Removal Of Arsenic From Copper Smelting Waste Acid By Nano Zero-valent Iron

Copper smelting waste acid has high acidity,high arsenic content and large output.The efficient treatment of arsenic is an important guarantee for the sustainable development of the copper smelting industry.Nanometer zero-valent iron(nZVI)can effectively remove heavy metal ions and other pollutants in sewage due to its unique oxidation,reduction,adsorption and co-precipitation capabilities,making it a new type of environmental remediation material.The application of nZVI technology to the removal of pollutants in the field of industrial wastewater has broad prospects.This article aims to explore a new method of arsenic removal of waste smelting acid,with copper smelting waste acid as the research object,and nZVI as the core agent.Using hydrometallurgical technology,combined with pre-neutralization,pre-oxidation,multi-component synergy,staged addition and other means,systematically study the arsenic morphology changes and removal process,and analyze the arsenic removal mechanism.Based on the existing forms of arsenic and iron in the aqueous solution and related thermodynamic data,the potential-p H diagram of the As-Fe-H₂O system is drawn.Studies have shown that As in solution can be precipitated as elemental arsenic and iron arsenate.Arsenic in aqueous solution can exist as oxyanions of As(V)and As(III).As(III)can be reduced to As(0)by Fe⁰ and the stable area is large.Under the oxidation condition of 1.04<p H<5.35,iron and arsenic can generate insoluble iron arsenate precipitation.Using nZVI to directly treat waste acid from copper smelting(As(III)).In the process of arsenic removal,the influence of reaction time and the amount of nZVI added on the arsenic removal rate and filter residue composition were mainly investigated.When nZVI was added according to the iron-arsenic molar ratio of 9:1and reacted for 150 min,nZVI had the best ability to remove arsenic,reaching 162 mg As/g Fe.When nZVI removes arsenic,it complexes and adsorbs As(III)to form a bidentate complex with strong binding.The Fe⁰ core reduces As(III)to As(0),and[H+]in waste acid consumes a large amount of nZVI.It is difficult for nZVI to directly treat arsenic in waste acid of copper smelting.It is difficult to meet the standard after treatment and consume a lot of nZVI.Subsequent experiments need to pre-neutralize the waste acid of copper smelting.Pre-neutralize and pre-oxidize copper smelting waste acid to obtain waste acid containing arsenic(V).Using nZVI and Ca O to explore the arsenic removal process and analyze the mechanism.Under optimal conditions,15%Ca O-nZVI can reduce the concentration of waste acid As from 16.21 g/L to about 500 mg/L.The arsenic removal process is mainly based on adsorption and co-precipitation,supplemented by reduction,and part of As(V)is reduced to As(III).Ca O provides more positive charge for nZVI and promotes the adsorption of arsenic ions.Pre-neutralize copper smelting waste acid to obtain waste acid containing arsenic(III).Using nZVI and H₂O₂ to explore the arsenic removal process and analyze the mechanism.When nZVI is added at a molar ratio of iron to arsenic of 2:1 and H₂O₂oxidation is performed,the arsenic removal efficiency reaches 99.89%,the filter residue arsenic content reaches 31%,and the filtrate arsenic concentration drops to about 10 mg/L.During arsenic removal,As(III)is oxidized to As(V),and Fe(0)is oxidized to Fe(II)and Fe(III).H₂O₂ can promote nZVI to produce more highly active iron oxides that can adsorb As,and promote the oxidation of As(III)to As(V),making As more easily adsorbed.Using nZVI to directly treat the low-concentration arsenic(V)wastewater generated in the previous experiment can make the low-concentration wastewater reach the standard discharge.When nZVI is added according to the iron-arsenic mass ratio of20:1,the residual As concentration of the filtrate can be reduced to less than 0.5 mg/L,which is in line with the national industrial wastewater comprehensive discharge standard(GB25467-2010).Properly increasing the concentration of hydrogen ions in arsenic-containing wastewater can promote the corrosion and activation of nZVI,and effectively improve the effect of arsenic removal.The process of arsenic adsorption by nZVI conforms to the pseudo-second-order reaction kinetic model,mainly based on chemical adsorption,and the adsorption isotherm conforms to the Langmuir isotherm adsorption model,which is monolayer adsorption,with a maximum adsorption capacity of 79.55 mg/g.