3461
Tailings Dewatering by Tannic Acid-Mediated Polymeric
Flocculation and Pressure Filtration
Daowei Wang, Dong Wang, Kaipeng Wang, Anthony Yeung, Qi Liu
Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada
ABSTRACT: Pressure filtration of mine tailings by filter presses has gained interest and commercial adoption in
the past decade. It potentially allows for quick dewatering of oil sands fluid fine tailings. In our study of using
flocculation-filtration to dewater the fluid fine tailings, we observed that a tannic acid-mediated associative
polymeric complex, including ferric chloride as a coagulant and polyethylene oxide (PEO) as a flocculant,
could significantly increase filtration rate compared with the coagulant-flocculant treatment without tannic
acid. The improved filtration performance was found to be due to the cross-linking function of the tannic
acid, a polyphenol compound, forming numerous hydrogen bonds with PEO, and coordination bonds with
ferric ions. These bonds helped develop a network-structured associative polymeric complex that was more
compression resistant, which in turn helped maintain the porosity of the filter cake to sustain filtration for
longer periods, thus achieving significantly improved filtration results. Such network-structured associative
polymeric complexes pointed to one of the directions to pursue for the filtration of various difficult-to-dewater
coal, ore and mineral slurries.
Keywords: Flocculation-filtration tannic acid polymeric network oil sands fine tailings dewatering
INTRODUCTION
In mineral processing, efficient dewatering of fine tailings
is significant for recycling processing water and managing
risks brought by tailings storage facilities. From academia
to giant mining companies, much R&D work has been
devoted to developing fast and cost-effective tailings dewa-
tering methods.
In recent years researchers have found that chemical
conditioning followed by mechanical/physical treatment is
a promising method for solid-liquid separation, the strategy
of which has gained broad applications in wastewater treat-
ment, sludge disposal, and mine tailings reclamation [1]. As
mechanical filtration equipment, pressure filters are more
popular to be used in the practice of tailings dewatering
because they are found energy efficient and cause less clog-
ging issues [2, 3]. The filtered cakes contain high solids
content and are suitable for dry stacking [4]. However, tail-
ings are becoming finer and filter cake resistance increases,
resulting in the pressure filtration process becoming inef-
ficient in filtration kinetics and/or obtaining target cake
moisture. To address this problem, the fine tailings slurry
needs to be first treated by coagulants/flocculants to aggre-
gate fine particles before feeding into the pressure filtration
unit. In the process, flocculation chemistry is an impor-
tant aspect that is worth studying for the optimization and
indemnification of flocculation-filtration efficiency.
From fundamental perspectives, fine particles are
usually negatively charged in tailings suspension. With
the addition of coagulants or flocculants, the suspension
Tailings Dewatering by Tannic Acid-Mediated Polymeric
Flocculation and Pressure Filtration
Daowei Wang, Dong Wang, Kaipeng Wang, Anthony Yeung, Qi Liu
Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada
ABSTRACT: Pressure filtration of mine tailings by filter presses has gained interest and commercial adoption in
the past decade. It potentially allows for quick dewatering of oil sands fluid fine tailings. In our study of using
flocculation-filtration to dewater the fluid fine tailings, we observed that a tannic acid-mediated associative
polymeric complex, including ferric chloride as a coagulant and polyethylene oxide (PEO) as a flocculant,
could significantly increase filtration rate compared with the coagulant-flocculant treatment without tannic
acid. The improved filtration performance was found to be due to the cross-linking function of the tannic
acid, a polyphenol compound, forming numerous hydrogen bonds with PEO, and coordination bonds with
ferric ions. These bonds helped develop a network-structured associative polymeric complex that was more
compression resistant, which in turn helped maintain the porosity of the filter cake to sustain filtration for
longer periods, thus achieving significantly improved filtration results. Such network-structured associative
polymeric complexes pointed to one of the directions to pursue for the filtration of various difficult-to-dewater
coal, ore and mineral slurries.
Keywords: Flocculation-filtration tannic acid polymeric network oil sands fine tailings dewatering
INTRODUCTION
In mineral processing, efficient dewatering of fine tailings
is significant for recycling processing water and managing
risks brought by tailings storage facilities. From academia
to giant mining companies, much R&D work has been
devoted to developing fast and cost-effective tailings dewa-
tering methods.
In recent years researchers have found that chemical
conditioning followed by mechanical/physical treatment is
a promising method for solid-liquid separation, the strategy
of which has gained broad applications in wastewater treat-
ment, sludge disposal, and mine tailings reclamation [1]. As
mechanical filtration equipment, pressure filters are more
popular to be used in the practice of tailings dewatering
because they are found energy efficient and cause less clog-
ging issues [2, 3]. The filtered cakes contain high solids
content and are suitable for dry stacking [4]. However, tail-
ings are becoming finer and filter cake resistance increases,
resulting in the pressure filtration process becoming inef-
ficient in filtration kinetics and/or obtaining target cake
moisture. To address this problem, the fine tailings slurry
needs to be first treated by coagulants/flocculants to aggre-
gate fine particles before feeding into the pressure filtration
unit. In the process, flocculation chemistry is an impor-
tant aspect that is worth studying for the optimization and
indemnification of flocculation-filtration efficiency.
From fundamental perspectives, fine particles are
usually negatively charged in tailings suspension. With
the addition of coagulants or flocculants, the suspension