Pulse Jet Mixing (PJM) vessels will be used in the waste treatment plant (WTP) being built by the Department of Energy at the Hanford site in order to immobilize nearly 50 million gallons of cold war era legacy nuclear waste currently stored in underground tanks well past their initially intended design life.  One of the primary mixing design requirements of mixing vessels is the ability to blend miscible fluids. A large majority of the WTP PJM vessels contain suspended solid waste particles and exhibit a wide range of solids loading from less than 5 wt% to as high as 20 wt%. It is well known that the addition of particles to a fluid modifies the flow behavior. For particles with very low Stokes number and at low concentrations, it is widely accepted that their effect on fluid flow is negligible and that has formed the basis for a number of measurement techniques, such as, PIV and LDV. In this work the boundary of this approximation is further explored under more relaxed criterion that although the flow might be affected locally, the bulk phenomena -- for example, the blending time of miscible fluids -- should remain similar. Lab-scale testing of a prototypic WTP PJM vessel is performed at two different scales to obtain accurate experimental datasets. Tests are conducted using mono-liquid and two-liquid (varying densities) systems, while varying the solids particle size, density, and concentration during mixing.  Particle velocities are measured using LDV, solids concentration measurements are made by extracting samples, and the overall blending time will be determined using the conductivity probes. The final outcome is to develop an envelope, a multi-property hyperspace, in which the effect of particles may be neglected for macroscopic design quantities of interest, as they are applied to the Hanford WTP.