Enhancing the Sustainability of Phosphogypsum Recycling by Integrating Electrodialysis with Bipolar Membranes

Abstract

Phosphogypsum−a byproduct of phosphoric acid production−piled near eco-sensitive regions, poses both environmental and health risks. By reacting phosphogypsum with NaOH, Ca(OH) 2 is produced, which can be utilized for CO 2 sequestration. The cost of NaOH, however, and the low market value of the byproduct, a concentrated Na 2 SO 4 stream, hinder the economic viability of this approach. Here, we propose to increase the cost-efficiency of phosphogypsum processing by converting the Na 2 SO 4 to NaOH and H 2 SO 4 using bipolar membrane electrodialysis (BMED). The result is a cleaner and more circular process, as NaOH can be recycled for dissolving phosphogypsum, while H 2 SO 4 can be reintroduced into the industrial phosphoric acid production or used to leach valuable metals out of the phosphogypsum. To assess the feasibility of BMED integration, we used a bench-scale system to probe the trade-off between obtaining high base-product concentration and obtaining high specific energy consumption. This was done for synthetic Na 2 SO 4 solutions at various concentrations, applied voltages, and types of anion-exchange membranes. Economic analysis based on the results showed that a two-step batch BMED process is able to reduce the chemical cost by 50%, as compared to purchasing NaOH. Integrating BMED with existing approaches can, therefore, improve the sustainability and cost-efficiency of phosphogypsum valorization.

Recovery of Acid and Base from Sodium Sulfate Containing Lithium Carbonate Using Bipolar Membrane Electrodialysis

“…Due to the low ion concentration in the initial acid and base chambers, the resistance of the membrane stack was larger. With the decomposition of the contents of the salt chamber by BMED, the concentration in the acid–base chamber increased gradually, and the resistance decreased and tended to a steady state [ 31 ]. In the late stage of the experiment, the salt chamber concentration decreased sharply, and the membrane stack resistance rose once again.…”

Decreasing Seawater Desalination Footprint by Integrating Bipolar-Membrane Electrodialysis in a Single-Pass Reverse Osmosis Scheme

“…For the BMED process, the current efficiencies (η in %) and SEC (kW h mol –1 ) for the acid and base products were calculated using eqs and and where F Faraday constant in coulomb mole –1 , V solution volume at time t in liters, Δ C concentration difference between the product at time t and that at t = 0 in molarity (M), n number of cell triplets, t time in seconds, t ′time in hours, and mmoles of the acid and base produced at time t ′.…”

“…BMED is an eco-friendly, cost-effective technique, which has been extensively studied for desalination of saline water, , in situ chemical production, , and many environmental and industrial applications. ,− Specific reports on different aspects of the beneficial reuse of the SWRO brine using the BMED process have recently been published. ,,,,− These include (1) use of monovalent ion-selective membranes ,, to improve the product (HCl and NaOH) purity, (2) integration of nanofiltration (NF) or precipitation , (alkali dose) processes with BMED to minimize the influence of divalent cations, and (3) inter-comparison between different possible pathways for NaOH production from SW or the SW concentrate. It stems from these studies ,− that BMED is a potentially eco-friendly, cost-effective method for SWRO brine management, yet techno-economical barriers and the lack of sufficient knowledge still limit the application of BMED on an industrial scale . Indeed, very few studies ,,, have included an economic evaluation related to the production of an acid and base from SWRO brine by BMED.…”

Electrodialysis Applications in Wastewater Treatment for Environmental Protection and Resources Recovery: A Systematic Review on Progress and Perspectives

“…Wastewaters from UF 6 production can be recycled as HF and KOH [ 251 ]. Phosphogypsum (CaSO 4 ) by-product from phosphoric acid production can be converted by NaOH into Ca(OH) 2 and Na 2 SO 4 , thus splitting the salt into base and sulphuric acid via BMED [ 273 ]. Other applications were proposed to convert NH 4 Cl into HCl and NH 3 [ 274 , 275 ], NH 4 HCO 3 into NH 3 and CO 2 [ 276 ], Na 3 PO 4 into H 3 PO 4 and NaOH [ 277 ], NaBr into HBr and NaOH [ 278 , 279 ], Na 2 SO 4 /(NH 4 ) 2 SO 4 into H 2 SO 4 and NaOH/NH 3 [ 280 ], NaCl/KCl into HCl and NaOH/KOH [ 281 ], boron into boric acid [ 282 , 283 , 284 ].…”