Patent Publication Number: US-2010111787-A1

Title: Method of recovering valuable metals from the vrds spent catalyst

Description:
TECHNICAL FIELD 
     This invention relates to a method of recovering metals, such as vanadium, molybdenum, nickel (hereafter, referred to as “valuable matals”), from the catalysts spent in the ‘Vacuum Residue Desulfurization’ (VRDS) process for desulfurization of pertroleum. 
     BACKGROUND ART 
     There is known a conventional method for recovering the valuable metals from the spent catalysts in the VRDS. 
     The conventonal method comprises removing the soaked oil from the spent catalysts by heating the catalysts over the boiling point of oil and thus evaporating the soaked oil from the catalysts. The spent catalysts are roeated at 400˜600° C. in the furnace with air (oxyzen) supplied to oxidize sulfur and metals in the catalysts. In the roasting process, the sulfur is oxidized into SO 2,  and further the metals, such as molybdenum, vanadium, nickel and cobalt are oxidized into MoO 3 , V 2 O 5 , NiO, and CoO, respectively. The SO 2  is induced into an absober (cap-type tower), and then absorbed in water solution of sodium hydoxide to be converted into solution of sodium sulfite (Na 2 SO3). The solution of sodium sulfite is dained out from the absorber. 
     In recovery of nickel and cobalt, the oxides of nickel and cobalt are milled, and then nickel and cobalt are extracted from the miled oxides of the metals in ammonia solution. As the extracted nickel and cobalt contains water soaked therein during the previous extraction process, an additional process of drying the soaked nickel and cobalt is required. This makes the whole processes for recovery of metals complex. Further, ammonium salts of nickel and cobalt are formed in the extraction process and thus make separation of the metals incomplete. Because of the above-mentioned disadvantages, a process for roasting proceeds without recovering nickel and cobalt. 
     The conventional process comprises inducing the oxidized waste catalysts with sodium carbonate (Na 2 CO 3 ) continuously and quantitatively into a rotary kiln, and maintaining the rotary kiln at a temperature of 600° C. to melt the oxides of the metals with the sodium carbonate therein. In this process, aluminium may be obtained in a form of mixture such as water-insoluble sodium aluminate. Vanadium and molybdenum are obtained in the form of their sodium salts, such as water-soluble sodium vanadate (NaVO 3 ) and sodium molybdate (Na 2 MoO 4 ). 
     The conventional process further comprises milling the roasted product obtained in the preceeding process, agitating the milled roasted-product in the warm water at a temperature of 80° C. and then leaching the formed sodium salts for one hours, washing the leachates at one or twice, controlling the washing liquid at pH 8.0, and agitating the washing liquids with ammonium chloride (NH 4 cl) mixed therein to precipitate crystals of amonium metavanadate (NH 4 VO 3 ). 
     In this process, the volume of ammonium chloride is used more than thioretical volume. Further, after separaing the precipiates from the mother solution, pH of the mother solution is lowered at the range of pH 2˜3. And then, solution of ammonium chloride is added to the mother solution lowered at pH 2-3 so as to remove sufate ion (SO 4   −2 ) therein, and thus calcium sulfate (CaSO 4)  is precipitated. After removing the precipitates of calcium sulfate and then increasing pH of the mother solution, solution of calcium chloride is added to the mother solution so as to precipiate calcium molybdate (CaMoO 4 ). molybdenum oxides can be obtained by leaching and washing the precipiated calcium molybdate, and then decompounding the precipiated calcium molybdate with hydrochloric acid. 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     The conventional method has disadvantages as followings. The method requires expensive equipments, such as a rotary Kiln, for roasting at a high temperature (900° C.). Because costs is very high, a recovery of nickel wolud not be performed. Though the waste catalysts contain aluminum oxide therein at a rate of 65 percentage, the aluminum oxide is discarded in a form of water-insoluble aluminum compound, thereby resulting in waste of resources. 
     Technical Solution 
     It is an object of the present invention to provide methods of recovering valuable matals from the waste catalysts used in the VRDS, which can increase high yield of vanadium and molybdenum from the waste catalyst at lower temperature and further recover aluminum as well as nickel and coblat without additional processes. 
     It is further object of the present invention to provide methods of recovering valuable matals from the waste catalysts without discharging waste water containing ammonia nitrogen, thereby reducing costs for purifying waster water. 
     In order to solve the above disadvantages, the present invention comprises pre-treating the waste catalysts for deoiling and desulfurization; forming sodium aluminate, sodium vanadate and sodium molybdate as water-soluble reactants, and nickel oxide, cobalt oxide as water-insoluble reactants by reacting the pre-treated waste crystals in solution of sodium hydroxide at a temperature of 135˜160° C.; and leaching the water-inslouble nickel oxide, cobalt oxide and impurities, thereby remaining the water-soluble sodium aluminate, sodium vanadate and sodium molybdate in the solution. 
     The present invention further comprises heating the filtrate containing the sodium aluminate, sodium vanadate and sodium molybdate so as to increase a temperature of the filtrate over a temerature of 80° C., and agitating the filtrate with adding hydrochloric acid or sulfhuric acid therein so as to maintain pH 9.5; forming aluminum oxide at the temperture over 110° C. with heat of the reaction; and recovering the aluminum oxide by leaching. 
     Furthermore, the present invention comprises forming a solution containing sodium vanadate and sodium molybdate bt treating the waste catalysts; heating the solution with the solution maintained in pH 1.0˜−1.0; and precipitating molybdenum oxide and vanadium oxide in the solution by aeration thereof. 
     The present invention further comprises adding ammonia water to the solution in which molybdenum oxide and vanadium oxide are precipitated and thus agitating the mixtured solution so as to precipitate amonium metavanadate with ammonium molybdate remaining in the solution; and recovering and separating the crystals of the precipitated amonium metavanadate from the solution. 
     Advantageous Effects 
     The present invention can increase yield of vanadium and molybdenum from the waste catalyst at lower temperature and further recover aluminum as well as nickel and coblat without additional processes. 
     Further, the present invention can recover valuable matals from the waste catalysts without discharging waste water containing ammonia nitrogen, thereby reducing costs for purifying waster water. 
     in addition, the present invention can reduce costs of maunfacturing beecause it does not require expensive equipments, such as a rotary Kiln, for roasting at a high temperature (900° C.). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a flow diagram of the process according to the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The present invention is desribed in detail with reference to the attached drawing. 
     The waste catalysts used in the ‘Vacuum Residue Desulfurization’ (VRDS) process for desulfurization of pertoleum may be pre-treated by the known various methods. That is, the pre-treatments of the waste catalysts, such as oil-removing, sulphur-removing, and oxidization of metals, are accomplished by generally known processes. For example, oils soaked in the waste catalysts are removed by heating the catalysts at a temperature over the boiling point of oil. 
     The deoiled waste catalysts are maintaining at a temperature of 400° C. with heating in the deoiling process. Before cooling, the waste catalysts are induced into the roasting furnace and roasted with the supplied oxygen at a temperature of 400˜600° C. 
     In the roasting process, the metals, such as molybdenum, vanadium, nickel, cobalt, in the waste catalysts are oxidized and thus coverted into their oxides, such as MoO 3 , V 2 O 3 , NiO, CoO, and also the sulphur is oxidized and converted into sulphuric acid gas (SO 2 ). 
     The sulphuric acid gas is absorbed in solution of sodium hydroxide (NaOH) and converted into sodium sulfite (Na 2 SO 3 ), which is drained out. 
     The waste catalysts are dissolved in solution of sodium hydroxide and then the solution is agitated. the non-reactants including NiO, Fe2O3 are leached and thus separated from the solution. 
     Preferably, 80 PBW (Parts By Weight) of and 80 PBW of sodium hydroxide are poured and then mixed in a reactor equipped with an agitator. In this process, the sodium hydroxide is dissolved with heat of dissolution. The solution is heated pressurelessly until the temperature of the solution reached at 135˜160° C. by adding 100 80 PBW of the oxidized waste catalysts therein. 
     To react the waste catalysts in the solution at 160° C. for 2˜3 hours, NiO, FeO and CoO would not be dissolved and thus remain in the solution. 400 PBW of water is added so as to prevent reprecipitation of reactants by dilution of the solution. Then, the residues including NiO are leached from the solution. Nickel can be simply recovered from the residues. 
     Then, aluminum is recovered from the filtrate. The filtrate contains sodium aluminate (NaAl(OH) 4 ). To separate the sodium aluminate from the filtrate, the filtrate is stirred with an agitator and heated at a temperature of 85˜90° C. and then sulphuric acid or hydrochloric acid (20˜30%) is added into the filtrate. The addition of the acid to the solution should be controlled to be maintained at pH 9.5. In this process, aluminum oxide (Al 2 O 3 ) is poducted and thus leached from the solution. The aluminum oxide is washed with water until vanadium is not detected in the water. The water in the aluminum oxide is dried with suction of a vacuum pump. 
     The above processes for recovering aluminum may be applied to the recovery of vanadium in the same manner. In the process of recovering vanadium, aluminum oxide is replaced with sodium aluminate and sodium tungstate exist in a form of water solution. 
     In the reaction of filtrate with HCl solution, the reaction temperature and the basicity or acidity are very critical. 
     The beolw reaction formulars show various products of aluminum oxide according to gradients of temperature at pH 9.5˜14. 
       NaAl(OH) 4 +HCl=Al(OH) 3 +NaCl+H2O (0° C.˜normal temperature)  {circle around (1)} 
       NaAl(OH) 4 +HCl=AlO(OH)+NaCl+2H2O (80° C.˜95° C.)  {circle around (2)} 
       2NaAl(OH) 4 +2HCl=Al 2 O 3 +2NaCl+5H2O (100° C.˜120° C.)  {circle around (3)} 
     In the reaction {circle around (1)}, the reactant, Al(OH) 3  can not be separted by leaching. Accordingly, a rotary kiln should be required for recovery of aluminum in the condition of the reaction {circle around (1)}. 
     In the reaction {circle around (3)}, the reactant, AlO(OH) by the reaction {circle around (2)} may remain but may also be leached. Therefore, the condition of reaction temperatures in the reaction {circle around (3)} is accepatable. When the reaction proceeds at a temperature over 80° C., the temperature get increased over 110° C. by the heat of reaction. 
     Accordingly, the above process of recovering aluminum is required to be proceeded at a temperature over 110° C. because the reactant, Al(OH) 3  is not produced at the temperature. The temperature of the reaction is not liminted by the upper limit but preferably maintained at a temperature of 100° C. 
     As the filtrate is maintained at 120° C. by applying pressure, solution of HCl is added to the filtrate of pH 9˜14. Then, sole Al 2 O 3  may be obtained by removing sodium oxide (Na 2 O) from the filtrate. There remain sodium vanadate (NaVO 3 ) and sodium molybdate (Na 2 MoO 4 ) in the filtrate from which Al2O3 is removed. Preferably, the filtrate is agitated below pH 1 (pH −1.0) at 85° C. until the reaction is completed. 
     As shown in the following reaction formulas I and II, the filtrate is agitated below pH 1 at 85˜100° C. and further aetated therein continuously or periodically. As a result of the process, mixtures of molybdenum oxide and vanadium oxide are precipitated in the solution. The precipitated molybdenum oxide and vanadium oxide may be obtained by leaching. 
     
       
         
         
             
             
         
       
     
     While the filtration is aerated by blowing air, reaction of hydration occurs and thus the metal oxides are precipitated in the solution of reaction. The aeration allows hydration to accur at a lower temperature, thereby allowing additonal heating to be eliminated. In this reaction, molybdenum oxide and vanadium oxide are precipitated as amorphous crystal and thus may be obtained by leaching and washing. 
     In the above process, acid solution should be used to maintain the solution below pH 2, preferably below pH 1 at a temperature of 80° C. This temperature of reaction is dominantly lower than that of the conventional procsess, which makes heating equipments of high price to be useless. 
     The present invention may further comprise adding ammonia water to the solution in which molybdenum oxide (MoO 3 ) and vanadium oxide (V 2 O 5 ) are precipitated, agitating the mixtured solution and thus precipitating amonium metavanadate (NH 4 VO 3 ) and ammonium molybdate ((NH 4 )2MoO4) by using diiference of solubilty thereof; and recovering and separating the crystals of the precipitated amonium metavanadate and ammonium molybdate from the solution. 
     After sepating ammonium molybdate from the mother solution, molybdenum oxide (MoO) and vanadium oxide (V 2 O 5 ) are furhter added to the mother solution with amonium water. Thus, molybdenum oxide (MoO 3 ) and vanadium oxide (V 2 O 5 ) are dissolved in the mother solution by re-heating, and then amonium metavanadate is obtained by cooling the mother solution. These processes are repeated until the specific weight of the mother solution reaches to 2.5. 
     Through the processes, ammonium molybdate and amonium metavanadate of high purity are obtained by minimizing dissoved amonium metavanadate. 
     After the process, the specific weight of mother solution may vary as quantity of water or molybdenum in the waste catalyst. When the specific weight is below 2.5, the mother solution may be reused as reaction solution. When the specific weight is over 2.5, the mother solution becomes ammonium molybdate with 0.0% vanadium by cooling and then removing amonium metavanadate therefrom. 
     Molybdenum oxide and/or vanadium oxide may be obtained by pyrolizing at least one of the amonium metavanadate and ammonium molybdate. Amonia gas generated in the process is converted into amonia water and then reused as a form of amonia water in the process. 
     INDUSTRIAL APPLICABILITY 
     The present invention can increase yield of vanadium and molybdenum from the waste catalyst at lower temperature and further recover aluminum as well as nickel and coblat without additional processes. 
     Further, the present invention can reduce costs of manunfacturing beecause it does not require expensive equipments, such as a rotary Kiln, for roasting at a high temperature (900° C.). 
     Additionally, the present invention can recover valuable matals from the waste catalysts without discharging waste water containing ammonia nitrogen, thereby reducing costs for purifying waster water.