The Biosorption of Platinum and Palladium in Chloride Real Leach Solution by Modified Biomass
Modern demands for technological goods have created a global problem of excess electronic wastes (e-wastes). Increasing demands of precious metals to supply factories around the world for these electronic goods may also pose a strain towards current global gold, platinum and palladium reserves. As e-wastes often contain prominent levels of toxic materials along with valuable metals, its recycling must be conducted on an industrial scale to ensure a steady supply of precious metals (PM) for future needs. Current conventional methods of recycling PM including pyrometallurgical and hydrometallurgical processes are often costly, environmentally unfriendly and potentially hazardous. Therefore, researchers have turned towards the study of biomass-based adsorbents, also known as biosorbents, for applications in PM recovery and recycling. In the research presented in the thesis herein, wheat straw, canola meal and wood bark nuggets were used and immobilized with dithiooxamide (DTO), ethylenediamine (EN) and primary amine (PA) to create 12 novel biosorbents. These biosorbents were examined for their effectiveness in recovering platinum (Pt) and palladium (Pd) from real leach solution provided by a PM refining plant in Ontario. From these 12 biosorbents, it was determined that dithiooxamide-immobilized wood bark (DTO-WB) was the most effective. Being able to recover up to 97.4% Pt and 99.8% Pd from diluted leach solution, DTO-WB was selected as the biosorbent of focus for the rest of the research. Characterization analysis including Fourier-Transform Infrared Spectroscopy (FT-IR) and Carbon, Hydrogen, Nitrogen and Sulfur (CHNS) content analysis confirmed that DTO immobilization was successful on the structure of WB. Further experimentation and data analysis revealed that the rate of adsorption of Pt and Pd on DTO-WB progressed via the pseudo-second order rate model. Adsorption isotherm model studies indicate that the adsorption of Pt and Pd by DTO-WB followed the Freundlich and Langmuir adsorption isotherm respectively. Calculated energy levels of activation by Pt and Pd suggests that adsorption progresses due to chemisorption. Thermodynamic studies reveal that DTO-WB adsorption of Pt and Pd is endothermic in nature and that adsorption efficiencies may be improved by increasing operating temperatures. Acknowledging that a variety of dissolved metals exists in real leach solution, performed co-adsorption experiments indicated that DTO-WB was efficient in recovering other PM, namely silver and rhodium. Selenium, a potentially toxic element commonly present in drinking water was also adsorbed in significant numbers by DTO-WB, suggesting that the adsorbent may potentially be used in water-treatment research.
Hydrometallurgy, Mining, Chemistry, Chemical Engineering, Biomass, Biomaterials, Adsorption, Biosorption, Value added products
Master of Science (M.Sc.)
Chemical and Biological Engineering