METSIM Modelling of Selenium Recovery on Lignin Using Bio-sorption

Abstract

Selenium is an important mineral for plants and living organisms; trace amounts are needed for our everyday function. However, when large amounts are consumed, it becomes really dangerous with adverse health effects; as a result of this, its removal has been the focus of many studies over the past decades. Selenium is found in most sulfide ores since they both share similar chemical attrib-utes, such as atomic radius. The mining and refining industries release the most amounts of selenium which are present in their wastewater in most cases. Current conventional methods of recycling selenium include pyrometal-lurgical and hydrometallurgical processes, which are often costly, environmentally unfriendly and potentially hazardous. Therefore, researchers have turned towards the study of biomass-based ad-sorbents, also known as biosorbents, for applications in selenium recovery and recycling. Biosorp-tion was the process of choice for reasons such as its operating cost, its recovery rates and reusa-bility In the research presented in the thesis herein, lignin which is a major component in plants was used to adsorb selenium from selenium monochloride (Se2Cl2) using METSIM as the simulation soft-ware of choice due to its versatility and flexibility to control numerous parameters, add new com-ponents and perform mass and heat balances. Lignin was the only component that was added, and the thermodynamic data was found via some research articles where it was plotted in excel and en-tered in METSIM. Further data analysis revealed that the adsorption rate of selenium (Se) on lignin progressed via the pseudo-second order rate model. Adsorption isotherm model studies indicate that the adsorption of Se by lignin followed the Freundlich adsorption isotherm. Calculated energy levels of activation by Se suggest that adsorption progresses due to chemisorption in nature. Thermodynamic studies re-veal that lignin adsorption of Se is exothermic in nature and that the increasing temperature reduces the efficiency of the adsorption process.

A recovery rate of 99.4% was achieved for Se2Cl2 at 25 °C temperature and 0.39M HCl. To fur-ther prove that this model is functional, the two other known chloride forms of selenium, SeCl2 and SeCl4 were tested; selenium recovery rate from SeCl2 and SeCl4 was 45% and 40%, respectively.