace have been removed. Other suitable gases may also be used as purging gases. After that, the reactor is opened in order to collect the obtained gold by filtration. To this end, 0 the gold may be slurried in the reactor and then drained from the reactor 17 The gold sponge collected by filtration may then be washed in a separate washing reactor. It is boiled in 2 to 16 % by weight of HC! at approx. 80 0C for about 5 to 30 min, whereat the gold sponge to be boiled is slurried. The gold sponge has a uniform particle size, due to the preceding precipitation by means of the "s rface effect 5 gassing" method, and does not agglomerate, not even after settling. After cooling to room temperature, the HCI solution is pumped off. The boiling process may be repeated, but, normally, one boiling cycle will be sufficient, if at all required. De ionized water is added, and the gold sponge is slurried and washed again. The de ionized water is pumped off then, and a new batch of washing water is added. The .0 purification process is completed, when the pH of the rinsing solution hss reached a value of 6 to 7. Usually, this will be the case after 2 to 4 washing cycles using de ionized water. In the end, the gold sponge is once again filtered. The obtained gold, for example, has the following composition: 5 Gold: 199.99 % Silver: 48.1 ppm Iron: 1.1 ppm The supernatant contains the following metals, amongst others: 0 Gold: 0.4 mg/I Silver: 26.7 ppm Iron: 0.5 ppm Example 2 5 Producing tetrachloroauric acid solution from gold alloys having a gold content of ; 98 % by weight by means of a reactor which is referred to as "Dissolvomat Au", and recovering of gold from this solution. A reactor equipped with a stirrer, a temperature controller, two gas inlets (C12, N 2 ), 0 one gas outlet, two liquid inlets (HCI and/or HBr, de-ionized water), with or without a liquid outlet, with a pressure measuring device, flow measuring devices for liquids and gases, and flow interrupting means (baffle) having a nominal volume of 400 I is filled with the above mentioned gold alloy. It is also possible to use a smaller reactor; a reactor having a nominal volume of 250 I may, for example, be filled with the above gold alloy. The reactor size may be scaled, a range from 15 to 1,200 I having proved advantageous, but the reactor size may be scaled according to the desired starting 5 quantity. The employed gold alloy preferably is present in the form of granules. The dissolving rate is determined by the effective overall surface area. the reactor is sealed, stoichiometric or hyperstoichiometric amounts of HCI and/or HBr are added according to the amount of the gold alloy filled into the reactor, the control settings for the gold concentration to be obtained, for example, amounting to 380 g/l, and the 10 volume of the gold solution, for example, amounting to 385 1. Then, the gas in the headspace is almost completely replaced by process gas, or the headspace is filled with process gas, The process gas is introduced via the gas inlet. The gas inlet is situated above the filling level of the reactor (surface effect gassing). 15 The process gas preferably consists of C1 2 of industrial grade. If only a small part, for example only about 30 %, of the headspace of the reactor is replaced with process gas, this, in principle, does not influence the process, the time/yield curves may become significantly reduced, however. Stirring is started, and the mixture is stirred at 50 to 400 RPM, depending on the reactor's degree of filling and gassing principle. o The reactor temperature is controlled according to a temperature profile to amount to between 35 and 98 *C. The gold is dissolved, for example in the system HCI/Cl 2 , according to the reaction equation (11): 2 Au + 2 HCI + 3 C1 2 ->2 H[AuCI 4 ] (II) .5 The C1 2 is consumed as oxidant by the reaction with the gold alloy, which leads to a decrease in pressure. The pressure inside the reactor amounts to approx. 0.2 to 1 bar; if suitable enamel devices are used instead of glass devices, it amounts to approx. 0.2 to 6 bar. The consumption rates of C1 2 vary in the course of the process 0 from 0.1 to 40 kg/h. Additional process gas is added as appropriate, until no Cl 2 consumption is detectable any more. Under normal operating conditions, the dissolution system remains closed during the dissolving process - the process gas is 29 not let off. The achievable dissolving rates are similar to that of those achieved in the aqua regia process; in a 400 liter reactor, it is, for example, possible to dissolve 125 kg gold within 6 to 10 hours. 5 If no C12 is consumed any more, the reactor is cooled to room temperature; after that, possible excess or negative pressure is let off at the safety washer. The gas outlet is also situated above the filling level of the reactor. N 2 is used for purging, until any residual amounts of process gas in the headspace have been removed. Other suitable gases may also be used as purging gases. After that, the reactor is opened, 10 and the thus obtained gold solution may be taken out, the insoluble AgCI being filtered off. Gold is recovered from this solution in the way described in Example 1. This process also works using gold alloys having a gold content of < 98 % by weight, 15 for example for the production of crude gold solutions or a gold electrolyte. In this case, the further processing of such solutions according to Example 1 may yield poorer purity results. Example 3 20 Producing a tetrachloroauric acid solution from gold alloys having a gold content of 2 98 % by weight, using a reactor, referred to as "Dissolvomat Au", with integrated HCI recovery, and recovering gold from this solution. The process is carried out as described in Example 2, a part of the HCI and/or HBr 25 present in the solution being distilled off before cooling the reactor to room temperature and collected in a condensation unit integrated into the "Dissolvomat Au", however. The HCI concentration and amount which may be obtained depends on the concentration and amount of the free HCI of the auric acid present in the reactor. Depending on the size of the reactor and the produced volume of gold 30 solution, it is usually possible to recover and recycle 30 to 150 I of HCI, the HCI concentration being 16 to 21 % by weight. The control of the "Dissolvomat Au" considers the collected amount of HCI for the subsequent cycle and, 20 correspondingly, adds less fresh HCL. Under normal operation conditions, the dissolving system "Dissolvomat Au" also remains closed during the recovery of HCI process gas or HCI vapors are not let off. It is also possible to recover HBr or HCI/HBr instead of HCI. 5 By the above method, the following advantages may be achieved: - a reduction of the content of free HCI in the auric acid, which leads to a poorer solubility of AgCI - the collected HCI may be recycled, which means that any traces of go d chloride in Lo the HCI remain within the dissolving system ("closed loop") - both the dissolution of gold and the recovery of HCI take place within the closed system and may, thus, be carried out in one single apparatus. The same holds true for HBr. 5 The recovery of gold from this solution is carried out as described for Example 1. Example 4 Recovering gold from gold alloys comprising significant amounts of platinum group metals (Pt, Pd, Ir, Rh, Ru, etc.), which will be referred to as "PGMs" below, by means o of a reactor which is referred to as "Dissolvomat PGM". Tetrachloroauric acid is produced as described for Examples 2 and/or 3, the combined content of gold and platinum group metals in the alloy amou ting 298 % by weight. The presence of PGMs does not affect the working principle of the 5 dissolving apparatus for PGM-containing gold alloys. The PGMs are dis solved in the dissolving systems HCI/Cl 2 and/or HBr/C1 2 in a way similar to gold. A hydrochloric solution is obtained, mainly comprising Au(Ill), Pt(IV), Pd(li), Rh(lll), lr(IV), Ag(l), Ru(Ill). The dissolution of platinum in the system HCI/Cl 2 , for example, takes place according to the reaction equation (111): 0 Pt + 2 HCI + 2 C1 2 ->H[PtCle] (111) 21 Any AgCl residues will be filtered off before the recovery of gold. The recovery of gold is carried out as described for Example 1. The presence of PGMs does not affect the procedural principle described in Example 1, as the 5 gaseous S02 selectively precipitates gold. The PGMs remain dissolved and may be selectively precipitated according to known chemical methods (Ullmanns Enzyklopsdie der technischen Chemie, vol. 18, (1979)) in subsequent steps; for example: - Step 1: Oxidation using Cl 2 , reduction of Ir(IV), precipitation using NH 4 CI. 10 Precipitate: (NH4) 2 PtCIl, which may be reduced to platinum, for example using H2 or by annealing. Pd(II), Rh(Ilil), Ir(Ill), Ru(Ill) remain in the solution. - Step 2: Oxidation of Ir(Ill). Precipitate: (NH 4

)

2 lrCle, which may be reduced to iridium, for example using H 2 or by 15 annealing. Pd(II), Rh(Ill), Ru(lll) remain in the solution. - Step 3: Oxidation using Cl 2 , precipitation using NH 4 CI. Precipitate: (NH 4

)

2 PdCI, which may be reduced to palladium, for example using H 2 or by annealing. 20 Rh(lIlI), Ru(IV) remain in the solution. - Step 4: Crystallization. Crystallization product: (NH 4

)

2 RhClr, which may be reduced to rhodium, for example using H 2 . Ru(IV) remains in the solution. 5 - Step 5: Removing NH 4 *, oxidizing distillation. Distillation product: RuO 4 . This process also works using alloys having a combined content of gold and PGMs of <98 % by weight. In this case, the further processing of such solutions according to o Example I may yield poorer purity results. Example 5 22 Dissolving alloys consisting mainly or completely of platinum group metals (Pt, Pd, Ir, Rh, Ru, etc.) by means of a reactor which is referred to as "Dissolvoniat PGM" and obtaining solutions suitable for the subsequent selective precipitation of the metals. 5 PGMs are dissolved by means of the "Dissolvomat PGM" according to the same procedural principle and similar processing parameters as described for gold alloys and the "Dissolvomat Au" in the examples 2, 3, and 4, the combined content of PGMs in the alloy amounting to ;:85 % by weight. The dissolution of platinum in the system HCI/Cl 2 , for example, takes place according to the reaction equation (111). A 1.0 hydrochloric solution is obtained, essentially comprising Pt(IV), Pd(lI), Rh(llI), Ir(IV), Ag(l), Ru(Ill), and, if present, Au(Ill). Any AgCI residues are filtered off after the dissolving process. If gold is present, it is first selectively precipitated using gaseous SO 2 , as described in Examples 1 and 4. 5 Then the individual PGMs can be precipitated selectively and according to known methods, as mentioned above in Example 4. This process also works using alloys having a combined gold and PGMs content of < 85 % by weight. In this case, the further processing of such solutions according to o Example 1 may yield poorer purity results. Example 6 Obtaining silver solutions and gold from silver/gold alloys based on a nitric acid separation. 5 A reactor equipped with a stirrer, a temperature controller, two gas inlets (02, N 2 ), one gas outlet, two liquid inlets (HNO 3 , de-ionized water), with or without a liquid outlet, a pressure measuring device, and flow interrupting means (baffle), having a nominal volume of 50 to 2,000 1, being referred to as "Dissolvomat Ag", is filled with a 0 silver alloy. The employed silver alloy is preferably present in the form of granules, the gold portion amounting to up to 25 % by weight (nitric acid separation, see Ullmanns Enzyklopsdie der technischen Chemie, Vol. 12, (1979)). The reactor is 23 sealed. The stoichiometric or hyperstoichiometric amount of HN0 3 is added, at the beginning and/or continuously in the course of the process, according to the amount of the silver alloy filled into the reactor, the control settings for the final silver nitrate concentration to be obtained, the content of free nitric acid, etc. 5 The reactor is sealed, and the gas in the headspace is almost completely replaced by process gas, or the headspace is filled with process gas. The process gas is introduced via the gas inlet, which is situated above the filling level of the reactor. The process gas preferably consists of 02 of industrial grade. If only a small part, for LO example only about 30 %, of the headspace of the reactor is replaced with process gas, this, in principle, does not influence the process, the time/yield curves may become significantly reduced, however. The reactor size may be scaled according to the desired starting quantity. Stirring is started, and the mixture is stirred at 5 to 600 RPM, depending on the reactors degree of filling. The reactor temperature is 5 controlled according to a temperature profile to amount to between 35 and 130 *C. The 02 is consumed as oxidant by the reaction with the silver alloy, which leads to a decrease in pressure. The pressure inside the reactor amounts to approx. 0.1 to 10 bar. The 02 consumption rates vary during the process from 0.1 to 60 kg/h. Silver and any other non-ferrous metals are dissolved. Gold does not dissolve. In brief, the o dissolution process takes place according to the following reaction equation (IV): 4 Ag + 4 HNO 3 + 02 + 1 Au -> 4 AgNO 3 + 2 H 2 0 + 1 Au(s) (IV) Additional process gas is added, until no 02 consumption is detectable any more. In 5 the course of the dissolving reaction, the formation of nitrous oxides is largely suppressed, maybe not completely, depending on the applied pressure range. Under normal operating conditions of the dissolving process, the dissolution system remains closed during the dissolving process - the process gas or any nitrous oxides are not let off. The dissolution takes place de facto free of nitrous oxides. If no 02 is 0 consumed any more, the reactor is cooled to room temperature, after that, possible excess pressure is let off at the safety washer, and the reactor is opened. The insoluble gold is filtered off from the nitrate solution which is rich in silver, and 24 washed in order to remove nitratic solution components. Depending on the target process parameters, the silver content In the solution amounts to approx. 100 to 1,150 g/l, the content of free nitric acid-to approx. 0.1 to 10 % by weight The filtered off gold residue has a concentration of 93 to 99.8 % by weight. S If suitable process parameters are chosen for the nitric acid separation, for example concerning the silver/gold ratio, the gold content of the gold residue may amount to > 98 % by weight. From the gold residue, fine gold may be recovered, as described in Examples 1 and 2. 0 Example 7 Dissolving silver alloys (silver-dore) having a gold content which is significantly lower than the gold content conventionally necessary for nitric acid separation, for example, or silver alloys having a negligible or no gold content, by means of a reactor which is S referred to as "Dissolvomat Ag" and obtaining nitrate solutions rich in silver for subsequent use in a silver refinery. Such silver alloys (silver-dore) are dissolved using a reactor which is referred to as "Dissolvomat Ag" according to the procedural principle described In Example 6, the 0 silver content amounting to 270 % by weight. If the gold content is low or no gold is contained, the main focus of this process lies on obtaining silver nitrate solutions, for example, by means of silver electrolyses according to the Moebius process. Contrary to conventional processes, silver-dore 5 may be dissolved de facto free of any nitrous oxide under normal operating conditions. In addition, applying this process, it is possible to efficiently dissolve silver-dore already at a low excess of nitric acid of about 0.5 to 3 % by, weight. It is, for example, possible to dissolve a batch of 500 kg silver-dore within 5 to 8 hours. 0 The thus obtained nitrate solution which is rich in silver may, depending on the quality of the dissolved silver-dore, for example, either be directly used as silver 25 electrolyte or further purified according to known chemical methods or used for the hydrometallurgical recovery of fine silvers The gold, independent of its quantity, remains as an insoluble residue and is filtered 5 off. Depending on the gold content, the gold is further purified, as described in Example 6, or introduced into other suitable processes; it may, for example, be melted for producing gold anodes. Example 8 10 Dissolving and purifying lithium carbonate by means of a reactor which is referred to as "Dissolvomat Li". A reactor equipped with a stirrer, a temperature controller, two gas inlets (C0 2 , N 2 ) above the filling level of the reactor, one gas outlet, two liquid inlets (LiHCO 3 and/or 15 Li 2

CO

3 solution and/or slurried Li 2

CO

3 , de-lonized/Na-free water), with or without liquid outlet, a pressure measuring device, and flow interrupting means (baffle) having a nominal volume of 50 to 10,000 1, being referred to as "Dissolvomat Li" is filled with water or recycled, concentrated LiHCO 3 and/or Li 2

CO

3 solution at room temperature or higher temperatures, depending on its dissolution equilibrium. The 20 reactor size may be scaled according to the desired starting amount. LiCO 3 is added in solid or slurried form. The amount of Li 2

CO

3 filled into the reactor depends on the reactor volume, the quantity of a possibly recycled LiHCO 3 and/or Li2CO 3 solution, and on the maximum soluble Li 2

CO

3 amount under "Dissolvomat Li" process conditions. ?5 The reactor is sealed, and the gas in the headspace is almost completely replaced by process gas, or the headspace is filled with process gas. The process gas is introduced via the gas inlet. The process gas preferably consists of C92 of industrial grade. If only a small part, for example only about 30 %, of the headspace of the o reactor is replaced with process gas, this, in principle, does not influence the process, the time/yield curves may become significantly reduced, however. Stirring is started, and the mixture is stirred at 5 to 1,000 RPM, depending on the reactors 26 degree of filling. The reactor temperature is controlled according to a temperature profile to amount to between -10 and 110 0C. The supplied Li 2

CO

3 dissoles, forming LiHC0 3 , in water containing carbonic acid, for example :70 g/l Li 2

CO

3 $t 1 bar C02 (Ullmanns Enzyklopsdie der technischen Chemie, Vol. 16, (1974-1978)) according to 5 reaction equation (V):

H

2 0 + CO 2 + Li 2

CO

3 --> 2 LiHCO 3 (V) The dissolution of the supplied C02 leads to a decrease in pressure. The pressure in 0 the reactor amounts to approx. 0.1 to 10 bar. The C02 consumption rates vary from 0.1 to 30 kg/h in the course of the process. Under normal operating conditions during the dissolving process, the dissolving system remains sealed - the process gas is not let off. The dissolution of Li 2

CO

3 preferably takes place at temperatures below room temperature, for example at temperatures from about -5 to +5 "C. Additional 5 process gas is added, until no C02 consumption is detectable any more. Then, the pressure in the "Dissolvomat Li" is relieved, the C02 present in the reactor's headspace may be collected and recycled. The reactor temperature is increased to 75 to 100 *C according to a temperature profile. Purified Li 2

CO

3 o precipitates according to its dissolution equilibrium according to reaction equation (VI): 2 LiHCO 3 -> Li 2

CO

3 + C02 + H 2 0 (VI) 5 The precipitated Li 2

CO

3 is filtered off, preferably hot-filtered at 70 to 95 C, and then washed with de-ionized water. Before that, any process gas remaining in the reactor's headspace is removed, as described in the above examples. The supernatant contains about 0.7 g/I Li 2

CO

3 . This corresponds to a yield in purified Li 2

CO

3 of t99.85 %. In a 400 I reactor, 28 kg Li 2

CO

3 per batch may be purified; in a 2,500 I reactor, accordingly, 175 kg Li 2

CO

3 per batch may be purified. Starting from chemically 27 pure Li 2

CO

3 , it is possible to produce i 2 0aving a lowNa-content in a first step. Starting from Li 2

CO

3 having a low Na-content, itiaspssible to obtain highly purified Li 2 CO3 in a second step. The composition of chemically pure Li 2

CO

3 , Li 2

CO

3 having a low Na-content, and highly purified Li 2

CO

3 is listed in the table below. 5 Table 1 Chemical composition of Li 2

CO

3 at different degrees of purity Li2CO 3 of chemical Li 2

CO

3 having a low puriy N-conenthighly purified Li 2 COs purity Na-content % Li 2

CO

3 99.38 ± 0.026 99.4 99.995 % Mg 0.004 ± 0.0006 0.0005 0.0002 0.00001 % Na 0.069 ± 0.005 0.0002 ± 0.001 0.0002 % K 0.0003 ± 0.00002 0.00015 ± 0.0001 0.00015 % Ca 0.014 ± 0.001 0.012 ± 0.0014 0.00007 % SO 4 0.037 ± 0.003 0.003 ± 0.037 0.003 % 0.0003 ± 0.00001 < 0.0001 < 0.0001 Principally, this process may also be used for purifying Li 2

CO

3 of lesser quality than 0 chemically pure. In order to achieve the above qualities, it will be necessary to repeat the process an appropriate number of times. 28

Claims (24)

1. A metal separation process, comprising the following steps: + introducing the metal to be separated together with a liquid into a reactor; 5 + adding process gas reacting with the metal to be separated and mixing; + recovering the metal to be separated, characterized in that the mixing of liquid and process gas is achieved by means of the "surface effect gassing" method and 1.0 - gas is introduced via at least one gas inlet above the maximum filling level of the reactor and discharged via at least on gas outlet above the maximum filling level of the reactor; - the liquid is introduced via at least on liquid inlet and discharged via at least one liquid outlet, wherein the discharging is preferably effected via the bottom of the .5 reactor; - the liquid is stirred with a stirrer; - wherein a homogeneous stirring in of the process gas is allowed via at least one flow interrupting means (baffle) in combination with the stirrer. o

2. The metal separation process according to claim 1, characterized in that the metal to be separated is precipitated from a solution containing the metal to be separated as metal or metal salt.

3. The metal separation process according to claim 1, characterized in that the 5 metal to be separated is dissolved out of a mixture containing the metal to be separated. 0 29

4. The metal separation process according to claim 2, characterized in that gold is precipitated, the process comprising the following steps: (i) introducing an aqueous gold solution into the reactor via at least one liquid inlet, (ii) sealing the reactor, 5 (iii) exchanging the gas in the headspace by a process gas which comprises SO 2 , wherein the gas is introduced via at least one gas inlet above the maximum filling level of the reactor and discharged via at least on gas outlet above the maximum filling level of the reactor, (iv) stirring the mixture, resulting in a self-aspirated gassing of the mixture according .0 to the method of surface effect gassing, wherein a homogeneous stirring in of the process gas is allowed via at least one flow interrupting means (baffle) in combination with the stirrer, (v) adding additional process gas, if need be, (vi) completing the conversion, if SO 2 is no longer consumed, 5 (vii) cooling/warming to room temperature, (viii) recovering the gold.

5. The metal separation process according to claim 4, characterized in that the aqueous gold solution is an aqueous solution of H[AuCl 4 ]. 0

6. The metal separation process according to claim 4 or 5, characterized in that the process is carried out at a temperature ranging from -10 to +120 *C.

7. The metal separation process according to claim 6, characterized in that the 5 process is carried out at a temperature ranging from 40 to 90 *C.

8. The metal separation process according to any one of the claims 4 to 7, characterized in that the pressure is adjusted to 0.05 to 6 bar by supplying process gas or by letting off excess pressure. 0 30

9. The metal separation process according to claim 8, characterized in that the pressure is adjusted to 0.05 to 4 bar by supplying process gas or by letting off excess pressure. 5

10. The metal separation process according to any one of the claims 4 to 9, characterized in that the stirring rate amounts to 10 to 800 RPM.

11. The metal separation process according to claim 10, characterized in that the stirring rate amounts to 100 to 300 RPM. LO

12. The metal separation process according to any one of the claims 4 to 11, characterized in that the precious metals remaining in the residue are recovered after step (viii) by the following steps: - Step 1: oxidizing with C1 2 , reducing of Ir(IV), precipitating with NH 4 CI, wherein 5 (NH 4 ) 2 PtCI 6 is obtained as precipitate, which can be reduced to platinum e.g. with H 2 or by tempering, wherein Pd(lI), Rh(Ill), Ir(Ill), Ru(Ill) remain in solution; - Step 2: oxidizing of lr(lll), wherein (NH 4 ) 2 lrCle is obtained as precipitate, which can be reduced to iridium e.g. with H 2 or by tempering, wherein Pd(II), Rh(lIl), Ru(lII) remain in solution; o - Step 3: oxidizing with C12, precipitating with NH 4 CI, wherein (NH 4 ) 2 PdCJ 6 is obtained as precipitate, which can be reduced to palladium e.g. with H 2 or by tempering, wherein Rh(lll), Ru(IV) remain in solution; - Step 4: crystallizing, wherein (NH 4 ) 2 RhCle is obtained as a crystallizate, which can be reduced to rhodium e.g. with H 2 , wherein Ru(IV) remains in solution; 5 - Step 5: removing of NH 4 *, oxidizing distillation, wherein RuO 4 is obtained as distillation product.

13. The metal separation process according to any one of the claims 4 to 12, characterized in that the gold is recovered by means of filtration. 0

14. The metal separation process according to any one of the claims 4 to 13, characterized in that the aqueous gold solution has a gold content of 5 t 450 g/l. 31

15. The metal separation process according to claim 14, characterized in that the aqueous gold solution has a gold content of 150 to 400 g/l. 5

16. The metal separation process according to any one of the claims 4 to 15, characterized in that, before step (1), the aqueous gold solution is obtained as follows: a) by dissolving gold using Cl 2 in HCl and/or HBr; or b) by dissolving gold in aqua regia and, subsequently, removing the nitrate; or c) by dissolving gold electrochemically. 0

17. The metal separation process according to claim 3, characterized in that Li 2 CO 3 is dissolved using CO 2 as process gas.

18. The metal separation process according to claim 3, characterized in that gold 5 or gold alloys are dissolved using HCI and/or HBr and C12 as process gas.

19. The metal separation process according to claim 3, characterized in that silver or silver alloys are dissolved using HNO 3 and 02 as process gas. 0

20. The metal separation process according to claim 3, characterized in that metals of the platinum group (Pt, Pd, Ir, Rh, Ru, Os) are dissolved using HCl and/or HBr and Cl 2 as process gas.

21. A device for use in a process according to any one of the claims 1 to 20, 5 characterized in that the device comprises: - at least one gas inlet and at least one gas outlet, said at least one gas Inlet and said at least one gas outlet being located above the maximum filling level of the reactor; - at least one liquid inlet and at least one liquid outlet, the latter being preferably located at the bottom of the reactor, 0 - a stirrer, - at least one flow interrupting means (baffle) which, together with the stirrer, allows for the process gas to be stirred in homogeneously. 32

22. The device according to caim 21 characterized in that the at least one flow interrupting means (baffle) is mounted to the react& wall or secured by means of a reactor connecting piece (reactor nozzle) or extends downwards form the reactor lid. 5

23. Use of a device according to any one of the claims 21 or 22 in a metal separations process.

24. Use of a device according to any one of the claims 21 or 22 In a process 10 according to any one of the claims 1 to 20. 33