In this study, a process design consisting of chemical precipitation, electrodialysis with monovalent-selective membranes, and bipolar membrane electrodialysis (BMED) is proposed to valorize seawater concentrate discharged from an RO (reverse osmosis) plant for the production of acid/base and coarse salt with high purity. After pre-precipitation and electrodialysis with monovalent-selective membranes, a high purity of coarse salt (∼92%) was obtained. Furthermore, the effect of current density and feed concentration of the BMED process on the production of acid/base with high purity was investigated. It is acceptable to attain acid/base with a purity of ∼95%/∼85% when operating at a current density of 10 mA/cm 2 and a feed conductivity of 100 mS/cm by applying the screened BMED stack. Finally, the total process cost for the acid/base production was estimated at $0.50/kg at the current density of 10 mA/cm 2 , which is appropriate and competitive for industrial application.
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.
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