Investigation of stabilization/solidification for treatment of electric arc furnace dust: Dynamic leaching of monolithic specimens

Diffusion-controlled leaching of heavy metals (Cr, Ni, Pb and Zn) from electric arc furnace dust treated with ground granulated blast furnace slag (GGBFS) and with ordinary Portland cement (OPC) was evaluated. Monolithic specimens were evaluated under dynamic leaching conditions for 84 days with periodic leachant renewal. The influence of leaching time, nature of the leachant, binder type and the water/solid ratio of the monoliths were investigated. Results obtained showed both binders can immobilize heavy metals in the monoliths under dynamic leaching conditions, with cumulative quantity of leached metal under 0.138 mg (Cr). Alkaline leachant increased metal release from specimens and reducing the water/solid ratio of the monolith allowed for a decrease in the cumulative mass of metals leached. Chemical and mineralogical characterizations indicated that the metals were evenly distributed throughout the specimens for both binders. Decalcification was observed on the OPC monolith border following leaching. This decrease in Ca corresponded to an altered zone (20 μm), identified by scanning electron microscopy. The GGBFS sample did not show an altered zone.     

Preparation and characterization of glass-ceramics via co-sintering of coal fly ash and oil shale ash-derived amorphous slag

A novel preparation method of glass-ceramics from coal fly ash (CFA) and oil shale ash-derived amorphous slag (OSAS) was developed in this study. Effects of important factors such as OSAS/CFA ratio and sintering temperature on the crystalline phase compositions, microstructure, mechanical-chemical properties, heavy metals leaching characteristics, and potential ecological risk assessment of glass-ceramics were investigated. The results showed that the properties of glass-ceramics increased with increasing OSAS/CFA ratio and sintering temperature, and S4 glass-ceramics (100% OSAS) showed the most superior product performances, followed by the S3 (80%OSAS-20%CFA), S2 (60%OSAS-40%CFA), and S1 (100% CFA). As for the products from the mixed sources, the best product properties of S2 glass-ceramics (density, 2.00 ± 0.04 g/cm³; water absorption, 3.11 ± 0.22%; and compressive strength, 106.67 ± 28.42 MPa) were achieved at 1085 °C. S3 glass-ceramics showed the highest density of 2.16 ± 0.04 g/cm³, and lowest water absorption of 0.22 ± 0.01%, and highest compressive strength of 195.99 ± 23.85 MPa at 1085 °C. Specially, the overall energy consumption for preparing S2 and S3 glass-ceramics was estimated to be reduced 23.66–27.00% and 11.67–13.50%, respectively, compared to that of S4 glass-ceramics. In addition, the good chemical stability, low heavy metals leaching concentrations and low potential ecological risk of OSAS-CFA-derived glass-ceramics further confirmed its potential and feasibility as building material in engineering application.     

含砷飞灰固化处理及浸出毒性试验研究

以含As飞灰作为研究对象,采用水泥固化对飞灰进行无害化处理,研究了pH值和液固比以及浸取时间对固化体中As浸出毒性的影响。结果表明：水泥固化体中As的浸出主要受pH值影响,在强酸OH〈2）和强碱（pH〉11）条件下的浸出质量浓度高,而在中性（pH值为5-11）条件下浸出质量浓度低。随着浸取剂与液固比的增加,As的浸出量逐渐增加,但As的浸出质量浓度受稀释作用影响逐渐降低。相对于去离子水体系,醋酸缓冲体系浸出结果较稳定。     

复合早强剂与粉煤灰双掺技术在普通混凝土中的应用

对混凝土进行了三乙醇胺复合早强剂和煤灰掺量实验,结果表明,采用“双掺”技术既可提高混凝土的早期强度,又可改善制品的外观质量,同时还可降低工程成本。     

Stabilization of electric arc furnace dust by the use of cementitious materials: Ionic competition and long-term leachability

Ionic competition in stabilization of major heavy metals from electric arc furnace dust (EAFD) was investigated. The cementitious materials tested (ground granulated blast furnace slag (GGBFS) and ordinary Portland cement (OPC)) were put in contact with solutions made of various combinations of Cr(VI), Pb(II), Zn(II), Ni(II) and Mo(VI) ions. The presence of Ni, Zn or Mo did not influence the Cr fixation by GGBFS and OPC. The ionic competition phenomenon between Cr and Pb was observed for GGBFS in particular.Long-term leaching tests with OPC-EAFD and GGBFS-EAFD showed that OPC is more effective in fixing Cr at 7 days (4.7 mg/L in solution) than GGBFS (79.4 mg/L in solution). GGBFS becomes effective with time and offers a better performance from 56 to 365 days (under 1 mg/L in solution) than OPC (until 11 mg/L in solution). GGBFS and OPC decreased Zn, Pb and Ni concentrations in leaching solutions under 2.5 mg/L.     

Model based prediction of required cut size diameter for fractionation of fly ash from a grate-fired wood chip incineration plant

Utilization of biomass ash as a soil improvement material is limited by the admissible input of heavy metals. It is well known that heavy metal concentrations are increased in fine ash fractions. In this study, two models are investigated to describe the distribution of various heavy metals in different size fractions of fly ash from a grate-fired biomass incineration plant incinerating wood chips. The second model assuming a dependence of the heavy metal concentration from the reciprocal particle diameter to the power of the variable N correlated well with measured concentrations. This model was then used in the calculation of the required cut size of a classifier for the production of a coarse fraction with heavy metal concentrations below limits from a fly ash sample exceeding the Austrian limits for a soil improvement material. The predicted concentrations of the critical heavy metals Cd and Pb and the total mass of the coarse fraction produced corresponded well with measured values, and although the concentration of Zn was considerably underestimated in the model, the produced coarse fraction was within the limits for utilization.     

Adsorption of heavy metal cations using coal fly ash modified by hydrothermal method

In this study, the adsorption properties of synthetic zeolite produced from Brazilian coal fly ash were investigated for some heavy metal cations (Zn, Cu, Mn and Pb). The batch method has been employed, using metal concentrations in solution ranging from 100 to 3000 mg/l. Preliminary statistical analysis has indicated that temperature and time of synthesis of zeolites were the most important variables that affect the their adsorption capacity. Results lead to the conclusion that a hydrothermal treatment can increase from 2 to 25 times the adsorption capacity (CA) of the coal ash comparing to its original capacity. The ion-exchange characteristic of the zeolites was determined using Langmuir, Freundlich and Dubinin-Kaganer-Radushkevich isotherms. The adsorption increases as cation concentrations in aqueous solution increases. The preference order observed for adsorption is Pb > Cu > Zn > Mn.     

Influence of dextrin content and sintering temperature on the properties of coal fly ash-based tubular ceramic membrane for flue gas moisture recovery

In this paper, in order to reduce the preparation cost of high-performance ceramic membrane, coal fly ash-based tubular ceramic membrane for flue gas moisture recovery was prepared, and its properties were optimized from two aspects: pore-forming agent (dextrin) content and sintering temperature. The results show that the ceramic membrane with dextrin content of 3 wt.% and sintering temperature of 1150 ℃ has the best performance. Through characterization, the ceramic membrane exhibits an open porosity of 42.0 %, mechanical strength of 26.6 MPa, average pore size of 0.49 μm, pure water flux of 5616 L/(m² barh). And, it has excellent corrosion resistance in acid and alkali. In addition, the flue gas moisture recovery performance of coal fly ash-based tubular ceramic membrane was studied experimentally. The highest water recovery ratio and the highest recovered water flux is 87.7 % and 6.01 kg/(m² h, respectively.     

Influence of additions of coal fly ash and quartz on hydrothermal solidification of blast furnace slag

Blast furnace water-cooled slag (BFWS) has been solidified hydrothermally with tobermorite formation. The experimental results showed that the addition of fly ash and quartz was favorable to the formation of tobermorite, and the strength development of solidified body depended on both of the tobermorite formation and filling degree of formed tobermorite in the spaces between BFWS particles. The fly ash added appeared to have a higher reactivity than the quartz used during the initial hydrothermal processing due to the higher solubility of glassy phase in fly ash. The tobermorite formation seemed to be very sensitive to the fly ash content, e.g., the addition of fly ash 10-20 mass% was favorable to tobermorite formation, while the excessive addition of fly ash (> 20 mass%) appeared to impede the tobermorite formation. The excessive addition of quartz was also shown to exert a negative effect on the tobermorite formation, which causes strength deduction.     

Hydration reactions of cement combinations containing vitrified incinerator fly ash

One treatment option for municipal solid waste incinerator fly ash (IFA) is vitrification. The process yields a material containing reduced levels of trace metals relative to the original ash. The material is glassy and potentially suitable as a cement component in concrete. This paper examines the vitrification of an IFA and studies the hydration reactions of combinations of this vitrified material and Portland cement (PC). Isothermal conduction calorimetry, powder X-ray diffraction (XRD), thermogravimetry (TG) and scanning electron microscopy were employed to study the hydration reactions. As the levels of vitrified ash increase, the quantities of AFt phase produced decrease, whilst quantities of AFm phase increase, due to the reduced levels of sulfate in the vitrified ash. The levels of calcium silicate hydrate (CSH) gel (inferred from estimates of quantities of gel-bound water) remain constant at 28 days regardless of vitrified ash content, indicating that the material is contributing toward the formation of this product.     

Waste recycling of coal fly ash for design of highly porous whisker-structured mullite ceramic membranes

Coal fly ash, a solid state waste massively produced from coal combustion, is considered to be highly hazardous to the environment due to its persistently toxic trace elements. High-value added waste recycling is a promising technique to address this issue. In this work, a waste-to-resource strategy is proposed for design of highly porous whisker-structured mullite ceramic membranes derived from waste coal fly ash and Al(OH)₃ as raw materials and MoO₃ as a single sintering additive. These were characterized in terms of their dynamic sintering behavior, shrinkage, bulk density, porosity, phase evolution, microstructure, pore size distribution, N₂ permeation flux, and mechanical strength. Addition of molybdenum trioxide effectively inhibited the sintering densification of membranes while at the same time forming a metastable low viscosity liquid at lower temperatures. This enables formation of a novel and more highly porous whisker-interlocked structure and accelerates the growth of mullite whiskers with controllable morphologies. Without degradation of mechanical properties, the open porosity increased significantly from 41.65 ± 0.13% to 58.14 ± 0.15% with increasing MoO₃ content from 0 to 20 wt.% without any pore-forming agent, while shrinkage and pore size decreased. The method proposed in this study is expected not only to give a new and facile insight for high-value added recycling of waste coal fly ash but also to fabricate low-cost high performance ceramic membranes with novel structures for further environmental applications.     

Behavior of combined fly ash/slag‐based geopolymers when exposed to high temperatures

The high temperature performance up to 800^°C of combined fly ash (FA) and slag geopolymers at the ratio of 100, 65/35, 50/50, 35/65 and 100% (wt‐%) is presented in this paper. Geopolymers are alternative novel binders to conventional Portland cement and are generally believed to provide superior fire resistant properties due to their ceramic‐like characteristics. This paper presents new data on the behavior of geopolymers made with combined FA/slag mentioned previously, which were mixed with alkaline materials with molecular silicate modulus (Ms=SiO₂/Na₂O) of 0, 0.5, 1.0, 1.5 and 2.0 with sodium (Na) dosages of 4 and 8 (wt‐%). Altogether 60 mixes were made yielding compressive strengths between 3 and 83 MPa. Behavior of the material to high temperatures was investigated by exposing the specimens to 800^°C and testing for compressive strengths. It was found that as the initial strength increases, the residual strength exponentially decreased. The compressive stress versus strain relationships showed that the ductility of the specimens decreased as the initial strength increased. The ability of the materials with high ductility (i.e. less brittleness) to accommodate thermal incompatibilities arising from uneven temperatures arising during heating is concluded to be the major factor contributing to the reduced strength losses. Copyright © 2009 John Wiley & Sons, Ltd.     

Simultaneous Removal of Heavy Metals and PCDD/Fs from Hospital Waste Incinerator Fly Ash by Flotation Assisted with Hydrochloric Acid

Hospital solid waste (HSW) incinerator fly ash was designated as a special controlled waste because of its high concentrations of toxic heavy metals, polychlorinated dibenzo-p-dioxins, and dibenzofurans (PCDD/Fs). Most of the PCDD/Fs along with carbon constituents including powder activated carbon and unburned carbon in fly ash could be removed by column flotation on the basis of their hydrophobicity. The feasibility of extracting heavy metals from fly ash by adding a little of hydrochloric acid to the slurry during the flotation process was examined in this paper. The results showed that the acidic pulp could contribute to the high extraction ratio of the heavy metals, but the performance of decarburization and removal of PCDD/Fs was inhibited at very low pH value. Given consideration to the removal of two toxic matter including PCDD/Fs and heavy metals in HSW incinerator fly ash, the appropriate pulp pH value should be controlled at about 5. After flotation, both PCDD/Fs and heavy metals in the tailings could simultaneously meet the permitted limits of a landfill site of municipal solid waste in China. It was suggested that flotation with the assistance of an appropriate amount of acid might be a potential technology for the treatment of HSW incinerator fly ash.     

Non-dispersive selective extraction of germanium from fly ash leachates using membrane-based processes

ABSTRACT

Non-dispersive selective extraction of Ge(IV) tartrates was carried out from simulated fly ash solutions containing heavy metals through supported liquid membranes (SLM). The optimum transport was obtained using a PTFE membrane containing Alamine 336 5%v/v in the condition of tartaric acid 2.76 mmol/L and HCl 1 mol/L in feed and strip phases, respectively. Under this condition, a hollow fiber (HF) SLM experiment was conducted. The results showed that this system could transport germanium from the feed to the strip phase so much faster than the flat sheet (FS) SLM system. The rate of transport through HFSLMs is comparable to dispersive extractions.

Abbreviation: A: Effective area of the membrane (cm²); BDL: Below detection limit; C_f,: Feed concentration (mg/L); C_t,: Initial concentration (mg/L); D: Distribution coefficient; ELM: Emulasion liquid membranes; FSSLM: Flat sheet supported liquid membrane; HF: Hollow fiber; LLX: Liquid-liquid extraction; P: Permeation coefficient (m/h); PTFE: Poly tetra fluoro ethylene; PVDF: Polyvinylidene difluoride; T: Tartrate species (C₄H₄O₆); T: Temperature (K); %T:Germanium transport effeciency; V: Volume of feed solution (cm³); t: time (h); η: Viscosity (P.s (c.P)); κ: Boltzmann constant; r: Ionic radius of species; τ: Tortuosity of the membrane; ρ: Porosity; α: Separation factor.     

利用响应面法优化皂角苷浸提飞灰中重金属的处理条件

通过响应面法对皂角苷浸提飞灰中Cu、Zn、Pb和Cd 4种重金属的实验条件进行优化,选取pH、皂角苷浓度、离子强度、温度、时间和固液比6个因素进行中心组合设计,使用design-expert8.0软件进行数据拟合,建立了Cu、Zn、Pb和Cd去除总量的工艺数学模型,通过方差分析得到6个因素对浸提液中4种重金属去除总量的主效应关系为： pH>固液比>离子强度>皂角苷浓度>温度>时间。对重金属去除总量数据进行design-expert8.0软件优化,得到皂角苷浓度为41.2g·L^-1、时间为13.54 h、离子强度为0.64 mol·L^-1、pH为2、固液比为1%和温度为23.4℃时,重金属总去除量达最大值,Cu、Zn、Pb和Cd的去除率分别达到55.12%、6.20%、17.80%和78.11%。     

硅铝调控与晶种诱导对水热稳定飞灰中重金属的协同影响

研究了选取的粉煤灰、膨润土、高岭土、硅藻土作为外源硅铝调理剂添加与雪硅钙石人工晶种诱导对150℃水热法稳定垃圾焚烧飞灰中重金属Pb、Zn、Cu、Cd、Cr的协同影响。飞灰由于富钙而低硅铝的元素特征,导致其在水热条件下无法直接合成沸石类,Pb的浸出浓度仍然超标;当单一或混合添加硅铝调理剂添加量为10%时,其水热产物中有水钙铝榴石或加藤石生成;提高添加量至30%时,均有目标雪硅钙石的生成,这与30%添加量下飞灰中Ca/（Al+Si）元素比接近雪硅钙石的理想元素比值0.67~1.20直接相关。混合添加30%的粉煤灰与硅藻土为最佳选择,水热产物Pb的浸出浓度降低至0.30 mg·L^-1,且在此基础上再添加3%的诱导晶种可加速从第6 h开始即合成雪硅钙石,并使Pb的浸出浓度下降到最低值0.28 mg·L^-1。硅铝调控（30%的复合硅铝调理剂,其中粉煤灰：硅藻土为1：1）与晶种诱导的协同影响下高效生成雪硅钙石,并显著抑制Pb、Zn等在水热过程中向液相的转移、降低其在水热液相中的浓度,使飞灰中的重金属在水热后确实稳定于水热固相产物中而非迁移至水热液相造成污染转移,真正实现了飞灰中重金属的固定化。     

Effect of pretreatment conditions on the determination of major and trace elements in coal fly ash using ICP-AES

Microwave-assisted acid digestion (MW-AD) followed by atomic spectrometries such as inductively coupled plasma-atomic emission spectrometry (ICP-AES) was examined for the determination of major and trace elements in coal fly ash (CFA). Effective digestion conditions were studied using four certified reference materials of CFA, with particular focus on the composition of acid mixture and the removal of HF after MW-AD. When MW-AD was conducted without using HF (HNO₃+H₂O₂), the tested elements yielded fairly poor recoveries. When MW-AD with HF (HNO₃+HF+H₂O₂) was carried out, two methods for HF removal were attempted, H₃BO₃ addition and evaporation of acids. In the former method, while the recoveries of major elements (Al, Ca, Fe, and Mg) were satisfactory, those of trace elements were not satisfactory; in particular, the recovery of Pb was fairly low. In the latter method, the recoveries of Al, Ca, and Mg were extremely poor; however, those of other elements including the trace elements (Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn) were satisfactory. In this paper, the optimization of the digestion method for ICP-AES is discussed. Further, the advantages and limitations of ICP-AES in the determination of elements in CFA are assessed.     

Adsorption of Cu from water using raw and modified coal fly ashes

In this study, we found that both raw and modified coal fly ashes effectively adsorb Cu²⁺ from wastewater. The adsorption capacities followed the order CFA> CFA-600> CFA-NaOH. The adsorption isotherms for Cu²⁺ on the raw and modified coal fly ashes fit the Langmuir, Freundlich, and DKR isotherms quite well. These adsorptions were endothermic in nature; the values of E (between 1.3 and 9.6 kJ mol⁻¹) were consistent with an ion-exchange adsorption mechanism. The adsorptions of Cu²⁺ onto CFA, CFA-600, and CFA-NaOH followed pseudo-second-order kinetics.     

Effect of CaO/SiO2 ratio on phase transformation and properties of anorthite-based ceramics from coal fly ash and steel slag

Anorthite-based ceramics were produced entirely from coal fly ash and steel slag. The effect of the CaO/SiO₂ ratio (0.12–0.8) on the phase transitions was examined by adding steel slag to coal fly ash in the range of 10–50 wt%, and a temperature range of 900–1200 °C. The influence of CaO/SiO₂ and sintering temperatures on the technological properties were assessed by response surface methodology (RSM) and correlated with the phase changes. The results revealed that anorthite was the main phase for the CaO/SiO₂ ratio ranging from 0.12 to 0.56, while at 1200 °C, a ratio of 0.8 involved a high content of gehlenite. RSM showed that the CaO/SiO₂ ratio was the main influencing factor on the density, while the variation of apparent porosity and compressive strength were more affected by sintering temperature. The crystallisation of the anorthite phase significantly enhanced the properties of the obtained ceramics, whereas the appearance of gehlenite reduced the mechanical strength. The optimum conditions to fabricate anorthite-based ceramics with suitable properties were found to be a CaO/SiO₂ ratio of 0.46 and a temperature of 1188 °C. The optimised anorthite-based ceramic exhibited a low thermal conductivity (0.39 W/m.K) and a dielectric constant of 6.03 at 1 MHz, along with a compressive strength of 41 MPa, which makes this sample a potential candidate for insulator applications.     

In-situ synthesis of NaP zeolite doped with transition metals using fly ash

Here, a novel approach has been proposed to synthesize NaP zeolite adsorbents doped with transition metals (M-NaP) using the Na₂SiO₃ and NaAlO₂ compounds extracted from fly ash via activation and stage treatment. The preparation process of M-NaP employed the in-situ synthesis in combination with organic complexation method. The effects of the addition amounts and valence state of transition metals on the zeolite products were investigated. The crystalline phase, morphology, and particle size of M-NaP were characterized using X-ray diffractometry (XRD), Scanning electron microscopy (SEM), and Laser particle size analyzer (PSD). The doping process was investigated using X-ray photoelectron spectroscopy (XPS) and Materials Studio. The adsorption performance of M-NaP was tested by the adsorption of Zn²⁺. The optimal molar ratio of n(Al₂O₃)/n(M) was identified as 8:1 for Co–NaP, Ni–NaP, and Fe–NaP, compared with 6:1 for Ti–NaP. The influence of transition metals on adsorption was: Co–NaP > Ni–NaP > Ti–NaP > Fe-NaP. Due to largest surface area of Co–NaP (162.5 m²/g, five times than that of NaP-RAW), the maximum removal rate of Zn²⁺ was above 99.50% at 25°C. The existence state of transition metals in M-NaP primarily included: isomorphous substitution and balance of the skeletal charge, with the latter in majority. The simulation of Materials Studio indicates that Si at T4 was first substituted and then, Si at T3 opposite T4 was replaced when the replacement of Si in different sites occurred.