| Various industrial processes produce wastes containing heavy metal compounds along with high suspended solids (up to 10% mass/volume). The heavy metals are most likely to be present in small amounts ({dollar}<{dollar}5% of the total mass or volume of the solid phase) as precipitates of salts with low solubility products, e.g., as hydroxides, carbonates, sulfides, etc., in the background of bulk amounts of innocuous solids such as sand, clay, calcite, humin, etc. The heavy metals may also be sorbed onto the ion-exchange sites of soil or other solid phase materials. Even though the percentage of heavy metal in the solid phase is very low, the waste sludge is most likely to be categorized as hazardous according to present environmental regulations and test protocols because of adverse effects to life and property by the leaching of heavy metals into the environment from it. Understandably, this problem has resulted in serious attempts by environmental engineering and science professionals to develop innovative technologies for the removal and recovery of these toxic heavy metals from the waste sources. Since the contaminant (heavy metal) constitutes a small fraction of the waste, an ideal treatment process to decontaminate the sludge/slurry would be to selectively remove the heavy metal present in the solid phase without affecting the remaining non-toxic materials. This would allow the remaining sludge to be labelled "non-toxic"; consequently it would require to fulfill much less stringent regulations as far as ultimate disposal is concerned.; Conventional treatment processes cannot meet the above listed criterion for efficient treatment, as discussed in detail in Chapter 1. This dissertation investigates a new class of composite sorptive/desorptive ion-exchange membranes and explores different scenarios where the material may be used in a reactor after understanding and tailoring the chemistry of the heterogeneous system comprising of the sludge, the composite membrane, and the aqueous phase in the reactor.; In the material studied, fine spherical beads ({dollar}<{dollar}100 {dollar}mu{dollar}m in diameter) of selective chelating exchangers or adsorbents are physically enmeshed or trapped in thin sheets ({dollar}approx{dollar}0.55 mm thick) of highly porous polytetrafluoroethylene (PTFE). These composite membranes, because of their thin-sheet like physical configuration, can be easily introduced into or withdrawn from a slurry reactor without any difficulty or fouling and the target solutes can be adsorbed onto the micro-adsorbents. Since the aim of this communication is to selectively remove heavy metals, the microbeads chosen were polymeric ion-exchangers containing covalently attached chelating functional group of iminodiacetate moiety. |
