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Chemical reclaiming of nickel sulfate from nickel-bearing wastes
Conwrvorron Printed
& Recycling,
Vol. 6, No.
I/2,
pp. 55
62, 1983
0361
in Great Britain
CHEMICAL
36!8/83
$3 011t
Pergamon
Pm\
.Gfl I.ld
RECLAIMING OF NICKEL SULFATE FROM NICKEL-BEARING WASTES
LUNG TSUEN-NI,
LIN JING-CHIE
Mining Research
and HUANG TEH-CHUNG
and Service Organization,
Republic
of China
Abstract - Two types of nickel-bearing wastes, spent Raney nickel (65% Ni) and segregated electroplated coatings (20% Ni), were used in this nickel reclaiming process study for nickel sulfate recovery. The spent catalyst from the petrochemical industry was first roasted with caustic soda at 500°C to convert its alumina to water-soluble aluminate. The nickel was then reclaimed as residue by simple water digestion to remove the aluminate. The nickel recovered was relatively pure and was used to prepare nickel carbonate, which was later applied in the process as a neutralizer to purify the nickel sulfate solution obtained from chemical processing of segregated electrocoatings. The coatings were derived from obsolete components of plated zinc die castings, after most of the zinc had been reclaimed by remelting. The coatings were further treated to separate zinc and copper from the nickel by selective dissolution. The nickel left was then dissolved in sulfuric acid to produce nickel sulfate solution. Before crystallisation, the solution was further treated with nickel carbonate recovered from spent catalyst to neutralize the excess acid and to precipitate the iron. The nickel salt reclaimed was an a form nickel sulfate hexahydrate (a - NiS0.,.6HIO) and may be used for chemical and electroplating purposes. The experimental results of pilot testing in the reclaiming process are sufficiently encouraging for further development to commercial application to take place.
INTRODUCTION Nickel has many uses in industry, mainly as an alloying element in the manufacture of stainless steels, nickel alloys and superalloys. Most of the nickel scraps now recycled by industry are recovered principally as alloys from scrapped stainless steels and nickel alloys[ 1,2]. Of the scrap recycled, 50% is estimated to be prompt industrial, and 50% obsolete[l]. Other secondary nickel resources are much less extensively recycled by the industry mainly because of their relatively small quantities and diversified uses. However the rapid increase in world consumption of nickel dictates a reassessment of the less economically-attractive secondary sources of nickel[3]. In this category, spent nickel catalysts and nickel electrodeposits from defective or obsolete parts are only two of the examples under consideration in this study. The copper - nickel - chromium system is the most commonly used electroplating system on zinc die castings. The nickel deposited on the copper provides most of the corrosion resistance of the coating on the zinc products. The increasing use of plated zinc die casting parts in car manufacture proves it is worthwhile to carry out a study on reclamation of nickel from segregated auto shredder rejects. By the technology of auto shredding, it is easy to separate obsolete zinc die castings from other metallic and non-metallic materials. The electrodeposits can easily be separated from the zinc by melting off the zinc alloy in low-temperature furnace operations. Owing to the difficulties of reprocessing, the stripped coatings are generally discarded as a waste, at least in places like Taiwan where adequate nickel resmelting facilities do not exist. One of the major purposes of this study is to try to develop a chemical process to reclaim the nickel, as its salts, from the stripped coatings by a hydrometallurgical route. Another nickel-bearing waste available in substantial quantities in Taiwan is spent nickel catalyst. Raney nickel is a commonly-used catalyst in many chemical processes in the petrochemical and fertilizer industries for different purposes. After a certain time in service, the nickel catalysts are spent but are essentially unaltered in primitive nature and quantity. If compared with other nickel-bearing sludges or wastes, spent nickel catalysts are easy to collect and normally have a high nickel content[3]. These properties make it relatively easy to reprocess them to reclaim nickel as nickel 55
56
LUNG TSUEN-NI, LIN JING-CHIE and HUANG TEH-CHUNG
salts. In this study the nickel is recovered as commercial nickel carbonate (3Ni(OH),.2NiC03*4H20) which can be used as a neutralizer for pH adjustment in processing, or for sale. These two above-mentioned nickel-bearing wastes are considered attractive secondary sources of nickel for reclamation purposes in the local market of Taiwan, The nickel salt reclaimed from the combined treatment of these two wastes is an a form nickel sulfate hexahydrate (a - NiS0,.6H20). This is a readily marketable form of nickel salt and it can be used by chemical or electroplating industries. The flowsheet of the chemical reclaiming is relatively simple and no special equipment is necessary. The experimental results of pilot testing in the process are encouraging for further development to commercial application.
WASTE MATERIALS Two different types of nickel-bearing waste were used in this nickel reclaiming study. The first one was the powder-form spent Raney nickel supplied by local petrochemical plants. The waste catalyst contained 65% nickel with 30% oxides and a small amount of constrained organics. Because of its relatively high nickel content, the spent catalyst was used to make nickel carbonate for pH conditioning whenever necessary during processing. Another nickel-bearing waste was from local zinc die casting scrap remelters after zinc foundry alloy had been reclaimed by remelting operations. The remelting extracted the alloy and left the multi-metallic electrocoatings as an unmelted residue which could be collected after completion of the operation. The recovered multi-metallic coatings consisted of different size metal fragments with a nickel content of 20% and balanced by zinc and other metals. The shape of the coatings was irregular, with a length ranging from a few cm to 20 cm in which its origin can still be identified as scrapped automobiles. This material was used to recover nickel as nickel sulfate. The chemical composition of the waste materials used in this study is given in Table 1.
THE RECLAIMING
PROCESS
The nickel reclamation process can be divided into two parts, each consisting of several steps. The first part of the processing is manufacturing nickel carbonate from the spent Raney nickel. The carbonate is later used as a neutralizer for solution purification in the process. In the preparation of nickel carbonate, the major steps are roasting, digestion, dissolution, neutralization and precipitation of nickel carbonate. The second part of the processing is production of nickel Table 1. Chemical analysis of the nickel wastes Waste material
Type
Nickel content
Other constituents AL03
Spent Raney nickel
Stripped electrocoatings
Powder
Metal fragments
65%
20%
CaO Fe,OJ SO, Volatile (110%) Zn CU Fe Cr
1%
12% 3% 8% 5% 14% 2% 3.5% 0.5%
CHEMICAL
RECLAIMING
OF NICKEL
SULFA TE PROM NICKEL-BEARING
WASTES
57
sulfate by using stripped electrocoatings as the feed mat,eriel. The major steps are metal separation, nickel dissolution, solution purification and crystallization of nickel sulfate. A simplified flowsheet of the proposed process is given in Fig. 1 which explains the chemical reaction of each step in the process.
SPENT NICKEL
ELECTROCOA.TINGS
CATALYST
(658
Ni)
NaOH 1 ROASTING
SELECTIVE
( 500%)
H20
ZIh’C
DISSOLUTION
1 DIGESTION (100%) WERY ‘__-__--
DISSOLUTION
FILTRATIONLCOPPER
NICKEL
SOLUTION
DlSSOLUTlON
NEUTRALIZATION ( P” 5.0) I
PRECIPITATE
I
$
FILTRAT,O+PREClPlTATE
I I FINAL l---___
-
FILTRATIONL
PURIFICATION ______..:
L
I
SOLUBLES
I--+
AL
CARBONATE
3Ni(OH)
2
#2’NiC03.4~~0
NICKEL
SULFATE
HEXAHYDRATE
d-~i~04~6~20
Fig. 1. Simplified
flow sheet of reclaiming
nickel sulfate
from
FILTRATION
PRECIPITATES
COMME!:
-NICKEL
nickel wastes.
OF
SULFATE -_
_
58
LUNG TSUEN-NI,
LIN JI’NG-CHIE
and HUANG
TEH-CHUNG
Reclaiming nickel as nickel carbonate? from spent catalyst a. Roasting the spent cataIyst with caustic soda. The spent catalyst was first mixed with caustic soda on a weight ratio of 5:l to convert the contained alumina to form water-soluble sodium meta-aluminate. The reaction is, 1.
ALO, + ?LrJ.aOH
500°C
, 2NaAI0,
+ H,O
After roasting, the contained o’;ganic matter was completely removed from the waste material. b. Digestion of roasted cataliyst. Hot water digestion was applied in this step to separate watersoluble sodium meta-aluminate from nickel. The reaction can be represented as: NaA102
+ 2H,O _, ‘Oooc
Na’+
Al(OH);
The nickel was then recovered as solid residue after solid - liquid phase separation. c. Nickel dissolution. The recovered nickel from previous digestion was dissolved in diluted sulfuric acid to obtain a nickel sulfate solution close to its saturation point [4]. The optimum sulfuric acid concent7iation was pre-determined from preliminary testings as 159 gl.-’ The solid/liquid ratio use;d for dissolution was l/5 (w/v). During the dissolution, nitric acid was gradually added to t’ne system to enhance the reaction, as an oxidizer. After filtering, the nickel sulfate solution was collected in a relatively pure state and all insolubles, such as silica, were removed. The nickel concentration in the solution was 112 gl.-’ with 4.8 gl.-’ of Fe as its major impurity. Free acid content in the solution was low and nickel sulfate content was quite close to its saturation point. The solution was further treated to neutralize its excess acid and to precipitate its iron. d. Excess acid neutralization and iron precipitation. The free acid in the unpurified nickel solution must first be neutralized before iron precipitation can take place. This was achieved by adding nickel carbonate to adjust the acidity of the solution to approximately pH 2.0. The nickel carbonate, as a form of 3Ni (OH),. 2NiC0,.4H,O, was obtained from the next step Of the reclamation. Further neutralization was carried on to reach a pH of nearly 5.0 and iron was precipitated from the solution by adding nickel carbonate and a small amount of hydrogen peroxide. The chemical reactions involved in this step are, Excess acid neutralization 3Ni(OH),.2NiC03.4H,0 + 5H,SO, -
5NiS04+
12H20 + 2C0, ?
Iron precipitation lOFeS0, + 5H,O, + 2(3Ni(OH)2.2NiC0,.4H20) lOFe(OH)&+ lONiS0,
+ 4C02
+ 4H,O. t The precipitate, iron hydroxide, was removed by filtering. The purified nickel solution comprised 102 gl-‘Ni, 0.005 gl-‘Fe and had a pH of 5.0 This solution was further processed in the next step for nickel carbonate precipitation. e. Preparation of nickel carbonate. Addition of soda powder into the purified nickel solution caused nickel to be precipitated as 3Ni(OH)z.2NiC03.4H,0. The precipitation was regulated at the pH range of 8.0- 8.2 by controlling the quantity of soda powder addition. The yield, nickel carbonate, was in an easily washed and filtered form. The soluble salts were removed by washing and nickel carbonate was later applied as a neutralizer for nickel solution purification whenever it was needed in the reclamation process. The principal reaction of nickel carbonate precipitation can be written generally as:
CHEMICAL
RECLAIMING
OF NICKEL
SULFATE
FROM
5NiS04 + SNa,CO, + lOH,Op 5Na,S04 + 3Ni(OH),.2NiC0,.4H20
NICKEL-BEARING
WASTES
59
+ 3H,CO,.
2. Reclaiming nickel as nickel sulfate from stripped electrocoatings f. Selective dissolution - zinc removal. The stripped electrocoatings collected from local zinc alloy reclaimers was a multi-metallic waste with zinc, nickel, copper and chromium as its major constituents. Since zinc is relatively more active in dilute sulfuric acid than are other base metals, it can be dissolved selectively in acid to produce zinc sulfate[6]. The initial reaction of zinc dissolution in sulfuric acid is quite strong and is accompanied by effusion of a large volume of hydrogen gas. The reaction is exothermic and usually no external heat is required to maintain the operating temperature. The reaction can be expressed: Zn + 2H+---+
Zn2+ + H, t
+ Heat
The sulfuric acid concentration used in the zinc-dissolving step was 153 gl.-‘H,SO,.The reaction temperature was kept around 77°C by controlling the rate of addition of waste into the acid. The resulting solution contained 140 gl.-‘Zn with a small amount of Cu and Fe. After filtration the solution was further treated to recover zinc sulfate and the residue was treated in the next step. g. Selective dissolution - copper removal. During the zinc dissolution, some of the copper was unavoidably dissolved. Because the copper ion is more reducing than is the nickel ion in an acid solution, most of the dissolved copper was reprecipitated on the surface of the nickel. The copper, undissolved and reciprocated, was eliminated in this step by ammoniacal leaching. The zinc-free waste was treated by addition of ammonia, ammonium sulfate and hydrogen peroxide into the system. The copper combined with ammonia to form the stable cuprammoniumion in this ammonia-oxygen environment. The main reaction taking place may be shown in the following: Cu + 4NH, + VzO, + Hz0 M
(CU(NH,)~)~+ + 20H-.
The dissolution rate of copper was influenced by temperature, oxygen pressure, concentration of reactants and agitation. The dissolution condition was controlled in the pH range of 9- 10 and was accompanied by vigorous mechanical agitation. After filtration, the copper was removed from the system by aqueous solution. h. Nickel dissolution. Nickel is dissolved quite readily in warm or hot sulfuric acid to produce nickel sulfate solution. Since the final solution should have as little free acid as is convenient, it is best to use an excess of nickel waste in the dissolving step. The reaction is exothermic, so no external heat is applied to maintain the operation temperature. The dissolution reaction taking place is, Ni + 2H,S04-
NiSO, + 2H,t.
The treated waste from previous step was almost free of zinc and copper and its nickel content was enriched to 99%. To dissolve nickel, 133gl.-’ sulfuric acid was applied and nitric acid was used to enhance the reaction. The operating temperature was maintained at 90°C - 95°C by the heat generated by the reaction and the time of the reaction depended greatly on the type of agitation. The resulting nickel sulfate solution had a composition of 114 gl.-‘Ni, 0.058 gl.-‘Fe and trace amounts of Zn and Cu. The chromium was unattacked in the operational environment and was eliminated as insolubles by filtration. i. Excess acid neutralization and iron precipitation. In order to prevent corrosion of the
60
LUNG TSUEN-NI, LIN JING-CHIE and HUANG TEH-CHUNG
evaporator and the crystallizer, and in preparation for solution purification, it is necessary to neutralize the residual free acid. At this point it becomes more economical to neutralize the solution to the required degree with nickel carbonate. To achieve this purpose the nickel carbonate produced from spent nickel catalyst was used to neutralize the solution and to precipitate iron. The nickel sulfate solution was neutralized to pH 5. After filtering iron was removed from the solution as precipitate. The iron content in the purified nickel sulfate solution was less than 0.001 gl.-’ and was suitable for nickel sulfate crystallization. j. Evaporation and crystallization. The specific gravity of the purified nickel sulfate solution was around 1.2 with a pH of 5; it was fed to a vacuum evaporator to concentrate the solution by evaporation of water. When the specific gravity of the solution reached 1.50, it was pumped into the crystallizer heated by hot water to recover nickel sulfate crystals. The temperature of crystallization was held at around 45°C to obtain nickel sulfate hexahydrate. The crystals of nickel sulfate hexahydrate were collected by centrifuging, and the mother liquor returned to the crystallizer. The product, a - NiS0,.6H,O, reclaimed from the process contained 22.2% Ni with limited impurities. It may be used for electroplating or in the chemical industry.
OPERATING
FEATURES
All important operating features and results based on the work of pilot scale testing are compiled in Table 2. Additional information concerning the process is given as follows: 1. The spent catalyst roasting was carried out in an electrical heating furnace. If direct gas or oil firing furnace is applied, care must be taken to avoid carbon contamination. 2. For dissolution plastic (polypropylene) vessels were used and agitation provided by air injection or by a circulating pump. Wooden tanks were also quite satisfactory. 3. The vacuum evaporator and crystallizer were constructed in stainless steel (SS 304) and were heated by hot water jackets to maintain the operating temperatures within a certain range. 4. The sulfuric acid must be of low impurity content. 5. Appropriate methods to purify the zinc solution need further work for recovery of zinc sulfate. 6. Another unit operation which may be involved in this process is final purification of the nickel sulfate solution by bubbling H2S to eliminate Zn and Cu as sulfides[5]. This operation is employed only when the impurity content of the solution is too high to crystallize the nickel sulfate and in our experience is not normally necessary. The proposed nickel reclaiming process is relatively straightforward and conventional and presents no unusual engineering problems. The nickel recoveries from the tested spent Raney nickel and stripped electrocastings by the suggested process were 85% and 83% respectively. The reclaimed nickel sulfate hexahydrate is suitable for electroplating purposes. The typical analysis of the reclaimed products and comparison with other market available commodities are given in Table 3.
CONCLUSIONS The information developed through research and testing indicates considerable promise for this chemical reclamation process to recover nickel sulfate from treatment of spent nickel catalyst and stripped electrocoatings. The reclaimed nickel sulfate hexahydrate generally meets the specifications of the electroplating industry and is comparable in quality with the product from commercial manufacturers. The production of commercial nickel carbonate as an intermediate
Electrocoatings (20% Ni) H,SO,, 3Ni(OH),.2NiC0,.4Hz0 (reclaimed)
8. Ni dissolution
9. Neutralization
IO. Evaporation Crystallization
(NH&SO.,
NH,,
7. Cu removal
HNO,
HISO,
Dilute
Hz02
Na,CO,
6. Zn removal
8.2
159 gl:‘,
removed Ni sol”:
3Ni(OH)I.2NiC0,’
Vacuum Evaporation Crystallization 45°C
to Ni I58 gl:’
o
85%
83%
Ni sol”: Ni 80 gl:‘, Ni recovery
& purified NiS0,.6H20,
Fe removed Neutralized
97% Ni dissolved Ni sol”: Ni 114 gl:‘,
Ni recovery
Fe 0.058 gl:
4H,O,
Zn removed Z” sol”: Z” 140 gl.?
99%
H,SO, 133 gl:‘, HNO, 23 gl.? S/L = l/9 (w/v), 94°C PH 5
Ni 112 gl.-‘, Fe 4.X gl.?
.._
Fe 0.001 gl:’
Fe removed Neu. & pur. Ni sol”: Ni 102 gl:’ Fe 0.005 gl:’
87% Ni dissolved,
98% Al,O,
87% Cu removed
40 gl:’
removed
result
organic
Typical kll
NH, 13 gl:‘, (NH&SO, 33 gl:‘, H,O, 13 gl:‘, S/L = l/25 (w/v) pH 9.0- 10.0
77°C
HNO,
500°C
Processing = l/5,
H,SO, 153 gl.-’ S/L = l/4 (w/v),
pH 8.0-
3Ni(OH),.2NiC0,.4Hz0 (reclaimed)
4. Neutralization
(65% Ni) pprn
PH 5
HNO,
H,SO,,
3. Ni dissolution
5. NiCO,
H,SO,
Hot Hz0
2. Digestion 100°C
Condition NaOH/waste
used
NaOH
Chemical
and results of nickel salts reclamation
1. Roasting
step
conditions
Catalyst
Waste
Table 2. Processing
z
LUNG TSUEN-NI, LIN JING-CHIE and HUANG TEH-CHUNG
62
Table 3. Typical analysis of nickel sulfate
Product
Form
Impurity (070)
Nickel content (Q)
Fe
cu
+Co, 22.0-22.4
<0.002
90.001
_
Zn
Pb
60.002
Selnic “Kanigen grade” (France)
NiS0,.6H,O
Into “Incomond” (Australia)
NiS0,.6H,O
Reclaimed “A” (With H,S purification)
NiS0,.6H,O
22.2
<0.002
tr.
Reclaimed “B” (Without H,S purification)
NiSO,*6H,O
22.2
0.1
tr.
+co,
22.20
0.001
o.ooo5
product was designed for processing uses, but it can be sold for electroplating as a pH conditioner too. The process is relatively simple and no special equipment or reagent is needed. Since the nickelbearing wastes studied, i.e. spent nickel catalysts and electrocoatings, are not available in large amounts, at least in developing countries such as Taiwan, it may be suitable for small scale commercial operations. The advantages of the process are as follows: 1. Only common chemicals and ordinary equipment are needed and no unusual engineering problem is involved with the process. 2. The process is quite flexible. It can be applied to reclaim nickel from other suitable wastes and scraps. It also can be converted for production of nickel chloride and nitrate with similar unit operations. 3. Capital investment is low and existing chemical plants can handle or adopt this process without any special difficulties. The processing concepts developed in this study could be further carried on to estimate economic criteria such as market prices of the waste materials and/or primary nickel sulfate.
REFERENCES 1. 2. 3. 4. 5. 6.
NARI, Recyling Nickel Alloys and Stainless Steel Scrap. National Association of Recycling Industries, New York. R. T. Brooks, G. M. Potter and D. A. Martin, Chemical Reclaiming of Superalloy Scrap. Bureau of Mines RI 7316, New York (1969). A. A. Cochran and L. C. George, The waste-plus-waste process for recovering metals from electroplating and other wastes. Plating Surface Fin., July, 38 - 43 (1976). C. I. Spostrolidis and P. A. Distin, The kinetics of the sulfuric acid leaching of nickel and magnesium from reduction roasted serpentine. Hydrometallurgy 3, 181 - 196 (1978). L. V. Muro, Method of Purifying Crude Nickel Sulfate. U.S. Patent 2959465 (1960). J. J. Moore, Recycling of non-ferrous metals. Int. Metals Rev. 5, 241-264 (1978).
& Recycling,
Vol. 6, No.
I/2,
pp. 55
62, 1983
0361
in Great Britain
CHEMICAL
36!8/83
$3 011t
Pergamon
Pm\
.Gfl I.ld
RECLAIMING OF NICKEL SULFATE FROM NICKEL-BEARING WASTES
LUNG TSUEN-NI,
LIN JING-CHIE
Mining Research
and HUANG TEH-CHUNG
and Service Organization,
Republic
of China
Abstract - Two types of nickel-bearing wastes, spent Raney nickel (65% Ni) and segregated electroplated coatings (20% Ni), were used in this nickel reclaiming process study for nickel sulfate recovery. The spent catalyst from the petrochemical industry was first roasted with caustic soda at 500°C to convert its alumina to water-soluble aluminate. The nickel was then reclaimed as residue by simple water digestion to remove the aluminate. The nickel recovered was relatively pure and was used to prepare nickel carbonate, which was later applied in the process as a neutralizer to purify the nickel sulfate solution obtained from chemical processing of segregated electrocoatings. The coatings were derived from obsolete components of plated zinc die castings, after most of the zinc had been reclaimed by remelting. The coatings were further treated to separate zinc and copper from the nickel by selective dissolution. The nickel left was then dissolved in sulfuric acid to produce nickel sulfate solution. Before crystallisation, the solution was further treated with nickel carbonate recovered from spent catalyst to neutralize the excess acid and to precipitate the iron. The nickel salt reclaimed was an a form nickel sulfate hexahydrate (a - NiS0.,.6HIO) and may be used for chemical and electroplating purposes. The experimental results of pilot testing in the reclaiming process are sufficiently encouraging for further development to commercial application to take place.
INTRODUCTION Nickel has many uses in industry, mainly as an alloying element in the manufacture of stainless steels, nickel alloys and superalloys. Most of the nickel scraps now recycled by industry are recovered principally as alloys from scrapped stainless steels and nickel alloys[ 1,2]. Of the scrap recycled, 50% is estimated to be prompt industrial, and 50% obsolete[l]. Other secondary nickel resources are much less extensively recycled by the industry mainly because of their relatively small quantities and diversified uses. However the rapid increase in world consumption of nickel dictates a reassessment of the less economically-attractive secondary sources of nickel[3]. In this category, spent nickel catalysts and nickel electrodeposits from defective or obsolete parts are only two of the examples under consideration in this study. The copper - nickel - chromium system is the most commonly used electroplating system on zinc die castings. The nickel deposited on the copper provides most of the corrosion resistance of the coating on the zinc products. The increasing use of plated zinc die casting parts in car manufacture proves it is worthwhile to carry out a study on reclamation of nickel from segregated auto shredder rejects. By the technology of auto shredding, it is easy to separate obsolete zinc die castings from other metallic and non-metallic materials. The electrodeposits can easily be separated from the zinc by melting off the zinc alloy in low-temperature furnace operations. Owing to the difficulties of reprocessing, the stripped coatings are generally discarded as a waste, at least in places like Taiwan where adequate nickel resmelting facilities do not exist. One of the major purposes of this study is to try to develop a chemical process to reclaim the nickel, as its salts, from the stripped coatings by a hydrometallurgical route. Another nickel-bearing waste available in substantial quantities in Taiwan is spent nickel catalyst. Raney nickel is a commonly-used catalyst in many chemical processes in the petrochemical and fertilizer industries for different purposes. After a certain time in service, the nickel catalysts are spent but are essentially unaltered in primitive nature and quantity. If compared with other nickel-bearing sludges or wastes, spent nickel catalysts are easy to collect and normally have a high nickel content[3]. These properties make it relatively easy to reprocess them to reclaim nickel as nickel 55
56
LUNG TSUEN-NI, LIN JING-CHIE and HUANG TEH-CHUNG
salts. In this study the nickel is recovered as commercial nickel carbonate (3Ni(OH),.2NiC03*4H20) which can be used as a neutralizer for pH adjustment in processing, or for sale. These two above-mentioned nickel-bearing wastes are considered attractive secondary sources of nickel for reclamation purposes in the local market of Taiwan, The nickel salt reclaimed from the combined treatment of these two wastes is an a form nickel sulfate hexahydrate (a - NiS0,.6H20). This is a readily marketable form of nickel salt and it can be used by chemical or electroplating industries. The flowsheet of the chemical reclaiming is relatively simple and no special equipment is necessary. The experimental results of pilot testing in the process are encouraging for further development to commercial application.
WASTE MATERIALS Two different types of nickel-bearing waste were used in this nickel reclaiming study. The first one was the powder-form spent Raney nickel supplied by local petrochemical plants. The waste catalyst contained 65% nickel with 30% oxides and a small amount of constrained organics. Because of its relatively high nickel content, the spent catalyst was used to make nickel carbonate for pH conditioning whenever necessary during processing. Another nickel-bearing waste was from local zinc die casting scrap remelters after zinc foundry alloy had been reclaimed by remelting operations. The remelting extracted the alloy and left the multi-metallic electrocoatings as an unmelted residue which could be collected after completion of the operation. The recovered multi-metallic coatings consisted of different size metal fragments with a nickel content of 20% and balanced by zinc and other metals. The shape of the coatings was irregular, with a length ranging from a few cm to 20 cm in which its origin can still be identified as scrapped automobiles. This material was used to recover nickel as nickel sulfate. The chemical composition of the waste materials used in this study is given in Table 1.
THE RECLAIMING
PROCESS
The nickel reclamation process can be divided into two parts, each consisting of several steps. The first part of the processing is manufacturing nickel carbonate from the spent Raney nickel. The carbonate is later used as a neutralizer for solution purification in the process. In the preparation of nickel carbonate, the major steps are roasting, digestion, dissolution, neutralization and precipitation of nickel carbonate. The second part of the processing is production of nickel Table 1. Chemical analysis of the nickel wastes Waste material
Type
Nickel content
Other constituents AL03
Spent Raney nickel
Stripped electrocoatings
Powder
Metal fragments
65%
20%
CaO Fe,OJ SO, Volatile (110%) Zn CU Fe Cr
1%
12% 3% 8% 5% 14% 2% 3.5% 0.5%
CHEMICAL
RECLAIMING
OF NICKEL
SULFA TE PROM NICKEL-BEARING
WASTES
57
sulfate by using stripped electrocoatings as the feed mat,eriel. The major steps are metal separation, nickel dissolution, solution purification and crystallization of nickel sulfate. A simplified flowsheet of the proposed process is given in Fig. 1 which explains the chemical reaction of each step in the process.
SPENT NICKEL
ELECTROCOA.TINGS
CATALYST
(658
Ni)
NaOH 1 ROASTING
SELECTIVE
( 500%)
H20
ZIh’C
DISSOLUTION
1 DIGESTION (100%) WERY ‘__-__--
DISSOLUTION
FILTRATIONLCOPPER
NICKEL
SOLUTION
DlSSOLUTlON
NEUTRALIZATION ( P” 5.0) I
PRECIPITATE
I
$
FILTRAT,O+PREClPlTATE
I I FINAL l---___
-
FILTRATIONL
PURIFICATION ______..:
L
I
SOLUBLES
I--+
AL
CARBONATE
3Ni(OH)
2
#2’NiC03.4~~0
NICKEL
SULFATE
HEXAHYDRATE
d-~i~04~6~20
Fig. 1. Simplified
flow sheet of reclaiming
nickel sulfate
from
FILTRATION
PRECIPITATES
COMME!:
-NICKEL
nickel wastes.
OF
SULFATE -_
_
58
LUNG TSUEN-NI,
LIN JI’NG-CHIE
and HUANG
TEH-CHUNG
Reclaiming nickel as nickel carbonate? from spent catalyst a. Roasting the spent cataIyst with caustic soda. The spent catalyst was first mixed with caustic soda on a weight ratio of 5:l to convert the contained alumina to form water-soluble sodium meta-aluminate. The reaction is, 1.
ALO, + ?LrJ.aOH
500°C
, 2NaAI0,
+ H,O
After roasting, the contained o’;ganic matter was completely removed from the waste material. b. Digestion of roasted cataliyst. Hot water digestion was applied in this step to separate watersoluble sodium meta-aluminate from nickel. The reaction can be represented as: NaA102
+ 2H,O _, ‘Oooc
Na’+
Al(OH);
The nickel was then recovered as solid residue after solid - liquid phase separation. c. Nickel dissolution. The recovered nickel from previous digestion was dissolved in diluted sulfuric acid to obtain a nickel sulfate solution close to its saturation point [4]. The optimum sulfuric acid concent7iation was pre-determined from preliminary testings as 159 gl.-’ The solid/liquid ratio use;d for dissolution was l/5 (w/v). During the dissolution, nitric acid was gradually added to t’ne system to enhance the reaction, as an oxidizer. After filtering, the nickel sulfate solution was collected in a relatively pure state and all insolubles, such as silica, were removed. The nickel concentration in the solution was 112 gl.-’ with 4.8 gl.-’ of Fe as its major impurity. Free acid content in the solution was low and nickel sulfate content was quite close to its saturation point. The solution was further treated to neutralize its excess acid and to precipitate its iron. d. Excess acid neutralization and iron precipitation. The free acid in the unpurified nickel solution must first be neutralized before iron precipitation can take place. This was achieved by adding nickel carbonate to adjust the acidity of the solution to approximately pH 2.0. The nickel carbonate, as a form of 3Ni (OH),. 2NiC0,.4H,O, was obtained from the next step Of the reclamation. Further neutralization was carried on to reach a pH of nearly 5.0 and iron was precipitated from the solution by adding nickel carbonate and a small amount of hydrogen peroxide. The chemical reactions involved in this step are, Excess acid neutralization 3Ni(OH),.2NiC03.4H,0 + 5H,SO, -
5NiS04+
12H20 + 2C0, ?
Iron precipitation lOFeS0, + 5H,O, + 2(3Ni(OH)2.2NiC0,.4H20) lOFe(OH)&+ lONiS0,
+ 4C02
+ 4H,O. t The precipitate, iron hydroxide, was removed by filtering. The purified nickel solution comprised 102 gl-‘Ni, 0.005 gl-‘Fe and had a pH of 5.0 This solution was further processed in the next step for nickel carbonate precipitation. e. Preparation of nickel carbonate. Addition of soda powder into the purified nickel solution caused nickel to be precipitated as 3Ni(OH)z.2NiC03.4H,0. The precipitation was regulated at the pH range of 8.0- 8.2 by controlling the quantity of soda powder addition. The yield, nickel carbonate, was in an easily washed and filtered form. The soluble salts were removed by washing and nickel carbonate was later applied as a neutralizer for nickel solution purification whenever it was needed in the reclamation process. The principal reaction of nickel carbonate precipitation can be written generally as:
CHEMICAL
RECLAIMING
OF NICKEL
SULFATE
FROM
5NiS04 + SNa,CO, + lOH,Op 5Na,S04 + 3Ni(OH),.2NiC0,.4H20
NICKEL-BEARING
WASTES
59
+ 3H,CO,.
2. Reclaiming nickel as nickel sulfate from stripped electrocoatings f. Selective dissolution - zinc removal. The stripped electrocoatings collected from local zinc alloy reclaimers was a multi-metallic waste with zinc, nickel, copper and chromium as its major constituents. Since zinc is relatively more active in dilute sulfuric acid than are other base metals, it can be dissolved selectively in acid to produce zinc sulfate[6]. The initial reaction of zinc dissolution in sulfuric acid is quite strong and is accompanied by effusion of a large volume of hydrogen gas. The reaction is exothermic and usually no external heat is required to maintain the operating temperature. The reaction can be expressed: Zn + 2H+---+
Zn2+ + H, t
+ Heat
The sulfuric acid concentration used in the zinc-dissolving step was 153 gl.-‘H,SO,.The reaction temperature was kept around 77°C by controlling the rate of addition of waste into the acid. The resulting solution contained 140 gl.-‘Zn with a small amount of Cu and Fe. After filtration the solution was further treated to recover zinc sulfate and the residue was treated in the next step. g. Selective dissolution - copper removal. During the zinc dissolution, some of the copper was unavoidably dissolved. Because the copper ion is more reducing than is the nickel ion in an acid solution, most of the dissolved copper was reprecipitated on the surface of the nickel. The copper, undissolved and reciprocated, was eliminated in this step by ammoniacal leaching. The zinc-free waste was treated by addition of ammonia, ammonium sulfate and hydrogen peroxide into the system. The copper combined with ammonia to form the stable cuprammoniumion in this ammonia-oxygen environment. The main reaction taking place may be shown in the following: Cu + 4NH, + VzO, + Hz0 M
(CU(NH,)~)~+ + 20H-.
The dissolution rate of copper was influenced by temperature, oxygen pressure, concentration of reactants and agitation. The dissolution condition was controlled in the pH range of 9- 10 and was accompanied by vigorous mechanical agitation. After filtration, the copper was removed from the system by aqueous solution. h. Nickel dissolution. Nickel is dissolved quite readily in warm or hot sulfuric acid to produce nickel sulfate solution. Since the final solution should have as little free acid as is convenient, it is best to use an excess of nickel waste in the dissolving step. The reaction is exothermic, so no external heat is applied to maintain the operation temperature. The dissolution reaction taking place is, Ni + 2H,S04-
NiSO, + 2H,t.
The treated waste from previous step was almost free of zinc and copper and its nickel content was enriched to 99%. To dissolve nickel, 133gl.-’ sulfuric acid was applied and nitric acid was used to enhance the reaction. The operating temperature was maintained at 90°C - 95°C by the heat generated by the reaction and the time of the reaction depended greatly on the type of agitation. The resulting nickel sulfate solution had a composition of 114 gl.-‘Ni, 0.058 gl.-‘Fe and trace amounts of Zn and Cu. The chromium was unattacked in the operational environment and was eliminated as insolubles by filtration. i. Excess acid neutralization and iron precipitation. In order to prevent corrosion of the
60
LUNG TSUEN-NI, LIN JING-CHIE and HUANG TEH-CHUNG
evaporator and the crystallizer, and in preparation for solution purification, it is necessary to neutralize the residual free acid. At this point it becomes more economical to neutralize the solution to the required degree with nickel carbonate. To achieve this purpose the nickel carbonate produced from spent nickel catalyst was used to neutralize the solution and to precipitate iron. The nickel sulfate solution was neutralized to pH 5. After filtering iron was removed from the solution as precipitate. The iron content in the purified nickel sulfate solution was less than 0.001 gl.-’ and was suitable for nickel sulfate crystallization. j. Evaporation and crystallization. The specific gravity of the purified nickel sulfate solution was around 1.2 with a pH of 5; it was fed to a vacuum evaporator to concentrate the solution by evaporation of water. When the specific gravity of the solution reached 1.50, it was pumped into the crystallizer heated by hot water to recover nickel sulfate crystals. The temperature of crystallization was held at around 45°C to obtain nickel sulfate hexahydrate. The crystals of nickel sulfate hexahydrate were collected by centrifuging, and the mother liquor returned to the crystallizer. The product, a - NiS0,.6H,O, reclaimed from the process contained 22.2% Ni with limited impurities. It may be used for electroplating or in the chemical industry.
OPERATING
FEATURES
All important operating features and results based on the work of pilot scale testing are compiled in Table 2. Additional information concerning the process is given as follows: 1. The spent catalyst roasting was carried out in an electrical heating furnace. If direct gas or oil firing furnace is applied, care must be taken to avoid carbon contamination. 2. For dissolution plastic (polypropylene) vessels were used and agitation provided by air injection or by a circulating pump. Wooden tanks were also quite satisfactory. 3. The vacuum evaporator and crystallizer were constructed in stainless steel (SS 304) and were heated by hot water jackets to maintain the operating temperatures within a certain range. 4. The sulfuric acid must be of low impurity content. 5. Appropriate methods to purify the zinc solution need further work for recovery of zinc sulfate. 6. Another unit operation which may be involved in this process is final purification of the nickel sulfate solution by bubbling H2S to eliminate Zn and Cu as sulfides[5]. This operation is employed only when the impurity content of the solution is too high to crystallize the nickel sulfate and in our experience is not normally necessary. The proposed nickel reclaiming process is relatively straightforward and conventional and presents no unusual engineering problems. The nickel recoveries from the tested spent Raney nickel and stripped electrocastings by the suggested process were 85% and 83% respectively. The reclaimed nickel sulfate hexahydrate is suitable for electroplating purposes. The typical analysis of the reclaimed products and comparison with other market available commodities are given in Table 3.
CONCLUSIONS The information developed through research and testing indicates considerable promise for this chemical reclamation process to recover nickel sulfate from treatment of spent nickel catalyst and stripped electrocoatings. The reclaimed nickel sulfate hexahydrate generally meets the specifications of the electroplating industry and is comparable in quality with the product from commercial manufacturers. The production of commercial nickel carbonate as an intermediate
Electrocoatings (20% Ni) H,SO,, 3Ni(OH),.2NiC0,.4Hz0 (reclaimed)
8. Ni dissolution
9. Neutralization
IO. Evaporation Crystallization
(NH&SO.,
NH,,
7. Cu removal
HNO,
HISO,
Dilute
Hz02
Na,CO,
6. Zn removal
8.2
159 gl:‘,
removed Ni sol”:
3Ni(OH)I.2NiC0,’
Vacuum Evaporation Crystallization 45°C
to Ni I58 gl:’
o
85%
83%
Ni sol”: Ni 80 gl:‘, Ni recovery
& purified NiS0,.6H20,
Fe removed Neutralized
97% Ni dissolved Ni sol”: Ni 114 gl:‘,
Ni recovery
Fe 0.058 gl:
4H,O,
Zn removed Z” sol”: Z” 140 gl.?
99%
H,SO, 133 gl:‘, HNO, 23 gl.? S/L = l/9 (w/v), 94°C PH 5
Ni 112 gl.-‘, Fe 4.X gl.?
.._
Fe 0.001 gl:’
Fe removed Neu. & pur. Ni sol”: Ni 102 gl:’ Fe 0.005 gl:’
87% Ni dissolved,
98% Al,O,
87% Cu removed
40 gl:’
removed
result
organic
Typical kll
NH, 13 gl:‘, (NH&SO, 33 gl:‘, H,O, 13 gl:‘, S/L = l/25 (w/v) pH 9.0- 10.0
77°C
HNO,
500°C
Processing = l/5,
H,SO, 153 gl.-’ S/L = l/4 (w/v),
pH 8.0-
3Ni(OH),.2NiC0,.4Hz0 (reclaimed)
4. Neutralization
(65% Ni) pprn
PH 5
HNO,
H,SO,,
3. Ni dissolution
5. NiCO,
H,SO,
Hot Hz0
2. Digestion 100°C
Condition NaOH/waste
used
NaOH
Chemical
and results of nickel salts reclamation
1. Roasting
step
conditions
Catalyst
Waste
Table 2. Processing
z
LUNG TSUEN-NI, LIN JING-CHIE and HUANG TEH-CHUNG
62
Table 3. Typical analysis of nickel sulfate
Product
Form
Impurity (070)
Nickel content (Q)
Fe
cu
+Co, 22.0-22.4
<0.002
90.001
_
Zn
Pb
60.002
Selnic “Kanigen grade” (France)
NiS0,.6H,O
Into “Incomond” (Australia)
NiS0,.6H,O
Reclaimed “A” (With H,S purification)
NiS0,.6H,O
22.2
<0.002
tr.
Reclaimed “B” (Without H,S purification)
NiSO,*6H,O
22.2
0.1
tr.
+co,
22.20
0.001
o.ooo5
product was designed for processing uses, but it can be sold for electroplating as a pH conditioner too. The process is relatively simple and no special equipment or reagent is needed. Since the nickelbearing wastes studied, i.e. spent nickel catalysts and electrocoatings, are not available in large amounts, at least in developing countries such as Taiwan, it may be suitable for small scale commercial operations. The advantages of the process are as follows: 1. Only common chemicals and ordinary equipment are needed and no unusual engineering problem is involved with the process. 2. The process is quite flexible. It can be applied to reclaim nickel from other suitable wastes and scraps. It also can be converted for production of nickel chloride and nitrate with similar unit operations. 3. Capital investment is low and existing chemical plants can handle or adopt this process without any special difficulties. The processing concepts developed in this study could be further carried on to estimate economic criteria such as market prices of the waste materials and/or primary nickel sulfate.
REFERENCES 1. 2. 3. 4. 5. 6.
NARI, Recyling Nickel Alloys and Stainless Steel Scrap. National Association of Recycling Industries, New York. R. T. Brooks, G. M. Potter and D. A. Martin, Chemical Reclaiming of Superalloy Scrap. Bureau of Mines RI 7316, New York (1969). A. A. Cochran and L. C. George, The waste-plus-waste process for recovering metals from electroplating and other wastes. Plating Surface Fin., July, 38 - 43 (1976). C. I. Spostrolidis and P. A. Distin, The kinetics of the sulfuric acid leaching of nickel and magnesium from reduction roasted serpentine. Hydrometallurgy 3, 181 - 196 (1978). L. V. Muro, Method of Purifying Crude Nickel Sulfate. U.S. Patent 2959465 (1960). J. J. Moore, Recycling of non-ferrous metals. Int. Metals Rev. 5, 241-264 (1978).