Method for recycling metals from carbon-containing waste molybdenum catalysts

METHOD FOR RECYCLING METALS FROM CARBON-CONTAINING WASTE MOLYBDENUM CATALYSTS

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates to a method for recycling metals and, more particularly, to a method for recycling metals from carbon-containing waste molybdenum catalysts.

2. Description of the Related Art

[0002] With the vigorous development of the petrochemistry industry, catalysts used for hydrodesulfurization (HDS) have been used in large quantities. With carbon as the vehicle, the catalysts absorb elements such as iron (Fe) and phosphorus (P), forming inactivated waste molybdenum catalysts.

[0003] Valuable metals such as vanadium (V) and molybdenum (Mo) are still present in the waste molybdenum catalysts; and therefore, by recovering the valuable metals from the waste molybdenum catalysts, the economic benefits of the waste molybdenum catalysts can be exerted. As an example, in the conventional method for recycling metals form waste molybdenum catalysts, the waste molybdenum catalysts are mixed with a base, followed by a roasting reaction. A filtrate is obtained after decantating

544 907 the roasted product. Finally, hydrochloric acid (HC1) is used to form molybdenum oxide (MoOs) from sodium molybdate (Na2MoO4) in the filtrate. That is, molybdenum in the form of molybdenum oxide can be recovered.

[0004] However, the roasting reaction should be carried out at a high temperature above 850°C. Especially when carbon is present in the waste molybdenum catalyst, the temperature of the roasting reaction bursts instantly and is difficult to control. Hence, there is a need of providing a method for recycling metals from carbon-containing waste molybdenum catalysts.

SUMMARY OF THE INVENTION

[0005] It is therefore the objective of the present invention to provide a method for recycling metals from carbon-containing waste molybdenum catalysts, in which the roasting reaction can be omitted.

[0006] One embodiment of the invention discloses the method for recycling metals from carbon-containing waste molybdenum catalysts. The method for recycling metals from carbon-containing waste molybdenum catalysts includes providing a carbon-containing waste molybdenum catalysts with molybdenum (Mo), vanadium (V), nickel (Ni), carbon (C) and sulfur (S). The carbon-containing waste molybdenum catalysts is

544 907 mixed with an alkaline solution in a volume ratio ranging from 1: 2 to 1: 4, followed by an alkali leaching reaction at a temperature ranging from 100° C to 400 °C and a pressure ranging from 3 kg/cm² to 15 kg/cm²for a time period ranging from 1 hour to 5 hours, obtaining an alkali leaching solution being an aqueous solution of sodium hydroxide (NaOH). The alkali leaching solution is filtered to obtain a carbon/nickel concentrate and a filtrate including sodium molybdate (Na2MoO4), sodium metavanadate (NaVOs) and sodium sulfide (Na2SO4). Finally, molybdenum oxide (MoOs) formed from sodium molybdate by hydrochloric acid (HC1), vanadium pentoxide (V2O5) formed from sodium metavanadate by sulfuric acid (H2SO4), and sodium sulfide are recovered from the filtrate.

[0007] Accordingly, in the method for recycling metals from carbon-containing waste molybdenum catalysts according to the present invention, the high-pressure alkali leaching reaction can replace the high temperature roasting reaction of the conventional method for recycling metals from waste molybdenum catalysts. Therefore, the reaction temperature can be lowered, preventing carbon in the carbon-containing waste molybdenum catalysts from bursting instantly due to the high temperature roasting reaction. That is, it is believed that the method for recycling metals from carbon-containing waste molybdenum catalysts

544 907 according to the present invention is significantly frugal of energy and cost, but highly security. Moreover, sulfur in the carbon-containing waste molybdenum catalysts can be recover in the form of sodium sulfate. Therefore, air pollution resulting from the effusion of sulfur oxide (SO_X) or hydrogen sulfur (H2S) can be effectively avoided.

[0008] In a preferred form shown, the alkaline solution can be an aqueous solution formed by dissolving a strong base in water. Thereby, the strong base would be sodium hydroxide (NaOH), and the alkaline solution can be the aqueous solution with a concentration ranging from 3% to 15%. As such, few amount of the alkaline solution is needed to react with molybdenum disulfide, as well as vanadium pentoxidethe, in the carbon-containing waste molybdenum catalysts, decreasing the volume of the alkaline reaction.

[0009] The carbon-containing waste molybdenum catalysts is mixed with the alkaline solution in the volume ratio ranging from 1: 2 to 1: 4. As such, the recovery rates of molybdenum and vanadium can achieve more than 99%, while the recovery rate of sulfur can achieve more than 95%.

[0010] In a preferred form shown, the alkali leaching reaction can be carried out at the temperature ranging from 150°C to 300°C. As such, the recovery rates of molybdenum and vanadium can achieve more than 99%,

544 907 while the recovery rate of sulfur can achieve more than 95%.

[0011] In a preferred form shown, the alkali leaching reaction can be carried out at the pressure ranging from 10 kg/cm² to 15 kg/cm². As such, the recovery rates of molybdenum and vanadium can achieve more than 99%, while the recovery rate of sulfur can achieve more than 95%.

[0012] In a preferred form shown, the alkali leaching reaction can be carried out for the time period ranging from 2 hours to 4 hours. As such, the recovery rates of molybdenum and vanadium can achieve more than 99%, while the recovery rate of sulfur can achieve more than 95%.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention will become more fully understood from the detailed description given hereinafter and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

[0014] FIG. 1 depicts a flow chart representing the method for recycling metals from carbon-containing waste molybdenum catalysts according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0015] The term “carbon-containing waste molybdenum catalysts” recites according to the present invention, besides carbon (C) and

544 907 molybdenum (Mo), can also include valuable metals such as vanadium (V) and nickel (Ni). As an example, the carbon-containing waste molybdenum catalysts can include, but not limited to, 10-20 wt% of molybdenum (Mo), 1-5 wt% of vanadium (V), 1-3 wt% of nickel (Ni), 50-60 wt% of carbon (C) and 10-20 wt% of sulfur (S), while the rest is impurities, which can be appreciated by a person having ordinary skill in the art.

[0016] Referring of FIG. 1, a method for recycling metals from carbon-containing waste molybdenum catalysts according to an embodiment of the present invention can include a step of mixing SI, a step of leaching S2 and a step of recovering S3.

[0017] Specifically, in the step of mixing SI, the carbon-containing waste molybdenum catalysts can be mixed with an alkaline solution to form a mixture. The alkaline solution can be an aqueous solution formed by dissolving a strong base in water. The strong base is sodium hydroxide (NaOH),. Moreover, the strong base can form the aqueous solution with a concentration ranging from 3% to 15%. That is, the strong base ranging from 3 to 15 grams (g) is dissolved to water of 100 milliliter (mL) to form the alkaline solution.

[0018] The carbon-containing waste molybdenum catalysts and the alkaline solution are mixed in a volume ratio ranging from 1: 2 to 1: 4 to

544 907 from the mixture.

[0019] In the step of leaching S2, the mixture can be placed in an autoclave, and an alkali leaching reaction can be carried out at a relatively low temperature and a relatively high pressure, forming an alkali leaching solution. At this time, molybdenum, which is usually present in the form of molybdenum disulfide (M0S2), in the carbon-containing waste molybdenum catalysts can form sodium molybdate (Na2MoO4) according to chemical equation (1), while vanadium, which is usually present in the form of vanadium pentoxide (V2O5), in the carbon-containing waste molybdenum catalysts can form sodium metavanadate (NaVOs) according to chemical equation (2). Moreover, both sodium molybdate and vanadium pentoxide are dissolved in the alkaline solution.

M0S2 + 6NaOH+4.5O2^Na₂MoO4+2Na2SO₄+3H₂O EQUATION (1)

V2O5 + 2NaOH^2NaVO₃ + H₂O EQUATION (2)

[0020] In this embodiment, the alkali leaching reaction is carried out at a temperature ranging from 100°C to 400°C and a pressure ranging from 3 kg/cm²to 15 kg/cm² for a time period ranging from 1 hour to 5 hours, obtaining the alkali leaching solution. Preferably, the alkali leaching reaction is carried out at the temperature ranging from 150°C to 400°C and

544 907 the pressure ranging from 10 kg/cm² to 15 kg/cm² for the time period ranging from 2 hours to 4 hours.

[0021] The step of recovering S3 includes a substep of Ni recovering S31. In the substep of Ni recovering S31, the alkali leaching solution can be filtrated using a 100-mesh filter. Thus, a carbon/nickel concentrate separated from a filtrate can form a carbon bar by subsequent processing process and can be used for fuel.

[0022] The filtrate can include molybdenum in the form of sodium molybdate, as well as sulfur in the form of sodium sulfate (Na2SO4). Moreover, in the case that the carbon-containing waste molybdenum catalysts include vanadium, the filtrate can also include vanadium in the form of sodium metavanadate.

[0023] Therefore, the step of recovering S3 also includes a substep of V recovering S32, a substep of Mo recovering S33 and substep of S recovering S34. In the substep of V recovering S32, sodium molybdate forms molybdenum oxide (MoOs) by the use of hydrochloric acid (HC1) in an acidic environment according to chemical equation (3). In the substep of Mo recovering S33, sodium metavanadate forms vanadium pentoxide (V2O5) by the use of sulfuric acid (H2SO4) in an acidic environment according to chemical equation (4). Finally, in the substep of S recovering

544 907

S34, sodium sulfate is supersaturated to participate in the form of sodium sulfate.

Na₂MoO₄ + HC1^MoO₃+NaCl + H₂O EQUATION (3)

2NaVO₃ + H₂SO₄^Na₂SO₄+V₂O₅ + H₂O EQUATION (4)

[0024] To evaluate the valuable metals of molybdenum, vanadium and nickel, as well as carbon and sulfur, can be effectively recovered according to the method for recycling metals from carbon-containing waste molybdenum catalysts, the following trials are carried out using the carbon-containing waste molybdenum catalysts with 15 wt% of molybdenum, 3.5 wt% of vanadium, 1.1 wt% of nickel, 50.1 wt% of carbon and 10 wt% of sulfur, while the rest being impurities.

[0025] Trial (A).

[0026] In trial (A), 1000 grams (g) of the carbon-containing waste molybdenum catalysts is mixed with the alkaline solution according to the volume ratio shown in TABLE 1. The alkali leaching reaction is then carried out at the temperature of 150°C and the pressure of 10 kg/cm² for the time period of 2 hours. Finally, recovery rates of molybdenum, vanadium, nickel, carbon and sulfur in the alkali leaching solution are measured.

TABLE 1

544 907

<td rowspan="2"> Group</td><td rowspan="2"> Volume Ratio</td><td colspan="5"> Recovery Yield (grams) [Recovery Rate (%)]</td>

<td> molybdenum</td><td> vanadium</td><td> nickel</td><td> carbon</td><td> sulfur</td>

<td> Al</td><td> 1: 1</td><td> 145.5 [97.0%]</td><td> 33.3 [95.1%]</td><td> 10.7 [97.3%]</td><td> 498.1 [99.4%]</td><td> 95.4 [95.4%]</td>

<td> A2</td><td> 1: 2</td><td> 148.5 [99.0%]</td><td> 34.7 [99.1%]</td><td> 10.8 [98.2%]</td><td> 498.5 [99.5%]</td><td> 95.8 [95.8%]</td>

<td> A3</td><td> 1: 3</td><td> 148.0 [98.7%]</td><td> 34.7 [99.1%]</td><td> 10.8 [98.2%]</td><td> 498.9 [99.6%]</td><td> 96.6 [96.6%]</td>

<td> A4</td><td> 1: 4</td><td> 149.1 [99.4%]</td><td> 34.8 [99.4%]</td><td> 10.4 [94.5%]</td><td> 498.8 [99.6%]</td><td> 97.1 [97.1%]</td>

[0027] Referring to TABLE 1, in the case that the volume ratio higher than 1: 2, the recovery rates of molybdenum and vanadium can achieve more than 99%. The recovery rate of sulfur can achieve more than 95%.

[0028] Trial (B).

[0029] In trial (B), 1000 grams (g) of the carbon-containing waste molybdenum catalysts is mixed with the alkaline solution according to the volume ratio of 1: 2. The alkali leaching reaction is then carried out at the temperature shown in TABLE 2 and the pressure of 10 kg/cm² for the time period of 2 hours. Finally, recovery rates of molybdenum, vanadium, nickel, 10 carbon and sulfur in the alkali leaching solution are measured.

544 907

TABLE 2

<td rowspan="2"> Group</td><td rowspan="2"> Temperature (°C)</td><td colspan="5"> Recovery Yield (grams) [Recovery Rate (%)]</td>

<td> molybdenum</td><td> vanadium</td><td> nickel</td><td> carbon</td><td> sulfur</td>

<td> Bl</td><td> 100</td><td> 146.5 [97.3%]</td><td> 32.8 [93.7%]</td><td> 10.5 [95.5%]</td><td> 499.1 [99.6%]</td><td> 93.4 [93.4%]</td>

<td> B2</td><td> 150</td><td> 148.5 [99.0%]</td><td> 34.7 [99.1%]</td><td> 10.8 [98.2%]</td><td> 498.5 [99.5%]</td><td> 95.8 [95.8%]</td>

<td> B3</td><td> 200</td><td> 149.1 [99.4%]</td><td> 34.7 [99.1%]</td><td> 10.6 [96.4%]</td><td> 498.3 [99.5%]</td><td> 96.9 [96.9%]</td>

<td> B4</td><td> 300</td><td> 149.2 [99.5%]</td><td> 34.8 [99.4%]</td><td> 10.7 [97.3%]</td><td> 498.6 [99.5%]</td><td> 98.1 [98.1%]</td>

[0030] Referring to TABLE 2, in the case that the temperature higher than 150°C, the recovery rates of molybdenum and vanadium can achieve more than 99%. The recovery rate of sulfur can achieve more than 95%.

[0031] Trial (C).

[0032] In trial (C), 1000 grams (g) of the carbon-containing waste molybdenum catalysts is mixed with the alkaline solution according to the volume ratio of 1: 2. The alkali leaching reaction is then carried out at the temperature of 150°C and the pressure shown in TABLE 3 for the time period of 2 hours. Finally, recovery rates of molybdenum, vanadium, nickel,

544 907 carbon and sulfur in the alkali leaching solution are measured.

TABLE 3

<td rowspan="2"> Group</td><td rowspan="2"> Pressure (kg/cm²)</td><td colspan="5"> Recovery Yield (grams) [Recovery Rate (%)]</td>

<td> molybdenum</td><td> vanadium</td><td> nickel</td><td> carbon</td><td> sulfur</td>

<td> Cl</td><td> 3</td><td> 145.5 [97.0%]</td><td> 33.8 [96.6%]</td><td> 10.6 [96.4%]</td><td> 498.9 [99.6%]</td><td> 94.4 [94.4%]</td>

<td> C2</td><td> 10</td><td> 148.5 [99.0%]</td><td> 34.7 [99.1%]</td><td> 10.8 [98.2%]</td><td> 498.5 [99.5%]</td><td> 95.8 [95.8%]</td>

<td> C3</td><td> 13</td><td> 148.9 [99.3%]</td><td> 34.9 [99.7%]</td><td> 10.7 [97.3%]</td><td> 499.3 [99.7%]</td><td> 95.9 [95.9%]</td>

<td> C4</td><td> 15</td><td> 148.7 [99.1%]</td><td> 34.8 [99.4%]</td><td> 10.7 [97.3%]</td><td> 498.9 [99.6%]</td><td> 96.1 [96.1%]</td>

[0033] Referring to TABLE 3, in the case that the pressure higher than 10 kg/cm², the recovery rates of molybdenum and vanadium can achieve more than 99%. The recovery rate of sulfur can achieve more than 95%.

[0034] Trial (D).

[0035] In trial (D), 1000 grams (g) of the carbon-containing waste molybdenum catalysts is mixed with the alkaline solution according to the volume ratio of 1: 2. The alkali leaching reaction is then carried out at the

544 907 temperature of 150°C and the pressure of 10 kg/cm² for the time period shown in TABLE 4. Finally, recovery rates of molybdenum, vanadium, nickel, carbon and sulfur in the alkali leaching solution are measured.

TABLE 4

<td rowspan="2"> Group</td><td rowspan="2"> Time Period (hours)</td><td colspan="5"> Recovery Yield (grams) [Recovery Rate (%)]</td>

<td> molybdenum</td><td> vanadium</td><td> nickel</td><td> carbon</td><td> sulfur</td>

<td> DI</td><td> 1</td><td> 145.5 [97.0%]</td><td> 32.9 [94.0%]</td><td> 10.7 [97.3%]</td><td> 498.9 [99.6%]</td><td> 92.4 [92.4%]</td>

<td> D2</td><td> 2</td><td> 148.5 [99.0%]</td><td> 34.7 [99.1%]</td><td> 10.8 [98.2%]</td><td> 498.5 [99.5%]</td><td> 95.8 [95.8%]</td>

<td> D3</td><td> 3</td><td> 149.4 [99.6%]</td><td> 34.8 [99.4%]</td><td> 10.7 [97.3%]</td><td> 499.3 [99.7%]</td><td> 95.8 [95.8%]</td>

<td> D4</td><td> 4</td><td> 149.7 [99.8%]</td><td> 34.8 [99.4%]</td><td> 10.8 [98.2%]</td><td> 498.9 [99.6%]</td><td> 96.5 [96.5%]</td>

[0036] Referring to TABLE 4, in the case that the time period more than 2 hours, the recovery rates of molybdenum and vanadium can achieve more than 99%. The recovery rate of sulfur can achieve more than 95%.

[0037] Accordingly, in the method for recycling metals from carbon-containing waste molybdenum catalysts according to the present invention, the high-pressure alkali leaching reaction can replace the high

544 907 temperature roasting reaction of the conventional method for recycling metals from waste molybdenum catalysts. Therefore, the reaction temperature can be lowered, preventing carbon in the carbon-containing waste molybdenum catalysts from bursting instantly due to the high temperature roasting reaction. That is, it is believed that the method for recycling metals from carbon-containing waste molybdenum catalysts according to the present invention is significantly frugal of energy and cost, but highly security.

[0038] Moreover, sulfur in the carbon-containing waste molybdenum catalysts can be recover in the form of sodium sulfate. Therefore, air pollution resulting from the effusion of sulfur oxide (SO_X) or hydrogen sulfur (H2S) can be effectively avoided.

[0039] In addition, carbon in the carbon-containing waste molybdenum catalysts can be effectively recovered (with the recovery rate achieving more than 99%). The recovered carbon/nickel concentrate can form the carbon bar by subsequent processing process and can be used for fuel.

[0040] Although the invention has been described in detail with reference to its presently preferable embodiment, it will be understood by one of ordinary skill in the art that various modifications can be made

544 907 without departing from the spirit and the scope of the invention, as set forth in the appended claims.