Final Report: Evaluating a New Class of Imprinted Sorbent Materials for Toxic Metals RemovalEPA Grant Number: R828163
Title: Evaluating a New Class of Imprinted Sorbent Materials for Toxic Metals Removal
Investigators: Sengupta, Arup K. , Miller, Alfred
Institution: Lehigh University
EPA Project Officer: Lasat, Mitch
Project Period: July 1, 2000 through June 30, 2002
Project Amount: $193,000
RFA: Exploratory Research - Engineering, Chemistry, and Physics) (1999) RFA Text | Recipients Lists
Research Category: Engineering and Environmental Chemistry , Water , Land and Waste Management , Air
The need for a selective yet cost-effective heavy metal sorbent is well recognized because of the nation’s diverse heavy metal contamination problems pertaining to groundwater, landfill leachates, acid mine drainage, and industrial wastewaters. The oxides of polyvalent metals Al(III), Fe(III), Ti(IV), and Zr(IV) exhibit ligand sorption properties through formation of inner-sphere complexes. Of them, hydrated Fe(III) oxide (HFO) is innocuous, inexpensive, readily available, and chemically stable over a wide pH range. Many previous studies confirmed that Fe(III) oxides have high sorption affinity toward both As(V) and As(III), which are Lewis bases (i.e., electron pair donors). Their selective sorption onto HFO particles results from ligand exchange in the coordination spheres of structural Fe atoms. At near-neutral to alkaline pH, HFO particles also offer high sorption affinity toward toxic metal cations, such as copper, lead, and zinc. Compared to crystalline forms of Fe(III) oxides, namely goethite, hematite, and magnetite, HFOs have the highest surface area per unit mass. As sorption sites reside primarily on the surface, HFOs offer the highest sorption capacity on a mass basis. In our laboratory, the sizes of freshly precipitated amorphous HFO particles were found to vary between 20-100 nanometers. In spite of high arsenic and metal removal capacity, such fine submicron particles and their aggregates are unusable in fixed beds or any flow-through systems because of excessive pressure drops and poor mechanical strength.
The general objective of the research project was to develop polymer-supported HFO nanoparticles that:
- exhibit high sorption affinity toward arsenic and other toxic metal ions;
- are amenable to efficient regeneration and reuse;
- offer favorable sorption/desorption kinetics;
- and are mechanically strong and durable.
Because of its application potential, the project received additional funding from the Pennsylvania Infrastructure Technology Alliance. It is very likely that the project findings will trigger the development of other new hybrid materials using oxides of zirconium, titanium, and aluminum. During the course of the project, it was found that pure iron oxide granules are not sufficiently durable and lack mechanical strength. During prolonged operation in fixed-bed flow-through systems, they tend to produce fires. Containing them in appropriate polymeric support overcame such shortcomings. Equally important was the observation that within porous polymer support, HFOs exhibit enhanced sorption capacity. Luis Cumbal and John Greenleaf worked on the project and received Ph.D. and M.S. degrees in Environmental Engineering in 2004 and 2003, respectively. John Greenleaf's M.S. thesis “Development of a New Hybrid Polymeric/Inorganic Sorbent: Arsenic Removal and Underlying Mechanism” received the outstanding M.S. thesis award from the Association of Environmental Engineering and Science Professors in October 2004. Some key accomplishments of the project are summarized below:
Development of Polymeric/Inorganic Hybrid Sorbent for Arsenic Removal
A fixed-bed sorption process can be very effective in removing trace concentrations of arsenic from contaminated groundwater provided the sorbent is very selective toward both As(III) and As(V) species; the influent and treated water do not warrant any additional pre- or post-treatment; pH and composition of the raw water with respect to all other electrolytes remain unchanged; and the sorbent is durable with excellent attrition resistance properties. We developed a hybrid sorbent particle that is essentially a spherical macroporous cation exchanger bead within which agglomerates of nanoscale HFO particles have been uniformly and irreversibly dispersed using a simple chemical-thermal treatment. The new sorbent, referred to as hybrid ion exchanger or HIX, combines excellent mechanical and hydraulic properties of spherical polymeric beads with selective As(III) and As(V) sorption properties of HFO nanoparticles at circum-neutral pH.
Donnan Membrane Effect of the Polymer Support
The Donnan membrane effect exerted by the polymer support influences the sorption characteristics of the metal oxide particles, all other conditions remaining identical. The conditions leading to the Donnan membrane equilibrium arise from the inability of ions to diffuse out from one phase in a heterogeneous system. This project clearly established that HFO particles supported within a polymeric cation exchanger offer much less arsenic removal capacity than HFO particles supported within an anion exchanger. On the contrary, HFO particles supported within a cation exchanger offer much higher copper removal capacity than with anion exchanger support. Experimental results from the project substantiate the role of polymer support in agreement with the Donnan membrane effect.
Development of Magnetically Active Dual-Zone Sorbent
The present study led to the development of a new class of hybrid dual-zone sorbent that is magnetically active and capable of removing a diverse group of commonly encountered toxic contaminants, namely Cu(II), As(III), As(V), and dichlorophenol, a synthetic organic compound. The preparation of this material is operationally simple and involves partial sulfonation of widely available polystyrene-divinylbenzene polymer beads, followed by dispersion of iron oxide nanoparticles within the polymer phase using a simple chemical-thermal technique. These new hybrid particles exhibit complementary attributes that are not present in currently-available commercial polymeric or inorganic ion exchangers. The newly developed polymeric-inorganic material can be used as passive monitoring agents for the detection of a diverse group of environmental contaminants.
Durability, Sorption Kinetics, and Efficiency of Regeneration
As the supporting spherical polymer beads are mechanically strong, the resulting hybrid sorbent particles are durable and offer excellent attrition resistance properties in fixed-bed columns. Experimental results confirmed that the intraparticle diffusion within the hybrid sorbent particle is the rate-limiting step. The regeneration of arsenic-selective material is very efficient, and the same material has been used for multiple cycles in our laboratory.
Journal Articles on this Report : 4 Displayed | Download in RIS Format
|Other project views:||All 16 publications||5 publications in selected types||All 4 journal articles|
||Cumbal LH, SenGupta AK. Preparation and characterization of magnetically active dual-zone sorbent. Industrial & Engineering Chemical Research 2005;44(3):600-605.||
||Cumbal L, Greenleaf J, Leun D, SenGupta AK. Polymer supported inorganic nanoparticles: characterization and environmental applications. Reactive & Functional Polymers 2003;54(1-3):167-180.||
||Cumbal L, SenGupta AK. Arsenic removal using polymer-supported hydrated iron(III) oxide nanoparticles: role of donnan membrane effect. Environmental Science & Technology 2005;39(17):6508-6515.||
||DeMarco MJ, Sengupta AK, Greenleaf JE. Arsenic removal using a polymeric/inorganic hybrid sorbent. Water Research 2003;37(1):164-176.||