الفهرس 
Rare Earth ElementsOnly 14 pages are availabe for public view
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Abstract
The main objective of the work presented in this thesis is
to study the separation of some lanthanides from Egyptian
monazite sand by solvent extraction technique. Application of
the bench-scale data on a continuous counter-current extraction
using a horizontal mixer-settler was carried out. The thesis is
classified into three chapters, namely, introduction,
experimental, and results and discussion.
The first chapter includes an introduction described
background of rare earths, their properties, abundance and
distribution in different minerals, short notes about lanthanides
in Egypt and in the world. Also, this chapter covers industrial
importance of lanthanides, and notes about rare earth elements
separation methods as well as a brief outline on the chemistry of
lanthanum, neodymium, samarium, europium and gadolinium.
Moreover, this chapter involves literature survey which is
related to the present work.
In the second chapter, experimental, the different
materials employed and their chemical purity as well as a
detailed description for the instrumentation used is given.
Preparation of working solutions and method of determination
of rare earths are outlined.
In the third chapter, Results and discussion, is divided into seven parts, namely, batch extraction of lanthanum,
neodymium, samarium, europium and gadolinium, separation
feasibility and the application of the extraction process.
In the first part, the extraction of lanthanum from
aqueous solution of pH = 4 by Cyanex 302 was studied by
investigating different parameters affecting on the extraction
process which are the effect of the extractant concentration
(Cyanex 302 dissolved in kerosene), the effect of contact time,
the metal concentration, the nitrate ion, the phase ratio, the
loading capacity of the organic phase as well as the effect of
temperature. This part ended with investigating of different
parameters affecting on the stripping of La3+ from the loaded
organic solvent which are the effect of three different strippants,
namely, HCl, H2SO4 and HNO3, the effect of HNO3
concentration, the effect of contact time and the effect of phase
ratio.
The results show that, the extraction of La3+ increased with
Cyanex 302 concentration and reached of 25 mg/l at
Cyanex 302 concentration of 0.075. The extraction was also
found to increase with (organic : aqueous) phase ratio and
increase with the increase in temperature and the
thermodynamic parameters were also calculated and found to be
(ΔH = 27.18 KJ.mol-1, ΔG= 12.77 KJ.mol-1 and ΔS = 48.00
J.mol-1.k-1). The equilibrium concentrate of La3+ in the organic
phase increases with its initial concentrate up to 300 mg/l while further increase in La3+ concentrate decreases the metal
concentrate in the organic phase. The extraction of La3+ slightly
decreased with the increase in nitrate ion concentration, whereas
the increase in shaking time had a negligible effect on the
extraction process. Nitric acid (0.5 M) was used for stripping
with 30 minutes for high stripping efficiency at organic/
aqueous phase ratio 1:1.
In the second part, the extraction of neodymium from
aqueous solution of pH = 4 by the same extractant used in case
of lanthanum was investigated. The same parameters were
studied, and it was found that, the extraction increases linearly
with increasing Cyanex 302. Slope analysis of the obtained data
indicated that two molecules of Cyanex 302 participate in the
extracted species of neodymium system. The extraction of neodymium was found to increase also with increasing pH till
pH = 3 beyond which there is no effect on the extraction
percent. For the time effect, 5 minutes were enough to reach the
extraction equilibrium. The extraction percent increases with
increasing the phase ratio (organic : aqueous). The effect of
temperature and the thermodynamic parameters also calculated
and found to be (ΔH = 19.31 KJ.mol-1, ΔG= -4.40 KJ.mol-1 and
ΔS = 79.50 J.mol-1.k-1). Nitric acid (1 M) was used for stripping
with 45 minutes for high stripping efficiency at organic/
aqueous phase ratio 2 : 1.In the third part, the extraction of samarium from
aqueous solution of pH = 4 by the same extractant used in case
of part one was investigated. The same parameters were studied
and it was found that; the extraction increases linearly with
increasing Cyanex 302. Slope analysis of the obtained data
indicated that two molecules of Cyanex 302 participate in the
extracted species of samarium system. The extraction of
samarium was found to increase also with increasing pH till
pH = 3 beyond which there is no effect on the extraction
percent. For the contact time effect, 5 minutes were enough to
reach the extraction equilibrium. The extraction percent
increases with increasing the phase ratio (organic : aqueous).
The effect of temperature and the thermodynamic parameters
also calculated and found to be (ΔH = 29.79 KJ.mol-1,
ΔG= -4.15 KJ.mol-1 and ΔS = 114.00 J.mol-1.k-1). Nitric acid (1
M) was used for stripping with 30 minutes for high stripping
efficiency at organic/ aqueous phase ratio (3 : 1).
In the fourth part, the extraction of Europium from
aqueous solution of pH = 4 by the same extractant used in case
of part one was investigated. The same parameters were studied
and it was found that; the extraction increases linearly with
increasing Cyanex 302. Slope analysis of the obtained data
indicated that two molecules of Cyanex 302 participate in the
extracted species of europium system. The extraction of
europium also was found to increase with increasing pH till pH = 3 beyond which there is no effect on the extraction
percent. For the contact time effect, 5 minutes were enough to
reach the extraction equilibrium. The extraction percent
increases with increasing the phase ratio (organic : aqueous).
The effect of temperature and the thermodynamic parameters
also calculated and found to be (ΔH = 34.00 KJ.mol-1,
ΔG= - 8.70 KJ.mol-1 and ΔS = 143.20 J.mol-1.k-1). Nitric acid
(1M) was used for stripping with 15 minutes for high stripping
efficiency at organic/ aqueous phase ratio 2 : 1.
In the fifth part, the extraction of gadolinium from
aqueous solution of pH = 4 by the same extractant used in case
of part one was investigated. The same parameters were studied
and it was found that; the extraction increases linearly with
increasing Cyanex 302. Slope analysis of the obtained data
indicated that two molecules of Cyanex 302 participate in the
extracted species of europium system. The extraction of
gadolinium also was found to increase with increasing pH till
pH = 3 beyond which there is no effect on the extraction
percent. For the contact time effect, 5 minutes were enough to
reach the extraction equilibrium. The extraction percent
increases with increasing the phase ratio (organic : aqueous).
The effect of temperature and the thermodynamic parameters
also calculated and found to be (ΔH = 15.30 KJ.mol-1,
ΔG= -6.50 KJ.mol-1 and ΔS = 88.00 J.mol-1.k-1). Nitric acid (0.5 M) was used for stripping with 10 minutes for high
stripping efficiency at organic/ aqueous phase ratio 1 : 1.
In the sixth part, the separation factors were found to
increase markedly with the increase in pH. Therefore, a better
separation of La3+ from Nd3+, Sm3+, Eu3+ and Gd3+ could be
obtained at high pH and low nitrate ion concentration and low
temperature at 10 min contact time when Cyanex 302 is used as
an extractant.
Finally, this thesis was ended by the application of the
extraction procedure of some rare earths by a continuous
counter-current extraction using a horizontal mixer-settler unit.
After a usual alkaline leaching of monazite and attack of
sulfuric acid to separate uranium from rare earths and thorium,
following by selective dissolution of thorium, the rare earths
were dissolved in nitric acid solution and using as a feed
solution for the continuous counter-current technique with a
flow rate of (200 ml/h). The feed solution was fed at the stage
No. (8), while the Cyanex 302-kerosene solution was fed at the
stage No. (1) with a flow rate of (200 ml/h), while the stripping
was achieved using 1M nitric acid and fed at stage No. (16) at a
flow rate of (100 ml/h). The number of the theoretical extraction
stages was calculated using McCabe-Thile diagram, and found
to equal (2) stages.