Fatty acid collectors for phosphate flotation and their adsorption behavior
using QCM-D
J. Kou a,b, D. Tao b,⁎, G. Xub
a School of Civil and Environment Engineering, University of Science and Technology Beijing, 30 Xueyuan Road, Haidian District, Beijing, 100083, PR China
b Department of Mining Engineering, University of Kentucky, Lexington, KY 40506, USA
a r t i c l e i n f o a b s t r a c t
Article history:
Received 31 July 2009
Received in revised form 5 March 2010
Accepted 11 March 2010
Available online 25 March 2010
Keywords:
Fatty acid
QCM-D
In this paper the relationship between the flotation performance of phosphate collectors and their adsorption
behavior was evaluated using a variety of techniques including the Crystal Microbalance with Dissipation
technique (QCM-D). The adsorption of the collectors on the surface of hydroxyapatite was primarily
characterized using QCM-D, which is a high sensitivity in-situ surface characterization technique. Additionally,
the collectors were evaluated via zeta potential and FTIR analyses. The flotation performance of the collectors
was evaluated using a laboratory mechanical flotation cell at different process parameters such as pH, collector
dosage, diesel dosage and flotation time. The two collectors evaluated were a commercial plant collector and a
refined tall oil fatty acid. The QCM-D data showed that the refined tall oil fatty acid adsorbed on phosphate
more readily and produced stronger hydrophobicity and better flotation performance than the plant collector.
The chemisorption and surface precipitation mechanisms of the refined tall oil fatty acid on the surface of
hydroxyapatite were demonstrated by means of zeta potential measurements and FTIR analysis.
1. Introduction
In the conventional phosphate flotation (Crago) process, a
significant amount of the silica present in the feed is floated twice,
first by fatty acid, and then by amine (Zhang et al., 1997). The Crago
process is therefore inefficient in terms of collector efficiency. The
phosphate mining industry is faced with higher fatty acid prices, lower
feed grade, and stricter environmental regulations (Sis and Chander,
2003). To meet the market demand for higher effectivity, lower cost
and better selectivity of phosphate flotation collectors, there is a need
to evaluate surface adsorption techniques that may help researchers
develop better collectors by understanding how the adsorption
behavior of materials affects their performance as flotation collectors.
In order to evaluate this relationship, a plant collector of proprietary
composition and a refined tall oil fatty acid were compared. The
refined tall oil fatty acid, referred to as GP193G75, was comprised of
47% oleic and 33% linoleic acids.1 Flotation tests were performed at
varying process parameters such as pH, collector dosage and flotation
time with phosphate ore from CF Industries' phosphate rock mine in
Hardee County, Florida. To better understand the behavior of the
collectors on an apatite surface, their adsorption on the surface of a
hydroxyapatite-coated sensor was studied using the QCM-D technique.
The adsorption and flotation characteristics of the two
collectors were then compared.
Most of the studies about the adsorption mechanism of collectors
on mineral surface were conducted based on ex-situ measurements
such as contact angle, adsorption isotherm, FTIR spectroscopy, and
zeta potential, which unfortunately cannot monitor the real-time
formation process and characteristics of adsorbed layer. QCM-D is the
second generation of QCM, which has been shown by many
investigators to be a sensitive tool for studying the behavior of protein
and surfactant adsorption in aqueous solutions, with sensitivity in the
ng/cm2 (submonolayer) region (Hook et al., 1998). It can simultaneously
determine changes in frequency and energy dissipation of a
quartz crystal at nanoscale in real-time and derives valuable in-situ
information on adsorbed mass as well as the mechanical (viscoelastic)/
structural properties of the adsorbed layer from experimentally
obtained data of energy dissipation in relation to frequency shift (Paul
et al., 2008). The purpose of this study was to investigate in-situ the
adsorption behavior of two collectors on the hydroxyapatite surface by
means of QCM-D technique and to determine whether the differences
observed may lead to differences in flotation performance.
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