Experimental study on the removal of Ca(II) from aqueous solution using a bulk liquid membrane with facilitated transport mechanism

Abstract

Calcium ion is one of the scale-forming cations in water, as it can readily produce sulfate and carbonate scales. Liquid membranes eliminate the equilibrium constraints of liquid-liquid extraction by integrating extraction and stripping processes into one unit and therefore offer tremendous potential for removing various metal ions from aqueous solutions. In this study, the ability of a bulk liquid membrane (BLM) containing di-(2-ethylhexyl) phosphoric acid (D2EHPA) as a carrier to remove Ca(II) ions from aqueous solutions was explored. D2EHPA showed good efficacy and significantly facilitated transport of Ca(II) through the BLM. The transport mechanism by D2EHPA was investigated using pH measurements, and it was found to be a coupled facilitated mechanism. The effect of key parameters such as solvent type, carrier concentration, concentration of the receiving phase, and transport duration on the extraction and transport efficiencies of Ca(II) were investigated. Results show that the maximum extraction (98.9 ± 0.3%) and transport (97.3 ± 1.2%) were achieved at optimal conditions of 0.05 M D2EHPA in the kerosene as the solvent, 0.1 M HCl, and 24 h. The BLM showed high selective transport for calcium over lithium (5.84). Additionally, the BLM was compared with a liquid-liquid extraction system, and it was shown that the bulk liquid membrane requires less carrier to extract a given amount of Ca(II).