| Arsenic and arsenic compounds had a greater toxicity and both had a carcinogeniceffect.The majority of arsenic were associated with non-ferrous metals in nature, state of thearsenic sulfide or salt got into the flue gas, waste water and sludge in the process ofnon-ferrous metal extraction, among them, most of the arsenic were stockpiling in the way ofarsenic-containing waste which had led to the most important arsenic-containing waste inChina. More research of the disposal of sludge, fly ash sintering technology in our nation, butrelative lack of the research of arsenic residue sintering. An experimental work was carriedout to investigate the effect of environmental release behavior of arsenic during sintering ofarsenic-containing waste with different additional contents like SiO2, Al2O3, MgO and CaO,and provide reference for arsenic-containing waste in high temperature processing. The rawmaterials were certain amount of arsenic-containing waste added with the mass fraction of30%SiO2, Al2O3, MgO, CaO, mixed the raw materials by flip vibration instrument, shapedunder the pressure of10MPa and exposed at4001100℃for1h, made the sinteredproducts after cooling, studied the arsenic solidified characteristics and leachingcharacteristics, analysied mineral occurrence form and microstructures in high temperaturesintered products by XRD and SEM, discussed the effect of arsenic solidified characteristics,leaching characteristics, mineral occurrence form and microstructures in sintered products byadditional contents. Results showed that:The arsenic leaching mass concentration decreased greatly in arsenic-containing wasteafter three methods of leaching tests at1300℃. Compared the microstructures of the originalsample and sintered products at1300℃found that particle became more densification insintered products and created the crystalline arsenate calcium. The arsenic was fixed in thestable crystalline arsenate calcium, which decreased the arsenic leaching characteristics.The fixed effects of arsenic by SiO2was not obvious. SiO2had the most inhibitory effectof arsenic leaching at1300℃, maybe because the melt inclusions phenomenon in thesintering body would occur and grew to the silicate crystals which had the grid structure, soarsenic was wrapped in the glassy silicate lattice which led to the lower arsenic leaching ratesignificantly.The inhibitory effect of arsenic solidified and leaching characteristics by Al2O3was not obvious.CaO had great inhibitory effect of arsenic solidified and leaching characteristics insintered products. The maximum arsenic curing rate was95.14%at1000℃, CaO had thestrongest inhibitory effect of arsenic evaporation characteristics. The possible reason was thatarsenic was wrapped in the crystalline arsenate calcium which enhanced the curing rate ofarsenic greatly.By horizontal vibration method, sulphuric acid&nitric acid method and TCLP method,the arsenic leaching mass concentration in sintered products added with CaO was far less thanthe original sample in400to1000℃, arsenic leaching mass concentration reached aminimum of1.33μg/L,0.13mg/L and0.85μg/L at1000℃, which indicated that CaOhad the strongest inhibitory effect of arsenic leaching characteristics.The arsenic leaching mass concentration had the significant growth above1100℃,thermodynamics analysis was: the gibbs free energy of the reaction by As2O3generated toAs2O5was greater than0, therefore the reaction can`t occur spontaneously which led to thereaction by As2O3â†'As2O5â†'Ca3（AsO4）2can`t complete. Thus, arsenic can`t be stable curingwhich led to a significant increase in the amount of arsenic leaching.X-ray diffraction patterns found that, the diffraction peaks of the calcium arsenate insintered products added with CaO appeared at1000℃, which indicated that arsenic was curedin a stable calcium arsenate so CaO had the strongest ability to inhibit the arsenicvolatilization and leaching.The scanning electron microscope image showed that there was no significant differencein morphology between the original sample added with CaO and sintered products at1100℃.MgO had a certain inhibitory effect to arsenic volatilization. MgO had greater inhibitoryeffect to arsenic leaching in400to1000℃. X-ray diffraction patterns illustrated that, arsenicwas existed in the form of calcium arsenate and magnesium arsenate at1100℃, calciumarsenate and magnesium arsenate were stable minerals which had small solubility. In this case,arsenic was cured in a stable crystalline phase which reduced the arsenic volatilization andleaching. The inhibitory effect of arsenic leaching characteristics by MgO was not obvious at1300℃.At last, this paper studied performance of arsenic-containing waste sintered productsadded with CaO in different added amount. CaO as an arsenic-containing waste additive,when the mass fraction was8%to10%, the sintered products had the potential for the use as alightweight aggregate building materials. |
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