Research On The Removal Of SO₄^2- From HPP-SO₂ Absorption Solution With Ion Exchange Resin

The work focused upon the sulfates removal from 1,4-Bis-(2-hydroxypropyl)-pip-erazine (HPP) sulfate aqueous solution, which contained high-concentration sulfates. A222 resin was best selected for elaborate batch and continuous ion-exchange adsorption studies via both dynamic and static methods. By means of elemental analysis, the exchange process was further studied. The exchange condition was optimized and the anion selectivity such as F-, Cl-, NO3- and SO42- was considered. Thermodynamics and kinetics for ion-exchange were investigated in detail.A222 resin was superior to other five resins in the way of capacity ability, eluent ability and impregnation stability. During the circulation exchange-desorption process in HPP-SO42-, average exchange capacity of sulfates was determined to be 139.5 mg·g-1, theoretical dynamic exchange capacity of sulfates was 196.9 mg·g-1 at RT. A222 resin can high effectively desorb sulfates with merely absorbent loss.FTIR, TG, SEM and BET analysis on A222 resin indicated the interaction of HPP adsorption process over the resin was physical adsorption, while the interaction of sulfates accompanied with the formation of chemical bond. The maximum exchange capacity was 163.6 mg·g-1 at the optimal condition (reaction temperature 50℃, contact time 2 h, HPP 0.5 mol·L-1, sulfates 0.3 mol·L-1, pH 5.1, solvent-to-resin ratio 80 gL-1). The regeneration percentage could reach 99%when 4% NaOH aqueous solution is recommended as the eluent at flow rate of 3 ml-min-1. Meanwhile, the regeneration percentage still kept above 95% after 10 times of repetition.The selectivity removal ability for A222 resin is SO42->NO3->Cl->F-.Attractively, the equilibrium data showed that the adsorption isotherm of sulfates on A222 resin was in good agreement with Freundlich equations in HPP aqueous solution. The themodynamic parameters showed that the adsorption process of SO42-onto A222 was spontaneous, endothermal and entropy-increase. Pseudo second order kinetic model can describe adsorption process well and the process was found to be controlled by the intra-particle diffusion, with apparent activation energy of 1.274 kJ·mol-1 and reaction.