The document describes recommended flowsheets for the electrolytic extraction of lead and zinc from a polymetal ore found in Egypt called Umm-Gheig. It consists of three main parts:
1) Characterization of the ore through mineralogical, chemical and thermal analyses, showing it contains 30.7% zinc, 7.99% lead and other minerals.
2) Hydrometallurgical treatment experiments including leaching the ore with nitric acid and electrodepositing metals from the leach solutions. The effects of various parameters on current efficiency are examined.
3) Recommended flowsheets involving leaching with nitric acid, electrolytic extraction of lead as PbO2 or Pb, and zinc from
A new technique to measure oxygen reduction kinetics underneath coatings using hydrogen permeation from the back side. Huge step towards characterising buried interface reactivity.
The impact of surface hydrogenation on the thermionic electron emission from ...PROMETHEUS Energy
In this work, thermionic electron emission (TEE) from hot
filament chemical vapour deposition polycrystalline diamond
films deposited on p-type silicon substrates was recorded in
the 25–650 8C temperature range. The studied surfaces were
as deposited, as well as hydrogenated by atomic hydrogen
under ultra-high vacuum conditions. The impact of substrate
temperature during hydrogenation, TH, on TEE was studied.
For TH ¼ 25 8C the TEE was found to display a broad maximum
at substrate temperature around 300 8C followed by an
exponential increase. Annealing at 700 8C results in irreversible
changes in surface conditioning, and drastic reduction of TEE
yield at low temperatures. For samples that underwent
hydrogenation at TH ¼ 300 and 500 8C, the TEE yield is
significant at higher temperatures only. The TEE from these
samples is stable also after 700 8C annealing treatment. We
associate these effects with irreversible thermal induced
physicochemical changes of the hydrogen bonding configuration
adsorbed on the polycrystalline diamond surface resulting
in changes in its surface electronic structure which occur upon
annealing to 300 8C.
Influence of Carbon in Iron on Characteristics of Surface Modification by EDM...drboon
Many surface modification technologies have been proposed and carried out practically by CVD, PVD et.al. Carbonized layer has been made using EDM method. In this paper, to make the nitride layer by EDM some new trials were carried out using a titanium electrode in liquid nitrogen. Experiments were carried out on carbon steel (S45C), pure iron and cast iron. TiN can be obtained on EDMed surface. Moreover, TiCN can be found on cast iron and steel (S45C) by XRD investigation. To confirm the fabrication mechanisms of modified layer on the steel, the following experimental factors were investigated by EDS.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
A new technique to measure oxygen reduction kinetics underneath coatings using hydrogen permeation from the back side. Huge step towards characterising buried interface reactivity.
The impact of surface hydrogenation on the thermionic electron emission from ...PROMETHEUS Energy
In this work, thermionic electron emission (TEE) from hot
filament chemical vapour deposition polycrystalline diamond
films deposited on p-type silicon substrates was recorded in
the 25–650 8C temperature range. The studied surfaces were
as deposited, as well as hydrogenated by atomic hydrogen
under ultra-high vacuum conditions. The impact of substrate
temperature during hydrogenation, TH, on TEE was studied.
For TH ¼ 25 8C the TEE was found to display a broad maximum
at substrate temperature around 300 8C followed by an
exponential increase. Annealing at 700 8C results in irreversible
changes in surface conditioning, and drastic reduction of TEE
yield at low temperatures. For samples that underwent
hydrogenation at TH ¼ 300 and 500 8C, the TEE yield is
significant at higher temperatures only. The TEE from these
samples is stable also after 700 8C annealing treatment. We
associate these effects with irreversible thermal induced
physicochemical changes of the hydrogen bonding configuration
adsorbed on the polycrystalline diamond surface resulting
in changes in its surface electronic structure which occur upon
annealing to 300 8C.
Influence of Carbon in Iron on Characteristics of Surface Modification by EDM...drboon
Many surface modification technologies have been proposed and carried out practically by CVD, PVD et.al. Carbonized layer has been made using EDM method. In this paper, to make the nitride layer by EDM some new trials were carried out using a titanium electrode in liquid nitrogen. Experiments were carried out on carbon steel (S45C), pure iron and cast iron. TiN can be obtained on EDMed surface. Moreover, TiCN can be found on cast iron and steel (S45C) by XRD investigation. To confirm the fabrication mechanisms of modified layer on the steel, the following experimental factors were investigated by EDS.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
Surfactant Assisted Growth and Optical Studies of NiCo2O4 Nanostructures thro...Editor IJCATR
A fast and facile method has been imposed for the preparation of NiCo2O4 nanostructures using metal nitrate as a precursor
material and CTAB as a surfactant. The prepared samples were characterized by Powder X-ray diffraction (XRD), Fourier transform
infrared (FT-IR), Scanning electron microscopy (SEM), Raman and PL spectroscopy. It was found that the synthesis route proposed in this
work favored the formation of NiCo2O4 spinel phase at low temperature. The surfactant CTAB was chosen to control over the nucleation,
growth and agglomeration nature of observed NiCo2O4 nanocrystalline products. With the effect of surfactant, the obtained NiCo2O4 has
been used for various promising potential applications. Based on the observed experimental observations and analysis, a possible
microwave reaction mechanism is proposed to synthesis NiCo2O4 nanostructured materials to enrich the structural, morphological and
optical properties of NiCo2O4 nanostructures
Madkour 1986-journal of-chemical_technology_and_biotechnologyAl Baha University
Thermodynamic Studies on Sulphate Roasting for Zinc Electrowinning from Carbonate Ore
The bulk of the work consists of a theoretical study of the possibility of submitting Umm-Gheig carbonate ore to sulphate roasting. The use of the admixture with pyrites is to enable a carbonate ore to be treated in a similar way to a sulphide ore, and by doing so, to produce a roasted product capable of being treated by orthodox zinc electrowinning methods using sulphate solutions. Thermodynamic studies have been made to find the optimum conditions for sulphate roasting, in either normal air or enriched 36% oxygen air. The results obtained from the experimental work at different roasting temperatures in a tube furnace indicated that a maximum dissolu- tion of 91.2% Zn with a 17.9% Fe could be obtained at a roasting temperature of 650°C for 4 h, followed by leaching in 4% H2S04 (by vol.) at 60°C. The results of the electron microscopic investigation confirmed by metal value data given in the ASTM cards coincide well with results given by chemical analysis
Halogen-substituted pyrazolo-pyrimidine derivatives as corrosion inhibitors f...Al Baha University
Sulfuric acid is widely used in several industrial fields, such as acid pickling, acid cleaning and acid descaling, which cause serious corrosion issues. Especially, copper being widely applied in industrial is vulnerable to be corroded by the acid. The usage of corrosion inhibitor is one of the most important techniques for controlling the corrosion. Several organic inhibitors containing hetero-atom, π-electrons and double bond have been applied for the corrosion inhibition of copper, which are found to exhibit high inhibiting properties by providing electrons to interact with metal surface. However, the use of several heterocyclic inhibitors has caused negative impact on the environment due to their toxicity and non-biodegradability. In this paper, pyrazolo-pyrimidine derivatives are found to attract great attention owing to their eco-friendly properties. Corrosion inhibited properties of three pyrazolo-pyrimidine derivatives namely 4-amino pyrazolo-pyrimidine (APP), 3-bromine 4-amino pyrazolo-pyrimidine (Br-APP) and 3-iodine 4-amino pyrazolo-pyrimidine (I-APP) on copper in 0.5 M H2SO4 solution were studied using electrochemical method and surface analysis techniques. Corrosion of copper has been largely inhibited by the inhibitors and the inhibited efficiency increase with the augment of concentration. The adsorption isotherms were simulated to explore the adsorption mode of inhibitors. Furthermore, theoretical calculations were applied to research the mechanism of inhibitors on copper.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
Surfactant Assisted Growth and Optical Studies of NiCo2O4 Nanostructures thro...Editor IJCATR
A fast and facile method has been imposed for the preparation of NiCo2O4 nanostructures using metal nitrate as a precursor
material and CTAB as a surfactant. The prepared samples were characterized by Powder X-ray diffraction (XRD), Fourier transform
infrared (FT-IR), Scanning electron microscopy (SEM), Raman and PL spectroscopy. It was found that the synthesis route proposed in this
work favored the formation of NiCo2O4 spinel phase at low temperature. The surfactant CTAB was chosen to control over the nucleation,
growth and agglomeration nature of observed NiCo2O4 nanocrystalline products. With the effect of surfactant, the obtained NiCo2O4 has
been used for various promising potential applications. Based on the observed experimental observations and analysis, a possible
microwave reaction mechanism is proposed to synthesis NiCo2O4 nanostructured materials to enrich the structural, morphological and
optical properties of NiCo2O4 nanostructures
Madkour 1986-journal of-chemical_technology_and_biotechnologyAl Baha University
Thermodynamic Studies on Sulphate Roasting for Zinc Electrowinning from Carbonate Ore
The bulk of the work consists of a theoretical study of the possibility of submitting Umm-Gheig carbonate ore to sulphate roasting. The use of the admixture with pyrites is to enable a carbonate ore to be treated in a similar way to a sulphide ore, and by doing so, to produce a roasted product capable of being treated by orthodox zinc electrowinning methods using sulphate solutions. Thermodynamic studies have been made to find the optimum conditions for sulphate roasting, in either normal air or enriched 36% oxygen air. The results obtained from the experimental work at different roasting temperatures in a tube furnace indicated that a maximum dissolu- tion of 91.2% Zn with a 17.9% Fe could be obtained at a roasting temperature of 650°C for 4 h, followed by leaching in 4% H2S04 (by vol.) at 60°C. The results of the electron microscopic investigation confirmed by metal value data given in the ASTM cards coincide well with results given by chemical analysis
Halogen-substituted pyrazolo-pyrimidine derivatives as corrosion inhibitors f...Al Baha University
Sulfuric acid is widely used in several industrial fields, such as acid pickling, acid cleaning and acid descaling, which cause serious corrosion issues. Especially, copper being widely applied in industrial is vulnerable to be corroded by the acid. The usage of corrosion inhibitor is one of the most important techniques for controlling the corrosion. Several organic inhibitors containing hetero-atom, π-electrons and double bond have been applied for the corrosion inhibition of copper, which are found to exhibit high inhibiting properties by providing electrons to interact with metal surface. However, the use of several heterocyclic inhibitors has caused negative impact on the environment due to their toxicity and non-biodegradability. In this paper, pyrazolo-pyrimidine derivatives are found to attract great attention owing to their eco-friendly properties. Corrosion inhibited properties of three pyrazolo-pyrimidine derivatives namely 4-amino pyrazolo-pyrimidine (APP), 3-bromine 4-amino pyrazolo-pyrimidine (Br-APP) and 3-iodine 4-amino pyrazolo-pyrimidine (I-APP) on copper in 0.5 M H2SO4 solution were studied using electrochemical method and surface analysis techniques. Corrosion of copper has been largely inhibited by the inhibitors and the inhibited efficiency increase with the augment of concentration. The adsorption isotherms were simulated to explore the adsorption mode of inhibitors. Furthermore, theoretical calculations were applied to research the mechanism of inhibitors on copper.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
Electro-Thermal and Semiconductivity Behaviour of Natural Sintered Complex Ca...Al Baha University
The polymetal (Zn, Pb, Fe, Ca, Mg, Cd, Ba, Ni, Ti, and SiO2) complex Umm-Gheig carbonate ore is subjected to sintering treatment at 573, 773, 973 and 1273 K respectively for four hours. Chemical, spectral, X-ray and differential thermal analyses are applied for the native ore as well as for the samples preheated and sintered. The I-V characteristics, bulk density (Db), percent shrinkage (%S), activation energy (Ea) and energy gap (Eg) are established for the sintered ore. The electrical conductivity (), thermal conductivity (K) and thermoelectric power coefficient () have been investigated as a function of applied temperature for the sintered ore materials. The electrical and thermal measurements show that the sintered ore has semiconductivity behaviour with temperature. The electrical conduction is mainly achieved by electrons or n-type. As the sintering temperature (Ts) increases the conduction of the ore is also increased owning to the recombination process takes place between the electrons and holes. Electrons hopping between Fe2+ and Fe3+ are the main charge carriers. The formation of Fe3O4 at high sintering temperature acts as an active mineralizer, thus inducing an increased degree of crystallinity and the more ordered crystal structure is produced.
Keywords
This work studied the effect of applying pulse current
(ton=off=1s) on the electrodeposition of silver nanoparticles on
carbon sphere surface as a substrate. The electrolyte is made of 0.1
M KNO3, 0.1 M KCN and 0.01M AgNO3. The pH value has been
adjusted in the alkaline region of 9.1 with the help of K(NO3)
addition. Experiments were carried out at room temperature for
periods up to 12 minutes. The cell is fitted with a mechanical stirrer
to keep the electrolyte in a dynamic state. Product(s) was
characterized with the help of SEM and EDX and field emission.
Results obtained show that silver nanoparticles has successfully
electrodeposited under pulse current conditions with a particle size
of 100–400 nm after 2 minutes. Deposition takes place on certain
accessible sites of the carbon surface of the substrate forming a
monolayer of scattered silver nanoparticles. Formation of macro
particles with larger diameter and multilayer in thickness takes
place with continuous deposition of silver nanoparticles on the
formerly deposited silver. Pulse current helps management of the
monolayer deposition as compared to the steady DC application
with respect to particle diameter and number of layers.
Some factors affecting on the behavior ofsteel electrode in citric acid solut...IJERA Editor
Potential-time curves are constructed for the steel electrode in naturally aerated citric acid solutions devoid of
and containing some aggressive and inhibitive compounds. Cl- and SO4
2- ions cause the destruction of passivity
and initiation of pitting corrosion. The rate of oxide film growth by citric acid and oxide film destruction by Cl-
and SO4
2- ions follows a direct logarithmic law as evident from the linear relationships between the open-circuit
potential and the logarithm of immersion time. Urea, phenylhydrazine and 1,2-phenylenediamine compounds
inhibit the pitting corrosion of steel. The rate of oxide film healing and thickening increases with their
concentrations. In presence of constant inhibitor concentration, the efficiency of pitting inhibition increases in
the order: (weak) urea<phenylhydrazine><1,2-phenylenediamine(strong).
Inhibitory Effect of Some Carbazides on Corrosion of Aluminium in Hydrochloric Acid and Sodium Hydroxide Solutions
The dissolution of aluminium in hydrochloric acid and sodium hydroxide solutions in the presence of semicarbazide, thiosemicar- bazide and sym.dipheny1carbazide as corrosion inhibitors has been studied using thermometric, weight-loss and polarization methods. The three methods gave consistent results. The higher inhibition efficiency of these compounds in acidic than in alkaline madia may be due to the less negative potential of aluminium in hydrochloric acid solution, favouring adsorption of the additive.The adsorption of these compounds were found to obey Frurnkin adsorption isotherm. Cathodic polarization measurements showed that these com- pounds are cathodic inhibitors and their adsorption in the double layer does not change the mechanism of the hydrogen evolution reaction. The results are analysed in terms of both molecular and cationic adsorption.
Electrolytic recovery of antimony from natural stibnite ore
Loutfy H. Madkour a, *, Ibrahim A. Salem b
a Chemistry Department, Faculty of Science, Tanta University, Tanta, Egypt b Geology Department, Faculty of Science, Tanta University, Tanta, Egypt
Received l0 November 1995; accepted 6 December 1995
Abstract
Stibnite ore at Wadi Abu Quraiya, situated in the central Eastern Desert of Egypt has been subjected to petrographical, mineralogical, infrared, X-ray diffraction, chemical and spectral analyses. Hydrometallurgical treatment based on leaching with acids, precipitation and electrode- position of metal values from the ore have been developed. Studies to investigate suitable electrolytic baths for the cathodic deposition of metallic antimony either directly from the leach liquor or in the presence of complexing agents have been carded out. The influence of various factors on the electrodeposition process of the element from its electrolyte solutions is discussed. Advantages of the flowsheet and various approaches depending on convenient electrolytes for the deposition of antimony from the stibnite ore have been investigated. The results of spectrophoto- metric and chemical analyses revealed that the purity of the metal is > 99%.
Influence of Carbon in Iron on Characteristics of Surface Modification by EDM...drboon
Many surface modification technologies have been proposed and carried out practically by CVD, PVD et.al. Carbonized layer has been made using EDM method. In this paper, to make the nitride layer by EDM some new trials were carried out using a titanium electrode in liquid nitrogen. Experiments were carried out on carbon steel (S45C), pure iron and cast iron. TiN can be obtained on EDMed surface. Moreover, TiCN can be found on cast iron and steel (S45C) by XRD investigation. To confirm the fabrication mechanisms of modified layer on the steel, the following experimental factors were investigated by EDS.
Inhibitive properties, thermodynamic, kinetics and quantumAl Baha University
Inhibitive properties, thermodynamic, kinetics and quantum
chemical calculations of polydentate Schiff base compounds
as corrosion inhibitors for iron in acidic and alkaline media
1. J. Chem. Tech. Biotechnol. 1985,35A,108-1 14
Recommended Flowsheets for the Electrolytic Extraction
of Lead and Zinc from Red Sea Polymetal Ore
Loutfy H. Madkour
Chemistry Department, Faculty of Science, Tanta University, Tanta, Egypt
(Manuscript received 12 April 1984 and accepted 21 November 1984)
The polymetal complex ore Umm-Gheig considered in Egypt as a rather rich
source of lead and zinc is subjected to mineralogical, chemical, spectral, X-ray and
differential thermal analyses. Hydrometallurgical treatments based on leaching,
precipitation and electrodeposition of metal from the ore are established. The
influences of current density, temperature and metal ion concentration on the
Faradic current efficiency are discussed. Advantages and disadvantages of flow-
sheets and various approaches depending on convenient baths for the electro-
deposition of metals are investigated. The results of electron microscopic investiga-
tion confirmed by metal value data given in the A.S.T.M. cards coincide well with
those given by chemical analysis.
Keywords: Umm-Gheig ore; lead and zinc extraction; flowsheet.
1. Introduction
The polymetal deposits of the Red Sea ore belt represent a rather complex morphogenetic type
of mineralisation,' and occupy the littoral zone extending NW-SE for a distance of 130km. The
investigated sample contains 30.7% Zn, 7.99% Pb, 5.05% Fe and 6.58% SOz. The minerals are
hydrozincite, zincblende, smithsonite and cerussite, whereas silica and carbonates constitute the
bulk of the gangue. The minerals present in this complex ore are often found in such close
intergrowth that it is either difficult to obtain suitable high-grade concentrates at high recoveries2by
physical methods, or the recovery of metals from the respective concentrates is poor.
Hydrometallurgical methods based on leaching and precipitation rather than smelting play an
important role in meeting the requirements for the treatment of complex3ores. Nitric acid as a direct
leacher in the decomposition of complex ore has been a~hieved.~The present investigation is
directed to the electrolytic extraction of zinc5-' and leads39from various baths. Also the role of
impurities'&'* on the electrodeposition processes is considered.
2. Experimental
2.1. Sampling
Mineralised horizon ore (500kg) was crushed to 100% minus 1.0mm:
2.2. Chemical and spectral analyses
Analysis13 of the ore sample was carried out at the Egyptian Geological Survey and Mining
Authority.
2.3. Thermal analysis
This was carried out by means of a MOM derivatograph with a-A1203 as reference. The
powdered sample (1g) was heated at the rate of 10°Cmin-' up to 1000°C(constant sensitivities:
DTA, $50; TG, 200 and DTG, %5).
108
2. Flowsheetsfor electrolytic extraction of lead and zinc 109
2.4. Preparation of the ore mother liquor
Ore sample (30g) (<l.OOmrn) was leached with 150cm3 twice-distilled H 2 0 and 300cm3
concentrated (16M)HNO~(S/L=1:15). The leached ore was completely decomposed by
evaporation without taking to dryness. The cooled concentrate was diluted with 300cm3 water
and heated with continuous agitation. The solution of decomposed ore was filtered, washed with
2% HN03and finally collected in a measuring flask.
2.5. Preparation of the standard solution
Lead nitrate and zinc sulphate solutions were prepared by dissolving the appropriate quantity of
the Analar grade product in twice-distilled water plus acid or alkali as required, to give similar
concentrations to those present in the ore mother liquor for comparison.
2.6. Electrolysis system
This comprised a constant current device (25PA-1000 mA); an electrometer for measuring
current through the circuit, the potential of the working electrode vs S.C.E.; a glass electrolytic
cell of 1dm-' capacity, fitted with a thermometer relay, holders for the electrodes and a magnetic
stirrer; electrodes of graphite core, stainless steel, Pt, Ag, Ni and Al.
3. Results and discussion
Table 1 reveals that the ore is rich in Zn and Pb. The arrangement of mineral^'^ according to
their abundance (Figure 1) is as follows: hydrozincite, Zns(C03)2(OH)6;zincblende, ZnS;
smithsonite, ZnC03and cerussite, PbC03.The total loss in weight due to heating up to 1000°Cwas
17.8%.X-ray powder diffraction data shows that galena ismainly converted to cerussite. Nitric acid
is an excellent direct leacher for treatment of the ore as shown in Table 2.
I I I 1 I I I I I I
100 200 300 400 500 600 700 000 900
Temperature ("C)
Figure 1. Thermal analysis of Umm-Gheig ore.
3. 110
Table 1. Chemical and spectral analyses of Umm-Gheig complex polymetal ore
L. H. Madkour
Content Content Content
Component (%) Component (%) Element (parts x
SiOz 6.58 Zn 30.70 Cd 800
Fe 5.05 PbS04 4.86 Ba 400
CaO 4.84 ZnC0, 59.76 co -
so:- 1.28 Moisture 0.97 Ag
AIzO, 0.83 Pb 7.99 Ti 0.06
MgO 2.58 PbCO, 6.02 Ni 40
-
L.O.I." 28.22 Au -
Loss on ignition in weight percent at 11M)"C.
Table 2. Efficiency of leaching the complex ore using (11~)HNO,
acid
Content (%)
Efficiency
Element Ore solid Ore liquor (%)
Zn 30.70 30.42 99.10
Fe 5.05 4.80 95.10
Pb 7.99 7.99 ioo.no
90t
I I I I I l l 1 J
10 20 30 40 50 (0.)
L I I I I I I I I 1
10 30 50 70 (AA)
Current density (mA cm-2)
I I I I I I 1 I I I I I I I /
20 30 40 50 60 70 (0.1
I I I I I I I 1 I I l l
30 40 50 60 70 (AA)
Temperature ("C)
Figure 2. (a) Effect of current density at constant temperature on PbO, deposition from nitrate (A, A)and plumbite (0,
0)solutions at 55 and 60°C respectively. A , 0, pure standard electrolytes; A,0, ore leach solutions. (b) Effect of
temperature at constant current density on Pb02 deposition from nitrate (A, A)and plumbite (0,O)solutionsat 45.5 and
37 mA cm-', respectively. A,0,pure standard electrolytes; A,0,ore leach solutions.
4. Flowsheets for electrolytic extraction of lead and zinc 111
3.1. Electrolytic extraction of metals
Duplicate relations of the current efficiency (a%)with respect to the current density,
temperature and metal ion concentration, either in the case of pure standard electrolytes or ore
leach solutions were drawn according to Faraday’s law in both Figures 2 and 3. In general, lower
current efficiency values are obtained in the case of ore leach solutions due to the effect of
impurities’(’-’2 and the presence of other metal cations during the deposition processes.
The results of chemical analysis reveal that the purities of the metals and the oxides are better
than 99.6%. The surface structure of the anodic oxide films were also investigated under the
electron microscope. The results from the electron microscope, confirmed by the X-ray standard
tables (A.S.T.M. cards) for the oxides, are coincident with those obtained by the chemical
analysis.
-
4
a-I00
a-“ 9 0
85
80
10 20 30 40 50 60
I / I I I I I I 1 J I
20 60 100 140 I80 220 (AA)
Current density (mA Cm-‘)
c0
(0.)
-4
a-
95r
85
I80
I o o ~
90g51
-20 30 40 50 60 70
Temperature (‘C)
Zn‘*lq d K 3 )
Figure 3. (a) Effect of current density at constant temperature on Zn deposition from sulphate (0,0)and zincate (A, A)
solutions at 38 and 50T, respectively. 0.A, pure standard electrolytes; 0,A,ore leach solutions. (b) Effect of temperature
at constant current density on Zn deposition from sulphate (0,0)and zincate (A, A)solutions at 50 and 100 mA cm-’,
respectively. 0, A , pure standard electrolytes; 0, A,ore leach solutions. (c) Effect of zinc ion concentration at constant
current density and temperature on Zn deposition from sulphate (0,0)and zincate (A, A)solutions at 50 mA cm-’, 38°C
and 100 mA cm-’, 50T,respectively. 0, A , pure standard electrolytes; 0,A,ore leach solutions.
3.1.1. Electrolytic extraction of lead
The different factors liable to affect the nature of the deposits including metal ion concentration,
complexing agents, pH, temperature, current density and presence of impurities were studied.
Difficulties associated with the electrodesposition of the lead oxides on the anode, are due to the
ease of their oxidation and non-coherent nature of the deposits. Difficulties arise over controlling
the potential and current density. To obtain a deposited layer of Pb02from Pb(N03)2that does
not fall off the graphite core, it was found necessary to change the anodic potential and
electrolyte temperature in 4 successive stages. The concentrations of Pb(N03)2and HN03in the
electrolyte affects the structure of the PbOz deposit.
The phase composition of Pb02 was determined by X-ray diffraction, the surface structure of
5. L. H.Madkour112
the deposits was studied by electron microscopy. The current density is the principal factor
determining the phase composition of the electrodeposits of Pb02. In case of deposition of Pb02
from Na2Pb02, an increase of applied anodic current density enhances rapid discharge of OH-
ions and leads to the formation of oxide with a higher oxygen content; on the other hand, a
decrease in current density favours the formation of the lower oxygen content oxide. Increasing
the concentration of NaOH to 4M enabled discharge of oxygen to occur and the yield of PbOl
fell. The rapid drop in the apparent coulombic efficiency as the pH is increased is thought to be
the result of the net oxidation state of Pb approximating 4.00. A remarkable decrease in current
efficiency was obtained with a rise of temperature due to enhanced discharge of oxygen at higher
temperatures.
The optimum conditions necessary for the anodic deposition of PbOz were finally reached as
shown in Figure 2. Pb is quantitatively obtained by cathodic deposition from ore leach plumbite
solution (pH39). Also bright, fine crystalline Pb can be deposited ~athodically'~from ore leached
nitrate solution. The distance between the stainless steel electrodes is maintained at 3cm. The
drying of the lead without oxidation is considered to be so difficult" that it is usually to take
advantage of the fact that Pb is deposited as PbOZ anodically; convenient baths are summarised
in Table 3.
Table 3. Suitable baths for the electrolytic extraction of Pb, Zn and PbO, from natural complex ore
Compobition of Current Tcmpera- Current
electrolyte holution density ture efficiency
Bath (in 1 dm3ore liquor) (mAcm-') ("C) Product (Q%) Recovery
Nitratesolution Ore leach nitrate (10% HNO,) pH 5
+3-5 dropsof conc. H2S04tomake
PbO: more adherent to anode
Ore leach nitrate (10%HN03)pH 5Nitrate solution
Plumbite solution Oreleach PbOi- pH. (9-10)
Plumbite solution Ore leach PbOi -,pH (%lo)
Sulphatesolution
Zincate solution
Ammonical solution
Ore leach ZnSO,, Fe2(S0,), +
IPlSgdm-'conc H2S0,
Ore leach ZnOS-, NaOH 3-5 mole
dm3pH(Ic12)
Ore leach in presence of excess
NHJOH Izn(NH3)61(OH)z
Anodic
45.5
Cathodic
8
Anodic
37
Cathodic
20
Cathodic
50
Cathodic
100
Cathodic
80
55 PbO, Anode 97.3%
96.8
55 Pb Cathode 98.7%
60 PbOz Anode 96.3%
25 Pb Cathode 98.9%
38 Zn Cathode 92.6%
50 Zn Cathode 98.1%
25 Zn Cathode 97.6%
98%
98.170
97.6%
67%
92.8%
93.4%
3.1.2. Electrolytic extraction of zinc
The ore mother liquor, freed from Pb ions (after deposition of Pb or PbOz), was evaporated with
the addition of drops of concentrated sulphuric acid to expel nitrogen oxides followed by dilution
and deposition of Zn. The presence of a higher concentration of 4.80% Fe in the ore showed a
deleterious effect on current yield (Table 3). The current efficiency and the ohmic voltage
decreased as the H2S04 content in the electrolyte increased, but the power consumption
remained nearly constant. At pH<2 the current efficiency was low and hydrogen evolution
occurred.
The decrease in the cathodic current efficiency (a%)is related to several factors, including a
decrease in hydrogen overvoltage on certain areas of the zinc electr~deposit,'~the formation of
local galvanic cells in the zinc which lead to increased corrosion, or an increase in the evolution
of hydrogen and the possible alteration of the growth morphology of zinc by impurities.
6. Flowsheets for electrolytic extraction of lead and zinc 113
Zinc is deposited from the ore zincate liquor after the chemical precipitation of Fe impurities
using NaOH, either in the absence of, or in the presence of, Pb ions. PbOz is simultaneously
anodically deposited from the same plumbite medium.
The dissolution of zinc in NaOH to give Zn(OH)',- takes place through ZnO or Zn(OH), as
intermediate. Zincate is considered to decompose slowly in solution and to precipitate ZnO as a
passivating film.
The ore sulphate liquor is treated by an excess of ammonia solution to convert Zn2+ to the
amino complex [Zn(NH3>,J(OH),. The precipitated hydrated Fe203.x-H20is then filtered off so
as to avoid any complication from galvanic cells" which favour the redissolution of zinc by acid
electrolyte. Zinc is subsequently deposited at 25°C without potential control.
Analytical results reveal that the purity of zinc produced is 299.99% and corresponds
completely to the requirements for the production of high grade Zn alloys. The current efficiency
of zinc deposition from SO',- bath and the cell voltage increase as the zinc content of the bath
and the power consumption decreases. In general, it is observed that an increase of metal ion
concentration increases both the rate of deposition and the yield.
After various experiments the optimum conditions necessary for the cathodic deposition of Zn
were reached (Figure 3) the more convenient baths are summarised in Table 3.
Complex
Zn-Pb ore
I HN03 (S/LI:15)
Leaching -I
Filtrotion
t
t
Ore mother liauor - Cake)residue
I 2O/o HNO,
10% 9N03 (byvol)
Electrolvtic cells
solution
Washing
II FiItrotion
I I
Silica Jroduct
To dump
I
1-
1
Lead electrolysis
I Lead product
Brine electrolyte
I5 g dmm3H, SO,
ISulphation t
I No'OH NH'~OH
Caustification Ammoniation
Fe precipitotion/
Na,ZnO, I e a c F Z n
Zinc electrolysis
Zn cathode product
1
Figure 4. Hydrometallurgical process flowsheet for treatment of complex zinc and lead ore as based on initial experimental
8
investigation.
7. 114 L. H. Madkour
3.2. Recommended flowsheets
The recommended flowsheet for the extraction of metals from Umm-Gheig ore sample after
leaching with nitric acid is illustrated in Figure 4. Two other alternate pathways have been
attempted successfully although each has its drawbacks. It was planned to precipitate iron by
adjustment of pH prior to any electrolysis step since iron present in the ore mother liquor
consumes energy in the Fe2+/Fe3+oxidation-reduction reaction and may contaminate zinc during
the electrodeposition process. Either sodium or ammonium hydroxide were used for the purpose.
When sodium hydroxide was used in excess 3-5 mol dm-3 (pH 1@-12), Fe203.x-H20 was
precipitated and discarded after filtration. Zinc and lead were obtained simultaneously from the
same alkaline zincate and plumbite bath solutions by electrolysis. Pb02is deposited at 4mA cm-2
anodic current density, whereas zinc is deposited at 100mA cm-2 cathodic current density. The
disadvantages of this flowsheet, were that metallic lead might deposit cathodically and
contaminate
In an alternative flowsheet, ammonia solution was used in excess to effect the precipitation of
Pb(OH)2and FezO3.x-H20 simultaneously and these were separated by centrifugation. Separation
of Fe,O, * x-H20 which should be accomplished before the electrolysis process is applied, was
achieved by dissolvingthe precipitate in nitric acid, followed by addition of excesssodium hydroxide
(pH 9-10). Metallic lead was deposited cathodically or anodically as dioxide. Zinc was deposited
cathodically from the ore mother liquor [Zn(NH3)6(OH)2]solution. The disadvantages of this
flowsheet are concerned with the numerous treatments such as additions, separations,dissolutions,
electrolysis and the large amounts of reagents consumed.
also excess of alkali is used (180 g dm-3 NaOH).
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
Sabet, A. H.; Tsogoev, V. B.; Bordonosov, V. P.: Kuznetsov, D. N.; El-Hakim, H. A. Annals of the Geological
Survey of Egypt According to Contract 1980, Vol VI, 1976.
Eid, A. M.; Abd-Rehim, M. M. Metallurgical Research on Zn-Pb Oxidised Ore of Umm-Gheig Deposit, Eastern
Desert. Geological Survey and Mineral Research Department, Egypt, 1963,p. 22.
Viswanathan, P. V.; Yedavalli, B. V. S . ; Srinivasan, S . R.; Bhatnagar, P. P. Symposium on Recent Development in
Non-Ferrous Metals Technology. Volume I f Copper, 4-7 December 1968, pp. 27, 32-40.
Cronjaeger, H. German Patent 2 418 441, 1975.
Kabanov, B. N.; Popova, T. I.; Oshe, A. I.; Kulyavik, Y. Elektrokhimiya 1969,5, 974.
Wilson, C. L.; Wilson, D. W. Comprehensive Analytical Chemistry, Volume IIA, Electrical Methods, 1964,pp. 1543.
Afifi, S.E.; Taha, F.: Madkour, L. H. Egypt. J. Chem. 1984,27, in press.
Tsvetkovskii, I. B.: Larionov, 0.V. Vestn. Leningr. Univ. Fiz. Khim. 1974, 4, 110.
Gancy, A. B. J.; Electrochem. Soc. 1969, 116, 1496.
Bressan, J.; Gaillochet, P.; Wiart, R. Int. Soc. of Electrochem 28th Meeting Druzhba, 1977.
Liebscher, R. (Ger) Neue Huette 1969. 14, 651.
Rodionova, T. M.; Gran, T. V.; Kheifets, V. L. Elektrokhimiya 1975, 11, 1976.
Merck, E. Complexornetric Assay Methodr Wirh Titriplex, Merck, Darmstadt, 1971,3rd edn.
Todor, D. N. Thermal Analysis of Minerals, Abacus Press, 1976.
Vogel, A,, Quantitative Inorganic Analysis, John Wiley and Sons, New York, 1975,pp. 608-615.
Mellor, .I.W. Inorganic and Theoretical Chemistry vol. VII, Longmans Green and '20.Ltd, 1946,pp. 411, 542.
Kerby, R. C.; Ingraham, I. R. Can Mines Br. Res. Rep., 1971 35, 243.
Milazzo, G. Electrochemistry, Theoretical Principles and Practical Applications, Elsevier Publishing Co., Amsterdam,
1963.