Study On Precipitation And Adsorption Of Arsenic And Selenium Pollutants From Desulfurization Wastewater Of Coal-Fired Power Plant

At present,more than 90% of China’s coal-fired power plants apply the triple box process to treat desulphurization wastewater.Although this technology can remove most heavy metals efficiently,the efficiency of arsenic and selenium removal is not high,and there is a lack of targeted treatment guidelines.At this stage,coal-fired thermal power generation in China accounts for more than 60%of the total,and the arsenic and selenium content in coal is higher than the world average.The severe situation of combustion-based arsenic and selenium pollution not only restricts the construction of zero-emission power plants but also makes it difficult to meet the ever-tightening heavy metal discharge standards for wastewater.Therefore,there is a strong need for further control studies on arsenic and selenium pollutants in desulphurization wastewater.In this paper,a modified lime and aluminum salt precipitation and adsorption method is proposed based on the triple box lime precipitation method for the study of arsenic and selenium pollutants in desulphurization wastewater.Using the property that soluble arsenic and selenium can form low solubility or insoluble compounds with certain ions,a calcium oxide-sodium meta-aluminate mixture precipitant is added to the wastewater.At the same time,calcium and aluminum salts can react in chlorinated wastewater to form layered double hydroxide precipitates with adsorption capacity.Based on this property,in order to investigate in-depth,the dual role of competitive precipitation and synergistic adsorption of mixed precipitants in the complex environment of desulphurization wastewater,as well as to reduce secondary pollution and achieve resource recovery,this paper used precipitation waste to prepare Ca-Al-Cl Friedel’s salt adsorbent and reused it for adsorption of Arsenic and selenium wastewater.The results of the precipitation experiments show that the lime aluminum salt has a good effect on arsenic and selenium removal,and the removal efficiency of a single solution reaches more than 80%.The controlled variable experiments showed that good precipitation results could be achieved when the reaction temperature was 35℃,calcium oxide and sodium met-aluminate feeding ratio=2:1 and pH was at alkaline conditions.The mixed heavy metal experiments showed that the doping of heavy metals affected the removal efficiency of arsenic and selenium,the effect of different heavy metals was different,and the removal efficiency was relatively high when pH=10-11 was controlled.The mixed MgCl2 experiments showed that the removal efficiency of arsenic and selenium decreased with the increase of MgCl2 concentration,and fairly good precipitation results could be achieved when arsenic:selenium:lead:MgCl2=1:1:1:2 and pH=11.The XRD and SEM-EDS characterization results and the adsorption experiments showed that the precipitated material obtained from the dechlorination of lime aluminum salts had the characteristics of Ca-Al-Cl Friedel’s salt and sound adsorption effects of arsenic and selenium.The adsorption process was monolayer chemisorption,and the adsorption kinetics and isotherms could be described by quasi-secondary kinetics and the Langmuir model,respectively.The mixed heavy metal adsorption experiments showed that Pb and Cu promoted the adsorption of arsenic and Cd,Zn and Ni hindered the adsorption.For selenium,all the heavy metals except lead have some promotion effect.As shown by the co-sorption experiments of eight heavy metals,the synthetic Ca-Al-Cl Friedel’s salt was still able to show good adsorption capacity in complex environments,with overall removal efficiencies above 80%.In this paper,the lime and aluminum salt precipitation and adsorption method is proposed based on the triplex box process,which achieves the efficient removal of arsenic and selenium and the secondary use of co-precipitation waste.The mechanisms and removal laws related to the synergistic competition of heavy metals in alkaline environments are investigated.It provides a theoretical basis for optimizing the treatment process of desulphurization wastewater from coal-fired power plants.It is of practical engineering guidance value to provide reference and assistance for realizing zero discharge treatment and waste resource utilization in coal-fired power plants.