CdO对硅酸三钙形成的影响及其固溶效应

C3S作为水泥熟料中最重要的矿物之一,其矿物结构和水化活性会受到固溶重金属离子的影响。利用化学分析、XRD、EDS-SEM和AFS等测试手段,研究了CdO对C3S矿物形成的影响及其在C3S中的固化能力,并探讨了镉离子在C3S中的固溶机理。研究表明:随着CdO掺量的增加,fCaO含量先减少后增加。当掺量小于1.0%时,CdO的掺入有利于C3S晶粒的形成和生长。掺杂后C3S中没有新相的行成,且C3S均为单斜结构:MⅠ型。烧成过程中,部分镉元素以CdO的形式挥发,且随着CdO掺量的提高,残留率逐渐降低。依据固溶体形成条件表明:镉离子主要取代钙离子形成置换固溶体((3-x)CaO·xCdO·SiO2),极少量的镉离子可能会进入钙氧八面体空隙形成间隙型固溶体(3CaO·yCdO·SiO2)。     

含铬熟料的烧成、水化及其浸出毒性

为探索水泥窑协同处置含铬固体废弃物的可行性,通过测定熟料的f-CaO含量、强度、铬浸出浓度,以及分析熟料的矿物、水化产物和水化放热,研究了CrO3对熟料烧成、水化及浸出毒性的影响规律及机制。结果表明:当CrO3掺量低于2%时,熟料的f-CaO含量和3d、28d、90d强度随掺量的变化不明显;Cr(Ⅵ)/∑Cr浸出浓度随CrO3掺量增加而增大,随养护龄期延长而减小。当CrO3掺量小于0.25%时,熟料Cr(Ⅵ)浸出浓度均低于0.05mg/L,符合Ⅱ类地表水环境质量标准限值;当CrO3掺量较高时,抑制C3S形成,并显著延缓水化;熟料对铬的固化可归因于熟料矿物和水化产物对铬的固溶和包裹。掺加少量CrO3对熟料烧成、水化、性能均无不利影响,产品的环境安全性能够得到保证,水泥窑协同处置含铬废弃物是值得深入研究的技术途径。     

污泥对水泥熟料烧成和强度的影响

利用污水处理厂污泥替代硅质原料配制多组水泥生料,污泥掺量变化范围0-10%,生料KH(石灰饱和系数)变化范围为0.88~0.97,在1400℃下煅烧,测定各熟料的f-CaO和强度,并结合XRD,SEM/EDS等分析,研究污泥掺量及生料KH对水泥熟料烧成和强度性能的影响。另外还对掺10%污泥所烧制的熟料进行了重金属溶出试验。结果表明,在生料KH保持0.94而污泥掺量变化的情况,污泥掺量在2.5%左右时对改善生料的易烧性和熟料强度均有利,而污泥超过这个掺量后,生料易烧性和熟料强度随污泥掺量增加而明显降低;在污泥掺量保持2.5%而KH变化的情况下,KH小于0.91时,掺入污泥对生料易烧性和熟料强度不利,而KH大于0.94时,污泥掺入能改善生料易烧性,对熟料强度也略有提高;即使水泥生料中污泥掺量高达10%,所烧制的水泥其重金属滤出值远远小于标准的规定值,不会对环境产生危害。从水泥生料易烧性、熟料强度和重金属溶出试验看,只要生料配比合理和污泥掺量合适,污泥可以在水泥生产中得到无害化处置和资源化利用。     

纳米CeO_2对铅锌尾矿中重金属离子溶出特性影响的研究

铅锌尾矿中含有多种重金属成分,在一定环境下会溶出并造成严重的污染。在对铅锌尾矿品的物相组成、化学成分、重金属离子含量、有机物含量和pH值等基本特性进行表征的基础上,研究了添加纳米CeO_2前后样品在不同pH值下重金属离子的浸出规律,探究了纳米CeO_2作为尾矿中重金属离子吸附剂的最佳掺量以及pH值对CeO_2吸附重金属离子的影响。结果表明,铅锌尾矿中重金属离子的溶出量随着pH值的增大而降低;CeO_2最佳掺量为尾矿质量的0.5%;pH值在5~8之间,CeO_2对各重金属离子均具有较高的吸附率。因此,提出了一种降低铅锌尾矿污染的新方案。     

不同环境条件下磷酸镁水泥对硝酸铅的固化

在不同pH值、碳化、氯离子侵蚀条件下,利用磷酸镁水泥对不同掺量的硝酸铅进行固化。研究不同条件下重金属铅的浸出率规律,并对不同掺量的硝酸铅对磷酸镁水泥水化产物种类、水化产物形貌进行了探讨。研究表明,在pH值为2时,铅的浸出率最大,随着pH值增加浸出率降低,但在pH值为12,浸出率又有所升高;在碳化条件下铅的浸出率随养护时间的延长先增加后趋于稳定;在氯离子侵蚀条件下,铅的浸出率随侵蚀时间的延长变化不明显。     

红土镍矿高浓度碱浸提硅的研究

通过正交试验,研究了红土镍矿高浓度碱浸脱硅过程中浸出温度、碱初始浓度、浸出时间、碱矿质量比对SiO2提取率的影响.结果表明,影响SiO2提取率的主次顺序为浸出温度＞碱初始浓度＞浸出时间＞碱矿质量比;并得到优化的浸出条件为:浸出温度220℃,碱初始浓度85%,浸出时间90min,碱矿质量比5∶1.在溶出过程探讨了加水量、时间和洗涤次数对SiO2提取率的影响,并确定了一次溶出两次洗涤的工艺.     

水泥熟料固化重金属Cu2+和Zn2+及水化浸出行为分析

危废处理是当前的热点问题,水泥窑协同处置作为一种有效的处理方式,逐步为社会所接受。多数的危废中包含Cu²⁺和Zn²⁺,文章研究了危废中重金属Cu²⁺和Zn²⁺在水泥熟料中的固化性能和在熟料中的分布,并探讨了重金属在水泥净浆中的浸出行为和环境安全性。通过熟料易烧性X射线衍射(XRD),矿物相分离萃取,浸出实验得出:Cu²⁺和Zn²⁺均改善了熟料易烧性;Cu²⁺促进了C₄AF的生成,同时也促进了C₃S晶粒的生长,并固溶在其中;Zn²⁺与熟料形成新的矿物相Ca₁₄Al₁₀Zn₆O₃₅。通过相对分布系数(D)和分配系数(K_f)说明Cu²⁺主要分布在硅酸盐相中,硅酸盐相固化Cu²⁺的能力强于中间相;Zn²⁺主要分布在中间相中,中间相固化Zn²⁺的能力强于硅酸盐相。掺量为2.0%的Cu²⁺和Zn²⁺在水泥净浆7 d龄期的浸出浓度最大,分别为1.724和0.387 mg·L^-1。水泥熟料固化Cu²⁺和Zn²⁺在水泥使用过程中不会对环境造成二次污染。     

NH_3-NH_4Cl-H_2O体系浸出氧化锌矿的试验研究

研究了用NH_3-NH_4Cl-H_2O体系浸出氧化锌矿,进行了正交试验和单因素试验,并对浸出渣进行了物相和能谱分析。通过正交试验得出浸出氧化锌矿工艺,影响锌浸出率的主要因素的较佳组合为:液固比4.5mL/g、浸出时间60min、浸出温度20℃、总氨浓度6.0mol/L。由正交试验结果适当调整工艺参数,进行单因素试验研究,考察液固比、浸出时间、温度及总氨浓度对锌浸出率的影响,得到优化工艺条件为:液固比5mL/g、浸出时间60min、浸出温度20℃、总氨浓度6.0 mol/L。在优化条件下,锌的浸出率达到88.1%,物相分析表明浸出渣主要成分是SiO2、针铁矿(FeOOH),含锌物相为ZnS,实现了锌选择性高效溶出,与铁、铝、硅等杂质元素的有效分离。     

铜渣基铁系磷酸盐化学键合材料的制备及其固化Pb2+的研究

利用富含铁氧化物的铜渣和磷酸二氢钾反应制备铁系磷酸盐化学键合材料,并将其作为基体材料固化重金属离子Pb~(2+)。研究了原料配比、缓凝剂及硝酸铅掺量对胶凝材料初凝时间和抗压强度的影响。结果表明,当m(P)/m(CS)为1/4及硼砂掺量为2%时,材料性能最好,自然养护28d和常压蒸汽养护24h抗压强度分别可达44.78 MPa和30.48 MPa。随着重金属铅掺量的增加,固化体抗压强度逐渐降低,铝掺量为4.5%时,自然养护28d和蒸汽养护24h固化块抗压强度均大于10 MPa。对固化体的重金属毒性浸出试验表明:铁系磷酸盐化学键合材料对重金属离子Pb~(2+)具有很好的固化效果,固化体毒性浸出质量浓度远低于国家浸出毒性鉴别标准限值(5mg/L)。通过XRD、SEM和FTIR对重金属固化体进行表征分析,发现固化体中形成了PbHPO_4和Pb_3(PO_4)_2等重金属磷酸盐产物,并被铁系磷酸盐胶凝相物质紧密包裹,从而通过化学键合和物理包裹等双重作用实现重金属Pb的稳定固化。     

纳米SiO_2对混凝土材料阻尼性能的改良研究

利用自主开发的三点弯曲梁阻尼测试装置对不同掺量纳米SiO2混凝土的阻尼性能进行了测试,通过X射线衍射仪和扫描电镜研究了不同掺量纳米SiO2对混凝土微观结构的影响,并对其阻尼增强机理进行了初步探讨。结果表明纳米SiO2掺量为4%时混凝土材料的损耗因子最大,为素混凝土的2.41倍,综合考虑成本、流动性、强度和阻尼等因素确定纳米SiO2的最优掺量为3%;纳米SiO2掺入混凝土中后,与之发生二次水化反应,使得混凝土中六方板状Ca（OH）2晶粒数量减少;纳米SiO2对于混凝土的阻尼增强机理在于纳米SiO2的掺入使得混凝土材料的内接触面数量增多,在外力作用下使应力不均匀分布增加,从而提高了材料摩擦阻尼耗能的能力。     

Role of the mixing conditions and composition of galvanic sludges on the inertization process in clay-based ceramics

Hydroxide-metal sludges from electroplating industry are a potential source of environmental contamination due to their high content of heavy metals. The incorporation of these residues in a ceramic matrix can be a promising way to suppress the harmful effect of metals normally present in those sludges. This work reports the role of the mixing time between the waste and ceramic materials and of the calcination step on the fixing level of several metal-containing species (Al, Zn, Ni, Fe, Ca, Cu, Cr) after sequential leaching in different media (aqueous, acetate and citrate). A strong and/or long mixing process will promote the deagglomeration of the coarser agglomerates and then will increase the reactivity of remaining grains towards the ceramic material during the calcination. As a consequence, inertization is improved for fired samples. With non-calcined samples leaching increases as a result of increasing dispersability/availability of species.     

Leaching behaviour of a galvanic sludge in sulphuric acid and ammoniacal media

Leaching studies of a sludge produced by the physico-chemical treatment of wastewaters generated by a Ni/Cr plating plant were carried out in both sulphuric acid and ammoniacal media aiming to decide which of them would be the best treatment for this kind of waste material. The dissolution behaviour of some metals (Cu, Ni, Cr and Zn) was studied in order to assure the best metal recovery conditions in subsequent processes by the use of some separation methods such as solvent extraction and precipitation techniques. Therefore, the study here presented deals with the first chemical stage of an integrated treatment process. For the sulphuric acid leaching, maximal conversions obtained were 88.6% Cu, 98.0% Ni and 99.2% Zn for the following experimental conditions: a 100 g L(-1) acid concentration, a 5:1 liquid-to-solid ratio (L/S), a particle size less than 1 mm, a digestion time of 1h, a stirring speed of 700 rpm (all at room temperature and under atmospheric pressure). As expected, no selectivity was achieved for the sulphuric acid leaching, despite this option yielding much higher metal ion dissolution when compared with that reached by ammoniacal leaching. The use of this latter medium allowed the extraction of Cu and Ni without Cr species, but rates of conversion were only about 70% for Cu and 50% for Ni, much lower than those obtained for sulphuric acid leaching.     

Fate of heavy metals during municipal solid waste incineration in Shanghai

The transfer behavior of heavy metals during municipal solid waste (MSW) incineration was investigated based on 2-year field measurements in two large-scale incinerators in Shanghai. Great temporal and spatial diversification was observed. Most of Hg and Cd were evaporated and then removed by air pollution control (APC) system through condensation and adsorption processes, thus being enriched in the fine APC residues particles. Cr, Cu, and Ni were transferred into the APC residues mainly by entrainment, and distributed uniformly in the two residues flows, as well as in the ash particles with different sizes. Pb and Zn in the APC residues were from both entrainment and evaporation, resulting in the higher concentrations (two to four times) compared with the bottom ash. Arsenic was transported into the flue gas mainly by evaporation, however, its transfer coefficient was lower. Though the heavy metals contents in the APC residues were higher than that in bottom ash, more than 80% of As, Cr, Cu, and Ni, 74-94% of Zn, as well as 46-79% of Pb remained in the bottom ash, due to its high mass ratio (85-93%) in the residues. While 47-73% of Cd and 60-100% of Hg were transferred into the APC residues, respectively.     

Evaluation of electrokinetic removal of heavy metals from sewage sludge

The presence of heavy metals is one of the main obstacles for agricultural use of million tonnes of dewatered sewage sludge produced in wastewater treatment plants. Electrokinetic (EK) treatment can be applied to remove heavy metals from sludge. The aim of this study was to increase the efficiency of electrokinetic removal of heavy metals from dewatered sewage sludge. EK experiments were carried out with and without pH adjustment in cathode chamber of acidified sewage sludge. The selective sequential extraction (SSE) was used to determine the fractionation of heavy metals in sewage sludge. The mobility of heavy metals in sludge significantly increased after its acidification at pH 2.7 and followed the order: Ni, Zn, Cu, As, Cr, Pb. Removal efficiencies of heavy metals in the experiment with acidified sewage sludge and pH adjustment at cathode chamber at 2.0 were: 95% for Zn, 96% for Cu, 90% for Ni, 68% for Cr, 31% for As and 19% for Pb. The concentrations of Zn, Cu, Ni, Cr and Pb after EK treatment were below the United States Environmental Protection Agency limits for biosolids applied to agricultural land, forest, public contact sites or reclamation sites.     

The effect of isosaccharinic acid (ISA) on the mobilization of metals in municipal solid waste incineration (MSWI) dry scrubber residue

Co-landfilling of incineration ash and cellulose might facilitate the alkaline degradation of cellulose. A major degradation product is isosaccharinic acid (ISA), a complexing agent for metals. The impact of ISA on the mobility of Pb, Zn, Cr, Cu and Cd from a municipal solid waste incineration dry scrubber residue was studied at laboratory using a reduced 2(5-1) factorial design. Factors investigated were the amount of calcium isosaccharinate (Ca(ISA)(2)), L/S ratio, temperature, contact time and type of atmosphere (N(2), air, O(2)). The effects of pH and Ca(ISA)(2) as well as other factors on the leaching of metals were quantified and modelled using multiple linear regression (alpha=0.05). Cd was excluded from the study since the concentrations were below the detection limit. The presence of Ca(ISA)(2) resulted in a higher leaching of Cu indicating complex formation. Ca(ISA)(2) alone had no effect on the leaching of Pb, Zn and Cr. A secondary effect on the mobilization was predicted to occur since Ca(ISA)(2) had a positive effect on the pH and the leaching of Pb, Zn and Cr increased with increasing pH. The leaching of Pb varied from 24 up to 66 wt.% of the total Pb amount (1.74+/-0.02 g(kgTS)(-1)) in the dry scrubber residue. The corresponding interval for Zn (7.29+/-0.07 g(kgTS)(-1)) and Cu (0.50+/-0.02 g(kgTS)(-1)) were 0.5-14 wt.% of Zn and 0.8-70wt.% of Cu. Maximum leaching of Cr (0.23+/-0.03 g(kgTS)(-1)) was 4.0 wt.%. At conditions similar to a compacted and covered landfill (4 degrees C, 7 days, 0 vol.% O(2)) the presence of ISA can increase the leaching of Cu from 2 to 46 wt.% if the amount of cellulose-based waste increases 20 times, from the ratio 1:100 to 1:5. As well, the leaching of Pb, Zn, and Cr can increase from 32 to 54 wt.% (Pb), 0.8-8.0 wt.% (Zn), and 0.5 to 4.0 wt.% (Cr) depending on the amount of cellulose and L/S ratio and pH value. Therefore, a risk (alpha=0.05) exists that higher amounts of metals are leached from landfills where cellulose-containing waste and ash are co-disposed. This corresponds to an additional 29 t of Pb and 17 t of Cu leached annually from a compacted and covered landfill in the north of Sweden.     

Typical pollutants in bottom ashes from a typical medical waste incinerator

Incineration of medical waste (MW) is an important alternative way for disposal of this type of hazardous waste, especially in China because of the outbreak of severe acute respiratory syndromes (SARs) in 2003. Thus, far, fly ash has received much attention but less attention has been paid to bottom ash. In this study, bottom ash samples were collected from a typical MW incinerator, and typical pollutants including heavy metals and polycyclic aromatic hydrocarbons (PAHs) in the ash were examined. X-ray fluorescence spectroscopy results indicated that CaO, SiO₂ and Al₂O₃ were the main components of the bottom ash. Inductively coupled plasma-optical emission spectroscopy showed that the ash contained large amounts of heavy metals, including Zn, Ti, Ba, Cu, Pb, Mn, Cr, Ni and Sn. Most of the heavy metals (e.g., Ba, Cr, Ni, and Sn) presented in the residual fraction; whereas Mn, Pb and Zn presented in Fe–Mn oxides fraction, and Cu in organic-matter fraction. Toxicity characteristic leaching procedure tests indicated that the leached amounts of heavy metals were well below the limits. The sum of 16 US EPA priority PAHs (ΣPAHs) varied from 10.30 to 38.14 mg kg^?1, and the total amounts of carcinogenic PAHs ranged between 4.09 and 16.95 mg kg^?1, exceeding the limits regulated by several countries. This research provides basic information for the evaluation of the environmental risk of MW incinerator bottom ash.     

Effect of metal spiking on different chemical pools and chemically extractable fractions of heavy metals in sewage sludge

A laboratory experiment was conducted to study the effect of metal spiking and incubation on some properties and sequentially extractable chemical pools of some heavy metals (F1, two extractions with 0.1 M Sr(NO3)2; F2, one extraction with 1 M NaOAc (pH 5.0); F3, three extractions with 5% NaOCl (pH 8.5) at 90-95 degrees C; F4, three extractions with 0.2 M oxalic acid + 0.2 M ammonium oxalate + 0.1 M ascorbic acid (pH 3.0); and F5, dissolution of sample residue in HF-HClO4 (residual fraction,) and also 1 M CaCl2 and 0.005 M DTPA extractable heavy metals in sewage sludge. Metal spiking and incubation decreased pH and easily oxidizable organic C content of sludge but increased electrical conductivity. Metal spiking and incubation increased F1 fraction of all heavy metals, F2 fraction of Ni, Pb, Cu, and Cd, F3 fraction of Pb, Cu, and Cd, F4 or reducible fraction of Ni, Cu, and Cd and residual fraction of Zn and Pb, but decreased F2 fraction of Zn, F3 of Zn and Ni, F4 fraction of Zn and F5 fraction of Ni, Cu, and Cd. Metal spiking and incubation increased 1 M CaCl2 and 0.005 M DTPA extractable amounts of all heavy metals in sludge except for 0.005 M DTPA extractable Zn, which registered only very marginal decrease.     

Use of sequential leaching, mineralogy, morphology and multivariate statistical technique for quantifying metal pollution in highly polluted aquatic sediments--a case study: Brahmani and Nandira Rivers, India

The particle size distribution, geochemical composition and sequential leaching of metals (Fe, Mn, Ni, Cu, Co, Cr, Pb, Zn and Cd) are carried out in core sediments (<88 microm) from the Brahmani and Nandira Rivers, India. To confirm the contamination of downstream sediments by fly ash, mineralogical and morphological characterizations were carried out. High environmental risk of Co, Pb and Ni is due to their higher availability in exchangeable fraction. The metals like Zn, Cu and Mn represent an appreciable portion in the carbonate phase. Metals such as Zn, Pb, Cd, Co and Ni are associated with reducible phase may be due to adsorption. The organic bound Cu, Zn, and Pb seem to be second dominant fraction among non-lithogenous in Nandira sediments. Factor analysis data reveals that textural parameters, Fe-Mn oxy/hydroxides, organic precipitation and coal fly ash disposals, are individually responsible for the enrichment of heavy metals. The relationships among the stations are highlighted by cluster analysis to identify the contamination levels.     

Removal of Zn(II), Cu(II), Ni(II), Ag(I) and Cr(VI) present in aqueous solutions by aluminium electrocoagulation

The performance of an electrocoagulation system with aluminium electrodes for removing heavy metal ions (Zn2+, Cu2+, Ni2+, Ag+, Cr2O7(2-)) on laboratory scale was studied systematically. Several parameters - such as initial metal concentration, numbers of metals present, charge loading and current density - and their influence on the electrocoagulation process were investigated. Initial concentrations from 50 to 5000 mg L(-1) Zn, Cu, Ni and Ag did not influence the removal rates, whereas higher initial concentrations caused higher removal rates of Cr. Increasing the current density accelerated the electrocoagulation process but made it less efficient. Zn, Cu and Ni showed similar removal rates indicating a uniform electrochemical behavior. The study gave indications on the removal mechanisms of the investigated metals. Zn, Cu, Ni and Ag ions are hydrolyzed and co-precipitated as hydroxides. Cr(VI) was proposed to be reduced first to Cr(III) at the cathode before precipitating as hydroxide.     

Characteristics of slag produced from incinerated hospital waste

Ash produced from a hospital waste incinerator was treated using a high temperature melting process at 1200 degrees C. The quality of the produced slag was characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), leaching tests and sequential chemical extraction of metals. The slag contained large amounts of SiO(2,) CaO, Al(2)O(3), Sn, Ni, Cu, Ba and B. XRD analysis revealed a moderate crystal structure for the melted slag and identified the main crystals as quartz (SiO(2)), kaolinite (Al(2)Si(2)O(5)(OH)(4)), albite (NaAlSi(3)O(8)) and gibbsite (Al(OH)(3)). The observed crystal structure assists in preventing the leaching of heavy metals from the slag. Furthermore, the leaching results found the produced slag to comply with disposal limits set by the US EPA. Results from sequential chemical extraction analysis showed that metals in the slag exhibited the strongest preference to be bound to the residual fraction (stable fraction), which is known to have very low leaching characteristics. Melting was found to stabilize heavy metals in hospital waste successfully and therefore it can be an acceptable method for disposal.