Iso-Electric Point and Iron Content in Iron

¶ … Iso-Electric Point and Iron Content in Iron Hydroxide Impregnated Aluminosilicate-Based Geopolymers

Rahil Abou Saleh

Dr. Kiril Hristovski

Iron hydroxide impregnated aluminosilicate-based geopolymers (Fe-ASG) is a novel water treatment media currently under development for simultaneous removal of arsenic and inorganic contaminants. The goal of this study was to determine whether varied iron contents impregnated aluminosilicate impacts the surface charge in different pH conditions. The study tests for media types of virgin and iron impregnated ASG diluted in potassium nitrate (KNO3) for charge dispersion. pH of the sample was gradually adjusted using potassium hydroxide (KOH) and nitric acid (HNO3). Results demonstrated no significant relationship between iron content impregnated ASG and iso electric point, which suggests that surface area properties impacts the relationship.

I am especially appreciative of the guidance, encouragement, and patience exuded by Dr. Hristovski throughout the duration of this research project. Also I would like to give special thanks to Robert Sandoval for his tremendous support and for offering solutions to unexpected complications that I experienced with Microsoft excel formulas, providing training on the Zeta PALS instrument, for sharing his knowledge, and for ensuring an uninterrupted supply of the acid and alkaline solutions. Finally, I would also like to thank Denish Medpelli for providing me with the sample media and potassium nitrate.

Table of Contents

Abstract 2

List of Tables & #8230;

List of Figures & #8230;6

I. Introduction & #8230;8

II. Literature Review & #8230;. 12

III. Methodology 16

IV. Results and Discussion & #8230;.20

V. Conclusion 24

Works Cited 25

Appendix A 28

Appendix B 29

Appendix C 36

Table 3.1: Summary Characterization of Test Media 17

Table 4.1: Data Collected of Test Media Iso-electric pH 22

Table 4.2: Surface Area Comparison of Test Media iso-electric point pH 23

List of Figures

Figure 4.1: 95% Confidence Interval Curve 21

I. Introduction

Among inorganic impurities, some of the greatest threats to health are associated with the presence of high levels of toxic or heavy metals in drinking water. The sources of contamination and resulting health effects include a wide spectrum of various chemical makeups that form these compounds. Some of these inorganic compounds are present due to the presence of natural formations in the earth's crust. However, they can also originate from industrial and agricultural waste products which subsequently enter major water systems.

Geopolymers and their engineering applications have attracted significant attention of the scientific community. This is due to properties such as good thermal stability and high resistance to aggressive environments. Researchers are currently undergoing exploration in hopes of identifying economically feasible ways to remove these heavy metal contaminants. This study was conducted with the purpose of testing an absorbent new media technology that stands the potential to assist in the removal of these contaminants. The methodology and experimental design were constructed in hopes of providing insights into this new field of research.

Inorganic particles dispersed in a solution are electrically charged due to their ionic characteristic. When particles are dispersed they are surrounded by oppositely charged ions. This is considered the particles surface or firs layers. Then a second layer is formed which contains varying compositions of ion. Zeta potential is the term used to determine the electrical potential of the first and second layers of the particle. A zero electrical potential allows particles to aggregate and become unstable, thus there is no force to prevent particles coming together. Units used to measure zeta potential are in form of velocity (meter/second). A general rule of thumb is the higher the value of zeta potential, whether positive or negative; the more stable the system will be more dispersed. Geopolymerization is a developing field of research for utilizing solid waste and by-products. It provides a mature and cost-effective solution to many problems where hazardous residue has to be treated and stored under acute environmental conditions.

Aluminum silicate-based geopolymer (ASG) media is an economically feasible technology suited for water treatment systems, and is the most commonly used adsorbent for the removal of inorganic contaminants (Khale & Chaudhary, 2007). Studies have already examined the inorganic materials removal capabilities of modified ASG (Duxson, et al., 2007). However, the instability of the ASG modified media under various pH ranges may result in leaching of targeted contaminant. By contrast the oxide metals such as iron have proven to be more stable in a wider pH range and could potentially serve as a viable and economically attractive alternative.

Iron hydroxide impregnated ASG is an emerging technology currently under investigation for the potential use in water treatment facilities. Initial results have suggested that there are favorable inorganic compound removal capabilities inherent in this new media. The primary objective of this study was to determine the relationship between the iso-electric point and iron content in iron hydroxide impregnated ASG. The examination of the iron content as well as the aluminum silicate ratio will help to determine the behavior of the tested media's reaction in regards to certain contaminants in different pH water conditions.

It was hypothesized that the iron content in each sample will affect the surface charge of modified media. In addition, alternating the pH from acidic to basic and using zeta potential for each pH reading determined the iso-electric point of each modified media. In order to test the hypothesis, zeta potential tests with two types of aluminum silicates in their virgin and eight iron hydroxide impregnated states were conducted. An analysis was then conducted to see if any correlation was present in the zeta potential tests.

This study was conducted under the following assumptions:

The samples were prepared and collected with accurate amounts of iron composition with aluminum silicate for each sample.

The collection equipment was clean and free of residues.

The zeta potential instrument was appropriately calibrated and running without faulty data.

The temperature during experiments did not affect the samples.

The modified media was diluted using 10mM HNO3 to suit the instrument analyses.

The following limitations apply to this study. First, the samples were prepared and collected by another party. There were also limitations due to the level of accuracy and the sensitivity of the equipment and instruments used. Furthermore the samples had to be diluted to achieve a suitable amount of particles which were also free of any air bubbles to conduct the analysis.

II. Literature Review

Geopolymerisation

Silicones are synthetic polymers that have unique physical properties that include relatively high melting and boiling point that are generally not found in other polymers. As a result of their enhanced thermal stability, silicones are inherently more resistant to the effects of heat, cold, sunlight, adverse weather, and common chemical assault. They have been integrated into thousands of household and medical products, including lubricants, breast implants, adhesives, dishware, and water repellents, and can be found within every major industrial segment of the marketplace (DeLuca, Kaszuba, & Mattison, 2006). During the last two decades geopolymerisation has emerged as a possible technological solution for the effective stabilization and immobilization of toxic materials (Jaarsveld, Deventer, & Lorenzen, 1997). However, the instability of the Aluminum silicate-based geopolymer (ASG) modified media under various pH ranges may result in leaching of targeted contaminant. By contrast the oxide metals such as iron have proven to be more stable in a wider pH range and could potentially serve as a viable and economically attractive alternative.

Some members of the Ain Shams University, the National authority for military productions, and the Atomic energy authority in Cairo constructed investigations of the various "parameters" that influence the adsorption of iron and aluminum copolymer impregnated with silica (Enein, Eissa, Diafullah, Rizk, & Mohammed, 2009). The parameters investigated included such items such as pH, mass, and agitation. These factors help to identify what affects the adsorption and removal of heavy metals; such as arsenic in this case. The study concluded that poly inorganic coagulants based on silica or iron are most effective in removing pollutants from wastewater. Iron and aluminum copolymer impregnated with silica was found to have maximum adsorption capacity for arsenic of "146 mg/g" media.

Practical Applications

Jang, Shin, Park, and Choi (2003) approached together to apply the "wetness impregnation" technique to synthesize and incorporate iron and aluminum oxides into silica media. The purpose of the study was to determine and compare adsorption capacities and kinetics of "metal -- ? impregnated SBA -- ?15" media to remove arsenic levels from water content. The behaviors of the impregnated media were found to have "greater" Arsenate adsorption capacities at "pH 7.2." The study results also suggest that the coagulation and fluctuation mechanism of the process, such as oxidation state, adsorption isotherms, kinetics and structure properties that facilitated the impregnation technique and composition of compounds, can create a next step method to remove arsenic from water.

Geopolymer involves the silicates and aluminates of by products to undergo process of geopolymerization. It is environmentally friendly and need moderate energy to produce (Nicholson, Fletcher, Miller, Stiling & Morries, 2005). Literature demonstrates that certain mix compositions and reaction conditions such as Al2O3/SiO2, curing temperature with time and pH significantly influences the formation and properties of a geopolymer. It is utilized to manufacture concrete pavements, concrete products and removal of toxic metal wastes that are resistant to heat and aggressive environment (Nicholson, Fletcher, Miller, Stiling & Morries, 2005).

The iron content impregnated is significant to determine the behavior of surface charge fluctuation in different pH conditions. Studies on geopolymers are mostly based on traditional foundation materials like metakaolinte (Fe2O3 content of 2%), fly ash (Fe2O3 content of 10%) and blast furnace slag (Fe2O3 content of 0.5%) (Stucki, Golden & Roth, 1984). Therefore, studies have indicated that fly ash with content of 10% is favorable in impregnating it into geopolymers (Stucki, Golden & Roth, 1984). Further research has also suggested that Calcium silica hydrate (CSH), although present at pH 12, was largely unobserved at high pH (pH=14), which is the optimal condition for the processing of aluminosilicate mineral wastes is important for the development of large-scale waste-based geopolymerisation (Phair & Van Deventer, 2002).

Biological Implications

Another study was conducted that examined Chang liver cells which were grown in an iron-rich medium for up to twenty weeks and monitored under a controlled environment to determine whether or not there was any fluctuation in the isoelectric shift due to an acidic shift (Hoy & Jacobs, 1981). Despite whether the cells were either normal or loaded with iron content, the researchers found a slight acid shift in their isoelectric point. This research suggests that the acidic ferritins on iron loading may be unrelated to subunit composition.

Another study examined the effects of iron concentration during growth on the physicochemical surface properties of the colonial variants of Neisseria gonorrhoeae which was assessed by aqueous two-phase partitioning in a dextran-polyethyleneglycol system containing positively charged trimethylamino-polyethyleneglycol or hydrophobic polyethyleneglycol-palmitate (Magnusson, Kihlstrom, Norqvist, Davies, & Normark, 1979). This study suggests that the complex effects of iron, in combination with other variables known to affect surface charge and hydrophobicity, have provided some clues as to the properties of the gonococcal surface that are important in promoting virulence.

Another research experiment used a Ferguson analysis as a method for simultaneously measuring the size and zeta-potential of gold nanoparticle-DNA (Au NP-DNA) conjugates; this approach was determined as highly suitable when the particle size is

III. Methodology

This chapter describes the properties of the media under investigation and details experimental and analytical procedures. It also provides the approach that was taken for modeling the iso-electric point of the media. All glassware, pH meter, electrode and equipment used were cleaned according to standard protocol, which is included in Appendix A.

Zeta PALS (phase analysis light scattering) instrument measures surface charge using phase analysis light scattering, and it determined the electrophoretic mobility of charged, colloidal suspensions in an electrical field. Particles move towards the electrode of opposite charge, their velocity is measured and expressed in unit field strength as their mobility. In most cases the measurements are conducted in conductive liquid such as KNO3 at different pHs. Avoiding dust and air bubbles are essential to carry out these measurements. Therefore, it is necessary to filter the solution of dispersant used for preparing the various dilutions, and to wash all vessels in order to avoid the presence of dust and air bubbles (Brookhaven Instruments Corporation, 2011).

Materials

The Fe-ASG was previously synthesized and obtained as media for this investigation. Aluminum silicate ratio and iron content for the virgin and FeO2 impregnated ASG are presented in the following table 3.1.

Table 3.1: ASG & Fe-ASG Media Tested in this Studty

Media

Fe content %

SBIR 3

10.00

SBIR 4

13.50

SBIR 5

19.60

SBIR 6

19.90

SBIR 7

17.00

SBIR 8

16.20

SBIR 9

16.00

SBIR 10

11.77

A laboratory technician in an engineering lab at Arizona State University prepared 10 millimeters (mm) concentrations of potassium nitrate (KNO3), for each experiment run it was used to dilute the Fe-ASG media. In addition, 1 molar and 0.1 molar of each Nitric acid (HNO3) and potassium hydroxide (KOH) was prepared to correct the pH of the media. Buffers of pH 4, 7 and 10 were provided to calibrate the pH meter. A magnetic stir bar was also provided to keep the diluted media mixing to avoid particle settling.

Other equipment included were disposable plastic cuvettes to sample suspension. Disposable plastic pipettes for liquid samples, acid and bases, 100 milliliter (mL) graduated beaker to hold the sample while mixing, a pH meter to read the pH of the adjusted sample, and a special electrode for zeta potential measurement reading.

Experimental Methods for Zeta Potential Analysis

A total of ten media were analyzed and eight of them were impregnated with FeOOH and two controls are the untreated ASG media. Each sample run was prepared using a 100 ml graduated beaker containing 10 ml of the media, and diluting it with KNO3 filling it up to 100 mL. The diluted media in beaker remained on a stirring plate at rate 10 and a magnetic stir bar inside to keep the media stirring for the particles to stay distributed and allow adequate mixing when HNO3 or KOH was added. Each concentration of HNO3 and KOH had a disposable pipette to gradually adjust the pH of the media, by adding drops until the desired pH was reached.

The pH meter was calibrated using buffers of pH 4 and 7 to measure the diluted media with acidic pH, and re-calibrated using buffers of pH 7 and 10 to measure for basic pH. The pH meter was rinsed with Nano pure water and gently dried using Kim wipes. Electrodes used for surface charge readings were soaked in Nano pure water in a cuvette at least 24 hours before running analysis.

After the desired pH was reached, samples were pipetted using a disposable pipette into a cuvette, making sure no air bubbles formed; then inserting the electrodes into the sample cuvette. The cuvette and electrodes were rinsed with Nano pure water three times before adding the adjusted sample to run. In addition, the cuvette was rinsed with the new adjusted sample before filling it up, to normalize it with the new sample pH. A standard deviation of +/- 5 (mV) is good and standard deviation of +/- 10 (mV) is acceptable (ZetaPals_protocol_v1, 2011).

IV. Results and Discussion

Figure 4.1 represents a 95% confidence in the trend of surface charge fluctuation among all 10 samples, starting at an acidic pH with high positive surface charge and then gradually the pH increases and the surface charge decreases, eventually reaching zero, indicating particle instability. All sample graphs leveled off at high negative surface charge at very high pH. This trend was an indication that when more alkali (KOH) was added to the suspension of the sample then the particles will tend to acquire more negative charge. If acid is then added a point will be reached where the negative charge is neutralized. Any further addition of acid causes a buildup of positive charge. There was no correlation in the 95% graph between the samples iron content and the iso electric point, because the surface area of each media influenced the relationship and behavior of the surface charge distribution. The larger the surface area, the greater the distribution of negative and positive surface charges, which requires higher basic pH conditions to reach the iso electric point of particle.