Experimental and numerical studies of a novel technique for abatement of toxic metals from aqueous streams

The objective of this project is to study the adsorption characteristics of fish scales that ensure efficient removal of toxic metals from wastewater. Removal of lead, cobalt and arsenic ions from both industrial and municipal water is of extreme importance prior to disposal to aqueous streams. The processes related to the removal of the ions include mainly adsorption and precipitation although flocculation, membrane separation and leaching are some of the viable alternative technologies. Materials such as granular activated carbon, metal oxides and synthetic resins are being extensively employed as adsorbent materials but the high cost of the products limits their large-scale usage.;Using fish scales as an adsorbent, 95% of the lead ions, 70% of the cobalt ions and 80% of arsenic ions were removed. The effect of precipitation of the lead ions in an alkaline medium (with no adsorbent) was analyzed to be insignificant for remediation levels. As sorption dictates the interactions between the bulk and adsorbed phases, it is the most important factor that influences the transport of the chemical species through the medium. The process of adsorption includes ion exchange, chemisorption and electrostatic attraction mechanisms for specific species in interaction with specific sites on the adsorbent. A series of multi-component experimental runs indicate that the degree of adsorptivity of a specific species is dependent on the estimated equilibrium sorption coefficients of all the components and the concentration of the specific adsorbate and all the interfering ions in the bulk phase. The number of the adsorption sites available on the adsorbent is also a very sensitive parameter for competitive adsorption phenomena. (Abstract shortened by UMI.).;In order to understand the mechanism of adsorption on fish scale, characterization of its substrate with Scanning Electron Microscope and Nuclear Magnetic Resonance techniques were carried out to evaluate the components on its surface that are related to the adsorption of metal ions. Applications of SEM and NMR techniques have proven that the fish scales are composites in nature. Static and dynamic experimental models were utilized to study the adsorption behavior at a pH range from 2-11. It is important to consider that given the unknown parameters of the substrate, the experimental runs are conducted to study the adsorption behavior in a qualitative approach. The quantitative approach is supplement by numerical studies based on surface excess and pore diffusion theories.