Patent Application
20150266991
The present disclosure relates generally to inorganic particle polymer hybrids, which may be used as flocculants.
Flocculation is a process where microscopic substances that are suspended in a liquid carrier aggregate to form larger-sized clusters, also known as flocs or flakes, and come out of suspension. Flocculation may be accelerated by the addition of a flocculating agent to the suspension, where the flocculating agent interacts with the microscopic substances to aid in the aggregation and formation of the flocs that come out of suspension.
Flocculation may be used in a variety of industries, such as: mining; mineral processing; coal mining; water treatment; pulp and paper processing, for example de-inking; wastewater treatment; soil cleaning; oil and gas industry, for example: waste oil recovery, or treatment of tailings or wastewater; or in any industry that uses solid-water separation.
Polyacrylamide (PAM) polymers have been used as flocculating agents. PAM-based flocculants that are commonly used in commercial processes often have shortcomings, for example:
Hybrid particle combinations of charged cores and PAM have been made (see: Yang, W.; Qian, J.; Shen, Z. A novel flocculant of Al(OH)3-polyacrylamide ionic hybrid. J. Colloid Interface Sci. 2004, 273, 400-405.; Wang, M., Qian, J., Zheng, B. and Yang, W. Preparation, characteristics, and flocculation behavior of modified palygorskite-polyacrylamide ionic hybrids. J. Appl. Polym. Sci. 2006, 101, 1494-1500.; and Qiao Feng et al., Synthesis of Macroporous Polyacrylamide and Poly (N-isopropylacrylamide) Monoliths via Frontal Polymerization and Investigation of Pore Structure Variation of Monoliths. Chinese J. Polym. Sci. 2009, 27, 747) and used as flocculants. These particles include: palygorskite-PAM particles, aluminum hydroxide-PAM particles; and N-isopropyl acrylamide-PAM particles.
Hybrid particle combinations of Fe(OH)3 cores and PAM, as well as Al(OH)3 cores and PAM, are disclosed in WO2012021987 (PCT Application No: CA2011/050338). The disclosed particles are formed by the synthesis of “sub-micron cores” of metal-hydroxide and subsequent polymerization of the sub-micron cores with acrylamide monomer. The sub-micron particles disclosed in WO2012021987 were made following a procedure disclosed in Yang et al. 2004. Yang states that the procedure produces a charged particle-polymer hybrid (CPPH) flocculant that includes a charged core and a polymerized surface polymer sized between 78 nm and 150 nm. The charged particle-polymer hybrid of WO2012021987 was found to have a charged core and a polymerized surface polymer size similar to Yang's but was determined to have a modified intrinsic viscosity of 766 mL/g.
It is, therefore, desirable to provide a charged particle polymer hybrid flocculant having improved flocculating properties, such as the ability to flocculate at elevate levels of solids or particles in fine size, or the ability to form flocs with high yield stress.
The inventors of the present disclosure have found that there is a surprising correlation between the size of the charged core of a hybrid particle-polymer flocculant and the performance in aggregation of solid microscopic substances. Flocculation is believed to be enhanced with charged particle-polymer hybrid flocculants that have core sizes larger than about 150 nm.
In a first aspect, the present disclosure provides a charged particle-polymer hybrid flocculant that includes charged core particles having an average size between about 150 nm and about 800 nm and each having a polymer polymerized thereon. Preferably, the charged core particles have an average size between about 340 nm and about 750 nm, and more preferably the charged core particles have an average size between about 500 nm and about 750 nm.
The charged core particle may include Al(OH)3 or Fe(OH)3. The polymer polymerized on the charged core particles may be a polyacrylamide.
In another aspect, there is provided a method of forming a charged particle-polymer hybrid flocculant. The method includes forming charged core particles having an average size between about 150 nm and about 800 nm; and polymerizing a monomer on the charged core particles.
Forming charged core particles may include reacting ammonium carbonate with a metal chloride, and may preferably include selecting a ratio between the ammonium carbonate to the metal chloride to control the size of the metal hydroxide particles. Preferably, the charged core particles have an average size between about 340 nm and about 750 nm, and more preferably the charged core particles have an average size between about 500 nm and about 750 nm.
In still another aspect, there is provided a method of separating fine solids from a suspension thereof. The method includes adding the charged particle polymer hybrid according to the present disclosure to the suspension to produce floccules and a supernatant, and separating the produced floccules from the supernatant.
Without wishing to be bound by theory, the authors of the present disclosure believe that the flocculating efficacy is a function of the size of the flocculant particles relative to the size of the solids being removed from suspension. It is believed that using flocculant particles that are too small for a given size of solid results in reduced efficacy because the contact frequency between the flocculant particles and the solids being removed from suspension is reduced as the size of the flocculant particles is decreased, while using flocculant particles that are too large for a given size of solids results in reduced efficacy because the specific total solid/liquid surface area and the number of the flocculant particles available for capturing the solids to be flocculated per unit weight of solids is reduced. It is believed that the contact frequency is decreased when reducing the size of flocculant particles because there is increased thermal motion of the flocculant particles as the size of the flocculant particles is reduced. It is also believed that an increase in thermal motion of flocculant particles increases the likelihood that captured solids will detach from the flocculant particles.
The authors of the present disclosure have identified flocculant particles that are particularly effective for flocculating oil sands mature fine tailings (MFT), which is also referred to as fluid fine tailings (FFT), which predominantly have clay particles with diameters smaller than 10 microns (10,000 nm), with the finest size fraction having diameters from about 50 to about 500 nm. Flocculant particles according to the present disclosure that are particularly effective for flocculating oil sands mature fine tailings have an average size between about 340 nm and about 750 nm.
Matured fine tailings, or fluid fine tailings in oil sands extraction may have up to about 35 wt. % solids after being consolidation for a period of time, for example a number of years. Greater than 97% of all the solids in MFT are smaller than 44 μm, and most samples of fine solids have an average size (d50) of less than 0.2 μm. Without wishing to be bound by theory, the authors of the present disclosure believe that, at least for some concentrations of oil sands mature fine tailings, the flocculating efficacy is more a function of the size of the flocculant particles for a given percent solids, and less a function of the concentration (ppm) of flocculant particles used. It is believed that both smaller flocculant particles according to the present disclosure, for example around 340 nm, and larger flocculant particles according to the present disclosure, for example between about 500 nm and about 750 nm, are effective at flocculating oil sands mature fine tailings or fluid fine tailings with lower percent solids, for example 5% solids, but that oil sands mature fine tailings or fluid fine tailings with higher percent solids, for example 10% solids, require larger flocculant particles according to the present disclosure, for example between about 500 nm and about 750 nm.
Yield stress of a floc is a factor in the floc strength. Yield stress is a reflection of how easily the flocs are broken into smaller particles. Smaller particles are less desirable than larger particles since the smaller particles are more difficult to remove and more readily foul separating equipment, such as filtration membranes. In selecting a flocculant to use, it is desirable to select a flocculant that generates a floc with a higher yield stress. Flocculants according to the present disclosure, having an average size of about 340 nm to about 750 nm generate flocs with yield stresses above about 500 Pa, such as between about 500 Pa and about 600 Pa. Flocs from oil sands mature tailings with yield strengths above about 500 Pa may resist breakdown by hydrodynamic forces during a solid-liquid separation process, such as filtration, thereby facilitating transport and further processing of the flocculated tailings.
Other aspects and features of the present disclosure will become apparent to those ordinarily skilled in the art upon review of the following description of specific examples in conjunction with the accompanying figures.
Examples of the present disclosure will now be described, by way of example only, with reference to the attached Figures.
Generally, the present disclosure provides a charged particle-polymer hybrid (CPPH) flocculant that includes charged core particles, each having a polymer polymerized thereon.
When solid microscopic substances are dispersed in an aqueous liquid carrier, the substance particles acquire electric charges due to, for example, dissolution of the solid surfaces, ionization of surface groups, adsorption of ions into the liquid carrier from the surface, substitution of ions in a lattice of the particle, or combinations thereof.
The inventors of the present disclosure have now observed that there is a surprising connection between the size of the charged core of the CPPH flocculants and the performance in aggregation of solid microscopic substances. Without being bound by theory, the inventors of the present disclosure believe that flocculation is enhanced when the charged core is of sufficient size to interact with suspended particles and draw those suspended particles towards the charged core by electrostatic attraction, thereby forming compact floccules. Accordingly, flocculation is believed to be enhanced with CPPH flocculants having larger core sizes than 150 nm.
The interaction between CPPH flocculants and microscopic substances is illustrated in
The inventors of the present disclosure have observed that the ability to interact with suspended particles becomes an important factor when the charged core of the CPPH flocculant have an average size between about 150 nm and about 800 nm in diameter. In particular examples, the charged core may have an average size between about 340 nm and about 750 nm. The charged particle-polymer hybrids that have an average core particle size between about 500 nm and about 750 nm are able to induce flocculation of slurries at solids concentrations higher than smaller sized CPPH particles (for example CPPH particles between 50 and 100 nm), as shown in the prior art.
The charged core may include a metal hydroxide. The metal hydroxide may be a transition metal hydroxide. The metal hydroxide may be a multivalent metal hydroxide. In particular examples, the metal hydroxide is Al(OH)3 or Fe(OH)3. The charged particle may include a mixture of metal hydroxides.
The size of the charged core may be varied by changing the ratio of reactants used to form the charged core. For example, the charged core may be metal hydroxide core and may be formed by reacting ammonium carbonate with a metal chloride. The ratio between the ammonium carbonate and the metal chloride may be selected in order to control the size of the metal hydroxide core.
Changing the size of the charged core changes the electrostatic forces between the charged cores and the suspended particles that are flocculated. Changing the electrostatic forces affects the flocculant properties. Charged particle polymer hybrids that have different sized charged cores were generated using varying ratios of (NH4)2CO3 to AlCl3.6H2O to form differently sized charged Al(OH)3 core particles. Acrylamide was used as the monomer to form the polymer. Because the polymers were formed under consistent conditions, the resulting polymers have similar average molecular weights of about 4.7*106 Daltons. The different flocculants are summarized in Table 1, below.
Sample “a” corresponds to a charged core particle made following the procedure disclosed by Yang et al. in “A novel flocculant of Al(OH)3-polyacrylamide ionic hybrid” (Journal of Colloid and Interface Science (2004), 273:2, pp 400-405).
The size distributions of the charged particle polymer hybrids were measured using a Zetasizer Nano Range from Malvern. The system measures size and microrheology using dynamic light scattering (DLS). Dynamic light scattering (DLS), sometimes referred to as Quasi-Elastic Light Scattering (QELS), is a non-invasive, well-established technique for measuring the size and size distribution of molecules and cores typically in the submicron region, and with the latest technology, lower than 1 nm. The size of the charged particle polymer hybrid (CPPH) correlates to the size of the charged particle.
These charged particle polymer hybrids were evaluated for their flocculating ability. Briefly, the CPPHs were tested against different slurries of oil sands MFT tailings from Syncrude (0.5%, 5%, 10% and 20% solids) for their ability to induce flocculation. Settling curves were determined by plotting the mudline position over time. Details of the tests are discussed below. However, a summary of the normalized settling (mudline travel distance at time=t/mudline position at time=0) after 25 minutes is shown in Table 2, below. A value approaching 0% for normalized settling reflects complete flocculation of the solids. A value of 100% for normalized settling reflects no flocculation of the solids.
The results summarized in Table 2 indicate that charged particle polymer hybrids that have a charged cores with an average size between about 150 nm and about 800 nm have the ability to flocculate slurries of solid particles from oil sands better than CPPHs having an average core size of 100 nm or smaller. In particular, CPPHs that have an average core size of between about 500 nm and about 800 nm have the ability to flocculate some solid particles under conditions where CPPHs with cores of 100 nm and below are not all effective. The inventors attempted to synthesize CPPH's with charged cores having average size above 1 μm but were unsuccessful as the charged cores settled out of solution even with agitation and polymerization with the monomer was not successful.
The polymer polymerized on the charged core particles may be a commercially available flocculating polymer, such as polyacrylamide (PAM). Without being bound by theory, the inventors of the present disclosure believe that flocculation is enhanced when (a) the polymer branches extend from the charged particle to which they are attached so as to increase the possibility that the polymer branches will contact and interact with suspended particles, but (b) the polymer branches do not extend so far as to inhibit suspended particles from being drawn towards the charged particle.
The intrinsic viscosity of the CPPH flocculants is affected by the length and shape of the polymer attached to the charged particles. Accordingly, intrinsic viscosity may be considered to be a representative measure of how the polymer branches affect the performance of the CPPH flocculants in aggregating the solid microscopic substances. If the intrinsic viscosity is too low, indicative of short or entangled polymer chains and branches, the effectiveness of the hybrid flocculant in capturing suspended particles is diminished. Conversely, high intrinsic viscosity is understood to indicate high average length for the polymer branches attached to the charged particles, and reduces the electrostatic attraction between captured suspended particles and the charged core particles of the hybrid flocculant, which may result in re-dispersion when over-dosed. In particular examples, the charged particle-polymer hybrid according to the present disclosure may have an intrinsic viscosity between about 210 mL/g and about 1400 mL/g. Preferably, the charged particle-polymer hybrids have an intrinsic viscosity between about 210 mL/g and about 930 mL/g.
Changing the concentration of initiator may change the intrinsic viscosity of the resulting hybrid flocculant. Increasing the concentration of initiator results in a lower intrinsic viscosity for the resulting hybrid flocculants. For example, as shown in Table 3, by doubling the free radical initiator concentration used in the synthesis of aluminum-hydroxide-PAM hybrid flocculants, the intrinsic viscosity is reduced by about 40%.
The CPPH flocculant according to the present disclosure may be used to help aggregate microscopic substances that are suspended in a liquid carrier, for example, in the treatment of oil sands tailings. It may be preferable to use particular examples of the CPPH flocculant according to the present disclosure in the treatment of oil sands tailings, such as MFT or FFT. As discussed above, oil sands tailings predominantly have clay particles with diameters smaller than 10 microns (10,000 nm), and may have particles with sizes from about 50 to about 500 nm. Such particles are preferably flocculated using CPPH flocculants between about 340 nm and about 750 nm. As discussed above, oil sands tailings may have up to about 35 wt. % solids. As shown in
The present disclosure also provides a method (10) of forming a charged particle-polymer hybrid flocculant (12) that includes charged particles having an average core size between about 150 nm and about 800 nm and each having a polymer polymerized thereon. The method is illustrated in
The charged particle may include a metal hydroxide. The metal hydroxide may be a transition metal hydroxide. The metal hydroxide may be a multivalent metal hydroxide. In particular examples, the metal hydroxide is Al(OH)3 or Fe(OH)3. The charged particle may include a mixture of metal hydroxides.
The method may include selecting an amount of polymerizing initiator to control the intrinsic viscosity of the charged particle-polymer hybrid flocculant. The amount of polymerizing initiator may be selected to result in the intrinsic viscosity being between about 210 mL/g and about 1400 mL/g. The wt/wt ratio of the initiator to the monomer may be between 0.667 and 0.133. The polymer may be a polyacrylamide polymer.
In one exemplary method (110), illustrated in
The following examples serve merely to further illustrate embodiments of the present invention, without limiting the scope thereof, which is defined only by the claims appended hereto.
A metal-hydroxide colloidal solution was prepared comprising sub-micron core particles of metal-hydroxide. Al(OH)3 colloid solutions are controlled by the mole ratio of reagents (NH4)2CO3 to AlCl3.6H2O. The smaller of the mole ratio, the larger the core.
The Al(OH)3 colloid solutions were prepared by dissolving a weighted amount of (NH4)2CO3 and AlCl3.6H2O in separate volumes of deionized (Dl) water. The (NH4)2CO3 solution was slowly added drop-wise into the AlCl3.6H2O solution in a beaker under strong agitation (approx. 1,500 rpm) at room temperature. Agitation increases the uniformity of the metal-hydroxide colloidal particulate size. The reagents reacted according to the following reaction:
2AlCl3+3(NH4)2CO3+3H2O→2Al(OH)3+6(NH4)Cl+3CO2
Charged core particle solutions were made at varying mole ratios of (NH4)2CO3/AlCl3. Acrylamide monomer was dissolved in the metal-hydroxide colloidal solutions and polymerized by the addition of (NH4)2S2O8—NaHSO3 as an initiator. Sufficient amounts of 0.075 wt % NaHSO3 and 0.15 wt % (NH4)2S2O8 were added to 30 ml of metal-hydroxide colloidal solution containing 4.5 g acrylamide in a 2000 ml flask to result in polymers having molecular weights of about 4.7*106 Daltons. Nitrogen gas was introduced to the flask for 30 minutes before addition of the initiator. After addition of the initiator, the flask was sealed and polymerization was allowed to proceed for 8 h at 40° C. This resulted in charged particle polymer hybrids of varying sizes, see Table 4.
The resulting charged particle polymer hybrids were extracted and purified by adding the reaction solutions to deionised water, precipitating impurities, and extracting pure charged particle polymer hybrid with an acetone solution. This procedure may be repeated two or more times. The extracted material was dried at 50° C. in a vacuum oven.
The size distribution of the charged particles was measured using a Zetasizer Nano Range from Malvern. The system measures size and microrheology using dynamic light scattering (DLS). Dynamic light scattering (DLS), sometimes referred to as Quasi-Elastic Light Scattering (QELS), is a non-invasive, well-established technique for measuring the size and size distribution of molecules and particles typically in the submicron region, and with the latest technology measuring at lengths less than 1 nm.
Intrinsic viscosity measurements were conducted with an Ubbelohde viscometer at 30° C.
The suspensions used for testing the charged particle polymer hybrids were prepared by mixing mature fine tailings slurry (37% wt. solids) from Syncrude with recycled water from Syncrude at specific solids concentrations (05.%, 5%, 10% or 20% solid concentration). Solutions of the CPPH particles were prepared at 4 mg/mL.
The fine solid suspension, CPPH solution, and sufficient recycled water were mixed to result in 50 mL of a testing solution. The 0.5% solids solution was tested with 30 ppm CPPH particles; the 5% solids solution was tested with 500 ppm CPPH particles; the 10% solids solution was tested with 800 ppm CPPH particles; and the 20% solids solution was tested with 2000 ppm CPPH particles.
Settling tests were conducted using a digital camera to take pictures of the testing solution in a 50 mL graduated cylinder.
The settling curves were determined by measuring the midline travel distance at various times. The settling curves are based on the normalized settling (%) vs. settling time (min), where normalized settling (%)=mudline travel distance at time=t/mudline position at time=0.
The results for the flocculation of the 0.5% solids are shown in the graph in
The initial settling rates for the data used in
As noted above, the authors of the present disclosure believe that, at least for some concentrations of oil sands mature fine tailings, the flocculating efficacy is more a function of the size of the flocculant particles for a given percent solids, and less a function of the concentration (ppm) of flocculant particles used. This is illustrated in
In
The results for the yield stress testing are shown in
CPPH particles according to the present disclosure having particle sizes of 340 nm and 716 nm provided flocs with yield stresses above 500 Pa, while CPPH particles having sizes of 67 nm and 100 nm provided flocs with yield stresses below 450 Pa.
In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the examples. However, it will be apparent to one skilled in the art that these specific details are not required.
The above-described examples are intended to be exemplary only. Alterations, modifications and variations may be effected to the particular examples by those of skill in the art without departing from the scope, which is defined solely by the claims appended hereto.
This application claims the benefit of priority of U.S. Provisional Patent Application No. 61/968,201 filed Mar. 20, 2014, which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61968201 | Mar 2014 | US |
