Investigation Of Separation Mechanism And Resource Reutilization Of Arsenic And Chloride And Fluorine Through Vacuum Evaporation Process

The highly acidic watstewater from metal smelting,flue gas washing and dust removing,and flue gas sulfuric acid production,and other sections is called Dirty Acid Wastewater?DAW?,which has a large amount of As,F,and Cl as well as other valuble elements such as Cu,Zu,Pb,and Cd.Traditional remediation methods apply the calcium salt,sulfide precipitation,and iron salt coagulation to dislodge As and other heavy metals in DAW.However,there were abundant toxic waste residue was produced at the same time.Those residues can be hardly stabilized and solidified so that leading environment threats in the long term.Meanwhile,the wastewater after the precipitation treatment was highly hard,and the recycling and reutilization of valuable heavy metals was difficult.In this paper the problems of DAW disposing were investigated.F,Cl was seprated through vaccum evaporation.Meanwhile,Cu,Zn.Pb,and Cd were precipitated by added sulfur.In the end,As was eventually recycled by means of oxidation crystallization.The evaporated F was recovered via MgCl2 so that Cl was left over.All these techquniques mention above made a green,resource reutilization.DAW was pre-oxidated by H₂O₂,which restrained the generation of AsH₃.The oxidants efficiencies of H₂O₂,NaClO,and KMnO₄ were explored through dosage,temperature,and reaction time on As???oxidation.The optimal experimental conditions were below:the molar ratio of H₂O₂ and As???was 1.5:1,oxidation temperature was 30?,and oxidation duration was 2.5 h.After the As???oxidation treatment,optimal experimental conditions of concentration multiples of 8,pH of 1,reaction temperature of 75?,rotary evaporation meter pressure of-0.1 MPa,and rotary evaporation meter rotate speed of 20 r·min^-11 were obrained from orthogonal and single factor experiments.Under the above experimental conditions,the removal rates of F and Cl were 93.49%,90.35%,respectively.As escaping rate was 0.01%(immediated the concentration of As in condensate was 0.01 mg·L^-1).The DAW was disposed by vacuum evaporation,53.71%of As was crystallized as As2O5 with a purity of 81.24%.The rest 46.28%uncrysallized As was retained in concentration liquid.The vacuum evaporation process could incarnate with quasi-primary reaction dynamics.The concentration of As,F,and other elements varies a lot during the industy production process so that study the F,Cl recovery efficiency under different initial concentration of As,F,Cl are important and critical.Results indicated that As and F can be successfully separated when As concentration ranged from 5 to 14 g·L^-1 and F concentration ranged from 2 to 14g·L^-1.Recycling heavy metals?Cu,Zn,Pb,Cd?step by step via sulfidization.The purity of CuS,ZnS,PbS,CdS were 95.65%,97.62%,96.73%and 97.14%,respectively.There were optimal experimental conditions of the gradual precipitation by vulcanization method:?a?Cu recovery rates was 98.58%when vulcanization conditions were pH 2.5,the molar ratio of Na₂S and Cu was 1.2:1,reaction temperature was 30?,sensor reaction time was 45 min.?b?Pb recovery rates was 99.54%when vulcanization conditions were pH 3,the molar ratio of Na₂S and Pb was 1.2:1,reaction temperature was 30?,sensor reaction time was 45 min.?c?Cd recovery rates was 98.96%when vulcanization conditions were pH 4,the molar ratio of Na₂S and Cd was 1.1:1,reaction temperature was 30?,sensor reaction time was 45 min.?d?Zn recovery rates was 99.25%when vulcanization conditions were pH 5.5,the molar ratio of Na₂S and Zn was 1.1:1,reaction temperature was 30?,sensor reaction time was 45 min.Post-vulcanization leachate could receive Na₃AsO₄·12H₂O with a purity of 87.94%via oxidating alkaline leaching crystallization.The Na⁺concentration in the control system was above 80 g·L^-1,and the optimal experimental conditions were below:the molar ratio of H₂O₂and As???was 1:1,oxidation and crystal temperature was 30?,stirring speed was 400r·min^-1,and reaction time was 2 hrs.After,As concentration was 0.19 mg·L^-1 in the oxidilized crystalline leaching Solution,which could be reused in the acid making system.F recovery rate was 95.11% through the MgCl₂ grade?F recovery experiment and a product of MgF₂ was achieved with a purity of 99.0%.The optimal experimental conditions were below:the molar ratio of Mg and F was 0.5:1,reaction temperature was 85?,pH 3.5,reaction time was 4 h.Through the above experimental operation,Mg concentration was46.54 mg·L^-1 in dilute acid,which contained Cl and could be recycled and reutilized.After processing at this stage,the DAW was achieved the recycling and utilization of resources.Material balance diagram showed that technology of resource recycling from DAW based vacuum evaporation was perfectly feasible.It achieved the recovery of As,F,Cl,heavy metals,dilute sulphuric acid,and dilute hydrochloric acid.Through the dispose of vacuum evaporation,DAW didn't produce the arsenic residue,which avoided the negative impacts on the environment.The heavy metal sulphides had high content with heavy metals.It was not susceptible to the concentration variations of As,F and other contents in DAW,which had the potential of large-scale industrialization and practical application capabilities.