Suppressing Ammonia Re-Emission with the Aid of the Co3O4-NPs@KIT-6 Catalyst in Ammonia-Based Desulfurization

Use of La-Co@NPC for Sulfite Oxidation and Arsenic Detoxification Removal for High-Quality Sulfur Resources Recovery in Desulfurization Process

Ammonia desulfurization is a typical resource-recovery-type wet desulfurization process that is widely used in coal-fired industrial boilers. However, the sulfur recovery is limited by the low oxidation rate of byproduct (ammonium sulfite), leading to secondary SO2 pollution due to its easy decomposability. In addition, the high toxic arsenic trace substances coexisting in desulfurization liquids also reduce the quality of the final sulfate product, facing with high environmental toxicity. In this study, nitrogen-doped porous carbon coembedded with lanthanum and cobalt (La-Co@NPC) was fabricated with heterologous catalytic active sites (Co0) and adsorption sites (LaOCl) to achieve sulfite oxidation and the efficient removal of high toxic trace arsenic for the recovery of high-value ammonium sulfate from the desulfurization liquid. The La-Co@NPC/S(IV) catalytic system can generate numerous strongly oxidizing free radicals (·SO5- and ·O2-) for the sulfite oxidation on the Co0 site, as well as oxidative detoxification of As(III) into As(V). Subsequently, arsenic can be removed through chemical adsorption on LaOCl adsorption sites. By using the dual-functional La-Co@NPC at a concentration of 0.25 g/L, the rate of ammonium sulfite oxidation reached 0.107 mmol/L·s-1, the arsenic (1 mg/L) removal efficiency reached 92%, and the maximum adsorption capacity of As reached up to 123 mg/g. This study can give certain guiding significance to the functional material design and the coordinated control of multiple coal-fired pollutants in desulfurization for high-value recovery of sulfur resources.

Ammonium Sulfite Slurry from Ammonia-Based Desulfurization Activates Water-Soluble Humic Substances from Lignite: Performance, Application, and Mechanism

Both ammonium sulfite slurry (ASS) from ammonia-based desulfurization and lignite are waste materials with low value. In this work, an innovative method was developed by applying ASS in lignite activation to produce water-soluble humic substances (WHSs) with a high bioactivity and economic value. The optimal activation method was to mix lignite and ASS at a 4:1-liquid-solid ratio by vortex blender and then oscillate it for 30 min at 25 °C. Compared with that of the unactivated lignite (UAL), the yield of WHSs from activated lignite (AL) increased by 42.72%. WHSs from AL consisted of a large number of aliphatic carbons with low molecular weight and functional groups such as amides, amines, sulfonic acid groups, C-O, and so forth. Moreover, WHSs from AL at lower concentrations (2 mg/L) has a more obvious root-elongation-promoting effect than WHSs from UAL (10 mg/L). Activation experiment with the lignite-related model compounds revealed that ASS caused the breakage of Caliph-O, Caliph-Caliph, and Carom-Caliph linkages between aromatic rings. These findings provide a theoretical basis for the development of green and sustainable technologies for the beneficial reuse of ASS and lignite in agriculture.

Multi-air-pollutant removal by using an integrated system: Key parameters assessment and reaction mechanism

How to cost-efficiently and cooperatively remove SO₂, NO and Hg⁰ in flue gas is a hot topic in the field of air pollution control. This work developed an integrated system that consists of a dual-absorption system and a vapor oxidation system, in which Na₂CO₃ and H₂O₂/Na₂S₂O₈ were used as the absorbent and oxidant. The results indicated that the efficiencies of SO₂ removal and NO conversion reached 99.5% and 93% respectively. Rising the vaporization temperature and decreasing the pH of H₂O₂/Na₂S₂O₈ could facilitate the NO conversion. The spent Na₂CO₃ after desulfurization was demonstrated to be a good absorbent for NO₂ removal. The best conditions of pH and temperatures for the dual-absorber were determined as 10/8 and 60/60 °C, respectively. The presence of 1000 mg/m³ SO₂ and 300 mg/m³ NO favored the Hg⁰ removal. TMT-15, an organic sulfur compound, was demonstrated to be useful in retaining Hg²⁺, with an efficiency of 92%. According to the analyses of electron spin resonance (ESR), ion chromatography (IC), atom fluorescence spectrometry (AFS) and X-ray photoelectron spectroscopy (XPS), SO₄^- and HO were proved to be the key radicals, and the existing forms of N- and Hg- species in the product were identified as NaNO₂/NaNO₃ and HgCl₂.

Simultaneous Catalysis of Sulfite Oxidation and Uptake of Heavy Metals by Bifunctional Activated Carbon Fiber in Magnesia Desulfurization

Sulfite and heavy metals are crucial pollutants in the slurry produced by flue gas desulfurization. In this study, a novel cobalt-based activated carbon fiber (Co-ACFs) catalyst-adsorbent was synthesized using an impregnation method; this bifunctional catalyst-adsorbent was used in wet magnesia desulfurization for the simultaneous catalytic oxidation of magnesium sulfite and uptake of heavy metal (Hg2+, Cd2+, and Ni2+) ions. The morphology and surface chemistry of ACFs before and after cobalt loading were investigated using various characterization methods. The kinetics on catalytic oxidation of magnesium sulfite was investigated, and the effects of operation conditions on the simultaneous adsorption capacity of heavy metals were examined. Relative to a non-catalysis material, the 40% Co-ACFs material increased the oxidation rate of magnesium sulfite by more than five times. The Langmuir model can describe the adsorption behavior of Co-ACFs on Hg2+, Cd2+, and Ni2+, indicating that the simultaneous uptake of heavy metals is a single-layer adsorption process. The maximum adsorption capacities for Hg2+, Cd2+, and Ni2+ are 333.3, 500, and 52.6 mg/g, respectively. A pseudo-second-order model confirmed that the removal of heavy metals is controlled by the chemisorption process.