Grantee Research Project Results
Final Report: Preparation of Ceramic Glaze Waste for Recycling using Froth Flotation
EPA Grant Number: R830420C007Subproject: this is subproject number 007 , established and managed by the Center Director under grant R830420
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: Center for Environmental and Energy Research (CEER)
Center Director: Earl, David A.
Title: Preparation of Ceramic Glaze Waste for Recycling using Froth Flotation
Investigators: Carty, William
Institution: Alfred University
EPA Project Officer: Aja, Hayley
Project Period: May 1, 2006 through April 30, 2007
Project Amount: Refer to main center abstract for funding details.
RFA: Targeted Research Center (2004) Recipients Lists
Research Category: Hazardous Waste/Remediation , Targeted Research
Objective:
The ceramic whitewares industry produces several hundred million units of tile, dinnerware, sanitaryware, and electrical porcelain each year, with annual U.S. sales of approximately $8.2 billion. Water is used in large quantities throughout whiteware manufacturing, and is typically discarded into a sewer or deep storage well following several lengthy physical and chemical processing steps. During the collection, processing, and storage of used water from various body and glaze formulations, particulates of different sizes and compositions are mixed together producing unusable slurry. This is particularly true of glazing systems, where waste solids are primarily a mix of components from different color glaze formulations. The glaze waste also frequently contains elements such as lead, chromium, and cadmium, which must be collected, stored, treated, and disposed of as hazardous waste. There is an opportunity to reuse frit, and possibly pigment, from glaze waste provided the materials can be separated.
It is proposed that froth flotation technology offers a unique opportunity to specifically separate the glass frit powder from the small amount of impurities (<10%) such as the ceramic pigments in the glaze waste stream by exploiting differences in the particle surface chemistries.
The objective of the project is the creation of a new waste handling system for whiteware production, which reduces dependence on natural resources and has the potential to dramatically reduce waste (both hazardous and non-hazardous) currently sent to land fills. It is expected that this waste can be reduced by at least half, and by approximately 80% with a reasonably efficient froth flotation process. In this way recovered frit can then be directly recycled into the process as a raw material without any concerns for product quality.
Froth Flotation Basics: Froth flotation is defined as a surface-chemistry-based process for the separation of solids that takes advantage of the differences in wettability at solid particle surfaces. Solid surfaces are often naturally wettable by water and are termed hydrophilic. A non-wettable surface is water repellant and termed hydrophobic. Surfaces that are hydrophobic are also typically aerophilic, strongly attaching to air interfaces which readily displace water at the solid surface. Separation of solids by flotation is characterized by the establishment of contact among the solid to be floated, an aqueous solution, usually water, and a gaseous phase, usually air. Separation is accomplished by the selective attachment of hydrophobic solid particles to gas bubbles, while hydrophilic solid particles remain in the liquid. The difference in density between the air bubbles and water provides buoyancy that preferentially lifts the hydrophobic solid particles to the surface were they remain entrained in a froth which can be drained off or mechanically skimmed away. Direct flotation is where the valuable mineral is the froth, whereas reverse flotation is where the unwanted material is floated, leaving behind the valuable material to be settled and removed. Froth flotation is often used to separate solids of similar densities and sizes which prevent other types of separations based on gravity mechanisms. Particles ranging in size from minus 20-mesh down to sub micron particles are responsive to flotation.
Collectors: In order to obtain a successful separation using froth flotation it is usually necessary to enhance the hydrophobicity of one of the solid components that is otherwise hydrophilic or not strongly hydrophobic by using reagents termed collectors to produce a hydrophobic film on the mineral particle. The vast majority of collectors are heteropolar organic substances which are asymmetrical in structure and consist of two parts which differ in their properties. The nonpolar part of the molecule is a long-chain or cyclic hydrocarbon group that is hydrophobic. The polar part of the molecule is an ionic group that directly bonds to the solid surface. With the nonpolar hydrocarbon group oriented towards the aqueous phase, hydrophobic behavior is induced on an otherwise hydrophilic solid surface.
Activators and Depressants: Two other classes of reagents are also common in froth flotation. Activators are added to chemically resurface the solid to increase the interaction with collectors that are otherwise ineffective alone. Depressants change the chemical composition of the mineral surface layer form a polar envelope around the solid particle that enhances hydrophobicity or selectively prevents interaction with collectors that may induce unwanted hydrophobicity.
Sub-Aeration Flotation: The most common appartus used in froth flotation is the sub-aerated impeller design. A shrouded impeller or agitator provides continuous recirculatory mixing of the solids and solution. Air is introduced through the shaft and exits into the solution at the bottom of the agitator (sub-aerated), creating the bubbles that are essential to collection of hydrophobic particles.
Experimental Procedure: The frit chosen for this study was 200 mesh Ferro 3124 Frit because it is a reasonable example of a typical glaze frit. The pigment selected was Mason Chrome Free Black, in part for color contrast with the frit. The cationic collector Dodecylamine was the primary collector used in the study, and the anionic collector used was Sodium Dodecyl Sulfate. Acetic Acid was tried as an anionic collector, and unmodified wheat starch was used as an iron phase depressant. Base-to-acid and acid-to-base titrations were performed on aqueous suspensions of frit and pigment to determine behavior with respect to pH.
The designated amount of frit, pigment, collector and depressant were pre-weighed before addition into the flotation cell. The solid raw material additions for every flotation trial were 7.5 grams frit and 2.5 grams of pigment. The frit and pigment were added simultaneously to 2.0 liters of distilled water and adjusted to the appropriate pH by 0.25N HCl or 0.25N KOH addition. The pH adjusted frit and pigment suspension was then mixed for 5 minutes. If applicable, the selected depressant was then added to the cell and allowed to mix for 2 minutes. After the initial premix, the designated collector was added. Flotation and subsequent collection of froth continued until it was clear that no material was being entrained in the bubbles. The froth was collected by scraping bubbles with attached material into a separate container. After collection, the froth was dried at 29° C for a minimum duration of 24 hours or until all aqueous medium was evaporated. Surface Area measurements (m2/g) were made on de-gassed 1.5-gram samples.
The density, and the single point, BET, and Langmuir surface area of the frit and pigment were measured. From the surface area (SA) and density (r) measurements the spherical particle diameter was estimated using the following equation: Diam. (mm) = 6 / SA (m2/g) x r (g/cm3).
The data are summarized below in Table I.
Table I Frit and Pigment Materials Characterization Data.
3124 Ferro Frit | Mason Chrome Free Black Pigment | |
Density (g/cm3) | 2.491 | 5.070 |
Single Pt SA (m2/g) | 0.679 | 1.814 |
Surface Area BET (m2/g) | 0.695 | 1.851 |
Surface Area Langmuir (m2/g) | 1.090 | 2.904 |
Calculated Diameter (mm) | 3.540 | 0.652 |
X-ray diffraction analysis of the frit and pigment indicated that the frit is glassy and amorphous (non-crystalline), and the Mason Chrome Free Black Pigmen was identified as Magnetite.
Separate acid-to-base and base-to-acid titrations of frit and pigment were conducted to identify and locate pH regions where the minerals within a multi-material system display significant differences in surface chemistry. The frit and pigment pH curves from acid-to-base were very similar in the pH range around 4.0 to 7.8; however, derivatives taken from the data showed that from pH 7.2 to 9.2 differential surface chemistry could be exploited for selective froth flotation. For base-to-acid titration, the data reveaked that the surface chemistries of the frit and pigment are significantly different at a pH value of 7.0. It was concluded that flotation at a pH of 7.0 had the best chance to be selective because the surfaces of the frit and pigment displayed maximum surface chemistry differences at that point.
Zeta potential data were used to determine at which pH values anionic or cationic collectors would be most effective. The surface charge of the frit (primarily silica) was negative for every pH value above 2.2, meaning that a cationic collector, such as Dodecylamine, was needed. Magnetite (the pigment) had a positive surface charge at pH values below 7.0 and a negative surface charge at pH values above 7.0. Therefore, anionic collectors were most suitable for the collection of pigment in the pH range < 7.0.
Since the pigment is more reactive at pH 7.0 than the frit because of higher surface area and more reactive sites, it was decided to attempt direct flotation of the pigment with standard anionic collectors Sodium Dodecyl Sulfate and Acetic Acid.
Sodium Dodecyl Sulfate: A standard froth flotation cell (7.5 grams 3124 Ferro Frit, 2.5 grams Mason Chrome Free Black Pigment) was run with the anionic collector Sodium Dodecyl Sulfate (SDS) at four different concentration levels: 0.20g, 0.10g, 0.05g and 0.01 g. Based on conclusions drawn from base to acid titration data, the pH was set at 7.0 for all trials. The system was then floated with the selected amount of Sodium Dodecyl Sulfate according to standard procedure. After drying, weight and density of the collected froth were measured. These results are tabulated below.
Table I Weight of Material Collected and Froth Density as a Function of Sodium Dodecyl Sulfate Collector Level at pH 7.0.
SDS Level (g) | Amount Collected (g) | Froth Density (g/cm3) |
0.20 | 5.6286 | 2.7708 |
0.10 | 4.8110 | 2.8253 |
0.05 | 4.7477 | 2.8284 |
0.01 | 4.6812 | 2.8295 |
Overall the collection with SDS was poor, from 46% to 56% of the total material amount added. A large amount of foam was generated, but it contained very little attached material, and large quantities of excess water came with the foam. When the density of the froth was measured, it became clear that excess SDS was collected along with the material froth (a mixture of frit and pigment). The trial was repeated at pH values of 3.0, 4.0, 5.0 and 6.0. After all experimentation was completed, it was concluded that no flotation behavior was found at any of the acidic pH values.
Upon analysis of the Sodium Dodecyl Sulfate trial data it is concluded that SDS is a poor collector for the system. A total of 5.629 grams was collected out of a possible 10.0 grams of material at a SDS level of 0.20g. All other SDS additions resulted in collection amounts less than 4.82 grams. Density results clearly show that non-specific flotation of frit and pigment was achieved. Neither pure frit nor pure pigment was reclaimed from the system; rather a significant portion of the material was floated resulting in a dark gray froth with an average density of frit and pigment. From an industrial point of view this setup is not useful because the as-is collected froth would not be suitable for introduction into virgin glaze batch without further purification steps.
Acetic Acid: Acetic acid is a member of the carboxylic collector group which are widely used in the flotation of non-sulfide minerals and ores. For the flotation trial, a standard froth flotation cell was floated with acetic acid as the primary collector at three concentration levels. The pH was set at 7.0 for all trials, and no other surfactant was added. The goal was to add only enough acetic acid to collect on the surface area of the pigment. Ideally, the pigment would be selectively collected out of the system and the frit would be left behind. After drying, weight and density of the collected froth were measured. These results are tabulated below.
Table II Weight of Material Collected and Froth Density as a Function of Acetic Acid Collector Level at pH of 7.0.
Acetic Acid Level (mg/m2) | Collected (g) | Density (g/cm3) |
0.115 | 4.3020 | 3.0079 |
0.230 | 6.3392 | 3.0104 |
0.460 | 6.3637 | 3.0205 |
Given that the system contained only 2.5 grams of pigment, collection values ranging from 4.302 to 6.364 grams showed that selective collection of pigment was not achieved. Over 60% of the collected froth material was frit. In general, the bubbles that were generated were unstable in nature, and after approximately ten minutes of flotation, no significant gains in material collection were observed.
To examine collection/selective separation differences at different pH set points, the same experimental setup was rerun with a constant level of acetic acid at pH values of 6.0 and 8.0. These results are tabulated in below.
Table III Weight of Material Collected and Froth Density at a Constant Acetic Acid Collector Level of 0.230 mg/m2 at pH 6.0, 7.0 and 8.0.
pH | Collected (g) | Density (g/cm3) |
6.0 | 3.9498 | 2.9647 |
7.0 | 6.3392 | 3.0104 |
8.0 | 4.3846 | 2.9477 |
From the raw data it is obvious to see that pH 7.0 collected the greatest amount of material (6.339 grams) at the highest density (3.010 g/cm3). A large drop off in the amount of material collected is seen at a pH of 6.0 (3.950 grams) and a pH of 8.0 (4.385 grams). However, because the density values slipped below 3.0 g/cm3 for both pH 6.0 and 7.0 it is concluded that no increase in selective collection of pigment was made.
It was concluded that acetic acid has the ability to collect a moderate amount of material (approximately 6.0 grams) at levels of 0.230 mg/m2 and 0.460 mg/m2. Overall separation and collection of the pigment from the frit was not achieved.
Dodecylamine: Titration, zeta potential and x-ray diffraction data indicated that frit could be floated by a cationic collector at pH values of 7.0 and above. A standard froth flotation cell was run with the cationic collector Dodecylamine at four different concentration levels, with a pH of 7.0 for all trials. Immediately following the Dodecylamine addition, frit and pigment attachment to the bubbles began and continued throughout the flotation process with a minimal amount of excess water being carried with the bubbles. Due to the strength of attachment between the frit/pigment material to collector and collector to the bubble, large amounts of entrained material were observed on the surface of each bubble. Five minutes of flotation was more than sufficient to collect all visible material from the system, leaving all remaining water clear. After drying, weight and density of the collected froth were measured. These results are tabulated below.
Table IV Weight of Material Collected and Froth Density as a Function of Dodecylamine Collector level at pH of 7.0.
Dodecylamine Level (g) | Amount Collected (g) | Froth Density (g/cm3) |
0.20 | 8.9586 | 2.8264 |
0.10 | 9.3080 | 2.8269 |
0.05 | 9.5035 | 2.8219 |
0.01 | 9.5317 | 2.8159 |
The highest collection amount was observed with the 0.01g and 0.05g Dodecylamine addition, and no excess collector was observed in the system when flotation had been completed. The saturation limit of Dodecylamine within the frit/pigment system had been exceeded at the 0.2g and 0.1g levels. The collected froth was a dark gray color indicating that a mixture of frit and pigment were collected. The density range of the collected froth represents a simple average of the constituents in their respective ratios.
Dodecylamine has the ability to collect a sufficient amount of material (95%), but flotation was non-specific. Dodecylamine attached to both frit and pigment surfaces making complete selectivity impossible. Additionally, surface area information revealed that the pigment has approximately 2.5 times the surface area of the frit and contributes 46% of the solid surface area in the system. From an industrial point of view this setup is not useful because the collected froth would not be suitable for introduction into virgin glaze batch without further purification steps.
Dodecylamine and Unmodified Wheat Starch: Flotation trials clearly showed that Dodecylamine is an excellent collector for the mixed frit/pigment system and can be used as the primary collector. To separate frit and pigment, the large portion of floatable surface area contributed by the pigment had to be made selectively unresponsive to the addition of Dodecylamine. Thus, unmodified wheat starch (a non-ionizing, nonpolar hydrocarbon compound that is insoluble in water) was employed as a selective depressant for the pigment.
A standard froth flotation cell was run with the cationic collector Dodecylamine at a constant concentration level of 0.05 grams, and gelatinized wheat starch as the pigment depressant at four different additions. The pH was set at 7.0 for all trials, and the system was then floated by first adding the gelatinized wheat starch depressant and then collecting with the Dodecylamine.
Selective frit attachment to the bubbles began immediately following the Dodecylamine addition, and continued throughout the flotation process. The collected froth consisted almost entirely of frit material, with minimal pigment inclusion and very little excess water coming with the bubbles. The attachment of Mason Chrome Free Black Pigment to the bubbles was depressed such that no noticeable traces of pigment were seen in the bubbles. Strong frit flotation behavior was observed and large amounts of entrained frit material were observed on the surface of each bubble. After approximately ten minutes selective flotation ceased and no additional system material was collected. Visual inspection revealed that the vast majority of pigment remained within the water and sank to the bottom of the vessel. After drying, the weight and density of the collected froth were measured. These results are tabulated below.
Table V Weight of Material Collected and Froth Density as a Function of Wheat Starch Depressant Level at pH of 7.0.
Starch Level (g) | Collected (g) | Density (g/cm3) |
1.0 | 4.3711 | 2.58247 |
0.7 | 4.7255 | 2.63130 |
0.5 | 4.7674 | 2.63540 |
0.3 | 6.7015 | 2.63590 |
The highest collection was observed with the 0.30 gram Wheat Starch addition, and the lowest collection was observed with 1.0 gram Wheat Starch. The 1.0 gram, 0.70 gram and 0.50 gram Wheat Starch additions partially depressed the frit flotation; at the 0.30 gram Wheat Starch addition, the frit was not depressed to same extent, which allowed for a large increase in material collection. Successful selective flotation and collection of frit was achieved through use of Wheat Starch and the cationic collector Dodecylamine at neutral pH 7.0.
Wheat Starch at pH of 9.0: Three, five and seven point derivatives calculated from pH data obtained from acid-to-base titrations pointed to a clear pH window from 7.2 to 9.2 of differential surface chemistry between frit and pigment that could be exploited for selective froth flotation. Zeta potential measurements illustrated that at pH 9.0 the frit surface is highly negative making it a candidate for more efficient flotation via a cationic collector. Combining information from the titration data and literature, it was decided to adjust the flotation pH to 9.0 in hopes of improved selective flotation of frit from the pigment surface. The amount of Dodecylamine collector was set at 0.05 grams and the amount of Wheat Starch depressant was trialed at 0.30 and 0.50 grams to insure pigment flotation would be depressed. The system was then floated by first adding the gelatinized wheat starch depressant and then collecting with the selected amount of Dodecylamine according to standard procedure.
The trial results are summarized below in Table VI. The results of trials using 0.30 and 0.50 grams of Wheat Starch were nearly identical. The collected froth was completely white in color and the measured density matched that of pure frit almost exactly. In the 0.30 gram Wheat Starch addition trial the density measurements indicate that approximately 5.130 grams of the total collected material was frit, which translates to a 68.4% frit flotation efficiency, with only 0.080 grams of pigment. In the 0.50 gram Wheat Starch addition trial, approximately 5.125 grams of the total collected material was frit, good for a 68.3% frit flotation, meaning only 0.065 grams of the 5.193 grams of collected material was pigment.
Table VI Collection, Density and Efficiency Data of Dodecylamine Collector with Wheat Starch Depressant at a pH of 9.0
Starch Level (g) | Collected (g) | Density (g/cm3) | Efficiency (%) |
0.3 | 5.2178 | 2.5301 | 68.4 |
0.5 | 5.1933 | 2.5222 | 68.3 |
Upon analysis of the trial data it was concluded that gelatinized wheat starch is a viable depressant of the pigment, allowing for selective collection of the frit. Dodecylamine was the primary collector for the system, Wheat Starch was the pigment depressant, and the resulting frit flotation efficiency was slightly better than 68% at a flotation pH of 9.0.
Conclusions:
Surface chemistry information obtained via titration indicated whether or not a system lends itself to separation via froth flotation by highlighting regions of differential surface chemistry between the glaze constituents. By analyzing derivative data from the original pH titration curves, potential flotation pH values became clear. The nature of the flotation collector (anionic or cationic) which must be used to obtain selective flotation was found by analysis of zeta potential data. When the surface chemistry information obtained from titration was combined with chemical composition information obtained via x-ray diffraction and the wealth of froth flotation literature, the specific collector and activator/depressant needed for selective flotation could be determined. A general overview of the experimental froth cells is shown below in Table VII.
Table VII Overview of Experimental Froth Flotation Cells.
Collector Type | Floation pH | Collector | Depressant | Target Material | Results |
---|---|---|---|---|---|
Anionic | 7 | Sodium Dodecyl Sulfate | None | Pigment | Non-Selective |
7 | Acetic Acid | None | Pigment | Non-Selective | |
Cationic | 7 | Dodecylamine | None | Frit | Non-Selective |
9 | Dodecylamine | Wheat Starch | Frit | Selective |
- Direct flotation of pigment not achieved with anionic collectors Sodium Dodecyl Sulfate or Acetic Acid due to the fact that the bulk of the system surface area is frit.
- Dodecylamine is an effective collector for the frit/pigment system as approximately 95% of material was recovered at pH 7.0.
- Wheat Starch is a selective depressant of iron oxide (Mason Chrome Free Black Pigment) even at low addition levels (0.3 – 0.5 g).
- Using titration data to select flotation pH of 9.0, selective separation between frit and pigment can be achieved resulting in 68-69% frit recovery.
Global Conclusions:
- Characterize and identify glaze components: Density, SA, X-Ray diffraction
- Determine surface chemistry of constituents via titrations and zeta potential
- Select optimum flotation pH(s) based on differential surface chemistry
- Select collector based on titration and zeta potential data
- Grid trial on collector to establish concentration and efficiency
- If necessary select depressant for one system component
- Trial collector with selective depressant
- Compare froth density with component densities to determine froth grade
- If necessary (i.e. multi-pigment systems) repeat steps 6 – 8
Supplemental Keywords:
froth flotation, flotation separation, whitewares glaze waste, recycling glaze waste, whitewares waste reduction, particle surface chemistry, sub-aeration flotation, zeta potential, sodium dodecyl sulfate, acetic acid, dodecylamine, wheat starch,, RFA, Scientific Discipline, Waste, TREATMENT/CONTROL, Ecosystem Protection/Environmental Exposure & Risk, Sustainable Industry/Business, Aquatic Ecosystems & Estuarine Research, Municipal, Environmental Chemistry, Sustainable Environment, Technology, Technology for Sustainable Environment, Aquatic Ecosystem, New/Innovative technologies, Environmental Engineering, waste reduction, clean technologies, alumina powder, municipal waste, ceramic waste, recycling, coating formulations, ceramic industrial waste, water quality, pollution preventionRelevant Websites:
Main Center Abstract and Reports:
R830420 Center for Environmental and Energy Research (CEER) Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R828737C001 Environmental Impact of Fuel Cell Power Generation Systems
R828737C002 Regional Economic and Material Flows
R828737C003 Visualizing Growth and Sustainability of Water Resources
R828737C004 Vibratory Residual Stress Relief and Modifications in Metals to Conserve Resources and Prevent Pollution
R828737C005 Detecting and Quantifying the Evolution of Hazardous Air Pollutants Produced During High Temperature Manufacturing: A Focus on Batching of Nitrate Containing Glasses
R828737C006 Sulfate and Nitrate Dynamics in the Canacadea Watershed
R828737C007 Variations in Subsurface Denitrifying and Sulfate-Reducing Microbial Populations as a Result of Acid Precipitation
R828737C008 Recycling Glass-Reinforced Thermoset Polymer Composite Materials
R828737C009 Correlating Clay Mineralogy with Performance: Reducing Manufacturing Waste Through Improved Understanding
R830420C001 Accelerated Hydrogen Diffusion Through Glass Microspheres: An Enabling Technology for a Hydrogen Economy
R830420C002 Utilization of Paper Mill Waste in Ceramic Products
R830420C003 Development of Passive Humidity-Control Materials
R830420C004 Microarray System for Contaminated Water Analysis
R830420C005 Material and Environmental Sustainability in Ceramic Processing
R830420C006 Interaction of Sealing Glasses with Metallic Interconnects in Solid Oxide and Polymer Fuel Cells
R830420C007 Preparation of Ceramic Glaze Waste for Recycling using Froth Flotation
R830420C008 Elimination of Lead from Ceramic Glazes by Refractive Index Tailoring
R830420C010 Nanostructured C6B: A Novel Boron Rich Carbon for H2 Storage
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.