PREPARATION AND CHARACTERIZATION OF N-ALKYL QUATERNIZED ACTIVATED CARBON FOR PERCHLORATE REMOVAL FROM GROUNDWATER

Open Access
Author:
Gu, Xin
Graduate Program:
Forest Resources
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 29, 2011
Committee Members:
  • Nicole Robitaille Brown, Thesis Advisor
  • Fred Scott Cannon, Thesis Advisor
Keywords:
  • QUATERNIZED ACTIVATED CARBON
  • PERCHLORATE REMOVAL
Abstract:
Chemicals that are released into our surface and subsurface waters are a pervasive environmental problem. Sources of chemical contamination range from incorrectly disposing of and treating chemical waste, to abandoned waste disposal sites, to leaking storage tanks that might contain hazardous chemicals. Perchlorate is one of those contaminants that, due to kinetic and thermodynamic properties, is quite difficult to remove from contaminated waters and soils. Because of this, perchlorate has become a significant en- vironmental contaminants. Conventional treatment techniques, including virgin granular activated carbon (GAC), air stripping and advanced oxidation had limited or no effect on low perchlorate concentrations in water. Ion exchange with quaternary ammonium or pyridinium groups is currently the most frequently used method for the treatment of perchlorate-contaminated drinking water. This study aims to prepare activated carbon tailored with pyridinium functional groups to remove perchlorate from ground water. To achieve this aim, three main phases of research activities were conducted. In Phase I, activated carbon with pyridinium functional groups and high pore volume was prepared. The sample preparation included three steps: nitric acid oxidation, thermal treatment in ammonia and the quaternization reaction. The surface chemistry and pore structure of samples from each step were characterized (phase II) and the reaction conditions were optimized. In phase III, the final products were tested with respect to perchlorate adsorption (isotherm test and rapid small scale column test). The nitric acid oxidation generated a large number of surface functional groups such as carbonyl, carboxyl, and phenol groups, which is a prerequisite for introducing a high amount of nitrogen containing moieties onto the carbon surface. During the second step of the treatment, amination, surface elemental analysis (by X-ray photoelectron spectroscopy, XPS) results showed that nitrogen was incorporated into the carbon matrix as high as 7.2% (atomic percentage). The temperature of the ammonia treatment, the degree of pre-oxidation and the fraction of ammonia in the carrier gas influenced the resulting populations of oxygen and nitrogen species. Based on the XPS study on N1s spectrum at different amination temperature, it is suspected that during the initial stages of heating, some intermediates such as amide, lactam and imide were formed. As temperature increased, these labile species were converted to more thermodynamically stable structures with heterocyclic aromatic moieties (pyridinic or pyrrolic functional groups). At higher temperature (> 600◦C), the fraction of quaternary nitrogen gradually increased and some nitrogen species might have decomposed. Through quaternization, pyridine groups at edge sites were successfully transformed to pyridinium groups (20% of total nitrogen). XPS in conjunction with chemical derivatization (by methyl iodide) was confirmed to be an effective way to qualitatively analyze the pyridinium species. Pyridinium-tailored carbon achieved as much as a 6-fold improvement in bed life for adsorbing perchlorate as determined by rapid small-scale column tests (RSSCT) using spiked groundwater with perchlorate (30 ppb).