MONETIZATION OF REJECT BRINE FOR THE RECOVERY OF CALCIUM AND MAGNESIUM IONS AND SEQUESTRATION OF CO2: REACTION KINETICS AND OPTIMIZATION

Abstract

The seawater desalination process is considered as one of the most sustainable means of water supply in arid and semi-arid regions. Despite its undeniable potential to meet global water demands, there are several environmental impacts associated with its operation. The process generates reject brine as a by-product, most of which is discharged back into the sea leading to its contamination. Additionally, the energy required for desalination processes are often supplied from fossil fuel sources that are infamous for their CO2 emissions. Hence, the passive CO2 emissions generated from the desalination process have become another major environmental concern. Therefore, modification of current desalination facilities is paramount to address the concerns related to brine disposal and CO2 emissions to protect the environment and also to ensure sustainable water supply. The research work presented in this dissertation aims to address these concerns through the developing potential process schemes for simultaneous management of reject brine and CO2 sequestration. Typically, brine generated from the desalination processes are rich in calcium and magnesium ions which can be separated to form corresponding metal hydroxides upon reaction with an alkali or easily converted into their corresponding carbonates through reaction with CO2 in presence of an alkali. In this dissertation, three potential schemes for brine management and CO2 capture using NaOH as an alkali were investigated. The experiments were conducted in batch mode using a patented inert particle spouted bed reactor (iPSBR), and response surface methodology was used to optimize various process parameters. The solid products obtained were characterized using different analytical techniques which confirmed the possibility of recovering high-purity calcium carbonate, magnesium hydroxide and hydromagnesite. The proposed schemes could simultaneously ensure the sequestration of 3.5 to 11.5 grams of CO2 for every liter of reject brine treated. The results clearly showed the potential of proposed schemes for simultaneous management of desalination reject brine and CO2 sequestration. Furthermore, incorporation of an electrolysis unit with schemes was suggested to eliminate the requirement of external addition of NaOH which can increase the commercial viability of the proposed schemes, thus, paving the way for sustainable reject brine management and CO2 sequestration.