Research On Resource Utilization Technology Of Coke Oven Flue Gas Desulfurization Waste Acid

The coking process generates a large amount of coke oven flue gas containing high concentration of sulfur dioxide（SO₂）,which can cause serious environmental problems and health hazards if emitted directly.Therefore,the development of low-cost and efficient technologies for the removal of pollutants from coke oven flue gas has been a long-term endeavor of researchers around the world.Carbon based catalytic desulfurization has gradually become the preferred process for coke oven flue gas desulfurization due to its high desulfurization efficiency and its ability to directly oxidize SO₂in flue gas to SO₃,which is then prepared into dilute sulfuric acid and used as a raw material for the subsequent ammonium sulfide process.However,the charcoal-based catalyst will be broken after repeated adsorption and washing,and the dust carried by the coke oven flue gas and the corrosion of the desulfurization system will lead to the production of sulfuric acid containing small amounts of iron,lead and mercury and other metal ions,which will affect the quality of the subsequent ammonium sulfur product,and will pose a serious threat to aquatic organisms and human beings if the dilute acid is directly discharged into water bodies.The traditional chemical precipitation method is used to treat this acidic wastewater,which has a high consumption of chemicals and cannot recover the resources in it,resulting in the waste of resources.Therefore,the resource utilization of waste acid from flue gas desulfurization is gradually attracting attention.Based on the physical and chemical characteristics of waste acid from flue gas desulfurization,a novel process combining diffusion dialysis and adsorption technology was proposed to study the treatment and resource utilization of waste acid.The research results are as follows:（1）The effects of acid-water flow rate ratio,acid mass fraction,acid flow rate and number of cycles on the recovery of acid from acidic wastewater and the separation performance of metal ions were investigated by diffusion dialysis tests.Under the optimal operating conditions,the acid mass fraction was 2%,the acid flow rate was 0.54 L/h,and the acid-water flow rate ratio was 1.0,the diffusion dialysis achieved 78%recovery of sulfuric acid and 92%retention of Fe（II）.Using a combination of 1%hydrochloric acid solution and deionized water chemical cleaning strategy,the recovery of sulfuric acid still reached more than 75%after 8 times of cleaning.Combined with Fick’s law regression mathematical model parameters,the model calculation results were compared with the actual measured values to verify the reliability of the mathematical model.（2）A novel pyridine-modified chitosan（PYCS）adsorbent was prepared by a multi-step process using 2-（chloromethyl）pyridine hydrochloride grafted with chitosan and cross-linked with glutaraldehyde.The prepared adsorbent was then used for the adsorption of metal ions from acidic wastewater.Batch adsorption experiments were conducted to investigate the effects of solution p H,contact time,temperature and Fe（III）concentration on the adsorption effect.The results showed that under the optimal experimental conditions（adsorption time=12 h,p H=2.5,T=303 K）,the adsorbent exhibited high capacity for Fe（III）with a maximum adsorption capacity of66.20 mg/g.The fitted second-order kinetic model and Sips model accurately described the adsorption kinetics and isotherm data.Thermodynamic studies confirmed that the adsorption is a spontaneous heat absorption process.In addition,the adsorption mechanism was investigated by Fourier transform infrared spectroscopy（FTIR）and X-ray photoelectron spectroscopy（XPS）.The results showed that the pyridine group formed stable chelates with Fe（III）.（3）Through the screening and optimization of the combined treatment process parameters,when the feed acid flow rate of diffusion osmosis is 0.54 L/h and the flow rate ratio is 1.0,the acid recovery rate can reach 80%,the concentration of H⁺in the recovered acid can reach 0.54 mol/L,and the heavy metal removal rate can reach96.3%.The operation cost of this process is 51.26 yuan/t,which realizes zero emission and reuse of waste acid.The recovered acid can be mixed with commercial acid for the subsequent ammonium sulfate production in the ammonium sulfide section,the Fe（II）in the residual solution can be configured with H₂O₂ to form Fenton reagent to treat coking wastewater,and the waste adsorbent is used for co-disposal of sintered raw materials.The research results show that the combined diffusion osmosis-adsorption process is feasible for treating coke oven flue gas desulfurization waste acid,with good economic,environmental and social benefits.