Separation of colloidal particles from groundwater by cross-flow electro-filtration processes for improving metal speciation exemplified by lead

The major goal of this research project is to develop an innovation solid-liquid separation technique for the determination of heavy metal in groundwater exemplified by lead. A prototype cross-flow electro-filtration system (CFEF) have been constructed to separate colloidal particles at selected size and charge levels. Model colloidal particles, gamma-Al2O3 and SiO 2, and naturally occurring colloidal particles collected from well waters were used to evaluate the performance of the CFEF. A mathematical model to predict nano-sized particle transport in CFEF unit was developed. The model results match well with those obtained experimentally. Based on model and experimental results, it is possible to separate the naturally occurring particles by adjusting the pH (or surface charge) and/or applied electrostatic field of the CFEF unit.; The well water samples were taken by low-flow-purging, bailing, and high-flow-purging techniques were used. Results indicate that water-sampling methods appear to strongly affect the particle size distribution, total solid content and total lead concentration. Apparently the disturbance caused by bailing and high-flow-purging technique brings high total solid concentration in the water samples. Results also show that the lead almost associated with colloid. The water samples were filtered using the CFEF unit at various field strength and pH. Generally, the concentration of lead species increases with increasing field strength, that is, the smaller the particles the greater the metal concentration content regardless of sampling method.; The particles in well water samples were separated into several size fractions using CFEF unit. The results show that the distribution of lead in the above fractions (Pb speciation) is very similar among the three well water samples. A small percentage of the total lead was in the easily mobile, exchangeable or bound to carbonate fractions. At other extreme, greater than 80% of the lead was found in the residual or organic form. Results also show that lead concentrations increase with increasing electrostatic field. Clearly, this indicates that the distribution of lead in particles of different size is different. Generally, the concentration of lead speciation increases with increasing field strength. The CFEF process can be an important technique for the speciation of various chemicals in natural water such as groundwater. Moreover, CFEF is able to separate naturally colloidal particles without operational difficulties such as clogging, the most common operational problem is eliminated.