Development of a performance threshold approach for identifying the management options for stabilisation/solidification of lead polluted soils

Two soils spiked with lead at different rates were stabilised/solidified using Portland cement and fy ash at different soil:binder ratios, and tested for their setting time, unconfined compressive strength, leachability and durability. A performance threshold approach was used in order to identify optimal management options for the products of the S/S treatment. Results show that soil texture, percentage of binders and lead concentration play an important part in the treatment, significantly influencing the performance of the resulting products in terms of curing, compressive strength and durability. Pb soil concentrations higher than 15000 mg kg-1 were found to heavily reduce the applicability of the treatment requiring the maximum amount of binder in order to satisfy the performance criteria. Te performance of sandy soils was shown to be limited by setting time and UCS features due to the retardation of the hydration reactions and also by its leaching behaviour, whereas for silt-clayey soils the critical parameter is the mechanical resistance

Physico-magnetic properties and dynamics of magnetite (Fe3O4) nanoparticles (MNPs) under the effect of permanent magnetic fields in contaminated water treatment applications

In this work, a modelling and experimental study was performed to understand the dynamic behaviour of magnetite nano-particles (MNPs) released in a water flow when subjected to an external magnetic field. MNPs physical and magnetic properties and their tendency to form aggregates were also investigated. A mathematical model was developed and applied using MNPs characterization and 3-D field maps generated by OPERA software, considering different magnet bar dimensions and particle aggregate sizes. Model was run to assess the MNPs trajectories, and the capture efficiency of a 10-cm height permanent magnet bar placed on the upper wall of a bench-scale rectangular duct in which MNPs are injected.Shorter MNPs trajectories were observed in the flow regions farther from the duct walls (lateral or bottom walls) where the frictional forces are lower. It is relevant to notice that the MNPs attraction is possible also in regions where the magnetic field is weak due to the high magnetic susceptibility of the system. MNP aggregate size significantly influences the particle dynamics with the trajectories of the larger particles converging more rapidly towards the magnet leading to their capture. However, this does not affect the global removal (similar to 90%) for aggregate diameters higher than 1.2 mu m, demonstrating the general effectiveness of the investigated magnetic capture system, which is only partially influenced by the aggregate size variation. The comparison of modelled and experimental results shows the goodness of the developed model. Along with magnetic and aggregation studies and generated 3-D magnetic field maps, it represents a valid tool for future studies towards the development of practical applications for the magnetic removal of MNPs loaded by water contaminants