Study of a New Process for the Efficient Regeneration of Ion-exchange Resins

摘要

Global demand for clean water is becoming a persistent concern and this has stimulated research into efficient and effective desalination and water treatment processes. Ion-exchange (IEX) resins have been used for water purification, but are limited by the continuous depletion of the resins and the need for large volumes of acid and base solutions for their regeneration. This Thesis presents a new chemical/thermal regeneration method and the novel use of mixed-bead and mixed-bed IEX resins for future desalination purposes.Mixed-bead resins composed of weak-acid and weak-base groups were synthesized and used for sorption studies with saline, followed by regeneration with ammonium bicarbonate (AB) and heating at 80°C. It was found that AB followed by heating provides 100% regeneration of these resins. Unfortunately, the low IEX capacities of polyampholytic resins restrict their commercial applications. However, a novel process was developed for increasing their IEX capacity by exposing Ni²⁺ and Ca²⁺ saturated resins to concentrated AB solutions, followed by heating. This was found to increase the IEX capacity by 4−5× with a corresponding increase in observable pore size and Brunauer-Emmett-Teller surface area.Although these mixed-bead resins could be completely regenerated using AB and heating, this also causes their thermal degradation, so the exhausted resins were also regenerated using AB washing but without heating. This was highly effective and showed an increased IEX capacity when in AB form, with higher selectivity for Na⁺ and HCO3‾ ions. It was also discovered that mixed-bed resin systems of strong-acid and strong-base resins, can be used to desalt 0.1M NaCl solution, producing about 6× the resin mass of drinking quality water, and this system can also be regenerated using concentrated AB in situ. In general, regeneration processes using AB could be applied for mixed-bead and mixed-bed systems in a continuous process, minimizing chemical waste, environmental impact, and costs.Lastly, a polystyrene based zwitterionic latex was synthesized with a particle size of about 110 nm to study the IEX behaviour of the polyampholytic resins. It was found that Na⁺, NH4⁺, Cl‾ and HCO3‾ ions readily exchanged with the surface groups following the Law of Mass Action.