2001 Progress 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. , Cumbal, Luis , Greenleaf, John , Miller, Alfred
Current Investigators: Sengupta, Arup K. , Miller, Alfred
Institution: Lehigh University
EPA Project Officer: Lasat, Mitch
Project Period: July 1, 2000 through June 30, 2002
Project Period Covered by this Report: July 1, 2001 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 objective of this research project is to develop a new class of hybrid sorbent materials for selective separation of dissolved heavy metals and metalloids.
During the last year, we: (1) developed a mechanistic understanding of As(III) removal by Hydrated Aluminum Oxide (HAO) versus Hydrated Fe(III) Oxide (HFO); (2) evaluated the performance of As(V) imprinted Hybrid Ion Exchanger (HIX); and (3) removed multiple contaminants simultaneously.
As(III) Removal By Hydrated Aluminum Oxide (HAO) Versus Hydrated Fe(III) Oxide (HFO)
Approach. As(III) is present primarily as electrically neutral HAsO2 or H3AsO3 at pH below 9.0. Compared to As(V) oxyanions where oxygens are the primary donor atoms, HAsO2 is a softer Lewis base. Al(III) is a very hard cation with an electronic configuration similar to that of inert argon. Conversely, Fe(III) is a transition metal cation with an incomplete 3D orbital. Thus, Fe(III) is a relatively soft Lewis acid compared to Al(III). Evidences are available in the open literature confirming that HFO has higher sorption affinity for As(III) than HAO. We postulated that stronger soft acid-soft base interaction is the underlying reason for higher As(III) affinity toward HFO. To confirm our hypothesis, we included fluoride (F-), a hard anion, in the study.
Results. Figure 1 shows the results of ferric chloride coagulation for a feed water containing both As(III) and fluoride. The exact composition of the feed is provided in Figure 1. Note that while As(III) concentration drops over 90 percent at 40 mg/L Fe(III) dosage, removal of fluoride is less than 20 percent.
Figure 2 shows the results of a similar coagulation test using aluminum as the coagulant, all other conditions remaining identical. Contrary to results obtained with Fe(III) coagulant, Al(III) coagulant showed good removal of F- but As(III) removal was less than 10 percent.
Figure 3 shows the results of a column run study using Hybrid Ion Exchanger (HIX). The composition of feed is essentially identical to the solution used in the coagulation experiments. HIX is essentially a macroporous cation exchanger within which, submicron HFO microparticles have been irreversibly dispersed. The preparation protocol for HIX has been described in the previous annual report. Effluent histories of fluoride and As(III) are provided in Figure 3. It is apparent that while fluoride breakthrough from the column takes place almost instantaneously, As(III) removal continues well beyond 200 bed volumes.
Remarks. Based on the fluoride and As(III) removal data by HAO and HFO, we have concluded that soft Lewis acid/soft Lewis base is the primary mechanism for selective As(III) sorption onto HFO. In a similar vein, hard acid-hard base interaction is responsible for HAO's high fluoride removal capacity.
Evaluating the Effect of Imprinting
Hybrid Ion Exchanger (HIX) with As(V) imprinting was prepared following the experimental protocol described in Figure 4. Subsequently, two fixed-bed column run experiments were carried out: one using HIX, and the other with Imprinted HIX or IHIX. Phosphate and arsenate have been known to possess similar sorption affinities toward HFO particles. That is why phosphate was used as a competing anion during the column runs. Figures 5 and 6 show the effluent histories of As(V) and P during the column runs. Arsenate/phosphate separation factor values were computed from the column run data. For Imprinted HIX or IHIX, As/P = 2.71; for HIX, As/P = 1.28.
Remarks. It is true that the selectivity toward As(V) is enhanced following imprinting. However, the overall arsenic removal capacity was only marginally increased under more representative conditions. Also, the effect of imprinting was greatly reduced following regeneration.
Simultaneous Removals of As(III), As(V) and Zn(II)
Hydrated Fe(III) Oxide (HFO) dispersed particles are capable of removing dissolved As(III), As(V) and heavy metals such as zinc, copper, lead, etc. The two protonation constants of the active functional groups present in HFO have been reported as follows:
FeOH2+ H+ + FeOH, pKa1 = 5.3
FeOH H+ + FeO-, pKa2 = 8.8
Bold represents the solid phase. The distribution of the three functional groups (FeOH2+, FeOH and FeO-) is depicted in Figure 7. Of them, protonated FeOH2+ has high affinity toward As(V) oxyanion, FeOH shows high affinity toward As(III), and FeO- is selective toward heavy metal cations-namely, zinc.
To validate whether HIX is capable of removing nonionized As(III), As(V) oxyanion, and dissolved zinc cations simultaneously, a fixed-bed HIX column run was conducted and the effluent histories are provided in Figure 8. Note that HIX is capable of removing As(III), As(V), and Zn(II) selectively from the background of other competing solutes. It is noteworthy that no commercially available polymeric ion exchanger is capable of removing these target contaminants (e.g., nonionized As(III), anionic As(V), and cationic zinc) simultaneously.
During the course of this investigation, we developed a new class of dual-zone polymeric particles. Every polymer bead has two distinct zones: first, a peripheral zone with sulfonic acid functional groups, and second, a core zone without any functional group. Once the peripheral zone is dispersed with HFO particles, the resulting polymer beads can simultaneously remove: (1) As(III) and As(V) species; and (2) synthetic organic contaminants such as chlorophenols. These new particles also are amenable to magnetization. We are currently working with this new material and the results will be reported in the next report.
During the next year, we propose to: (1) perform the kinetic tests under representative conditions to determine effective intraparticle diffusivities for As(III) and As(V) sorption onto HIX particles; (2) confirm unique sorption properties of newly prepared dual-zone polymer beads for simultaneous removal of both synthetic organic compounds and arsenic species; and (3) magnetize dual-zone particles and examine sorption behaviors of magnetically active particles.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
|Other project views:||All 16 publications||5 publications in selected types||All 4 journal articles|
||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.||
||DeMarco MJ, Sengupta AK, Greenleaf JE. Arsenic removal using a polymeric/inorganic hybrid sorbent. Water Research 2003;37(1):164-176.||