Research On The Harmless Treatment Of Arsenic-containing Acid In Copper Smelting By Magnetite

Waste acid is an important source of pollution in the heavy smelting industry.It has the characteristics of high arsenic content,strong toxicity and refractory treatment,and is the main source of arsenic-containing pollutants.Due to the lack of economic and efficient pollution-free or resource-based disposal technologies,the existing waste acid disposal has become a major environmental issue that limits the sustainable development of the heavy-colored smelting industry.Currently commonly used waste acid treatment technologies such as vulcanization,concentration and lime-iron salt methods,due to the problem of secondary pollution and post-maintenance costs caused by the large amount of arsenic-containing slag,the arsenic in the waste acid cannot be obtained effective processing.According to advantages of scorodite（FeAsO₄·2H₂O）in fixing arsenic,it is starting from“zero-risk waste”,“small slag amount”and“low cost”.At the same time,combined with the characteristics of the waste acid itself and the natural advantages of iron oxides in removing arsenic.In this study,we report a green process for the self-enhanced and efficient removal of arsenic from waste acid using magnetite as an in situ iron donator.Firstly,the effects of different iron oxides on the treatment of waste acid under different reaction time,pH value and iron to arsenic molar ratio were investigated by experiments,and the best in situ iron source provider was found.The experimental results show that three different iron ores（hematite,limonite,magnetite）can dissolve in the waste acid and release certain iron ions to synthesize scorodite crystals.However,due to the structure of different iron oxides,the difference in impurity elements and iron content,the resulting scorodite crystallinity and arsenic removal efficiency are different.Through the analysis of the experimental results,it is found that magnetite（Fe₃O₄）has advantages over hematite（Fe₂O₃）and limonite（FeO（OH））in the efficiency and stability of the treatment of waste acid to synthesize scorodite.Subsequently,magnetite was used as a solid iron source for removing arsenic from the waste acid.Under atmospheric pressure,the influence of magnetite on the treatment of waste acid under different pre-dissolution time,heating reaction time,pH value,iron to arsenic molar ratio and reaction temperature was revealed,and the reaction mechanism of synthetic scorodite was also explored.The results show that the room-temperature predissolution of magnetite in waste acid provides initial iron ions as a starting precipitator of arsenic,simultaneously providing a suitable pH range and an active surface that are ready for the nucleation and growth of scorodite.Afterwards,arsenic is precipitated in form the of scorodite,which is driven by a mutually improved cycle composed of arsenic precipitation and magnetite dissolution on the surface of magnetite particles.This cycle creates a low supersaturation of iron and constant pH in the waste acid,ensuring the continuous precipitation of arsenic as well-crystallized and environmentally stable scorodite by using magnetite as an in situ iron donator via the reaction of 2Fe₃O₄+6H₃AsO₄+H₂O₂=6FeAsO₄+10H₂O.Under optimal conditions,including a 6-hour room-temperature predissolution,a 12-hour atmospheric reaction at90°C and a pH of 2.0 with a magnetite dosage at the Fe₃O₄/As molar ratio（the molar ratio of Fe₃O₄ in magnetite to As in waste acid）of 1.33,99.90%of arsenic was successively removed from waste acid with an initial arsenic concentration of 10300mg/L.Finally,this study carried out different properties of waste acid research and prospective process exploration to prove that the process has good applicability.The experimental results show that iron oxide has great potential to remove arsenic ions from waste acid and can be applied on a large scale.