Grantee Research Project Results
Final Report: Fundamental Studies on Management of Industrial Sludges Enhanced Flocculation of Fine Particle Suspensions by Manipulation of Polymer Conformation.
EPA Grant Number: R823301Title: Fundamental Studies on Management of Industrial Sludges Enhanced Flocculation of Fine Particle Suspensions by Manipulation of Polymer Conformation.
Investigators: Somasundaran, P.
Institution: Columbia University in the City of New York
EPA Project Officer: Aja, Hayley
Project Period: October 1, 1995 through September 1, 1998
Project Amount: $300,000
RFA: Exploratory Research - Engineering (1995) RFA Text | Recipients Lists
Research Category: Safer Chemicals , Land and Waste Management
Objective:
Flocculation behavior of colloidal suspensions using polymers is determined by both macroscopic adsorption characteristics (such as the amount adsorbed) and microscopic characteristics (such as the conformation of the interfacial polymers), the latter having not been studied experimentally due to lack of reliable techniques to probe the small amount of interfacial species in situ. In this research project, using fluorescence and electron spin resonance (ESR) techniques, we have measured in situ the conformation of interfacial polymer in flocculated suspensions and have experimentally correlated it to the flocculation behavior of suspensions.The major objective of this research was to establish correlation of polymer adsorption, polymer conformation, and electrokinetic properties to flocculation responses of model suspension systems. In this regard, this work has identified some major controlling factors that should help in obtaining enhanced flocculation of sludges.
Summary/Accomplishments (Outputs/Outcomes):
Our work was conducted as proposed using aqueous alumina suspension as the model system. The work includes determination of adsorption behavior of polymers along with its flocculation characteristics on alumina, and monitoring polymer conformation using ESR and fluorescence labeled polymers as a function of solution condition (such as pH) and addition of a second polymer.While electrostatic forces are dominant in controlling the adsorption of polyelectrolytes such as polyacrylic acid on charged substrates such as alumina, the adsorption and the surface coverage can be controlled by altering the solution pH; the conformation of the adsorbed polymers also is affected by pH shifted with drastic effect of flocculation.
Electron spin resonance studies have shown that as polymer adsorption proceeds, the configuration of the polymer molecules at the solid-liquid interface also changes significantly. At low adsorption densities, the bound fraction of polymer segments is high, suggesting a flat conformation on the surface. At higher adsorption densities, there are more free segments from which we infer that the polymer molecules have less anchoring sites with resultant dangling into solution.
Charge neutralization is the primary mechanism for PAA/alumina flocculation while polymer bridging coexists. Flocculation response varies drastically with pH, with maximum flocculation near to the isoelectric point (IEP) due to such charge neutralization. It is clear, however, that polymer bridging also contributes markedly to the flocculation because higher molecular weight polymer does cause greater flocculation.
Fluorescence study indicates a pH-independent conformational change of adsorbed polymer chains given a long mixing time. At short durations, the conformation and flocculation are very much dependant on pH perturbation. While the slow conformational rearrangement may not affect rapid flocculation processes, it can be expected to affect retarded flocculation as well as deaggregation and reaggregation processes.
From the study on kinetics of polymer conformational changes, it is observed that when adsorbed polymer was perturbed by pH shift from 4.5 to 10.5, the flocculation shows a maximum as a function of mixing time. It is proposed to result from combined effects of polymer stretching upon pH change and floc breakage with time.
Combination of oppositely charged polymer has been found to enhance flocculation of sediments markedly. In this research, studies were conducted to understand the mechanism of dual polymer flocculation. Flocculation of alumina fines with combinations of polyacrylic acid and high molecular weight cationic copolymer of acrylamide and quaternary acrylate salt (Percol) was investigated. Effects of molecular weights of both polymers as well as Percol charge density also were investigated. To determine the role of the polymer conformation and changes in it due to the presence of another polymer, conformation of polyacrylic acid at the alumina/water interface was studied under different addition modes (i.e., sequential addition of two polymers vs. co-addition). Importantly, polymer size distribution was found to have a marked effect depending on the polymer type: while in the case of polyacrylic acid, a broader distribution yielded better flocculation, no such effect was observed with Percol. Based on the results, an overall mechanistic picture of dual polymer flocculation is proposed for the system under study.
Conformation of adsorbed polymers can be manipulated through many different ways. It can be altered by changing the solution conditions such as pH and salt concentration, or by adding a second species such as a secondary polymer or another surfactant. In a complex system, addition mode is found to be important in most cases. It is clear that the manipulation of polymer conformation offers a powerful mean to control flocculation of dispersed systems.
Journal Articles on this Report : 5 Displayed | Download in RIS Format
Other project views: | All 7 publications | 6 publications in selected types | All 5 journal articles |
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Type | Citation | ||
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Somasundaran P, Yu X. Dispersions: progresses and prospects. Powder Technology 1996;88(3):305-307. |
R823301 (Final) |
not available |
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Somasundaran P, Das KK, Yu X. Selective flocculation. Current Opinion in Colloid and Interface Science 1996;1(4):530-534. |
R823301 (Final) |
not available |
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Somasundaran P, Krishnakumar S. Adsorption of surfactants and polymers at the solid-liquid interface. Colloids and Surfaces. A, Physicochemical and Engineering Aspects 1997;123:491-513. |
R823301 (Final) |
not available |
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Yu X, Somasundaran P. Kinetics of polymer conformational changes and its role in flocculation. Journal of Colloid and Interface Science 1996;178(2):770-774. |
R823301 (Final) |
not available |
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Yu X, Somasundaran P. Role of polymer conformation in interparticle-bridging dominated flocculation. Journal of Colloid and Interface Science 1996;177(2):283-287. |
R823301 (Final) |
not available |
Supplemental Keywords:
waste management, environmental engineering, industrial waste slimes, industrial sledges, enhanced flocculation, polymer conformation, spectroscopic techniques of fluorescence, electron spin resonance, optimum parametric conditions for desired flocculation, consolidation., RFA, Scientific Discipline, Waste, Sustainable Industry/Business, Environmental Chemistry, Hazardous Waste, New/Innovative technologies, Hazardous, Environmental Engineering, hazardous waste management, hazardous waste treatment, advanced treatment technologies, industrial waste, optimum parametric conditions, polymer conformation, waste management, innovative technologies, alternatives to incineration, hazardous waste identification, enhanced flocculation, electron spin resonanceProgress and Final Reports:
Original AbstractThe 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.