Research On The Removal Of Arsenic From Arsenic-containing Waste Acid By Iron-based Materials And Its Mechanis

Arsenic-containing wastewater is an important pollution source in the nonferrous smelting industry,which has the characteristics of complex composition,high acidity and strong toxicity.The traditional lime iron salt method and sulfide method have simple operation technology,but the As-bearing precipitation produced has high toxic leaching,poor stability and large amount of slag,which seriously threaten human life safety and pollute the ecological environment.Therefore,the development of more stable,safe and reliable arsenic fixation materials and methods for arsenic-containing wastewater has been a hot topic of research in this field.In this study,iron oxides,natural iron-containing minerals,steel slag and iron-based molecular sieve adsorbents were used as arsenic fixation materials for arsenic-containing sewage acids,and the interaction mechanism between arsenic removal materials and arsenic and the purification mechanism of different iron sources were investigated through multi-factor coupling experiments.The main research contents and results are as follows:（1）Using Fe₃O₄and Fe₂O₃as solid iron sources,the effects of Fe₃O₄and Fe₂O₃on arsenic removal under different pre-dissolution,reaction temperature,initial p H,Fe/As molar ratio and reaction time were studied.The physical and chemical characterization of the obtained arsenic-containing precipitates were analyzed to reveal the mechanism of arsenic removal and curing of Fe₃O₄and Fe₂O₃.The pre-solubilization of Fe₃O₄and Fe₂O₃provides sufficient initial iron source for arsenic deposition reaction,and neutralizes the H⁺ions in the solution to create a stable p H environment for iron arsenate synthesis.In the process of arsenic deposition reaction,Fe ions in the solution combine with As ions to form amorphous ferric arsenate and generate additional H⁺ions.The newly formed H⁺ions promote the dissolution of Fe₃O₄and Fe₂O₃,forming a driving process of dissolution and reaction to form ferric arsenate.Under the optimal conditions,Fe₃O₄reacts with wastewater to form a large scorodite particles with good crystallinity,and the concentration of As ions in the solution decreases from the initial 8276.1 to 80.8mg/L.The leaching concentration of arsenic precipitated with arsenic is lower than the standard of solid waste storage.However,after the reaction of Fe₂O₃with wastewater,the residual arsenic ion concentration in the solution decreased from the initial 8276.1 to 584.6mg/L,and the arsenic leaching concentration of arsenic precipitated was higher than the specified storage standards.The arsenic removal effect of Fe₃O₄is better than that of Fe₂O₃.The arsenic containing precipitate obtained after Fe₃O₄reacts with wastewater is more stable and has great utilization value.（2）Using magnetite as solid iron sources,the effects of magnetite on the release of iron ions and the balance regulation of solution acid-hydrolysis under different process conditions were studied,and the changes of the concentration of iron and arsenic ions in solution,the p H of solution and the microstructure of magnetite during the process of magnetite dissolution and arsenic deposition were explored.The arsenic deposition rule of magnetite revealed the dissolution mechanism of natural magnetite.Pre-dissolution of magnetite is conducive to adsorption of arsenic ions before heating reaction and to provide a large amount of Fe ions for arsenic deposition reaction.At the same time,the neutralization reaction between magnetite and polluted acid creates a suitable p H environment for the synthesis of osmolyte.When the Fe/As molar ratio is 2.5,the pre-solubilization time is 5h,the reaction time is 24h,and the reaction temperature is 90℃,the residual As ion concentration in the wastewater rapidly decreases from the initial 6259mg/L to 3.76mg/L,the corresponding arsenic removal is99.94%,and the obtained leach concentration is only 0.4mg/L,which was lower than 5mg/L stipulated in the Identification Standard of Hazardous Waste GB5085.3-2007（3）Using pyrite as solid iron sources,the influence mechanism of arsenic removal process on the physical and chemical properties,arsenic valence morphology and arsenic phase structure of arsenic precipitation is studied.Pyrite dissolves in wastewater and releases S（-II）ions and Fe（II）ions,and S（-II）ions react with As（III）ions to form As₂S₃sediment.Subsequently,S（-II）ions are oxidized to H₂SO₄by H₂O₂,which promotes the dissolution of pyrite and releases more S（-II）ions and Fe（II）ions.At the same time,Fe（II）and As（III）ions are gradually oxidized to Fe（III）and As（V）ions by H₂O₂,and Fe（III）and As（V）ions form amorphous ferric arsenate on the surface of pyrite,and then evolve into regular octahedral scallion particles.Under the optimal conditions,99.4%of arsenic ions in the wastewater（initial arsenic ion concentration was 11200mg/L）were successfully removed,and the leaching arsenic concentration of the obtained arsenic containing precipitation was about1.78mg/L,which was lower than the national discharge standard for solid waste.（4）Using steel slag as the iron source,the behavior and mechanism of arsenic removal from polluted acid with high arsenic content were analyzed.The results showed that under the condition of initial arsenic concentration of 1834mg/L and sulfuric acid concentration of2800mg/L,arsenic removal rate was 91.37%and arsenic adsorption capacity was 32.37mg/g after steel slag and potassium permanganate treatment of polluted acid.The reaction of steel slag with dirty acid releases Fe and Ca ions and increases the p H of the solution.As（III）and Fe（II）ions in solution are oxidized to As（V）and Fe（III）ions in the presence of potassium permanganate,and the oxidized As（V）ions react with Fe（III）ions to form an amorphous flocculation of Fe As O₄and Fe（OH）₃,thus removing the arsenic ions.In the reaction process,H⁺ions and Mn O₂are produced,which further promote the dissolution of copper slag and the oxidation of As（III）and Fe（II）,effectively ensuring the continuous precipitation and adsorption of As ions in the solution.By adjusting the p H value of the solution,the residual Fe,Ca and Si ions in the solution were further hydrolyzed to form a new Fe（OH）₃flocculation and Ca₂Si O₄gel,which further removed the residual arsenic ions.（5）Study on the deep purification of arsenic containing wastewater with new ZSM-5/Fe adsorbent.The results show that the adsorption mechanism of As ions by ZSM-5/Fe adsorbent is heterogeneous nucleation adsorption,including electrostatic adsorption and Fe-AS-O complex adsorption,and the effective adsorption from weak acid to weak base is achieved.Under the conditions of p H value of 4-10,dosage of ZSM-5/Fe adsorbent of 0.5g and reaction time of 2h,the concentration of arsenic ion in the solution was reduced from 100mg/L to0.006mg/L,the adsorption capacity of arsenic was 40mg/g,and the adsorption rate was as high as 99.99%.The co-existing anions Cl^-,NO^3-and SO₄^2-had little effect on arsenic ion removal.CO₃^2-had little effect on the adsorption of As,while PO₄^3-inhibited the adsorption of As ions.Zsm-5/Fe adsorbent showed superior arsenic removal effect in the process of industrial arsenic-containing wastewater treatment.