Study On The Mechanism Of Arsenic Fixation In Silica Gel

Arsenic pollution mainly comes from non-ferrous metal smelting and processing industry.Large quantities of solid,liquid and gaseous wastes containing arsenic are discharged during mining and smelting activities.Arsenic-containing wastewater treated by chemical precipitation and sulfurization method will leave a large amount of sludge,resulting in secondary pollution.The main components in the sludge are gypsum and calcium arsenate.About one million tons of sludge containing various metal elements are stored in safe places each year.If left untreated,this sludge can pollute the surrounding environmental resources.The solidification/stabilization treatment of solid waste containing arsenic with strong mobility is an important means to reduce arsenic pollution.Copper slag is a large amount of solid waste rich in iron and silicon,which is produced by copper pyrometallurgy industry.In view of this,this paper used pure Fe-Si gel and copper slag gel as raw materials to solidify arsenic-containing sludge and different arsenic-containing solid wastes.Through kinetics and various characterization,the arsenic fixation reaction behavior and rules of Fe SO₄composite SiO₂ based gel and copper slag gel were explored respectively,the reaction kinetics process was clarified,and the arsenic fixation mechanism of Fe-Si gel was revealed.In this paper,SiO₂ gel composite Fe SO₄ was first used to explore the arsenic fixation effect of pure materials,and on this basis,copper slag gel was used to explore the arsenic fixation effect of industrial waste residue.Both of them have the same main ion composition and can provide a large number of Fe and Si ions for solid arsenic.Fe SO₄and composite SiO₂ gels have good curing effect on arsenic-containing solid waste under neutral conditions.When Si/As=1:1,Si/Fe=1:4,reaction temperature of 60^oC,reaction time of 20 h,the optimal reaction conditions were reached.The toxic leaching of As in sludge was 4.98 mg/L,and the curing rate reached 99.4%.Copper slag gel has excellent properties of arsenic fixation under neutral conditions.When the p H value of copper slag gel is 7,Si/As=0.5:1,reaction temperature is 60^oC,reaction time is 20 h,the toxic leaching of As in sludge is 2.19 mg/L,curing rate reaches 99.7%.The gel solidified sludge of copper slag in the above two experimental parts is an upgrade treatment of SiO₂ gel composite Fe SO₄ solidified sludge,which alleviates part of the cost problem in industrial application.At the same time,the leaching toxicity of cured products of both of them all reached the standard.Finally,the solidification of arsenic containing solid waste by Fe SO₄ and SiO₂ gel and arsenic containing sludge by copper slag gel formed a core-shell structure with Ca SO₄,Ca₃（AsO₃）₂ and Fe AsO₄ as the cores and C-S-H gel,Fe₂SiO₄ gel,Fe（OH）₃ gel and Fe SO₄ flocculant as the shells under the combined action of physical encapsulation and chemical precipitation.Therefore,the use of SiO₂ gel or copper slag gel as a functional material to solidify arsenic containing solid waste can provide considerable environmental and economic benefits.