SEPARATION OF PARTICLES OF DIFFERENT SURFACE ENERGIES THROUGH CONTROL OF HUMIDITY

Information

  • Patent Application
  • 20220072466
  • Publication Number
    20220072466
  • Date Filed
    September 03, 2021
    a year ago
  • Date Published
    March 10, 2022
    10 months ago
Abstract
An impact test apparatus can be used to determine particle interfacial energies with varying relative air humidity. It was observed that capillary condensation increased the adhesive forces of hydrophilic materials. A systems humidity separation window was identified and the differences in interfacial energy for a hydrophilic surface and for a hydrophobic surface can be exploited in order to achieve the separation of particles. Separation and concentration of particles, particularly particles within a mineral ore body, can be obtained.
Description
FIELD OF THE INVENTION

The present disclosure relates to humidity and its effect on the surface energies of particles. More particularly, but not exclusively, the present disclosure relates to the separation of particles of different surface energies through the control of humidity.


BACKGROUND

Many of the methods to classify and concentrate minerals and the subsequent extraction of metals takes place in water-based environments (aqueous solutions). These processes include hydrocyclone classification, gravity-based concentration methods, froth flotation and leaching. In this regard, the consumption of water in the mineral industry can be on the order of 1.5 to 3.5 m3 of water per metric ton of ore processed. Compounding the use of water results in subsequent issues presented by storage of moisture-laden tailings in dams.


Therefore, sustainable processing of the present disclosure (based upon differing adhesive forces) through the reduction of water consumption will become a key factor to make mining operations viable in the long term.


SUMMARY

Therefore, it is a primary object, feature, and/or advantage of the present disclosure to improve on the state of the art and overcome the deficiencies within the art.


It is a further object, feature, or advantage of the present disclosure is to provide a method and system for separating particles of different surface energies through control of relative humidity (RH).


It is a still further object, feature, or advantage of the present disclosure to provide a method and system for separating particles of different surface energies through control of humidity that uses less water than convention separation technologies.


Another object, feature, or advantage is to provide a method and system for mining operations for separating minerals of different surface energies through control of humidity within a separation environment.


Yet another object, feature, or advantage is to provide a viable, long term solution to classify and concentrate minerals.


Still another object, feature, or advantage is to provide a new method and process for classifying and concentrating particles (both mineral and non-mineral types) that can be used in combination with existing methods and processes.


In an aspect of the present disclosure, a method for separating particles of different surface energies through control of humidity is disclosed. The method includes, for example, in at least one aspect, the steps of providing a separation platform with a controlled environment for separating a plurality of particles, identifying one or more particle types to separate from the plurality of particles, controlling humidity within the controlled environment based on one or more properties of the one or more particles, and separating the one or more particle types from the plurality of particles by controlling the humidity within the controlled environment based on the one or more properties of the one or more particles.


In another aspect of the present disclosure, a system for separating particles of different surface energies through control of humidity is disclosed. The system includes, for example, a separation platform with a controlled environment for separating a plurality of particles, an intelligent controller operably connected to a data store, the separation platform, and one or more actuators, one or more properties of the plurality of particles accessible to the intelligent controller and the data store, and one or more operating conditions for the controlled environment accessible to the intelligent controller and the data store. In a preferred aspect, the separation platform identifies one or more particle types to separate from the plurality of particles, controls the one or more operating conditions for the controlled environment based on one or more properties of the one or more particles for separating one or more particle types from the plurality of particles.


In another aspect of the present disclosure, a method for classifying and concentrating minerals and the subsequent extraction of metals is disclosed. The method includes, for example, in at least one aspect, the steps of providing one or more known particle separation processes, performing a particle separation process on an input to or an output of the one or more known particle separation processes, wherein the particle separation process comprises a separation platform with a controlled environment for separating a plurality of particles, identifying one or more particle types to separate from the plurality of particles, controlling humidity within the controlled environment based on one or more properties of the one or more particles, and separating the one or more particle types from the plurality of particles by controlling the humidity within the controlled environment based on the one or more properties of the one or more particles.


In at least one other aspect of the present disclosure, a method for separating particles of different surface energies through control of relative humidity and substrate surface roughness is disclosed. The method includes, for example, in at least one aspect, the steps of providing a separation platform with a controlled environment having a substrate surface roughness for separating a plurality of particles, identifying one or more particle types to separate from the plurality of particles, controlling humidity and the substrate surface roughness within the controlled environment based on one or more properties of the one or more particles, and separating the one or more particle types from the plurality of particles by controlling the humidity and the substrate surface roughness within the controlled environment based on the one or more properties of the one or more particles.


One or more of these and/or other objects, features, or advantages of the present disclosure will become apparent from the specification and claims that follow. No single embodiment need provide each and every object, feature, or advantage. Different embodiments may have different objects, features, or advantages. Therefore, the present disclosure is not to be limited to or by any objects, features, or advantages stated herein.





BRIEF DESCRIPTION OF THE DRAWINGS

Illustrated embodiments of the disclosure are described in detail below with reference to the attached drawing figures, which are incorporated by reference herein, and where:



FIG. 1 is an exemplary schematic diagram representing the capillary of a sphere and a flat surface;



FIGS. 2A-2B are a schematic diagram representing removal and adhesive forces involved in a low relative humidity environment and in a high relative humidity environment in accordance with an exemplary aspect of the present disclosure;



FIG. 3 is a schematic of impact test apparatus in accordance with an exemplary aspect of the present disclosure;



FIG. 4 is plot illustrating the results of interfacial energy for different surface treatments at varying RH in accordance with an exemplary aspect of the present disclosure;



FIG. 5 is an image of plasma cleaned beads on a plasma cleaned disk before (left) and after (right) the impact at (a.) 16% RH and (b.) 75% RH in accordance with an exemplary aspect of the present disclosure;



FIG. 6 is an image TCOD treated beads on TCOD treated disk before (left) and after (right) the impact at (a.) 16% RH and (b.) 63% RH in accordance with an exemplary aspect of the present disclosure;



FIG. 7 is a plot illustrating the results of interfacial energy for different particle surface treatments on a plasma cleaned disk at varying RH in accordance with an exemplary aspect of the present disclosure;



FIG. 8 is an image of TCOD treated beads on plasma cleaned disk before (left) and after (right) the impact at (a.) 50% RH and (b.) 75% RH in accordance with an exemplary aspect of the present disclosure;



FIG. 9 is an image of TCOD treated beads and plasma cleaned beads on plasma cleaned disk before (left) and after (right) the impact at a) 37% RH and b) 52% RH in accordance with an exemplary aspect of the present disclosure;



FIG. 10 is a plot illustrating the recovery of particles with varying RH in accordance with an exemplary aspect of the present disclosure;



FIG. 11 is a plot illustrating relative air humidity measured average by month in 2019;



FIGS. 12-16 are images of an exemplary impact test apparatus, humidifier chamber, and humidity sensor in accordance with an exemplary aspect of the present disclosure;



FIG. 17 are images of different cases of particle adhesion of rough surfaces in accordance with an exemplary aspect of the present disclosure;



FIG. 18 is an image for an exemplary set up of particles and rough substrate on an aluminum stub for mechanical impact tests in accordance with an exemplary aspect of the present disclosure;



FIG. 19 is a laser image of a mesh in accordance with an exemplary aspect of the present disclosure;



FIG. 20 is a 3D display of a mesh in accordance with an exemplary aspect of the present disclosure;



FIG. 21 is a plot illustrating correlation of interfacial energy versus relative air humidity for a plasma-cleaned mesh and different particles in accordance with an exemplary aspect of the present disclosure;



FIG. 22 is a plot illustrating differential recovery of plasma-cleaned beads/TCOD beads in accordance with an exemplary aspect of the present disclosure; and



FIG. 23 is an image of 30 μm bead (left) and 50 μm bead (right) sitting on the stainless-steel mesh wires in accordance with an exemplary aspect of the present disclosure.





BRIEF DESCRIPTION OF THE TABLES

Illustrated embodiments of the disclosure are described in detail below with reference to the attached tables, which are incorporated by reference herein, and where:


Table 1 is a summary of experimental studies of the influence of RH on a sphere on flat surface systems;


Table 2 provides results of interfacial energy calculations for different RH levels for TCOD treated particles and plasma cleaned substrates;


Table 3 provides results of interfacial energy calculations for different RH levels for plasma cleaned particles and plasma cleaned substrates; Table 4 provides results of interfacial energy calculations for different RH levels for TCOD treated particles and TCOD treated substrates; and


Table 5 provides dimension and surface roughness of a mesh.


DETAILED DESCRIPTION

The present disclosure contemplates many different aspects for a method and system for separating particles of different surface energies through control of humidity. Representative applications of methods and systems are described in this section. These examples are being provided solely to add context and aid in the understanding of the described aspects of the disclosure. It will thus be apparent to one skilled in the art that the described aspects of the disclosure may be practiced without some and/or all of these specific details. In other instances, well known process steps have not been described in detail in order to avoid unnecessarily obscuring the described embodiments. Other applications are possible, such that the following examples should not be taken as limiting.


In the following detailed description, references are made to the accompanying drawings, which form a part of the description and show, by way of illustration, specific embodiments in accordance with the methods and systems of the present disclosure. Although aspects of the disclosure are described in sufficient detail to enable one skilled in the art to practice the described embodiments, it is understood that these examples are not limiting; other aspects may be used, and changes may be made without departing from the spirit and scope of the described aspects of the disclosure.


1.0 INTRODUCTION

Many of the methods to classify and concentrate minerals and the subsequent extraction of metals takes place in water-based environments (aqueous solutions). These processes include, for example, hydrocyclone classification, gravity-based concentration methods, froth flotation and leaching. In this regard, the consumption of water in the mineral industry can be on the order of 1.5 to 3.5 m3 of water per metric ton of ore processed. Compounding the use of water is the subsequent issues presented by storage of moisture-laden tailings in dams. Thus, sustainable processing through the reduction of water consumption will become a key factor to make mining operations viable in the long term.


Froth flotation is the most common aqueous-based process to concentrate minerals with different surface properties. Specifically, particle wettability is the main property that influences the interaction between air bubbles and mineral surfaces. A hydrophobic mineral surface will adhere to air bubbles and be carried to the water/air interface, forming a mineralized froth. Minerals with hydrophilic surface character will not adhere to air bubbles. Thus, the governing mechanism for flotation is adhesion (or not) between the air bubble and the mineral particle. However, the flotation process requires tremendous amounts of water to achieve the desired concentrate grade.


The differences in adhesive forces between particles and a flat substrate have been investigated with the goal of development of a sustainable particle concentration system. Toward this end, many of the concepts associated with flotation mineral surface treatments have been utilized without the need for the continuous aqueous phase or water-based environment being present. Key to the methods and systems of the present disclosure is a means to measure particle adhesive forces, and an understanding of the forces involved. In this regard, there are various techniques that have been applied to measure adhesive forces and the techniques used herein will be discussed subsequently. When a dry particle is in contact with a dry surface, the primary adhesion forces involved are the van der Waals and electrostatic forces. According to known practices, the van der Waals forces can be heightened by increasing the contact area between particle and surface, i.e. causing deformation on either the particle or the substrate. This is not the case in at least one aspect of the present disclosure since the particles and substrates used were rigid, and the deformation was neglected as it is expected to be small.


In humid environments, capillary condensation of liquids (e.g., water, although other liquids are contemplated) can occur between the particle and substrate. FIG. 1 shows an example of capillary condensation between a spherical particle and a flat surface. The presence of capillary condensation engenders a capillary force, which is large compared to the van der Waals force and the electrostatic force. Thus, the relevant adhesive forces present in this particle/surface system are: van der Waals adhesion force (Fvdw), electrostatic image force (Fcl) and capillary force (Fc), represented by Equations 1 to 3, respectively.











F

v

d

w


=


A

R


6


z
2




,




(
1
)








F

c

l


=

Q

6



(

D
+
z

)

2




,




(
2
)








F
c

=

4

π

R


γ

L

V




,




(
3
)







Where A is the Hamaker constant, R is the radius of the spherical particle, z is the separation distance (also taken as 4 Å), Q is the charge carried by the particle, D is the particle diameter, and γLV is the surface tension of the condensed liquid. In at least one aspect, to obtain the pull-off force related to the capillary force, Fc (Equation 3), it is necessary to consider the area where the Laplace pressure has influence. From the Kelvin equation, the Laplace pressure and the area have inverse dependence on the Kelvin radius (rK). Therefore, Equation 3 is independent of relative air humidity. However, experimentation by others tends to suggest that the adhesion increases as the humidity increases. Thus, Equation 3 is contradicted. This is likely because of assumptions made in the derivation of Equation 3 related to the vapor pressure used in the Kelvin equation. A review of the influence of relative humidity on particle adhesion from various studies in the art indicated that the roughness on the surface of the substrate and on the particle hinder the adsorption of water at the particle/substrate interface. Some studies concluded that increasing roughness decreased adhesion. The decrease in adhesion happens when the thickness of the film of water at the interface is on the same order of magnitude as of the asperity height. In these cases, there are in fact many points of contact between the rough particle with the flat surface, or between the smooth particle and the rough surface, causing a decrease in adhesion. This aspect of the present disclosure is expected to be very important when crushed minerals are evaluated. For purposes of illustration, the exemplary experiments performed with glass beads that will be presented in the present disclosure, the roughness effect was neglected.


Exemplary experiments conducted using an atomic force microscope (AFM) with a glass sphere (R≈10 μm) at the tip of the AFM cantilever on polished silicon wafers (roughness of 1-2 nm) showed a variation in adhesion between a glass sphere and a silicon wafer. Specifically, a threshold in adhesion was observed around 60% relative air humidity (RH). Above this value, the adhesion force increased significantly. The pull-off force was approximated by Equation 3.


Similar behavior was achieved in experiments conducted on other exemplary systems. In one aspect, polystyrene latex (PSL) spheres (22 μm diameter) were deposited on polished silicon wafers. Here, the silicon wafer was rotated at 8,500 rpm for 120 seconds, generating detachment forces (drag force, lift force and centrifugal force). This procedure was repeated with humidity ranging from 10% to 90%.


In this case it was rationalized that at low relative humidity values the charge build-up is predominant, since PSL particles are insulators and silicon wafer is a semi-conductor. A gradual increase in the adhesion force when the RH varied from 45% to 80% was seen and a steep increase in the adhesion force was seen when the RH varied from 80% to 85% this occurred due to capillary condensation (increasing capillary force). In this example, the PSL is hydrophobic and the substrate is hydrophilic. The steep increase occurs at a greater relative humidity (80% versus 60%) than for the silica-based system, possibly because of the difference in hydrophobic character between the two systems.


For the case where spherical particles are sitting on a flat surface, a normal tensile force can cause separation if the lift-off force is greater than the adhesive forces. FIG. 2 shows the forces involved in low and high relative humidity environments.


Here Fpo is the pull-off force given by the Johnson-Kendall-Roberts (JKR) model, represented by Equation 4.






F
poWad  (4)


Where Wa is the thermodynamic work of adhesion and d is the particle diameter. The lift-off force required to remove the particle from the surface is then: Fpo+Fc. Other methods to calculate the force necessary to remove the particles were used and are contemplated in the present disclosure and discussed here, and in more detail under the Materials and Methods heading.


Various studies by others investigated the influence of RH in particle adhesion. The measurement techniques used in various studies includes, for example, pendulum testing, deflection of fibers, centrifugal testing, use of electro-balances and AFM, with RH varying from 0% to 100%. Other exemplary studies have been investigated. A table that encompassing findings of the present disclosure are shown, by way of example, in Table 1. Only the parameters comparable to the work presented in the present disclosure are shown in Table 1. The first comparison was the size of the particles involved. For example, in froth flotation a common size range is 10 μm and 150 μm—however, for completeness, studies with a top size of 1 mm were included in Table 1. The second relative comparison shown in Table 1 is the particle/substrate interaction. Finally, it should be noted that computer simulations were performed by research in the art comparing other works also indicated the influence of RH in the particle adhesion.









TABLE 1







Summary of experimental studies of the influence of RH on a sphere on flat surface systems












Measurement
Contact




Authors
Technique
Geometry
Materials
RH range





McFarlane and Tabor
Pendulum
Sphere-flat
Glass spheres 0.25
78%-100%





mm to 1 mm in





diameter


Zimon
Centrifuge Pulsed
Sphere-flat
Glass spheres 30 μm
25%-90% 



vibration

to 70 μm in diameter





Flat surface of glass,





quartz and steel


Harnby et al.
Particle array and
Particle-flat
Glass particles 80 μm
20%-98% 



microbalance

to 460 μm and sand





particles on brass,





glass or stainless-steel





surface.


Berard et al.
AFM
Particle on flat
Zanamivir drug 10 μm
0%, 32%, 85%





to 100 μm on lactose





compact


Jones et al.
AFM
Sphere on flat
Si probe tip and glass
0%-90%





microsphere (40 μm to





200 μm in diameter)





on glass silicon flat.


Rabinovich et al.
AFM
Sphere on flat
Glass spheres 20 μm
0%-80%





to 40 μm in diameter





on treated silica flat





surfaces


Feiler et al.
AFM
Sphere on flat
Glass beads 20 μm in
5%-88%





diameter on silicon





wafers


Farshchi-Tabrizi et al.
AFM
Sphere on flat
Borosilicate glass
 0%-100%





beads 4 μm in





diameter; Silica





microspheres 3.5 μm





in diameter









With this background information, the objective of the present disclosure is to identify separation windows in which control of relative air humidity yields different substrate adhesion for hydrophilic and hydrophobic particles of different values of interfacial energy. Others have used a mechanical approach to measure particle interfacial energies. In such research the RH in which the experiments were performed was reported (between 45% and 60% RH), but this parameter was not deliberately controlled. A similar mechanical approach was used, for purposes of illustration, in the present disclosure; however, unlike the work done by others, relative humidity was controlled and varied for the measurement of particle separation. Therefore, a primary object of the present disclosure is to determine whether particles with different surface properties (hydrophobic and hydrophilic), and hence different adhesive forces, can be separated as a function of RH.


2.0 MATERIALS AND METHODS

This section sets forth exemplary materials and methods in accordance with one or more illustrative aspects of the present disclosure. As presented herein, the interfacial energy was determined based on an earlier impact test, which was modified to achieve the objectives of the present disclosure. In at least one example, a glass disk with the desired treatment was glued to an aluminum stub (25 mm long and 15 mm in diameter). A monolayer of glass spheres acquired from PolyScience (size range between 10 and 150 μm and density of 2.48 g/cm3) was dispersed on the substrate. This size range was chosen because it is comparable to the size range of various types of minerals often encountered in mineral beneficiation, such as silicates, sulfides, sulfates, oxides, hydroxides, carbonates, phosphates, halides, and native elements. Imaging of the disk and the beads was performed using an optical profilometer (Keyence VK 200) prior to the impact test. After initial imaging, the stub is placed in the testing apparatus 10. The aluminum stub was propelled through a glass tube 12 using an air compressor 14 with a pressure regulator 16. The pressure was adjusted in order to achieve the desired velocity inside a horizontal tube 12 with maximum (preferred) length of 50 cm, although other lengths are contemplated. An aluminum backstop 18 with an opening of 12 mm was placed at the end of the glass tube 12. Other backstop and opening sizes are contemplated. The stub accelerated and impacted on the backstop 18 against the opening at the end of the tube. To record the velocity of impact and the duration of impact, a high-speed camera (IDT MotionProY Series 4) was used at 70,000 fps. FIGS. 3 and 12-13 show a schematic diagram of the testing equipment 10.


Equations (5) to (7) were used, where Fad is the JKR adhesive force, Γ is the interfacial energy and R is the particle radius of the largest particle left on the substrate to calculate the interfacial energy between two bodies. Equation (6) calculated the detachment force caused by a deacceleration of a given particle of mass m, where Fdet is the detachment force, Δt is half of the time of impact (i.e., half of the time of contact between stub and backstop) and ν is the impact velocity. The interfacial energy was then estimated from Equation (7), with Fdet=Fad.











F
ad

=


3
2


π





R





Γ


,




(
5
)







F
det

=


m

Δ

v


Δ

t






(
6
)






Γ
=



m

Δ

v


Δ





t





π





R




2
3






(
7
)







For the cases when the adhesive force is greater than the detachment force (Fad>Fdet), at a given particle size, the particles will not detach from the disk. When the adhesive force is equal to the detachment force, a critical particle size can be identified. The critical particle size is used in Equation 7 to calculate the interfacial energy.


Initial adhesion testing was conducted with no humidity control. It was found that the relative humidity fluctuated daily and the fluctuations were largely seasonal. For example, the average humidity measured inside the laboratory varied from 16% during the winter, to 55% during the summer. Measured relative air humidity levels are shown, by way of example, in FIG. 11. Consequently, the testing apparatus 10 (FIGS. 3 & 14-16) was placed inside a transparent polycarbonate chamber 22 to create a controlled humidity environment testing system 20. Other environments for controlling humidity are also contemplated. In one exemplary aspect, humidity was fed into the chamber using a humidifier 24 (Homasy Model HM161B) that was plugged into a controller 16 (Inkbird Humidity Controller IHC200) capable of measuring relative air humidity from 5% to 99%. To decrease the humidity inside the chamber a renewable silica-gel-based dehumidifier (Eva-Dry E-500) was used. The humidity controller 26 was set to the desired level, the sensor then turned the humidifier on and turned it off as soon as the desired humidity was achieved. With the humidifier 24 it is possible to increase the tested humidity above seasonal maximums, such as 55% humidity and exploit the interaction between surface treatments and water present in the air, in order to determine the effect of humidity on the ability to separate particles based upon adhesive forces.


In at least one exemplary aspect of the present discourse, and to ensure that the particles and substrates would be conditioned to the set relative air humidity, the particles were sprinkled over the glass and left inside the chamber 12 for at least 30 minutes prior to testing to allow all of the particles to contact the moisture in the air. The glass was glued on top of an aluminum stub and the test was performed as described earlier. For tests under controlled air humidity, two different glass treatments were used: plasma cleaned glass (hydrophilic and higher surface energy) and trichloro(octadecyl)silane (TCOD) (hydrophobic and lower surface energy). The purpose of using these two treatments, in accordance with at least one aspect of the present disclosure, was to compare the response of the interaction between hydrophilic surfaces, hydrophobic surfaces and a combination of hydrophobic particles and hydrophilic substrates.


At least one example of a TCOD treatment was performed mixing 0.7 ml of TCOD and 20.0 ml of toluene for each gram of glass treated. The solution was then mixed for 2 hours in a beaker. After the solution mixing, the glass specimens were dried at 150° C. for 2 hours. To ensure that the hydrophobic treatment was effective, the contact angle between a drop of water and a glass disk was measured. For the glass beads, a fraction of beads was put in contact with water. The plasma cleaned glass beads would sink when in contact with water, and the TCOD treated beads would float/not mix with water.


Also, two different types of particles were placed on the same glass disk, in a way that it was possible to compare two treatment types under the same velocity of impact and duration of impact. Imaging of the beads on the disk was performed before and after the tests using the same profilometer mentioned in the previous section. The beads that remained attached to the disk after the impact were analyzed and the diameter was measured using ImageJ.


3.0 RESULTS AND DISCUSSION

For the plasma cleaned glass beads and plasma cleaned glass disks, the interfacial energy was calculated by applying Equation 7 and varying the RH from 16% to 79%. For the TCOD treated beads and TCOD treated disks, the interfacial energy was calculated for RH levels from 16% to 63%. The results of these tests are shown in Tables 3 and 4, respectively.



FIG. 4 graphically shows the results of the two surface treatments as a function of RH. It can be seen that the interfacial energy of plasma cleaned treated (hydrophilic and high surface energy) material is dependent on RH. Between 16% and 33% RH there is no significant change in the interfacial energy for the plasma cleaned (hydrophilic) particles. As the RH increases beyond 33%, the interfacial energy increases quite linearly from an average of 13.4 mJ/m2 to 124.8 mJ/m2 at 79% RH. Thus, it is possible to compare this behavior with the results from prior work, where at an RH threshold the capillary force will overcome the van der Waals force and hold the particles more strongly than the contact forces. In a subsequent investigation this effect was determined using an AFM where a maximum or continuous increase of adhesion force with increasing RH for hydrophilic surfaces was found.


With respect to the TCOD treatment, with the RH varying from 16% to 63%, there is relatively little change associated with the interfacial energy of this surface treatment.


The interfacial energy varied from 17.2 to 27.5 mJ/m2. Exemplary literature values for this surface treatment indicate that TCOD coated surfaces should have a surface tension between 20 to 24 mJ/m2.


Therefore, at RH values beyond ˜35%, a separation window was explored by using the surface interaction of different surface treatments and properties to achieve a separation of particles. The first two analyses compare the same type of surface treatment for the substrate and particles. In order to evaluate the separation of particles with different surface properties in a single system, tests were performed using only plasma cleaned disks as substrate and having the two different types of beads treatment (plasma cleaned and TCOD) as particles.


To help demonstrate how RH impacts the adhesive forces, the difference for the hydrophilic and higher surface energy treatment for the hydrophobic and lower surface energy treatment are shown in FIGS. 5 and 6. FIG. 5 shows a plasma cleaned disk with plasma cleaned beads before and after the impact at a) 16% RH and at b) 75% RH. FIG. 6 shows a TCOD treated disk with TCOD treated beads before and after the impact at a) 16% RH and at b) 63% RH. The visual before-and-after inspection clearly demonstrates the influence of RH on particle adhesion.


Nevertheless, for the TCOD treated material, capillary condensation may occur for the hydrophobic systems.


A third group of tests was performed, with plasma cleaned (hydrophilic) and TCOD particles (hydrophobic) sharing the same substrate, a plasma cleaned glass disk (hydrophilic). This ‘mixed’ system was chosen to help demonstrate the possibility of an actual mineral separation using a common substrate. Due to the limitations associated with the optical microscope used (featureless, same size, same color) surfaces, the particles were placed in different regions on the same disk. The results of interfacial energy at varying RH levels for plasma cleaned disk/substrates and TCOD treated particles are shown in Table 2.









TABLE 2







Results of interfacial energy calculations for different RH levels


for TCOD treated particles and plasma cleaned substrates.
















Critical


Half of




Glass
Bead
Radius of
Mass of
Impact
duration of
Interfacial


Disk
Type
Particles
Particle
Velocity
impact
Energy
Relative


Treatment
Treatment
(m)
(kg)
(m/s)
(s)
(mJ/m2)
Humidity

















Plasma
TCOD
2.74E−05
2.142E−10
1.59
0.00020
13.15
41%


Cleaned

2.67E−05
1.988E−10
1.59
0.00015
16.77
41%




2.61E−05
1.844E−10
1.40
0.00014
15.48
42%




2.42E−05
1.464E−10
1.21
0.00015
10.38
45%




1.62E−05
4.428E−11
1.49
0.00014
6.04
45%




2.66E−05
1.959E−10
1.81
0.00014
19.82
45%




4.70E−05
1.080E−09
1.54
0.00011
65.49
50%




5.06E−05
1.350E−09
1.75
0.00010
98.71
50%




3.64E−05
5.014E−10
1.55
0.00013
35.12
51%




4.73E−05
1.101E−09
1.24
0.00013
47.76
52%




3.73E−05
5.369E−10
1.45
0.00013
34.48
54%




5.16E−05
1.430E−09
1.47
0.00015
57.75
56%




4.81E−05
1.158E−09
1.49
0.00013
59.16
56%




5.17E−05
1.437E−09
1.46
0.00018
48.16
76%




5.17E−05
1.436E−09
1.57
0.00017
53.97
77%




4.87E−05
1.197E−09
1.58
0.00011
72.02
79%










FIG. 7 shows the results from Table 2 and Table 3 graphically. It is possible to observe that the interaction of hydrophobic particles and hydrophilic substrate (TCOD treated beads versus plasma cleaned disk) has changed when compared to particles and substrate of the same time (TCOD beads versus TCOD disks). However, and most importantly, there is still a difference of interfacial energy that can be exploited to reach separation of particles with different surface energies.









TABLE 3







Results of interfacial energy calculations for different RH levels


for plasma cleaned particles and plasma cleaned substrates.
















Critical


Half of




Glass
Bead
Radius of
Mass of
Impact
duration of
Interfacial
Relative


Disk
Type
Particles
Particle
Velocity
impact
Energy
Air


Treatment
Treatment
(m)
(kg)
(m/s)
(s)
(mJ/m2)
Humidity

















Plasma
Plasma
2.95E−05
2.667E−10
0.67
0.00017
7.54
16%


Cleaned
Cleaned
2.55E−05
1.723E−10
1.46
0.00018
11.71
16%




2.75E−05
2.160E−10
1.57
0.00014
18.27
16%




2.40E−05
1.436E−10
1.84
0.00017
13.61
16%




2.20E−05
1.106E−10
1.65
0.00018
9.89
16%




2.40E−05
1.436E−10
1.10
0.00015
9.35
16%




2.78E−05
2.231E−10
0.67
0.00021
5.33
33%




3.88E−05
6.083E−10
1.48
0.00016
29.94
33%




2.88E−05
2.484E−10
1.30
0.00022
10.77
33%




2.71E−05
2.064E−10
1.12
0.00024
7.48
33%




4.48E−05
9.367E−10
1.72
0.00016
46.29
40%




4.35E−05
8.574E−10
1.72
0.00016
43.75
40%




4.63E−05
1.033E−09
1.75
0.00016
50.51
40%




4.78E−05
1.136E−09
1.59
0.00016
48.72
40%




4.20E−05
7.675E−10
1.42
0.00016
33.61
40%




4.66E−05
1.052E−09
1.58
0.00016
45.95
40%




4.11E−05
7.190E−10
1.50
0.00017
32.49
40%




7.00E−05
3.567E−09
1.59
0.00020
85.78
41%




4.68E−05
1.064E−09
1.59
0.00015
51.29
41%




3.48E−05
4.383E−10
1.40
0.00014
27.56
42%




7.12E−05
3.745E−09
1.70
0.00011
166.40
47%




5.11E−05
1.388E−09
1.75
0.00010
100.57
50%




5.02E−05
1.311E−09
1.54
0.00011
74.52
50%




6.28E−05
2.578E−09
1.55
0.00013
104.62
51%




5.16E−05
1.428E−09
1.23
0.00014
50.39
51%




5.00E−05
1.301E−09
1.15
0.00013
49.48
51%




5.80E−05
2.030E−09
1.34
0.00014
69.81
51%




4.93E−05
1.244E−09
1.15
0.00011
57.36
51%




7.15E−05
3.792E−09
1.24
0.00013
108.88
52%




7.75E−05
4.844E−09
1.45
0.00013
149.42
54%




6.18E−05
2.447E−09
1.43
0.00015
80.24
56%




5.04E−05
1.329E−09
1.48
0.00009
96.64
60%




6.56E−05
2.931E−09
1.39
0.00014
92.01
60%




5.89E−05
2.126E−09
1.09
0.00013
64.92
75%




7.03E−05
3.609E−09
1.23
0.00011
125.52
75%




5.83E−05
2.062E−09
1.41
0.00012
87.36
77%




5.97E−05
2.212E−09
1.47
0.00009
124.76
79%









Notably, as the plasma cleaned beads on a plasma cleaned surface/substrate interfacial energy continues to rise (see results from Table 3) with the increase in relative humidity.


Because the substrate is now hydrophilic and has higher surface energy, the hydrophobic particles have a different behavior at high RH levels, compared to the data shown in FIG. 4 (common particle/substrates), which shows the results from Table 3 and Table 4.









TABLE 4







Results of interfacial energy calculations for different RH levels


for TCOD treated particles and TCOD treated substrates.
















Critical


Half of




Glass
Bead
Radius of
Mass of
Impact
duration of
Interfacial
Relative


Disk
Type
Particles
Particle
Velocity
impact
Energy
Air


Treatment
Treatment
(m)
(kg)
(m/s)
(s)
(mJ/m2)
Humidity

















TCOD
TCOD
4.93E−05
1.241E−09
1.07
0.00021
27.50
16%




4.18E−05
7.588E−10
1.39
0.00024
22.12
16%




3.09E−05
3.078E−10
1.72
0.00014
26.82
40%




2.49E−05
1.598E−10
1.80
0.00014
17.22
40%




2.66E−05
1.956E−10
1.76
0.00014
20.27
40%




2.53E−05
1.687E−10
1.78
0.00011
21.98
40%




2.86E−05
2.425E−10
1.13
0.00010
20.40
63%




4.13E−05
7.302E−10
1.16
0.00016
26.44
63%




2.85E−05
2.398E−10
1.19
0.00011
19.93
63%










FIG. 7 shows that between 56% and 77% RH the increase in interfacial energy plateaus. The quantity of particles that remained attached after impact can be seen in FIG. 8, which shows a plasma cleaned disk with TCOD treated beads before and after the impact at a) 16% RH and at b) 75% RH.


From FIG. 7 it can be ascertained that the best separation parameter would be between 55% and 75% RH. However, from FIG. 8, at 75% RH, a considerable amount of TCOD treated beads remained attached after the impact. Few TCOD treated beads were present after testing at 50% RH. Thus, a series of tests between 45% and 55% RH was performed to evaluate the separation and recovery of particles with different surface treatment on the same substrate. Plasma cleaned beads were poured on the upper region and TCOD treated beads were poured on the lower region of the same substrate. FIG. 9 shows the results of tests at a) 37% RH and b) 52% RH.


As expected, as the RH increases, the adhesion of hydrophobic particles on the hydrophilic substrate increases. Using Image J, it was possible to measure the area covered by the particles before and after the impact with the objective to estimate the recovery of particles retained using Equation 8. The recovery was calculated as follows:









Recovery
=


Area





occupied





by





the





beads





after





impact


Acrea





occupied





by





the





beads





before





impact






(
8
)







At least on object of the present disclosure is to have a good recovery of plasma cleaned particles (considerable quantity of beads remaining attached after the impact) and a low recovery of TCOD treated particles (few low-surface-energy particles remaining). FIG. 10 shows the results of the tests from 37% to 54% of RH.


Examination of FIG. 10 shows that the recovery of plasma cleaned particles is relatively small when the RH is between 37-45%. However, when the RH is between 45-54% the recovery increases. For the tests between 47% and 54% the recovery of plasma cleaned particles was, on average, five times greater than the recovery of TCOD treated particles. These results indicate that a method of particle separation can be exploited in controlled relative air humidity environments for particles with different adhesive properties.


The present disclosure contemplates methods for evaluating the separation of mineral particles with different surface properties; as well as sustainable methods to modify particle surfaces in order to achieve separation for a given ore. It is at least one object of the present disclosure to provide particle separation methods and systems that address the consumption of water, since the water consumed to control RH in a room is smaller than the consumption of water by flotation process. In addition, the present disclosure contemplates particle separation methods and systems based on the effect of surface roughness of various particles.


4.0 CONCLUSIONS

An impact test apparatus, methods and systems can be used to determine the interfacial energies of a model system with varying relative air humidity. The behavior of the interfacial energy with varying RH is comparable to other methods used. It was observed that capillary condensation did increase the adhesive forces of hydrophilic materials. A separation window was identified and the differences in interfacial energy for a hydrophilic surface and for a hydrophobic surface can be exploited in order to achieve the separation of particles.


When in contact with a hydrophilic substrate, hydrophobic particles can be attached more strongly due to capillary condensation with higher-surface-energy substrates. In the cases where two different types of particles were under the same test conditions, plasma cleaned particles showed a higher recovery in 80% of the tests when the RH varied from 37% to 54%. And the recovery of the plasma cleaned particles proved to be five times greater, on average, when compared to the TCOD treated particles for RH between 47% and 54%. In at least one aspect of the present disclosure, measurements can be used in the development of sustainable methods and systems that uses little water to separate and concentrate fine minerals. In at least one exemplary aspect, data can be coupled with computer simulations in order to predict ideal conditions to achieve mineral separation. Also, in another exemplary aspect, a lab scale separator can be designed to determine the efficacy of mineral separations based upon adhesive forces with controlled relative humidity.


Since the surface energy is the sum of the different energy components—dispersion forces, polar forces, hydrogen bonding, metallic bonding—per unit area, when one surface is ideally flat and this surface is at the interface with another surface (from a particle or other material) that is also ideally flat, the interfacial area is simply defined as A. Unfortunately, most surfaces are not perfectly flat nor are the particles that are in contact with the substrate. Thus, there is a degree of roughness in most surfaces.


A. D. Zimon in Adhesion of Dust and Powder discussed three cases of particles residing on rough surfaces. The first case being the contact of a spherical particle and an ideally smooth surface; the second case is of a spherical particle which has dimensions larger than the asperities of the rough surface; and the third case is where the dimensions of the particle are smaller than the asperities of the rough surface. These three cases are shown schematically in FIG. 17.


In all three cases, as the area of contact increases, the adhesive force increases. Zimon assumed a uniform distribution of contacts between the particle and asperities, and as shown in Equation 9, determined the adhesive force (Fad) as related to the number of contacts (represented by i) between the particle and the surface.






F
ad
=iF
ad
i  (9)


Also, the number of contacts is related to the equivalent radius of curvature, as introduced by Zimon. The effective contact radius was introduced to evaluate the influence of surface roughness on adhesion. In Equation 10, the effective contact radius takes into account the roughness of the contiguous bodies, as determined by the formula:










r
e

=



r
1



r
2




r
1

+

r
2







(
10
)







The radius of the particle and surface asperity will influence the capillary force, which is affected by the roughness of the contiguous surfaces. The capillary force shown in Equation 11 can be written as:






F
c=2πLVr cos θi  (11)


In the case where a smooth spherical particle is in contact with a rough surface the number of contacts is either one, two or three. The presence of capillary condensation will then occur in one to three points of contact. Assuming an approximation of the contact of one rough particle (ground mineral) on a smooth surface the number of contacts can also vary from one to three points of contact; here the capillary condensation can occur in one to three points of contact, increasing the adhesive forces.


The above equations were used to evaluate the interaction of particles on substrates with varying magnitudes of roughness. The objective was to identify separation windows of particles of different surface energies on rough surfaces. Particle surface treatment, relative air humidity and surface roughness levels were controlled in order to achieve separation of different particles by applying removal forces.


Following the impact test procedures first developed and performed by Zafar et al. and later modified by Sansao et al., the impact test was performed inside a transparent polycarbonate chamber 22. Air of a desired RH was fed into the chamber 22 using a humidifier 24 (Homasy Model HM161B) that was coupled to a humidity sensor 26 (Inkbird Humidity Controller IHC200). This sensor 26 can measure RH from 5% up to 99% with 3% accuracy. Similarly, a passive dehumidifier—i.e., with no motor to force the air around it—(Eva Dry E-500) was used to decrease the humidity inside the chamber when necessary. The humidity sensor 26 was set to the desired level, the sensor then turned the humidifier 24 on and off when the desired humidity was achieved. Plasma-cleaned (hydrophilic) glass beads and beads treated with trichlogo(octadecyl)silane (TCOD), giving the particles a hydrophobic character, were used to vary the behavior of particles of different wettability in contact with a rough surface and RH present.


The approach to establish roughness on the substrate was to use a fine stainless-steel wire mesh. The mesh provided a reproducible substrate. The mesh surface investigated was a 325×2300 mesh (rectangular, Dutch weave). Each mesh roughness was measured, the mesh was surface plasma-cleaned and then mechanical impact tests under different relative air humidity levels were performed.


The preparation of the mesh to be used for the mechanical impact test involved two nylon washers to suspend the mesh away from aluminum stub. The first nylon washer was glued onto the aluminum stub, then tape was used on the edges of the washer; the mesh was then glued onto the washer edges. A second washer, also with glue on its edges, was glued on top of the mesh, leaving a clear area on the middle for viewing. An exemplary schematic of this set up is shown in FIG. 18.


The set up shown in FIG. 18 was designed, for example, so that the central part of the mesh was not in contact with the glue. This setup also allowed the desired area to be visualized for bead presence/absence.



FIG. 19 shows a laser image of 325×2300 mesh, and FIG. 20 shows a 3D laser profilometer display of this mesh.


The opening dimensions and the surface roughness (Ra) of the 325×2300 mesh is shown in Table 5. Also, due to the size of the openings, the smallest diameter of beads used was 30 μm and the largest was 50 μm.









TABLE 5







Dimension and surface roughness of the 325 × 2300 mesh.











Opening
Roughness




dimensions
(Ra)
Rz


Mesh
(μm)
(μm)
(μm)





325 × 2300
25 × 45
9.516 ± 1.094
47.430 ± 0.353









At 46% RH the recovery of particles is almost 100%, and this behavior remains at 85% RH. This higher recovery at 46% is explained by the higher number of points of contact between the particle and the rough substrate. Since the opening of this mesh is 25 μm×45 μm and the particle size varies from 30 to 50 μm, some particles interact with the mesh in a similar fashion to the third case showed in FIG. 17, allowing a greater area of contact than a single point.


Due to the constraint in the area available to pour the beads on the mesh (limited by the washer-mesh-washer arrangement) it was not possible to have both TCOD (hydrophobic) and plasma-cleaned (hydrophilic) beads on the same mesh to perform the test under the same parameters (mainly velocity and duration of impact). Nevertheless, tests were performed for both types of particles under similar parameters. The hydrophobic particles did not interact (adhere) as well as hydrophilic particles with greater RH. Even though there were more points of contact, the low wettability of the particle was an important factor to hinder the presence of capillary condensation in the same way as occurred using the sanded glass disk.



FIG. 21 shows the correlation of recovery of the different bead types on the mesh surface under different RH levels. The rough surface facilitated the recovery of plasma-cleaned beads, between 80% and 100% recovery. In addition, the variability of interfacial energy appears to be greatly reduced on these more similar surfaces. It can be concluded that a separation of different particle types can be achieved with controlled relative humidity and rough mesh surfaces.



FIG. 22 shows the differential average recovery of plasma-cleaned beads over the TCOD beads at the same relative humidity level. The recovery of plasma-cleaned beads is significantly higher than the recovery of TCOD beads at 46% and 55% RH. At 75% the differential recovery decreases due to the fact that the capillary condensation on the hydrophilic surface can now affect the adhesion of hydrophobic particles. In other words, more TCOD particles remained attached on the mesh surface.


Using the stainless-steel mesh, the particle's dimensions were at the same order of magnitude as the asperities of the mesh. The opening of the mesh could hold the particle without trapping it. FIG. 23 shows a graphical representation of a 30 and 50 μm bead sitting on the mesh wires (25 μm aperture).


The smaller spherical particles have relatively more area of contact with the wires than the larger spheres. Because of capillary condensation happening at each point of contact, the adhesion of the beads on the mesh showed to be even stronger. For the plasma-cleaned beads the recovery values had an average of 92.5% recovery when the RH was between 46% and 85%. For the TCOD treated beads, the average recovery was 19.0% between 46% and 75%, indicating that the hydrophobic characteristic of the particle influenced its lower interaction with the mesh. This difference in recovery can be exploited to achieve separation of particles based upon adhesive forces.


The disclosure is not to be limited to the particular aspects described herein. In particular, the disclosure contemplates numerous variations in methods and systems for particle separator methods and systems. The foregoing description has been presented for purposes of illustration and description. It is not intended to be an exhaustive list or limit any of the disclosure to the precise forms disclosed. It is contemplated that other alternatives or exemplary aspects are considered included in the disclosure. The description is merely examples of embodiments, processes, or methods of the disclosure. It is understood that any other modifications, substitutions, and/or additions may be made, which are within the intended spirit and scope of the disclosure.

Claims
  • 1. A method for separating particles of different surface energies through control of humidity, comprising: providing a separation platform with a controlled environment for separating a plurality of particles;identifying one or more particle types to separate from the plurality of particles;controlling humidity within the controlled environment based on one or more properties of the one or more particles; andseparating the one or more particle types from the plurality of particles by controlling the humidity within the controlled environment based on the one or more properties of the one or more particles.
  • 2. The method of claim 1, further comprising: treating the plurality of particles with one or more particle treatments to affect a surface energy of the one or more particle types.
  • 3. The method of claim 1, further comprising: treating the controlled environment with one or more treatments to affect a surface energy of the controlled environment.
  • 4. The method of claim 1, further comprising: identifying a specific particle type to separate from the plurality of particles, identifying a surface energy for the specific particle, providing a particle treatment for the specific particle, and controlling the humidity within the controlled environment based on one or more properties of the specific particle and the particle treatment.
  • 5. The method of claim 4, wherein the one or more properties of the specific particle comprises at least the surface energy and the hydrophobicity inherent of the material of which the particle is made.
  • 6. The method of claim 1, further comprising: identifying a first specific particle type and a second specific particle type to separate from the plurality of particles, identifying a surface energy for the first and second specific particles, providing a particle treatment for the first and second specific particle types, and controlling the humidity within the controlled environment based on one or more properties of the first and second specific particles and the particle treatment.
  • 7. The method of claim 1, further comprising: treating the plurality of particles with one or more particle treatments to separate a first specific particle type from the plurality of particles and a second specific particle type from the plurality of particles.
  • 8. The method of claim 1, further comprising: treating the controlled environment with one or more treatments to separate a first specific particle type from the plurality of particles and a second specific particle type from the plurality of particles.
  • 9. The method of claim 1, further comprising: separating one or more desired minerals from the plurality of particles during mining, wherein the separating step involves less water consumption than known methods for classifying and concentrating minerals.
  • 10. A system for separating particles of different surface energies through control of humidity, comprising: a separation platform with a controlled environment for separating a plurality of particles;an intelligent controller operably connected to a data store, the separation platform, and one or more actuators;one or more properties of the plurality of particles accessible to the intelligent controller and the data store; andone or more operating conditions for the controlled environment accessible to the intelligent controller and the data store;wherein the separation platform identifies one or more particle types to separate from the plurality of particles, controls the one or more operating conditions for the controlled environment based on one or more properties of the one or more particles for separating one or more particle types from the plurality of particles.
  • 11. The system of claim 10, wherein the one or more properties of the plurality of particles comprises surface energy and hydrophobicity.
  • 12. The system of claim 10, wherein the one or more operating conditions comprise humidity.
  • 13. The system of claim 10, further comprising: one or more particle treatments corresponding to the one or more particle types for affecting a surface energy of the one or more particle types.
  • 14. The system of claim 10, wherein the one or more actuators control the one or more particle treatments.
  • 15. The system of claim 10, further comprising: one or more environment treatments corresponding to the one or more particle types for affecting a surface energy of the separation platform.
  • 16. The system of claim 15, further comprising: a first treatment regimen for separating a first specific set of particles from the plurality of particles.
  • 17. The system of claim 16, further comprising: a second treatment regimen for separating a first specific particle type from the first specific set of particles.
  • 18. The system of claim 10, further comprising: a first separation program accessible by the intelligent controller for identifying a first specific particle type to separate from the plurality of particles, identifying a surface energy for the first specific particle, actuating a particle treatment for the first specific particle, and controlling the humidity within the controlled environment based on one or more properties of the first specific particle, a particle treatment, and an environment treatment.
  • 19. The system of claim 10, further comprising: an acceleration chamber operated by the one or more actuators for accelerating the plurality of particles for separation by collision.
  • 20. The system of claim 10, wherein the one or more particle types of the plurality of particles comprise one or more desired mining minerals, wherein separating involves less water consumption than known systems for classifying and concentrating minerals.
  • 21. A method for classifying and concentrating minerals and the subsequent extraction of metals, comprising: providing one or more known particle separation processes;performing a particle separation process on an input to or an output of the one or more known particle separation processes, wherein the particle separation process comprises: a separation platform with a controlled environment for separating a plurality of particles;identifying one or more particle types to separate from the plurality of particles;controlling humidity within the controlled environment based on one or more properties of the one or more particles; andseparating the one or more particle types from the plurality of particles by controlling the humidity within the controlled environment based on the one or more properties of the one or more particles.
  • 22. The method of claim 21, wherein the one or more particle types comprise silicates, sulfides, sulfates, oxides, hydroxides, carbonates, phosphates, halides, and native elements.
  • 23. A method for separating particles of different surface energies through control of relative humidity and substrate surface roughness, comprising: providing a separation platform with a controlled environment having a substrate surface roughness for separating a plurality of particles;identifying one or more particle types to separate from the plurality of particles;controlling humidity and the substrate surface roughness within the controlled environment based on one or more properties of the one or more particles; andseparating the one or more particle types from the plurality of particles by controlling the humidity and the substrate surface roughness within the controlled environment based on the one or more properties of the one or more particles.
  • 24. The method of claim 23, further comprising: treating the one or more particles with a particle surface treatment to affect a surface energy of the one or more particle types for separating the one or more particle types from the plurality of particles.
PRIORITY STATEMENT

This application claims priority to U.S. Provisional Patent Application No. 63/074,616 filed on Sep. 4, 2020, titled SEPARATION OF PARTICLES OF DIFFERENT SURFACE ENERGIES THROUGH CONTROL OF HUMIDITY, all of which is hereby incorporated by reference in their entirety.

Provisional Applications (1)
Number Date Country
63074616 Sep 2020 US