(539a) Study of the Tcep-Zeolite System: Kinetics and Surface Chemistry Analysis Investigations

Emerging contaminants (ECs) and micropollutants are becoming a global environmental problem as there is increasing information linking them to environmental and human health hazards. One micropollutant of interest is tris-2-chloroethyl phosphate (TCEP), an organo-phosphate ester used as a plasticizer and flame retardant.  Recent studies by others have focused on the presence of TCEP in environmental and drinking waters, and several of these previous studies indicated that TCEP was the most frequently detected compound of the ECs investigated. Transport of TCEP from wastewater effluents to raw water sources is supported by research that identifies the presence of TCEP in surface waters similar to those detected in wastewater effluents.  This supports the premise that the TCEP is not being removed from the water cycle. 

In our previous work presented last year, adsorption of TCEP to zeolite was studied.  Equilibrium adsorption isotherms and surface hydrophobicity/energy measurements were conducted.  These results demonstrated excellent removal of TCEP using laboratory water and zeolite (>99% removal; Langmuir sorption capacities of 23 mg/g to 103mg/g).  Adsorption was determined to be a function of both solution pH and adsorbent type.  The observations of pH-dependant adsorption (given a non-ionizing adsorbate) and the additional lack of adsorption related to low zeolite concentrations and higher pH values suggested a complex function of pH and hydrophobic/hydrophilic interaction which required further investigation.

This paper presents the continued research efforts to better understand the adsorption mechanisms of the TCEP-zeolite system.  Kinetic modeling and measurements at various TCEP-zeolite ratios were conducted.  These data suggest a system with fast kinetics.  The modeling was used to establish characteristics of possible reaction mechanisms.  Also zeta potential and surface area measurements were conducted to support the kinetic data and better understand the effects of pH on adsorption.  These results will be presented.

Thermo Gravimetric Analyses (TGA), Nuclear Magnetic Resonance (NMR), High Perforamnce Liquid Chromatography (HPLC), and Fourier Transform Infrared Technology (FTIR) were used to characterize the TCEP-zeolite adsorption system and postulate the potential adsorption mechanisms occurring.  The results of these data will be presented and discussed.