Radial migration of water-soluble agents in high-pressure rotary jetting remediation

The high-pressure rotary jetting (HPRJ) is a new technology for the in-situ remediation of contaminated soils. However, the radial migration of water-soluble remediation agents in HPRJ is still not clear, resulting in a lack of reliable theoretical guidance in engineering practice. The laboratory and in-situ HPRJ tests as the well as numerical simulations are performed using the sodium chloride and fluorescein sodium as the tracers to investigate the radial migration and distribution of agents under the effects of jet and advection-diffusion. The results of the in-situ tests after 5 d show that the agent concentration decreases along the radial direction and is significantly affected by the rotary jetting parameters. The optimum combination of the rotary jetting parameters is an injection pressure of 25 MPa, a lifting speed of 25 cm/min, a rotation speed of 22 r/min, a nozzle diameter of 1.6 mm and jetting of twice. The laboratory tests and the numerical simulations show that concentration of the agent in the mixing zone decreases linearly, with a relative concentration of 0.54 to 0.91 near the nozzle. The radius of the mixing zone increases with the increase in the nozzle diameter, injection pressure and the number of jetting times, and decreases with the increasing rotation speed. The agent concentration and radial uniformity are correlated positively with the rotation speed, nozzle diameter and the number of jetting times. The migration of the agent due to advection and diffusion reduces the agent in the mixing zone and increases the agent in the diffusion zone, and homogenizes the radial agent distribution. The advection only lasts for a few minutes, however, it dominates the agent migration in the first 30 d, and thereafter the diffusion becomes more important.