Title of Invention

"A PROCESS FOR EXTRACTION NICKEL FORM SPENT CATALYST

Abstract

A process for extraction of nickel from spent nickel catalyst which comprises i) characterized in that adding a persulphate based additive along with fine sized nickel catalyst in the sulphuric acid solution and stirring by known methods and maintaining the solid-liquid ratio in the range of ½-1/10 (wt./vol.) to obtain a slurry, ii) keeping the temperature of the slurry obtained in step(i) in the range of 40 to 100°C for a period of 0.5 to 6 h, iii) allowing the slurry to settle and then filtering the slurry to obtain leach liquor containing nickel and alumina as solid residue, iv) washing the solid residue to remove entrapped liquor and drying at 110-120 °C to get the byproduct containing high alumina v) purifying the said leach liquor by precipitating by precipitating iron and other impurities using lime and filtering to obtain pure nickel sulphate solution, vi) crystallizing or precipitating the leach liquor to obtain nickel sulphate crystal or nickel hydroxide, vii) reducing nickel hydroxide by known process for producing nickel metal powder or nickel oxide.

Full Text

The present invention relates to a process for extraction of nickel from spent catalyst. This invention particularly relates to a process for extraction of nickel from spent catalyst by direct leaching with sulphuric acid in presence of small amount of an additive. The invention is useful for recovery of nickel from the waste material such as spent catalyst, which is one of the rich sources of nickel and therefore important from the view of environmental protection, resource recycling and conservation. The consumption of nickel in India is about 20,000 MTPY (metric tonnes per year) which is entirely imported. Though several by-products/wastes such as nickel sludge generated during the pickling of stainless steel, grinding waste of AINiCo magnets, and spent catalyst from the fertiliser, petrochemical and hydrogenation plants are available, at present none of such sources are being exploited commercially. Therefore, to meet the ever-growing demand, the effort has been made to provide an innovative and cost effective process for recovery of nickel from the spent catalyst of the fertiliser plants. Nickel based catalysts are the catalyst of choice in several industries due to their low cost compared with other competing substitutes. Such catalysts use alumina and silica as supports. Deactivated nickel catalysts are not considered to be regenerable by ordinary techniques and also pose a significant waste disposal problem. Hence, it is necessary to develop new extraction techniques for processing of such spent catalyst to obtain pure metal for reuse. Considerable efforts have been made to recover nickel from spent catalyst by hydrometallurgical processes. In most of the earlier work the spent catalyst had to undergo pre-treatment step to processing (Inooka Masayoshi, Japan, Kokai, Yokyo, Koho 7811621, 11 Oct. 1978; Telly, George L., US 4, 721600, 20 Jan. 1988; Giurea et al ROM RO 85578, 29 Sept. 1984). In general chlorination (Gravey, G., LeGroff J. and Gonin C., Jan. 8, 1980, U. S. Patent 4182747), pressure leaching with ammonium hydroxide - ammonium carbonate or sodium hydroxide (Gutnikov G. March 2, 1971, U. S. Patent 3567433; Millsap W. A. and Reisler N., 1978, Eng. And Min. J., Vol. 179(5), p. 105.) and sodium carbonate roasting (Castanga H., Gravey G. and Roth A, Feb. 21, 1978, U. S. Patent 4075277) were applied. After a pre-treatment spent catalyst is directly leached with water/acid/alkali. Reduction roasting followed by sulphuric acid leaching of a spent catalyst from hydrogenation plant to produce nickel oxide reported only 83% of overall recovery (P. Alex, T. K. Mukherjee and M. Sundaresan, 1991, Metals Materials and processes, Vol. 3(2), p.-81). Roasting followed by selective chlorination at 400 °C of spent catalyst under Cl2 + air, Cl2+N2 and Cl2 + N2 was investigated and maximum recovery of only 80% was reported (Gaballah I. and Dona M., 1993, The Paul E. Queneau Int. Symp. on Extractive Metallurgy of Copper, Nickel and Cobalt, Vol. I, p. 1253, Ed. R. G. Reddy and R.N. Weizenbach, minerals, Metals and Material Society). Direct leaching of spent catalyst has several disadvantages such as requirement of high strength acid as high as 20 -30% and poor nickel dissolution with simultaneous dissolution of other metalions which are the major problems for the subsequent processing steps of final product recovery. Neutralisation of highly acidic leach liquor requires high amount of a kali and will generate huge quantity of waste cake which will add cost to the prodess, besides creating environmental problem. Though several attempts have been made to recover nickel by various processes involving pre-treatment such as roasting, reduction/alkali/chlorination roasting etc. followed by acid/alkali/neutral leaching to recover nickel. However, there are rarely any attempt made to accelerate the metal dissolution process by adding catalytic oxidants such as sodium/hydrogen peroxide, persulphate salts etc. The main object of the present invention is to provide a process for extraction of nickel from spent catalyst which obviates the drawbacks as detailed above. Another object of the present invention is to provide a leaching process for extraction of nickel from spent nickel catalyst in presence of little amount of catalytic additive which eliminates necessity of pre-treatment steps usually common to all established processes and avoids requirement of high strength acid for selective and quantitative dissolution of nickel from this resource. Still another objective of the present invention is to develop a suitable process for the recovery of nickel from an indigenous spent catalyst generated in substantial quantity in fertiliser industry, which can operate in medium and small scale. Accordingly, the present invention provides a process for extraction of nickel from nickel catalyst which comprises i) characterized in that adding a persulphate based additive along with fine sized nickel catalyst in the sulphuric acid solution and stirring by known methods and maintaining the solid-liquid ratio in the range of !4-1/10 (wt./vol.) to obtain a slurry, ii) keeping the temperature of the slurry obtained in step(i) in the range of 40 to 100°C for a period of 0.5 to 6 h, iii) allowing the slurry to settle and then filtering the slurry to obtain leach liquor containing nickel and alumina as solid residue, iv) washing the solid residue to remove entrapped liquor and drying at 110- 120 0 C to get the byproduct containing high alumina v) purifying the said leach liquor by precipitating by precipitating iron and other impurities using lime and filtering to obtain pure nickel sulphate solution, vi) crystallizing or precipitating the leach liquor to obtain nickel sulphate crystal or nickel hydroxide, vii) reducing nickel hydroxide by known process for producing nickel metal powder or nickel oxide. In an embodiment of the present invention the spent nickel catalyst used may be selected from the nickel catalyst having particle size in the range of -150 to +50 +50 µM and having composition in the following range: Ni: 5-20%, Fe: 0.1-1%, AI2O3 : 70-90%, SiO2 : 0-6% In another embodiment of the present invention the additives may be selected from persulphate salts of sodium, potassium and ammonium and may have concentration in the range of 0.25-4%(w/w). In still another embodiment of the present invention the sulphuric acid may be of commercial grade and may have concentration in the range of 2-6% (v/v). This acid concentration is obtained after mixing with the wash solution generated from the leaching step earlier and is used for further leaching. In the process of present invention the leach slurry is filtered and the residue is washed with very dilute sulphuric acid solution. The wash liquor containing 10-30 g/l Ni is recycled for the leaching of the fresh spent catalyst by adding the desired amount of acid. In the present invention the nickel catalyst is leached in sulphuric acid medium using a catalytic additive. Nickel present in the spent catalyst is in oxide phase and dissolution in sulphuric acid occurs as : additive NiO + H2S04 → NiS04 + H2O (1) The iron free leach liquor is evaporated crystallise nickel as nickel sulphate. The purified leach liquor can also be precipitated as nickel hydroxide and nickel metal from this can be obtained by known method called hydrogen/carbothermic reduction process. Alternatively nickel metal powder can be produced by the known process by aqueous hydrogen reduction of purified leach liquor. Novelty of the present invention is the use of a catalytic additive which has not been used earlier for direct leaching of nickel from nickel catalyst. Another feature of the invention is complete nickel dissolution (more than 99.5%) from the spent catalyst without any prior treatment such as roasting, reduction/alkali/chlorination roasting etc. which are necessary steps in earlier developments. The following examples are given by way of illustration and should not be construed to limit the scope of invention. EXAMPLE -1 A conical flask containing 200 ml of 3 vol% sulphuric acid is kept over a thermostatically controlled hot plate fitted with stirring arrangement by a magnetic needle. The temperature of the solution is maintained at 70 °C. 50 g of nickel catalyst of composition : 9.70% Ni, 0.31% Fe, 81.3% A12O3, and 3.77% SiO2 is added to the flask with stirring. Samples collected at different time intervals are filtered and analysed for nickel content. Recovery of nickel increases with leaching time. Recovery data at different time intervals are incorporated in Table 1. A maximum of 11.95% nickel recovery is achieved in 6 h. Table 1 : Percentage nickel recovery at different time intervals. (Table Removed) EXAMPLE - 2 A conical flask containing 200 ml of 3 vol.% of concentrated sulphuric acid is kept over a thermostatically controlled hot plate fitted with a magnetic stirrer. Temperature of the solution is raised to 90 °C and 50 g of nickel catalyst of composition : 9.70% Ni, 0.31% Fe, 81.3% A12O3, and 3.77% SiO2 is added. Once the leaching proceeded with stirring, the samples are collected at different time intervals, filtered and analysed for nickel. Extraction data at different time intervals are incorporated in Table 2. Recovery of nickel increases with leaching time and a maximum of 50.39% nickel recovery is achieved in 6 h. Table 2 : Recovery of nickel at different time intervals. (Table Removed) EXAMPLE -3 200 ml of water containing 3 vol.% of concentrated sulphuric acid in a conical flask is kept over a thermostatically controlled hot plate fitted with a magnetic stirrer. After maintaining the temperature of the solution at 70 °C, 50 g of nickel catalyst of composition : 9.70% Ni, 0.31% Fe, 81.3% A12O3, and 3.77% SiO2 and 0.5 g of persulphate salt are added. Temperature of the slurry is maintained through out the leaching experiment. Leaching is carried out by agitating the slurry. Samples collected at different time intervals are filtered and leach liquor is analysed for nickel. The recovery data at different time intervals are incorporated in Table 3. A maximum of 97.5% of nickel recovery is achieved in 6 h of leaching time as compared to only 11.95% nickel recovery in absence of additive. Table 3 : Effect of additive on the percentage nickel recovery at different time intervals. (Table Removed) EXAMPLE - 4 A solution containing 200 ml of water with 3 vol.% concentrated sulphuric acid in a conical flask is kept over a thermostatically controlled hot plate fitted with a magnetic stirring system. The solution temperature is raised to 70 °C and 50 g of spent nickel catalyst of composition : 9.70% Ni, 0.31% Fe, 81.3% A12O3, and 3.77% SiO2 and 1.0 g of persulphate salt are added to the system. The above temperature is maintained while stirring through out the leaching experiment. Very fast reaction occurs in presence of additive. Samples collected at different time intervals are filtered and the leach liquor analysed for nickel. Recovery data at different time intervals are incorporated in Table 4. About 98% of nickel recovery is achieved within 2 h of leaching and a maximum of 99.6% nickel recovery is achieved in 6 hours of leaching. Table 4 : Effect of higher dose of additive on the percentage nickel recovery at different time intervals. (Table Removed) EXAMPLE - 5 The temperature of a solution containing 200 ml of 3 vol.% of concentrated sulphuric acid in a conical flask is maintained at 90 °C by a thermostatically controlled hot plate fitted with a magnetic stirring arrangement. 50 g of nickel catalyst of composition : 9.70% Ni, 0.31% Fe, 81.3% A1203, and 3.77% SiO2 and 1 g of persulphate salt are added to the system. Temperature of the reaction is maintained through out the leaching experiment. Samples collected at different time intervals are filtered and leach solution is analysed for nickel content. Nickel recovery at different time intervals is summarised in Table 5. About 99% of leaching is achieved within 1 h of leaching. Table 5 : Effect of higher temperature in presence of an additive on the nickel recovery. (Table Removed) EXAMPLE - 6 2L of 6 vol.% sulphuric acid solution in a 3L beaker is kept over a hot plate and temperature is maintained at 80 °C. It is kept under stirring with the help of a glass stirrer fitted to a motor. 1 kg of spent catalyst of composition : 9.70% Ni, 0.31% Fe, 81.3% A12O3, and 3.77% Si02 and 15 g of persulphate salt are added to the acid solution under stirring. After 2 h of leaching the slurry is kept for settling. Within 2 h about 70% of the slurry settles. The clear supernatant is taken out and the thick slurry is filtered. The leach liquor, wash solution and residue analysis are given in Table 6. Residue basis recovery obtained is more than 99.9%. Table 6 : Results of leaching experiment on 1 kg scale. (Table Removed) The major advantages of the present invention are given here ; 1. Elimination of pre-treatment step which is carried out at higher temperature, prior to leaching as required in the developed process, results in cost and energy saving. 2. With no gas emission, the process is much eco-friendly. 3. The process requires only little excess to the stoichiometric amount of acid for complete dissolution of nickel. 4. Leach residue containing alumina can be produced as a value added by product. 5. The process operates at very low temperature and low acid concentration, and therefore special material of construction is not required. 6. The process require less amount of alkali in the purification step and generates less amount of residue, and therefore account for low loss of metal values at this stage. 7. Leaching with higher pulp density generates concentrated leach solution and requires less heat energy for crystallisation. 8. The process is much less corrosive as compared to chlorination roasting often followed. 9. The process is much easier and involves lesser number of steps. 10. The process requires much less capital investment and can be operational in medium and small scale. . We claim : 1. A process for extraction of nickel from spent nickel catalyst which comprises i) characterized in that adding a persulphate based additive along with fine sized nickel catalyst in the sulphuric acid solution and stirring by known methods and maintaining the solid-liquid ratio in the range of ½-1/10 (wt./vol.) to obtain a slurry, ii) keeping the temperature of the slurry obtained in step(i) in the range of 40 to 100°C for a period of 0.5 to 6 h, iii) allowing the slurry to settle and then filtering the slurry to obtain leach liquor containing nickel and alumina as solid residue, iv) washing the solid residue to remove entrapped liquor and drying at 110- 120 °C to get the byproduct containing high alumina v) purifying the said leach liquor by precipitating by precipitating iron and other impurities using lime and filtering to obtain pure nickel sulphate solution, vi) crystallizing or precipitating the leach liquor to obtain nickel sulphate crystal or nickel hydroxide, vii) reducing nickel hydroxide by known process for producing nickel metal powder or nickel oxide. 2. A process as claimed in claim 1 wherein the spent catalyst used is selected from the nickel catalyst of particle size in the range of -150 to +50 (am and having composition in the following range: Ni: 5-20%, Fe : 0.1-1%, AI2O3 : 70-90%, SiO2 : 0-6% 3. A process as claimed in claims 1-2 wherein the persulphate based additive is selected from persulphate salts of sodium, potassium and ammonium and have concentration in the range of only 0.25-4% (w/w). 4. A process as claimed in calims 1-3 wherein the used sulphuric acid is of commercial grade and have concentration in the range 2-12 vol%(v/v). 5. A process for extraction of nickel from spent catalyst substantially as herein described with reference to the examples.

Documents:

1013-del-2001-abstract.pdf

1013-del-2001-claims.pdf

1013-del-2001-correspondence-others.pdf

1013-del-2001-correspondence-po.pdf

1013-del-2001-description (complete).pdf

1013-del-2001-form-1.pdf

1013-del-2001-form-18.pdf

1013-del-2001-form-2.pdf

1013-del-2001-form-3.pdf

1013-del-2001-petition-137.pdf