Al-mans 2002 - Recovery Of Nickel Oxide From Spent Catalyst
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Waste Management 22 (2002) 85–90 www.elsevier.nl/locate/wasman
Recovery of nickel oxide from spent catalyst N.M. Al-Mansi*, N.M. Abdel Monem Chemical Engineering Department, Faculty of Engineering, Cairo University, Giza, Cairo, Egypt Received 2 May 2000; received in revised form 10 January 2001; accepted 20 March 2001
Abstract This study investigates the possibility of recovering nickel from the spent catalyst (NiO/Al2O3) resulting from the steam reforming process to produce water gas (H2/H2O) in many industries. In the extraction process, nickel is recovered as sulfate using sulfuric acid as a solvent. The considered parameters affecting nickel recovery were acid concentration, temperature and time of digestion solid:liquid ratio, particle size and stirring rate. Nickel was to be directly recovered as a sulfate salt by direct crystallization method. The conversion was 99% at 50% sulfuric acid concentration, solid: liquid ratio (1:12) by weight, particle size less than 500 micron for more than 5 h and 800 rpm at 100 C. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Spent catalyst; Nickel oxide; Nickel recovery; Leaching
1. Introduction For many years, nickel has been considered as the most suitable metal in steam reforming of hydrocarbons. Nickel is cheap, sufficiently active, and allows suitable catalysts to be economically produced. Invascanu and Roman [1] studied the recovery of nickel from a spent catalyst in an ammonia plant by leaching it in sulfuric acid solution. Ninety-nine percent of the nickel was recovered as nickel sulfate when the catalyst, having a particle size of 0.09 mm, was dissolved in an 80% sulfuric acid solution for 50 min in at 70 C. In another study, Loboiko et al. [2] found that the recovery of nickel is increased by dissolution with 60–70% nitric acid concentration at 120 C for 2–3 h. By leaching the spent catalyst with hydrochloric acid, Chandhary et al. [3] found the recovery of nickel from a low grade spent catalyst to be 17.7%. Vicol et al. [4] tried to recover nickel by extraction of the spent catalyst with an aqueous solution of 15–23% ammonia at 60–90oC and at pH 7.5–9. Optimum leaching conditions of nickel from Al2O3 support using (NH4)2CO3 were achieved by Floarea et al. [5] for 600 mm particle size at 80 C. Further, a high temperature metal recovery process was developed by INMET CO to recycle nickel, chromium and iron catalysts. This technology includes four basic
* Corresponding author.
steps: feed preparation, reduction, smelting and casting. For the past 16 years, the INMET CO process has been the only thermal recovery technology for metals [6]. The acceptance of a waste to be processed depends on both the total chemical analysis carrier out by INMET CO’s laboratory and on the information supplied by the generator. The extraction of rare metals from the hydrodesulfurization catalyst by leaching with sulfuric acid yields an acidic solution rich in rare metals such as molybdenum, vanadium, cobalt and nickel in addition to aluminum [7]. Mixtures of LIX63 (5,8-diethyl-7 hydroxy-6-dodecanone oxime) and CYANEX272 (containing bis (2,4,4-tri-methylpentyl) phosphinic acid as the active components or PIA-8 (containing the active component bis(2-ethylhexyl)phosphinic acid) were considered to be the most suitable for separating and recovering cobalt and nickel from sulfuric acid solutions in the presence of an appreciable amount of aluminum at a low pH value. Although different acids have been previously used for leaching nickel from spent catalyst, sulfuric acid has been selected as the cheapest and the most effective. Also, applying sulfuric acid in the extraction process allows aluminum to be readily recovered as a sulfate salt by direct crystallization from the raffinate. The aim of this work is to recover nickel from the spent nickel catalyst based alumina (NiO/ Al2O3) used in the steam reforming industry. The spent catalyst on being dumped would cause severe pollution and thus using this method helps in preventing the
0956-053X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0956-053X(01)00024-1
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accumulation of nickel which is considered a major source of contamination. The study is mainly based on leaching nickel oxide from the spent catalyst to produce nickel sulfates and alumina, which is considered as an inert. Different experiments were done to show the effect of various factors affecting the optimum conditions. The parameters considered were: acid concentration, time and temperature of digestion, solid:liquid ratio, crushed spent catalyst, particle size and stirring velocity.
The rate of the side reaction is very weak because alpha alumina is completely inert towards acids [8] because it was previously produced by calcination of Al(OH)3 above 1000 C which gives it great stability towards acids. Alpha alumina is used in the refractory industry for making crucibles, bricks and spark plugs. The cost of alpha alumina in Egypt is estimated to be L.E. 6770 per ton according to the Academy of Scientific Research and Technology.
3. Materials 2. Theoretical background The reaction of nickel oxide with sulfuric acid is a heterogeneous reaction. In a heterogeneous reaction system the overall rate expression becomes complicated because of the interaction between physical and chemical processes. The reactants in one phase have to be converted to another phase in which the reaction takes place. The mechanism of the uncatalyzed heterogeneous reaction may take place as follows. Initially, the reactants diffuse from the bulk of the first phase to the interface between the phases. If an additional layer of solid product and inert material is present at the interface the reactants would have to overcome the resistance of this layer before reaching the surface of the second phase. Then, diffusion of reactants from the interface to the bulk of the second phase takes place. Further, chemical reactions between the reactants in phase one and those in phase two occur. Finally, the products diffuse within the second phase and/or out of phase two into the bulk of phase one. The reactions involve: (1) Main reaction: NiO þ H2 SO4 ! NiSO4 þ H2 O Where NiO is the limiting reactant. The nickel sulfate crystals are used in electroplating and in the ceramic industries. According to Sedasa Misr Company for Chemicals, nickel sulfate has a cost of L.E. 8000 per ton. (2) Side reaction: Alpha-Al2 O3 þ 3H2 SO4 ! Al2 ðSO4 Þ3 þ3H2 O
The specifications of the sample collected from AbuQuir Fertilizer Company [9] are shown in Table 1.The price of the spent catalyst was determined according to the amount of nickel. However, its price (in our case) is around one $ per kg. Sulfuric acid of commercial grade was chosen as a solvent for treating metal oxides to convert them into metal sulfates. Using sulfuric acid has the following advantages: 1. nickel sulfate is commercially the most important nickel compound due to its various uses especially in electroplating; 2. sulfuric acid is a cheap solvent compared to other acids. The price of the commercial acid (98% by weight) is L.E. 600 per ton from Abuzabal Company. Fig. 1 shows the sequence of the applied process.
Table 1 Specifications of the sample collected from Abu-Quir Fertilizer Company Company
Abu-Quir
Process used in
Primary steam Secondary steam Methanator reformer reformer
30 Volume m3/unit Bulk density kg/l 1.1 Crushing strength kgf 18.1 Nickel oxide% 7.12 Alumina% 92.88
Fig. 1. Flow diagram of the process.
35 1.1 24.8 12.59 87.41
28 1.1 18.6 81.4
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87
Fig. 2. Effect of particle size on percentage conversion.
5.2. Effect of sulfuric acid concentration
Table 2 Factors affecting nickel recovery Acid concentration Digestion temperature Digestion time Solid:liquid Particle size Stirring velocity
(10–98%) by weight (20–120) C (15–60) min (1/12–3/4) by weight (as received–less than 500 micron) (50–1400) rpm
4. Experimental procedure Spent catalyst was crushed and screened to attain the required particle size. In each experiment, 1 g of spent catalyst was added to a certain amount of sulfuric acid having a specified concentration. Temperature, reaction time, solid:liquid ratio, particle size, and stirring velocity were adjusted. The reaction took place in a sealed container and the resulting slurry was filtered on sintered glass. Atomic Absorption Spectroscopy was used to determine the nickel content in the filtrate after a suitable dilution. Table 2 shows the different factors affecting nickel recovery.
Fig. 3 illustrates the effect of varying sulfuric acid concentration from 10 to 90% by weight. The percentage recovery of nickel increased with increasing sulfuric acid concentration up to a certain range and then decreased with further increase in concentration. A maximum of 99% conversion took place at 50% acid concentration. This indicates that the rate of dissolution of low acid concentration was small, then increased, reaching a maximum value at 50% acid concentration; the rate of dissolution then started to decline by increasing the acid concentration. 5.3. Effect of solid:liquid ratio
5. Results and discussion
Experiments were carried out using different waste solid:sulfuric acid ratios with 50% acid concentration and particle size < 500 micron. It was found that using the stoichiometric amounts of solid:liquid gives a low conversion (26.3%) while increasing the acid amount improves the conversion reaching 98% at a solid:liquid ratio (1:12) as shown in Fig. 4. As the amount of acid increases, the conversion increases, but the further separation of sulfates from the excess acid is difficult and is achieved by many ways.
5.1. Effect of particle size
5.4. Effect of temperature
The influence of spent catalyst particle size was studied using the particle size range (as received, >2000, 850 < 2000, < 500 micron). Fig. 2 represents the effect of the particle size of the spent catalyst on the percentage conversion at different sulfuric acid concentrations (10, 20, 35, and 50% by weight), at room temperature without mixing. The data show that as the particle size decreases to < 500 micron, a maximum conversion was obtained at 50% acid concentration.
The effect of temperature on the system was studied by performing experiments at 20, 40, 60, 80, 100 and 120 C. Fig. 5 reveals that the conversion was influenced by the temperature of the reaction. The recovery increases as temperature increases reaching 99% conversion at reaction temperatures of 80–100 C, with acid concentration of 50%. At higher temperatures, the recovery decreases because water evaporates and the solution becomes concentrated. This may be due to the fact that
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Fig. 3. Effect of sulfuric acid concentration on percentage conversion.
Fig. 4. Effect of solid:liquid ratio.
Fig. 5. Effect of temperature on percentage conversion.
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89
Fig. 6. Effect of time of digestion on percentage conversion.
Fig. 7. Effect of stirring velocity on percentage conversion.
Table 3 Cost aspects based one ton of spent catalyst charge Cost of raw materials (L.E.) Average cost of spent catalyst according to nickel content=L.E. 308.8 Cost of sulfuric acid consumed=L.E. 92.32
Price of products (L.E.) Price of nickel sulfate crystals (assuming 100% conversion)=L.E. 3526 Price of alpha alumna produced=L.E. 591
the reaction between nickel atoms and sulfuric acid form a layer of nickel oxide which surrounds the nickel atoms and decreases the amount of nickel recovered. Nickel sulfate solution is heated and the nickel sulfate salt is crystallized as separate single nickel salt crystals (NiSO4.7H2O).
depending on the time of the reaction. For more than 5 h, 99% conversion was achieved.
5.5. Effect of time of digestion Fig. 6 illustrates the significant effect of time on the recovery of nickel. Prolonging the contact time is accompanied by a noticeable increase in the metal removal which means that nickel recovery is a rate process
5.6. Effect of stirring velocity A series of experiments were undertaken to study the influence of agitation on conversion. Different stirring rates ranging between 50 and 1400 rpm have been applied. The experimental results shown in Fig. 7 indicate that the rate of reaction is controlled by the degree of agitation and the conversion increases with increasing the stirring velocity. The optimum stirring rate which gives the maximum percentage removal is
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obtained at 800 rpm. Increasing stirring above that rate has no effect on conversion.
6. Cost aspects The cost items based on a ton of spent catalyst charge can be calculated as shown in Table 3 Douglas [10]: Cost of products/Cost of raw materials =L.E. 10.26, which indicates that the process is profitable, where $=3.9 L.E.(Egyptian pound). Actually, there are several methods to remove excess sulfuric acid from nickel sulfate solution: 1. sulfuric acid can be separated by using membranes [8]; 2. adding calcium hydroxide which reacts with sulfuric acid to form a white precipitate of calcium sulfate at room temperature; 3. adding barium hydroxide solid in stoichiometric amounts to the excess acid react to form barium sulfat; and 4. nickel sulfate solution is evaporated and nickel is crystallized as single nickel salt crystals (NiSO4.7H2O).
7. Conclusions It is possible to utilize spent catalyst (NiO/Al2O3) obtained from the steam reforming plants to produce nickel sulfates by using sulfuric acid. According to environmental considerations it is very useful to reuse the solid waste to produce a salable product such as nickel sulfates which can be used in electroplating. Moreover, the efficient separation of nickel from spent catalyst create a possibility for reusing the alumina
support in the catalyst and thus the solid waste spent catalyst is completely utilized. The operating conditions required to reach 99% conversion were 50% acid concentration, solid: liquid ratio (1:12), less than 500 micron particle size for a contact time higher than 5 h and 800 rpm stirring rate a temperature of 100 C. References [1] Ivascanu St, Roman O. Nickel recovery from spent catalysts. I Solvation process. BulInst Politeh Iasi Sect 2 1975;2(21):47. [2] Loboiko AYa, Atroshchenko VI, Grin GI, Kutovoi VV, Fedorova NP, Volovikov AN, Alekseenko DA, Golodenko NI, Pantaz’ev GI. Recovering nickel from spent catalyst. Otkrytiya, Izobret, PromObraztsy,Tovarnye Zanki 1983;14:33. [3] Chandhary AJ, Donaldson JD, Boddington SC, Grimes SM. Heavy metal in the enviroment. Part II: a hydrochloric acid leaching process process for the recovery of nickel value from a spent calalyst. 1993;34:137. [4] Vicol M, Heves A, Potoroaca M. Recovery of nickel from spent catalysts. Combinatul de Ingrasaminte Chimice, Piatra-Neamt 1986;112:832. [5] Floarea O, Mihai M, Morarus M, Kohn D, Sora M. Filteration. Physical models and operating coditions. Rev Chim (Bucharest) 1991;42:553. [6] Hanewald RH, Onuska JC, Schweers ME. Recycling nickel, chromium and iron catalysts through the high temperature metals recovery process. Third international symposium on recycling of metals and engineered materials. In: Queneau PB, Peterson RD, editors. The Minerals, Metals and Materials Society. 1995. p. 371. [7] Inoue K, Zhang P, Tsuyama H. Separation and recovery of rare metals from spent hydrodesulfurization catalysts.Third international symposium on recycling of metals and engineered materials. In: Queneau PD, Peterson RD. editors. The Minerals, Metals, Metals and Meterials Society. 1995. p. 393. [8] Treybal RE. Mass transfer operations. 3rd ed. USA: McGrawHill, 1980. [9] Aub-Quir for Fertilizers and Chemical Industries Company, ElTabia-RAHID Road, Alex. Egypt, Personal communication. [10] Douglas JM. Conceptual design of chemical processes. USA: McGraw-Hill, 1998.
Recovery of nickel oxide from spent catalyst N.M. Al-Mansi*, N.M. Abdel Monem Chemical Engineering Department, Faculty of Engineering, Cairo University, Giza, Cairo, Egypt Received 2 May 2000; received in revised form 10 January 2001; accepted 20 March 2001
Abstract This study investigates the possibility of recovering nickel from the spent catalyst (NiO/Al2O3) resulting from the steam reforming process to produce water gas (H2/H2O) in many industries. In the extraction process, nickel is recovered as sulfate using sulfuric acid as a solvent. The considered parameters affecting nickel recovery were acid concentration, temperature and time of digestion solid:liquid ratio, particle size and stirring rate. Nickel was to be directly recovered as a sulfate salt by direct crystallization method. The conversion was 99% at 50% sulfuric acid concentration, solid: liquid ratio (1:12) by weight, particle size less than 500 micron for more than 5 h and 800 rpm at 100 C. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Spent catalyst; Nickel oxide; Nickel recovery; Leaching
1. Introduction For many years, nickel has been considered as the most suitable metal in steam reforming of hydrocarbons. Nickel is cheap, sufficiently active, and allows suitable catalysts to be economically produced. Invascanu and Roman [1] studied the recovery of nickel from a spent catalyst in an ammonia plant by leaching it in sulfuric acid solution. Ninety-nine percent of the nickel was recovered as nickel sulfate when the catalyst, having a particle size of 0.09 mm, was dissolved in an 80% sulfuric acid solution for 50 min in at 70 C. In another study, Loboiko et al. [2] found that the recovery of nickel is increased by dissolution with 60–70% nitric acid concentration at 120 C for 2–3 h. By leaching the spent catalyst with hydrochloric acid, Chandhary et al. [3] found the recovery of nickel from a low grade spent catalyst to be 17.7%. Vicol et al. [4] tried to recover nickel by extraction of the spent catalyst with an aqueous solution of 15–23% ammonia at 60–90oC and at pH 7.5–9. Optimum leaching conditions of nickel from Al2O3 support using (NH4)2CO3 were achieved by Floarea et al. [5] for 600 mm particle size at 80 C. Further, a high temperature metal recovery process was developed by INMET CO to recycle nickel, chromium and iron catalysts. This technology includes four basic
* Corresponding author.
steps: feed preparation, reduction, smelting and casting. For the past 16 years, the INMET CO process has been the only thermal recovery technology for metals [6]. The acceptance of a waste to be processed depends on both the total chemical analysis carrier out by INMET CO’s laboratory and on the information supplied by the generator. The extraction of rare metals from the hydrodesulfurization catalyst by leaching with sulfuric acid yields an acidic solution rich in rare metals such as molybdenum, vanadium, cobalt and nickel in addition to aluminum [7]. Mixtures of LIX63 (5,8-diethyl-7 hydroxy-6-dodecanone oxime) and CYANEX272 (containing bis (2,4,4-tri-methylpentyl) phosphinic acid as the active components or PIA-8 (containing the active component bis(2-ethylhexyl)phosphinic acid) were considered to be the most suitable for separating and recovering cobalt and nickel from sulfuric acid solutions in the presence of an appreciable amount of aluminum at a low pH value. Although different acids have been previously used for leaching nickel from spent catalyst, sulfuric acid has been selected as the cheapest and the most effective. Also, applying sulfuric acid in the extraction process allows aluminum to be readily recovered as a sulfate salt by direct crystallization from the raffinate. The aim of this work is to recover nickel from the spent nickel catalyst based alumina (NiO/ Al2O3) used in the steam reforming industry. The spent catalyst on being dumped would cause severe pollution and thus using this method helps in preventing the
0956-053X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0956-053X(01)00024-1
86
N.M. Al-Mansi, N.M. Abdel Monem / Waste Management 22 (2002) 85–90
accumulation of nickel which is considered a major source of contamination. The study is mainly based on leaching nickel oxide from the spent catalyst to produce nickel sulfates and alumina, which is considered as an inert. Different experiments were done to show the effect of various factors affecting the optimum conditions. The parameters considered were: acid concentration, time and temperature of digestion, solid:liquid ratio, crushed spent catalyst, particle size and stirring velocity.
The rate of the side reaction is very weak because alpha alumina is completely inert towards acids [8] because it was previously produced by calcination of Al(OH)3 above 1000 C which gives it great stability towards acids. Alpha alumina is used in the refractory industry for making crucibles, bricks and spark plugs. The cost of alpha alumina in Egypt is estimated to be L.E. 6770 per ton according to the Academy of Scientific Research and Technology.
3. Materials 2. Theoretical background The reaction of nickel oxide with sulfuric acid is a heterogeneous reaction. In a heterogeneous reaction system the overall rate expression becomes complicated because of the interaction between physical and chemical processes. The reactants in one phase have to be converted to another phase in which the reaction takes place. The mechanism of the uncatalyzed heterogeneous reaction may take place as follows. Initially, the reactants diffuse from the bulk of the first phase to the interface between the phases. If an additional layer of solid product and inert material is present at the interface the reactants would have to overcome the resistance of this layer before reaching the surface of the second phase. Then, diffusion of reactants from the interface to the bulk of the second phase takes place. Further, chemical reactions between the reactants in phase one and those in phase two occur. Finally, the products diffuse within the second phase and/or out of phase two into the bulk of phase one. The reactions involve: (1) Main reaction: NiO þ H2 SO4 ! NiSO4 þ H2 O Where NiO is the limiting reactant. The nickel sulfate crystals are used in electroplating and in the ceramic industries. According to Sedasa Misr Company for Chemicals, nickel sulfate has a cost of L.E. 8000 per ton. (2) Side reaction: Alpha-Al2 O3 þ 3H2 SO4 ! Al2 ðSO4 Þ3 þ3H2 O
The specifications of the sample collected from AbuQuir Fertilizer Company [9] are shown in Table 1.The price of the spent catalyst was determined according to the amount of nickel. However, its price (in our case) is around one $ per kg. Sulfuric acid of commercial grade was chosen as a solvent for treating metal oxides to convert them into metal sulfates. Using sulfuric acid has the following advantages: 1. nickel sulfate is commercially the most important nickel compound due to its various uses especially in electroplating; 2. sulfuric acid is a cheap solvent compared to other acids. The price of the commercial acid (98% by weight) is L.E. 600 per ton from Abuzabal Company. Fig. 1 shows the sequence of the applied process.
Table 1 Specifications of the sample collected from Abu-Quir Fertilizer Company Company
Abu-Quir
Process used in
Primary steam Secondary steam Methanator reformer reformer
30 Volume m3/unit Bulk density kg/l 1.1 Crushing strength kgf 18.1 Nickel oxide% 7.12 Alumina% 92.88
Fig. 1. Flow diagram of the process.
35 1.1 24.8 12.59 87.41
28 1.1 18.6 81.4
N.M. Al-Mansi, N.M. Abdel Monem / Waste Management 22 (2002) 85–90
87
Fig. 2. Effect of particle size on percentage conversion.
5.2. Effect of sulfuric acid concentration
Table 2 Factors affecting nickel recovery Acid concentration Digestion temperature Digestion time Solid:liquid Particle size Stirring velocity
(10–98%) by weight (20–120) C (15–60) min (1/12–3/4) by weight (as received–less than 500 micron) (50–1400) rpm
4. Experimental procedure Spent catalyst was crushed and screened to attain the required particle size. In each experiment, 1 g of spent catalyst was added to a certain amount of sulfuric acid having a specified concentration. Temperature, reaction time, solid:liquid ratio, particle size, and stirring velocity were adjusted. The reaction took place in a sealed container and the resulting slurry was filtered on sintered glass. Atomic Absorption Spectroscopy was used to determine the nickel content in the filtrate after a suitable dilution. Table 2 shows the different factors affecting nickel recovery.
Fig. 3 illustrates the effect of varying sulfuric acid concentration from 10 to 90% by weight. The percentage recovery of nickel increased with increasing sulfuric acid concentration up to a certain range and then decreased with further increase in concentration. A maximum of 99% conversion took place at 50% acid concentration. This indicates that the rate of dissolution of low acid concentration was small, then increased, reaching a maximum value at 50% acid concentration; the rate of dissolution then started to decline by increasing the acid concentration. 5.3. Effect of solid:liquid ratio
5. Results and discussion
Experiments were carried out using different waste solid:sulfuric acid ratios with 50% acid concentration and particle size < 500 micron. It was found that using the stoichiometric amounts of solid:liquid gives a low conversion (26.3%) while increasing the acid amount improves the conversion reaching 98% at a solid:liquid ratio (1:12) as shown in Fig. 4. As the amount of acid increases, the conversion increases, but the further separation of sulfates from the excess acid is difficult and is achieved by many ways.
5.1. Effect of particle size
5.4. Effect of temperature
The influence of spent catalyst particle size was studied using the particle size range (as received, >2000, 850 < 2000, < 500 micron). Fig. 2 represents the effect of the particle size of the spent catalyst on the percentage conversion at different sulfuric acid concentrations (10, 20, 35, and 50% by weight), at room temperature without mixing. The data show that as the particle size decreases to < 500 micron, a maximum conversion was obtained at 50% acid concentration.
The effect of temperature on the system was studied by performing experiments at 20, 40, 60, 80, 100 and 120 C. Fig. 5 reveals that the conversion was influenced by the temperature of the reaction. The recovery increases as temperature increases reaching 99% conversion at reaction temperatures of 80–100 C, with acid concentration of 50%. At higher temperatures, the recovery decreases because water evaporates and the solution becomes concentrated. This may be due to the fact that
88
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Fig. 3. Effect of sulfuric acid concentration on percentage conversion.
Fig. 4. Effect of solid:liquid ratio.
Fig. 5. Effect of temperature on percentage conversion.
N.M. Al-Mansi, N.M. Abdel Monem / Waste Management 22 (2002) 85–90
89
Fig. 6. Effect of time of digestion on percentage conversion.
Fig. 7. Effect of stirring velocity on percentage conversion.
Table 3 Cost aspects based one ton of spent catalyst charge Cost of raw materials (L.E.) Average cost of spent catalyst according to nickel content=L.E. 308.8 Cost of sulfuric acid consumed=L.E. 92.32
Price of products (L.E.) Price of nickel sulfate crystals (assuming 100% conversion)=L.E. 3526 Price of alpha alumna produced=L.E. 591
the reaction between nickel atoms and sulfuric acid form a layer of nickel oxide which surrounds the nickel atoms and decreases the amount of nickel recovered. Nickel sulfate solution is heated and the nickel sulfate salt is crystallized as separate single nickel salt crystals (NiSO4.7H2O).
depending on the time of the reaction. For more than 5 h, 99% conversion was achieved.
5.5. Effect of time of digestion Fig. 6 illustrates the significant effect of time on the recovery of nickel. Prolonging the contact time is accompanied by a noticeable increase in the metal removal which means that nickel recovery is a rate process
5.6. Effect of stirring velocity A series of experiments were undertaken to study the influence of agitation on conversion. Different stirring rates ranging between 50 and 1400 rpm have been applied. The experimental results shown in Fig. 7 indicate that the rate of reaction is controlled by the degree of agitation and the conversion increases with increasing the stirring velocity. The optimum stirring rate which gives the maximum percentage removal is
90
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obtained at 800 rpm. Increasing stirring above that rate has no effect on conversion.
6. Cost aspects The cost items based on a ton of spent catalyst charge can be calculated as shown in Table 3 Douglas [10]: Cost of products/Cost of raw materials =L.E. 10.26, which indicates that the process is profitable, where $=3.9 L.E.(Egyptian pound). Actually, there are several methods to remove excess sulfuric acid from nickel sulfate solution: 1. sulfuric acid can be separated by using membranes [8]; 2. adding calcium hydroxide which reacts with sulfuric acid to form a white precipitate of calcium sulfate at room temperature; 3. adding barium hydroxide solid in stoichiometric amounts to the excess acid react to form barium sulfat; and 4. nickel sulfate solution is evaporated and nickel is crystallized as single nickel salt crystals (NiSO4.7H2O).
7. Conclusions It is possible to utilize spent catalyst (NiO/Al2O3) obtained from the steam reforming plants to produce nickel sulfates by using sulfuric acid. According to environmental considerations it is very useful to reuse the solid waste to produce a salable product such as nickel sulfates which can be used in electroplating. Moreover, the efficient separation of nickel from spent catalyst create a possibility for reusing the alumina
support in the catalyst and thus the solid waste spent catalyst is completely utilized. The operating conditions required to reach 99% conversion were 50% acid concentration, solid: liquid ratio (1:12), less than 500 micron particle size for a contact time higher than 5 h and 800 rpm stirring rate a temperature of 100 C. References [1] Ivascanu St, Roman O. Nickel recovery from spent catalysts. I Solvation process. BulInst Politeh Iasi Sect 2 1975;2(21):47. [2] Loboiko AYa, Atroshchenko VI, Grin GI, Kutovoi VV, Fedorova NP, Volovikov AN, Alekseenko DA, Golodenko NI, Pantaz’ev GI. Recovering nickel from spent catalyst. Otkrytiya, Izobret, PromObraztsy,Tovarnye Zanki 1983;14:33. [3] Chandhary AJ, Donaldson JD, Boddington SC, Grimes SM. Heavy metal in the enviroment. Part II: a hydrochloric acid leaching process process for the recovery of nickel value from a spent calalyst. 1993;34:137. [4] Vicol M, Heves A, Potoroaca M. Recovery of nickel from spent catalysts. Combinatul de Ingrasaminte Chimice, Piatra-Neamt 1986;112:832. [5] Floarea O, Mihai M, Morarus M, Kohn D, Sora M. Filteration. Physical models and operating coditions. Rev Chim (Bucharest) 1991;42:553. [6] Hanewald RH, Onuska JC, Schweers ME. Recycling nickel, chromium and iron catalysts through the high temperature metals recovery process. Third international symposium on recycling of metals and engineered materials. In: Queneau PB, Peterson RD, editors. The Minerals, Metals and Materials Society. 1995. p. 371. [7] Inoue K, Zhang P, Tsuyama H. Separation and recovery of rare metals from spent hydrodesulfurization catalysts.Third international symposium on recycling of metals and engineered materials. In: Queneau PD, Peterson RD. editors. The Minerals, Metals, Metals and Meterials Society. 1995. p. 393. [8] Treybal RE. Mass transfer operations. 3rd ed. USA: McGrawHill, 1980. [9] Aub-Quir for Fertilizers and Chemical Industries Company, ElTabia-RAHID Road, Alex. Egypt, Personal communication. [10] Douglas JM. Conceptual design of chemical processes. USA: McGraw-Hill, 1998.
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