JPS6144808B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention focuses on vanadium, molybdenum, and sulfur, which are valuable metals that are strongly adsorbed deep into the interior of petroleum, which occur during desulfurization, hydrogenation, isomerization, thermal decomposition, etc. Sodium carbonate is added as a solvent to the spent catalyst containing combustible substances such as carbon, and the mixture is oxidized and roasted to penetrate into the fine grains of the spent catalyst and chemically bond through strong adsorption. At the same time, the combustible substances contained in the spent catalyst are removed by oxidative combustion, and the valuable metal vanadium, which is also contained in the fine particles of the spent catalyst and bound by strong adsorption, is removed. In carrying out the method of converting molybdenum into their liquid-soluble salts and extracting and recovering them with water, an alkaline solution, or an acidic solution, the roasted material obtained by adding sodium carbonate to the above spent catalyst is heated to 800 to 900 g. It is heated to a temperature of This relates to a processing device that converts the insoluble vanadium and molybdenum contained into water-soluble compounds and compounds that are soluble in alkaline or acidic solutions by oxidizing and roasting the used catalyst to make valuable metals soluble in liquid. . That is, the present invention burns gaseous fuel or liquid fuel in a short-bodied rotary roasting furnace that has dam parts at both ends for maintaining residence time, and increases the temperature inside the furnace to 800 to 800°C.
The temperature is raised to 900°C, and a to-be-roasted material consisting of a mixture of spent catalyst containing combustible materials and sodium carbonate as a solvent is fed continuously or intermittently into this rotary roasting furnace, and Oxygen-enriched air mixed with air or oxygen to a concentration of 30% or less is placed in a rotary roasting furnace over approximately the entire length of the furnace body without heating or heating. Through the air pipe, a large number of fumarole holes perforated through the wall of the air pipe are used to gradually apply a pressure of 500 to 650 mm of water column from the bottom of the sediment layer of the material to be roasted to the top of the sediment layer. Flame-retardant combustible substances are blown into the spent catalyst and maintained in a heated state at the above temperature for a long period of time from 5 to 25 hours while being in intimate contact with the to-be-roasted material, thereby adsorbing the flame-retardant combustible substance into the spent catalyst. At the same time, insoluble vanadium and molybdenum, which are also adsorbed in the spent catalyst, are reacted with sodium carbonate mixed as a solvent, and they are transferred to liquid-soluble salts. Dissolved metal salts are extracted from the roasted product using water, an alkaline solution, or an acidic solution in an extraction tank, and the exhaust gas is sent to an exhaust gas treatment tank.The spent catalyst is oxidized and roasted to extract valuable metals. The gist of the present invention is to provide a processing device for making a substance soluble in liquid, and the gist of the present invention is to install a large number of combustion air supply pipes in a position close to the inner circumferential wall of the furnace body of a rotary roasting furnace having dam parts on both sides. The air pipes are suspended and supported by fittings at appropriate intervals, each end of which is closed, and each mounting tip is opened, and this open tip is passed through an annular pedestal that is integrally attached to the furnace body. established,
In addition, a slip body is provided which is always elastically and slidably pressed against the annular pedestal, and this slip body is box-shaped with an open rear, or the opening of the air pipe is provided on the sliding surface with respect to the annular pedestal. A matching discharge port is opened, and a pressure pipe for pumping air or oxygen-enriched air is connected to the front part of the slip body, thereby sending the air or oxygen-enriched air under pressure into the slip body. to supply the trachea,
Furthermore, each air pipe is equipped with a large number of injection holes that inject air or oxygen-enriched air upward from the bottom of the pile of materials to be roasted in the furnace, extending over approximately the entire length of the furnace body. The configuration consists of the following. To explain the operation of oxidizing and roasting a spent catalyst using the apparatus of the present invention, the spent catalyst containing carbon, oil, and sulfur, which is extremely flame retardant but gradually burns, is carbonated. Sodium (Na ₂ CO ₃ ) is added and fed into a short-bodied rotary roasting furnace with dam parts at both ends, and gaseous or liquid fuel is burned in the furnace to produce 800 to 900 The spent catalyst is heated and roasted for a long period of 5 to 25 hours while being kept in an oxidizing atmosphere at ℃ to oxidize the combustible substances contained in the spent catalyst and evaporate them by combustion. Air or oxygen in the furnace with its concentration
Either heat the mixed oxidized enriched air to a level of 30% or less, or heat it without heating it and use the air pipe installed in the rotary roasting furnace to run approximately the entire length of the furnace body. Then, the air is gradually sprayed from the bottom of the pile of torrefied materials to the top through a large number of fumaroles drilled in a row on the wall of the air pipe, bringing it into uniform contact with the torrefied materials, thereby discharging the material into the spent catalyst. The combustible substances contained in the catalyst are sufficiently oxidized and burned to volatilize, and the vanadium and molybdenum also contained in the spent catalyst are converted into water-soluble compounds, alkaline liquid-soluble compounds, or acidic liquid-soluble compounds. It is converted into sodium molybdate (Na ₂ MoO ₄ ) and sodium vanadate (NaVO ₃ ), and then the roasted product is extracted with water, hot water, an alkaline solution or an acidic solution, and separated and recovered from the spent catalyst. In addition, the exhaust gas is sent to an exhaust gas treatment tank. Even in the case of conventional oxidation roasting, cylindrical rotary roasting furnaces and short-body tilting rotary roasting furnaces are mainly used as roasting furnaces, but in either case, gaseous or liquid fuel is burned. The temperature of the material to be roasted at atmospheric temperature is raised by Combustible substances are removed by heating the inside of the furnace to the higher temperature required to combine with the mixed solvent so that it coexists with the catalyst, and then remaining at that temperature and in the oxidizing atmosphere for the required time. Measures have been taken to oxidize and volatilize the carbon, oil, and sulfur content, and to cause a chemical reaction between the valuable metals contained in the spent catalyst and the solvent. In order to accomplish such processing operations efficiently, the amount of heat required to raise the temperature inside the furnace must be evenly distributed to the roasted material, and the oxygen necessary for the oxidation reaction due to the combustion of combustible materials must be uniformly supplied. It is necessary for the combustion oxidation reaction of combustible substances that have penetrated deeply into the carrier and in an adsorbed state, and also for the chemical reaction that has penetrated deeply and made valuable metals that have been adsorbed with the carrier soluble in liquid. It is essential to maintain the temperature at 800-900° C. without overheating for a sufficiently long time of 5-25 hours. In order to smoothly achieve the above matters, it is also important to prevent sintering or fusion due to local overheating. Therefore, the roasting furnace itself operates at a relatively slow speed of 1 to 10 r.p.
It was believed that it would be effective to use a rotary roasting furnace that rotates at a speed of 1.5 h and stirs the various parts of the roasted material while intermingling with each other. However, the components of the spent catalyst contain large amounts of flammable carbon, oil, and sulfur, which are distributed finely and deeply into the center of the catalyst carrier's surface and internal structure. It is kept in a state where it cannot be easily removed by combustion and volatilization. When attempting to oxidize and burn these combustible substances efficiently, the exhaust gases generated by the combustion of fuel and the exhaust gases generated by the combustion of combustible substances in the spent catalyst, mainly carbon dioxide and sulfur dioxide gas, are used. This actually inhibits the progress of the subsequent oxidation reaction. Furthermore, since carbon dioxide is released from the sodium carbonate added as a solvent, the combined effect of these exhaust gases tends to further retard the oxidation rate of the combustible material. Furthermore, since the reaction between sodium carbonate and valuable metals such as vanadium and molybdenum is an oxidation mainly based on an endothermic reaction, it is significantly affected by the temperature in the roasting furnace itself, which may lead to unfavorable results. In addition, the temperature and heat transfer caused by the combustion of fuel are carried out by using the exhaust gas generated by the combustion and the excess air used for combustion as the medium, and the exhaust gas is transferred only to the surface of the deposited layer of the material to be roasted. Its effect is limited to the time it makes contact with it in a stroking manner and passes in that state. Therefore, deep oxidation reactions and heat transfer, which are important objectives, cannot easily take place. In particular, the reaction between sodium carbonate added as a solvent and valuable metals is an oxidizing action that is mainly endothermic under the condition that the temperature is maintained at 800 to 900°C. There is a large temperature difference between this section and the discharge port section, making it difficult for the chemical reaction between the valuable metals and the solvent to proceed smoothly. On the other hand, short-body rotary roasting furnaces have the advantage that the temperature difference between the ore feed side (charging inlet side) and the non-ore side (non-ore side) is relatively small and the temperatures are close to each other. However, since it is difficult to allow sufficient residence time for the materials to be roasted in the furnace, the oxidation reaction of combustible substances contained in the spent catalyst is as insufficient as in a simple cylindrical furnace. It is still insufficient to make the species soluble. As a result, with such treatment, the recovery rate of valuable metals cannot exceed 85%. Therefore, in order to compensate for these insufficiencies, it is necessary to carry out secondary roasting to further bring the oxygen-containing component into contact with it, or to shorten the residence time in the oxidizing atmosphere in the furnace. In order to increase the length, it is necessary to take measures such as using a cylindrical rotary roasting furnace with a particularly long roasting zone to increase the recovery rate of valuable metals in the roasted material. However, when using a rotary roasting furnace with a long roasting zone, the inner volume of the rotary furnace is only 10 to 25 mm due to the structure of the rotary furnace.
% is occupied by the material to be roasted, and the remaining internal volume merely serves as a passage for air and combustion gases. Furthermore, even if the temperature of the object to be roasted is increased and the amount of heat necessary to maintain that temperature is supplied, the hot gas that is the heat source will simply pass through the surface of the accumulated layer of the object to be roasted. Because it is only due to the effect of a very short period of time,
The efficiency and effect of heat transfer cannot be expected to be great. As a result, an excessive amount of heat must be supplied. In other words, an additional amount of exhaust gas must be handled correspondingly, which is extremely uneconomical in terms of operation. Furthermore, even if an attempt is made to oxidize the combustible substances, such as carbon, oil, and sulfur, which are deeply contained in the spent catalyst from the beginning and evaporate them from the roasted material through combustion, the Air also simply passes through the surface of the object to be roasted, but cannot penetrate deeply into the deposited layer of the object to be roasted.Therefore, the effect of burning and volatilizing combustible substances is sufficient. cannot be expected to. However, it is an undeniable fact that such a means is convenient for stirring the roasted material by smoothly moving it in and out. In the present invention, in order to improve the above-mentioned drawbacks of the roasting furnace and utilize its advantages at the same time, an air supply pipe with a length that spans approximately the entire length of the furnace body is inserted into the roasting furnace. It is appropriate that the pipe be made of steel or refractory material with good properties, and the wall of the air pipe should be provided with a large number of fumarole holes in a row, so that the material to be roasted can be heated through the fumarole holes. The oxygen-enriched air mixed with air or oxygen to a concentration of 30% or less is directed upward from the bottom of the deposited layer in the furnace, without heating or heating, and minimizing the generation of dust from the roasted materials. The water column pressure is
By injecting at a low pressure of about 500 to 600 mm, the temperature of the roasted material is maintained at 800 to 900℃, and carbon dioxide, sulfur dioxide, etc. that volatilize from the surface of the roasted material are quickly converted into combustible substances. At the same time, the combustible substances remaining as unburned substances are sufficiently burned, and the oxidation of valuable metals or the chemical reaction with the added solvent is significantly promoted. It was designed so that As a result of the above method, when the present invention is used, the oxidation of valuable metals and the reaction with sodium carbonate added as a solvent are carried out efficiently and smoothly, and therefore the recovery of valuable metals is also highly efficient. . The industrial effect of using the oxidation roasting apparatus of the present invention is that the purpose of roasting can be fully achieved and the oxidation zone can be made extremely short in terms of the structure of the furnace. Therefore, the roasting furnace can be downsized, which is economical in terms of equipment costs, and has the advantage of requiring less fuel consumption. The temperature inside the roasting furnace is raised evenly, and evenly throughout the roasting process.
The amount of heat required to maintain a constant temperature in the range of 800 to 900°C is determined by an auxiliary combustion burner installed at the charging port (ore feed port) that supplies the spent catalyst or a mixture of used catalyst and solvent into the roasting furnace. This can be achieved by adjusting the fuel. Furthermore, the combustible substances contained in the roasted material in a deeply adsorbed state gradually generate a considerable amount of heat due to the smooth oxidation combustion reaction which is an effect of the present invention. The present invention also has the advantage that the amount of heat can be used in addition as an effective amount of heat. Air or oxygen-enriched air as described above is supplied into a torrefaction furnace for oxidative torrefaction of a mixture of a spent catalyst and a solvent, and the air or oxygen-enriched air is suspended and supported close to the inner circumferential wall of the torrefaction furnace, and By injecting under pressure upward from the bottom of the torrefaction material accumulation layer in the furnace through numerous fumaroles of the air pipe installed over almost the entire length of the furnace, a synergistic effect is exerted. This makes it possible to efficiently extract and recover valuable metals at a high recovery rate while oxidizing the roasted material at elevated temperatures. In addition, according to the present invention, there is no need to provide any injection holes for combustion air on the peripheral wall of the roasting furnace, and the air supply pipe only needs to be suspended and supported by the attachment, so that the air supply pipe is heat resistant. Even if the air pipe is worn out during use, it can be easily and conveniently replaced, and the treatment operation can be carried out economically. Since the temperature inside the roasting furnace is relatively low and there is no direct contact with the combustion air, we recommend using hanging hardware made of 18-8 nickel chromium steel as a fitting for the air pipe. It is preferable that the air pipe be suspended and supported on the peripheral wall of the furnace. Next, the short-barrel tilting rotary roasting furnace according to the present invention and the equipment attached thereto will be explained. FIG. 1 shows a precedent that was tried in the process of completing the present invention. As shown in FIG. 1, the used catalyst a and the solvent b are placed under the spent catalyst hopper 1 and the solvent hopper 2 by a screw feeder 3 and a feeder 4.
A mixture of spent catalyst a and solvent b is supplied through a guide trough 5 into a rotary roasting furnace 6 having dam parts on both sides. This rotary roasting furnace 6 is rotated in one direction at a relatively slow speed by a transmission gear mechanism 7, and has an exhaust gas receiving tank 8 which also serves as a roasted product receiving tank in contact with the discharge port side of the roasting furnace 6. An exhaust gas discharge pipe 9 is opened in the upper part of the receiving tank 8, and the tip thereof is connected to the exhaust gas treatment device via the blower 10, and the exhaust gas is treated by appropriate means to be rendered harmless and released into the atmosphere. The roasted material after the roasting process is dropped from the lower part of the chamber 8 through the exhaust port 11, and is further received in an extractor, where soluble valuable metal compounds are extracted as a solution using water, hot water, an alkaline solution, or an acidic solution. equip Further, a heavy oil burner 12 is installed toward the inner side of the charging port of the rotary roasting furnace 6, and the temperature inside the furnace 6 is raised by the heat of combustion of the fuel. In the case shown in FIG. 1, the long air supply pipe 14 for pressure-feeding combustion air by the blower 13 is closed at its tip and is inserted over almost the entire length inside the furnace. Furthermore, a large number of injection holes 15 are provided in a row in the tube wall so as to inject combustion air toward substantially the entire surface of the roasted material accumulation layer c in the furnace, and the air supply pipe 14 is provided outside the furnace. An oxygen supply pipe 16 that supplies oxygen gas to an appropriate location is connected via a control valve 17, and compressed oxygen or oxygen sent from a liquefied oxygen supply device 18 is mixed with air to an oxygen concentration of 30% or less. It is also possible to inject the enriched air through the air pipe 14 toward the surface of the torrefaction material accumulation layer in the furnace, but in the case shown in FIG. 1, the injection hole 15 of the air pipe 14 is The combustion air injected from the torrefied material is directed toward the surface of the torrefied material accumulation layer c, and therefore most of the combustion air strokes the surface of the torrefied material accumulation layer c and is burned. It was recognized that it was insufficient to sufficiently exert its effect on the bottom and inside of the deposited layer c. In view of these points, the present invention has been devised so that the combustion air supply pipes are suspended and supported by fixtures at appropriate intervals at positions close to the inner circumferential wall of the furnace shell, as shown in Fig. 2. By doing so, combustion air is injected upward from the bottom of the to-be-roasted material accumulation layer from the injection hole of the air pipe. In implementation, as shown in FIG.
It is also possible to inject the combustion air from 5 toward the surface of the to-be-roasted material pile c. Next, the apparatus of the present invention shown in FIG. 2 will be described. An annular pedestal 19 is set integrally with the furnace body on the outer periphery of the charging port side of the roasting furnace 6, and the annular pedestal 19 is in sliding contact with the outside of the annular pedestal 19. A slip body 20 having a substantially half-moon shape or a substantially quarter-moon shape similar thereto is installed in a fixed position so as to be able to be pressed by an elastic force 21 so as to be slidably pressed against the outer surface of the base 19. A large number of air supply pipes 22 are installed inside the annular pedestal 19 so that their mounting tips open outward. Attachment 23 at a position close to the inner peripheral wall.
At the same time, the length of each air pipe 22 is set to be approximately the entire length of the furnace body, and the pipe wall is provided with combustion air or A large number of injection holes 24 for injecting oxygen-enriched air are provided in rows. The sliding slip body 20 has a box shape with an open rear end, or has an outlet opening on the rear side that matches the opening of the air pipe 22 in the annular pedestal 19. On the front side, there is a pressure pipe 25 for pumping air or product-enriched air.
are connected in series to supply air or oxygen-enriched air into the slip body 20. As mentioned above, the slip body 20 is not made into an annular shape, but is made into a substantially half-moon shape, or a substantially quarter-moon shape similar thereto, because the layer c As shown in Figs. 4 and 5, the particles were deposited unevenly in an area of about one-fourth of a circle from the lower part toward one side in the direction of rotation of the roasting furnace 6. Therefore, it is sufficient to inject air or oxygen-enriched air from the lower part to the upper part of the deposited layer c of the roasted material only in the areas where the deposited layer c exists unevenly; Since it is not necessary, in order to forcefully feed air or oxygen-enriched air into the furnace through the air supply pipe 22, the slip body 20 for feeding it is not circular but approximately half-moon-shaped or quarter-moon-shaped. This is because there is no difference in the shape of the circular ring, and even if it is sprayed somewhere else, it will simply pass over the surface of the deposited layer c, and not much effect can be expected. That is, when the opening of the air supply pipe 22 of the pedestal 19 is in a position opposite to the discharge port of the slip body 20, air or oxygen-enriched air is supplied from the slip body 20 through the air supply pipe 22 of the base 19 to the material to be roasted in the furnace. can be injected under pressure upward from the bottom of the deposited layer c. Note that the pedestal 19 is located at a location other than that facing the approximately half-moon-shaped or approximately quarter-moon-shaped slip body 20.
Atmospheric air is drawn into the air pipe 22 attached to the air pipe 22 through its open opening by natural suction and is discharged into the furnace through the air pipe 22. However, there is no particular need to pump air. All of the air pipes 22 are preferably made of heat-resistant and corrosion-resistant steel pipes or refractory pipes. Since the slip body 20 and the pedestal 19 are kept slidable only by pressing the slip body 20 elastically from the outside, it is inevitable that some air or oxygen-enriched air leaks from their contact surfaces. do not have. In addition, instead of immediately communicating the end of the rotary roasting furnace 6 on the discharge port side to the exhaust gas receiving/roasted product receiving tank 8, a rigid fixed secondary roasting furnace is interposed between them. A separate fuel burner is installed, and after performing the secondary roasting of the roasted material in a self-combustion type, the exhaust gas is sent to the exhaust gas treatment equipment via the exhaust gas exhaust pipe, and the roasted material is fed down to the extractor for extraction operation. You can also do it. Next, examples of operations performed using the apparatus of the present invention will be described. The raw material was 750 kg of spent catalyst with alumina as a carrier. Its chemical composition is as follows. Alumina 65.0% (weight) Cobalt 0.1% Nickel oxide 1.5% Sulfur 10.0% Vanadium 5.5% Molybdenum 4.8% Oil 3.2% To this spent catalyst, 21.5% by weight of sodium carbonate (Na ₂ CO ₃ ) was added as a solvent. The short-bodied tilting rotary roasting furnace 6
Continuously supplied within. The temperature inside the roasting furnace 6 is controlled by the heavy oil burner 12.
The temperature was maintained within the range of 850°C ± 50°C. Combustible substances contained in the roasted material are passed through the oxygen supply pipe 1 outside the combustion air of this heavy oil burner 12.
Oxygen-enriched air mixed with oxygen adjusted in step 6 is directly injected from the injection hole 24 of the air pipe 22 at a water column pressure of 550 mm toward the surface of the deposited layer c of the material to be combusted, to ensure sufficient oxidation. Burnt it. In this way, combustion of combustible substances in the spent catalyst, oxidation of insoluble valuable metals, and reaction with sodium carbonate as an additive solvent were carried out. At this time, the extraction rate of valuable metals was tested by varying the oxygen concentration in the air pumped into the furnace through the air pipe 22 from 21% (volume) to about 30%. The results are shown in Table 1 below. . In this case, the shortest distance between the air pipe 22 and the object to be roasted is
20 cm, and the amount of spent catalyst fed into the roasting furnace 6 was 65 kg/hour.

【table】

[Table] As can be seen from the results shown in Table 1 above, the surface of the deposited layer c of the roasted material was simply stroked with only the excess air for combustion and the combustion exhaust gas without using the injection device of the present invention. When oxidative combustion was carried out, the extraction rate of vanadium (V) was only 53.7%, but by injecting air or oxygen-enriched air using an injection device, it can be extracted all at once.
The extraction rate increased to 83.5%. The extraction rate of molybdenum (Mo) is also 66.7.
% increased to 84.0% by injecting air or oxygen-enriched air. This also shows whether the operation using the oxidation roasting apparatus of the present invention is effective. The oxidized and roasted material was directly fed to a wet mill filled with water, and after being finely ground, soluble vanadium and molybdenum were extracted by a known method. Further, the exhaust gas from the roasting furnace was desulfurized and denitrated using a known treatment device to render it harmless, and then released into the atmosphere.

[Brief explanation of the drawing]

Fig. 1 is a partially longitudinal front view schematically showing a rotary roasting furnace device attempted before the invention was completed;
The figure is a partially longitudinal front view schematically showing the rotary roasting furnace apparatus according to the present invention, FIG. 3 is a partially cutaway perspective view showing the rotary roasting furnace, and FIG. A sectional view illustrating the arrangement of the air pipes in the fifth figure.
The figure is a cross-sectional view illustrating the positional relationship between the pedestal and the slip body in the roasting furnace, and FIG. 6 is a partially cutaway perspective view illustrating the positional relationship between the pedestal and the slip body in the roasting furnace. 1... Spent catalyst hopper, 2... Solvent hopper, 3, 4... Feeder, a... Spent catalyst, b... Solvent, 5... Guidance, 6... Rotary roasting furnace, 7... Transmission gear mechanism, 8... Exhaust gas receiving tank and roasted material receiving tank, 9... Exhaust gas discharge pipe, 10... Air blower, 11... Roasted material discharge port, 12... Heavy oil burner, c... Roasted material Deposition layer, 14...Air pipe, 1
5... Injection hole, 16... Oxygen supply pipe, 17... Control valve, 18... Oxygen supply device, 19... Annular pedestal, 20... Slip body, 21... Bullet machine, 22...
...Air pipe, 23...Mounter, 24...Injection hole, 2
5...Oxygen pressure pipe.

Claims (1)

[Claims] 1. Spent catalysts containing valuable metals such as vanadium and molybdenum produced during desulfurization, hydrogenation, isomerization, thermal decomposition, etc. of petroleum and combustible substances such as sulfur and carbon, mixed with sodium carbonate as a solvent. In an oxidation roasting device for spent catalysts, the spent catalyst is fed into a short-body rotary roasting furnace, and a plurality of air blowholes are provided on the wall of the rotary roasting furnace or in the roasting furnace.
A large number of combustion air supply pipes are installed at appropriate intervals and are suspended and supported by fixtures in a position close to the inner circumferential wall of the furnace body of a rotary roasting furnace that has dam parts on both sides. A slip body whose end is closed and each mounting tip is opened, and the open tip is inserted through an annular pedestal that is integrally attached to the furnace body, and is always elastically and slidably pressed against the annular pedestal. The slip body is box-shaped with an open rear end, or has a discharge port that matches the opening of the air pipe on the sliding surface against the annular pedestal, and the front part of the slip body is A pressure feed pipe for feeding air or oxygen-enriched air under pressure is connected to the air pipe, so that the air or oxygen-enriched air forced into the slip body is supplied to the air pipe. A spent catalyst is oxidized and roasted, which is made up of a number of injection holes that are arranged in a row to inject combustion air upward from the bottom of the accumulated layer of materials to be roasted in a furnace over almost its entire length. Processing equipment that makes valuable metals soluble in liquid.