A solid-state electrolysis process for upcycling aluminium scrap.

The recycling of aluminium scrap today utilizing a remelting technique downgrades the quality of the aluminium, and the final sink of this downgraded recycled aluminium is aluminium casting alloys1-9. The predicted increase in demand for high-grade aluminium as consumers choose battery-powered electric vehicles over internal combustion engine vehicles is expected to be accompanied by a drop in the demand for low-grade recycled aluminium, which is mostly used in the production of internal combustion engines2,7,10,11. To meet the demand for high-grade aluminium in the future, a new aluminium recycling method capable of upgrading scrap to a level similar to that of primary aluminium is required2-4,7,11. Here we propose a solid-state electrolysis (SSE) process using molten salts for upcycling aluminium scrap. The SSE produces aluminium with a purity comparable to that of primary aluminium from aluminium casting alloys. Moreover, the energy consumption of the industrial SSE is estimated to be less than half that of the primary aluminium production process. By effectively recycling aluminium scrap, it could be possible to consistently meet demand for high-grade aluminium. True sustainability in the aluminium cycle is foreseeable with the use of this efficient, low-energy-consuming process.

Effect of modified basic oxygen furnace slag on the controlled release of nitrate nitrogen and the functional microbial community in soil.

The specific surface area and active adsorption sites of basic oxygen furnace (BOF) slag increase after BOF modification. The addition of modified BOF slag to the soil may enable the control of nitrate nitrogen (NO3-N) leaching and also affect the functional microflora in the soil. In this study, soil column leaching experiments were conducted to explore the effects of adding modified slag to the soil on the controlled release of NO3-N and the main functional microbial communities involved in nitrification and denitrification processes. The experimental design included seven column groups: a soil control group (CT); soil groups with 2.5%, 5%, and 10% raw slag (S1, S2, S3); and soil groups with 2.5%, 5%, and 10% modified slag (MS1, MS2, MS3) that were subjected to three cycles of leaching, each of which were comprised of five leaching treatments. After the three cycles of leaching, significantly less NO3-N had leached from the modified slag group compared to the CT and the raw slag groups (P < 0.05). Although both slag treatments increased soil pH and decreased the oxidation reduction potential of the soil leaching solution, the addition of modified slag had less effect on soil pH than the addition of raw slag. During column leaching, the group with modified slag had a higher gene abundance of functional microflora compared with the group with raw slag. Similarly, the modified slag group had a higher diversity and richness of denitrifying bacteria, ammonia-oxidizing archaea, and ammonia-oxidizing bacteria than the raw slag group. In conclusion, the addition of modified slag to soil effectively decreased the NO3-N leaching and had relatively little effect on the functional microbial community in the soil.

Thermodynamic criteria of the end-of-life silicon wafers refining for closing the recycling loop of photovoltaic panels.

The collected end-of-life (EoL) silicon wafers from the discharged photovoltaic (PV) panels are easily contaminated by impurities such as doping elements and attached materials. In this study, the thermodynamic criteria for EoL silicon wafers refining using three most typical metallurgical refining processes: oxidation refining, evaporation refining, and solvent refining were systemically and quantitatively evaluated. A total of 42 elements (Ag, Al, Au, B, Be, Bi, C, Ca, Ce, Co, Cr, Cu, Fe, Ga, Gd, Ge, Hf, In, La, Mg, Mn, Mo, Na, Nb, Ni, Os, P, Pb, Pd, Pt, Re, Ru, Sb, Sn, Ta, Ti, U, V, W, Y, Zn, Zr) that are likely to be contained in the collected EoL silicon-based PV panels were considered. The principal findings are that the removal of aluminum, beryllium, boron, calcium, gadolinium, hafnium, uranium, yttrium, and zirconium into the slag, and removal of antimony, bismuth, carbon, lead, magnesium, phosphorus, silver, sodium, and zinc into vapor phase is possible. Further, solvent refining process using aluminum, copper, and zinc as the solvent metals, among the considered 14 potential ones, was found to be efficient for the EoL silicon wafers refining. Particularly, purification of the phosphorus doped n-type PV panels using solvent metal zinc and purification of the boron doped p-type PV panels using solvent metal aluminum are preferable. The efficiency of metallurgical processes for separating most of the impurity elements was demonstrated, and to promote the recycling efficiency, a comprehensive management and recycling system considering the metallurgical criteria of EoL silicon wafers refining is critical.

The stability of the compounds formed in the process of removal Pb(II), Cu(II) and Cd(II) by steelmaking slag in an acidic aqueous solution.

The potential feasibility of steel slag as a low cost removal agent for heavy metal ions Pb(II), Cu(II) and Cd(II) in acidic conditions was investigated in this study. The initial pH effect on heavy metal ion removal efficiency, the compounds formed after heavy metal ion removal, and the binding force of metals with the compounds were determined. The results showed that the efficiency of removing heavy metal ions by steel slag was low at low initial pH levels, yet it sharply increased and then became stable as the initial pH increased. The pseudo-second order model provided the best description for the removal of Pb, Cu, and Cd ions, indicating that the predominant heavy metal ion removal mechanism was chemisorption. The images obtained by the Fourier transform infrared spectroscopy (FTIR) and the X-ray diffraction (XRD) analysis indicated that the main compounds formed after the removal of Pb, Cu, and Cd ions by steel slag in an aqueous solution were heavy metal ferrites, silicates, carbonates, hydroxides and oxides. Sequential extraction experiments showed that these three heavy metals bond to the compounds mainly in the carbonate fraction (F2), the Fe oxide bound fractions (F3 (a) and F3 (c)), and the residual fraction (F4) in which F2 corresponded to the carbonates, and F3(a), F3(c) and F4 corresponded to the amorphous or crystalline ferrites and silicates, respectively. The F3 (a), F3 (c) and F4 are relatively stable and do not tend to re-release metal ions in acidic solutions. However, F2 and heavy metal hydroxides have relatively low stability and dissolve readily, re-leaching heavy metal ions into the acid solution. When these three heavy metal ion mixtures were removed by steel slag, the Pb, Cu and Cd deposits were at higher levels in the F3 and F4 fractions. Therefore, it was concluded that the co-existence of heavy metal ions in an aqueous solution is beneficial for their removal by steel slag in acidic conditions.

Optimal Recycling of Steel Scrap and Alloying Elements: Input-Output based Linear Programming Method with Its Application to End-of-Life Vehicles in Japan.

Importance of end-of-life vehicles (ELVs) as an urban mine is expected to grow, as more people in developing countries are experiencing increased standards of living, while the automobiles are increasingly made using high-quality materials to meet stricter environmental and safety requirements. While most materials in ELVs, particularly steel, have been recycled at high rates, quality issues have not been adequately addressed due to the complex use of automobile materials, leading to considerable losses of valuable alloying elements. This study highlights the maximal potential of quality-oriented recycling of ELV steel, by exploring the utilization methods of scrap, sorted by parts, to produce electric-arc-furnace-based crude alloy steel with minimal losses of alloying elements. Using linear programming on the case of Japanese economy in 2005, we found that adoption of parts-based scrap sorting could result in the recovery of around 94-98% of the alloying elements occurring in parts scrap (manganese, chromium, nickel, and molybdenum), which may replace 10% of the virgin sources in electric arc furnace-based crude alloy steel production.

MaTrace: tracing the fate of materials over time and across products in open-loop recycling.

Even for metals, open-loop recycling is more common than closed-loop recycling due, among other factors, to the degradation of quality in the end-of-life (EoL) phase. Open-loop recycling is subject to loss of functionality of original materials, dissipation in forms that are difficult to recover, and recovered metals might need dilution with primary metals to meet quality requirements. Sustainable management of metal resources calls for the minimization of these losses. Imperative to this is quantitative tracking of the fate of materials across different stages, products, and losses. A new input-output analysis (IO) based model of dynamic material flow analysis (MFA) is presented that can trace the fate of materials over time and across products in open-loop recycling taking explicit consideration of losses and the quality of scrap into account. Application to car steel recovered from EoL vehicles (ELV) showed that after 50 years around 80% of the steel is used in products, mostly buildings and civil engineering (infrastructure), with the rest mostly resided in unrecovered obsolete infrastructure and refinery losses. Sensitivity analysis was conducted to evaluate the effects of changes in product lifespan, and the quality of scrap.

Simultaneous material flow analysis of nickel, chromium, and molybdenum used in alloy steel by means of input-output analysis.

Steel is not elemental iron but rather a group of iron-based alloys containing many elements, especially chromium, nickel, and molybdenum. Steel recycling is expected to promote efficient resource use. However, open-loop recycling of steel could result in quality loss of nickel and molybdenum and/or material loss of chromium. Knowledge about alloying element substance flow is needed to avoid such losses. Material flow analyses (MFAs) indicate the importance of steel recycling to recovery of alloying elements. Flows of nickel, chromium, and molybdenum are interconnected, but MFAs have paid little attention to the interconnected flow of materials/substances in supply chains. This study combined a waste input-output material flow model and physical unit input-output analysis to perform a simultaneous MFA for nickel, chromium, and molybdenum in the Japanese economy in 2000. Results indicated the importance of recovery of these elements in recycling policies for end-of-life (EoL) vehicles and constructions. Improvement in EoL sorting technologies and implementation of designs for recycling/disassembly at the manufacturing phase are needed. Possible solutions include development of sorting processes for steel scrap and introduction of easier methods for identifying the composition of secondary resources. Recovery of steel scrap with a high alloy content will reduce primary inputs of alloying elements and contribute to more efficient resource use.

Quality- and dilution losses in the recycling of ferrous materials from end-of-life passenger cars: input-output analysis under explicit consideration of scrap quality.

Metals can in theory be infinitely recycled in a closed-loop without any degradation in quality. In reality, however, open-loop recycling is more typical for metal scrap recovered from end-of-life (EoL) products because mixing of different metal species results in scrap quality that no longer matches the originals. Further losses occur when meeting the quality requirement of the target product requires dilution of the secondary material by adding high purity materials. Standard LCA usually does not address these losses. This paper presents a novel approach to quantifying quality- and dilution losses, by means of hybrid input-output analysis. We focus on the losses associated with the recycling of ferrous materials from end-of-life vehicle (ELV) due to the mixing of copper, a typical contaminant in steel recycling. Given the quality of scrap in terms of copper density, the model determines the ratio by which scrap needs to be diluted in an electric arc furnace (EAF), and the amount of demand for EAF steel including those quantities needed for dilution. Application to a high-resolution Japanese IO table supplemented with data on ferrous materials including different grades of scrap indicates that a nationwide avoidance of these losses could result in a significant reduction of CO(2) emissions.

Synergistic removal of As(V) from aqueous solution by nanozero valent iron loaded with zeolite 5A synthesized from fly ash.

Nanozero valent iron (NZVI) loaded on zeolite 5A can efficiently remove As(V) in water through the synergism of zeolite 5A and NZVI. In this study, zeolite 5A was first obtained by ion exchange using zeolite 4A synthesized from fly ash and CaCl2, and then NZVI-5A zeolite was synthesized by a reduction method to load NZVI on zeolite 5 A. NZVI-5A zeolite had a specific surface area of 238 m2/g. The As(V) removal capacity by NZVI-5A zeolite was 72.09 mg/g by the Langmuir model fitting, and the removal capacity was almost not affected by solution pH in the pH range of 4-12. As(V) was removed by the precipitation of Ca2+ in zeolite 5A with As(V), Ca2+ and NZVI with As(V), and the reduction and inner ball complex reaction of NZVI. The As(V) removal efficiency by NZVI-5A zeolite was almost unaffected by the coexistence of CO32-, SO42-, NO3- and Cl- but decreased with high concentrations of PO43- in solution. The NZVI-5A zeolite could efficiently remove metal ions coexisting with As(V) in solution. The As(V) removal efficiency by the NZVI-5A zeolite was 84.0% after 5 cycles, and the NZVI-5A zeolite could be separated from the solution with an external magnetic field.

Ammonium continuous removal by zeolite P synthesized using fly ash combined with bacteria in aqueous solution.

The new composite product synthesized by zeolite P and bacteria consisting of nitrobacteria and denitrobacteria can efficiently and continuously remove ammonium in solution through zeolite adsorption and bacteria degradation. In this study, we used fly ash to prepared zeolite P, and then combined bacteria to synthesize the composite product. The adsorption efficiency and mechanism of products for ammonium were further studied by batch and dynamic experiments, and adsorption model. The zeolite P with a relative crystallinity of 84.7% was synthesized using fly ash by an alkali fusion-hydrothermal method. The synthetic zeolite P could combine with bacteria to be prepared an integral adsorption composite that had hierarchical pore structure including macropores, mesopores, and micropores, and its maximum compressive strength reached 106.2 N. The zeolite P could remove ammonium from solution, and Freundlich, Temkin, and Dubinin-Radushkevich models as well as thermodynamic models all showed that the ammonium adsorption by zeolite was mainly physical adsorption. Thus, the adsorbed ammonium was easy to be desorbed and became the nitrogen source for bacteria in composites. By batch experiments, the ammonium adsorption rate of composite product was significantly improved (P < 0.05) compared with zeolite P due to zeolite adsorption and the bacteria degradation. Through dynamic experiments, the composite product could efficiently and continuously remove ammonium from solution than zeolite P and bacteria alone. Therefore, the composite product could form a stable system for the adsorption, desorption, and degradation of ammonium in solution.

UPIOM: a new tool of MFA and its application to the flow of iron and steel associated with car production.

Identification of the flow of materials and substances associated with a product system provides useful information for Life Cycle Analysis (LCA), and contributes to extending the scope of complementarity between LCA and Materials Flow Analysis/Substances Flow Analysis (MFA/SFA), the two major tools of industrial ecology. This paper proposes a new methodology based on input-output analysis for identifying the physical input-output flow of individual materials that is associated with the production of a unit of given product, the unit physical input-output by materials (UPIOM). While the Sankey diagram has been a standard tool for the visualization of MFA/SFA, with an increase in the complexity of the flows under consideration, which will be the case when economy-wide intersectoral flows of materials are involved, the Sankey diagram may become too complex for effective visualization. An alternative way to visually represent material flows is proposed which makes use of triangulation of the flow matrix based on degrees of fabrication. The proposed methodology is applied to the flow of pig iron and iron and steel scrap that are associated with the production of a passenger car in Japan. Its usefulness to identify a specific MFA pattern from the original IO table is demonstrated.

Analysis of atomic scale chemical environments of boron in coal by 11B solid state NMR.

Atomic scale chemical environments of boron in coal has been studied by solid state NMR spectroscopy including magic angle spinning (MAS), satellite transition magic angle spinning (STMAS), and cross-polarization magic angle spinning (CPMAS). The (11)B NMR spectra can be briefly classified according to the degree of coalification. On the (11)B NMR spectra of lignite, bituminous, and sub-bituminous coals (carbon content of 70-90mass%), three sites assigned to four-coordinate boron ([4])B with small quadrupolar coupling constants (≤0.9 MHz) are observed. Two of the ([4])B sites in downfield are considered organoboron complexes with aromatic ligands, while the other in the most upper field is considered inorganic tetragonal boron (BO(4)). By contrast, on the (11)B NMR spectra of blind coal (carbon content >90mass%), the ([4])B which substitutes tetrahedral silicon of Illite is observed as a representative species. It has been considered that the organoboron is decomposed and released from the parent phase with the advance of coal maturation, and then the released boron reacts with the inorganic phase to substitute an element of inorganic minerals. Otherwise boron contained originally in inorganic minerals might remain preserved even under the high temperature condition that is generated during coalification.

Thermodynamic analysis for the controllability of elements in the recycling process of metals.

This study presents the results of chemical thermodynamic analysis on the distribution of elements in the smelting process of metallic materials to examine the controllability of impurities in the pyrometallurgical technique. The results of the present work can give an answer against the frequently given question; "Which impurity element can be removable in metallurgical process?" or "How far can the impurity level be controlled?". The proposed method was applied to estimate the distribution of 29 elements for a copper converter and 26 elements for a steel-making process and shows the distribution tendency of elements among the gas, slag, and metal phases as well as clarifying which metals can be recovered or removed from secondary resources in metallurgical processes. The effects of temperature, oxygen partial pressure, and slag composition on the distribution ratio of elements were also evaluated, and the removal limit or controllability of impurity in these two processes was presented. This study results in thermodynamic features of various elements in the pyrometallurgical process and also shows, even by varying process parameters such as temperature and oxygen partial pressure, no drastic improvement of removal efficiency should be expected, except for lead and tin in copper.

Thermodynamic criteria for the removal of impurities from end-of-life magnesium alloys by evaporation and flux treatment.

In this paper, the possibility of removing impurities during magnesium recycling with pyrometallurgical techniques has been evaluated by using a thermodynamic analysis. For 25 different elements that are likely to be contained in industrial magnesium alloys, the equilibrium distribution ratios between the metal, slag and gas phases in the magnesium remelting process were calculated assuming binary systems of magnesium and an impurity element. It was found that calcium, gadolinium, lithium, ytterbium and yttrium can be removed from the remelted end-of-life (EoL) magnesium products by oxidization. Calcium, cerium, gadolinium, lanthanum, lithium, plutonium, sodium, strontium and yttrium can be removed by chlorination with a salt flux. However, the other elements contained in magnesium alloy scrap are scarcely removed and this may contribute toward future contamination problems. The third technological option for the recycling of EoL magnesium products is magnesium recovery by a distillation process. Based on thermodynamic considerations, it is predicted that high-purity magnesium can be recovered through distillation because of its high vapor pressure, yet there is a limit on recoverability that depends on the equilibrium vapor pressure of the alloying elements and the large energy consumption. Therefore, the sustainable recycling of EoL magnesium products should be an important consideration in the design of advanced magnesium alloys or the development of new refining processes.

A composite adsorbent of ZnS nanoclusters grown in zeolite NaA synthesized from fly ash with a high mercury ion removal efficiency in solution.

In this study, the nanocomposite adsorbent (ZnS-zeolite NaA) was prepared by a simple ion-exchange method, which modified the zeolite NaA synthesized from fly ash. The removal efficiency, adsorption mechanism of mercury ions by ZnS-zeolite NaA and release of zinc ion into aqueous solution during the adsorption process were determined. The results showed that ZnS nanoclusters were introduced the supercages of zeolite by ion exchange to synthesize the ZnS-zeolite NaA with high removal capacity for Hg2+ in the initial pH 2-7 of solution. Determination of the adsorption kinetics and thermodynamic parameters, in combination with X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy analyses, revealed that the Hg2+ adsorption by ZnS-zeolite NaA was Hg2+ complexed and ion exchanged with ZnS in the ZnS-zeolite NaA to form stable HgS, and then, the released Zn2+ was adsorbed by the zeolite, preventing Zn2+ pollution. The Hg2+ removal rate was greater than 99.90% with the coexistence of either Zn2+ or Cu2+, Cd2+ and Pb2+. After five repetitions, the Hg2+ removal rate by the ZnS-zeolite NaA was only slightly decreased by 2%. Therefore, ZnS-zeolite NaA synthesized using fly ash has potential for broad application as a Hg2+ adsorbent.

Immobilization persistence of Cu, Cr, Pb, Zn ions by the addition of steel slag in acidic contaminated mine soil.

Adding steel slag to the acidic contaminated mine soil can immobilize heavy metal ions, but immobilization persistence of the metal ions needs to be determined. In this study, dynamic column simulation experiments were set up to compare the immobilization persistence of Cu, Cr, Pb and Zn ions in original soil and with the addition of slag, lime or fly ash to the soil during a simulated 36-month of acid rain leaching. After adding slag and lime, the pH, organic matter content and cation exchange capacity of soil were significantly increased. Compared with the original soil, additions of slag and lime to the soil were able to persistently immobilize the metal ions, whereas fly ash additions had little effect. During simulation, the metal ion concentrations in the slag group leaching solution were essentially consistent with Standard IV for groundwater. The metal ions were immobilized to form instable hydroxides and stable fractions following adding slag to soil. The hydroxide could rerelease metal ions by acid rain leaching, part of which were re-immobilized into stable fractions by entering slag lattice and complexing with soil organic matter. Therefore, adding slag to soil can persistently immobilize metal ions for heavy metal-contaminated acidic mine soil.

Effect of basic oxygen furnace slag on succession of the bacterial community and immobilization of various metal ions in acidic contaminated mine soil.

As an immobilizing agent for metal ions, basic oxygen furnace slag may affect bacterial community succession, thus further promote metal ion immobilization in acidic contaminated soil. In this work, pot experiments were conducted to study the effects of adding 10 g/kg (S10) and 15 g/kg (S15) slag on soil properties, plant growth, bacterial community succession and various metal ion immobilization in acidic mine soils contaminated by Pb, Zn, Cu, Cr and Cd. The results showed that after 93 days of potting, the soil pH, electrical conductivity, total nitrogen and organic carbon content increased significantly (P < 0.05), and the dry weight of Poa pratensis L. increased significantly (P < 0.05) in S10 and S15 compared with in original soil group. With slag addition and plant growth, the diversity and richness indices of bacterial communities greatly improved, and at the genus level, the abundance of metal-tolerant bacteria and bacteria beneficial to plant growth increased, while the abundance of acidophiles decreased. After adding slag to the soil, the various metals were immobilized because slag could not only immobilize metal ions through ion exchange and coprecipitation, but also benefit plant growth and bacterial community succession which further promote the immobilization of metal ions.

Global land-use change hidden behind nickel consumption.

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 1.9km2, and that induced by Japanese final demand for nickel was 0.38km2. 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).

Hydrometallurgical extraction of zinc from CaO treated EAF dust in ammonium chloride solution.

Zinc in Electric Arc Furnace dust or EAF dust mainly exists as ZnFe2O4 and ZnO. While ZnO can be simply dissolved into either an acidic or alkaline solution, it is difficult to dissolve ZnFe2O4. In our previous work, we introduced a process called "CaO treatment", a preliminary pyrometallurgical process designed to transform the ZnFe2O4 in the EAF dust into ZnO and Ca2Fe2O5. The halogens and others heavy metals were favorably vaporized during CaO treatment with no essential evaporation loss of zinc and iron, leaving CaO treated dust which consisted mainly of ZnO and Ca2Fe2O5 and no problematic ZnFe2O4 compound. In this work, the selective leaching of zinc over iron and calcium in the CaO treated dust was investigated using an NH4Cl solution. The effects of temperature, reaction time and NH4Cl concentration on dissolution behavior were examined. While most of the zinc in the CaO treated dust was extracted after 2 h at 70 °C with 2 M NH4Cl, only about 20% of calcium was leached in NH4Cl solution. However, the iron did not dissolve and remained as Ca2Fe2O5 in residue. It was confirmed that zinc can be effectively recovered using NH4Cl solution.

Innovations in steelmaking technology and hidden phosphorus flows.

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.