Date of Award
Master of Science
Benjamin Church, Patrick McNamara
Water contamination by various heavy metal pollutants such as, Lead, Arsenic, Cadmium, and Mercury, have severe toxic effects on living organisms and humans. High concentrations of arsenic in drinking water cause serious damage to the central and peripheral nervous systems, as well as, the dermal, cardiovascular, gastrointestinal, and respiratory systems. Arsenic contamination of ground water poses a substantial concern in many countries throughout the world, including the United States.
Considerable research work, aimed at finding and developing various separation and treatment techniques, has been conducted over the past few decades. The conventional treatment methods of arsenic involve coagulation with ferric chloride or aluminum sulfate coagulants, followed by the separation of the produced insoluble products by settling, or by direct filtration through sand beds. Other treatment techniques for arsenic removal are reverse osmosis, ion exchange, lime softening, flotation, and adsorption on hydrated iron oxide or activated carbon. Solid phase Nano-adsorbents are becoming the core of most recent works in removing heavy metals due to their high capacity and affinity to heavy metal ions.
In this research work, a new bulk modified nanocomposite material (adsorbent) is developed for arsenic (As) removal from drinking water, in ppb concentrations. Iron oxide nanoparticles (IONPs) was impregnated in an open cell polyurethane (PU) foam in order to exploit the inherent advantages of porous PU foam structures and the ability of iron compounds to react with arsenic species by adsorption and ion exchange mechanisms, which offer higher removal capacities.
The prepared adsorbents were characterized using several techniques. Scanning Electron Microscopy and Energy Dispersive X-ray (SEM/EDX) were utilized to examine the distribution of IONPs inside the foam matrix and the surface adsorption of arsenic species; respectively. Optical Microscopy was used to observe the cellular structure of the composite foams. Mercury Porosimetry technique was used to measure the porosity and density of the PU-IONPs nanocomposites. Atomic Absorption Spectrometer (AAS) was used to measure the removal capacity of the nanocomposite foams.
To obtain the best removal capacity of arsenic species, several variables were investigated. Primarily, the composition ratio of polypropylene glycol (PPG) and toluene di-isocyanate (TDI) in the PU foam, the percentage loading weight, the size of IONPs, and the foam shape were studied. Moreover, the effects of contact time, pH of solutions, the used weight of adsorbents, and the concentration of As solutions were examined. A long-term cyclic operation mode was applied to study the performance of the adsorbents in removing arsenic.
It was found that the composition ratio of PPG:TDI (1:2) with 12% IONPs yields the highest affinity towards arsenic species, compared to other possible combinations, with a removal capacity of 40% using single stage batch analysis. Experimental results revealed that decreasing the size of IONPs from 50-100 nm to 15-20 nm yields a higher removal capacity. In addition, granular adsorbents exhibit higher removal capacity compared to cubical shaped adsorbents in the order of 20% - 100%. The uptake of As increased with time and the highest removal capacity occurred at 24 hr. However, the rate of adsorption was rapid in the first 12 hr after which the rate slowed down as the equilibrium state was approached.
The adsorption process of As is affected by the pH level of the contaminated solution. The removed amount of As was found to be higher in acidic solutions compared to the basic ones. The removed amount of As increased from 40 ppb to 60 ppb, when the weight of PU-IONPs nanocomposite foam increased from 0.5 g to 2 g; respectively. As well as, the removal capacity of arsenic decreased as the As concentration increased in the solution. In column study, the adsorption of arsenic species was very rapid on the first few cycles with an approximately 50% arsenic removal within 2 cycles. After that, a constant increase in the removal rate occurred. All arsenic species were removed in 22 cycles (approximately 9 days) of operating period.
Sorption isotherms models were applied to determine the adsorption mechanisms and modeling parameters. The experimental data correlated well to Freundlich and Langmuir models with R2 0.953 and 0.949; respectively. Kinetic models were applied to determine the mechanisms which control the adsorption process. A pseudo-second-order model was found to be the best fit model for the adsorption data.
The proposed system of polyurethane nanocomposite foam offers a potential for the removal of arsenic with higher capacity at lower costs than conventional arsenic removal systems. In addition, the incorporation of the adsorbent particles in a foam media allows for easier post-treatment step. Multi-stage setup and applications can increase the removal capacity significantly.
Hussein, Faten Bakri, "Synthesis and Performance Analysis of Polyurethane Foam Nanocomposite for Arsenic Removal from Drinking Water" (2016). Theses and Dissertations. 1154.