JPH07316677A - Method for recovering valuable metal from steelmaking dust - Google Patents

Abstract

PURPOSE:To recover valuable metals from the steelmaking dust contg. zinc, iron, fluorine, chlorine, etc., and to more efficiently remove the fluorine and chlorine. CONSTITUTION:Sulfuric acid is added to the steelmaking dust, and the mixture is kneaded and then subjected to sulfating roasting. The waste sulfating roasting gas is washed with water, the washing water is neutralized to precipitate the fluorine compd., and the neutralized washing water is filtered to transfer the chlorine into the filtrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering valuable metals from steelmaking dust. More specifically, chlorine and fluorine in steelmaking dust are efficiently separated from valuable metals such as zinc. It relates to a processing method.

[0002]

2. Description of the Related Art When steelmaking dust is directly processed in a zinc dry smelter, chlorine and fluorine are concentrated in the process, and the boiler,
Corrosion of waste gas treatment equipment such as electric dust collectors. Also,
When sulfuric acid leaching is carried out as a wet treatment of steelmaking dust, chlorine and fluorine enter the leachate and attack the electrode in the electrolytic refining process.
Due to this background, for example, Japanese Patent Publication No. 53-2
A method for recovering valuable metals from dust and the like of Hiraden furnace steelmaking disclosed in Japanese Patent No. 9122 has been proposed. This method is a step of washing the Hiraden furnace steelmaking dust with water and removing chlorine, sodium, potassium, and granulating by adding coke to the washing dust containing zinc, lead, cadmium, iron, etc. obtained in that step. , A step of obtaining sintered iron ore containing zinc and lead, etc., and a dust obtained by removing the sintering gas from the step is washed with alkaline water to remove fluorine, and a non-ferrous metal containing lead and cadmium. It consists of the process of obtaining slag. The first water wash removes more than 95% of chlorine.

In this method, regarding fluorine, about 8 is obtained by sintering coke-washed water-washed dust at a high temperature of about 1000 ° C. and then performing alkali washing.
0% fluorine is eluted in the wash water. As discussed in the specification, high temperature treatment during sintering plays an important role in making fluorine soluble in an aqueous solution.

Further, JP-A-55-104434 proposes a method for treating zinc-containing iron dust. In this method, the secondary dust generated during reduction firing of iron-making dust is repulped with water, then subjected to a wet magnetic separator, and then solid-liquid separated to separate and collect non-magnetic halogen compounds with high iron and zinc contents. is doing.

Further, steelmaking dust, coke, and limestone are mixed by the Weltz method, and the mixture is heated in a reduction kiln at 1200 ° C.
When treated in a moderate amount, zinc oxide in steelmaking dust is reduced to become zinc vapor and volatilize. This zinc vapor is oxidized in the exhaust gas to become zinc oxide, which is collected in the dust collection facility. Chlorine and fluorine also volatilize in the reduction kiln and enter zinc oxide. Zinc oxide is washed with alkali to remove chlorine and fluorine and used as a zinc scouring material.

[0007]

[Problems to be Solved by the Invention] Japanese Patent Publication No. 53-29
The method disclosed in Japanese Patent No. 122 and the Weltz method require high temperature treatment, and the fluorine separation rate is not high. Further, in the method disclosed in Japanese Patent Laid-Open No. 55-104434, since fluorine is contained in both the magnetic substance and the non-magnetic substance, the fluorine separation rate is not so high. Therefore, the present invention overcomes the above-mentioned problems of the prior art, separates chlorine and fluorine in steelmaking dust from valuable metals such as zinc at a high rate, and interferes with these chlorine and fluorine in the subsequent valuable metal recovery processing. It is intended to provide a low temperature process that can eliminate In particular, the present invention has a high zinc quality and is important as a zinc recycling raw material, but an object thereof is to efficiently remove fluorine from steelmaking dust that is difficult to process by the conventional method because it contains a large amount of fluorine. Further, the present invention is
It is also an object to provide a method for further separating chlorine and fluorine separated from valuable metals by the above low temperature process.

[0008]

The present invention is a method for recovering valuable metals such as zinc from steelmaking dust by kneading steelmaking dust and sulfuric acid and then performing sulfation and roasting at a temperature of 350 to 550 ° C. It is a method of recovering valuable metals from steelmaking dust, which is characterized by migrating chlorine and fluorine into roasting exhaust gas. In the present invention, when the roasting temperature is lower than 350 ° C., the roasting time becomes long, and when it exceeds 550 ° C., there is no advantage of energy saving and the roasting effect is saturated. Therefore, in the present invention, the roasting temperature of 350 to 550 ° C. Adopt temperature. A roasting temperature of 400 to 450 ° C. is particularly preferable. After separating valuable metals from chlorine and fluorine as described above, especially zinc in the valuable metals is recovered, and exhaust gas is purified to remove chlorine and fluorine. Preferred post-processes for doing this are a step of washing the exhaust gas from the sulfation roasting step with water, a step of neutralizing the washing liquid obtained in the water washing step to produce a fluorine compound solid, and a neutralization step. And filtering the subsequent washing liquid to transfer chlorine into the filtrate. Hereinafter, the constitution of the present invention will be described in more detail.

The steelmaking dust to be treated by the present invention is generated from a steelmaking process such as a sintering furnace, an open furnace, an electric furnace, etc., and particularly Zn: 20 to 70%, Fe: 1 to 30%,
F: 0.5 to 6%, Cl: 4 to 20% are contained. Other components are Pb, C of 0 to 50% in total.
d, Cr, Ca, SiO2, Al2 O3, MgO, S and the like. Particularly preferred steelmaking dust for applying the method of the present invention having high fluorine removal efficiency contains 4% or more of fluorine. Further, there is no particular limitation on the particle size of the steelmaking dust to be kneaded with sulfuric acid to sufficiently react with it, and the particle size of the dust discharged from the steelmaking plant may be the same. The sulfuric acid and the steelmaking dust are usually kneaded at a temperature of room temperature to 100 ° C.

In the sulphation roasting step, the steelmaking dust is mainly converted in order to convert Zn and Fe in the steelmaking dust into sulfates and to reduce the amounts of F and Cl in the roasting cake as a zinc smelting raw material as much as possible. This is done by heating while making sufficient contact with air.

The preferable addition rate of sulfuric acid will be described below with reference to the results of preliminary experiments conducted by the present inventor. 25 g of steelmaking dust was mixed with a predetermined sulfuric acid, charged into a crucible, heated to 450 ° C. in an electric furnace and held for 3 hours, and then the steelmaking dust was analyzed to determine the residual ratio of each element. The test results are shown in the table below, and Table 1 shows the addition rate of sulfuric acid (weight of H2 SO4 to dust) and the residual rates of chlorine and fluorine in the sulfate.

[0012]

[Table 1] Sulfuric acid addition rate Residual rate (%) (g / g-dust) Zn Fe Pb Cd F Cl 0.0 99 -100 100 100 100 87-93 97 -100 0.35 98 -100 100 100 100 64-77 100 0.70 91 -100 100 100 100 21−33 65 − 90 1.05 100 100 100 100 2 0

From Table 1, it can be seen that as the addition rate of sulfuric acid increases, the residual rates of chlorine and fluorine decrease and the amount of these that migrate into the exhaust gas increases. When the sulfuric acid addition rate was 1.05, the residual rates of chlorine and fluorine were 2 and 0%, respectively. This addition rate = 1.0 was equal to the amount of sulfuric acid that converted all zinc and iron in the grade steelmaking dust used in the experiment to sulfate. On the other hand, valuable non-ferrous metals such as zinc, lead, and cadmium remain in the roasting dust in the total amount or almost the entire amount even if the sulfuric acid addition rate increases, and it can be seen that the roasted steel-making dust can be used as a raw material for zinc smelting.

Further, the sulfuric acid addition rate is 1.05, 1.1.
Tables 2 and 3 show the results of conducting the same experiment with other conditions changed to 5 and 1.3.

[0015]

[Table 2]

[0016]

[Table 3]

From Tables 2 and 3, it is understood that chlorine and fluorine cannot be removed by simply kneading the steelmaking dust and sulfuric acid. From the above results, it is preferable that the addition amount of sulfuric acid is based on the amount of zinc oxide and iron oxide in the steelmaking dust as sulfates, and the reference amount is within + 30% to −30%. When the amount is less than the standard amount, the residual rate of chlorine is slightly increased, but in this case, it is desirable to take measures to raise the sulphation roasting temperature. Further, in an actual operation, by adding an appropriate amount of water to the kneaded product, sulfuric acid can quickly wet the entire steelmaking dust, and the kneading efficiency can be improved.

Since the product obtained in the above-mentioned roasting step is mainly composed of sulfate and does not contain chlorine and fluorine, it is subjected to oxidative roasting or sintering treatment in a zinc dry smelting plant, and then zinc smelting is carried out. To recover zinc, etc. Further, it is also possible to perform wet pulverization as it is at a zinc electrolytic refining plant and add sulfuric acid to use as a zinc electrolytic solution.

Next, the same experiment as above was carried out by changing the addition rate of sulfuric acid and the roasting temperature, and the results will be described with reference to FIGS. FIG. 2 is a graph showing the residual rate of fluorine with respect to the addition rate of sulfuric acid, using the roasting temperature as a parameter,
FIG. 3 is a graph showing the residual rate of chlorine with respect to the addition rate of sulfuric acid, using the roasting temperature as a parameter. From Figures 2 and 3, sulfuric acid /
Steelmaking dust ratio is about 0.9 or more and roasting temperature is 350-4
It can be seen that there is a remarkable effect of removing fluorine and chlorine at 50 ° C.

Removal of chlorine and fluorine contained in the exhaust gas in the sulfation / roasting step can be carried out by a known exhaust gas treatment technique such as treatment with a scrubber or a spray tower. The chlorine and fluorine in the cleaning liquid obtained by turning chlorine and fluorine in the exhaust gas in the cleaning tower are neutralized to form fluorine as a solid fluoride substance. pH
As can be seen from FIG. 4, which shows the relationship between the F concentration in the sulfuric acid solution and the F concentration in the sulfuric acid solution, when the pH is less than 2.5, a large amount of fluorine is dissolved in the solution, and when the pH exceeds 5.5, the pH increases. However, since the dissolved fluorine does not decrease much, pH =
The range of 2.5-5.5, especially 3.5-4.5 is preferable. Neutralization is preferably by addition of CaCO3, Ca (OH) 2 and / or NaOH, especially CaCO3
, Ca (OH) 2 has fluorine as a fluorinated compound and can be used as a raw material for steelmaking.
H adjustment additive. After neutralization, chlorine is separated from the residue.

[0021]

[Function] Almost all chlorine and fluorine are volatilized at a relatively low temperature during the sulfation and roasting of steelmaking dust. This is because chlorine and fluorine contained in the steelmaking dust in the form of chlorides (ZnCl2, CaCl2) and fluorides (CaF, ZnF) change into HCl and HF during the kneading process with sulfuric acid, respectively. Conceivable. The steelmaking dust that has undergone such changes can be roasted at a very low temperature and has a high mutual separation rate of chlorine, fluorine and zinc. An embodiment of this method will be described below with reference to the process diagram and the distribution balance shown in the flowchart of FIG.

[0022]

EXAMPLE Steelmaking dust (200 t) having the composition shown in Table 4 and sulfuric acid (200 t in terms of H2 SO4; sulfuric acid addition rate = 1.0)
And are kneaded in a rotary kiln at a rotation speed of 10 to 20 rpm for 5 to 15 minutes. The elements other than those shown in Table 4 are mainly oxygen.

[0023]

[Table 4] Quality of raw material (200t) Zn Fe Pb Cd Cr F Cl Quality (%) 41.7 6.51 0.68 0.28 0.63 4.5 6.6 Amount (t) 83.4 13.02 1.36 0.56 1.26 9.0 13.26

Subsequently, roasting is carried out at a temperature of 450 ° C. for 2 to 5 hours in a rotary kiln type roasting furnace using heavy oil as a fuel. Almost all chlorine and fluorine in steelmaking dust were volatilized during roasting, and a roasted cake containing no valuable metals and chlorine and fluorine was obtained. The grade is shown in the following table.

[0025]

[Table 5] Roasted cake quality (350 Dt, moisture 0%) Zn Fe Pb Cd Cr F Cl Quality (%) 28.83 3.72 0.39 0.16 0.36 0.05 0.00 Amount (t) 83.40 13.02 1.36 0.56 1.26 0.18 0.00 Distribution (%) 100 100 100 100 100 2 0

The roasted cake is oxidized and roasted to recover sulfuric acid,
Alternatively, sintering is performed as it is, sulfurous acid gas in the exhaust gas is neutralized with 200 t of limestone, and then zinc smelting is performed. The flow rate of the exhaust gas from the roasting furnace is in the range of 20 to 60 Nm3 / min (average 45 Nm3 / min), and the average temperature of the exhaust gas is 250 ° C.
Is. The exhaust gas is led to the scrubber washing tower and the total amount is 120
Wash with 0 Nm3 of water (equivalent to 0.1 m3 per minute). Table 6 showing the quality of scrubber wash water shows that the distribution ratio of fluorine and chlorine is very high.

[0027]

[Table 6] Scrubber cleaning water Zn Fe Pb Cd Cr F Cl Grade (g / l) 0.0 0.0 0.0 0.0 0.0 17.6 26.4 Amount (t) 0.0 0.0 0.0 0.0 0.0 8.82 13.20 Distribution (%) 0 0 0 0 0 98 100

Exhaust gas is discharged from the scrubber washing tower at a temperature of about 60.degree. Since this exhaust gas contains sulfuric acid mist, sulfuric acid is recovered by the mist cotrel and the purified clean gas is released. On the other hand, in the scrubber cleaning tower, scrubber cleaning water containing chlorine, fluorine, sulfurous acid, etc. is circulated, and when these reach a predetermined concentration, the scrubber cleaning water is withdrawn from the scrubber cleaning tower. The pH at that time is in the range of 1-2. Subsequently, the wash water is neutralized to pH = 2.5 to 5.5 with CaCO3, Ca (OH) 2 or NaOH. This p
The amount of addition required to neutralize to H range is CaCO3 = 5
0.2t, Ca (OH) 2 = 37.1t, or Na
OH = 40.1t. Filtrate obtained by filtering with a filter press after adding CaCO3 (Table 7, 1195 m
3) and the quality of the residue (Table 8, 30D.t) are shown in each table.

[0029]

[Table 7] Filter after defluorination treatment (1195 m3) Quality Zn Fe Pb Cd Cr F Cl Quality (g / l) 0.0 0.0 0.0 0.0 0.0 0.4 10.8 Amount (t) 0.0 0.0 0.0 0.0 0.0 0.53 12.94 Distribution (%) 94 0 0 95 0 6 98

[0030]

[Table 8] Defluorination treatment residue (30 Dt, 49 Wt, moisture 60%) Zn Fe Pb Cd Cr F Cl Quality (%) 0 0 0 0 0 28 0.892 Amount (t) 0.00 0.00 0.00 0.00 0.00 8.29 0.26 Distribution (%) 6 100 100 4 100 94 2

From Tables 7 and 8, it is clear that chlorine and fluorine are almost completely separated.

[0032]

INDUSTRIAL APPLICABILITY As described above, the present invention is a technology of recovering valuable metals from steelmaking dust that achieves energy saving and has a good working environment, and thus has a high industrial value. Further, since it is possible to treat steelmaking dust having a high fluorine content, which was difficult to treat by the conventional technique, it is also valuable in terms of resource recovery.

[Brief description of drawings]

FIG. 1 is a flow chart according to an embodiment of the method of the present invention.

FIG. 2 is a graph showing a relationship between a sulfuric acid addition rate and a fluorine residual rate.

FIG. 3 is a graph showing a relationship between a sulfuric acid addition rate and a chlorine residual rate.

FIG. 4 shows the relationship between pH and the fluorine leaching rate in a sulfuric acid solution as CaC.
6 is a graph showing pH adjusting / fluorine fixing agents such as O3, NaOH and Ca (OH) 2 as parameters.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] June 2, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction content]

The steelmaking dust to be treated by the present invention is generated from a steelmaking process such as a sintering furnace, an open furnace, an electric furnace, etc., and particularly Zn: 20 to 70%, Fe: 1 to 30%,
F: 0.5 to 6%, Cl: 4 to 20% are contained. Other components are Pb, C of 0 to 50% in total.
d, Cr, Ca, SiO ₂ , Al ₂ O ₃ , MgO, S and the like. Particularly preferred steelmaking dust for applying the method of the present invention having high fluorine removal efficiency contains 4% or more of fluorine. Further, there is no particular limitation on the particle size of the steelmaking dust to be kneaded with sulfuric acid to sufficiently react with it, and the particle size of the dust discharged from the steelmaking plant may be the same. The sulfuric acid and the steelmaking dust are usually kneaded at a temperature of room temperature to 100 ° C.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

The preferable addition rate of sulfuric acid will be described below with reference to the results of preliminary experiments conducted by the present inventor. 25 g of steelmaking dust was mixed with a predetermined sulfuric acid, charged into a crucible, heated to 450 ° C. in an electric furnace and held for 3 hours, and then the steelmaking dust was analyzed to determine the residual ratio of each element. The table below shows the test results, and Table 1 shows the addition rate of sulfuric acid (weight of H ₂ SO _{4 to} dust) and the residual rates of chlorine and fluorine in the sulfate.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

Removal of chlorine and fluorine contained in the exhaust gas in the sulfation / roasting step can be carried out by a known exhaust gas treatment technique such as treatment with a scrubber or a spray tower. The chlorine and fluorine in the cleaning liquid obtained by turning chlorine and fluorine in the exhaust gas in the cleaning tower are neutralized to form fluorine as a solid fluoride substance. pH
As can be seen from FIG. 4, which shows the relationship between the F concentration in the sulfuric acid solution and the F concentration in the sulfuric acid solution, when the pH is less than 2.5, a large amount of fluorine is dissolved in the solution, and when the pH exceeds 5.5, the pH increases. However, since the dissolved fluorine does not decrease much, pH =
The range of 2.5-5.5, especially 3.5-4.5 is preferable. Neutralization is preferably by addition of CaCO ₃ , Ca (OH) ₂ and / or NaOH, especially CaCO 3.
₃ , Ca (OH) ₂ is preferable because it fixes fluorine as a fluorinated compound and can be used as a steelmaking raw material.
H adjustment additive. After neutralization, chlorine is separated from the residue.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction content]

[0021]

[Function] Almost all chlorine and fluorine are volatilized at a relatively low temperature during the sulfation and roasting of steelmaking dust. The reason for this is that chlorine and fluorine contained in the steelmaking dust in the form of chloride (ZnCl ₂ , CaCl ₂ ) and fluoride (CaF, ZnF) change into HCl and HF during the kneading process with sulfuric acid, respectively. It is thought to be because. The steelmaking dust that has undergone such changes can be roasted at a very low temperature and has a high mutual separation rate of chlorine, fluorine and zinc. An embodiment of this method will be described below with reference to the process diagram and the distribution balance shown in the flowchart of FIG.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Name of item to be corrected] 0022

[Correction method] Change

[Correction content]

[0022]

Example Steelmaking dust (200 t) having the composition shown in Table 4 and sulfuric acid (200 t in terms of H ₂ SO ₄ ; sulfuric acid addition rate = 1.0)
And are kneaded in a rotary kiln at a rotation speed of 10 to 20 rpm for 5 to 15 minutes. The elements other than those shown in Table 4 are mainly oxygen.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction content]

The roasted cake is oxidized and roasted to recover sulfuric acid,
Alternatively, sintering is performed as it is, sulfurous acid gas in the exhaust gas is neutralized with 200 t of limestone, and then zinc smelting is performed. Flow rate of the exhaust gas from the roasting furnace is 20 to 60 nm ³ / min range (average 45 Nm ³ / min), the average temperature of the exhaust gas is 250 ° C.
Is. The exhaust gas is led to the scrubber washing tower and the total amount is 120
Wash with 0 Nm ³ of water (equivalent to 0.1 m ³ per minute). Table 6 showing the quality of scrubber wash water shows that the distribution ratio of fluorine and chlorine is very high.

[Procedure Amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction content]

Exhaust gas is discharged from the scrubber washing tower at a temperature of about 60.degree. Since this exhaust gas contains sulfuric acid mist, sulfuric acid is recovered by the mist cotrel and the purified clean gas is released. On the other hand, in the scrubber cleaning tower, scrubber cleaning water containing chlorine, fluorine, sulfurous acid, etc. is circulated, and when these reach a predetermined concentration, the scrubber cleaning water is withdrawn from the scrubber cleaning tower. The pH at that time is in the range of 1-2. Subsequently, the wash water is neutralized to pH = 2.5 to 5.5 with CaCO ₃ , Ca (OH) ₂ or NaOH. This p
The amount of addition required to neutralize to the H range is CaCO ₃ = 5
0.2t, Ca (OH) ₂ = 37.1t, or Na
OH = 40.1t. Filtrate obtained by performing filtration with a filter press after adding CaCO ₃ (Table 7, 1195 m
³ ) and the quality of the residue (Table 8, 30D.t) are shown in each table.

[Procedure Amendment 8]

[Document name to be amended] Statement

[Name of item to be corrected] 0029

[Correction method] Change

[Correction content]

[0029]

[Table 7] Filter after defluorination treatment (1195 m ³ ) Quality Zn Fe Pb Cd Cr F Cl Quality (g / l) 0.0 0.0 0.0 0.0 0.0 0.4 10.8 Amount (t) 0.0 0.0 0.0 0.0 0.0 0.53 12.94 Distribution (%) 94 0 0 95 0 6 98

[Procedure Amendment 9]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a flow chart according to an embodiment of the method of the present invention.

FIG. 2 is a graph showing a relationship between a sulfuric acid addition rate and a fluorine residual rate.

FIG. 3 is a graph showing a relationship between a sulfuric acid addition rate and a chlorine residual rate.

FIG. 4 shows the relationship between pH and the fluorine leaching rate in a sulfuric acid solution as CaC.
It is a graph showing a pH adjusting / fluorine fixing agent such as O ₃ , NaOH and Ca (OH) ₂ as parameters.

Claims (8)

[Claims] 1. A method for recovering valuable metals such as zinc from steelmaking dust in a range of 350 to 350 after kneading steelmaking dust and sulfuric acid.
A method for recovering valuable metals from steelmaking dust, which comprises migrating chlorine and fluorine into the roasting exhaust gas by carrying out sulfate roasting at a temperature of 550 ° C. 2. A step of washing exhaust gas from the sulfate roasting step with water, a step of neutralizing the washing solution obtained in the water washing step to produce a fluorine compound solid, and a washing solution after neutralization. The method of recovering valuable metals from steelmaking dust according to claim 1, further comprising the step of: 3. The pH in the neutralization step is about 2.5-5.
5. The method for recovering valuable metals from steelmaking dust according to claim 2, wherein the value is adjusted to 5. 4. The neutralizing step, wherein one or more selected from caustic soda, calcium carbonate and calcium hydroxide is added to the cleaning liquid obtained in the water cleaning step. For recovering valuable metals from steelmaking dust in Japan. 5. The steelmaking dust according to claim 4, wherein in the neutralization step, one or two kinds selected from calcium carbonate and calcium hydroxide are added to the cleaning liquid obtained in the water cleaning step. Method for recovering valuable metals from the market. 6. Steelmaking dust contains 20 to 70% zinc, 1 to 30% iron, 0.5 to 6% fluorine, and 4 to 20% chlorine.
The method for recovering valuable metals from steelmaking dust according to any one of claims 1 to 5, wherein the valuable metal is contained. 7. The method for recovering valuable metals from steelmaking dust according to claim 6, wherein the steelmaking dust contains 4% or more of fluorine. 8. The steelmaking dust according to claim 6, wherein 0.7 to 1.3 parts by weight of sulfuric acid is kneaded with 1 part by weight of the steelmaking dust in the sulfating and roasting step. Valuable metal recovery method.