Simultaneous Recovery of Nickel and Aluminium from Spent Reformer Catalyst

By Dipak J. Garole and A. D. Sawant
June 2005

The Author is Research Scholar at the Institute of Science in Mumbai, India. The Paper was presented at the 23rd annual conference of the Indian Council of Chemist, at K.C. College, University of Mumbai. Prof. Arun Sawant, Pro Vice Chancellor of The Mumbai University, is the guiding teacher.

Large quantities of spent nickel catalysts are available from fertilizer, petrochemical, vegetable oil and other industries. Disposal of spent catalyst is a problem as it falls under category of hazardous industrial waste. The recovery of metals from these catalysts is an important economic aspect as most of these catalysts are supported catalyst usually with alumina / silica with varying percent of industrially important element nickel, in the reference catalysts alone; nickel concentration varies from 2.5-20%. A spent reformer catalyst was treated with caustic soda solution of varying concentrations at temperature 90-100°C for different times to dissolve aluminium as sodium aluminate. The recovery of aluminium was 97.4%. The residue was digested with aqua-regia for different time period at 90-100°C. The recovery of nickel obtained was 95-96% in the form of NiSO4.7H2O.

Keywords: Separation; Nickel and Aluminium recovery; Spent catalyst.

Introduction

Metals like Ni, Mo, Co, Rh, Pt, Pd, etc., are widely used as a catalyst in chemical and petrochemical industries. They are generally supported on porous materials like alumina and silica through precipitation or impregnation processes. In many of the cases, the metals are in the form of oxides, however, in the other cases, they are reduced into active metals for catalyzing the appropriate reactions. After periodical use of the catalysts, due to poisoning effect of foreign material and impurities, which deposit on the surface of the catalyst, they will become inactive. In such cases, fresh catalysts have to be substituted and the spent catalyst will be discarded as waste material.

Disposal of such catalyst materials, which contains appreciable amounts of heavy metals, is environmentally hazardous. Therefore, a suitable and economically viable method is required for recovery of metals at the same time method should not pose the risk of environmental hazards. Therefore, recovery of nickel and aluminium from such catalyst attracted the attention of investigators.

Various processes have been developed by number of researchers. Amad et al. (1970) studied recovery of nickel from spent hydrogenation catalyst by digestion of it with different acids. Recovery of nickel with inorganic acid was 85-94.5%, however, with HCOOH it was 80-5% and with ACOH about 65-8%. Tiwari et al. (1972) reported dry carbonylation process as well as wet extraction with acids for different types of nickel catalyst. The carbonylation process recovered 90-98% of the nickel metal and NiO where as extraction with HNO3 and HNO3-HCl mixture recovered 65-99% of the metal and its oxide depending on the nature of catalyst. The poor recovery by acid treatment in some cases was attributed to the higher amount of NiAl2O4 and NiSiO3, which has higher resistance towards acid leaching. Shinohara et al. (1976) studied leaching of spent catalyst with caustic soda solution and treating the residue with sulfuric acid solution for recovery of nickel. Drule minela liana et al. (1979) studied spent catalyst fused with NaOH and NaNO3 and treated the residue with H2SO4 for recovery of nickel. Loboiko et al. (1983) studied leaching of nickel oxide with 60-70% nitric acid concentration at 120°C for 2-3 h. Manoliu et al. (1985) studied leaching of spent nickel catalyst first with 50% NaOH in autoclave at 150-175°C to dissolve Al as Na-aluminate. The residue treated with HNO3 (1:1) at 60°C to dissolve nickel in the solution. Vicol et al. (1986) studied leaching of spent catalyst with an aqueous solution of 15-23% ammonia at 60-90°C at pH 7.5-9 and nickel was recovered as nickel nitrate. Sinka et al. (1988) studied extraction of nickel from spent nickel catalyst based alumina (NiO/Al2O3) leaching with sulfuric acid solution 90% nickel was recovered. Ganguli et al. (1988) studied spent nickel catalyst with 32% hydrochloric acid concentration at 70°C and nickel recovery was found to be 96%. Molnar et al. (1988) reported a spent hydrocracking catalyst roasted at 390°C with NH4Cl, leaching with water at 80°C and crystallization as NiCl2 at 85% nickel yield. Pamela et al. (1991) studied reduction roasting-sulfuric acid leaching of nickel from spent nickel catalyst. About 98% of nickel was recovered as nickel oxide under the following conditions: sulfuric acid concentration: 1.87 M; reaction time: 2 h.; reaction temperature 80°C. Chaudhary et al. (1993) studied leaching the low-grade spent catalyst with hydrochloric acid. They obtained low Ni extraction efficiency (only 18%). Sibban Singh (1993) studied leaching spent nickel catalyst with 1-3 normal nitric acid at 100°C for 1-3 h. Khanna et al. (2000) studied reclamation of nickel catalyst from spent catalyst by dry reduction method. The study investigates the leaching aluminium and nickel from spent catalyst (NiO/Al2O3) with caustic soda and aqua regia. The process conditions studied include caustic soda and aqua regia concentrations, temperature, time and solid-liquid ratio.

Experiment

Materials and Apparatus

The spent reformer catalyst used in this study was provided by RCF (India). The grayish black rings of spent catalyst were crushed and powdered. The reagents like Na2CO3, H2O2, H2SO4, HCl, HNO3, NaOH, used were of AR grade. The reaction between spent catalyst and caustic soda and aqua- regia was performed in a 500-mL round bottom flask on hot plate.

Procedure

Hundred gram of spent catalyst was added at a time to the agitated caustic soda solution (200-mL) of the required concentration, time and temperature. The leached solution was filtered. Aluminium was dissolved into sodium aluminate and pH was adjusted to 5-5.5 by adding dilute sulfuric acid Aluminium precipitated as aluminium hydroxide was converted into its oxide. The residue left after removal of aluminium is then digested with aqua-regia at 100°C for 2 hrs and filtered. To the filtrate containing Ni, Fe, Al, and Mg was added H2O2 and Na2CO3 and pH was adjusted to 5-5.5 Al/Fe precipitates its hydroxide and its removed by filtration. Then the pH was adjusted at 6.5 by adding NaF/HF to precipitates Mg as MgF2 to obtained nickel sulfate solution and its precipitate which was convert carbonate by adding Na2CO3. The amount of sulfuric acid was added to it and recovery of nickel in the form of nickel sulfate crystals was found to be 95-96%. The samples were analyzed for determination of metals content using spectrophotomery and atomic absorption spectroscopy (AAS). After that the percentage of nickel and aluminium were calculated.

Results and Discussion

Effect of caustic soda concentration on extraction of aluminium

The effect of caustic soda concentration on leaching of spent nickel catalyst was studied using different concentrations in the range 5-25% at a constant temperature at 80°C. The solid/ liquid ratio was kept constant at 1:2 g/mL. The results are shown in (Fig.1). The caustic soda concentration also has a pronounced effect on the dissolution of Al2O3. About 97.4% of the Al present in the spent catalyst were extracted using 20% caustic soda solution after 120 min.

Effect of caustic soda concentration

Effect of aqua-regia concentration on extraction of nickel

The plot of Ni extraction against aqua-regia concentration is presented in (Fig.2) The extraction of nickel was found to be quantitatively. Higher aqua-regia concentration in range 80-100% at constant temperature 80°C. The solid/liquid ratio was kept constant at 1:3 g/mL. The aqua regia concentration also has a pronounced effect on the dissolution of NiO. About 98% of the Ni present in the spent catalyst was extracted using 80% aqua-regia solution after 120 min.

Effect of aqua-regia concentration

Effect of Time on Extraction of aluminium and nickel

A spent catalyst with of 20% caustic soda, 80% aqua- regia and time period in the range of 0.5-2.5 h. at a constant temperature of 80°C was carried out (Fig 3). The solid/liquid ratio was kept constant at 1:2 g/mL and 1/3g/mL. For aluminium and Nickel respectively. The time has significant effect on dissolution of nickel aluminium oxide. After 2h leaching time 97.7% Al, and 98% Ni were extracted.

Effect of Time on Extraction

Effect of Temperature on Extraction of aluminium and nickel

The effect of reaction temperature on Al and Ni extraction is plotted in (Fig.4) for spent catalyst of 2h.timeb period and 20% caustic concentration and 80% aqua-regia concentration. In the temperature range of 60-100°C. The solid/liquid ratio was found to be best for 1:2 and 1:3 g/mL for Al and Ni extractions. About 97.4% and 98% of the Al and Ni present in the spent catalyst is extracted after 2h at a reaction temperature 90°C.

Effect of Temperature on Extraction

Solid-Liquid ratio (S/L) on extraction of aluminium and nickel

The minimum S/L ratio of 1 /2 g/ml. was found to be sufficient for aluminium extraction and the S/L ratio increases upto 1/3 g/ml. had no adverse effect on extraction of aluminium is shown in Table 1.

Table 1. The effect of Solid/ Liquid ratio on leaching efficiency and the concentration of Aluminium in the caustic soda solution
S/L ratio {g/ml) Recovery (%)
1/1 96.60
1/2 97.40
1/2.5 97.40
1/3 97.40

While in case of nickel the S/L ratio 1/3 g/ml. was found to be best for nickel extraction and the S/L ratio increases upto 1/4 g/ml.the extraction efficiency negligible. The results are shown in Table 2.

Table 2. The effect of Solid/ Liquid ratio on leaching efficiency and the concentration of Nickel in the aqua-regia
S/L ratio {g/ml) Recovery (%)
1/1 40.0
1/2 60.0
1/2.5 97.70
1/3 98.0
1/4 98.0

Conclusion

  1. The spent catalyst needs to leached with NaOH at 90-100°C to form soluble aluminium compound and it is easy to recovery of aluminium.
  2. The rate of extraction of aluminium was found maximum at temperature 80°C further increase temperature no adverse effect on aluminium extraction.
  3. Very high recovery of aluminium obtained in very short time.
  4. The residue left after recovery of aluminium leaching with aqua regia at a temperature 90-100°C dissolution 2 hrs. Could bring 98% of nickel in solution.
  5. Recovery of nickel as NiSO4.7H2O crystals was obtained 95-96%.

Reference

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