【作者】 孙立；

【导师】 吴新；

【作者基本信息】 东南大学 ， 动力工程及工程热物理， 2017， 硕士

【摘要】 与其他生活垃圾处理技术相比,焚烧法占地面积小,消毒彻底,减容效果显著,还能回收一部分热能,因此在我国发展迅速。但焚烧产生的垃圾焚烧飞灰富含大量有毒重金属,被列为危险废弃物,必须经有效处理后方可填埋。水泥固化、化学药剂稳定化及热处理是目前垃圾焚烧飞灰处理的主要方式。水泥固化技术工艺成熟、操作方便、成本低,但飞灰增容增重比大,加之飞灰中的盐分高,固化体易破裂;化学药剂稳定化技术稳定化程度高、增容增重小,但多种重金属的同步固化实现困难,药剂生产成本高;热处理技术重金属浸出浓度低,处理后的飞灰化学性能和机械性能好,但高温热处理消耗大。寻找一种重金属稳固化效果好、成本低、能耗少、可实现飞灰的资源化利用的方法是目前亟需解决的问题。本文提出一种使用少量硅灰或硅胶等无定形纳米级SiO2材料进行中温热处理稳固垃圾飞灰重金属的方法,并与NaH2PO4处理法和硅灰/硅胶养护法进行对比,采用国标醋酸溶液缓冲法和欧盟去离子水法两种浸出标准,对三种处理后的飞灰固化体进行浸出实验,研究相关工艺参数对重金属浸出浓度的影响规律,通过BCR连续浸提实验考察反应前后重金属形态的变化,并结合XRD、SEM、BET等测试手段观察反应前后飞灰物相、微观形貌、孔隙分布的变化,分析重金属的稳固化机理。本文得到的主要结论如下:NaH2PO4处理垃圾飞灰可有效降低浸出液中Pb的浓度。随着NaH2PO4的添加量的增加,国标和欧标浸出液中重金属的浓度均呈下降趋势。当NaH2P04添加量达到4%后,重金属浓度下降趋势变缓。反应温度越高,国标和欧标浸出液中重金属浓度越高,当反应温度为20℃时,重金属稳固化效果最好。固化时间越长,国标和欧标浸出液中重金属浓度越低,对于NaH2P04处理后的飞灰而言,3天的固化时间已经足够。随着初始液固比的升高,国标法浸出液中Pb、Cd、Cu、Zn浓度大致呈下降趋势,而在欧标法浸出液中其浓度趋势相反。XRD分析结果显示,NaH2PO4与CaClOH等物质反应生成Ca5(PO4)3Cl和Ca5(P04)30H等物质,转变了重金属的化学形态,将重金属稳固在磷酸盐晶格中,降低了飞灰的浸出毒性。硅灰和硅胶处理垃圾飞灰,若采用空气养护,欧标法浸出液中Pb、Cd、Zn、Cu的浓度稍有下降;若采用蒸汽养护,欧标法浸出液中重金属的浓度均显著降低。当硅灰添加量为10%或JN-40硅胶添加量25%,蒸汽养护30天时,欧标法浸出液中Pb的浓度下降到0.04 mg/L和0.05 mg/L,Cd的浓度可下降到0.049 mg/L和0.045 mg/L,Cr的浓度可下降到0.58 mg/L和0.48 mg/L,Cu的浓度可下降到0.03 mg/L和0.01 mg/L,Zn的浓度可下降到0.04 mg/L和0.05 mg/L,选择合适的参数适当调节Cr的浸出浓度,硅灰/硅胶蒸汽养护样可满足欧盟填埋场标准。XRD分析结果显示,在蒸汽养护条件下,硅灰和硅胶与飞灰中的含钙物质和重金属物质反应生成CSH胶体或硅酸盐如CaSiO3、PbSiO3等;此外,飞灰中的碱性物质CaClOH与重金属物质、空气中的CO2反应生成CaCO3、Cu2(OH)2CO3、ZnCO3、Zn(OH)2等物质。在高pH值如欧盟去离子水浸出标准下,CSH胶体、硅酸盐、重金属碱类和碳酸盐比较稳定,可有效抑制重金属的浸出;而在低pH值如国标醋酸法浸出标准下,CSH胶体遭酸蚀破坏,重金属碱类和碳酸盐完全溶解,导致重金属稳固效果不佳。硅灰和硅胶中温热处理飞灰过程中,硅灰和硅胶与飞灰中的钙基物质反应生成CaSiO3、Ca2SiO4、Ca3SiO4Cl2、Ca3Fe2(SiO4)3以及氢氧硅磷灰石等硅酸盐相,转变了重金属的化学形态,将重金属稳固在硅酸盐晶格中,降低了飞灰的浸出毒性;在硅灰添加量为10%或JN-40硅胶添加量25%,热处理温度600℃条件下,热处理1h后,飞灰国标法浸出液中Pb的浓度由11.91 mg/L分别降至0.79 mg/L和0.78 mg/L,Cd的浓度由3.18 mg/L分别降至0.09 mg/L和0.10 mg/L,Zn的浓度由9.48 mg/L分别降至0.28 mg/L 和 0.74 mg/L,Cu 的浓度由 7.45 mg/L 分别降至 0.65 mg/L 和 0.69 mg/L;热处理过程中Cr的浓度有所上升但未超出我国生活垃圾填埋场控制标准。本方法热处理温度为600℃,低于熔融、烧结处理温度,可抑制重金属挥发。热处理过程可在流化床中进行,引入焚烧炉烟气直接加热飞灰,产生的气体进入焚烧炉的尾气处理系统,节约能源,不需要额外增加设备。更多还原

【Abstract】 Compared with other waste disposal technologies,incineration has the advantage of occupied area,volume reduction,detoxification and energy recovery.Therefore,it is developing rapidly in China.However,municipal solid waste incineration fly ash(MSWIFA),which is classified as hazardous waste due to the accumulated soluble heavy metals,will be generated after incineration.Therefore,MSWIFA must be treated effectively before landfill.At present,the main ways of fly ash treatment are cement solidification,chemical stabilization and heat treatment.Cement solidification is mature,easy to operate and cost low,but the weight and volume gain is high.In addition,the generated cement is easy to rupture due to the high salt content in MSWIFA.Chemical stabilization has a nice effect of heavy metal stabilization and a little weight and volume gain,but it is difficult to stabilize a variety of heavy metals simultaneously and the production cost of chemicals is high.After the heat treatment,the leaching toxicity of fly ash is low and the treated fly ash has a nice chemical and mechanical properties.However,heat treatment consumes a lot of energy due to the high temperature.At present,the main problem is to find out a way which has a nice effect of heavy metal stabilization,small cost,low energy consumption and can reuse the MSWIFA.In this study,a new method for stabilizing heavy metals from fly ash was proposed by heat treatment with a small amount of amorphous nano-SiO2 materials such as silica fume or silica gel.The new method was compared with conventional NaH2PO4 treatment and silica fume/silica gel curing treatment,which is a popular research topic recently.The effects of the relevant process parameters on the leaching of heavy metals were studied by leaching experiments on the three kinds of treated fly ash with two kinds of leaching standards,such as standard HJ/T 300-2007 and CEN EN 12457-2.The changes of chemical speciation of heavy metals,crystal structure,microstructure and pore distribution during treatment were observed by BCR continuous extraction experiment,XRD,SEM and BET to analyze the mechanism of the stabilization of heavy metals.The main conclusions of this paper are as follows:NaH2PO4 treatment could effectively reduce the concentration of Pb in leaching solution.With the increase of the amount of NaH2PO4,the concentration of heavy metals in Chinese and EU standard leaching solution was decreased.When the addition amount of NaH2PO4 reached 4%,the decrease trend was slowed down.The higher the reaction temperature,the higher leaching concentration of heavy metals in Chinese and EU standard leaching solution.The best temperature for heavy metals stabilization was 20 ℃.With the increase of curing time,the concentration of heavy metals in Chinese and EU standard leaching solution decreased.For NaH2PO4 treated fly ash,the 3-day curing time was sufficient.With the increase of the initial liquid-solid ratio,under the HJ/T 300-2007 standard,the leaching concentration of Pb,Cd,Cu and Zn decreased,while the European standard is the opposite.The XRD results showed that NaH2PO4 reacted with CaClOH to form Ca5(PO4)3Cl and Ca5(PO4)3OH,changing the chemical speciation of heavy metals and stabilizing heavy metals in the phosphate lattice,which reduced the leaching toxicity.Silica fume or colloidal silica treatment could slightly reduce the leaching concentration of Pb,Cd,Cu and Zn in EU standard leaching solution if natural curing conditions are used.Silica fume or colloidal silica treatment could significantly reduce the leaching concentration of heavy metals in EU standard leaching solution if steam curing conditions are used.Under the conditions of adding 10%silica fume or 25%JN-40 colloidal silica and steam curing for 30d,the concentration of Pb in EU standard leaching solution could be reduced to 0.04 mg/L or 0.05 mg/L,the concentration of Cd could be reduced to 0.049 mg/L or 0.045 mg/L,the concentration of Cr could be reduced to 0.58 mg/L or 0.48 mg/L,the concentration of Cu could be reduced to 0.03 mg/L or 0.01 mg/L,the concentration of Zn could be reduced to 0.04 mg/L and 0.05 mg/L.If appropriate parameters were selected to properly adjust the leaching concentration of Cr,silica fume/colloidal silica steam samples could meet the EU landfill standards.XRD analysis showed that colloidal silica and silica fume could react with calcium and heavy metals in fly ash to produce CSH colloids or silicates such as CaSiO3 and PbSiO3 under steam curing conditions.In addition,alkaline substances CaClOH in fly ash could react with heavy metals and CO2 to form CaCO3,Cu2(OH)2CO3,ZnCO3,Zn(OH)2 and other substances.Under the high pH condition,such as EU standard,CSH colloids,silicates,heavy metal bases and carbonates were relatively stable,which could effectively inhibit the leaching of heavy metals.Under the low pH condition,such as HJ/T300-2007 standard,CSH colloid was destroyed by acid corrosion,heavy metal bases and carbonates completely dissolved,resulting the poor stabilization effects.During the medium heat treatment,silica fume and colloidal silica could react with calcium-based materials in fly ash to form silicate phases such as CaSiO3、Ca2SiO4、Ca3SiO4Cl2、Ca3Fe2(SiO4)3 and hydroxyl-ellestadite during the heat treatment,changing the chemical speciation of heavy metals and stabilizing heavy metals in the silicate lattice,which reduced the leaching toxicity.Under the conditions of adding 10%silica fume or 25%JN-40 colloidal silica and heat treatment at 600℃ for 1h,the concentration of Pb in Chinese standard leaching solution decreased from 11.91 mg/L to 0.79 mg/L and 0.78 mg/L,the concentration of Cd decreased from 3.18 mg/L to 0.09 mg/L and 0.10 mg/L,the concentration of Zn decreased from 9.48 mg/L to 0.28 mg/L and 0.74 mg/L,the concentration of Cu decreased from 7.45 mg/L to 0.65 mg/L and 0.69 mg/L.During the medium heat treatment,the concentration of Cr in Chinese standard leaching solution increased but did not exceed the Chinese standard for pollution control on the landfill site of municipal solid waste.The heat treatment temperature of the method was 600℃,which was lower than the melting and sintering temperature,and could suppress the evaporation of heavy metals.The heat treatment process could be carried out in a moving bed,introducing the incinerator flue gas to heat the fly ash directly.The produced gas entered the incinerator gas treatment system.This method saves energy and does not require additional flue gas treatment equipment.更多还原