Removal of thorium and zirconium from aqueous streams by biosorption
Creators: name: Varala, Sayanasri
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400409
subject: Separation technologies
classificationCode: 400410
subject: Wastewater treatment processes
classificationCode: 400499
subject: Chemical engineering not elsewhere classified

description: Thorium and zirconium are the most stable radionuclides used in various nuclear operations, and the separation of these from aqueous industrial streams is essential. The conventional technologies followed for the treatment of high concentrate nuclear discharges containing these radionuclides are the precipitation, electro precipitation, electro coagulation, cementing, membrane separation, solvent extraction, ion-exchange resins, oxidation–reduction, adsorption, reverse osmosis, and evaporative recovery, etc. However, afore mentioned treatment methods have certain disadvantages like the high cost of implementation and operation, especially for the concentrations below 100 ppm. Hence, the necessity to invent new treatment technologies with acceptable costs is compulsory for the treatment of low concentrate radioactive wastes. One of the promising alternatives is the application of biosorption process that utilizes biomass or bio-based materials as sorbents in the waste water treatment as a pollution control process for most of the industrial discharge. The advantages of biosorption over the conventional methods are low operating cost, selectivity for specific metal, short operational time and no chemical sludge. Biosorption entails the use of living or dead biomass and their derivatives with the involvement of either ligands or functional groups (situated on the outer surface of the biomass) in the mechanism of sorption. This treatment method is based on utilizing the ability of biological materials to accumulate metal ions from liquid wastes either by metabolically mediated or physicochemical pathways. <br><br>In the present research, an attempt has been made to explore the potentiality regarding adsorption characteristics of a new agro-industrial by-product namely, de-oiled Karanja seed cake for the removal and recovery of radionuclide metal ions (Th and Zr) from aqueous solutions via biosorption method. The relevant process conditions for the sorption of these metal ions (pH, sorbent mass, ionic concentration, and temperature) were studied. Furthermore, adsorption isotherm and kinetic sorption modeling, thermodynamics were investigated to determine the probable physical characteristics of the biosorption process. Also, the bound metal ions (Th and Zr) were isolated from the loaded biomass adapting desorption technique using elution agents since biosorption will be more attractive if loaded biomass can be regenerated for reuse in multiple sorption cycles. The biosorption and desorption studies were carried out in batch mode, and the process variables were optimized for the maximum biosorption/desorption efficiency through DOE concepts like Taguchi OA and RSM. The property of new biomass was investigated using characterization techniques like SEM, FTIR, EDX, pHpzc and physicochemical properties.<br><br>Deoiled Karanja seed cake has shown good potentiality regarding biosorption capacity in the removal of thorium and zirconium from aqueous streams, and obtained high Kd values when compared to commercially available adsorbents, implying an important feature of DKSC to treat large volumes of low concentration metal wastes. The thorium equilibrium biosorption data fitted very well to the Langmuir isotherm model, whereas the zirconium biosorption data fitted the best with Freundlich model representing the mono-layer sorption and complex heterogeneity of the biomass respectively at optimum conditions. The sorption kinetic data followed pseudo-second order model conveying the chemisorption mechanism by the probable involvement of hydroxyl, carboxyl, amine, and nitro molecular groups. The desorption results revealed that Th ions could be eluted using 0.1M HCl and 0.1M NaHCO3 can be used for eluting Zr ions from the loaded biomass respectively. It was also proved that desorption kinetics follows pseudo-second order model for both thorium and zirconium at optimal conditions. Also, the regenerated DKSC was found to possess similar properties as of native DKSC. Hence, the research work conveys that proposed biosorption/desorption method using DKSC (new low-cost bi-sorbent) is most cost-effective and efficient treatment method that is suitable for the effluent treatment of nuclear and hydrometallurgical industries. Thus, DKSC could be effectively used as a natural and economic biosorbent for the separation of Th and Zr ions from contaminated sites.