Ping Dong,Yong-hui Song,Lei Wu,Ya Wang,Ning Yin,Yi-fan Wang,Yi-fan Li
In this study, the persulfate and cyanide tailings (PS-CTs) were used for the synergistic treatment of semi-coke wastewater to achieve advanced oxidation and in-situ coagulation removal of organics in semi-coke wastewater. The effects of persulfate concentration, reaction temperature, cyanide tailing concentration and initial pH on chemical oxygen demand (COD) removal efficiency were investigated, and the synergistic mechanism in the treatment process was further explored. The results showed that the removal efficiency of COD in semi-coke wastewater was 94.49 % under the conditions of persulfate concentration 0.025 mol/L, reaction temperature 60 °C, cyanide tailings concentration 5 g/L, the initial pH value of 3. The results of the mechanistic analysis showed that in PS-CTs system, pyrite was oxidized by persulfate. The dissolved Fe 2+ activated the persulfate to produce SO 4 − and OH and generated Fe 3+ in situ. The hydrolysis of Fe 3+ produced a series of complex ions and amorphous iron hydroxides, which could remove some organics by adsorption and sweeping netting. The organics in semi-coke wastewater were effectively removed by the combined effect of oxidation and coagulation. In addition, the PS-CTs system also achieved the oxidative de-cyanidation of cyanide tailings simultaneously, and the total cyanide concentration of treated cyanide tailings was 8.21 mg/kg, and the leaching cyanide concentration was 0.12 mg/L, which was in line with the emission standards. This process implemented the concept of “treating waste with waste”, and provided theoretical support for the treatment of semi-coke wastewater and other organic wastewater.
Heteroatom-doped porous carbon has attracted enormous attention in fabricating high-performance supercapacitors . However, designing heteroatoms containing carbon materials through an eco-friendly and cost-effective route remains challenging. In this work, N-O-S self-doped porous carbon materials are prepared from semi-coking wastewater-based phenolic resin (SWPR) via a simple Na 2 CO 3 activation strategy. The abundant phenols , NH 4 + , and SO 4 2- in semi-coking wastewater endows the versatile N, O, and S doping in porous carbon material, remarkably enhancing its conductivity. The optimal SWPR-700–2.5 porous carbon material is obtained at an activation temperature of 700 °C and a mass ratio of 2.5:1 for SWPR: Na 2 CO 3 . The symmetrical supercapacitor is assembled with SWPR-700–2.5, exhibiting a high specific capacitance of 170.5 F g −1 at 0.5 A g −1 , with a high energy density of 5.92 Wh kg −1 at 124.9 W kg −1 . After 10,000 cycles, the Coulombic efficiency and capacity retention are 100% and 99.4%, respectively, at a current density of 20 A g −1 . The excellent performance of SWPR-700–2.5 based capacitor is attributed to the porous structure with a large specific surface area (718 m 2 g −1 ) and abundant N-O-S self-doping (2.739 at% N, 8.627 at% O and 1.378 at% S). This study provides a simple route to prepare N-O-S self-doped porous carbon for supercapacitors and pushes forward the advancement of semi-coking wastewater treatment.
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