Research On Copper Slag Disposal Of Arsenic-containing Polluted Acid And Arsenic-fixing Process

Arsenic-containing wastewater,one of the most hazardous arsenic-bearing waste with complex composition,high acidity and strong toxicity,was formed the washing and purification of flue gas before making sulfuric acid in the process of nonferrous smelting.The disposal methods of wastewater affect the sustainable development of nonferrous metallurgical enterprises.Although the traditional disposal methods of wastewater via neutralization and sulfidization are simple operation and high-efficiency arsenic removal,they have many shortcomings such as high maintenance cost,a large amount of arsenic-containing hazardous waste and secondary pollution.Copper slag,a by-product from the copper smelting plant with rich iron source,is likely to serve as arsenic removal regent.In order to harmless,recycling and reduce arsenic-containing wastewater,copper slag as solid iron source and neutralizer for the arsenic removal and immobilization from wastewater were investigated through thermodynamic and kinetic analysis,which explore the copper slag dissolution-arsenic immobilization in situ encapsulation,and the reaction behavior of copper slag with wastewater for scorodite synthesis and the rule of arsenic removal to elucidate the reaction kinetics and arsenic removal mechanism.Copper slag is mainly composed of fayalite（Fe₂Si O₄）and magnetite（Fe₃O₄）,and a small amount of alkaline oxide,which exhibits a superior performance for the arsenic removal.The p H value of copper slag leaching solution is 9.11,which is alkaline.In order to obtain the thermodynamic date from the reaction between copper slag and wastewater,the thermodynamic analysis of Si-Fe-S-H₂O,Fe-H₂O and As-Fe-S-H₂O systems were studied.The results show that Fe₂Si O₄ could be easily dissolved in sulfuric acid to form stable H₄Si O,Fe SO₄,and Fe₂（SO₄）₃ complexes phases.Fe₃O₄ is mainly from Fe³⁺and Fe²⁺in the acidic system and Fe（OH）₃ and Fe（OH）₂ phases in the alkaline system.Arsenic exists in ionic state in sulfuric acid and its existence phases show a high affinity toward the p H value of the solution in the As-Fe-S-H₂O system,while Fe and S are from Fe SO₄ and Fe₂（SO₄）₃complexes phases.The copper slag dissolution-arsenic immobilization in situ encapsulation was described by a pseudo-second-order kinetic equation.The process of arsenic removal was limited by the release rate of iron ion.Arsenic was removed via the ion exchange adsorption and the chemical precipitation,which were also beneficial to the arsenic stabilization.A large number of iron ions were released from copper slag and reacted with arsenate ion in the form of amorphous arsenate ferric.The dissolved Si ion hydrolyzed and formed silicide,warping on the surface of ferric arsenate and generating the ferric arsenate@silica gel core-shell precipitate.Under optimal conditions,including a solid-liquid ratio of 1:8 g/ml,a reaction temperature at 23℃,a reaction time of 48 hours,an initial p H value of 0.77,and a copper slag particle size of 200～300 mesh,a maximum adsorption capacity of copper slag of 81.06mg/g was achieved,following by an arsenic removal efficiency of 98.85%.The leaching toxicity of arsenic-fixed copper slag was 3.45 mg/L,which is lower than the standard threshold value of hazardous waste.In addition,the feasibility analysis of the disposal of wastewater using copper slag was studied and a prospective disposal method was proposed.When the Fe/As molar ratio was 2,the reaction temperature was 80℃,and the reaction time was 12 hours,the arsenic removal rate was 97.86%and the arsenic leaching concentration of arsenic-bearing precipitate was 3 mg/L,which was lower than the standard for safe storage.Firstly,copper slag and wastewater neutralized and created a suitable p H surroundings for scorodite syntheses,and then iron ions reacted with arsenate ion in the form of the stable scorodite.The results of XRD、SEM and TEM show that Fe SO₄/Fe₂（SO₄）₃ and H₄Si O₄ were superior to the formation of scorodite and provide abundant nuclear sites for arsenic precipitate.The copper slag exhibits a superior performance for the arsenic removal from waste acid and provides a high-efficient method for the disposal of waste acid from heavy nonferrous smelting industry.