Method for recovering tin

Abstract

To provide a method for recovering tin as tin oxide from tin-containing sludge while removing impurity elements.SOLUTION: The tin-containing sludge is subjected to washing using washing water to obtain washed tin-containing sludge from which at least a part of the impurity elements is removed. The washed tin-containing sludge is dissolved with an acid solution to obtain a tin-containing liquid A. A sulfurizing agent is added to the tin-containing liquid A to precipitate impurity elements, and a tin-containing liquid B from which the precipitated impurity elements are removed is obtained. The pH of the tin-containing liquid B is adjusted with a pH adjuster to precipitate a tin oxide precursor. The tin oxide precursor is fired to obtain tin oxide.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for recovering tin. [Background technology]

[0002] In recent years, there has been a growing demand for resource recycling from the perspective of environmental protection. In particular, the recycling rate of tin (Sn) is low compared to other metal elements, so there is a need to improve this rate. Sludge (tin-containing sludge) generated during the production of a tin-plated layer on the surface of a substrate such as a steel sheet contains a large amount of tin and is useful as a recycled material. Patent Documents 1 and 2 disclose methods for recovering tin from tin-containing sludge. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 63-277782 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-315865 Summary of the Invention [Problem to be solved by the invention]

[0004] Tin oxide has higher added value than metallic tin. However, the methods described in Patent Documents 1 and 2 are all methods for recovering tin as metallic tin.

[0005] Furthermore, when recovering tin from tin-containing sludge, it is necessary to remove impurity elements contained in the tin-containing sludge. For example, tin-containing sludge generated when forming a tin-plated layer on the surface of a steel sheet contains a large amount of iron (Fe) as an impurity element, and also contains copper (Cu) and the like. However, Patent Document 2 does not describe Fe removal. Furthermore, Patent Document 1 does not describe the removal of impurity elements other than Fe.

[0006] The present invention has been made in view of the above points, and an object of the present invention is to provide a method capable of recovering tin as tin oxide from tin-containing sludge while removing impurity elements. [Means for solving the problem]

[0007] As a result of extensive research, the present inventors have found that the above object can be achieved by employing the following configuration, and have completed the present invention. That is, the present invention provides the following [1] to

[13] . [1] A method for recovering tin, comprising: washing tin-containing sludge with wash water to obtain washed tin-containing sludge from which at least a portion of impurity elements have been removed; dissolving the washed tin-containing sludge with an acid solution to obtain tin-containing liquid A; adding a sulfiding agent to tin-containing liquid A to precipitate impurity elements; obtaining tin-containing liquid B from which the precipitated impurity elements have been removed; adjusting the pH of tin-containing liquid B with a pH adjuster to precipitate a tin oxide precursor; and calcining the tin oxide precursor to obtain tin oxide. [2] The method for recovering tin according to [1] above, wherein the tin-containing sludge contains Sn and at least one element selected from the group consisting of Fe, Cu, Zn, Al, Mg, Ca, Cl, Na, Co, Ni, Mn, F, P, S and Si. [3] A method for recovering tin described in [1] or [2] above, wherein in the washing of the tin-containing sludge, a process of stirring a mixture of the tin-containing sludge and the washing water and then separating the solid and liquid is repeated at least once and at most five times. [4] The method for recovering tin according to any one of the above [1] to [3], wherein the acid solution is at least one selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, and acetic acid. [5] The method for recovering tin according to any one of [1] to [4] above, wherein the temperature of the acid solution is 45°C or higher. [6] A method for recovering tin according to any one of [1] to [5] above, wherein the acid solution contains a reducing agent, and the reducing agent is at least one selected from the group consisting of hydrogen peroxide, sodium sulfide, sodium hydrogen sulfide, sodium thiosulfate, and oxalic acid. [7] The method for recovering tin according to any one of the above [1] to [6], wherein the sulfiding agent is at least one selected from the group consisting of hydrogen sulfide, sodium hydrogen sulfide, and sodium sulfide. [8] The method for recovering tin according to any one of the above [1] to [7], wherein the amount of the sulfiding agent added is 1.0 equivalent or more. [9] The method for recovering tin according to any one of [1] to [8] above, wherein the pH of the tin-containing liquid A before the addition of the sulfiding agent is 1.5 or less.

[10] The method for recovering tin according to any one of [1] to [9] above, wherein the pH adjuster is at least one selected from the group consisting of sodium hydroxide, calcium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, and aqueous ammonia.

[11] The method for recovering tin according to any one of [1] to

[10] above, wherein the pH of the tin-containing liquid B is adjusted to 2.5 or higher with the pH adjuster.

[12] The method for recovering tin according to any one of [1] to

[11] above, wherein a process of stirring a mixture of the tin oxide precursor and washing water and then subjecting the mixture to solid-liquid separation before calcining the tin oxide precursor is repeated at least once but not more than five times.

[13] The method for recovering tin according to any one of the above [1] to

[12] , wherein the tin oxide precursor is calcined at a temperature of 600°C or higher. [Effects of the Invention]

[0008] According to the present invention, it is possible to recover tin as tin oxide from tin-containing sludge while removing impurity elements. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a flowchart showing the flow of a tin recovery method. [Figure 2]1 shows XRD charts of the fired products of Examples 15 and 16 and the dried product of Example 17. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Tin recovery method] The tin recovery method of this embodiment will be described with reference to FIG. FIG. 1 is a flowchart showing the flow of the tin recovery method.

[0011] Preparation of tin-containing sludge First, a tin-containing sludge from which tin is to be recovered is prepared. Tin-containing sludge is sludge containing tin (Sn) that is generated when forming a tin-plated layer on the surface of a substrate such as a steel sheet. The tin-containing sludge contains, for example, Sn and at least one element selected from the group consisting of iron (Fe), copper (Cu), zinc (Zn), aluminum (Al), magnesium (Mg), calcium (Ca), chlorine (Cl), sodium (Na), cobalt (Co), nickel (Ni), manganese (Mn), fluorine (F), phosphorus (P), sulfur (S), and silicon (Si). Since the element recovered from the tin-containing sludge is Sn, elements other than Sn can basically be considered impurity elements, such as at least one element selected from the group consisting of Fe, Cu, Zn, Al, Mg, Ca, Cl, Na, Co, Ni, Mn, F, P, S, and Si. When tin-containing sludge is generated during the production of a tin-plated layer on the surface of a steel sheet, it contains a large amount of Fe as an impurity element and may also contain Cu.

[0012] <Cleaning> First, the tin-containing sludge is washed with washing water (e.g., ion-exchanged water). This removes at least some of the impurity elements contained in the tin-containing sludge. In this way, a washed tin-containing sludge is obtained, which is the tin-containing sludge from which at least some of the impurity elements have been removed. Specifically, in the washing process, for example, a mixture of tin-containing sludge and washing water is stirred, and the resulting slurry is subjected to solid-liquid separation. Through the solid-liquid separation, a filtrate containing impurity elements (e.g., Fe) removed from the tin-containing sludge and a residue are obtained. Thus, a washed tin-containing sludge, which is a tin-containing liquid sludge from which the impurity elements (e.g., Fe) have been removed, is obtained as the residue.

[0013] The method of solid-liquid separation is not particularly limited, and examples thereof include methods using suction filtration, a filter press, etc. This also applies to the solid-liquid separation performed in the dissolution, addition of a sulfiding agent, and pH adjustment described below.

[0014] The temperature of the washing water is, for example, 10°C or higher, and may be 15°C or higher. There is no particular upper limit, and it may be, for example, 90°C, 70°C, or 50°C.

[0015] The tin-containing sludge is preferably crushed prior to washing. The particle size after crushing is not particularly limited, and may be, for example, 10 mm or less, or 500 μm or less.

[0016] The number of times that the mixture of tin-containing sludge and wash water is stirred and then subjected to solid-liquid separation is, for example, one or more times, preferably two or more times, and more preferably three or more times, because impurity elements are more easily removed. The upper limit is not particularly limited, and is, for example, five times.

[0017] The time for stirring the mixture of tin-containing sludge and washing water is adjusted appropriately depending on the mass ratio (tin-containing sludge / washing water) described later and the like.

[0018] If the amount of washing water used relative to the tin-containing sludge is too small, the efficiency of removing impurity elements may decrease, whereas if the amount of washing water used relative to the tin-containing sludge is too large, a large vessel is required for stirring, which tends to increase costs. For this reason, the mass ratio of the tin-containing sludge to the washing water (tin-containing sludge / washing water) is preferably 1 / 2 to 1 / 20, and more preferably 1 / 4 to 1 / 15. The mass of the tin-containing sludge in this mass ratio means the mass (dry mass) of the tin-containing sludge in a state where the tin-containing sludge has been dried to remove moisture.

[0019] <Dissolution> Next, the washed tin-containing sludge is dissolved using an acid solution. This causes tin (Sn), a component contained in the washed tin-containing sludge, to be leached into the acid solution. In this way, a tin-containing solution A, which is an acid solution from which Sn has been leached, is obtained. Specifically, in the dissolution process, for example, a mixture of the washed tin-containing sludge and an acid solution is stirred, and the resulting slurry is subjected to solid-liquid separation. The solid-liquid separation yields a filtrate and a residue. Thus, the filtrate obtained is a tin-containing solution A, which is an acid solution containing Sn leached from the washed tin-containing sludge.

[0020] The acid solution is preferably at least one selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, and acetic acid.

[0021] If the concentration of the acid solution is too low, the tin-containing sludge may not be sufficiently dissolved after washing, resulting in a reduced amount of Sn leaching. Therefore, the concentration of the acid solution is preferably 1.0 M or more, more preferably 3.0 M or more, even more preferably 7.0 M or more, and particularly preferably 9.0 M or more. On the other hand, increasing the concentration of the acid solution gradually saturates the amount of Sn leached. Therefore, from the viewpoint of avoiding high costs due to excessively increasing the concentration of the acid solution, the concentration of the acid solution is, for example, 20.0 M or less, preferably 18.0 M or less, and more preferably 15.0 M or less.

[0022] The temperature of the acid solution is, for example, 25°C or higher, but is preferably 45°C or higher, more preferably 60°C or higher, because this makes it easier to dissolve the tin-containing sludge after washing. On the other hand, from the viewpoint of reducing heating costs, the temperature of the acid solution is preferably 100°C or lower, and more preferably 90°C or lower.

[0023] In order to improve the efficiency of leaching Sn, the acid solution may contain a reducing agent. The reducing agent may be, for example, at least one selected from the group consisting of hydrogen peroxide, sodium sulfide, sodium hydrogen sulfide, sodium thiosulfate, and oxalic acid.

[0024] The time for stirring the mixture of the washed tin-containing sludge and the acid solution is adjusted appropriately depending on the mass ratio (washed tin-containing sludge / acid solution) described later.

[0025] If the amount of acid solution used relative to the amount of tin-containing sludge after washing is too small, the tin-containing sludge after washing becomes saturated in the acid solution, and the amount of Sn leaching does not increase and tends to plateau.On the other hand, if the amount of acid solution used relative to the amount of tin-containing sludge after washing is too large, costs tend to increase. Therefore, the mass ratio of the washed tin-containing sludge to the acid solution (washed tin-containing sludge / acid solution) is preferably 1 / 2 to 1 / 20, and more preferably 1 / 5 to 1 / 15. The mass of the washed tin-containing sludge in this mass ratio means the mass (dry mass) of the washed tin-containing sludge in a state where the sludge has been dried to remove moisture.

[0026] <Addition of sulfurizing agent> Next, a sulfurizing agent is added to the tin-containing liquid A. This causes at least a portion of the impurity elements to react with the sulfurizing agent and precipitate as sulfide precipitates. The precipitated sulfides of the impurity elements are then removed. In this way, tin-containing liquid B, which is the tin-containing liquid A from which the precipitated impurity elements have been removed, is obtained.

[0027] The sulfiding agent may be, for example, at least one selected from the group consisting of hydrogen sulfide, sodium hydrogen sulfide, and sodium sulfide.

[0028] The reaction formula when sodium sulfide (Na2S) is used as the sulfiding agent and reacts with the divalent metal element Me, which is an impurity element, to precipitate sulfide (MeS) is shown below. Me 2+ +Na2S → MeS+2Na +

[0029] Specifically, for example, by adding a sulfiding agent such as sodium sulfide to tin-containing liquid A, a precipitate of a sulfide (e.g., copper sulfide CuS) of an impurity element (e.g., Cu) contained in tin-containing liquid A is precipitated.

[0030] The tin-containing liquid A to which the sulfiding agent has been added may be stirred as appropriate. Thereafter, solid-liquid separation is performed to obtain a filtrate and a residue. The residue is a sulfide of the impurity element (metal element). In this way, the filtrate obtained is the tin-containing liquid A from which the impurity element (metal element) has been removed, that is, the tin-containing liquid B.

[0031] The time for stirring the tin-containing liquid A to which the sulfurizing agent has been added is adjusted appropriately depending on the amount of sulfurizing agent added (described later) and other factors.

[0032] The particle size of the sulfiding agent is not particularly limited, and may be, for example, 10 mm or less, or 500 μm or less.

[0033] From the viewpoint of sufficiently precipitating the impurity elements as sulfides, the amount of sulfiding agent added is preferably 1.0 equivalent or more, more preferably 1.5 equivalents or more, and even more preferably 2.0 equivalents or more, relative to the impurity elements. On the other hand, there is no particular upper limit. However, if the amount of sulfurizing agent added is too large, costs tend to increase. Therefore, the amount of sulfurizing agent added is preferably 10.0 equivalents or less, more preferably 8.0 equivalents or less, and even more preferably 6.0 equivalents or less, relative to the impurity elements. For example, when copper sulfide (CuS) is produced using 1.0 equivalent of sodium sulfide (NaS) as a sulfiding agent, 1 mol of sodium sulfide (NaS) is used for 1 mol of Cu contained in tin-containing liquid A.

[0034] Before adding the sulfurizing agent to the tin-containing liquid A, an alkali (for example, a pH adjuster described later) may be added to the tin-containing liquid A. Specifically, the pH of the tin-containing liquid A before adding the sulfurizing agent is, for example, 0 or more, and may be 0.3 or more, or 0.5 or more. On the other hand, if too much alkali is added to the tin-containing liquid A, Sn contained in the tin-containing liquid A may precipitate as hydroxide. Therefore, the pH of the tin-containing liquid A before the addition of the sulfiding agent is preferably 2.0 or less, more preferably 1.8 or less, even more preferably 1.5 or less, and particularly preferably 1.0 or less.

[0035] <pH adjustment> Next, a pH adjuster is added to the tin-containing liquid B to adjust the pH of the tin-containing liquid B, thereby precipitating a tin oxide precursor (specifically, for example, tin hydroxide). The pH adjuster may be, for example, at least one selected from the group consisting of sodium hydroxide, calcium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, and aqueous ammonia.

[0036] The pH of the tin-containing liquid B after the addition of the pH adjuster is, for example, 2.0 or higher, and is preferably 2.5 or higher, more preferably 3.0 or higher, and even more preferably 3.5 or higher, because this facilitates precipitation of the tin oxide precursor (tin hydroxide). On the other hand, the pH of the tin-containing liquid B after the addition of the pH adjuster is, for example, 7.0 or less, preferably 6.5 or less, more preferably 6.0 or less, and even more preferably 5.5 or less.

[0037] The tin-containing liquid B from which the tin oxide precursor has precipitated is subjected to solid-liquid separation to obtain a filtrate and a residue, and the tin oxide precursor is thus obtained as the residue.

[0038] The obtained tin oxide precursor is preferably washed with washing water (for example, ion-exchanged water) to remove impurity elements contained in the tin oxide precursor. Specifically, for example, a mixture of the tin oxide precursor and the washing water is stirred, and then subjected to a solid-liquid separation treatment. This treatment is repeated, for example, once or more and five times or less. The temperature of the washing water is, for example, 25°C or higher and 90°C or lower.

[0039] If the amount of washing water used relative to the tin oxide precursor is too small, the efficiency of removing impurity elements may decrease, whereas if the amount of washing water used relative to the tin oxide precursor is too large, a large vessel is required for stirring, which tends to increase costs. Therefore, the mass ratio of the tin oxide precursor to the washing water (tin oxide precursor / washing water) is preferably 1 / 2 to 1 / 20, and more preferably 1 / 4 to 1 / 15. The mass of the tin oxide precursor in this mass ratio means the mass (dry mass) of the tin oxide precursor after drying to remove moisture.

[0040] <Firing> Next, the tin oxide precursor (for example, tin hydroxide) is calcined to obtain tin oxide. Before calcining, the tin oxide precursor may be dried. The drying temperature is not particularly limited and is, for example, 80 to 120°C. The temperature (calcination temperature) when calcining the tin oxide precursor is preferably 300°C or higher, more preferably 450°C or higher, even more preferably 600°C or higher, and particularly preferably 750°C or higher, because this facilitates the production of tin oxide. Although there is no particular upper limit, if the firing temperature is too high, the particle size of the resulting tin oxide may become excessively large and the cost may increase. Therefore, the firing temperature is preferably 1200°C or less, more preferably 1100°C or less, and even more preferably 1000°C or less. The atmosphere in which the tin oxide precursor is dried and fired is not particularly limited as long as it contains oxygen, for example, air.

[0041] In this way, tin (Sn) can be recovered as tin oxide from the tin-containing sludge while removing impurity elements. [Example]

[0042] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples described below.

[0043] Preparation of tin-containing sludge As the tin-containing sludge, sludge S1 generated when forming a tin-plated layer on the surface of a steel sheet was prepared. A part of the component composition of sludge S1 is shown in Table 1 below.

[0044] [Table 1]

[0045] As shown in Table 1 above, the sludge S1 contains impurity elements such as Fe and Cu in addition to Sn.

[0046] <Cleaning: Example 1 to Example 3> The sludge S1 was washed with washing water (ion-exchanged water), and after washing, sludge S2 was obtained. More specifically, in Example 1, 10 g of sludge S1 was placed in a glass container, and 100 mL of ion-exchanged water and a stirring bar were added. The mixture was stirred at 25°C for 30 minutes using a stirrer to obtain a slurry that was a mixture of sludge S1 and ion-exchanged water. The obtained slurry was subjected to solid-liquid separation by suction filtration to obtain a filtrate and a residue. This process (stirring to solid-liquid separation) was repeated three times. Example 2 was the same as Example 1, except that 20 g of sludge S1 was used. Example 3 was the same as Example 1, except that 20 g of sludge S1 was used and the sludge S1 was crushed in a mortar before washing. After each treatment (from stirring to solid-liquid separation), the filtrate obtained was subjected to X-ray fluorescence (XRF) analysis to determine the contents (unit: mass%) of some elements. The results are shown in Table 2 below.

[0047] [Table 2]

[0048] As shown in Table 2 above, the filtrate (especially the first filtrate) contained a large amount of Fe. This indicates that by washing the sludge S1, a large amount of Fe, one of the impurity elements contained in the sludge S1, was removed. Fe exists in the sludge S1 as ions, and it is believed that it was removed from the sludge S1 as ions. Compared with the first filtrate, the Fe content of the third filtrate was significantly lower.

[0049] Comparing Example 1 and Example 2, it can be seen that in Example 1, where a larger amount of wash water was used relative to the sludge S1, the Fe content of the first filtrate was higher than in Example 2, and therefore a larger amount of Fe was removed from the sludge S1.

[0050] Furthermore, comparing Example 2 and Example 3, it can be seen that when the amount of wash water used for the sludge S1 is the same, more Fe can be removed from the sludge S1 by crushing the sludge S1 in advance.

[0051] In all cases, the Cu content of the filtrate was below the detection limit of XRF analysis, which indicates that Cu could not be removed from the sludge S1 by washing it.

[0052] <Dissolution: Examples 4 to 7> Next, the post-wash sludge S2 of Example 1 was dissolved in an acid solution (hydrochloric acid) to obtain a tin-containing solution A. More specifically, in Example 4, 10 g of washed sludge S2 was placed in a glass container, and 100 mL of 35% by mass (11.3 M) hydrochloric acid and a stirring bar were added. The mixture was stirred at 80°C for 30 minutes using a stirrer to obtain a slurry. The obtained slurry was subjected to solid-liquid separation by suction filtration to obtain a tin-containing liquid A as a filtrate and a residue. The residue was dried at 100°C, and its mass (dry mass) was determined. In Example 5, the procedure was the same as in Example 4, except that the dissolution was carried out at 65°C. In Example 6, the procedure was the same as in Example 4, except that the dissolution was carried out at 40°C. Example 7 was carried out in the same manner as Example 4, except that 1 g of washed sludge S2 and 17.5 mass % (5.7 M) hydrochloric acid were used. The mass (dry mass) of the washed sludge S2 when dried at 100°C was determined in advance, and the dissolution rate (unit: mass%) of the washed sludge S2 was calculated from the dry mass of the washed sludge S2 and the dry mass of the residue. The results are shown in Table 3 below.

[0053] [Table 3]

[0054] As shown in Table 3 above, higher dissolution rates were obtained in Examples 4 and 5, which were dissolved in acid solutions at 80°C or 65°C, than in Example 6, which was dissolved in acid solution at 40°C. Furthermore, when Example 4 and Example 7 are compared, Example 4, which had a higher concentration of the acid solution, achieved a higher dissolution rate.

[0055] <Addition of sulfurizing agent: Examples 8 to 11> Next, a sulfiding agent was added to the tin-containing liquid A of Example 4 to obtain a tin-containing liquid B. More specifically, in Example 8, a sodium hydroxide aqueous solution was added to 100 mL of tin-containing liquid A to adjust the pH to 0.8. Then, 2.0 mg (2.0 equivalents) of sodium hydrogen sulfide was added as a sulfiding agent, and a stirring bar was added, followed by stirring at 25°C for 30 minutes using a stirrer. After stirring, tin-containing liquid A was subjected to solid-liquid separation by suction filtration to obtain tin-containing liquid B as a filtrate and a residue. In Example 9, the same procedure as in Example 8 was carried out except that 3.0 mg (3.0 equivalents) of sodium sulfide was added as the sulfiding agent. In Example 10, the same procedure as in Example 8 was carried out except that 0.5 mg (0.5 equivalents) of sodium hydrogen sulfide was added as a sulfiding agent. In Example 11, the same procedures as in Example 8 were carried out except that the pH of the tin-containing liquid A before the addition of the sulfiding agent was set to 2.0. The obtained filtrate, tin-containing liquid B, was subjected to ICP atomic emission spectroscopy to determine the Cu content (unit: mass%) and Sn content (unit: mass%). The Sn recovery rate (unit: mass%) was calculated from the calculated Sn content and the initial Sn content of sludge S1 (see Table 1). The results are shown in Table 4 below.

[0056] [Table 4]

[0057] As shown in Table 4 above, the Cu content of the tin-containing liquid B in Examples 8 and 9 was lower than the initial Cu content of the sludge S1 (see Table 1). This shows that in Examples 8 and 9, the addition of the sulfurizing agent caused Cu sulfides to precipitate, and the Cu sulfides were removed as residues. In Example 10, the Cu content of the tin-containing liquid B remained the same as the initial Cu content (see Table 1). This is thought to be because the amount of sulfurizing agent added to the tin-containing liquid A was small, and Cu sulfides were not precipitated (Cu sulfides were not removed as residue). In addition, in Example 11, the Cu content of the tin-containing liquid B decreased, but the Sn recovery rate also decreased, similarly to Examples 8 and 9. This is thought to be because Sn precipitated as hydroxide and was removed as a residue.

[0058] <pH adjustment: Example 12 to Example 14> Next, the pH of the tin-containing liquid B of Example 8 was adjusted to precipitate a tin oxide precursor. More specifically, in Example 12, an aqueous sodium hydroxide solution was added dropwise as a pH adjuster to the tin-containing liquid B to adjust the pH to 4.0. Thereafter, solid-liquid separation was performed by suction filtration to obtain a filtrate and a residue, which was a tin oxide precursor. In Example 13, the same procedure as in Example 12 was carried out except that the pH of the tin-containing liquid B was adjusted to 6.6. In Example 14, the same procedures as in Example 12 were carried out except that the pH of the tin-containing liquid B was adjusted to 2.3. The obtained filtrate was subjected to ICP atomic emission spectroscopy to determine the Sn content (unit: mass%). The Sn recovery rate (unit: mass%) in the obtained tin oxide precursor was calculated from the determined Sn content and the initial Sn content of sludge S1 (see Table 1). The results are shown in Table 5 below.

[0059] [Table 5]

[0060] As shown in Table 5 above, in Examples 12 and 13 in which the pH of tin-containing liquid B was adjusted to 4.0 or higher, the Sn recovery rate was close to 100 mass %, and it is believed that almost the entire amount was precipitated as a tin oxide precursor. On the other hand, in Example 14, in which the pH of tin-containing liquid B was adjusted to 2.3, the Sn recovery rate was approximately 50 mass %. This is thought to be because the reaction of the Sn ions contained in tin-containing liquid B to form a tin oxide precursor did not proceed sufficiently, and the ions remained as they were.

[0061] <Firing: Examples 15 to 17> Next, the tin oxide precursor of Example 12 was calcined to obtain tin oxide. More specifically, in Example 15, a tin oxide precursor was dried at 100° C. in an air atmosphere and then calcined at 800° C. for 2 hours to obtain tin oxide. In Example 16, the tin oxide precursor was dried at 100° C. in an air atmosphere and then calcined at 1000° C. for 2 hours to obtain tin oxide. Example 17 was the same as Example 15, except that only drying at 100°C was carried out (calcination was not carried out). An X-ray diffraction (XRD) chart was obtained for the obtained fired product (or dried product) using an XRD device, and the results are shown in Figure 2. FIG. 2 is an XRD chart of the fired products of Examples 15 and 16 and the dried product of Example 17. As shown in FIG. 2, the XRD charts of Examples 15 and 16 show SnO2 peaks without any other phases, which indicates that tin oxide was obtained. On the other hand, the XRD chart of Example 17 shows no SnO2 peak, and it is understood that the dried product had low crystallinity and was amorphous.

[0062] <Cleaning - Firing: Example 18 - Example 20> Using the above-described sludge S1 as the tin-containing sludge, a fired product (tin oxide) was obtained by carrying out processes from washing to firing under the conditions shown in Table 6 below. Conditions other than those shown in Table 6 below were the same as those in Examples 1, 4, 8, 12, and 15 above. The resulting fired product (tin oxide) was analyzed by ICP atomic emission spectroscopy to determine the Sn, Fe, and Cu contents. The Sn recovery rate (unit: mass%) was calculated from the determined Sn content and the initial Sn content of sludge S1 (see Table 1). The results are shown in Table 6 below.

[0063] [Table 6]

[0064] As shown in Table 6 above, in Examples 18 and 19, the Sn recovery rate was higher than in Example 20, and the Fe content and Cu content were lower.

Claims

1. washing the tin-containing sludge with wash water to obtain a washed tin-containing sludge from which at least a portion of the impurity elements have been removed; After the washing, the tin-containing sludge is dissolved in an acid solution to obtain a tin-containing solution A. A sulfurizing agent is added to the tin-containing liquid A to precipitate impurity elements, and a tin-containing liquid B is obtained from which the precipitated impurity elements have been removed. The pH of the tin-containing liquid B is adjusted with a pH adjuster to precipitate a tin oxide precursor, The tin oxide recovery method comprises calcining the tin oxide precursor to obtain tin oxide.

2. 2. The method for recovering tin according to claim 1, wherein the tin-containing sludge contains Sn and at least one element selected from the group consisting of Fe, Cu, Zn, Al, Mg, Ca, Cl, Na, Co, Ni, Mn, F, P, S, and Si.

3. 3. The tin recovery method according to claim 1, wherein in the washing of the tin-containing sludge, a process of stirring a mixture of the tin-containing sludge and the washing water and then separating the tin-containing sludge into solid and liquid is repeated one to five times.

4. 3. The method for recovering tin according to claim 1, wherein the acid solution is at least one selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, and acetic acid.

5. 5. The method for recovering tin according to claim 4, wherein the temperature of the acid solution is 45°C or higher.

6. The acid solution contains a reducing agent, 5. The method for recovering tin according to claim 4, wherein the reducing agent is at least one selected from the group consisting of hydrogen peroxide, sodium sulfide, sodium hydrogen sulfide, sodium thiosulfate, and oxalic acid.

7. 3. The method for recovering tin according to claim 1, wherein the sulfiding agent is at least one selected from the group consisting of hydrogen sulfide, sodium hydrogen sulfide, and sodium sulfide.

8. 8. The method for recovering tin according to claim 7, wherein the amount of the sulfiding agent added is 1.0 equivalent or more.

9. The tin recovery method according to claim 7, wherein the pH of the tin-containing liquid A before the addition of the sulfiding agent is 1.5 or less.

10. 3. The method for recovering tin according to claim 1, wherein the pH adjuster is at least one selected from the group consisting of sodium hydroxide, calcium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, and aqueous ammonia.

11. The method for recovering tin according to claim 10, wherein the pH of the tin-containing liquid B is adjusted to 2.5 or higher by the pH adjuster.

12. Before calcining the tin oxide precursor, a treatment of stirring a mixture of the tin oxide precursor and washing water and then subjecting the mixture to solid-liquid separation is repeated one to five times. The method for recovering tin according to claim 1 or 2.

13. The method for recovering tin according to claim 1 or 2, wherein the tin oxide precursor is calcined at a temperature of 600°C or higher.

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