Enhanced oxidation and recovery of phosphorous from hypophosphite wastewater: Key role of heterogeneous E-Fenton system with MOFs derived hierarchical Mn-Fe@PC modified cathode

Hypophosphite has high solubility and stable chemical structure, however, the effective oxidation of hypophosphite wastewater with high purity phosphate by-product recovery remains a big challenge. In this work, hypophosphite was oxidized by heterogeneous Electro-Fenton system (hetero-EF) with Metal organic Frameworks (MOFs) derived Mn-Fe co-doped porous carbon (Mn-Fe@PC) modified cathode. The effects of cathode material, current intensity and pH value were investigated. The results indicated that the Mn-Fe@PC modified cathode performed much better on hypophosphite oxidation than Fe doped porous carbon (Fe@PC) or Mn doped porous carbon (Mn@PC) modified cathodes, and the optimal Mn/Fe doping ratio was 1: 2. In the hetero-EF system, H2PO2− (10 mM) was completely oxidized within 240 min at 10 mA/cm2 of current density and 3 of pH. The radical quenching experiments results indicated that •OH was the main active species on the oxidation of H2PO2− into H2PO4−. In addition, the actual wastewater tests confirmed the feasibility of recycling high-purity lithium iron phosphate and struvite from the phosphate solution after the oxidation of hypophosphite in hetero-EF oxidation process, which would provide a new green approach for recycling phosphorus from hypophosphite wastewater.