Method for recovering valuable metal

Abstract

To provide a method for economically and advantageously recovering valuable metals from biomass.SOLUTION: A method for recovering valuable metals contained in seaweeds comprises: a hydrothermal treatment step in which seaweeds are mixed with water and subjected to hydrothermal treatment, followed by separating solids and a heavy oil-containing liquid material from a resulting treated product to obtain wastewater; and a collection step in which the wastewater is brought into contact with a metal-collecting material to collect the valuable metals contained in the wastewater on the metal-collecting material. The metal-collecting material used in the collection step is a sintered body containing iron particles and solid carbonaceous matter. The iron particles and the solid carbonaceous matter are bonded and integrated together.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for recovering valuable metals contained in seaweed. [Background technology]

[0002] Japan relies on imports from overseas for most of its industrial resources, including valuable metal elements. Meanwhile, in the vast Exclusive Economic Zone (EEZ) surrounding Japan, many valuable rare metals are dissolved in the seawater. Although the total amount is enormous, the extremely low concentrations make it difficult to recover these metals economically. Therefore, it is important to develop economically advantageous methods for recovering these valuable metals.

[0003] Patent Document 1 proposes a carbon-metal composite for water treatment, which contains metal particles coated with a water-soluble coating agent, carbon particles, and a binder, in order to remove harmful substances contained in wastewater, etc. It is conceivable that the wastewater treatment material described in Patent Document 1 could be diverted to recover valuable metals, but the material in Patent Document 1 removes heavy metals from wastewater by co-precipitating them with aluminum hydroxide, which necessitates the recovery of the resulting aluminum hydroxide flocs, which is extremely difficult. Furthermore, in order to use the recovered material as a metal resource, various post-treatments such as dehydration, separation, and concentration are required, making this method disadvantageous in terms of cost.

[0004] On the other hand, it is known that valuable rare metals (hereinafter referred to as valuable metals) dissolved in seawater are concentrated in living organisms. Therefore, there is a need to develop an economically advantageous method for recovering valuable metals from living organisms. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2011-25160 A (claims, examples, etc.) Summary of the Invention [Problem to be solved by the invention]

[0006] The present inventors have focused on seaweed as a biomass containing concentrated valuable metals that are present in small amounts in nature, and have investigated methods for recovering valuable metals from seaweed in an economically advantageous manner. That is, the problem to be solved by the present invention is to provide a method for recovering valuable metals from biomass in an economically advantageous manner. [Means for solving the problem]

[0007] The present invention provides a method for recovering valuable metals contained in seaweed, A hydrothermal treatment step in which seaweed is mixed with water and subjected to hydrothermal treatment, and then solids and heavy oil-containing liquids are separated from the treated product to obtain wastewater; and a capturing step of contacting the wastewater with a metal capturing material to capture valuable metals contained in the wastewater on the metal capturing material, This is a valuable metal recovery method, characterized in that the metal adsorption material used in the adsorption step is a sintered body containing iron particles and solid carbonaceous matter, in which the iron particles and the solid carbonaceous matter are bound together to form an integrated body. [Effects of the Invention]

[0008] The present invention provides an economically advantageous method for recovering valuable metals that are naturally present in small amounts. Moreover, the hydrothermal treatment process can simultaneously produce carbon materials, fuel oil, and the like, which is also economically advantageous. DETAILED DESCRIPTION OF THE INVENTION

[0009] In the present invention, seaweed is used as a raw material. As seaweed, large seaweeds are particularly preferably used. Specifically, green algae, brown algae, and red algae are preferably used. Large brown algae, such as kelp, are most preferably used. This is because large seaweeds can maintain their growth rate even when the algae density is increased, and are therefore more productive than microalgae.

[0010] The seaweed may be naturally grown or grown in a culture environment. Dried seaweed can also be used. Using seaweed grown by photosynthesis using sunlight indirectly leads to resource production using natural energy. The seaweed is crushed, and preferably a solvent such as water is added to form a slurry, which is then subjected to a hydrothermal treatment process.

[0011] <Hydrothermal treatment process> The hydrothermal treatment step of the present invention is a step of mixing seaweed with water to carry out a hydrothermal reaction, and then separating the aqueous phase from the reaction product and recovering the wastewater. In the hydrothermal treatment step, the mixture of seaweed and water is heated. The temperature in the hydrothermal treatment step is preferably 120 to 370° C., more preferably 200 to 370° C. The treatment time for the mixture of seaweed and water in the hydrothermal treatment step is preferably 3 to 60 minutes, more preferably 5 to 30 minutes.

[0012] The concentration of seaweed in the mixture of seaweed and water during hydrothermal treatment is 0.05 g / cm 3 It is preferable that the seaweed concentration in the mixture is 0.05 g / cm or more. 3 If the temperature is lower than this, the concentration of valuable metals in the wastewater will be too low, making it difficult to recover the valuable metals. Also, the energy required to raise the temperature of the water during hydrothermal treatment will be large. During the hydrothermal treatment, the organic components that make up the seaweed undergo decomposition and recombination reactions, producing solids and liquids in addition to small amounts of gas.

[0013] The solid produced is mainly composed of carbide and can be used as a carbon material such as carbon black. The resulting liquid consists of an oil phase and an aqueous phase, which are separated into liquid and liquid. The oil phase contains heavy oil as the main component. Therefore, the resulting oil phase can be refined as needed to produce tar, pitch, fuel oil for combustion furnaces, etc. The gas produced is mostly CO2, which can be captured with calcium hydroxide and recovered as calcium carbonate.

[0014] In the hydrothermal treatment step of the present invention, solids are separated from the hydrothermal treatment product, and an oil phase is separated from a liquid to obtain an aqueous phase. In the present invention, this aqueous phase is referred to as "wastewater." The wastewater contains water as its main component, and the valuable metals contained in the seaweed are transferred to and dissolved in the water. In other words, the valuable metals contained in the seaweed are dissolved and extracted into the wastewater.

[0015] The hydrothermal treatment step of the present invention may be a two-stage hydrothermal treatment. The two-stage hydrothermal treatment includes a first step of performing low-temperature hydrothermal treatment at 120 ° C to 250 ° C using seaweed, followed by solid-liquid separation to obtain a first liquid and a first solid residue having an O / C ratio of 0.3 to 0.8; This is a method for industrializing seaweed resources, which includes a second step in which the first liquid obtained in the first step is subjected to high-temperature hydrothermal treatment at 250°C to 370°C, followed by solid-liquid separation to obtain a second liquid containing a heavy oil-containing liquid and a second solid residue. The two-stage hydrothermal treatment allows for efficient production of a heavy oil-containing liquid using seaweed, and is therefore economically preferable.

[0016] The first step in the two-stage hydrothermal treatment includes a step of performing low-temperature hydrothermal treatment at 120°C to 250°C using seaweed, and a step of performing solid-liquid separation of the product. The low-temperature hydrothermal treatment step is carried out by heating the seaweed in a treatment tank to a temperature of 120°C to 250°C, preferably 140°C to 230°C, and more preferably 160°C to 210°C.

[0017] If the treatment temperature in the low-temperature hydrothermal treatment step is less than 120°C, the hydrolysis reaction will not proceed, which is not preferable, and if it exceeds 250°C, the decomposition of the organic matter in the solid residue will proceed too quickly.

[0018] The amount of water added to the seaweed is preferably 1 to 20 times, and more preferably 2 to 15 times, the weight of the seaweed in a dry state. The atmosphere in the treatment tank is preferably an inert gas. The pressure is preferably equal to or higher than the saturated vapor pressure at the treatment temperature.

[0019] The treatment method may be a batch method or a flow method as long as the above treatment conditions are ensured, and the treatment vessel used is preferably a pressure vessel equipped with a heater and a mixer.

[0020] The treatment time is preferably 3 to 120 minutes, more preferably 10 to 60 minutes, in either the batch method or the flow method.

[0021] The product of the low-temperature hydrothermal treatment is mainly a mixture of liquid and solid. The product is subjected to solid-liquid separation to obtain the liquid and solid. In the present invention, the former liquid produced by the low-temperature hydrothermal treatment is referred to as a first liquid, and the latter solid is referred to as a first solid residue. In addition, a small amount of decomposition gas may be produced.

[0022] The first solid residue can be obtained by separating it from the liquid by a conventional solid-liquid separation method such as decantation, filtration, or centrifugation. The first solid residue is a solid having an O / C ratio of 0.3 to 0.8, preferably 0.35 to 0.6. Here, the O / C ratio is the ratio of the number of oxygen atoms to the number of carbon atoms contained in the solid residue.

[0023] An O / C ratio of less than 0.3 is not preferable because the decomposition of organic matter proceeds too quickly, resulting in a reduced yield of charcoal, while an O / C ratio of more than 0.8 is not preferable because the decomposition of organic matter does not proceed quickly, resulting in a reduced yield of liquid.

[0024] The first solid residue is a precursor of the carbonized product and is used as the raw material for the third step described below to produce the carbonized product. The first solid residue is in a semi-carbonized state, with a portion carbonized. By subjecting the raw seaweed to hydrothermal treatment, dehydration and decarboxylation reactions proceed, so the first solid residue has a lower O / C ratio than the raw seaweed.

[0025] The first liquid consists of an aqueous phase containing water-soluble substances and an organic phase containing organic solvent-soluble substances, and either the mixture of the two or only the aqueous phase is collected by oil-water separation and sent to the second step. The first liquid can also be obtained by separating the organic phase containing organic solvent-soluble substances from the aqueous phase containing water-soluble substances by oil-water separation, and then combined with the heavy oil-containing liquid described below.

[0026] The second step includes a step of performing high-temperature hydrothermal treatment at 250°C to 370°C using the first liquid material containing an aqueous phase containing at least water-soluble matter obtained in the first step, and a step of performing solid-liquid separation of the product.

[0027] The high-temperature hydrothermal treatment step is carried out by heating the first liquid material in a treatment tank to a temperature of 250°C to 370°C, preferably 270°C to 360°C, and more preferably 300°C to 350°C. If the treatment temperature in the high-temperature hydrothermal treatment step is less than 250°C, the dehydration reaction will not proceed smoothly, resulting in a reduced yield of heavy oil, and if it exceeds 370°C, the decomposition of organic matter will proceed too quickly, resulting in a reduced yield of liquid material.

[0028] The atmosphere in the treatment tank is preferably an inert gas, and the pressure is in the range of 2.5 MPa to 22 MPa, depending on the treatment temperature. The treatment method may be a batch or flow type as long as the above treatment conditions are ensured, and the treatment tank used is preferably a pressure vessel equipped with a heater and a mixer. In either the batch or flow type, the treatment time is preferably 3 to 60 minutes, more preferably 5 to 30 minutes.

[0029] The product of the high-temperature hydrothermal treatment is mainly a mixture of liquid and solid matter. The product is subjected to solid-liquid separation to obtain the liquid and solid matter. In the present invention, the former liquid matter produced by the high-temperature hydrothermal treatment is referred to as the second liquid matter, and the latter solid matter is referred to as the second solid residue. In addition, decomposition gas is produced, but most of it is CO2, which can be recovered as calcium carbonate by capturing it with calcium hydroxide.

[0030] The second solid residue can be obtained by separation using a typical solid-liquid separation method such as decantation, filtration, centrifugation, etc. The second solid residue is combined with the first solid residue and subjected to the third step described below to form a raw material for producing a carbonized product.

[0031] The second liquid is composed of an aqueous phase containing water-soluble substances and an organic phase containing organic solvent-soluble substances. The second liquid is separated by an oil-water separation operation to obtain a liquid containing a heavy oil component consisting of light oil, heavy oil, pitch, tar, or a mixture of two or more of these.

[0032] The heavy oil-containing liquid obtained in the second step is preferably refined and separated into useful components, which are then used for chemicals, fuels, or the like.

[0033] As described above, by going through the first and second steps, a first solid residue, a second liquid matter, and a second solid residue can be obtained from the raw seaweed.

[0034] As described above, both the first liquid and the second liquid are composed of an aqueous phase containing water-soluble substances and an organic phase containing organic solvent-soluble substances. The first liquid has a higher proportion of water-soluble substances than organic solvent-soluble substances. On the other hand, the second liquid has a higher proportion of organic-soluble substances than water-soluble substances.

[0035] The main component of raw seaweed is polysaccharides. By subjecting this raw seaweed to the first step, the polysaccharides are hydrolyzed to produce water-soluble substances (mainly water-soluble low-molecular-weight or oligomers). A portion of this water-soluble substance becomes heavy and becomes organic solvent-soluble. An example of an organic solvent-soluble substance is polyunsaturated fatty acid. By subjecting the first liquid material obtained through the first step to the second step, at least a portion of the water-soluble substance in the first liquid material becomes heavy and becomes organic solvent-soluble. Furthermore, at least a portion of the organic solvent-soluble substance in the first liquid material becomes even heavier, increasing the carbon residue rate.

[0036] The first liquid material may be supplied in its entirety to the second step, or only a portion of it may be supplied. In other words, desired liquid hydrocarbons can be efficiently produced from seaweed by adjusting the conditions of the first step and the second step (such as the temperature, pressure, and time of each step, and the components of the first liquid material supplied to the second step).

[0037] Here, in order to produce liquid hydrocarbons with high productivity, it is essential to combine the first and second steps. If the first step is not carried out, as mentioned above, the seaweed will decompose too much, leaving little organic matter in the solid residue, resulting in a low carbonized product yield. Furthermore, if the second step is not carried out, the seaweed will not decompose and subsequent heavy oil formation will be difficult, resulting in a low heavy oil content, and as a result, organic solvent-soluble matter cannot be produced efficiently.

[0038] The aqueous phase containing water-soluble matter obtained by oil-water separation in the second step contains valuable metals and is subjected to the collection step as wastewater of the present invention.

[0039] The solid residue obtained in the first step and / or the second step can be subjected to a third step in which the carbonization reaction proceeds, thereby co-producing a char. A preferred embodiment of the present invention includes a third step in which the first solid residue obtained in the first step and / or the second solid residue obtained in the second step are subjected to high-temperature treatment to obtain a char.

[0040] The high-temperature heat treatment in the third step can be carried out depending on the application, and is usually carried out by heating at a temperature in the range of 400°C to 1000°C in an oxygen-free state. If the temperature of the high-temperature heat treatment in the third step is less than 400°C, the decomposition of the organic matter will not proceed, resulting in a large amount of residual oxygen, which is undesirable for the quality of the carbonized product. Furthermore, if the temperature exceeds 1000°C, the treatment will be carried out at an unnecessarily high temperature, resulting in a waste of energy. During the high-temperature treatment, the atmosphere in the treatment tank is preferably an inert gas. The pressure is preferably in the range of normal pressure to 1 MPa.

[0041] The time for the high-temperature treatment is preferably 20 to 120 minutes, more preferably 30 to 90 minutes. The treatment method may be a batch method or a flow method as long as the above treatment conditions are ensured, and the treatment tank used is preferably an incinerator or an electric furnace.

[0042] The O / C ratio of the carbide obtained in the third step is preferably 0 to 0.2, more preferably 0 to 0.1. The physical properties of the carbide can be controlled by managing the temperature and time of the high-temperature heat treatment step. The obtained carbide can be suitably used as a raw material for carbides such as activated carbon.

[0043] <Collection process> The collection step is a step in which the wastewater obtained in the hydrothermal treatment step is brought into contact with a metal adsorbent to collect valuable metals contained in the wastewater onto the metal adsorbent. The metal adsorbent used in the adsorption step contains iron particles and solid carbonaceous matter, and is preferably a sintered body in which the iron particles and the solid carbonaceous matter are bound together to form an integrated body.

[0044] A valuable metal recovery method, characterized in that the metal adsorption material used in the adsorption step is a sintered body containing iron particles and solid carbonaceous matter, in which the iron particles and the solid carbonaceous matter are bound together to form an integrated body. Specifically, the metal adsorption material used in the adsorption step contains iron particles and solid carbonaceous matter, and the iron particle content per 100 parts by weight is in the range of 5 to 90 parts by weight, preferably 25 to 90 parts by weight, and more preferably 50 to 90 parts by weight, and is a sintered body in which the iron particles and the solid carbonaceous matter are bound together and integrated. The metal adsorbent generates iron ions in an aqueous solution by local cell action, which causes the ions of valuable metals in the aqueous solution to precipitate as metal bodies on the surface of the sintered body.

[0045] The metal trapping material can be produced by a production method including the following steps A to C in this order. Process A: A process of mixing a precursor consisting of metal particles 1 and solid carbonaceous material 2, and, if necessary, auxiliary agents (carbon aggregate 3, binding aid, water, organic solvent, etc.). Process B: A process in which the mixture obtained in process A is granulated, and the contained metal particles 1 and precursors of the solid carbonaceous material 2 are adhered to each other to form a granular composite. Process C: A step in which the composite obtained in step B is fired at a temperature of 600°C or higher in an inert or reducing atmosphere to form a sintered body. The obtained sintered body is used as a metal adsorbent in a collection step for recovering valuable metals from wastewater.

[0046] In the collection step, the lower limit of the amount of the metal adsorption material used is 0.2 or more, preferably 0.3 or more, and more preferably 0.4 or more, in weight ratio relative to the raw seaweed. If the amount of the metal adsorption material used relative to the raw seaweed is less than 0.2, the recovery rate of valuable metals will decrease. On the other hand, the upper limit of the amount of the metal adsorption material used is 90 or less, preferably 70 or less, more preferably 50 or less, even more preferably 30 or less, and even more preferably 15 or less, in weight ratio relative to the raw seaweed. If the amount of the metal adsorption material used relative to the seaweed is too high, costs will increase.

[0047] The iron particles 1 contained in 100 parts by weight of the metal adsorbent ranges from 5 to 90 parts by weight, preferably from 25 to 90 parts by weight, and more preferably from 50 to 90 parts by weight. If the proportion of the iron particles 1 is less than 5 parts by weight, the area of ​​the iron particles 1 that comes into contact with water is small, and fewer iron ions are generated, resulting in a lower recovery efficiency of valuable metals. On the other hand, if the proportion of the iron particles 1 exceeds 90 parts by weight, the carbonaceous material is too small, resulting in fewer battery-forming sites and fewer iron ions being generated, which is undesirable.

[0048] The iron particles 1 used in the metal adsorbent of the present invention are recovered and recycled using a material in which iron, which has a lower electric potential than carbon, is composited with carbon. The particle shape of the iron particles 1 is not particularly limited, and may be, for example, spherical, irregular, or fibrous. The particle diameter of the iron particles 1 is preferably in the range of 10 μm to 5 mm, and more preferably in the range of 100 μm to 3 mm.

[0049] The origin of the solid carbonaceous material 2 is not important as long as it is a solid, electrically conductive carbon capable of forming a local battery in water upon contact with iron. The precursor of the solid carbonaceous material 2 sintered together with the iron particles 1 is not limited as long as it is a substance that carbonizes when fired at 600°C or higher in a non-oxidizing atmosphere. Examples of precursors of the solid carbonaceous material 2 that can be used include natural organic substances such as starch paste, corn syrup, and lignin, and organic synthetic resins such as epoxy resins and phenolic resins. However, pitch produced from heavy oils derived from petroleum or coal-based sources is preferred, as it has a high carbon yield (residual carbon ratio of 50% or higher) and produces highly conductive carbon. Pitch with a softening point of 70°C or higher is particularly preferred as a precursor, as it can be used as a powder and can be easily granulated by mixing with the iron particles 1 and heating. It also produces a large amount of solid carbonaceous material 2 after sintering.

[0050] To the metal adsorbent of the present invention, it is possible to further add a carbon aggregate 3 as desired for the purposes of adjusting the surface area or apparent specific gravity, improving the local cell effect, etc. As the carbon aggregate 3, it is preferable to use, for example, pulverized graphite, needle coke, or pitch coke.

[0051] Examples of metal collecting materials using carbon aggregate 3 include those obtained by mixing iron particles 1 and pulverized carbon aggregate 3 such as graphite, needle coke, or pitch coke with pitch, which is a precursor to solid carbonaceous material 2, and granulating the mixture and then sintering the mixture; and those obtained by sintering iron particles 1 together with solid carbonaceous material 2 onto the surface of carbon aggregate 3 such as graphite, needle coke, or pitch coke.

[0052] When pulverized graphite, needle coke, pitch coke, or the like is used as the carbon aggregate 3, the particle size thereof is preferably in the range of 10 μm to 10 mm, more preferably in the range of 50 μm to 5 mm. The compounding ratio of the precursor of the solid carbonaceous material 2 to 100 parts by weight of the pulverized material is preferably in the range of 3 to 50 parts by weight, more preferably in the range of 5 to 25 parts by weight.

[0053] Furthermore, various additives can be blended into the metal adsorbent of the present invention to adjust the apparent specific gravity or to provide secondary effects, within a range that does not impair its performance. Examples of additives include ceramics such as silica, alumina, and brick, as well as lumps of magnetic substances such as magnetite, but the blending of magnetic substances is preferred because it enables the metal adsorbent that has captured valuable metals to be recovered by magnetism.

[0054] The apparent specific gravity of the metal adsorbent is, for example, 1.1 g / cm 3 More than 1.2 g / cm is preferable. 3 More preferably, the apparent specific gravity is 1.1 g / cm or more. 3 This is preferable because separation from water in the collection step is easy.

[0055] In the capture process of the present invention, the metal adsorbent can precipitate valuable metal ions dissolved in the wastewater from the hydrothermal treatment process as metal bodies on the surface of the metal adsorbent, triggering the large and sustained release of iron ions due to the local cell effect. This makes it easy to recover valuable metals from the wastewater, simplifies post-recovery dehydration and concentration procedures, and reduces overall recovery costs. Therefore, valuable metals contained in seaweed can be recovered economically and advantageously.

[0056] Valuable metals that can be recovered include rare metals such as beryllium, boron, titanium, vanadium, chromium, manganese, cobalt, nickel, germanium, arsenic, selenium, rubidium, strontium, zirconium, niobium, molybdenum, indium, antimony, tellurium, cesium, barium, hafnium, tantalum, tungsten, rhenium, thallium, and bismuth; rare earths such as scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium; and precious metals such as ruthenium, rhodymium, palladium, silver, osmium, iridium, platinum, and gold. [Example]

[0057] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the scope of these examples. In the following examples, various measurements and evaluations were performed as follows unless otherwise specified.

[0058] [Reference example 1] <Preparation of metal adsorbent> Iron powder (Takeuchi Industries Co., Ltd., cast iron powder, 28 mesh or smaller; carbon: 2-4 wt%, Si: 4 wt% or less, Mn: 0.5-1.5 wt%, P: 0.03 wt% or less, S: 0.03 wt% or less) and solid carbonaceous material (Nippon Steel & Sumikin Chemical Co., Ltd., pitch coke lump) were mixed using a mixer, and then the mixture was loaded into a pan pelletizer (Yoshida Seisakusho Co., Ltd., Model 1237-S-3). While the pan pelletizer containing the mixture was rotating at 30 rpm, carbon aggregate (pitch coke lump size 1-5 cm) that had been heat-treated in an electric furnace at 230°C for 2 hours in an air atmosphere was loaded into the pan pelletizer, and the mixture was rotated for 3 minutes to produce a composite with iron powder particles adhering to the carbon aggregate surface. The produced composite was heated at a rate of 100°C / hour in a reducing atmosphere firing furnace packed with coke powder, and fired at 900°C for 2 hours. After that, the composite was allowed to cool naturally in the furnace until the temperature was below 50°C, and the sintered body was removed and used as a metal adsorbent. The iron content in the obtained metal adsorbent was 40%, and the carbon content was 60%.

[0059] [Example 1] Dried kelp (ma-konbu) was crushed as the raw material, and the kelp concentration was 0.2 g / cm 3 A raw material solution was prepared by mixing kelp and water so that the raw material solution was 40.8 g. A 75 mL stainless steel pressure vessel (autoclave) was charged with 40.8 g of the raw material solution, and a hydrothermal treatment reaction was carried out at 350 °C for 10 minutes. Next, the reaction mixture after the hydrothermal treatment reaction was washed with THF and water, and the solid matter was separated by filtration. The filtrate was then separated into an oil phase by liquid-liquid separation using a separatory funnel, and the wastewater was subjected to the hydrothermal treatment step. The metal adsorption material of Reference Example 1 was added to the container containing the wastewater in an amount three times the weight of the raw kelp, and the material was immersed in the wastewater and stirred at room temperature for 1 hour, thereby carrying out the adsorption process.

[0060] The wastewater samples were dried and an analytical solution was prepared using microwave-assisted decomposition, after which the types and concentrations of valuable metals were determined using an ICP-MS (inductively coupled plasma mass spectrometer). The concentrations of valuable metals in the dried kelp and in the wastewater after the collection process were measured, and the metal recovery rate was calculated.

[0061] [Example 2] Dried kelp (ma-konbu) was crushed as the raw material, and the kelp concentration was 0.09 g / cm 3 A raw material solution was prepared by mixing kelp and water so that the concentration of the metal adsorbent of Reference Example 1 was 6 times the weight of the raw kelp. After the hydrothermal treatment step was carried out under the same conditions as in Example 1, an adsorption step was carried out by adding the metal adsorbent of Reference Example 1 in an amount six times the weight of the raw kelp that had been added. The concentration of valuable metals in the wastewater after the adsorption step was measured, and the recovery rates of valuable metals before and after the addition of the metal adsorbent were calculated.

[0062] [Example 3] Dried kelp (ma-konbu) was crushed as the raw material, and the kelp concentration was 0.2 g / cm 3 A raw material solution was prepared by mixing kelp and water so that the concentration of the metal adsorbent of Reference Example 1 was 0.5 times the weight of the raw kelp. After carrying out a hydrothermal treatment step under the same conditions as in Example 1, the metal adsorbent of Reference Example 1 was added to the resulting wastewater, and the wastewater was immersed and stirred for 1 hour at room temperature, thereby carrying out an adsorption step. The concentration of valuable metals in the wastewater after the adsorption step was measured, and the recovery rates of valuable metals before and after adding the metal adsorbent were calculated.

[0063] The conditions for the hydrothermal treatment step, the characteristics of the metal adsorption material used in the adsorption step, and the results of the adsorption step for each example are shown in Table 1. As valuable metal elements for which recovery rates were evaluated, attention was focused on the rare metals cobalt and vanadium, and the rare earth lanthanum.

[0064] [Table 1]

[0065] [Comparative Example 1] Dried kelp (ma-konbu) was crushed as the raw material, and the kelp concentration was 0.01 g / cm 3 A raw material solution was prepared by mixing kelp and water so that the concentration of the metal adsorbent of Reference Example 1 was 100 times the weight of the raw kelp added to the wastewater. The wastewater was then immersed and stirred at room temperature for 1 hour to carry out an adsorption process. The concentration of valuable metals in the wastewater after the adsorption process was measured, and the recovery rates of valuable metals before and after the addition of the metal adsorbent were calculated.

[0066] Comparative Example 2 Dried kelp (ma-konbu) was crushed as the raw material, and the kelp concentration was 0.20 g / cm 3 A raw material solution was prepared by mixing kelp and water so that the concentration of the metal adsorbent of Reference Example 1 was 0.1 times the weight of the raw kelp added to the wastewater. The wastewater was then immersed and stirred at room temperature for 1 hour to carry out an adsorption process. The concentration of valuable metals in the wastewater after the adsorption process was measured, and the recovery rates of valuable metals before and after the addition of the metal adsorbent were calculated.

[0067] The conditions for the hydrothermal treatment step, the characteristics of the metal adsorption material used in the adsorption step, and the results of the adsorption step for each comparative example are shown in Table 2. The recovery rates of valuable metal elements in the comparative examples were lower than those in the examples.

[0068] [Table 2] [Industrial Applicability]

[0069] The present invention provides an economical method for utilizing biomass to recover valuable metals that are naturally present in small amounts.

Claims

1. A method for recovering valuable metals contained in seaweed, comprising: A hydrothermal treatment step in which seaweed is mixed with water and subjected to hydrothermal treatment, and then solids and heavy oil-containing liquids are separated from the treated product to obtain wastewater; and a capturing step of contacting the wastewater with a metal capturing material to capture valuable metals contained in the wastewater on the metal capturing material, A method for recovering valuable metals, characterized in that the metal adsorption material used in the adsorption step is a sintered body containing iron particles and solid carbonaceous matter, in which the iron particles and the solid carbonaceous matter are bound together to form an integrated body.

2. 2. The method for recovering valuable metals according to claim 1, wherein the content of iron particles contained in the metal adsorbent used in the adsorption step is 5 to 90 parts by weight per 100 parts by weight of the metal adsorbent.

3. In the hydrothermal treatment step, the seaweed concentration in the mixture of seaweed and water when performing the hydrothermal treatment is 0.05 g / cm ３ The method for recovering valuable metals according to claim 1, wherein

4. 2. The method for recovering valuable metals according to claim 1, wherein the amount of the metal adsorbent used in the adsorption step is in the range of 0.2 to 90 weight percent based on the amount of seaweed used as the raw material.

5. 2. The method for recovering valuable metals according to claim 1, wherein in the hydrothermal treatment step, the hydrothermal treatment is carried out in the range of 120°C to 370°C.

6. 2. The method for recovering valuable metals according to claim 1, wherein the hydrothermal treatment step is a two-stage hydrothermal treatment.

7. 2. The method for recovering valuable metals according to claim 1, wherein the valuable metal is one or more metal elements selected from the group consisting of rare metals, rare earths, and precious metals.

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