Synthesis Of Arsenic Sodium Alunite By Solid State Reaction And Its Stability

Arsenic waste water and arsenic residue are the main way of arsenic pollution, and which is the research focus in the field. At present, the arsenic solidification/stabilization method and resource utilization for arsenic waste are the main treatment method.The main treatment method for arsenic wastewater are chemical precipitation, physic-chemical method, biological oxidation and so on, which the chemical precipitation method is the widely used. By precipitation of each compound (calcium arsenate, scorodite, arsenatehydroxyapatite, alunite minerals) of the basic physical and chemical properties of comparative, the analysis showed that the arsenical natroalunite solid solutions can be an effective means of arsenic immobilization.On the basis ofhydrothermal synthesis of arsenical natroalunite solid solution, arsenical natroalunite solid solutions by solvent-free approaches to analysishave been investigated as a new method for arsenic solidification/stabilization in this paper. The factors of synthesis arsenic natroalunite solid solution by solvent-free are discussed, and used response surface methodology (RSM) to optimize to give optimum conditions. The main factors affecting the leaching arsenic concentration c(As) is analyzed and their stability under different conditions is discussed by toxicity characteristic leaching procedure (TCLP) test for arsenical natroalunite solid solution. It is the research achievements and conclusions as follows:(1) The influence of reaction time t and the reaction temperature T on the synthesis, structure and properties of As-free natroalunite are researched. It is showed that the preferred experimental conditions by XRD, SEM-EDS, FT-IR and TG-DSC and other analytical:the reaction temperature T for 200℃, the reaction time t for 2.5h, and it is only the synthesis of arsenic natroalunite solid solution crystal; The final pH value is similar to trends with the theoretical results, and complete crystal, good crystallinity, uniform grain size, the ratio of the constituent elements and the lattice parameters are closed to the theoretical value.(2) AsO43--for-SO42- substitution in natroalunite by solvent-free approaches to synthesishas been investigated. The influence of reaction time t and the reaction temperature Ton the synthesis, structure and properties of arsenic natroalunite solid solutionhave been researched. It is showed that the preferred experimental conditions by XRD, SEM-EDS, FT-IR and TG-DSC and other analytical:the reaction temperature T for 200℃, the reaction time t for 2.5h, the arsenic content ｎ(As/A1) for 0.35. Under the reaction conditions, the synthesis of arsenic natroalunite solid solution crystal is a cube and cube assembly, and complete crystal growth, good crystallinity, uniform grain size.(3)The theoretical formula arsenic natroalunite solid solution is NaAl3(SO4)2-χ(AsO4)χ(OH)6-χ. The x is up to 0.12 and the mass fraction of arsenic reached 2.42%when the reaction temperature T is 200℃, reaction time t 2.5h, arsenic content ｎ(As/Al) is 0.35.(4) The yields Y of arsenic natroalunite solid solution regression modelhas been obtained by using the Box-Behnken design and multivariate regression:Ｙ=-765.46 +7.26z1+6.66z2+128.72z3-0.00636z1z2-0.0166z1Z3+0.156z2Z3-0.0177z12-1.08z22-170.5 9z32, R2=0.9857. The optimal parameters are 200℃ for reaction temperature,2.7h for reaction time, and 0.35 for ｎ(As/Al). The result of verification experiment showed that the precipitation yield of arsenic natroalunite solid solution prepared under the optimal condition was 17.05%, which is consistent with the predicted value. So the optimal parameters obtained using response surface methodology (RSM) are reliable andhas practical value.(5) The arsenic leaching characteristics of arsenic natroalunite solid solution show that the arsenic concentration c(As)increased with the increase of leaching time t, the leaching time t is about 6 weeks in balance, and the balance of arsenic leaching concentration c(As) are the pHjnjtial=2>pHinitial=10>pHinitial=7; Arsenic concentration c(As) reached a maximum about l0mg/L for pHinitial=1; Arsenic concentration c(As) is less than 5mg/L for pHinitial≥2; The reaction time of solvent-freehas no effect on the leaching arsenic concentration c(As).(6) The analysis of arsenic leaching rate of arsenic natroalunite solid solution showed a lower arsenic leaching rate, overall less than 0.02%. Under the neutral conditions, arsenic leaching rate is the lowest, which indicates that arsenical natroalunite solid solution is the most stable in a neutral environment, and arsenic leaching rate reach stable about six weeks.(7) The crystalline phase, chemical composition and surface morphology of the solid samples before and after dissolution were analyzed by XRD and SEM, which the results showed the solid solutionhad no change.