Abstract
Mineral carbonation routes have been extensively studied for almost two decades at Åbo Akademi University, focusing on the extraction of magnesium from magnesium silicates using ammonium sulfate (AS) and/or ammonium bisulfate (ABS) flux salt followed by carbonation. There is, however, a need for proper recovery and recirculation of chemicals involved. This study focused on the separation of AS, ABS and aqueous ammonia using different setups of bipolar membrane electrodialysis using both synthetic and rock-derived solutions. Bipolar membranes offer the possibility to split water, which in turn makes it possible to regenerate chemicals like acids and bases needed in mineral carbonation without excess gas formation. Tests were run in batch, continuous, and recirculating mode, and exergy (electricity) input during the tests was calculated. The results show that separation of ions was achieved, even if the solutions obtained were still too weak for use in the downstream process to control pH. Energy demand for separating 1 kg of NH4+ varied in the range 1.7, 3.4, 302 and 340 MJ/kg NH4+, depending on setup chosen. More work must hence be done in order to make the separation more efficient, such as narrowing the cell width.
Highlights
The total greenhouse gas emissions in Finland in 2017 were 15.8 million tonnes CO2 eq.(approximately 22%) less than in 1990, according to preliminary data for 2017 from Statistics Finland [1].The target for 2050 is that the greenhouse gas emissions will be reduced by at least 80% compared to the emission levels in 1990 [2,3]
The process developed at Åbo Akademi University (ÅA), the ÅA route, involves letting magnesium silicate rock (preferably containing serpentinite, Mg3 Si2 O5 (OH)4 ) react with ammonium sulfate (AS) to extract magnesium, which subsequently reacts with CO2 of flue gas and form stable magnesium carbonates
Process parameters and composition solution given in Tables composition of starting solution are given in Tables 2 and 3
Summary
The total greenhouse gas emissions in Finland in 2017 were 15.8 million tonnes CO2 eq. The target for 2050 is that the greenhouse gas emissions will be reduced by at least 80% compared to the emission levels in 1990 [2,3]. The process developed at ÅA, the ÅA route, involves letting magnesium silicate rock (preferably containing serpentinite, Mg3 Si2 O5 (OH)4 ) react with ammonium sulfate (AS) to extract magnesium, which subsequently reacts with CO2 of flue gas and form stable magnesium carbonates. A challenging step in the ÅA route is the extraction of magnesium from the serpentinite rock [4,6,8]. Ammonium bisulfate (ABS) has been used as input chemical and one option is a pH-swing process sometimes referred to as the UK route [9,10]. Different options for optimizing the process have recently been presented [13]
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