Study On The Mechanism Of Potassium Ferrate In Treating High Arsenic Acid Wastewate

As the main arsenic pollution source in the non-ferrous metal smelting industry,high arsenic acid wastewater has the characteristics of high arsenic content,strong acidity and complex composition,which is harmful to the environment and human health.The traditional oxidation+iron salt method needs to oxidize As（Ⅲ）to As（Ⅴ）with less toxicity and solubility before treating acidic wastewater,so as to achieve the purpose of efficient arsenic removal by iron salt.In this study,potassium ferrate（K₂FeO₄）was used as both oxidant and iron donor to treat high arsenic acid wastewater to simplify the wastewater treatment process.In addition,the stronger solubility and oxidation of potassium ferrate under acidic conditions are beneficial to the maximum utilization of its performance.In this study,by changing the reaction temperature and pH value of the reaction system,potassium ferrate generates two different precipitates in acidic wastewater to achieve the harmlessness of wastewater and the stabilization of arsenic-containing slag.Based on the effect of oxidation on the removal of arsenic in wastewater,the experiment of arsenic removal by potassium ferrate oxidation at room temperature and pressure was carried out.When the solid-liquid ratio is 45 g/L,the initial pH value of wastewater is 1.5 and the reaction time is 8 h,the arsenic concentration in wastewater decreased from 5762.1 mg/L to 42.8 mg/L,and the pH value of wastewater increased to6.88.The analysis of arsenic-containing precipitate shows that ferrihydrite precipitate is generated by potassium ferrate in acidic wastewater.This multi-core hydroxyl iron oxide can provide a place for arsenic adsorption and chemical precipitation.In the whole reaction,As（Ⅲ）is oxidized to As（Ⅴ）while Fe（Ⅵ）is reduced to Fe（Ⅲ）.Fe（Ⅲ）is hydrolyzed to form ferrihydrite.As in the wastewater is coordinated with-OH on the surface of ferrihydrite.Exchange,As is adsorbed while releasing a large amount of-OH,resulting in a decrease in arsenic concentration in the wastewater and a decrease in wastewater acidity.In this study,the application of potassium ferrate oxidation,arsenic removal and neutralization was realized.Based on the arsenic removal experiment at room temperature,the TCLP of the precipitate at different reaction temperatures shows that high temperature conditions are conducive to the stability of the arsenic-containing precipitate.Based on thermodynamic analysis,the high temperature arsenic removal and arsenic fixation experiments of potassium ferrate showed that under the optimal reaction conditions of Fe/As molar ratio of 2.5,reaction pH of 2,reaction temperature of 85°C and reaction time of 10 h,the arsenic concentration in wastewater decreased from 8705.2 mg/L to112.6 mg/L.TCLP showed that the leaching arsenic concentration of the precipitate was 1.8 mg/L.Combined with the characterization analysis of arsenic-containing precipitates,the rapid dissolution of potassium ferrate in the wastewater provides an online iron source for the subsequent arsenic precipitation reaction.Iron arsenate and sulfate in the wastewater promote the crystal growth of scorodite.The formation of large particles of scorodite indicates that arsenic in the wastewater is effectively removed and fixed.For the low-arsenic wastewater after the treatment of high-arsenic wastewater,the concentration of As,Cu,Zn and Cd in the wastewater decreased to 0.36mg/L,0.23 mg/L,0.94 mg/L and 0.07 mg/L,respectively,after 90 min of reaction with0.2 g potassium ferrate,below the limit of’Integrated Wastewater Discharge Standard’.