Hexavalent chromium in tricalcium silicate: Part I Quantitative X-ray diffraction analysis of crystalline hydration products

The hydration products of CrVI-doped tricalcium silicate (C3S) have been investigated. C3S is the main constituent of Portland cement responsible for the strength and stability of hardened Portland cement paste. Chromium trioxide (CrO3), added as a dopant to C3S, simulates hexavalent chromium waste that may be stabilized in ordinary Portland cement. X-ray diffraction was used to monitor the development of the hydration reaction products from the early stages to the late reaction stages. Leaching studies were carried out to evaluate the stability of the CrVI-containing phases in the hydrated C3S matrix.In monolithic waste forms containing hexavalent chromium, CaCrO4·2H2O was found to form within a few minutes of the hydration reaction. With increasing concentration of Ca2+ in the pore solution, Ca2CrO5·3H2O became the stable species. The chromium in this phase was found to be very mobile in a standard acetic acid leaching test.     

X-ray fluorescence analysis of hexavalent chromium using Kβ satellite peak observed as counterpart of X-ray absorption near-edge structure pre-edge peak

A Kβ satellite peak in X-ray fluorescence (XRF) spectra is observed as a counterpart of the pre-edge peak of the X-ray absorption near edge structure (XANES). In Kβ emission of chromium, a small satellite peak is observed at 5.983-5.988 keV only for hexavalent chromium compounds such as CrO(3), Na(2)CrO(7)·2H(2)O, Na(2)CrO(4)·4H(2)O, K(2)Cr(2)O(7), K(2)CrO(4), Zn(2)CrO(4)(OH)(2)·2H(2)O, PbCrO(4), and BaCrO(4), together with the main peak at 5.947 keV, while trivalent chromium compounds such as Cr(2)O(3) and Cr(OH)(3)·nH(2)O show only the main peak at 5.947 keV. This corresponds to the fact that the K pre-edge peak in XANES is observed only for the hexavalent chromium compounds. The electronic level causing the satellite peak is almost at the same energy level as that causing the pre-edge peak. Our finding not only affects the interpretation of the origin of the pre-edge peaks but also leads to the simple speciation method of chromium compounds using XRF.     

Synthesis of chromium containing pigments from chromium galvanic sludges

In this work the screening results of the scientific activity conducted on laboratory scale to valorise chromium(III) contained in the galvanic sludge as chromium precursor for ceramic pigments are reported. The valorisation of this waste as a secondary raw material (SRM) is obtained by achievement of thermal and chemical stable crystal structures able to color ceramic material. Two different pigments pink CaCr(0.04)Sn(0.97)SiO(5) and green Ca(3)Cr(2)(SiO(4))(3) were synthesized by solid-state reactions using dried Cr sludge as chromium oxide precursor. The obtained pigments were characterized by X-ray diffraction and SEM analysis. Furthermore the color developed in a suitable ceramic glaze was investigated in comparison with the color developed by the pigments prepared from pure Cr(2)O(3). The characterization carried out corroborates the thermal and chemical stability of the synthesized pigments and, especially for the Cr-Sn pink pigment, the powders develop an intense color that is very similar to the color developed by the pigments obtained starting from pure Cr(2)O(3).     

Investigation into the stabilization/solidification performance of Portland cement through cement clinker phases

This research studied the influence of individual heavy metal on the hydration reactions of major cement clinker phases in order to investigate the performance of cement based stabilization/solidification (S/S) system. Tricalcium silicate (C3S) and tricalcium aluminate (C3A) had been mixed with individual heavy metal hydroxide including Zn(OH)2, Pb(OH)2 and Cu(OH)2, respectively. The influences of these heavy metal hydroxides on the hydration of C3S and C3A have been characterized by X-ray diffraction (XRD) and differential scanning calorimetry-thermogravimetry (DSC-TG). A mixture of Zn(OH)2, Pb(OH)2 and Cu(OH)2 was blended with Portland cement (PC) and evaluated through compressive strength and dynamic leach test. XRD and DSC-TG data show that all the heavy metal hydroxides (Zn(OH)2, Pb(OH)2 and Cu(OH)2) have detrimental effects on the hydration of C3A, but only Zn(OH)2 does to the C3S at early curing ages which can completely inhibit the hydration of C3S due to the formation of CaO(Zn(OH)2).2H2O. Cu6Al2O8CO(3).12H2O, Pb2Al4O4(CO3)(4).7H2O and Zn6Al2O8CO(3).12H2O are formed in all the samples containing C3A in the presence of metal hydroxides. After adding CaSO4 into C3A, the detrimental effect of heavy metals increases due to the coating effect of both calcium aluminate sulphates and heavy metal aluminate carbonates. The influence of heavy metal hydroxide on the hydration of C3S and C3A can be used to predict the S/S performance of Portland cement.     

Antimony leaching from uncarbonated and carbonated MSWI bottom ash

The recycling potential of municipal solid waste incinerator (MSWI) bottom ash may be limited by the leaching of antimony (Sb). Therefore, treatment methodologies need to be developed. The pH-dependent leaching behaviour of this oxyanion-forming element in fresh and weathered bottom ash is, however, not understood. Sb leaching was investigated in a wide range of both pH and extent of carbonation. Sb came close to equilibrium with calcium antimonate (Ca[Sb(OH)(6)](2)) at acid and neutral pH. Therefore, adsorption experiments with synthetic calcite (CaCO(3)), ettringite (Ca(6)Al(2)(SO(4))(3)(OH)(12) x 26H(2)O), gypsum (CaSO(4) x 2H(2)O), and portlandite (Ca(OH)(2)) and adsorption modelling to hydrous ferric oxides (HFO) and amorphous aluminium minerals (AAM) were conducted to investigate which minerals decrease Sb leaching below equilibrium with calcium antimonate. At pH>12, calcium antimonate comes into solution due to portlandite formation, but the subsequent increase in Sb leaching is reduced due to strong interaction of Sb with portlandite and ettringite. Ettringite appears to be an important host mineral for Sb at the natural pH of mildly weathered bottom ash (11.8) because a minimum in leaching is observed. When pH is decreased below 10.5, ettringite dissolves and Sb comes into solution, approaching equilibrium with calcium antimonate near pH 9. Gypsum showed no affinity for Sb. The interaction of calcite with Sb was not clear. Adsorption modelling suggested that HFO, rather than AAM, control Sb leaching when pH<9. During carbonation, Sb leaching first increased, most likely due to dissolution of ettringite. Then, Sb leaching decreased, since the pH became low enough to allow sorption by HFO.     

Chloride influence on the incorporation of Cr(2)O(3) and NiO in clinker: a laboratory evaluation

Co-incinerating wastes in cement rotary kilns may introduce elements not usually found in the raw material into the process or even increase the quantity of some minor elements. Chromium and nickel are present in some electroplating sludges. These wastes are hazardous and must be treated and disposed of in a controlled landfill. The objective of this work was to study the incorporation of chromium and nickel oxides when they were added to clinker raw meal. The clinker raw meal used in this study was prepared by mixing pure compounds in the ratio that made it possible to obtain the same phases of an industrial Portland clinker at the end of the heating process. Twelve samples were prepared by adding 0.05, 0.1, 0.3, 0.5, 0.8 and 1.0wt.% of Cr(2)O(3) and 0.05, 0.1, 0.3, 0.5, 0.8 and 1.0wt.% of NiO to the base charge. Also, four more samples were prepared with additions of 0.6% Cr(2)O(3) and 0.1% NaCl, 0.7% Cr(2)O(3) and 0.1% KCl, 0.8% NiO and 0.1% NaCl and 0.8% NiO and 0.1% KCl. In order to study the Cr and Ni incorporation, thermogravimetric (TG) tests were performed, as well as tests in an assembled experimental device. The products were characterized by X-ray fluorescence chemical analysis, microprobe analyses by energy disperse scanning (EDS) and leaching tests. The results showed that the chromium and nickel added were incorporated into the clinker, even when chlorides were present.     

Size-controllable synthesis of chromium oxyhydroxide nanomaterials using a soft chemical hydrothermal route

Chromium oxyhydroxide nanomaterials were synthesised through a simple soft chemical hydrothermal method. The chromium oxyhydroxide materials display platelet morphology with clear edges, ~11 nm in diameter. CrO(OH) nanomaterials synthesised under different conditions were fully characterised by X-ray diffraction (XRD), transmission electron microscopy (TEM) combined with selected area electron diffraction (SAED), scanning electron microscopy (SEM), BET specific surface area analysis, X-ray photoelectron spectroscopy (XPS) and thermal gravimetric analysis (TGA). Bonding of the trivalent chromium from the oxyhydroxide nanomaterials was defined through the analysis of their high resolution XPS spectra for Cr 2p_3/2 and O 1s. The thermal stability of the nanomaterials CrO(OH) was established. This research has developed methodology for the synthesis of chromium oxyhydroxide nanoplates.     

CrO3对Fe2O3+Al铝热反应系统反应过程的影响

用铝热-重力分离法制备了不含铁铝尖晶石（FeAl2O4）的陶瓷内衬复合钢管，并通过热力学计算分析了有关反应的优先顺序，结果表明，在Fe2O3-Al系统中强氧化剂CrO3与Al的反应并不是一步完成而是分步反应，FeAl2O4优先于Cr2O3与Al反应，因而加入CrO3添加剂可有效地去除陶瓷层中的尖晶石相，从而提高复合钢管的耐蚀性能。     

Mechanism of hologram formation in dichromated gelatin with x-ray photoelectron spectroscopy

The mechanism of hologram formation in dichromated gelatin is studied from all aspects with x-ray photoelectron spectroscopy (XPS). It is indicated that the Cr2p(3/2) XPS spectrum of chromium used for hologram formation shows the property of exhibiting a continuousspectrum during the process of dichromated-gelatin hologramformation. By means of curve fitting and drawing a comparisonbetween the obtained spectra and those of some standard substances, itis found that during the process of hologram formation the valence of chromium used for hologram formation changes from Cr(6+) to a quasi-trivalent state to Cr(4+), and finally to Cr(3+). Accordingly, the corresponding compound experiences a change from (NH(4))(2)Cr(2)O(7) to the transient state close to the feature of Cr(OH)(3) to CrO(2), and finally to Cr(3+), cross linking with the gelatin. The essence of the chemical change at different stages of the process of hologram formation was found, and so the present mechanism, which is determined with comparatively abundant proof, should replace previously reported mechanisms, which were too simple, varied, and sometimes even mutually contradictory. According to the experimental results and the fact that a solid-film reaction, which differs from that of the liquid-phase reaction, was studied, possible chemical-reaction equations of the process of hologram formation are established. This becomes the basis for explaining previous findings and expanding further research.     

Full phase analysis of portland clinker by penetrating synchrotron powder diffraction

Fabrication of portland cements commonly depends on X-ray fluorescence (XRF), which measures the elemental compositions. XRF is used to adjust the raw material proportions and to control the process conditions. However, to predict the mechanical strength of the resulting concrete, it is essential to know the phase composition which is, so far, indirectly inferred by the Bogue method. Here, we report a phase analysis of an industrial portland clinker containing six crystalline phases, Ca3SiO5, Ca2SiO4, Ca4Al2Fe2O10, Ca3Al2O6, NaK3(SO4)2, and CaO, by Rietveld refinement of synchrotron X-ray powder diffraction data (lambda = 0.442377 A). Even the minor component, CaO 0.45(2)%, was readily analyzed. We have also carried out a phase study of the same clinker with laboratory X-rays to characterize the changes in the detection limit and errors. Furthermore, by adding a suitable crystalline standard to the same clinker, we have determined the overall amorphous phase content. The procedure established for this state-of-the-art phase analysis shows the high precision that can be achieved by using penetrating X-rays, which is of interest not only in cement chemistry but in other industrially important multiphase systems such as slags, superalloys, or catalysts.     

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.     

Modelling the leaching of Pb, Cd, As, and Cr from cementitious waste using PHREEQC

A leaching model was developed using the United States Geological Survey public domain PHREEQC geochemical package to simulate the leaching of Pb, Cd, As, and Cr from cementitious wastes. The model utilises both kinetic terms and equilibrium thermodynamics of key compounds and provides information on leachate and precipitate speciation. The model was able to predict the leaching of Pb, Cd, As, and Cr from cement in the presence of both simple (0.1 and 0.6M acetic acid) and complex municipal landfill leachates. Heavy metal complexation by the municipal landfill leachate was accounted for by the introduction of a monoprotic organic species into the model. The model indicated Pb and As were predominantly incorporated within the calcium silicate hydrate matrix while a greater portion of Cd was seen to exist as discrete particles in the cement pores and Cr (VI) existed mostly as free CrO4(2-) ions. Precipitation was found to be the dominant mechanism controlling heavy metal solubility with carbonate and silicate species governing the solubility of Pb and carbonate, silicate and hydroxide species governing the solubility of Cd. In the presence of acetic acid, at low pH values Pb and Cd acetate complexes were predominant whereas, at high pH values, hydroxide species dominated. At high pH values, the concentration of As in the leachate was governed by the solubility of Ca3(AsO4)2 with the presence of carbonate alkalinity competing with arsenate for Ca ions. In the presence of municipal landfill leachate, Pb and Cd organic complexes dominated the heavy metal species in solution. The reduction of As and Cr in municipal landfill leachate was crucial for determining aqueous speciation, with typical municipal landfill conditions providing the reduced forms of As and Cr.     

Hydrothermal treatment of bottom ash from the incineration of municipal solid waste: retention of Cs(I), Cd(II), Pb(II) and Cr(III)

The retention of Cs+, Cd2+, Pb2+ and Cr3+ by the compounds formed as a result of the hydrothermal treatment of the bottom ash from the fluidized-bed incineration of municipal solid wastes is examined in this work. The amount of Cs+ retained and the distribution coefficient, Kd, were considerably lower than those for Cd2+, Pb2+ and Cr3+, independently of the type of compounds formed by the different bottom ash treatments. The high percentage of Cs+ retained (31%), with a Kd of 222 ml/g, occurred after treatment of the bottom ash in NaOH at 200 degrees C, where zeolite-type A (Na6[AlSiO4]6.4H2O) was the major compound, together with aluminum tobermorite (Ca5Si5Al(OH)O17.5H2O). In the case of Cd2+, Pb2+ and Cr3+, the amount retained was approximately 99% under all of the conditions studied.     

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.     

Immobilization of heavy metals (Pb, Cu, Cr, Zn, Cd, Mn) in the mineral additions containing concrete composites

The presented work determines the level of heavy metals (Pb+2, Cu+2, Zn+2, Cr+6, Cd+2, Mn+2) immobilization in the composites produced using Ordinary Portland Cement (OPC) as well as of binders containing large amount of mineral additives in its composition-siliceous fly ash (FA), fluidized bed combustion ash (FFA) and ground granulated blast furnace slag (GGBFS). Heavy metals were introduced to cementitious materials in the form of soluble salts as well as components of hazardous wastes (medical ash, metallurgical dust). It has been stated, that the level of heavy metals immobilization is combined with composites composition. Majority of analyzed heavy metals, added to binders' composition in the form of heavy metal salts achieves high level of immobilization, in mortar based on binder with 85% GGBFS and 15% OPC. The lowest immobilization level was reached for chromium Cr+6 added to hardening mortars as Na2Cr2O72H2O. The level ranges from 85.97% in mortars made on blended binder (20% OPC, 30% FFA and 50% GGBFS) to 93.33% in mortar produced on OPC. The increase of the so-called immobilization degree with time of hardened material maturing was found. This should be attributed to the pozzolanic or pozzolanic/hydraulic properties of components used; their effect on microstructure of hardened material is also important. Mineral additions enter the hydration reactions in the mixtures and favor the formation of specific microstructure promoting the immobilization of hazardous elements.     

Reduction of chromate from electroplating wastewater from pH 1 to 2 using fluidized zero valent iron process

Fluidized zero valent iron (ZVI) process was conducted to reduce hexavalent chromium (chromate, CrO(4)(2-)) to trivalent chromium (Cr(3+)) from electroplating wastewater due to the following reasons: (1) Extremely low pH (1-2) for the electroplating wastewater favoring the ZVI reaction. (2) The ferric ion, produced from the reaction of Cr(VI) and ZVI, can act as a coagulant to assist the precipitation of Cr(OH)(3(s)) to save the coagulant cost. (3) Higher ZVI utilization for fluidized process due to abrasive motion of the ZVI. For influent chromate concentration of 418 mg/L as Cr(6+), pH 2 and ZVI dosage of 3g (41 g/L), chromate removal was only 29% with hydraulic detention time (HRT) of 1.2 min, but was increased to 99.9% by either increasing HRT to 5.6 min or adjusting pH to 1.5. For iron species at pH 2 and HRT of 1.2 min, Fe(3+) was more thermodynamically stable since oxidizing agent chromate was present. However, if pH was adjusted to 1.5 or 1, where chromate was completely removed, high Fe(2+) but very low Fe(3+) was present. It can be explained that ZVI reacted with chromate to produce Fe(2+) first and the presence of chromate would keep converting Fe(2+) to Fe(3+). Therefore, Fe(2+) is an indicator for complete reduction from Cr(VI) to Cr(III). X-ray diffraction (XRD) was conducted to exam the remained species at pH 2. ZVI, iron oxide and iron sulfide were observed, indicating the formation of iron oxide or iron sulfide could stop the chromate reduction reaction.     

Effect of NaOH on the vitrification process of waste Ni-Cr sludge

This study investigated the effect of NaOH on the vitrification of electroplating sludge. Ni, the major metal in the electroplating sludge, is the target for recovery in the vitrification. Sludge and encapsulation materials (dolomite, limestone, and cullet) were mixed and various amounts of NaOH were added to serve as a glass modifier and a flux. A vitrification process at 1450 °C separated the molten specimens into slag and ingot. The composition, crystalline characteristics, and leaching characteristics of samples were measured. The results indicate that the recovery of Ni is optimal with a 10% NaOH mass ratio; the recoveries of Fe, Cr, Zn, Cu, and Mn all exhibited similar trends. The results of the toxicity characteristic leaching procedure (TCLP) show that leaching characteristics of the slag meet the requirements of regulation in Taiwan. In addition, a semi-quantitative X-ray diffraction analysis revealed that the main crystalline phase of slag changed from Ca(3)(Si(3)O(9)) to Na(4)Ca(4)(Si(6)O(18)) with a NaOH mass ratio of over 15%, because the Ca(2+) ions were replaced with Na(+) ions during the vitrification process. Na(4)Ca(4)(Si(6)O(18)), a complex mineral which hinders the mobility of metals, accounts for the decrease of metal recovery.     

Extent of oxidation of Cr(III) to Cr(VI) under various conditions pertaining to natural environment

Calculations show that oxidation of chromium oxide (Cr2O3) by oxygen and oxidation of chromium hydroxide (Cr(OH)3) by manganese dioxide (MnO2) are thermodynamically feasible in both aerobic and mildly anoxic environments. Experiments were carried out to determine the rate and extent of chromium oxidation under various conditions, i.e., when Cr2O3 was heated in the presence of oxygen, when Cr(OH)3 and MnO2 mixtures were suspended in aerobic or anoxic aqueous media at various pH values, when Cr(OH)3 and MnO2 mixtures interacted in moist aerobic conditions and when chromium assumed to be Cr(OH)3 and manganese assumed to be MnO2 interacted in the presence of competing electron donors/acceptors, as is the case in chromium-contaminated sludge. Results indicate that trivalent chromium in Cr2O3 could be readily converted to hexavalent chromium at a temperature range of 200-300 degrees C, with conversion rates of up to 50% in 12 h. In aqueous media, Cr(OH)3 was slowly converted to dissolved Cr(VI) in the presence of MnO2, both in aerobic and anoxic conditions, with conversion rates of up to 1% in 60 days. In moist aerobic conditions and in the presence of MnO2, Cr(OH)(3) slowly converted to hexavalent chromium, with up to 0.05% conversion observed in 90 days. Chromium oxidation also occurred in sludge samples, especially under aerobic conditions. However, such transformation was found to be transitory, with the Cr(VI) formed being ultimately reduced back to Cr(III) due to the presence of various reducing agents in the sludge. Nevertheless since up to 17% conversion of Cr(III) to Cr(VI) occurred in sludge under aerobic conditions by 30 days, there is real danger under field conditions of spreading Cr(VI) pollution due to possible intervening rainfall, runoff and percolation.     

Characterisation of products of tricalcium silicate hydration in the presence of heavy metals

The hydration of tricalcium silicate (C(3)S) in the presence of heavy metal is very important to cement-based solidification/stabilisation (s/s) of waste. In this work, tricalcium silicate pastes and aqueous suspensions doped with nitrate salts of Zn(2+), Pb(2+), Cu(2+) and Cr(3+) were examined at different ages by X-ray powder diffraction (XRD), thermal analysis (DTA/TG) and (29)Si solid-state magic angle spinning/nuclear magnetic resonance (MAS/NMR). It was found that heavy metal doping accelerated C(3)S hydration, even though Zn(2+) doping exhibited a severe retardation effect at an early period of time of C(3)S hydration. Heavy metals retarded the precipitation of portlandite due to the reduction of pH resulted from the hydrolysis of heavy metal ions during C(3)S hydration. The contents of portlandite in the control, Cr(3+)-doped, Cu(2+)-doped, Pb(2+)-doped and Zn(2+)-doped C(3)S pastes aged 28 days were 16.7, 5.5, 5.5, 5.5, and <0.7%, respectively. Heavy metals co-precipitated with calcium as double hydroxides such as (Ca(2)Cr(OH)(7).3H(2)O, Ca(2)(OH)(4)4Cu(OH)(2).2H(2)O and CaZn(2)(OH)(6).2H(2)O). These compounds were identified as crystalline phases in heavy metal doping C(3)S suspensions and amorphous phases in heavy metal doping C(3)S pastes. (29)Si NMR data confirmed that heavy metals promoted the polymerisation of C-S-H gel in 1-year-old of C(3)S pastes. The average numbers of Si in C-S-H gel for the Zn(2+)-doped, Cu(2+)-doped, Cr(3+)-doped, control, and Pb(2+)-doped C(3)S pastes were 5.86, 5.11, 3.66, 3.62, and 3.52. And the corresponding Ca/Si ratios were 1.36, 1.41, 1.56, 1.57 and 1.56, respectively. This study also revealed that the presence of heavy metal facilitated the formation of calcium carbonate during C(3)S hydration process in the presence of carbon dioxide.     

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。