THE EFFECT OF CARBONATE IONS ON THE ELECTROKINETIC PROPERTIES
OF BASTNÄSITE, MONAZITE AND DOLOMITE
*E.R.L. Espiritu, G.R. da Silva and K.E. Waters
Department of Mining and Materials Engineering
McGill University
3610 University Street
Montreal, Quebec, Canada H3A 0C5
(*Corresponding author: eileen.espiritu@mail.mcgill.ca)
ABSTRACT
Rare earth (RE) elements are essential components of emerging green technologies. The increase
in demand for these applications have driven the search and development of new rare earth deposits such as
the Niobec project in Quebec, Canada. This deposit consists primarily of dolomite with significant amount
of RE minerals bastnäsite and monazite, the primary sources of RE elements. Due to the minerals’ fine
liberation sizes, flotation is commonly used as a concentration method. To develop an efficient process, the
electrokinetic properties of the minerals must be understood. In this study, electrokinetic properties of
bastnäsite, monazite and dolomite (a common RE gangue mineral) are investigated by zeta potential
measurements. These measurements are affected by various ions present in solution. For bastnäsite, monazite
and dolomite, some of these ions are H +, OH-, PO43- and CO32-. Dolomite, being a sparingly soluble mineral
and a primary component of the ore, may have the most contribution to the ions in the solution in the form
of CO32- ions. In this study, different sources of CO32- ions (from dolomite dissolution and from Na2CO3) are
investigated. The research work aims at determining the effect of pH and this ion (CO32-) on the zeta potential
of bastnäsite, monazite and dolomite.
KEYWORDS
Rare earth minerals, Bastnäsite, Monazite, Dolomite, Zeta potential, Sodium carbonate, Supernatant
INTRODUCTION
The increase in demand for RE elements have driven the search and development of new rare earth
deposits. Currently, 19 out of 53 rare earth projects in the world are found in Canada [1]. Among these
projects is the Niobec project of Magris Resources Company in Quebec. The deposit contains primarily of
carbonates (such as dolomite) as gangue minerals with significant amount of rare earth minerals such as
bastnäsite and monazite.
Bastnäsite (REFCO3) is a RE fluorocarbonate mineral while monazite (REPO4) is a RE phosphate
mineral. Both minerals are typically beneficiated using flotation due to their fine liberation sizes. However,
these minerals are considered salt-type minerals making flotation system more complex than it already is.
Salt-type minerals have relatively higher solubilities than most minerals but lower than salt minerals (e.g.
halite and sylvite) [2]. Since these type of minerals are sparingly soluble in water, constituent ions that are
being dissolved may influence other mineral surfaces. Thus, for efficient flotation process, surface chemistry
of these minerals must be understood.
When minerals are submerged in a liquid, they may acquire a charge in various ways depending on
their nature and the medium [3, 4]. The charging mechanisms can be adsorption of potential determining
ions (PDI), adsorption of other types of surface ions and specific adsorption of other ions [5]. Surface ions
are those ions that are highly attracted to the mineral surface; sometimes, they are part of the adsorbent (PDI)
or they are the H+ or OH- ions (in the case of most oxides) [5]. Specific adsorption of ions occur through the
adsorption of indifferent or specifically adsorbing ions. Indifferent ions adsorb due to Coulombic force where
the mechanism of adsorption is based on electrostatic forces; while specifically adsorbed ions adsorb not
only because of the Coulombic force but also with other forces such as Van der Waals, π-electron exchange
and complexation [5]. When these ions adsorbed onto the mineral surface, they cause an unequal distribution
of ions in the solution leading to the formation of the electrical double layer (EDL) [6]. The EDL results to
a family of electrokinetic effects such as electrophoresis, electro-osmosis, streaming potential and
sedimentation potential. In the estimation of the surface charge, one of the most widely studied electrokinetic
property is electrophoresis [6]. It is a phenomenon in which the particle moves due to an applied electric
field [6]. This electrophoretic mobility, measured at a certain distance from the surface, indicates a measure
of the zeta potential (ζ) [4].
Dolomite, being a sparingly soluble mineral and a primary component of the ore, may have the most
contribution to the PDI in the solution in the form of CO 3- ions. In this study, the effect of carbonate ions
(from Na2CO3 and dolomite dissolution) to the electrokinetic properties of dolomite, monazite and bastnäsite
are investigated through zeta potential measurements.
EXPERIMENTAL
60
NaCl
50
Na2CO3
40
Supernatant
Zeta Potential (mV)
30
20
10
0
-10
-20
-30
-40
3
4
5
6
7
8
9
10
11
pH
60
NaCl
50
Na2CO3
40
Supernatant
Zeta Potential (mV)
30
20
10
0
-10
-20
-30
-40
3
4
5
6
7
pH
8
9
10
11
60
NaCl
50
Na2CO3
40
Supernatant
Zeta Potential (mV)
30
20
10
0
-10
-20
-30
-40
3
4
5
6
7
8
9
10
11
pH
REFERENCES
1.
2.
3.
4.
5.
6.
Hatch, G. TMR Advanced Rare-Earth Projects Index. Advanced Rare-Earth Projects 2015;
Available from: http://www.techmetalsresearch.com/metrics-indices/tmr-advanced-rare-earthprojects-index/.
Yuehua, H., R. Chi, and Z. Xu, Solution Chemistry Study of Salt-type Mineral Flotation Systems: Role of Inorganic Dispersants. Industrial & Engineering Chemistry Research, 2003. 42(8): p.
1641-1647.
Shaw, D.J. and B. Costello, Introduction to colloid and surface chemistry. 1993, Elsevier.
Hunter, R.J., Introduction, in Zeta Potential in Colloid Science, R.J. Hunter, Editor. 1981,
Academic Press. p. 1-10.
Lyklema, J., Nomeclature, Symbols, Definitions and Measurements for Electrified Interfaces in
Aqueous Dispersions of Solids. Pure and Applied Chemistry, 1991. 63(6): p. 12.
Hunter, R.J., Zeta Potential in Colloid Science, in Zeta Potential in Colloid Science, R.J. Hunter,
Editor. 1981, Academic Press. p. ii.