FIELD OF INVENTION
The present invention relates to a process for recovery of transition metal from spent catalyst
by chelation technology using EDTA as chelating agent.
BACKGROUND AM) PRIOR ART
The use of metals has increased considerably over years in fertilizer industry due to their
importance as valuable intermediate as catalysts. Heavy metals such as nickel, cobalt,
molybdenum, vanadium, chromium etc. supported on alumina doped with other metals (Ca,
K etc.) as promoters are frequently used in different forms viz. hydrodesulphurization
catalyst, steam reforming catalyst, water gas shift catalyst etc. After a definite period of use,
these catalysts get deactivated. The three most common cause of deactivation are fouling,
poisoning and thermal degradation or sintering. Fouling involves deposition of material on
the catalyst surface to block active sites. Coke deposition is the most common process but the
deposition of rust and scale from elsewhere is not uncommon. Poisoning involves strong
interaction between a component of feed or product and active sites of the catalyst. The
poison involves molecules that can chemisorb strongly to a catalyst and are entirely specific.
Sulphur poisoning of metals is most widely quoted example. Catalyst overheating often leads
to loss of surface area and to unwanted chemical reactions and also, to rearrangement of most
solids especially in oxide form. The formation of nickel aluminates from the reaction between
nickel and alumina is a good example of phase change, as the catalytic activity of the nickel
aluminates is virtually non-existent.
After the deactivation of the catalyst, they are usually discarded as solid wastes. The quantity
of spent catalyst discharged from different processing unit depends largely on the amount of
fresh catalyst used, their life and the deposits formed on them. The volume of spent catalyst
discarded as solid waste has increased significantly due to a steady increase in the processing
and manufacturing of heavier feed stocks containing sulphur nitrogen and metal contents.
Environmental laws concerning the spent catalyst disposal have been increasingly more
severe in recent years. Spent catalysts have been classified as hazardous waste by the
Environmental Protection Agency (EPA) in USA. The most important characteristics of spent
catalyst are their toxic nature due to presence of heavy metals viz. Ni, Cr, Mo, Co, V etc.
These metals present in the catalyst can be leached by water after their disposal and pollute
the environment. The hazardous nature of spent catalyst is attracting the attention of
*environmental authorities globally and the user industries of the catalysts are experiencing
pressures from pollution control bodies for safe disposal of spent catalyst. Several alternative
methods such as safe disposal in land fills, reclamation of metals, regenerationlrejuvenation
and reuse, and utilization as raw material to produce other useful products are available to
deal with spent catalyst problem. The choice between these options depends on technical
feasibility and economic considerations.
The common adopted methods for metal recovery from spent catalyst are acid leaching
(hydrometallurgical routes), salt roasting, electrolysis (pyrometallurgical routes) and
bioleaching.
Ivascanu and Roman (Ivascanu St., Roman O., Bullnst Politech lasi Sect 2, 1975; 2 (21):
47) studied the recovery of Nickel from spent catalyst from an ammonia plant by leaching it
in H2S04 solution. 90% 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 mm in at 70°C. Chandhary et al. (Chandhary, J, Donaldson, I. D, Boddingtons, S. C,
Grimes, S. M.; Heavy Metal in the Environment. Part 11: A (1993) 34:137) studied the
leaching of the low grade spent catalyst with hydrochloric acid and obtained about 18%
recovery of nickel.
A1 Mansi and Abdel Monet (Waste Management. 22 (2002), 85-90) studied the extraction
of nickel from Egyptian spent catalyst. They crushed and screened the spent catalyst to obtain
the required particle size. In each experiment, Ig catalyst was added to a certain amount of
H2S04 of specified concentration (10-90%), temperature (20-120°C), reaction time (1-5
hours), solid liquid ratio(lll2, 116, 113, 112, 111, and 2/3), particle size (>2000, 800-2000,
<500 micron) and stirring speed (100-1400 rpm) was adjusted. The reaction took place in a
sealed container and the resulting slurry was filtered on sintered glass. AAS was used for the
determination of nickel concentration. Nickel was recovered as a sulfate salt by direct
crystallization method. The conversion was 99% at 50% sulfuric acid concentration at a solid:
liquid ratio (1 : 12) by weight with particle size less than 500 micron for more than 5 h and 800
rpm at I00 degrees C.
Deepak J. Garole and A. D. Sawant (73rd Annual Conference of Indian Council of
Chemist, 2005) had investigated the leaching of aluminum and nickel from spent catalyst
(NiO/AI2O3) with caustic soda and aqua regia. They added 100 gram of spent catalyst, the
* agitated caustic soda solution (200ml) of the required concentration (5-25%), Aqua Regia
(80-loo%), temperature (60- 100°C), solid liquid ratio(0.3-1) and time of leaching (0.5h -
2.5h). The leached solution was filtered and the aluminum was dissolved into sodium
aluminate and pH was adjusted to 5-5.5 by adding dilute sulfuric acid. Aluminum
precipitated as aluminum hydroxide, which was converted into its oxide. The residue left
after removal of aluminum 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 H202 and Na2C03 and pH was adjusted
to 5-5.5 AIIFe precipitates its hydroxide and is removed by filtration. Then the pH was
adjusted at 6.5 by adding NaFIHF to precipitate Mg in order to obtained nickel sulfate
solution. The precipitate was later converted into carbonate by adding Na2C03. 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).
Sahu et al (K. K. Sahu, A. Agrawal B. D. Pandey, Waste Management & Research. 23,2005,
1-7) developed a process for Nickel recovery from spent catalyst of definite composition
from fertilizer industry. The process includes direct sulfuric acid leaching followed by
separation of iron as-well-as silica and other impurities. For a 152 pm particle size catalyst,
extraction of about 98% nickel was achieved at 363k in 2h using sulfuric acid concentration
(v/v) of 80% and a pulp density of 10%. The dissolution of Nickel, followed diffusioncontrolled
leaching kinetics. Increase in temperature and sulfuric acid concentration resulted
in increase in the nickel recovery. The activation energy of nickel dissolution was calculated
to be 62.8kJ mol. Nickel was recovered as value added products such as sulfide and oxalate
with over all recovery of 90% and 88% of nickel respectively.
Y.Chen et a1 (Yumn Chen, Qiming Feng, Yanhai Shao, Guofan Zhang Leming Ou, Yiping
Lu, 2005, Mineral Engineering) extracted metals and other products from spent catalyst (Ni
4.77%, Co 0.35%, Mo 0.48%~V~ 0 .55% and Alumina 70.95%). The process involves mixing
the catalyst and alkali, followed by roasting and dissolution in water, leading to the formation
of nickel aluminate solution. The nickel and cobalt concentrate after filtration is leached with
30% (wlw) sulphuric acid, solid liquid ratio 1 :8, temperature 80°C and stirring velocity at 800
rpm. The reaction time for the leaching of Ni-Co concentrate was 4 hours. The reaction was
carried out in a sealed container and the resulting slurry was filtered in a sintered glass. The
recovery of the alumina was upto 90.6% having 99.9% purity. With barium hydroxide and
@barium aluminate, the precipitation rate of Vanadium and Molybdenum is about 94.8% and
92.6% respectively. The Ni-Co concentrate was leached by H2S04 a nickel recovery of
98.2% and over 98.5 %Cobalt recovery was obtained.
Y.D. Lai et at (Y.D.Lai and J.C. Liu, 1997, Journal of Hazardous Materials, 53, 213-224)
studies the effect of pH and reduction potential on the leaching behavior of Ni and V from the
spent catalyst (10 g) of spent catalyst using 150 cm3 of 0.05 N NaN03, aqueous solution were
put into a 250 cm3 polyethylene bottle; the pH was adjusted with IN NaOH and 1N HN03,
and the suspension then placed on a shaker. After shaking for 48h, the pH was measured and
the suspension then filtered and concentration of Ni and V determined by atomic absorption
spectroscopy. In the second experiment, spent catalyst suspension was equilibrated under
controlled redox potential and pH conditions. The automatic pH/redox control apparatus
allowed either oxygen or nitrogen to flow into the reactor to adjust the redox potential to the
preset value. Meanwhile, IN HN03, and IN NaOH aqueous solution were automatically
pumped into the spent catalyst suspension to maintain the pH at the preset value. Both
slightly acidic (pH 5.0) and slightly alkaline (pH 8.0) conditions were chosen for
investigation. The amount of metal leached under acidic conditions (pH 5.0) and six different
redox potentials (-100, 0, 100, 250, 330, 400 mV) was first investigated. Additionally, the
leaching of metals under slightly alkaline conditions (pH 8.0) and seven different redox
potentials (- 330, -300, - 200, - 100, 0, 150, 250 mV) was also examined. Since - 330 mV was
the lowest achievable redox potential by nitrogen bubbling, sodium thioglycollate was added
to decrease the redox potential further. The solubilizing effect of sodium thioglycollate on Ni
and V through complexation was calculated on the basis of stability constants and proved to
be negligible.
The sequential extraction showed that residual and exchangeable fraction constituted the
majority of Ni, whereas Fe-Mn oxide-bound V was the dominant portion. Fractionation is
believed to effect the leaching of Ni and V. Ni solubility was negligible when the pH was
higher than 6.0. Minimum solubility was found for V in the pH range of 4.0-8.0. The leached
concentrations of Ni and V were about 460 and 70 mg kg-', respectively, under continuous
nitrogen aeration. Neither was significantly affected by redox potential. No systematic pattern
was found for Ni leaching at pH 5.0 and various redox potentials. The leaching of V
increased with decreasing redox potential.
* B. B. Kar et al (B. B. Kar, B. V. R. Murthy and V. N. Misra, Regional Research Laboratory
Bhubaneshwar, India: International Journal of Mineral Processing. 76, 2005, 143-147)
investigated the technology for recycling spent AI2O3 based hydro refining catalyst by
roasting- extraction method. Spent hydro-refining catalysts mainly consists of 20-22%
Moo3, 5-696 NiO, 4-5%, 1-2% Co304, 1.3-1.5% Fez03, 3--4% Si02 and the balance is
A1203. The, roasting of molybdenum spent catalyst with sodium chloride at 900°C leads to
the formation of sodium molybdate. The sodium molybdate was further purified by chemical
treatment to obtain a pure grade molybdenum trioxide. For salt-roasting, the NaCl used was
of analytical grade. The charge composed of a weighed amount of spent catalyst and sodium
chloride. This charge was kept in a crucible and heated gradually in a crab-like furnace to a
predetermined temperature. The roasted mass was then cooled inside the furnace and also to
room temperature. The calcined mass was then leached in deionized water with pulp density
of 20 wt.% at 70-90°C for 60 mm to extract water-soluble sodium molybdate. The amount of
molybdenum recovered as Na2Mo04 was determined by the volumetric oxime method. Under
optimum experimental conditions, i.e., roasting temperature at 900°C, 20 wt.% addition of
NaCl to the feed and a roasting period of 10 min, it is possible to extract up to 90% of
molybdenum from hydro-refining spent catalyst.
Heavy metals can also be remediated from contaminated soil and water by using chelating
agents where the extent of contamination is of the order of ppm and ppb. The chelating
agents such as EDTA, DTPA etc. extract the metal from the contaminated sample. They
immobilize the metal by complexation (Chelation). The chelating agents have an advantage
of low biodegradability in ground water and high level of complexing capacity with respect
to heavy metals. In addition to this, the use of EDTA in the extraction process is supposed to
be an environmentally friendly technique. EDTA is the most versatile synthetic chelating
agent used for the metal remediation from metal contaminated soil. It is an effective,
recoverable and reusable chelating agent that could be used for full scale application. Many
researchers used EDTA for extracting a high percentage of Pb and Cd from contaminated
soils (Steele, M.C., Pichtel, J., 1998. J. Environ. Eng. 124, 639-645.; Papassiopi, N.,
Tambouris, S., Kontopoulos, A., 1999. Water, Air, Soil Pollut. 109. 1-15.: Garrabrants,
A.C.. Kosson, D.S., 2000. Waste Manage. 20, 155-165.; Kim, C.S., Ong, S.K., 2000. Pract.
Period. Haz., Toxic Radioact. Waste Manage. 4, 16-23.; Wasay, S.A., Barrington, S.,
Tokunaga, 5., 2001. Water Air Soil Pollut. 127, 301- 314.). Earlier a problem associated
with the EDTA usage was it has to be destroyed before discharge. The chelate is regarded as
j n o n biodegradable and can be found in sewage effluent and well accumulated in ground as
well as surface water (Bergers, P.J.M., de Groot, A.C., 1994. Water Res. 28. 639-642.. Kari.
F.G., Giger. W., 1996. Water Res. 30, 122-1 34.). However commercial EDTA is very
expensive and such forms of remediation are not very economical.
Previous work have reported three possible techniques to recover and regenerate EDTA. The
first method involves electrochemical reduction of Metal-EDTA complex in which metal ions
are reduced on the cathode surface while EDTA is released into the solution and isolated
from the anode using cation exchange membrane (Juang, R. S., Wang, S. W., 2000. Water
Res. 34. 3795-3803.; Arevalo, E. F., Stichnothe, H., Thorning, J., Calmano, W., 2002.
Environ. Technol. 23, 571-58 1. ASTM, 1998.. C1 14-97a, ASTM, Philadelphia, PA.). This
method proved to be very costly due to several potential operational problems such as
membrane fouling or degradation and EDTA precipitation Kim, C.S., Ong, S.K., 1999. J.
Haz. Mater. B 69, 273-286). The second method involves the precipitation of metallic
contaminants from the metal chelate, thereby liberating EDTA (Lee, C.C., Marshall, W.D.,
2002. J. Environ. Monit. 4, 325-329). The third method involves destabilization of metal
complexes followed by precipitation of liberated metals by using suitable reagents like
NaOH, Ca(OH)2, Na2S, FeS04, FeCI3, NaH2P04, Na2HP04, and diethyl dithiocarbamate
(Tunay, Kabdasli, N.J., 1994. Water Res. 28, 21 17-2124; Chang, L.Y., 1995, Waste
Manage. 15, 209-220; Steele & pichtel, 1998; Hong, A.P.K., Li, C., Banerji, S.K., Regmi,
T., 1999. J. Soil Contamin. 8, 81-103; Kim & Ong , 1999; Xie, I., Marshall, W.D., 2001. J.
Environ. Monit. 3. 41 1-416; Di Palma, L., Ferrantelli, P., Merli, C., Biancifiori, F., 2003. J.
Haz. Mater. B 103, 153-168). The method of hydroxide precipitation was least expensive
and easy to operate but it was not very effective to dechelate the Metal EDTA complex.
OBJECTIVE OF THE INVENTION
The main objective of the present invention is to provide a process for extraction of transition
metals from spent catalyst which obviates the drawbacks as detailed in the previous sections.
Another objective of the present invention is to provide an environmentally friendly process
by chelating the transition metals from spent catalysts using EDTA as chelating agent which
could be recycled after dechelation, making this present invention economically viable.
* Yet another objective of the present invention is to develop a suitable process for the
recovery of EDTA from the Metal-EDTA complex by dechelation which could be recycled
and reused several times.
Still another objective of the present invention is the recovery of transition metals as solution
of high purity which can be used in several applications like electroplating and preparation of
fresh catalyst.
Yet another objective of the invention is use of components in the process of extraction that
are not flammable or corrosive.
Still another objective of the present invention is almost 99.9% recovery of EDTA and
support material.
Yet another objective of the invention is to develop a cost effective process of extraction
which can be prepared from indigenously and commonly available chemicals.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a process for the extraction of transition metal
from spent catalyst (fine size) which comprises steps of dissolving EDTA in water maintaing
a high pH by addition of NH3. Adding mineral acid to the Metal-EDTA complex (dark blue)
formed thus, we obtain the EDTA (white powder) for reuse in subsequent experiments. The
metal sulphate or nitrate in the solution (light green in color) is obtained as well which may
be crystallized or used as a fresh catalyst precursor.
DETAILED DESCRIPTION:
Accordingly the present invention relates A process for recovery of transition metal from
spent metal catalyst which comprises:
a. dissolving 0.2 M to 0.8 M of EDTA in water by dropwise adding ammonia or
NaOH for maintaining pH in the range of 8 to 10 to obtain a solution,
b. adding 5-40 gm of finely grounded spent catalyst to the solution and keeping it
for digestion for 5-6 hours with constant stirring at 100°C to obtain dark blue
colour solution,
* c. filtering and cooling the blue solution and thereby obtaining clear solution
after several washing with water,
d. adding mineral acid to the clear solution to obtain EDTA and residue,
crystallizing the residue to obtain transition metal crystals of 100 pm particle
size.
In another embodiment of the present invention wherein spent metal catalyst used is selected
from group, containing nickel, cobalt, and copper.
In still another embodiment of the invention, wherein spent metal catalyst is nickel catalyst.
In yet another embodiment of the invention, wherein mineral acid is selected from group
consisting of acetic acid, formic acid, oxalic acid, concentrated nitric acid, concentrated
hydrochloric acid, lactic acid and mixture thereof.
In still another embodiment of the invention, wherein nickel catalyst is selected from catalyst
having particle size in the range of 100 to 500 pm and has a composition in range of Ni 25-
28%, Ca: 1 -2%, AI2O3: 6570%.
In an embodiment of the present invention the spent nickel catalyst is selected from the
nickel catalyst having particle size in the range of 100-500 pm and has a composition in
range:
Ni: 25-28%, Ca: 1-2%. A1203: 6570%
In still another embodiment of the present invention, the spent nickel catalyst used is selected
from the fertilizer plant and has calcium as promoter in the range of 1-2%.
In still another embodiment of the present invention the commercial grade EDTA (the
disodium salt) was dissolved in water and pH of the solution adjusted by addition of
ammonia or sodium hydroxide pellets. This EDTA after dechelation by acid, may be recycled
several times in the experiments.
In still another embodiment of the present invention the solidlliquid ratio is in the range of
1 : 10 to 1 : 15 and leaching of the transition metal from spent catalyst in the range of 90-98%.
The higher pulp density leaching, generates concentrated leach solution requiring low capital
investment and energy.
+A chelate is a chemical composed of a metal ion and a chelating agent. A chelating agent is a
substance whose molecules can form several bonds to a single metal ion. In other words a
chelating agent is multidentates ligands. A chelating agent of a particular economic
significance is ethylenediaminetetraacetic acid (EDTA). EDTA is a versatile chelating agent.
It can form four or six bonds with a metal ion and it forms chelate with both transition metal
ions and main group ions. The metal has a higher affinity for the chelating agent than the
support material like alumina and silica, thus the metal contaminant goes into the liquid phase
during the extraction procedure. Afterward the support material is separated from the metalchelate
complex solution. The chelating agent can than be recovered for reuse by appropriate
manipulation. The extracted metal can be precipitated for the use of preparation of catalyst or
some other purposes where metals are used.
The chelating extraction process for recovery of metals from the catalyst can be economically
successful only if the chelating agent can be recovered and reuse at least several times.
Furthermore, chelating agents used for catalyst are non biodegradable during repeated
extraction and reuses.
In the process of the present invention, the range of concentration of EDTA is (0.2M to
0.8M) which was dissolved in water after adjusting the pH by addition of NH3 or NaOH. To
this clear solution, fine grounded and sieved catalyst of IOOpm is added and digested for 5-6
hours with constant stirring at 100°C in a flask, fitted with thermometer to control the
temperature. The washed liquor containing Metal-EDTA complex (dark blue colour) was
filtered so as to separate the support material. The support material was washed several times
by distilled water in order to remove the Ni-EDTA complex, entrapped in the support. The
resulting filtrate (Blue color) is subjected to dechelation by adding conc. &SO4 (or HNO3)
till a light green solution of metal sulphate (or Nitrate) is obtained and EDTA used in the
process is completely precipitated from the chelated solution.
0
\C-OH
EDTA EDTA-Metal Complex
*Six binding sites
4 H on carboxylic acid groups (H's are removed, so -COOm)
2 lone pairs of electrons on nitrogen
Forms stable complex with the transition metals
M-EDTA (complex) + H2S04- Metal-SO4 (solution) + EDTA (precipitate)
The leach liquor obtained is evaporated and crystallized nickel as nickel sulphate.
EXAMPLE I: Concentration of EDTA or Molarity
Chelation Experiments were conducted at different molar concentration
Spent catalyst was roasted in the furnace at 700°C in order to remove coke from the catalyst.
Roasted catalyst was taken in a round bottomed flask of 1000ml capacity fitted with a reflux
condenser, and a thermometer to maintain the temperature. Stirring speed of 1400 rpm was
maintained by the inbuilt speed controller. EDTA of different molarities (0.2-0.8 M) was
taken in the flask and dissolved in water by adjusting the pH 7.0 by addition of NaOH or
ammonia (lml-1 00ml) of mixture thereof of the basic medium. To this clear solution, 5 - 40 g
catalyst was added and solution was agitated by the agitator at the stirring speed maintained
at 1400 rpm). Temperature was maintained at 100°C and dark blue colour solution was
obtained after five to six hrs of digestion with constant stirring. Dark blue solution of EDTA
Ni complex was filtered after cooling. The support material was washed with water to get rid
of the adhered EDTA-Ni complex from the support material. Washing was done till a clear
solution was obtained.
After cooling the solution dechelation was done by a mineral acid e.g., acetic acid, formic
acid, oxalic acid, concentrated HN03, conc. HCI. lactic acid and mixture thereof (10 -100 ml)
was added to precipitate EDTA, leaving behind the Ni as ~ i io~ns 'in a green solution.
Concentration of Ni in ~ iwa~s ca+lcu lated by UV-Vis Spectrophotometer at a wavelength of
395 nm.
* Table -1: Percentage Nickel recovery at different concentrations of EDTA
EXAMPLE I1 (Solid/ liquid ratio)
Parameters
Time 6h. S: L ratio 1: 7. Particle
100-1 50p, stirring speed : 1400
rPm
Weights ranging from 5 to 40 g of roasted catalyst was taken in a flask Solidlliquid ratio
ranging from (1.2 -1:25) the mixture was stirred in a stirrer set up for (1-10 hrs.) for the
extraction of the Ni from the support of spent catalyst at temperature ranging from 50-
1000°C. After completion of the reaction, the mixture was cooled, filtered followed by
dechelation using mineral acids.
Concentration of EDTA
0.2M 0.3M 0.4M 0.5M 0.6M 0.8M 0.9M
Percentage recovery (%)
30 40 45 70 80 91.5 91.5
DECHELATION
After cooling the solution, dechelation was done by a mineral acid e.g., acetic acid, formic
acid, oxalic acid, concentrated FINO3, conc. HCI. lactic acid and mixture thereof (10 -100 ml)
was added to precipitate EDTA, leaving behind the Ni as ~ i io~ns +in a green solution.
Concentration of Ni in ~ iwa~s ca+lcul ated by UV-Vis Spectrophotometer at a wavelength of
395 nm.
Table - 2: Percentage Nickel recovery at different SIL ratio
EXAMPLE 111 (Particle Size)
Parameters
Concentration of EDTA 0.8M; Time 6h
Particle size: 100-150~S. tirring speed : 1400
Different particle sizes ranging from 100 - 500 pm, were taken for the experiments to
optimize the maximum recovery of nickel from spent catalyst. 50g catalyst was taken for the
experiments. 45g of EDTA was weighed and dissolved in water by addition of NH3 or NaOH
and the clear solution was taken in a round bottom flask. To this solution 50g catalyst of 100p
Solid/liquid ratio
1:2 1:5 1:lO 1:15 1:20 1:25
Percentage recovery (%)
15 2 0 60 90 9 1 9 1
+size was slowly added and the mixture was stirred at 1400 rpm for 6 hrs. Here again, a dark
blue solution obtained, was filtered and allow it to cool at room temperature. Same
experiment was conducted for different particle size. Maximum recovery was obtained with
lOOp particle size - lower particle sizes did not have any effect on Ni recovery.
DECHELATION
After cooling the solution dechelation was done by a mineral acid e.g., acetic acid, formic
acid, oxalic acid, concentrated HN03, conc. HCI. lactic acid and mixture thereof (10 -100 ml)
was added to precipitate EDTA, leaving behind the Ni as ~ i io~ns' in a green solution.
Concentration of Ni in ~ i w~as c'alc ulated by UV-Vis Spectrophotometer at a wavelength of
395 nm.
Table - 3: Percentage Nickel recovery at different particle size
EXAMPLE IV (Effect of Time):
Parameters
Concentration of EDTA 0.8M Time
6h
S/L ratio1 :7, stirring speed : 1400
Effect of time on percentage recovery of nickel from spent catalyst was conducted at different
temperature ranging from 50°C -100°C by taking 50g of spent catalyst, 45g of EDTA was
weighed and dissolved in water by addition of NH3 or NaOH and the clear solution was taken
in a round bottom flask. To this solution 50g catalyst of 100p size was slowly added and the
mixture was stirred at 1400 rpm for 6 hrs. Dark blue solution obtained was filtered and allow
it to cool at room temperature. Same experiment was conducted for different time intervals to
get the maximum recovery which was after 6 hours of chelation. After this period there is no
increase in the percentage recovery of Ni.
Particle size
500pm 300pm 100-75pm
Percentage recovery (96)
89 92 92
DECHELATION
After cooling the solution dechelation was done by a mineral acid e.g., acetic acid, formic
acid, oxalic acid, concentrated HN03, conc. HCI. lactic acid and mixture thereof (10 -100 ml)
was added to precipitate EDTA, leaving behind the Ni as ~ i io~ns 'in a green solution.
.)Concentration of Ni in Ni2' was calculated by UV-Vis Spectrophotometer at a wavelength of
395 nm.
Table 4: Percentage Nickel recovery at different digestion time
EXAMPLE V: Recovery using hydrothermal conditions - higher temperatures and
au togeneous pressure.
Parameters
Concentration of EDTA 0.8M particle size
100
150pm. SIL ratio stirring speed 1 : 1400
Table 5: Effect of hydrothermal conditions
Digestion Time
1.5h 2h 2.5h 4h 4.5h 5h 6h
Percentage recovery (%)
18 40 75 89 90 91 9 1
Nickel-recovery from catalysts has been done under hydrothermal conditions (autogeneous
pressure). A suitable S:L ratio raging from 1:25 to 150 (Catalyst wt: volume of chelating
solution) has been used, at various temperatures, ranging from 100' to 175OC, with very high
recoveries (up to 96%) obtained in less than 4 hours batch time.
Parameters
C = 0.8M; Stirring Speed = 1400 rpm
dp = 100pm; S:L = 1 :50; T = 1 50°C
DECHELATION
After cooling the solution dechelation was done by a mineral acid e.g., acetic acid, formic
acid, oxalic acid, concentrated HN03, conc. HCI. lactic acid and mixture thereof (10 -100 ml)
was added to precipitate EDTA, leaving behind the Ni as Ni2+ ions in a green solution.
Concentration of Ni in ~ iwa~s ca+lcula ted by UV-Vis Spectrophotorneter at a wavelength of
395 nm.
Digestion Time
Hrs
%
R
lhr 2hr 3hr 4hr 5hr 6hr
45 64 83 91 91.5 92
62.4 91.7 92.5 95.2 95.8 96
Extraction of Copper from Spent Catalyst
EXAMPLE VI: Concentration of EDTA or Molarity
The effect of EDTA concentration on extraction of Cu from spent Methanation catalyst was
studied by varying the initial concentration of EDTA from 0.2 to 0.8 M. The experimental
results show that the extraction of Cu increases with increase in EDTA concentration. The
experiments to study the concentration effect were perform with constant time of digestion
6hr, solid to liquid ratio 1:20, particle size <300 micrometers, rpm 800, pH 10 and at
atmospheric reflux condition.
Table -6: Percentage Copper recovery at different concentrations of EDTA
DECHELATION
Parameters
Time 6h. S: L ratio 1: 20. Particle
300p, stirring speed :SO0 rpm
After cooling the solution dechelation was done by a mineral acid e.g., acetic acid, formic
acid, oxalic acid, concentrated HN03, conc. HCI. lactic acid and mixture thereof (10 -100 ml)
was added to precipitate EDTA, leaving behind the Cu as cu2+ ions. Concentration of Cu in
cu2' was calculated by UV-Vis Spectrophotometer.
Concentration of EDTA
0.2M 0.4M 0.6M 0.8M
Percentage recovery (96)
69 76 78 79
Extraction of Cobalt from Spent Catalyst
EXAMPLE VII: Concentration of EDTA or Molarity
The effect of EDTA concentration on extraction of Co from spent catalyst was studied by
varying the initial concentration of EDTA from 0.2 to 0.6M. The experimental results show
that the extraction of Co increases with increase in EDTA concentration. The experiments to
study the concentration effect were perform with constant time of digestion lOhr, solid to
liquid ratio 1 :lo, particle size