The present invention relates to a process for preparation ferronickel from spent nickel catalyst.
This invention particularly relates to a process for recovery of nickel as ferronickel from spent nickel catalyst by electrothermic smelting route. Spent nickel catalyst is treated as industrial waste and controlled under strict environmental protection law. The invention will be useful for recovery of nickel from such waste material which is one of the rich sources of nickel and is 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 recover nickel as ferronickel from the nickel spent catalyst of the fertiliser plants.
Nickel based catalysts are often preferred in several industries due to their effective catalytic properties and low cost compared to 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 establish economic methods for processing of such spent catalyst to obtain pure metal/alloy for reuse.
Considerable efforts have been made to recover nickel from spent catalyst by hydro-metallurgical processes. In most of the earlier work the spent catalyst had to undergo a pre-treatment for further processing (Inooka Masayoshi, 11 Oct. 1978, Japan, Kokai, Yokyo, Koho 7811621; Telly, George L. 20 Jan. 1988, US 4, 721600; Giurea et al, 29 Sept. 1984, ROM RO 85578), which in general involves chlorination (Gravey G., LeGroff J. and Gonin C; Jan. 8. 1980, U. S. Patent 4182747:. Gaballah I, Djona M, Mugica J. C. and Solozobal R, 1994, Resour., Conserv. Recycl., Vol. 10(1-2), p.-86; Gaballah I, Djona M, 1995, 1995, Met. Trans. B, Vol. 26B(1), p.-41; Chaudhary A. J., Donaldson J. D., Boddington S. C and Grimes S. M, 1993, Hydrometallurgy, Vol. 34 (2),p.-137), pressure leaching with ammonium hydroxide - ammonium carbonate or sodium hydroxide (Gutnikov G., March 2,
1971, US 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). After a pre-treatment spent catalyst is directly leached with water/acid/alkali followed by various purification steps. From the purified leach solution the final product is recovered as metal/salt/oxide. Sometimes in the purification step, the requirement of high acid make the purification step much more complicated. Thus, most of the hydrometallurgical methods require elaborate processing steps including pretreatment to recover nickel which may not yield high economic return every time. Presence of high soluble silica as noticed in the present case makes it extremely difficult to purify the leach liquor for recovery of nickel economically.
Virtually no attempts have been made so far to recover nickel from the spent catalysts by pyrometallurgical methods which imvolves only single step. The ferronickel of 18% nickel grade was prepared from a nickel ash sample by aluminothermic process (Murthy D. S. R., Mohanty M. S. and Akerkar D. D., 1989, Trans. Ind. Inst. Met., Vol. 42(5), p.-503). Till date no attempt has been made to recover nickel from the spent catalyst of the fertiliser industries by electrothermal smelting process.
The main object of the present invention is to provide a process for preparation of ferronickel from spent nickel catalyst which obviates the drawbacks as detailed above.
Another object of the present invention is to provide a process for recovery of nickel as ferronickel from spent nickel catalyst
Still Another object of the present invention is to provide an electrothermic smelting process for preparation of ferronickel from spent nickel catalyst using carbon as reductant.
Yet another object of the present invention is to provide a process by which nickel content in ferronickel could be increased by the process of enrichment or in single step by controlling the parameters.
Yet another object of the present invention is to provide a suitable process by which Si
(silicon) level in the ferronickel could be maintained very low while using a starting
material containing high silica.
Yet another object of the present invention is to use scrap iron, another waste to produce
ferronickel from spent nickel catalyst.
Accordingly, the present invention provides a process preparation of ferronickel from
spent nickel catalyst which comprises:
i) mixing carbon powder and lime with ground spent nickel catalyst,
ii) adding water in the above mixture and making pallets of 5-20 mm size
iii) allowing the said pallets to dry in the range of 110-120 °C for a period of 12-24 h to
remove moisture completely,
iv) melting iron scrap or ferronickel in a graphite crucible by electric arc heating process
to make a pool for proper conduction,
v) charging the said dried pallets as obtained in step(iii) by adding this slowly into the
above said iron scrap or ferronickel melt for complete smelting to obtain the iron to nickel
ratio in the range of 8:2 to 1 :9,
vi) cooling and separating the metal and slag by the known process.
In an embodiment of the present invention the ground spent nickel catalyst may have particle size in the range of - 211 to + 38 µm.
In an another embodiment of the present invention the spent nickel catalyst used has composition in the range : Ni: 7 - 20%, Fe : 0.1 - 5%, Ah03: 10 - 90%, Si02: 2 - 20%
In yet another embodiment of the present invention the carbon used is selected from the group consisting of charcoal, coke and petroleum coke and is commercial grade.
In still another embodiment of the present invention, the lime used is of commercial grade and is used for slagging purpose and also for controlling the silicon level of ferronickel.
In still another embodiment of the present invention, the nickel component in the ferronickel is increased by the process of enrichment through recycling of the ferronickel.
In the process of present invention the nickel catalyst is smelted under reducing conditions using carbonaceous substances such as charcoal, coke and petroleum coke. Nickel present in the spent catalyst is in oxide phase reduced to metallic nickel along with the part of iron to form ferronickel.
Silica present in the catalyst forms calcium silicate in presence of lime and separates as slag along with alumina.
In the present invention, the ferronickel of varied composition even above 75% Ni grade can be produced suitable for alloying purpose in the steel making.
Novelty of the present invention is the use of a spent catalyst to produce high grade ferronickel with very low Si from the spent nickel catalyst containing high silica by electrothermal route, an energy efficient process. Another feature of the invention is the possibility of increasing the nickel content of ferronickel by the process of enrichment and also in a single step by controlling the process parameters.
The following examples are given by way of illustration and should not be construed to limit the scope of invention.
EXAMPLE - 1
Spent nickel catalyst (NC) of composition : 17.3% Ni, 3.6% Fe, 11.4% AI2O3, and 14.0% Si02 along with other ingredients such as lime, 125 g and charcoal powder, 75 g are mixed thoroughly and palletised to 10 mm size. The pallets are dried at 120 °C for 12 h to remove moisture completely.
Smelting operation is carried out in an electric arc furnace using a graphite crucible of 4 L capacity and a graphite rod as electrode. First 250 g iron chips are melted to create a metal pool and raise the temperature by the process of arcing and then nickel catalyst charge in the form of pallet is added
slowly. Arcing is continued till the total charge is smelted. Metal and slag are separated, weighed and analysed for various components.
Table 1 : Nickel recovery as ferronickel on 1 kg scale
(Table Removed)
NC: Spent Nickel Catalyst
EXAMPLE -2
150 g of lime and 300 g of charcoal powder are mixed thoroughly with 2 kg of spent nickel catalyst of composition : 17.3% Ni, 3.6% Fe, 11.4% A1203, and 14.0% SiO2 are mixed thoroughly and palletised to 10 mm in size. Prepared pallets are dried at 120 °C for 12 h to remove moisture completely.
Smelting of charge is carried out in a submerged arc furnace using a graphite crucible and a graphite electrode. First 375 g of ferronickel of composition : 37.9% Ni and 60.5% Fe is melted and then nickel catalyst charge is added slowly. Arcing is continued till the smelting of the total charge. After cooling the metal and slag are separated for necessary characterisation. Analysis results of different components are as follows :
Table 2 : Nickel enrichment study in previously prepared ferronickel
(Table Removed)
NC : Spent Nickel Catalyst
EXAMPLE - 3
4 kg of spent nickel catalyst of composition : 17.3% Ni, 3.6%) Fe, 11.4% AI2O3, and 14.0%) S1O2 along with 400 g of lime and 250 g of charcoal powder are mixed thoroughly and palletised to 10 mm in size. Prepared pallets are dried at 120 °C for 12 h to remove moisture.
50 g of iron chips are added to a graphite crucible of 4 L capacity properly fitted to the arc furnace. Arc is started to melt the iron chips and dried pallets are added to the melt gradually. Till complete melting of the charge, arc is continued and the graphite electrode is removed from the melt. After cooling the metal and slag are separated for necessary characterisation. Weight of ferronickel obtained is 810 g. Analysis results for different components are as follows :
Table 3 : Nickel recovery as ferronickel on 4 kg scale.
(Table Removed)
NC: Spent Nickel Catalyst
The slag produced in the process was analysed for Fe and Ni which were found to be 0.67 and 1.8% respectively.

The major advantages of the present invention are
1. Production of a high value product directly from a waste material.
2. It is a single step process and avoids multistage operation as in case of hydrometallurgical processes.
3. Process requires low cost ingredients like scrap iron, lime and a carbonaceous substance.
4. High grade ferronickel can be produced which is suitable for direct alloying purposes by steel industries.
5. The unique feature of the process is the possibility of producing varied grade of ferronickel product.
6. Composition of each metal components can be controlled effectively by the process.
7. Silica can be maintained as low as possible by effective slagging
8. Non-leachable and a vitreous brittle slag produced is safe for disposal and can be used for land filling or road making.
9. The process requires less capital investment and can be operational in small and medium scale units.

We Claim
1. A process preparation of ferronickel from spent nickel catalyst which comprises:
i) mixing carbon powder and lime with ground spent nickel catalyst,
ii) adding water in the above mixture and making pallets of 5-20 mm size
iii) allowing the said pallets to dry in the range of 110-120 °C for a period of 12-24 h to
remove moisture completely,
iv) melting iron scrap or ferronickel in a graphite crucible by electric arc heating process
to make a pool for proper conduction,
v) charging the said dried pallets as obtained in step(iii) by adding this slowly into the
above said iron scrap or ferronickel melt for complete smelting to obtain the iron to nickel
ratio in the range of 8:2 to 1 : 9,
vi) cooling and separating the metal and slag by the known process.
2. A process as claimed in claim 1 wherein the ground spent nickel catalyst used is of particle size in the range of - 211 to + 38 µm.
3. A process as claimed in claims 1-2 wherein the spent nickel catalyst used have composition in the range of Ni : 7 - 20%, Fe: 0.1 - 5%, Al203: 10 - 90%, SiO2: 2 - 20%
4. A process as claimed in claims 1 - 3 wherein the carbon used is selected from of charcoal, coke and petroleum coke.
5. A process as claimed in claims 1 - 4 wherein the nickel component in the ferronickel is increased by the process of enrichment through recycling of the ferronickel.
6. A process for preparation of ferronickel from spent nickel catalyst substantially as herein described with reference to the examples.