Research On Diffusion Dialysis-electrolysis Combined Treatment Of High Arsenic And Sulphuric Acid And Safety Evaluation

High arsenic content wastewater is the most common contaminated waste produced in the process of acid production from flue gas in metal mining and metallurgical industry.It has the characteristics of high arsenic,high acid,high heavy metals,great harm and difficult to treat.There are a lot of improper disposal of High arsenic content wastewater in China every year.Traditional sulphuric acid treatment processes,such as chemical neutralization and precipitation,have a series of problems such as waste of sulfuric acid resources,generation of low-quality waste slag,high disposal cost,etc.In this paper,a diffusion dialysis-electrolysis process is proposed to treat high arsenic waste acid to achieve the purpose of recovery of sulfuric acid resources and efficient purification of dirty acid.The feasibility of the process was demonstrated by experiments.The separation and interaction of As?III?and sulfuric acid in the process of diffusion dialysis recovery of sulfuric acid are investigated in detail.The effects of current density,electrode material,concentration of As?III?and cell structure on the arsenic removal efficiency in the process of electrolysis were also investigated.The electrolytic products and the possible mechanism of electrical arsenic removal and the existing role of iron are analyzed.Futhermore,the basic safety evaluation of the process in practical industrial application is carried out.The diffusion dialysis simulation experiment shows that the diffusion dialysis method has a higher separation effect on arsenic?III?and sulfuric acid.The diffusion dialysis of arsenic?III?is an independent process,and the dialysis coefficient U_As=1.98×10-4 m/h.The diffusion rate is only affected by the arsenic?III?concentration difference driving force,which is independent of the sulfuric acid concentration;The diffusion dialysis of sulfuric acid is affected by the combination of sulfuric acid concentration and arsenic?III?concentration,the influence of arsenic?III?concentration is quantitatively affected,and the degree of influence is related to the concentration of sulfuric acid itself.When the recovery rate of sulfuric acid reached the limit in 24 h of static diffusion dialysis,the leakage rate of arsenic?III?was less than 16.5%.It was deduced that the leakage rate of arsenic?III?was much lower than 16.5%after using dynamic diffusion dialysis to shorten the dialysis time in actual industry,and the process was feasible.The arsenic?III?dialysis coefficients and a series of sulfuric acid dialysis coefficients were calculated,which provided guidance parameters for practical industrial design.Electrolytic simulation experiments show that direct electrolysis has good arsenic removal effect,and the whole arsenic removal effect of mixed cell is better than that of two chamber.Within the current density range of 5-50 mA/cm²,the arsenic removal rate is proportional to the current density.High concentration of arsenic?III?can increase the rate of arsenic electrolysis to some extent,but it may be due to the current density limitation that the rate of iron anodization is not equal to the change of arsenic?III?concentration,resulting in a decrease in the overall removal rate.The removal efficiency of carbon steel and pure iron electrode materials is much better than that of 304 and 201 stainless steel electrodes,which is about 1.4 times.However,there are some problems such as too fast oxidation rate of iron anode and corrosion consumption of electrolytic materials.In practical industrial applications,the optimal relationship between current density,arsenic?III?concentration and electrode materials should be further explored.For example,the experimental results show that when the concentration of arsenic?III?is maintained above 200 mg/L and the current density is 50mA/cm2 and 304 stainless steel is used as the electrode material,the high efficiency of arsenic removal can be achieved while the excessive waste of current can be prevented,which is less than 200 mg/L.The current density can be reduced appropriately,and the arsenic removal rate can reach 100%under suitable conditions.The mechanism of electric arsenic removal may be that arsenic?III?is oxidized to arsenic?V?and the combination with iron is reduced at the cathode and then precipitated with arsenic.The arsenic element is oxidized in hydrogen peroxide and other oxides to form As₂O₃ crystals,which is difficult to be directly dissolved in dilute sulfuric acid environment.The iron plays an important role in promoting flocculation and crystallization.The electrolytic slag is As₂O₃ with high purity,which is conducive to subsequent resource recovery.The pre-hazard analysis method?PHA?is used to qualitatively analyze the hazard source of the process,and the operating condition risk analysis method?LEC?carries out the basic safety evaluation of the process hazard source,and on this basis,the corresponding safety decision and protection is proposed,which provide a scientific basis for the stable and safe operation of the diffusion dialysis-electrolysis method.