Search

The EAF steelmaking process generates 10–20 kg of dust per ton of steel, containing 15–30% zinc, making it a valuable secondary zinc resource. In this work, selective dissolution and kinetics of leaching zinc from lime (CaO) treated EAF dust using NaOH, KOH, and LiOH alkaline solutions were investigated. By reacting with CaO, insoluble ZnFe 2 O 4 in EAF dust is converted to soluble ZnO and stable Ca 2 Fe 2 O 5. Optimal zinc leaching conditions were achieved after 2 h at 70 °C and a S/L ratio of 1/300 (mg/ml). Among the alkaline solutions used, the zinc leaching rate was highest using 2 M NaOH solution at 99% zinc recovery. On the other hand, thermodynamic solubility calculations indicate that KOH is a better candidate for practical extraction as it can dissolve 6–8 times more zinc than NaOH. The prevailing rate-controlling mechanisms when using NaOH, KOH, and LiOH solutions were found to be the same. From 25 °C to 50 °C, chemical reaction was primarily rate-limiting. In contrast, from 50 °C to 70 °C, the controlling step later shifted to a product layer diffusion control – implying that higher temperatures and finer particle size are vital to achieving high zinc leaching rates. Finally, a solid by-product containing Ca 2 Fe 2 O 5 and CaO only, which can be recycled in the iron and steelmaking process, was obtained via calcination at 500 °C. • Alkaline leaching of CaO-treated EAF dust ensures selective zinc dissolution. • NaOH leaching allows fastest zinc dissolution followed by KOH and LiOH leaching. • KOH solution dissolves 6-8 times more zinc than NaOH solution of same concentration. • Leaching kinetics shifts from chemical-reaction control to diffusion control at 50 °C. • Calcination of leaching residue generates recyclable Ca 2 Fe 2 O 5 and CaO by-products. [ABSTRACT FROM AUTHOR]

The physicochemical properties of the Ni-Co-Fe-O system are important to the high-temperature oxidation of the Ni-Co-Fe based alloy, such as superalloys and high-alloy steels. The equilibrium phase relations between the Ni-Co-Fe alloy and its oxide at elevated temperature were systematically investigated using experimental and assessment method. The iso- p O 2 lines and iso-concentration lines of oxides in the entire range of the oxygen partial pressure and composition at 1673 K were evaluated, and the high-temperature oxidation path of the Ni-Co-Fe alloy was qualitatively examined. Using the thermodynamic findings allows to ascertain the high-temperature oxidation phenomena of the Ni-Co-Fe based alloy. [ABSTRACT FROM AUTHOR]

Abstract: Boron-containing compounds have been listed as one of environmentally hazardous substances in Japan since 2001, and known to condense in coal fly ash particles during coal combustion and coal fly ash formation in coal-fired electric power stations. So far, the authors have revealed that the speciation of boron-containing compounds in coal fly ash particles is mostly a calcium orthoborate or pyroborate. In this research, the speciation of boron compounds in standard coals and their char generated by laboratory-scale combustion test has been investigated by using a microwave-assisted acid digestion method and a Magic-Angle-Spinning Nuclear Magnetic Resonance (MAS-NMR) in order to reveal the vaporization behavior of boron in standard coals during combustion at relatively low temperature. Three isolated peaks are observed in 11B MAS-NMR spectra of standard coals, and all of them are attributed to four-oxygen-coordinated boron atom. Around 50% of boron vaporizes even though heating condition is 200°C and O2 =25%, and the percentage of vaporization reaches higher value than 80% at 400°C and O2 =25%. The remaining boron contents in ash components are relatively small, and it suggests that most of boron in standard coals exist with relatively volatile carbon contents, and they volatilize in the very early stage of coal combustion. [Copyright &y& Elsevier]

Steel slag is a waste produced in the steelmaking process. Because of its physical structure and chemical composition, it can be used as a metal ion removal agent in wastewater. In this study, column and batch experiments were carried out in order to determine the removal efficiency, competitive adsorption mechanism and influencing factors of the Cr3+ and Zn2+ by slag in acidic condition. A single column experiment showed that the removal rates of Cr3+ and Zn2+ by slag were 85.79% and 76.52%, respectively. However, when the two ions coexisted, the presence of Cr3+ could promote slag hydrolysis and produce more active adsorption sites since the solubility product of Cr(OH) 3 was 6.3 × 10−31, which was smaller than that of Zn(OH) 2 (3.0 × 10−17) at 25 °C. Moreover, the kinetic adsorption constant of Zn2+ was larger than that of Cr3+, and the hydration radius of Zn2+was smaller than that of Cr3+; thus Zn2+ could rapidly occupy more active sites on slag than Cr3+, which might increase the removal efficiency of Zn2+ and decrease the removal efficiency of Cr3+ in mixed column. The Cr3+ or Zn2+ and OH− released by the slag hydrolysis formed precipitation when the pH value of the solution was greater than 4.6 or 6.8, respectively. In addition, amorphous carbonate, calcium silicate hydrate deposit, and ferrate or silicate could also be formed after the Cr3+ and Zn2+ were removed by the slag. However, the hydroxide and carbonate would rerelease metal ions and reduce the removal efficiency of the slag in an acidic flow column. Image 1 • The coexistence of Cr3+ and Zn2+ will affect the removal efficiency of steel slag. • Different Ksp, k 2 and hydration radius of two ions leads to competitive adsorption. • Stability of the formed compounds affects the removal rate of metal ions by slag. • Hydroxides and amorphous carbonates might release metal ions in acidic conditions. [ABSTRACT FROM AUTHOR]

Abstract A high-purity zeolite 4A was synthesized by the hydrothermal method using fly ash as the raw material. The effects of sodium hydroxide (NaOH) or/and sodium carbonate (Na 2 CO 3) on the activation of fly ash were studied, and the removal efficiency of Cu2+ in aqueous solution was also investigated for the synthesized zeolite. The formation process of the zeolite from fly ash was surveyed by ex situ techniques such as X-ray diffraction (XRD), thermogravimetric analysis and differential scanning calorimetry (TG-DCS), scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDX) and Fourier transform infrared spectroscopy (FTIR). The important influential factors of energy and water consumption were analysed by orthogonal tests, and the best conditions for green synthesis were accurately determined through batch tests. The factors affecting the green synthesis of zeolite are the alkali mixture ratio, alkali melting temperatures, solid-to-liquid ratios, crystallization times and crystallization temperatures. The alkali mixture ratio was indicated to be an important factor for green synthesis according to the results of the orthogonal test. Compared with the use of alkali alone, when NaOH and Na 2 CO 3 were mixed at a mass ratio of 1:2.8, the alkali melting temperature (760 °C) and solid-to-liquid ratios (1:5) were both lower, the crystallization time (4 h) was shorter in the zeolite synthesis process, and the relative crystallinity was the highest at 75.8%. The removal rate of 100 mg/L Cu2+ solution from pH 3 to pH 7 by 0.18 g of zeolite synthesized for 60 min was close to 100%, and the adsorption capacity was 55.5 mg/g. After the zeolite was desorbed and reused 4 times, the removal efficiency of Cu2+ was maintained at 73% at a pH of 3. Highlights • The synergistic reaction of NaOH and Na2CO3 has an important effect on the zeolite green synthesis. • The optimal parameters gained by batch test are as green synthesis condition of two alkali mixture. • The synthetic zeolite can efficiently adsorb Cu2+ from acid solution and be reused. [ABSTRACT FROM AUTHOR]

Economic growth is associated with a rapid rise in the use of natural resources within the economy, and has potential environmental impacts at local and/or global scales. In today's globalized economy, each country has indirect flows supporting its economic activities, and natural resource consumption through supply chains influences environmental impacts far removed from the place of consumption. One way to control environmental impacts associated with consumption of natural resources is to identify the consumption of natural resources and the associated environmental impacts through the global supply chain. In this study, we used a global link input–output model (GLIO, a hybrid multiregional input–output model) to detect the linkages between national nickel consumption and mining-associated global land-use changes. We focused on nickel, whose global demand has risen rapidly in recent years, as a case study. The estimated area of land-use change around the world caused by nickel mining in 2005 was 1.9 km 2 , and that induced by Japanese final demand for nickel was 0.38 km 2 . Our modeling also revealed that the areas of greatest land-use change associated with nickel mining were concentrated in only a few countries and regions far removed from the place of consumption. For example, 57.7% of the world's land-use changes caused by nickel mining were concentrated in five countries in 2005: Australia, 13.7%; Russia, 12.9%; Indonesia, 12.5%; New Caledonia, 10.4%; and Colombia, 8.2%. The mining-associated land-use change induced by Japanese final demand accounted for 19.5% of the total area affected by land-use change caused by nickel mining. The top three countries accounted for 70.6% (Indonesia: 47.0%, New Caledonia: 16.0%, and Australia: 7.7%), and the top five accounted for 82.4% (the Philippines: 7.5%, and Canada: 4.3%, in addition to the top three countries and regions). [ABSTRACT FROM AUTHOR]

[Display omitted] • Wet-grinding could destroy the crystal structure of insoluble phase in fly ash. • High polymer aluminosilicate in fly ash was broke into oligomer by wet-grinding. • Without aging, wet-grinding material could directly synthesize zeolite P. • Pb2+ ion adsorption capacity by synthetic zeolite in solution reached 497.01 mg/g. • Pb2+ ion removal rate of the synthetic zeolite was more than 92 % after 6 recycles. Using fly ash as a raw material to synthesize zeolite is an effective way to obtain cheap adsorbent. However, the high energy consumption of activating the insoluble silica-alumina phase of fly ash limits its practical application. In this study, a low-energy, wet-grinding hydrothermal method was used to activate the insoluble phase of fly ash to synthesize zeolite P, and the adsorption capacity of zeolite for lead ion in solution was studied. Wet-grinding can reduce fly ash particle size to nanometer scale and break long-chain Q4(Al) into short-chain low-polymer. Without aging, the activated material could directly synthesize zeolite P with a relative crystallinity of 89.37 %. Compared with the common alkali-fusion method, the wet-grinding method reduced energy consumption by 45.93 % and increased synthetic zeolite relative crystallinity by 7.51 %. The synthesized zeolite P could effectively remove Pb2+ ions from solution through ion exchange and hydroxyl reaction, and the adsorption capacity reached 497.01 mg/g. [ABSTRACT FROM AUTHOR]

Zeolite-geopolymer composites synthesized using industrial solid waste have mechanical strength, high specific surface area and cation exchange ability. This self-supporting adsorbent can replace natural heulandite zeolite to remove metal ions. In this study, a zeolite-geopolymer composite with a high zeolite content was synthesized by a simple two-step process using fly ash and metakaolin as raw materials. The compressive capacity, pore structure and adsorption ability for Pb(II) in the solution of the composite were analyzed and compared with natural heulandite zeolite. Through the two-step synthesis, the dynamic conditions of zeolite crystallization and geopolymer solidification were determined, and the zeolite-geopolymer composite with 57.5% zeolite A content and 6.42 MPa compressive strength was successfully prepared. The composite had hierarchical pore sizes, including microporous, mesoporous and macroporous pores, and its specific surface area was larger than that of natural heulandite zeolite. The Pb(II) adsorption capacity of the composite could reach 446.73 mg/g through ion exchange and hydroxyl reactions in solution, which was higher than the value of 323.37 mg/g for natural heulandite zeolite. Therefore, zeolite-geopolymer composites with high zeolite content synthesized by the simple two-step method can be used as self-supporting adsorbents to replace natural heulandite zeolites for removing metal ions from water. [Display omitted] • The zeolite-geopolymer block was synthesized by a two-step method using fly ash and metakaolin. • The block composite had the zeolite content of 57.5% and compressive strength of 6.42 MPa. • During two-step synthesis, the kinetic conditions for crystallization and curing was analyzed. • The zeolite-geopolymer composite removed Pb(Ⅱ) by ion exchange and hydroxyl group reaction. • The removal capacity of Pb(II) by zeolite-geopolymer composite reached 446.73 mg/g. [ABSTRACT FROM AUTHOR]

This article will outline the historical transition in the flow of phosphorus in steelmaking technology, and examine the current and future phosphorus flow in steel production and the peripheral steelmaking processes. History provides many instances of innovative changes in steelmaking processes driven by various issues associated with raw materials which emerged over time, such as supply, quality and cost issues. The major steel countries with a long history, including Sweden and Japan, have shown flexibility in their ability to adapt to the changes in the value of resources and geopolitical conditions over times, and have enacted survival resource utilization measures over many centuries, leading to improvements in their respective steelmaking processes. Considering these success stories, it stands to reason that the ideal state of steelmaking is one with a clear stance with regard to resource policy. [ABSTRACT FROM AUTHOR]

Zinc ferrite (ZnFe 2 O 4 ), one of the major forms of zinc in Electric Arc Furnace (EAF) dust, is very difficult to chemically dissolve in aqueous solutions. In our previous work, a pretreatment process referred to as “CaO treatment” was proposed as a key technology for transforming the ZnFe 2 O 4 in EAF dust to ZnO and Ca 2 Fe 2 O 5 without carbothermic reduction. Because this CaO treatment also enables the preferential removal of chloride, fluoride and heavy metals during heating with essentially no evaporation loss of zinc or iron, the CaO treated product, or “CaO treated dust”, consists mainly of ZnO and Ca 2 Fe 2 O 5 , and contains no chloride, fluoride or heavy metals. Zinc leaching, which involves dissolving ZnO into either acidic or alkaline solutions, makes it possible to recover zinc from the CaO treated dust. In this study, the feasibility of the alkaline leaching of CaO treated dust was investigated using a NaOH solution for the selective leaching of zinc over iron and calcium, and the effect of temperature, reaction time, NaOH concentration and solid/liquid (S/L) ratio were examined. It was found that significantly more zinc was extracted from the CaO treated dust than the as-supplied raw dust by the NaOH solution. Nearly complete zinc extraction from the CaO treated dust was achieved without any notable dissolution of iron and calcium, which remained as Ca 2 Fe 2 O 5 and Ca 3 Fe 2 (OH) 12 in the leach residue. These residues can be supplied to the steel making industry as flux for the dephosphorization of hot metal or a raw material for the blast furnace. [ABSTRACT FROM AUTHOR]

Abstract: Coal fly ash emitted from coal-fired electric power stations generally contains environmentally regulated trace elements. In particular, boron, arsenic, and selenium have been recognized as troublesome trace elements because elutions from the fly ash contain them. In order to design an effective removal process for these trace elements, we have developed and investigated an acid-washing process. The dissolution behavior of selenium from coal fly ash particles was focused on for the improvement of the process, and was found to greatly depend on the pH of the acid solutions. The species of selenium in solutions with a pH of around 0–1 was determined to be H2SeO3. The dissolved H2SeO3 transformed into and adsorbed onto the surface of the ash particles in solution upon elevation of the pH. The re-elution of the absorbed as at a pH of 10 was also confirmed, and will cause the elution of the excess selenium from the acid-washed ash. [Copyright &y& Elsevier]

Abstract: Phosphorus is indispensable for agricultural production. Hence, the consumption of imported food indirectly implies the import of phosphorus resources. The global consumption of agricultural products depends on a small number of ore-producing countries. For sustainable management of phosphorus resources, the global supply and demand network should be clarified. In this study, we propose the virtual phosphorus ore requirement as a new indicator of the direct and indirect phosphorus requirements for our society. The virtual phosphorus ore requirement indicates the direct and indirect demands for phosphorus ore transformed into agricultural products and fertilizer. In this study, the virtual phosphorus ore requirement was evaluated for the Japanese economy in 2005. Importantly, the results show that our society requires twice as much phosphorus ore as the domestic demand for fertilizer production. The phosphorus contained in “eaten” agricultural products was only 12% of virtual phosphorus ore requirement. [Copyright &y& Elsevier]

Abstract: Coal fly ash emitted from coal thermal power plants generally contains tens ppm of arsenic, one of the hazardous elements in coal, during combustion and their elution to soil or water has become a public concern. In this study, the acid washing process developed by the authors was applied to the removal of arsenic from coal fly ash. Laboratory- and bench-scale investigations on the dissolution behavior of arsenic from various coal fly ash samples into dilute H2SO4 were conducted. Arsenic in the coal fly ash samples were dissolved into H2SO4 solutions rapidly. However, its concentrations decreased with an increase in the pH of H2SO4 solution in some cases. The species of arsenic in the dilute H2SO4 was estimated as H3AsO4, and its anionic species was considered to adsorb with the elevation of pH under the presence of ash particle. Such adsorption behavior was enhanced under the presence of Fe ion in the solution. The sufficient removal of arsenic was achieved by controlling pH and avoiding the adsorption of arsenic on the surface of coal fly ash particles, and the elution of arsenic from coal fly ash sample was successfully below the regulation limit. [Copyright &y& Elsevier]

Abstract: The chemical states of boron in coal fly ash, which may control its leaching into the environment, were investigated by focused-ion-beam time-of-flight secondary ion mass spectrometry (FIB-TOF-SIMS) and satellite-transition magic angle spinning nuclear magnetic resonance (STMAS NMR) spectroscopy. The distribution of boron on the surface and in the interior of micron-sized fly ash particles was directly observed by FIB-TOF-SIMS. Coordination numbers of boron and its bonding with different atoms from particles of bulk samples were investigated by STMAS NMR. Boron in coal fly ash with relatively poor leaching characteristics appears as trigonal BO3 and coexists with Ca and Fe at the outer layer of every particle and inside CaO–MgO particles. In contrast, boron in coal fly ash with better leaching characteristics appears as CaO- or MgO-trigonal BO3 and tetragonal BO4, and it is distributed only on the outer surface of each ash particle without showing any correlation with a particular element. [Copyright &y& Elsevier]

Abstract: Boron and its compounds are environmentally hazardous substance and are well-known condensed products that appear in coal fly ash during combustion of coal in coal-fired electric power stations. In a previous study, we suggested that boron in coal fly ash obtained from Nantun coal in China, identified as Ash–N, may exist on the surface of relatively large coal fly ash particles or as very fine particles generated by homogeneous nucleation. Although the characterization of boron in coal fly ash is important for its effective stabilization or removal, its detection is quite difficult because of its low concentration in coal fly ash and its light atomic weight. In the present work, solid-state magic angle spinning nuclear magnetic resonance (MAS-NMR) technique has been applied to reveal the local chemical structures of boron in Ash–N. In the 11B MAS-NMR spectrum of Ash–N, two peaks which are attributed to a three-oxygen coordinated boron unit (BO3) and a four-oxygen coordinated boron unit (BO4) were observed with high resolution. We have estimated quadrupole parameters of the BO3 unit in Ash–N using computer simulation, and we have fingerprinted these moieties with the parameters of borates. The result of the present analysis shows that calcium- or magnesium-bearing orthoborate or pyroborate are the most likely forms of boron in Ash–N. [Copyright &y& Elsevier]

Abstract: Boron as an environmentally regulated substance is well known to condense in the coal fly ash generated from coal combustion plants. Since boron in the coal fly ash tends to elute into the soil easily, a technology for its stabilization or removal from fly ash is required. An acid washing process is proposed and studied as one of the candidate technologies for the removal of boron from coal fly ash. A laboratory-scale investigation is conducted on the dissolution behavior of boron in the coal fly ash in a diluted HCl solution. The dissolution of boron and alkaline species is considerably fast and exhibits a behavior different from that of aluminum and silicon, which are major components of the ash. From the kinetic model, it is expected that boron in the ash may mainly be in the form of alkaline or alkaline earth borates that are deposited on the surface of relatively large ash particles of alumino-silicate or may be precipitated as fine particles during coal combustion. This acid washing process is extended to a bench-scale plant and boron is successfully removed from the coal fly ash until its content is less than the regulation limit. [Copyright &y& Elsevier]