| With the higher demand of environmental protection, more and more attention is being paid to the pollution brought by wastewater of sulphuric acid production. Effluent from sulphuric acid production is characterized by deep chromaticity color, high acidity and many harmful substances because the raw material of the plant is usually low in grade and its variety is complicated. If this type of wastewater is discharged into natural environment without being treated, it will make the water body and soil acidified, the ecological environment damaged and a great number of resources wasted. So the treatment of wastewater from sulphuric acid plants includes not only improving its appearance characteristics and removing its strong corrosivity but also removing the harmful substances such as arsenic and fluorine. Many treating methods such as adsorptive process, floatation process, ion-exchange technique and membrane separation technique etc. have promising future in the application of the sulphuric acid plant wastewater treatment. But there is still a long way to go to the practical operation. At present Lime-Ferric Salt Process (LFSP) is the common way to treat the sulphuric acid plant wastewater. It has many advantages such as a simple process, lower operating cost and less ground occupation when it is applied in the wastewater treatment of small or middling plants. It will also be used widely in the future, but more research is needed to improve related technology thus to fully make use of it.On the basis of forerunner's work, by taking the production wastewater from Jin Shan Dian Sulphuric Acid Plant in Hubei province as the research object, the research was done on the process conditions and treatment effects of Lime Neutralization and Precipitation Process (LNPP), Lime Neutralization-Air Oxidation Process (LNAP), Lime Neutralization-Ferric Salt Coprecipitation Process (LNFC), Lime Neutralization-Air Oxidation-Ferric Salt Coprecipitation Process (LNAFC), Lime Neutralization-Air Oxidation-Ferric Salt Coprecipitation-Crystal Seed Recycling (LNAFCC) and Ferrite Process (FP), which were used to treat the production wastewater from the said sulphuric acid plant. The main aim was to find out a simple but effective process and the correlative operating conditions. The experimental results showed that the arsenic concentration of the effluent was above 0.5mg/l when using the former three processes. And when using the latter three processes the effluent quality can meet the demand of the effluent-quality standard. The arsenic concentration of theeffluent was lower than 0.5mg/l and the arsenic removal efficiency was above 99%, and the turbidity of the effluent was lower than 6 degree. By comparing these processes and combining with the intrinsic treating establishments of the said plant, the Lime Neutralization-Air Oxidation-Ferric Salt Coprecipitation-Crystal Seed Recycling Process (LNAFCC) is proposed to treat its wastewater.As stated above, when air oxidation and ferric salt were applied in experiments, the arsenic removal efficiency was improved and pH played an important role, the reasons of which were further analyzed. According to the theory of ionization equilibrium, solubility product theory and the experimental results, it was helpful to the arsenic removal that As(III) in the wastewater was oxidized to As( V) because arsenate with lower solubility can be formed through air oxidation. It was demonstrated by theoretical analysis that under low pH condition AsO43" reacted with Fe3+ and formed FeAsO4, whose solubility is very low. When lime milk was mixed with wastewater, coarser Fe(OH)3 granules can be formed and the flocculation was accelerated, thus the removal efficiencies of arsenic and other heavy metal ions were improved. The regulation that the Ca3(AsO4)2 solubility (expressed by the total concentration of arsenic in the solution) changed with the pH of solution was established. It was concluded that the concentration of total arsenic fell with the increase of the pH. But it rose when the p... |
PDF Full Text Request