Model Simulation and Column Test of the Transport of Nanoscale Zero Valent Iron in Saturated Porous Media

Dense non-aqueous phase liquids (DNAPLs) is sometimes formed when chlorinated hydrocarbons has been released into groundwater aquifers. The use of nanoscale zero valence iron (NZVI) to treat DNAPLs by direct injection to contaminated aquifer has been proven effective. Unfortunately, due to the exceedingly narrow distance between nanoparticles, the attraction force between each particle is so huge that they could easily aggregate into lumps and became hard to disperse. Recently, the use of surface modifier such as surfactant or polymer to enhance the stability and mobility of nanoscale particles in aquifer by increacing surface electrostatic forces or steric forces have become popular. For this reason, the objective of this research was to investigate the effects of three types of surfactant/polymers, which are: (1) poly acrylic acid, PAA. (2) cocamide diethanolamine, CDE. (3) sodium dodecyl sulfate, SDS, on the mobility and tendency to be collected of NZVI. The results demonstrated that when PAA and the total iron concentrations were both 1250 mg/L, the most stable suspension could be reached with 82% of particles remain in suspension. A less satisfactory result 66% of particles are properly suspended was reached when the concentration of CDE increases to 2500 mg/L and the concentration of total iron remains at 1250 mg/L. The worst particle dispersion phenomenon was observed with only 35% of patricles suspended when the final concentration of SDS and total iron were both 1250 mg/L. The amount of NZVI modified with PAA, CDE, and SDS, respectively, breaking through 10 cm saturated soil column were 20 %, 60 %, and 12.5 % of the originally input amount respectively.

In addition, simulations of the NZVI transportation in saturated porous media were performed. The trajectory simulation algorithm was developed to describe the efficiency of a single collector to catch submicrometer particles moving through saturated porous media. Modification of Wei and Wu’s model, established in 2010, a constricted-tube model incorporating the van der Waals force, Brownian diffusion, electrostatic and steric repulsion force mechanisms, developed to predict the transportation and deposition of surface modified NZVI particles by Lagrangian trajectory analytical approach.The oscillatory structural force had been taken into consideration in the modified Wei and Wu’s model. The results from column tests were compared with the trajectory simulation results. The results indicate that simulation of PAA-modified NZVI with consideration of steric repulsion force are fairly consistent with experimental results with only 0.042% in variation. Simulation results of CDE-modified NZVI differ from experimental results with 0.086% while simulation results of SDS-modified NZVI differ with 0.039%. The results of research has shown that the modified model is able to describe the transportation of NZVI in a collector with various surface modification and to successfully predict the behavior of nanoscale particles moving through saturated soil columns.