Zinc stabilization efficiency of aluminate spinel structure and its leaching behavior

The feasibility of immobilizing zinc in contaminated soil was investigated by observing the role of zinc reacting with aluminum-rich materials under thermal conditions. To observe the process of zinc incorporation, mixtures of ZnO with alumina precursors (γ-Al(2)O(3) and α-Al(2)O(3)) were fired at 750-1450 °C. Both precursors crystallochemically incorporated zinc into the ZnAl(2)O(4) spinel structure. The incorporation efficiencies of a 3 h sintering scheme were first quantitatively determined by Rietveld refinement analysis of X-ray diffraction data. Different zinc incorporation behavior by these two precursors was revealed, although both resulted in nearly 100% transformation at the highest temperature. Different product microstructures and thermal densification effects were found by observing the sintered products from these two precursors. The leaching performances of ZnO and ZnAl(2)O(4) were compared by a prolonged acid leaching test for 22 d. The leachability analysis pointed to superiority of the ZnAl(2)O(4) structure in stabilizing zinc, suggesting a promising technique for incorporating zinc into the aluminum-rich product. Finally, the sludge collected from water treatment works was calcined and used as an aluminum-rich material to test its ability to stabilize zinc. Successful formation of ZnAl(2)O(4) indicated good potential for employing waterworks sludge to thermally immobilize hazardous metals as a promising waste-to-resource strategy.     

Nickel stabilization efficiency of aluminate and ferrite spinels and their leaching behavior

Stabilization efficiencies of spinel-based construction ceramics incorporating simulated nickel-laden waste sludge were evaluated and the leaching behavior of products investigated. To simulate the process of immobilization, nickel oxide was mixed alternatively with gamma-alumina, kaolinite, and hematite. These tailoring precursors are commonly used to prepare construction ceramics in the building industry. After sintering from 600 to 1480 degrees C at 3 h, the nickel aluminate spinel (NiAl204) and the nickel ferrite spinel (NiFe204) crystallized with the ferrite spinel formation commencing about 200-300 degrees C lower than for the aluminate spinel. All the precursors showed high nickel incorporation efficiencies when sintered at temperatures greater than 1250 degrees C. Prolonged leach tests (up to 26 days) of product phases were carried out using a pH 2.9 acetic acid solution, and the spinel products were invariably superior to nickel oxide for immobilization over longer leaching periods. The leaching behavior of NiAl2O4 was consistent with congruent dissolution without significant reprecipitation, but for NiFe2O4, ferric hydroxide precipitation was evident. The major leaching reaction of sintered kaolinite-based products was the dissolution of cristobalite rather than NiAl2O4. This study demonstrated the feasibility of transforming nickel-laden sludge into spinel phases with the use of readily available and inexpensive ceramic raw materials, and the successful reduction of metal mobility under acidic environments.     

Spinel formation for stabilizing simulated nickel-laden sludge with aluminum-rich ceramic precursors

The feasibility of stabilizing nickel-laden sludge from commonly available Al-rich ceramic precursors was investigated and accomplished with high nickel incorporation efficiency. To simulate the process, nickel oxide was mixed alternatively with gamma-alumina, corundum, kaolinite, and mullite and was sintered from 800 to 1480 degrees C. The nickel aluminate spinel (NiAl2O4) was confirmed as the stabilization phase for nickel and crystallized with efficiencies greater than 90% for all precursors above 1250 degrees C and 3-h sintering. The nickel-incorporation reaction pathways with these precursors were identified, and the microstructure and spinel yield were investigated as a function of sintering temperature with fixed sintering time. This study has demonstrated a promising process for forming nickel spinel to stabilize nickel-laden sludge from a wide range of inexpensive ceramic precursors, which may provide an avenue for economically blending waste metal sludges via the building industry processes to reduce the environmental hazards of toxic metals. The correlation of product textures and nickel incorporation efficiencies through selection of different precursors also provides the option of tailoring property-specific products.     

Synthesis of Cu-rich, Al2O3-stabilized oxygen carriers using a coprecipitation technique: redox and carbon formation characteristics

Chemical looping combustion (CLC) is an emerging, new technology for carbon capture and storage (CCS). Copper-based oxygen carriers are of particular interest due to their high oxygen carrying capacity and reactivity, low tendency for carbon deposition, and exothermic reduction reactions. In this work, CuO-based and Al(2)O(3)-stabilized oxygen carriers with high CuO loadings were developed using a coprecipitation technique. The cyclic redox performance of the synthesized oxygen carriers was evaluated at 800 °C in a laboratory-scale fluidized bed reactor using a reducing atmosphere comprising 10 vol. % CH(4) and 90 vol. % N(2). The CuO content in the oxygen carrier was found to increase with the pH value at which the coprecipitation was performed. The oxygen carrying capacity of the oxygen carrier containing 87.8 wt % CuO was found to be high (5.5 mmol O(2)/g oxygen carrier) and stable over 25 redox cycles. Increasing the CuO content further, i.e. > 90 wt %, resulted in materials which showed a decreasing oxygen carrying capacity with cycle number. It was also shown that the incorporation of K(+) ions in the oxygen carrier can avoid the formation of the spinel CuAl(2)O(4) and significantly reduce carbon deposition.     

Extraction of nanosize copper pollutants with an ionic liquid

Speciation and possible reaction paths of nanosize copper pollutants extracted with a RTIL (room-temperature ionic liquid ([C4mim][PF6], 1-butyl-3-methylimidazolium hexafluorophosphate)) have been studied in the present work. Experimentally, in a very short contact time (2 min), 80-95% of nanosize CuO as well as other forms of copper (such as nanosize Cu, Cu2+, or Cu(II)(ads) (in the channels of MCM-41)) in the samples could be extracted into the RTIL. The main copper species extracted in the RTIL as observed by XANES (X-ray absorption near edge structure) were Cu(II). Existence of Cu-N bondings with coordination numbers (CNs) of 3-4 for copper extracted in the RTIL was found by EXAFS (extended X-ray absorption fine structural) spectroscopy. Interestingly, chelation of Cu(II) with 1-methylimidazole (MIm) in the RTIL during extraction was also observed by 1H NMR (nuclear magnetic resonance). At least two possible reaction paths for the rapid extraction of nanosize copper pollutants with the RTIL might occur: (1) an enhanced dissolution of nanosize CuO (to form Cu2+) and (2) formation of [Cu(MIm)4(H2O)2]2+ that acted as a carrier of copper into the RTIL matrix.     

Low‐ and High‐temperature Processes and Mechanisms in the Preparation of Porous Ceramics via Starch Consolidation Casting

Starch consolidation casting (SCC) is a versatile and well established process for shaping ceramic green bodies by casting starch‐containing suspensions into impermeable molds. The process is based on the ability of starch to swell and absorb water from aqueous ceramic suspensions after heating to approx. 80°C. The swelling factor is highest for potato starch (3.7) and significantly lower for the other starch types (down to approx. 2). A simple mathematical model is presented that allows the minimum consolidation time to be estimated on the basis of the swelling kinetics of starch granules as measured via laser diffraction. The critical temperature range for starch burnout before sintering the ceramic is 300–500°C, as determined by thermal analysis (thermogravimetry and differential thermal analysis). In this temperature range gaseous products may ignite, leading to strongly exothermic thermal effects. If the bodies are large and the starch content high this may lead to defects in the (still unsintered) ceramic green bodies. Therefore this temperature range has to be carefully controlled in the production of ceramics prepared by SCC. The residual pores (remaining after starch burnout) are too large to be closed during the firing step (insufficient driving force for sintering due to too low surface curvature). Therefore they do not contribute to shrinkage, and shrinkage is determined by the ceramic matrix alone. Porosities higher than 50% (corresponding to the maximum nominal starch content) may be obtained by combining SCC with partial sintering (resulting in porosities up to 70%).     

掺La的锆锡钛酸铅陶瓷制备及介电性能

锆锡钛酸铅(Pb(Zr,Sn,Ti)O3)系列陶瓷具有优异的铁电、压电等性能,为制备高质量的陶瓷材料,采用传统的氧化物固相烧结工艺,制备了一组镧(La)元素微量掺杂的锆锡钛酸铅陶瓷,并对样品的铁电和介电性能进行测试表征.结果表明,所采用的制备工艺良好,成瓷好,4组陶瓷样品的组分位于铁电/反铁电相界附近,铁电相和反铁电相共存.     

Mineralization of CCl4 with copper oxide

Experimentally, CCl4 was effectively mineralized by CuO to yield stable inorganic species of CO2 and CuCl2 (CCl4 + 2CuO --> 2CuCl2 + CO2). High CCl4 conversions (63-83%) were found in the mineralization process performed at 513-603 K for 10-30 min. Using X-ray-absorption near edge structure (XANES) and X-ray photoelectron spectroscopies, we found that most CuCl2 was encapsulated in the CCl4-mineralized product solid (mineralization at 513 K for 30 min). At higher mineralization temperatures (563-603 K), CuCl2 was found to be predominant on the surfaces of the mineralization product. Speciation of copper in the mineralization product solid was also studied by extended X-ray absorption fine structure (EXAFS) spectroscopy. Bond distances of Cu-O and Cu-Cl in the CCl4-mineralized product solid were 1.93-1.94 and 2.10-2.12 , respectively, which were greater than those of normal CuO and CuCl2 by 0.03-0.07 A. The increase of the bond distances for Cu-O and Cu-Cl might be due to Cl insertion and concomitant structural perturbation of unreacted CuO in the mineralization process. Forthe second shell around copper atom, bond distances of Cu-(O)-Cu also increased by 0.03-0.05 A, and the coordination numbers of Cu-O and Cu-(O)-Cu decreased, as expected, in the mineralization process. In addition, stoichiometrically excess oxygen atoms were found on the solid surfaces, and they might play an important role in the mineralization of CCl4, leading to the formation of CO2 and Cl. Chloride atoms might be further captured by CuO, yielding CuCl2 in the mineralization process. This work exemplifies the utilization of X-ray spectroscopies (XANES, EXAFS, and XPS) to reveal the speciation and possible reaction pathway in a very complex mineralization process in detail.     

Ozone removal in the sampling of parts per billion levels of terpenoid compounds: an evaluation of different scrubber materials

Some reactive volatile organic compounds (VOCs) are prone to degradation during sampling in an ozone-rich environment. A wide variety of different chemicals have been used to remove the ozone prior to sampling, but the possibility of interference by such chemicals with the sampled VOCs has not been thoroughly examined. In the present investigation, the retention/degradation of four terpenes (alpha-pinene, beta-pinene, 3-carene, and limonene) and isoprene together with some of their oxidation products (alpha-pinene oxide, nopinone, 4-acetyl-1-methylcyclohexene (AMCH), methylglyoxal, and methacrolein) has been studied, using various ozone-removing chemicals in an attempt to evaluate their potential as ozone scrubbers in the sampling of ambient air. The chemicals included in this first screening and their ozone-removing capacity are as follows: KI, MnO2, and Na2SO3 removed ozone for more than 24 h when exposed to 73-78 ppb (150-160 microg/m3) at a sampling flow rate of 500 mL/min. Silanized poly(1,4-phenylene sulfide) (PFS) removed ozone for 5 h, unsilanized PFS removed ozone for 1 h and 50 min, and Na2S2O3 removed ozone for 20 min. The recovery of the selected compounds with the different scrubbers was >95% for all compounds for KI; >95% for the terpenes oxidation products; >90% for the terpenes and isoprene for PFS; >90% for the terpenes and isoprene for MnO2 on copper nets, Na2SO3, and Na2S2O3; and <90% for the terpenes and isoprene for carulite (a commercial mixture between MnO2, CuO, and Al2O3), CuO, and indigo carmine.     

An infrared and X-ray spectroscopic study of the reactions of 2-chlorophenol, 1,2-dichlorobenzene, and chlorobenzene with model cuO/silica fly ash surfaces

The surface-mediated reactions of 2-chlorophenol, 1,2-dichlorobenzene, and chlorobenzene were studied using CuO/ SiO2 as a fly ash surrogate. These compounds served as model precursors that have been implicated in the formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). With FTIR, we determined that reactions of the model precursors with a substrate composed of CuO dispersed on silica result in the formation of a mixture of surface-bound phenolate and carboxylate partial oxidation products from 200 to 500 degrees C. Chemisorption of 2-chlorophenol and 1,2-dichlorobenzene resulted in the formation of identical surface-bound species. Using X-ray absorption near-edge structure spectroscopy, we measured the time- and temperature-dependent reduction of Cu(II) in a fly ash surrogate during reaction with each precursor. It was demonstrated that CuI2O is the major reduction product in each case. The rate of Cu(II) reduction could be described using pseudo-first-order reaction kinetics with Arrhenius activation energies for reduction of Cu(II) of 112, 101, and 88 kJ mol(-1) for 2-chlorophenol, 1,2-dichlorobenzene, and chlorobenzene, respectively. We demonstrate that chlorinated phenol and chlorinated benzene both chemisorb to form chlorophenolate. Although chlorinated phenols chemisorb at a faster rate, chlorinated benzenes are found at much higher concentrations in incinerator effluents. The implication is that chlorinated benzenes may form 10 times more chlorophenolate precursors to PCDD/Fs than chlorinated phenols in combustion systems.     

Solid waste management of a chemical-looping combustion plant using Cu-based oxygen carriers

Waste management generated from a Chemical-Looping Combustion (CLC) plant using copper-based materials is analyzed by two ways: the recovery and recycling of the used material and the disposal of the waste. A copper recovery process coupled to the CLC plant is proposed to avoid the loss of active material generated by elutriation from the system. Solid residues obtained from a 10 kWth CLC prototype operated during 100 h with a CuO-Al2O3 oxygen carrier prepared by impregnation were used as raw material in the recovery process. Recovering efficiencies of approximately 80% were obtained in the process, where the final products were an eluate of Cu(NO3)2 and a solid. The eluate was used for preparation of new oxygen carriers by impregnation, which exhibited high reactivity for reduction and oxidation reactions as well as adequate physical and chemical properties to be used in a CLC plant. The proposed recovery process largely decreases the amount of natural resources (Cu and Al203) employed in a CLC power plant as well as the waste generated in the process. To determine the stability of the different solid streams during deposition in a landfill, these were characterized with respect to their leaching behavior according to the European Union normative. The solid residue finally obtained in the CLC plant coupled to the recovery process (composed by Al2O3 and CuAl2O4) can be classified as a stable nonreactive hazardous waste acceptable at landfills for nonhazardous wastes.     

Roles of Li+ and Zr4+ cations in the catalytic performances of Co(1-x)M(x)Cr(2)O(4) (M = Li, Zr; x = 0-0.2) for methane combustion

Co(1-x)M(x)Cr(2)O(4) (M = Li, Zr; x = 0-0.2) catalysts were prepared via the citric acid method and investigated for catalytic combustion of methane. Substitution at tetrahedral (A) sites with monovalent (Li) or tetravalent (Zr) metal ions led to a decrease or increase of the catalytic activity, respectively. The Co(0.95)Zr(0.05)Cr(2)O(4) catalyst proved to be the most active and its catalytic activity reached 90% of methane conversion at 448 °C, which dropped by 66 °C compared with that of the undoped CoCr(2)O(4) catalyst. XRD and Raman results indicated that lithium or zirconium substitution could modify the spinel structure and electronic properties. For lithium-doped catalysts, oxygen deficiency and a strong surface enrichment in lithium and chromium were detected. Zirconium substitution enhanced the reducibility of zirconium-doped catalysts and decreased the strength constant of both the Co-O band and the Cr-O band, which may contribute to the catalytic activity toward methane combustion. In addition, the prevalent catalytic combustion activity of the zirconium-substituted catalysts could be explained by their higher concentration of suprafacial, weakly chemisorbed oxygen.     

高压烧结AlN（Y2O3）陶瓷的物相组成分析及热导率

用国产六面顶压机在5．0GPa,1300℃～1800℃条件下实现了以Y2O3为烧结助剂的AlN陶瓷体的高压烧结。用XRD对AlN高压烧结体的相组成进行了表征。研究表明：高压制备陶瓷体材料能够有效降低烧结温度和缩短烧结时间,可比传统烧结方法降低400℃以上。Y2O3是AlN有效的低温烧结助剂,在1300℃、1400℃烧结的AlN陶瓷体材料第二相物质以YAlO3和Y4AL2O9为主。当烧结温度高于1600℃,AlN陶瓷的第二相物质主要以Y3Al5O12为主。烧结条件为5．0GPa／1700℃／75min,样品的热导率可达135W／（m·K）。     

纳米铜氧化物的制备及气敏特性研究

分别采用CuCl2,Cu(NO3)2和CuSO4溶液制备出CuO和Cu2O,并测定了其对丁烷、乙醇、汽油、氢气的气敏特性.结果表明:采用CuCl2溶液制备的CuO或Cu2O的灵敏度较高,选择性较好,且Cu2O比CuO的气敏性好.     

The display of retail packs of ground beef after their storage in master packages under various atmospheres

Batches of coarsely ground beef trimmings were each divided into four portions. One portion from each batch was vacuum packaged, then stored at -1·5°C. The other portions were finely ground and distributed in retail packs. The retail packs were master packaged under atmospheres of N(2), CO(2) or O(2) + CO(2) (2:1, v/v), then stored at 2°C. The product was assessed after storage times of up to 32 days. For each assessment, a vacuum pack and a master pack of each type, each containing products from the same batch, were withdrawn from storage. The vacuum packaged product was finely ground and distributed into retail packs. The newly prepared retail packs and those from the master packs were displayed in a retail cabinet in which air temperatures averaged 4 ± 2°C. The appearance of the displayed product from each storage packaging was assessed twice daily until it was judged to be unacceptable. At the beginning and end of the display, the product in each pack was assessed for discoloration and off-odours, the chemical states of the muscle pigment at the exposed surface were estimated, and the surface microflora was characterized. The appearance of the product displayed after storage in a vacuum pack, for times up to 32 days, became unacceptable within 48 h. A product stored in any of the master packs for 1 day appeared unacceptable after 6 h of display. The display life of products stored under N(2) or CO(2) was similar to that of the vacuum packaged products when storage times were between 2 and 24 days but the display life was shorter when the storage times were 28 or 32 days. The display life of products stored under O(2) + CO(2) was similar to that of the vacuum packaged product when storage times were 2, 4 or 6 days, but the appearance of products stored under O(2) + CO(2) for 8 days or longer was unacceptable when master packs were opened. Apart from those latter packs, a product was not discoloured when storage packs were opened. However, all products were discoloured, and the metmyoglobin fractions of the surface pigments had increased, when the product was withdrawn from display. The products in all storage packagings developed flora dominated by lactic acid bacteria. The spoiage flora on products stored in vacuum pack or under O(2) + CO(2) did not attain the maximum numbers of 10(7)/g during either storage or display. Those maximum numbers were attained on products stored under N(2) and CO(2) after 16 and 28 days storage respectively. Some products stored under N(2) for 16 days or longer developed moderate or strong off-odours during display that were ascribable to microbial action. Other products developed only slight, non-microbial off-odours during display. Retail-ready packs or ground beef master-packaged under an oxygen-depleted atmosphere could then have a useful storage life of about 30 days in commercial circumstances.     

陶瓷制品铅镉迁移量食品安全国家标准对比分析研究

GB 4806.4-2016《食品安全国家标准陶瓷制品》已发布和正式实施。该标准为食品接触用陶瓷制品的国家强制性标准,因此国内生产与销售的该类陶瓷制品,都必须符合GB 4806.4标准的要求。该标准基于食品接触用陶瓷制品相关标准清理的研究,整合了铅、镉迁移量食品安全卫生指标,新增了检验技术方法,全面替代了以往针对日用陶瓷器的铅、镉溶出量限制标准,如GB 12651-2003《与食品接触的陶瓷制品铅、镉溶出量的允许极限》、GB 13121-1991《陶瓷食具容器卫生标准》、GB 14147-1993《陶瓷包装容器铅、镉溶出量的允许极限》和GB 8058-2003《陶瓷烹调器铅、镉溶出量的允许极限和检测方法》等国家标准,形成了一套相对完整的陶瓷制品食品安全国家标准体系。本研究对比了陶瓷制品铅、镉迁移量食品安全国家标准和已被替代的国家标准,采用能力验证试验对标准陶瓷样品和市场陶瓷制品进行对比测试分析研究,并对新旧标准进行对比评价,以便于检验监管部门和消费者更好地理解与应用。     

Changes in flavor precursors, pungency, and sugar content in short-day onion bulbs during 5-month storage at various temperatures or in controlled atmosphere

Short-day onion bulbs (cv. TG 1015Y) were stored in 1% O(2,) 99% N(2) air at 5 °C (controlled atmosphere [CA]), or in ambient air at 5, 24, or 30 °C, for 5 mo. Changes in flavor precursors, pungency, and sugar content were investigated. After 5 mo of storage, 1-propenyl-L-cysteine sulfoxide concentrations increased continuously at 5 °C, gradually decreased in CA, slightly increased for 3 mo, and returned to initial levels at 24 °C and decreased below initial levels at 34 °C. Methyl-L-cysteine sulfoxide concentrations remained unchanged in all storage conditions. Onion pungency levels significantly increased at 5 °C, and decreased at 30 °C. Storage in CA and at 24 °C resulted in some fluctuations in pungency but the levels remained similar to initial levels. The calculated pyruvic acid concentrations were approximately 1.0 μmole/mL higher than the measured concentrations, and showed an increase at 5 °C and a slight reduction at 30 °C, consistent with the pungency results. Storage at 5 °C and in CA resulted in slight increases in fructose and glucose concentrations for 3 to 4 mo with subsequent rapid decreases, while sucrose concentrations remained unchanged. However, at 24 and 30 °C, fructose and glucose concentrations continuously decreased, accompanied by a continuous increase in sucrose concentrations. Storage in CA maintained the quality of onions best, as evidenced by the smallest changes in flavor precursors, pungency, and sugar concentrations, while storage at 5 °C resulted in increased pungency. Storage at 24 and 30 °C was tested for the purpose of comparison only; these temperatures are not recommended for commercial storage.     

ETHYL CARBAMATE FORMATION IN GRAIN BASED SPIRITS: PART II THE IDENTIFICATION AND DETERMINATION OF CYANIDE RELATED SPECIES INVOLVED IN ETHYL CARBAMATE FORMATION IN SCOTCH GRAIN WHISKY

Ion chromatographic procedures are described for the identification and determination of a series of cyanide related precursors involved in ethyl carbamate formation in maturing grain whisky produced by the continuous distillation Coffey still process. These precursors include cyanide and copper cyanide complex anions, lactonitrile and isobutyraldehyde cyanohydrin (collectively determined as “measurable cyanide” or MC) and cyanate and thiocyanate anions. The components comprising MC may be determined individually using a pre-chromatographic separation procedure based on anion exchange resins. These techniques have been shown to be applicable for monitoring precursors involved in post-distillation ethyl carbamate formation in maturing grain whisky. Similar ion chromatographic procedures are described for the detection of a range of copper salts, incorporating cyanide, cyanate and thiocyanate, which are naturally occurring deposits within the copper Coffey still. These results are correlated with those based upon X-ray diffraction and secondary ion mass spectrometric techniques. Species identified included cuprous cyanide, cuprous thiocyanate, cuprous oxide, cuprous and cupric sulphide and copper cyanide cluster ions such as CuCN^?, Cu(CN)₂^?, Cu₂(CN)₃^? and Cu₃(CN)₄^? and mixed species Cu(CN)₂S^?, CuSCN^? and CuCNO⁺. In addition, an ion chromatographic procedure developed to investigate the role of carbamyl phosphate in ethyl carbamate formation, showed that conversion took place by means of its thermal decomposition into cyanate ion.     

Toxicity and internalization of CuO nanoparticles to prokaryotic alga Microcystis aeruginosa as affected by dissolved organic matter

This is the first study investigating the toxicity of nanoparticles (NPs) to algae in the presence of dissolved organic matter (DOM). Suwannee river fulvic acid (SRFA), a type of DOM, could significantly increase the toxicity of CuO NPs to prokaryotic alga Microcystis aeruginosa. Internalization of CuO NPs was observed for the first time in the intact algal cells using high resolution transmission electron microscopy (HRTEM), and the cell uptake was enhanced by SRFA. A fast Fourier transformation (FFT)/inversed FFT (IFFT) process revealed that a main form of intracellular NPs was Cu(2)O, and an intracellular environment may reduce CuO into Cu(2)O. The internalization behavior alone did not seem to pose a hazard to membrane integrity as shown from the flow cytometry data. Elevated CuO nanotoxicity by SRFA was related to a combination of a lesser degree of aggregation, higher Cu(2+) release, and enhanced internalization of CuO NPs.     

Ironmaking with ammonia at low temperature

This paper describes the reduction of hematite with ammonia for ironmaking, in which the effect of temperature on the products was examined. The results showed that the reduction process began at 430 °C during heating, and with an increase in temperature, the reduction mechanism changed apparently from a direct reduction of ammonia (Fe(2)O(3) + 2NH(3) → 2Fe + N(2) + 3H(2)O) to an indirect reduction via the thermal decomposition of ammonia (2NH(3) → N(2) + 3H(2), Fe(2)O(3) + 3H(2) → 2Fe + 3H(2)O) at temperatures over 530 °C. The final product obtained at 600 and 700 °C was pure metallic iron, in contrast with that formed at 450 °C, that is, a mixture of metallic iron and iron nitride. The results suggest the possibility of using ammonia as a reducing agent for carbonless ironmaking, which is operated at a much lower temperature than 900 °C in conventional coal-based ironmaking.