Integration of Bipolar Membrane Electrodialysis with Ion-Exchange Absorption for High-Quality H 3 PO 2 Recovery from NaH 2 PO 2

Abstract

H 3 PO 2 has emerged as an indispensable reducing agent for electroless nickel plating. Commercial preparation of H 3 PO 2 , with high purity and low cost, is a great challenge. In this work, a novel technique by the integration of bipolar membrane electrodialysis (BMED) with ion-exchange absorption was designed to prepare high-quality H 3 PO 2 aqueous solution. The critical parameters, such as voltage drop, NaH 2 PO 2 concentration, and different types of anion-exchange membranes, were systematically investigated. Continuous experiments indicated that a high yield of up to 80.06% with a low energy consumption of 4.99 kW h/kg was achieved under optimal operation conditions (voltage drop of 20 V, feed concentration of 15 wt % NaH 2 PO 2 , and anion-exchange membrane of AHA). Moreover, leakage of Na + ions through the bipolar membrane was observed. By using T-52H cation-exchange resin, the final concentration of Na + ions in H 3 PO 2 aqueous solution was reduced to 20.91 mg/L. Subsequently, a long-term experiment was performed to evaluate the stability of the BMED stack, and the concentration of H 3 PO 2 in the acid compartment reached 4.15 mol/L. Under optimal conditions, the H 3 PO 2 production cost was estimated at $0.937 kg -1 , which was competitive and economically friendly for industrial application.