pH值对含砷水泥熟料制品中砷释放的影响

通过模拟煅烧实验制取水泥熟料，并制取混凝土样品。参照NEN-7375浸出方法，设定5种不同pH值的浸取液，研究了pH值对混凝土块中重金属As释放的影响。结果表明，浸取液的pH为2.0、3.5、5.0、7.35和10.0时，混凝土中As的观测累积释放量分别为0.0553、0.04253、0.0157、0.00939和0.0148 mg/kg；酸性范围内，观测累积释放量随着pH值的增大而减小，并在弱碱性条件下达到最小值，碱性范围内，随pH值的增大而呈增加的趋势。pH值对As的释放过程有影响，在前期，pH=2.0、3.5和10.0的浸取液中，释放曲线与斜率为0.5的直线拟合较佳，并且在1～4区间修正累积释放量曲线的斜率均在0.35～0.65范围内，其释放表现为扩散控制，而pH=5.0和7.35的浸取液中，则分别发生了表面冲刷作用和延滞现象；在中后期，pH=2.0的浸取液中，As的释放出现了耗竭现象，而pH=3.5和10.0则出现了溶解现象，pH=5.0和7.35则均为扩散控制。     

废物水泥窑共处置产品中Cd释放的pH影响

用高温电炉模拟煅烧试验制取水泥熟料后再制作混凝土,参考EA NEN 7375:2004浸出试验,设定5种不同pH的浸取液对混凝土进行长期浸出试验,研究了pH对水泥窑共处置混凝土中Cd释放量以及释放过程的影响.结果表明:(1)pH为2.00、3.50、5.00、7.35和10.00的浸取液中,Cd的累积释放量分别为0.408 0、0.005 8、0.000 7、0.000 4、0.001 2 mg/kg.在酸性条件下,随pH的增大,Cd的累积释放量减小.在碱性条件下,随pH的增大,Cd的累积释放量增大.(2)pH为7.35的浸取液中,Cd累积释放量的释放曲线与斜率为0.5的直线拟合最佳.pH为7.35的浸取液中,混凝土中Cd的释放机制为扩散控制;pH为2.00和5.00的浸取液中,Cd的释放在前期为扩散控制,后期发生了耗竭作用;pH为3.50和10.00条件下,Cd的释放在前期发生了延滞作用,中期为扩散控制,后期发生了耗竭作用.     

干湿交替中碳酸化对废物水泥窑共处置产品中重金属浸出的影响

通过比较连续浸出、碳酸化保存间歇浸出和密封保存间歇浸出3种浸出条件下,废物水泥窑共处置产品--混凝土中Cr、Ni、As、Cd和Pb的浸出量,研究了干湿交替的环境中碳酸化对混凝土中重金属浸出的影响.结果表明,不同的漫出条件对混凝土中重金属的浸出产生了一定的影响.间歇浸出过程降低了重金属在混凝土固相与孔隙水(液相)中的浓度...     

废物水泥窑共处置产品中重金属释放模型研究——混凝土路面场景

通过模拟煅烧试验制取水泥熟料,并制得混凝土样品。在混凝土路面场景分析的基础上,参照欧盟固体中无机组分有效量测试方法(EA NEN7371),以pH=3.2的HNO3/H2SO4溶液(质量比为1∶2)为浸取液,在液固比为20 L/kg条件下,对混凝土样品进行模拟浸出实验;参照欧盟块状材料中无机组分的扩散实验方法(EA NEN7375)测定混凝土样品中重金属的有效释放量。模拟浸出实验结果表明,Cr、Ni和Cd在浸出过程中扩散控制是其释放的主要因素。在此基础上建立了重金属在混凝土路面中的释放模型。实验室实测累积释放量(实测值)与模型预测累积释放量(预测值)的拟合检验结果表明,实测值与预测值之间差异不显著,释放模型能较好地预测混凝土路面中重金属的长期累积释放量。     

液固比对含重金属水泥熟料制品中重金属释放的影响

通过模拟煅烧试验制取水泥熟料，参照JGJ 55-2000（《普通混凝土配比设计规程》）制取混凝土样品，参考SR003.1和NEN 7375浸出试验，分别研究液固比对粒状及块状混凝土样品中重金属（Cr、Ni和As）释放的影响。结果表明，在不同液固比条件下粒状混凝土中的重金属浸出浓度为Cr>Ni>As，Cr、As浸出浓度基本保持不变，分别为2 500 μg/L左右和5～6 μg/L，Ni在液固比（L∶S）<6时，浸出浓度随着液固比的增加而降低，在L∶S>6时，浸出浓度较稳定，为35.7～41.5 μg/L；浸出量均随着液固比的增加而增大。液固比（L∶S）<10时，块状混凝土中重金属累积释放量及扩散系数均随液固比的增加而增大，当L∶S>10时两者基本保持不变。     

pH值对烧结砖中重金属释放的影响

采用酸消解实验和NEN 7371浸出实验研究了烧结砖中重金属总量和有效释放量,采用pH-dependence实验研究pH对破碎烧结砖样品中重金属(Cr、Ni、As、Cd和Pb)浸出特性的影响,以及烧结砖样品的酸碱缓冲容量。结果表明,烧结砖中重金属的有效释放量低于总量,释放率从大到小依次为CdAsPbNiCr;烧结砖的酸缓冲容量较小,浸出液pH从7.03降到3.64,消耗了29.33 mmol/kg硝酸,碱缓冲容量较大,pH从7.03升到12.40,共消耗256 mmol/kg氢氧化钠溶液,因此在使用烧结砖的过程中要特别注意环境pH;浸提液的酸碱性是影响烧结砖中重金属浸出的重要参数,在实验研究的pH范围内,不同重金属的浸出规律不同。Cr和As的释放受pH影响较小,而Ni和Cd的浸出量随pH的增大而降低,Pb的浸出量在强酸和强碱条件下均较大,当pH在5.59~9.86的范围内浸出量很低。     

燃煤电厂粉煤灰中汞的稳定性研究

燃煤飞灰中高度富集了痕量元素汞,而汞具有易挥发特性、较强的毒性和不易降解等特点,在粉煤灰的利用过程中汞极易逸出,造成二次污染,对人体健康有极大危害,所以对燃煤飞灰中汞稳定性的研究具有重要的意义。通过模拟加工利用和储存的自然环境,对飞灰和漂珠进行煅烧实验,研究飞灰和漂珠中汞的含量与煅烧温度之间的关系;对飞灰进行浸取实验,研究飞灰中汞的含量受浸取液pH以及浸取时间的影响情况。结果表明:在煅烧实验中,煅烧温度是影响汞释放的主要原因,随煅烧温度的增加汞的流失量越大,随煅烧时间的延长汞的流失量越大,在相同煅烧温度(500℃)和不同煅烧时间条件下,飞灰中汞的流失率最高达98.5%,漂珠中汞的流失率最高达86.4%,在相同煅烧时间和不同煅烧温度条件下,飞灰中汞的流失率最高达97.8%,漂珠中汞的流失率最高达85.7%;在浸取实验中,浸取时间越长,汞的流失量越大,当浸取液pH为1、浸取时间24h时,飞灰中的汞由0.331 8μg/g降低至0.137 1μg/g,说明浸取时间越长,汞浸出率越高,在不同pH条件下,汞含量随pH的降低而减少,飞灰中汞的浸出率最高达58.7%,最低为15.7%。     

氧化亚铁硫杆菌对酸化铅锌尾矿中Zn、As淋溶释放的影响

以青海某铅锌尾矿为研究对象进行酸预处理加速模拟静态淋溶实验,重点研究了氧化亚铁硫杆菌(At.f菌)接种量变化对尾矿中重金属Zn、As迁移释放的影响。结果表明,随时间延长,接种量变化均可导致淋溶体系pH值下降、电导率上升,氧化还原电位先上升后下降。At.f菌可明显促进Zn、As的释放,不同接种量对重金属的迁移释放作用不同;At.f菌存在下,Zn的释放能力大于As,Zn优先于As溶出,Zn、As浓度均表现为快速释放和缓慢释放并趋于平稳两个阶段,Evolich模型和Guass模型可分别描述Zn、As的释放过程。通过对细菌淋溶前后残渣SEM-EDS及XRD图谱分析发现,淋溶后尾矿颗粒结构疏松,表面腐蚀明显,生成了CaSO_4、钙磷石等不溶物,使Zn、As后期释放减慢。     

粉煤灰对Cr(Ⅵ)的吸附特性

通过间歇实验研究了粉煤灰对重金属Cr(Ⅵ)的吸附特性。探讨了固液比、pH、反应时间、温度、离子强度和初始浓度等因素的影响。实验结果表明,固液比、pH、温度与离子强度都对去除率有较大影响。当温度为20℃、pH=1、Cr(Ⅵ)的初始浓度为10 mg/L,固液比为100 g/L时,去除率达到50.13%。动力学实验结果表明,粉煤灰对Cr(Ⅵ)的吸附为快速反应,在180 min内可达到平衡,伪二级动力学模型可较好地拟合实验结果。等温吸附实验结果表明,Freundlich模型与Langmuir模型均可较好地拟合等温吸附实验结果。低温有助于粉煤灰对Cr(Ⅵ)的吸附。     

基于生态水泥的再生混凝土中重金属浸出动力学研究

使用生态水泥、再生骨料制备再生混凝土.分别通过快速浸出实验和长期连续浸出实验对混凝土中的重金属进行浸取,并采用原子吸收光谱法检测浸出溶液中的重金属含量,对比研究再生混凝土与普通混凝土重金属浸出性能差异.研究发现,快速浸出实验条件下,再生混凝土浸出液各重金属浸出浓度高于普通混凝土浸出浓度,但仍低于《危险废物鉴别标准浸出毒性鉴别》(GB5085.3-2007)标准规定的限值.快速浸出实验条件下重金属浸出量与重金属总量相关性不显著,说明快速实验方法有局限性.长期连续浸出实验结果表明,再生混凝土各重金属元素的扩散系数高于普通混凝土(除Zn外),这是由再生混凝土独特的显微结构引起的.     

Wet deposition of mercury within the vicinity of a cement plant before and during cement plant maintenance

Hg species (total mercury, methylmercury, reactive mercury) in precipitation were investigated in the vicinity of the Lehigh Hanson Permanente Cement Plant in the San Francisco Bay Area, CA., USA. Precipitation was collected weekly between November 29, 2007 and March 20, 2008, which included the period in February and March 2008 when cement production was minimized during annual plant maintenance. When the cement plant was operational, the volume weighted mean (VWM) and wet depositional flux for total Hg (Hg_T) were 6.7 and 5.8 times higher, respectively, compared to a control site located 3.5 km east of the cement plant. In February and March, when cement plant operations were minimized, levels were approximately equal at both sites (the ratio for both parameters was 1.1). Due to the close proximity between the two sites, meteorological conditions (e.g., precipitation levels, wind direction) were similar, and therefore higher VWM Hg_T levels and Hg_T deposition likely reflected increased Hg emissions from the cement plant. Methylmercury (MeHg) and reactive Hg (Hg(II)) were also measured; compared to the control site, the VWM for MeHg was lower at the cement plant (the ratio = 0.75) and the VWM for Hg(II) was slightly higher (ratio = 1.2), which indicated the cement plant was not likely a significant source of these Hg species to the watershed.     

石灰污泥共热法在水泥煅烧中的应用

利用水泥窑尾的高温废气干化污泥是处理污泥且节约能源的新方法。为了模拟窑尾废气干化污泥的生产工艺,试验对污泥与石灰共热干化,研究了石灰(CaO)在污泥热干化过程中作用,可提高污泥的干化速率,减少有害气体排放及提高干化污泥的稳定性。研究表明,当石灰掺量质量百分含量达到10%时,250℃下污泥干化速率同比提高了19.6%;释放的H2S气体减少了95.1%;污泥中有机物含量减少了77.87%。     

水泥窑共处置污染土壤的污染排放研究

以被DDT和六六六污染的土壤为研究对象，开展了利用水泥窑进行共处置的工程试验研究，分析了共处置过程对尾气排放的影响。结果表明，水泥窑共处置对农药污染物的焚毁去除率很高，DDT达到99.99991%，六六六达到99.99964%，均高于我国危险废物焚烧炉规定99.99％的焚烧效率；与空白处理相比，尾气排放中有机污染物（包括二恶英/呋喃，简称PCDD/F、多氯联苯PCB、六氯苯HCB、挥发性有机物VOC）、酸性气体和重金属的排放在共处置过程中没有显著增加，且都低于相应的规定限值。试验结果表明，水泥窑共处置固体废物不会导致污染负荷的增加。     

Formation, release and control of dioxins in cement kilns

Co-processing of hazardous wastes in cement kilns have for decades been thought to cause increased emissions of PCDD/PCDFs--a perception that has been evaluated in this study. Hundreds of PCDD/PCDF measurements conducted by the cement industry and others in the last few years, on emissions and solid materials, as well as recent test burns with hazardous wastes in developing countries do not support this perception. Newer data has been compared with older literature data and shows in particular that many emission factors have to be reconsidered. Early emission factors for cement kilns co-processing hazardous waste, which are still used in inventories, are shown to be too high compared with actual measurements. Less than 10 years ago it was believed that the cement industry was the main contributor of PCDD/PCDFs to air; data collected in this study indicates however that the industry contributes with less than 1% of total emissions to air. The Stockholm Convention on POPs presently ratified by 144 parties, classifies cement kilns co-processing hazardous waste as a source category having the potential for comparatively high formation and release of PCDD/PCDFs. This classification is based on early investigations from the 1980s and 1990s where kilns co-processing hazardous waste had higher emissions compared to those that did not burn hazardous waste. However, the testing of these kilns was often done under worst case scenario conditions known to favour PCDD/PCDF formation. More than 2000 PCDD/PCDF cement kiln measurements have been evaluated in this study, representing most production technologies and waste feeding scenarios. They generally indicate that most modern cement kilns co-processing waste today can meet an emission level of 0.1ngI-TEQ/m(3), when well managed and operated. In these cases, proper and responsible use of waste including organic hazardous waste to replace parts of the fossil fuel does not seem to increase formation of PCDD/PCDFs. Modern preheater/precalciner kilns generally seems to have lower emissions than older wet-process cement kilns. It seems that the main factors stimulating formation of PCDD/PCDFs is the availability of organics in the raw material and the temperature of the air pollution control device. Feeding of materials containing elevated concentrations of organics as part of raw-material-mix should therefore be avoided and the exhaust gases should be cooled down quickly in long wet and long dry cement kilns without preheating. PCDD/PCDFs could be detected in all types of solid samples analysed: raw meal, pellets and slurry; alternative raw materials as sand, chalk and different ashes; cement kiln dust, clinker and cement. The concentrations are however generally low, similar to soil and sediment.     

Possible reuse of Egyptian controlled cement dust

Possibilities for the reuse of controlled cement dust, collected from the hopper of the electrostatic precipitators installed on the different cement kilns of two of the three biggest companies for Portland cement production located to the south of Cairo, have been investigated. Twenty-one factors representing the physical properties and mineral and chemical composition of the cement dust were estimated and discussed. The results have been compared with the corresponding figures of three Portland cement companies in the United Arab Emirates and also with the British Standard Requirements of ordinary Portland cement. The study found that the cement dust can be reused after some feasible treatments, such as increasing the fineness and tricalcium silicate ratio and decreasing its alkalinity. Consequently, in this circumstance, pollution prevention at source is proving to be a boon as it can not only bring down pollution levels but also add to the companies' profits through efficient use of resources.     

水泥分解炉掺烧干污泥对NO_x排放的影响

针对水泥窑炉NOx排放问题,提出了在分解炉上采用掺烧干污泥对烟气进行脱硝的方法。通过在水泥分解炉进行实验,研究了掺烧干污泥对NOx的影响。实验表明,在保持CO浓度和含氧量在一定范围内相对不变的条件下,NOx浓度随着干污泥掺烧量增加而减少。在保持干污泥掺烧量、CO浓度在一定范围内相对不变的情况下,NOx排放浓度随着含氧量的增加而增加,表明在富氧环境下,NOx比较容易生成。在保持干污泥掺烧量、含氧量不变的情况下,NOx排放浓度随着CO浓度的增加而减少,说明在高温环境下,干污泥暴露在烟气中的碳不断与氧反应,加快了干污泥活性炭化的进程,并促使NOx不断被吸附。同时,NOx生成所需的氧被碳原子掠夺,从而使CO浓度增加,并抑制了NOx的生成。     

水泥窑协同处置过程中Pb、Cd的挥发特性

对铅、镉2种重金属的氧化物开展了热重实验、熟料煅烧以及熟料消解实验，以重金属的挥发率为主要指标，研究了水泥窑协同处置过程中铅、镉在等温条件下随时间的挥发特性。结果表明，2种重金属的挥发率均是随温度的升高，时间的增加而增大。Pb的挥发率为96%，Cd的挥发率达到98%，根据等温动力学及阿累尼乌斯方程，对Pb，Cd的挥发率随时间变化的规律进行动力学模拟，得到较好的线性拟合效果，其中，Pb挥发反应的表观活化能E为88.73 kJ/mol，Cd挥发反应可以分2个部分：1 200℃以下的表观活化能E为61 kJ/mol；1 250℃以上的表观活化能E为184.6 kJ/mol。     

水泥行业用喷雾增湿塔的改型设计

介绍了喷雾法增湿的基本原理、设备的结构设计及附件的选型,讨论了对实际生产中可能发生的操作故障的防止与消除措施。实践证明,这种新型喷雾增湿塔能较好地应用于水泥生产。