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%。     

产黄青霉浸出修复重金属污染土壤

采集铅锌冶炼厂周边表层土壤,分析其污染情况,并用产黄青霉菌浸出修复,用正交法考察温度、培养基pH值和浸出时间对浸出率的影响,拟寻找最佳修复方案。结果表明:根据GB 15618-95二级土标准值,铅锌冶炼厂周边表层土壤中Zn和Cd已达重度污染程度,Cu达中度污染,Pb为轻度污染,Cr未污染;综合污染指数表明铅锌冶炼厂周边表层土壤已达严重污染程度;Pb和Zn的最适浸出温度为30℃,Cd和Cu的最适浸出温度为20℃;当培养基pH值为7.0时,Pb、Zn、Cd和Cu的浸出率之和最高,Pb和Zn的浸出率之和均在浸出7 d时最高。极差分析表明,培养基pH值和浸出时间是影响产黄青霉浸出修复重金属污染土壤的主要因素;方差分析表明,培养基pH值和浸出时间对Zn的浸出率影响显著,3种因素对Pb、Cd和Cu浸出率的影响均不明显。当温度为30℃,pH值为7.0,浸出7 d时各重金属的浸出率均最高,故产黄青霉浸出修复重金属污染土壤的最优方案为A2B2C3。     

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。     

几种硫化物对紫色土汞的稳定化效果及优化稳定条件

以西南地区广泛分布的紫色土-灰棕紫泥为对象,探讨了硫化物种类(S、Na_2S、FeS、Na_2S_2O_3和DTCR(二硫代氨基甲酸盐))、用量对不同水平汞污染土壤的稳定化效果。结果表明5种硫化物对土壤汞均具有显著的稳定化效果。固定S:Hg摩尔比为1:1条件下,在1.5～250 mg·kg~(-1)汞污染土壤中,几种硫化物稳定效率相对大小顺序:DTCRNa_2SNa_2S_2O_3SFeS。Na_2S和DTCR在高浓度汞污染土壤中均表现较高的稳定化效果,在不同汞污染浓度下均能在3d内使土壤浸出汞浓度满足美国固体废弃物毒性浸出程序(TCLP)浸出标准要求(0.2 mg·L~(-1)),Na_2S_2O_3稳定效果相对较差,对250 mg·kg~(-1)的汞污染土壤,稳定化处理时间需要15d才能达到浸出标准要求,当汞污染浓度≥150 mg·kg~(-1)时,S和FeS不能满足浸出标准要求。固定汞污染浓度为150 mg·kg~(-1)稳定化效果取决于硫化物的用量,其中,仍然以DTCR效果最好,S:Hg=1稳定化处理3 d时即可达汞浸出标准。Na_2S和Na_2S_2O_3则均需要在较高的浓度下才能实现汞的稳定化,但是过高的用量会导致土壤中HgS再次溶解,两者的最佳施用量为S:Hg=5。元素S和FeS则需要以S:Hg5稳定化处理7 d以上才能达到浸出标准要求。土壤中汞的浸出活性与其赋存形态有关,交换态(Exc-Hg)和碳酸盐结合态汞(Carb-Hg)与土壤浸出汞浓度呈显著正相关,高效稳定剂显著促进了汞向有机质结合态(OM-Hg)和残渣态(Res-Hg)转化。硫化物稳定化处理9个月内土壤中浸出汞浓度始终维持在极低水平,满足持续稳定化要求。     

废汞触媒中汞的浸出及其再生活性炭的吸附性能

对电石法生产聚氯乙烯产生的废汞触媒进行浸出及再生活性炭的研究,以6 mol·L~(-1)HCl溶液作为浸出剂,在浸出反应温度为65℃、浸出反应时间为90 min和液固比为15∶1的实验条件下得到Hg~(2+)的优化浸出率为61.25%。采用扫描电镜(SEM)、Brunauer-Emmet-Tller(BET)比表面积等方法分析再生活性炭特征。结果表明焙烧废汞触媒浸出渣热再生活性炭是可行的,焙烧最佳工艺条件为:焙烧温度850℃,焙烧时间90 min。得到的焙烧产物亚甲基蓝吸附值为120.5 mg·g~(-1),BET表面积为704.25 m~2·g~(-1),平均孔径为3.28 nm。再生前后的汞含量与从1.067%降至0.351%,再生后能再次作为汞触媒生产的催化剂载体材料,同时减缓固废堆积过程中汞流失造成的一系列环境问题。     

中温焙烧/钠化氧化法回收电镀污泥中的铬

采用中温焙烧/钠化氧化法从电镀污泥中回收铬.结果表明,影响铬浸出率的最主要因素为焙烧温度.电镀污泥与碳酸钠质量比、焙烧时间、水浸时间对铬浸出率的影响较接近,在水浸水固比为10.0 ; 1.0(质量比)、室温、焙烧温度为650℃、焙烧时间为2.0h、电镀污泥与碳酸钠质量比为1:1、水浸时间为60 min的最佳浸出条件下,铬浸出率为99.3%;去除氢氧化铝、氢氧化锌的最佳反应温度和pH分别为90～95℃和7.5;去除硫酸钠晶体的最佳pH为4.0,在最佳试验条件下,铬回收率为90.57%.     

钢铁厂固体废物汞的分析方法及浸出毒性研究

以山西某钢铁厂各工艺单元产生的固体废物为研究对象,采用实验对比研究的方法,测定汞的分布特征及其浸出毒性。结果表明:(1)汞的最优推荐分析方法为DMA-80或Lumex RA-915+汞分析仪直接测定汞含量较低的烧结钢渣、高炉渣及转炉渣,微波辅助酸消解电感耦合等离子体质谱仪间接测定汞含量较高的除尘灰和粉煤灰,可以提高数据的精确度和可信度。(2)除尘灰及粉煤灰中汞浸出质量浓度分别为0.25、0.12 mg/L,超过《危险废物鉴别标准浸出毒性鉴别》(GB 5085.3—2007)限值(0.1mg/L),因此除尘灰和粉煤灰属于危险固体废物,应采取无害化处理措施后综合利用;烧结钢渣、高炉渣及转炉渣属于一般工业固体废物,可安全无害堆放或使用。     

温度对生物淋滤废旧MH/Ni电池中重金属影响研究

在15～35℃内,探索温度对生物淋滤浸出废旧MH/Ni电池中重金属效果的影响.试验结果表明,温度越高,体系pH下降及SO2-4浓度上升的速率越快,电极材料中重金属Ni和Co的浸出率也相应提高.在35℃条件下,Ni的浸出率为98.0%,Co的浸出率为77.9%.     

优化化学浸提法对造纸白泥中汞形态的分析

《固体废物浸出毒性浸出方法水平振荡法》(HJ 557—2010)中规定的固体废物中各形态汞的逐级化学浸提周期较长,制取浸提液时的浸提时间为搅拌后恒温振荡8h,静置16h。对美国环境保护署提出的相关方法(US EPA Method 7471B,固体和固体废弃物中汞的测定(冷原子蒸汽技术))进行了改进,将水溶态汞、酸溶态汞测定的浸提液制取时间设定为搅拌后恒温振荡30min,静置2h(其他2种形态汞测定时未做优化),采用优化的化学浸提法来测定2种造纸白泥样品中不同形态汞的含量。测定结果表明,按照国标方法和优化方法测得的浸提液中水溶态汞、酸溶态汞含量的偏差均小于6%,在可接受的范围(小于10%)内,优化方法的测定结果可靠;不同种类的造纸白泥中各形态汞的分布趋势是相同的,含量分别为水溶态汞酸溶态汞过氧化氢溶态汞残渣态汞;2种造纸白泥样品中所含水溶态汞的比例均较高,这也为造纸白泥的安全资源化利用提供了有利条件。     

废弃印刷线路板碘化法浸金研究

针对碘化法从废弃印刷线路板中提取金的工艺设计，分别考察了碘的质量分数、n(I₂)/n(I^-)比值、固液比、双氧水的质量分数、pH值、浸出时间和浸出温度对金浸出率的影响。结合正交设计优化实验方法,提出了从废弃印刷线路板中碘化法浸取金的最佳工艺条件：碘的质量分数为1.1％，n(I₂)∶n(I^-)=1∶10，双氧水的质量分数为1.5％，浸出时间4 h，固液比为1∶10，浸出温度为常温（25℃），溶液pH值为中性，此时金浸出率可达97.5％。     

生物法和化学法回收制革污泥中铬的对比研究

研究了嗜酸性硫杆菌(Thiobacillus)生物沥滤法和1:1硫酸化学沥滤法分离回收制革污泥中的铬.比较了嗜酸性硫杆菌生物沥滤法和化学沥滤法回收制革污泥铬过程中pH、氧化还原电位(ORP)、沉降比(SV)以及铬的沥滤率的变化.试验结果表明,pH是影响制革污泥中铬的沥滤率的关键因素.生物沥滤法在使污泥pH大幅度降低的同时,能很好地改善污泥的沉降性能,对铬的沥滤效果好于化学沥滤法.     

提高生物法分离制革污泥中铬分离效率的研究

在已确定污泥驯化最佳条件的基础上，通过改变滤材、液固分离条件，添加营养物质继续降低pH等方法，进行提高生物沥滤法分离制革污泥中铬的分离效率的研究。同时考察化学沥滤法（1∶1硫酸）在相同条件下的分离效率。试验结果表明：用相应pH值酸液（1∶1硫酸配制）淋洗，淋洗+闷洗和抽真空＋酸液淋洗等过滤方式可提高铬的分离效率。生物沥滤中当pH值下降至1.8时，分离效率即可达到94.65%，与直接用蒸馏水淋洗相比要高得多。化学沥滤中当pH值下降到1时，分离效果可达96.7%，沥滤污泥中剩余铬含量可达到制革污泥农用标准。     

氧化亚铁硫杆菌浸出线路板中铜的研究

从煤堆积水中分离得到氧化亚铁硫杆菌，利用该菌种对线路板中的铜进行了浸出实验。研究了不同线路板粉末添加量对浸出效果的影响，观察了浸出过程中pH和氧化还原电位（Eh）的变化，结果表明添加量为10g／L和20g／L时，在15d内线路板Cu几乎全部浸出，而50g／L和100g／L在15d内亦有较高的浸出效率，并呈持续上升趋势。     

氧化亚铁硫杆菌浸出线路板中铜的研究

从煤堆积水中分离得到氧化亚铁硫杆菌,利用该菌种对线路板中的铜进行了浸出实验.研究了不同线路板粉末添加量对浸出效果的影响,观察了浸出过程中pH和氧化还原电位(Eh)的变化,结果表明添加量为10 g/L和20 g/L时,在15 d内线路板Cu几乎全部浸出,而50g/L和100g/L在15 d内亦有较高的浸出效率,并呈持续上升趋势.     

高氯离子废水CODCr测定的方法研究

对CODCr值较低，但氯离子浓度很高的水样中CODCr的测定方法进行了初步研究，比较了稀释法、硝酸银法、硫酸汞加入法各自的优缺点。结果表明，用硝酸银法测定悬浮颗粒物较少的水样中CODCr，既可去除水样中Cl^-的干扰，又可真实地测定CODCr值，同时也不会带来二次污染。     

Stabilization of mercury-containing wastes using sulfide

This paper summarizes the findings of our studies on mercury stabilization using sulfide. Primary stabilization variables such as stabilization pH and sulfide/mercury molar ratio were tested. Mercury stabilization effectiveness was evaluated using the Toxicity Characteristic Leaching Procedure (TCLP) and the constant pH leaching tests. The influence of interfering ions on mercury immobilization was also tested. The experimental results indicate that the sulfide-induced treatment technology is an effective way to minimize mercury leaching. It was found that the most effective mercury stabilization occurs at pH 6 combined with a sulfide/mercury molar ratio of 1. The combined use of increased dosage of sulfide and ferrous ions ([S]/[Hg]=2 and [Fe]/[Hg]=3 at pH=6) can significantly reduce interferences by chloride and/or phosphate during sulfide-induced mercury immobilization. The sulfide-treated waste stabilization efficiency reached 98%, even with exposure of the wastes to high pH leachants.     

Modeling batch leaching behavior of arsenic and selenium from bituminous coal fly ashes

Correctly predicting the leaching potential of arsenic (As) and selenium (Se) is critical for assessing the environmental impact of coal fly ash. This study investigated the impacts of several key environmental factors, including pH, leaching time, and ash washing on the batch leaching behavior of As and Se from bituminous coal fly ashes. The experimental results demonstrated that As and Se leaching from fly ash increased beyond the minimal leaching pH ranges. Increasing leaching time increased As leaching but decreased Se leaching in the alkaline pH condition. A speciation-based adsorption model was used to quantify the batch leaching data, and determine the intrinsic leaching parameters including the total batch leachable mass and the adsorption constant of As or Se. The modeling approach was validated by correctly predicting the independent batch leaching data in a broad pH range and a different L/S condition. Experimental and modeling results also demonstrated that ash washing and ash aging (longer leaching time) did not change the adsorption constants of As and Se on the ash surface. However, ash washing could increase the availability of As and Se for leaching.     

EDTA and HCl leaching of calcareous and acidic soils polluted with potentially toxic metals: remediation efficiency and soil impact

The environmental risk of potentially toxic metals (PTMs) in soil can be diminished by their removal. Among the available remediation techniques, soil leaching with various solutions is one of the most effective but data about the impact on soil chemical and biological properties are still scarce. We studied the effect of two common leaching agents, hydrochloric acid (HCl) and a chelating agent (EDTA) on Pb, Zn, Cd removal and accessibility and on physico-chemical and biological properties in one calcareous, pH neutral soil and one non-calcareous acidic soil. EDTA was a more efficient leachant compared to HCl: up to 133-times lower chelant concentration was needed for the same percentage (35%) of Pb removal. EDTA and HCl concentrations with similar PTM removal efficiency decreased PTM accessibility in both soils but had different impacts on soil properties. As expected, HCl significantly dissolved carbonates from calcareous soil, while EDTA leaching increased the pH of the acidic soil. Enzyme activity assays showed that leaching with HCl had a distinctly negative impact on soil microbial and enzyme activity, while leaching with EDTA had less impact. Our results emphasize the importance of considering the ecological impact of remediation processes on soil in addition to the capacity for PTM removal.     

Arsenic release from iron rich mineral processing waste: Influence of pH and redox potential

This paper presents the effect of pH and redox potential on the potential mobility of arsenic (As) from a contaminated mineral processing waste. The selected waste contained about 0.47 g kg(-1) of As and 66.2 g kg(-1) of iron (Fe). The characteristic of the waste was identified by acid digestion, X-ray diffraction and sequential extraction procedures. Less than 2% of the total As was acid extractable with the remaining 98% associated with Fe-oxyhydroxides and oxides. Batch leaching tests at different pH conditions showed a strong pH dependence on arsenic and iron leaching. Arsenic leaching followed a "V" shaped profiles with significant leaching in the acidic and alkaline pH region. Acid extractable phases dissolved at acidic pH, while desorption of arsenic due to increase in pH resulted in high arsenic concentration at alkaline pH. Under aerobic conditions and pH 7, As solubility was low, probably due to its precipitation on Fe-oxyhydroxides. Maximum As solubilization occurred at pH 11 (3.59 mg l(-1)). Similarity in the As and Fe leaching profiles suggested that the release of As was related to the dissolution of Fe in the low pH region. In general, redox potential did not play a significant role in arsenic or iron solubilization. It was thus concluded that for this solid waste, desorption was the predominant mechanism in arsenic leaching. A simple thermodynamic model based on arsenic and iron redox reactions was developed to identify the more sensitive redox couple.     

重金属污染土壤的草酸和EDTA混合淋洗研究

采用不同浓度的草酸(oxalic acid,OX)和乙二胺四乙酸(EDTA)混合的淋洗方法研究重金属污染土壤的最佳混合淋洗方式,探讨了液固比、淋洗时间及pH对淋洗效果的影响,并分析了0.2 mol/L OX+0.2 mol/L EDTA处理前后土壤中重金属形态的变化。结果表明,采用0.2 mol/L OX+0.2 mol/L EDTA混合的淋洗法可同时去除多种重金属,且对Cu、Zn、Ni和Cr的去除率明显高于单用OX和EDTA,去除率分别为Cu 41.29%、Zn 84.73%、Ni 54.2%和Cr 66.01%。0.2mol/L OX+0.2 mol/L EDTA在液固比为5∶1、淋洗时间为4 h、pH为6时可分别达到最佳淋洗效果,且分别为Cu 62.59%、Zn 93.48%、Ni 55.95%和Cr 71.57%;Cu 50.47%、Zn 86.67%、Ni 61.53%和Cr 72.68%;Cu 44.40%、Zn 81.82%、Ni68.76%和Cr 74.93%。形态分析结果表明,0.2 mol/L OX+0.2 mol/L EDTA能较好地改变土壤中重金属形态的分布。