Removal Of Metal Ions By Bio-adsorbents And Chitosan-based Sorbent

A number of industries currently produce varying concentrations of heavy metal laden waste streams with significant consequences for any receiving environmental compartment. Many large-scale uranium mines tailing in China has been in operation for many years and rudimental radioactive nuclides have led to the pollution of the surface water and groundwater to various extents. The threat posed to the environment arises not only from the radioactive emissions from uranium series radionuclides, but also from the chemical toxicity of uranium. The steel fabrication, paint and pigment production, wood treatment, leather tanning, and chromium mining and milling industries release large amounts of chromium every day. The chromium pollution may result in liver necrosis, nephritis, stomach upset and ulcers, and even death in humans.Biosorption is regarded as an innovative method which has superiority over traditional processing methods in separating and recycling heavy metal ions from aqueous solutions. Some microorganisms such as bacteria, algae and fungi are known to accumulate heavy metals. Fungal biosorption is an emerging field for metal sequestering as various fungal biomasses have proven to be effective for metal biosorption from aqueous solutions. The cell wall of Rhizopus arrhizus and Aspergillus fumigatus consists of large quantity of functional groups such as carboxyl (-COOH), amide (-NH2), thiol (-SH), phosphate (PO43-) and hydroxide (-OH), which are believed to play important roles in metal chelation. This study involved an investigation of the use of Rhizopus arrhizus biomass and immobilized Aspergillus fumigatus beads for the removal of U (VI) from aqueous solutions. The experimental results showed that Rhizopus arrihizus has a high tolerance to U (VI) ions and Rhizopus arrihizus can grow normally in200mg/L uranium-contained medium. The adsorption capacity is strongly affected by initial pH and initial U (VI) concentration, and optimum biosorption was observed at solution pH4.0and the maximum biosorption capacity (112.2mg/g) was obtained at initial U(VI) concentration of200mg/L. At the temperature in the range of25-50℃, the influence of temperature on biosorption of U (VI) is slight. The adsorption of U (VI) proceeded very rapidly in the first30min and the adsorptive capacity achieved to above95%of the saturated adsorptive capacity after an hour. The equilibrium was established within90min. Pseudo-second model was suitable to describe the kinetic process. FT-IR analysis and SEM morphology indicated that the cell structure kept unbroken after biosorption. Functional groups, such as amino, hydroxyl and carboxyl groups play important roles in the biosorption process.The immobilized microbial cell systems have many advantages compare with freely suspended biomass, such as ease of regeneration and reuse of the biomass, easier solid-liquid separation and minimal clogging in continuous flow systems. In this study the Aspergillus fumigatus was successfully immobilized by sodium alginate. The immobilized Aspergillus fumigatus beads was used to remove uranium (VI) ions in a batch system. The influences of solution pH, biosorbents dose, U (VI) concentration, and contact time on U (VI) biosorption were studied. The results indicated that the adsorption capacity was strongly affected by the solution pH, the biosorbent dose and initial U (VI) concentration. Optimum biosorption was observed at pH5.0, biosrobent dose (W/V)2.5%, initial U (VI) concentration60mg/L Biosorption equilibrium was established in120min. The adsorption process is conformed to the Freunlich and the Temkin isothermal adsorption model. The dynamics adsorption model is conformed to pseudo-second order model.Chitosan is the deacetylated form of chitin, which is a linear polymer of acetylamino-d-glucose. Chitosan, in many instances are relatively cheap, abundant in supply and have significant potential for modification and ultimately enhancement of its structure and its adsorption capabilities. Chitosan was successfully crosslinked and modified by glutaraldehyde and ethylenediamine, respectively, and the adsorbent (EMCMCR) was obtained. The adsorbent have strong magnetism through addition of magnetic fluid (Fe3O4). The adsorption of Cr (VI) ions from aqueous solution by EMCMCR was studied in a batch adsorption system. The results show that Cr (VI) removal is pH dependent and the optimum adsorption was observed at pH2.0. The adsorption rate was extremely fast and the equilibrium was established within6-10min. The adsorption data could be well interpreted by the Langmuir and Temkin model. The maximum adsorption capacities obtained from the Langmuir model are51.813mg/g,48.780mg/g and45.872mg/g at293K,303K and313K, respectively. The adsorption process could be described by pseudo-second-order kinetic model. The intraparticle diffusion study revealed that film diffusion might be involved in the present case. Thermodynamic parameters revealed the feasibility, spontaneity and exothermic nature of adsorption. The sorbents were successfully regenerated using0.1N NaOH solutions.