SEPARATION OF TANTALUM AND NIOBIUM FROM NIGERIAN TANTALITE USING AQUEOUS BIPHASE SYSTEM
SEPARATION OF TANTALUM AND NIOBIUM FROM NIGERIAN TANTALITE USING AQUEOUS BIPHASE SYSTEM
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Date
2014-05
Authors
MAINA, NEHEMIAH SAMUEL
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Abstract
The study was carried out to determine the separation of tantalum (Ta), niobium (Nb) and
other metal ions using aqueous biphase system (ABS). The metal ions were produced from
alkali fusion and dissolution of local tantalite ores procured from Plateau, Nasarawa and
Niger states. The tantalite ore samples were crushed, ground and ball-milled for six hours in
a laboratory ball mill and sieved through a 200 sieve mesh (74 μm). The elemental/oxide
composition was determined using energy dispersive X-ray florescence (EDXRF) and Xray
florescence (XRF). From the elemental analysis results, the Ta content was highest,
about 29 %, for the ore from Plateau state; as such all experiments were done using this ore.
X-ray diffraction (XRD) and scanning electron microscopy (SEM) were also carried out on
the tantalite ore and its residues after leaching with mineral acids. A number of leaching
processes were carried out using mineral acids (H2SO4 and HF) varying the molar
concentration of the HF used. Fifty grams of the -74 μm ball-milled sample was leached
with 150 g (≈ 81.6 ml) of 10.8M H2SO4 acid at an acid/ore wt. ratio of 3:1 and also with
81.6 ml a mixture of 15M HF and 2M HF acid (1:1 ratio) in order to improve on the
dissolution of Ta and Nb. The residues and leached liquors were analyzed by XRF. Results
showed that the mineral acid leaching was not effective and therefore alkali fusion method
was employed. Two g of the ground tantalite ore was weighed and mixed with 10 g of
potassium hydroxide (KOH), which was earlier crushed in a ceramic hand mortar and
pestle. Another 2 g of tantalite ore was weighed and mixed with 10 g of crushed sodium
hydroxide. The fusion experiments were performed in an electric furnace using ceramic
crucibles at 400oC for one hour. After the reaction, the fused mass was cooled and
subsequently leached with de-ionized water at room temperature. The resulting leached
solution known as the leached liquor and the residues were analyzed for Ta and Nb by XRF
and inductively coupled plasma – atomic emission spectroscopy (ICP – AES). The leached
liquor was the stock solution used in the aqueous biphase separation experiments.
Polyethylene glycol (PEG) of various molecular weights (PEG3350, PEG4000, PEG6000,
PEG8000, PEG7000-9000, PEG10,000, PEG12,000 and PEG20,000) and three salts-
Na2SO4, (NH4)2SO4 and K2CO3 were used to form the aqueous biphase systems (ABS) at
PEG to salt ratio of 2:1. The ABS formed was subsequently mixed with 1ml each of the
leached liquor and shaken vigorously to facilitate partitioning between the two phases
formed. Results showed that Ta and Nb were extracted and separated using ABS, the
calculated distribution coefficients (D) were from 0.1 to 1.0 for Ta and 0.1 to 1.1 for Nb.
The separation factors for Ta and Nb being 1.83, 3.01, 2.41, 1.27, 1.94 and 0.93 for the
various PEG molecular weights used. For a second set of extractions, results further
showed that Ta and Nb were extracted in ABS with D from 0.1 to 0.5 for Ta and 1.0 to 1.2
for Nb with separation factors of 3.43, 4.15, 8.0, 10.7, 3.55, 2.62 and 2.87 for the PEGs
used. Tantalum and niobium were effectively separated using ABS. The separation factor
was highest, 10.7 for PEG of average molecular weight 7000-9000.
Chapter one focuses on the general background of the study, it also examines the research
problem statement, research aim and objectives, justification and the significance of the
study. The scope of the study was also highlighted. Chapter two looks at separation
processes and their roles. It further looks at the history of tantalum and niobium, their
properties, markets for the metals and their uses; sources of ore and mining methods. The
demand and supply trends and tantalum prices were examined. The chapter also looks at
solvent extraction and separations of polyethylene glycols; aqueous biphase systems were
examined and methods of separating tantalum and niobium were examined.
Chapter three focuses on the materials and methods, showing general outline of the
procedure with reference to preparation of feed materials and protocol for digesting
samples, preparation of aqueous biphase systems and actual separation of tantalum and
niobium in aqueous biphase systems. Chapter four presents the results of the analyses of the
feed materials, the leaching process and alkali fusion; the ABS formation and actual
separation of tantalum and niobium in ABS. chapter five is concerned with the general
discussion of the various results obtained in the study.
Chapter six concludes the investigation by bringing out numbered statements of facts
proven in the work and also made some recommendations on ways to further improve the
work.
Description
A DISSERTATION SUBMITTED TO THE SCHOOL OF POSTGRADUATE
STUDIES, AHMADU BELLO UNIVERSITY, ZARIA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD
OF A
DOCTOR OF PHILOSOPHY (PH.D) IN CHEMICAL ENGINEERING
DEPARTMENT OF CHEMICAL ENGINEERING
FACULTY OF ENGINEERING
AHMADU BELLO UNIVERSITY, ZARIA
NIGERIA
MAY, 2014
Keywords
SEPARATION,, TANTALUM,, NIOBIUM,, TANTALITE,, AQUEOUS BIPHASE SYSTEM