Macroporous Poly(calcium acrylate-divinylbenzene) Bead - A Selective Orthophosphite Sorbent

The objective of this work is to develop an anion sorbent that could offer chemically recognizable affinity with orthophosphite (H₂PO ^3-) species from a binary aqueous solution containing hypophosphite (H₂PO^2-) as another solute. The macroreticular network, poly(calcium acrylate-divinylbenzene) [P(CaAc-DVB)], has been synthesized and identified to possess the desired chemical selectivity in this separation process. The resin takes advantage of the Lewis acid property of calcium ion, which shows different affinity with the two phosphite species. The P(CaAc-DVB) resin has the spherical shape (d = 0.1-0.3 mm); it was synthesized initially from the polymerization of divinylbenzene and methylacrylate (DVB/MA) in a suspension system. The porosity and pore-size distribution of the beads were adjusted primarily through the variation of the molar ratio DVB/MA and the use of a specific porogen system. The porous structure was found to be crucial for the accomplishment of high sorption efficiency and the preferred chemical selectivity. On the basis of the kinetic assessment of the competitive sorption reaction, it is found that the sorption process could be divided into three stages with using an intraparticle-diffusion model to simulate the kinetic data. A pseudo-second-order reaction model was also used to fit the kinetic data of the early sorption stage by assuming the reaction as the rate-limiting step. It is suggested that this sorption process is governed by the two different kinetic steps at different stages. The study conducted in this work attempts to develop a sorbent feasible ultimately for the rejuvenation of spent electroless nickel solution.