Treatment Of Slags Research Articles

Selective stabilization of chromium and sustainable treatment of stainless steel slags

Selective stabilization of chromium and sustainable treatment of industrial stainless steel electric arc furnace slags was investigated. The crystallization and phase distribution of stainless steel slags after equilibration at 1500 °C with varying basicity between 1.8 and 1.0 using quartz sand were studied. Results showed chromium in the slag can be fully stabilized into the Cr-spinel phase, which accumulate at the crucible bottom under the influence of gravity at a basicity of 1.2. The top liquid portion corresponding to about 72 % of the total slag can be quenched to an amorphous phase after a slag discharge treatment with the bottom residual solid portion in the form of a Cr-spinel enriched slag. The leaching experiments of the two separated slags were implemented according to the standard HJ/T 301–2007, and the Cr leaching concentrations were 0.059 mg/L and 0.136 mg/L, respectively. This was within the national comprehensive utilization standard of Cr-bearing solid wastes. Furthermore, the feasibility analysis of operation and potential application to the stainless steel industry was also addressed to provide the fundamentals for industrial scale utilization of stainless steel slags.

Present Situation and Research Progress of Comprehensive Utilization of Antimony Tailings and Smelting Slag

The production process of antimony produces a large amount of solid waste, such as waste rock in mining, tailings in the beneficiation, metallurgical slag in the smelting, and so on. At present, most of these solid wastes are currently in storage, and the storage of a large amount of solid wastes is not only harmful to the local ecological environment but also a waste of resources. In view of this situation, this paper will take antimony tailings and metallurgical slag as examples and summarize them according to their different treatment methods. The comprehensive utilization of antimony tailings is mainly recovering metals by beneficiation and metallurgy and using antimony tailings as building materials and underground filling materials, while the comprehensive utilization method of antimony metallurgical slag is mainly the recovery of valuable metals by pyrometallurgy or hydrometallurgy or the stabilization technology. This paper summarizes the advantages and disadvantages of different treatment methods and puts forward the prospect of future research directions for the treatment of different metallurgical slags and tailings.

Assessment of industrial by-products as amendments to stabilize antimony mine wastes

The spread of antimony from mine wastes to the environment represents a matter of great concern due to its adverse effects on impacted ecosystems. There is an urgent need for developing and adopting sustainable and inexpensive measures to deal with this type of wastes. In this study the Sb leaching behavior of mine waste rocks and mine tailings derived from the exploitation of Sb ore deposits was characterized using standard batch leaching tests (TCLP and EN-12457-4) and column leaching essays. Accordingly, these mine wastes were characterized as toxic (>0.6 mg Sb L−1) and not acceptable at hazardous waste landfills (>5 mg Sb kg−1), showing also an ongoing Sb release under prolonged leaching conditions. Two industrial by-products were evaluated as amendments to stabilize them, namely deferrisation sludge (DFS) and a by-product derived from the treatment of aluminum salt slags (BP–Al). Mine wastes were amended with different doses (0–25%) of DFS or BP-Al and the performance of these treatments was evaluated employing also batch and column leaching procedures. The effectiveness of DFS to immobilize Sb was much higher than that exhibited by BP-Al. Thus, treatments with 25% BP-Al showed Sb immobilization levels of approximately 33–53%, whereas treatments with 5 and 25% DFS already attained Sb immobilization levels up to approximately 80–90 and 90–99%, respectively. Mine tailings amended with 5% DFS and mine waste rocks amended with 25% DFS decreased their leachable Sb contents below the limit for non-hazardous waste landfill acceptance (<0.7 mg Sb kg−1). Likewise, these DFS treatments were able to revert their toxic characterization. Moreover, the 25% DFS treatment showed to be a long-lasting stabilizing system, efficient at least during a leaching period equivalent to 10-year rainfall with a great Sb leaching reduction (close to 98%). After this long-term leaching process, DFS-treated mine wastes kept their non-hazardous and non-toxic characterization. The amorphous Fe (oxyhydr)oxides composing DFS were responsible for the important Sb removal capacity showed by this by-product. Thus, when DFS was applied to mine wastes mobile Sb was importantly fixed as non-desorbable Sb, showing also a considerable Sb removal capacity in presence of strong competing anions such as phosphate. The application of DFS as amendment presents a great potential to be used as a sustainable long-term stabilizing system of Sb mine wastes.

Processes of salt slag recycling in aluminum production to obtain powder material with a high content of aluminum oxide phases

The processing of salt slags in aluminum production in order to obtain a powder material with a high content of aluminum oxide phases and the results of thermodynamic assessment of the hydrolysis reactions of aluminum carbide and nitride during the hydraulic treatment of slags are discussed. It is reported that water‑soluble fluorine compounds, such as Na3AlF6, CaF2, MgF2, K2ZrF6 , in the composition of refining fluxes complicates the processing of aluminum slags, which involve leaching of salts by water. A rational solution seems to be the replacement of sparingly soluble salts in refining fluxes with sodium or potassium fluorides with a higher solubility in water. It is shown that the powder mixture obtained after hydraulic treatment of aluminum slag includes various forms of structural components in the form of films, shells, submicroand nanostructures of various morphologies with the participation of various types of nano‑components, in which the phases of non‑metallic compounds predominate, mainly ceramic substances and salts (corundum Al2O3, aluminum oxynitride Al2.85O3.45N0.55, aluminum nitride AlN, sodium chloride NaCl) and metallic aluminum. It is indicated that the possibility of forming eutectic mixtures of ceramic compounds of aluminum oxide and aluminum oxynitride, which are more fusible than pure oxides and nitrides, must be taken into account when developing salt slag recycling technologies in order to obtain ceramic powder materials with a high content of alumina phases.

Recycling of ironmaking and steelmaking slags in Japan and China

The mass production of steel is inevitably accompanied by large quantities of slags. The treatment of ironmaking and steelmaking slags is a great challenge in the sustainable development of the steel industry. Japan and China are two major steel producing countries that have placed a large emphasis on developing new technologies to decrease slag emission or promote slag valorization. Slags are almost completely reused or recycled in Japan. However, due to stagnant infrastructural investments, future applications of slags in conventional sectors are expected to be difficult. Exploring new functions or applications of slags has become a research priority in Japan. For example, the utilization of steelmaking slags in offshore seabeds to create marine forests is under development. China is the top steel producer in the world. The utilization ratios of ironmaking and steelmaking slags have risen steadily in recent years, driven largely by technological advances. For example, hot stage processing of slags for materials as well as heat recovery techniques has been widely applied in steel plants with good results. However, increasing the utilization ratio of basic oxygen furnace slags remains a major challenge. Technological innovations in slag recycling are crucial for the steel industries in Japan and China. Here, the current status and developing trends of utilization technologies of slags in both countries are reviewed.

Research on integrated CO2 absorption-mineralization and regeneration of absorbent process

The hot potassium-alkali method provides excellent performance for the absorption of CO2 from flue gas. However, the high energy consumption by absorbent regeneration poses a critical barrier to the widespread industrialization of the hot potassium-alkali method. In this study, an integrated CO2 absorption-mineralization and regeneration of absorbent (IAMR) process was proposed using K2CO3 solution as the absorbent and steel slag as the desorbent at normal temperature and pressure. This method greatly reduced the energy consumption and costs compared with the traditional thermal regeneration method. Under the optimal conditions, i.e. a K2CO3 concentration of 1.0 mol/L, reaction temperature of 60 °C and liquid-solid (K2CO3 solution-steel slag) ratio of 14 mL/g, the carbonation conversion of the steel slag reached 58.63% after 120min, corresponding to a CO2 storage capacity of 212 kg/t steel slag. The reaction process showed that the main component Ca2SiO4 in the steel slag had high solubility activity in K2CO3 solution which significantly enhanced the rate and efficiency of CO2 sequestration. Moreover, the performance stability of K2CO3 solution during CO2 absorption-desorption circulation was discussed. This research is of great significance for the simultaneous treatment of alkaline waste slags (steel slag, fly ash, etc.) and mitigation of greenhouse gases.

A mathematical model of the technology of extraction of copper from industrial slags

The article substantiates the relevance and necessity of developing mathematical models in foundry production, as well as the problems and prospects of their use. Based on an analytical review of the world literature on foundry production, it was emphasized that in many studies of the authors and literary sources, not enough attention is paid to the development of mathematical models of the technological process of extracting non-ferrous metals from slag and industrial waste. A brief description of the developed technologies for the high-temperature treatment of industrial slags and waste, separation treatment in electric furnaces, and metals extracted from liquid slag is given. During the development and analytical implementation of the mathematical model, the developed technology for extracting copper from slags is presented as an research object. Based on the study of the dynamics of changes in the thermophysical properties of the components as a function of temperature, a mathematical model of high-temperature treatment of slags is compiled. This will allow you to predict the process of processing slags and the results obtained. Also, a mathematical model of the extraction of copper from the slag is compiled, taking into account the chemical properties of metal inclusions in the slag. This serves as the basis for automating the process of extracting copper from slags and waste products.

Hydrothermal Production of H2 and Magnetite From Steel Slags: A Geo-Inspired Approach Based on Olivine Serpentinization

The interaction between ultramafic rocks and hot seawater at slow-spreading mid-oceanic ridges triggers hydrothermal redox reactions which are known to produce magnetite and H2 under appropriate pressure and temperature conditions. Steel slags share some common properties with ultramafic rocks. They are composed of anhydrous and refractory minerals formed at temperatures exceeding 1200°C and they contain ferrous iron in comparable amounts. Consequently, both types of materials, natural and anthropogenic, when submitted to hydrothermal conditions are prone to form magnetite and H2 according the simplified redox reaction: 3[FeO] + H2O => Fe3O4 + H2 (1) where [FeO] is the ferrous iron component of the corresponding material that can be present under different mineralogical forms. Since H2 and magnetite, Fe3O4, especially when occurring as nanomaterial, are two valuable products for new-technology applications, the hydrothermal treatment of steel slags can be seen as a way to valorize a by-product of the steel industry of which a few tenths of billion tons are produced yearly. The hydrothermal behavior of steel slags which arise from basic oxygen furnace (BOF) operations and that of olivine, (Mg,Fe)2SiO4, the main mineral constituent of abyssal peridotites, is described here based on literature data. The thermochemical characteristics of Reaction 1 are reviewed for both types of materials in the perspective of optimizing a process that would valorize BOF steel slags for the production of nanomagnetite (and high-purity H2). In particular the kinetics effect of temperature, pH and solution-to-solid mass ratio on the hydrothermal oxidation of wustite (FeO), considered here as an analogue of ferrous-iron component of steel slags, is modeled. The possible role of additive (impurity) on the hydrothermal oxidation of wustite though the catalysis of the water-splitting reaction is discussed. Finally, the lack of kinetics constraints on nanomagnetite growth under hydrothermal conditions in a wide range of pH is identified has a major gap to understand two important issues, (1) the catalysis of abiotic molecules in the course of serpentinization reactions and (2) tailoring the size of the magnetite produced by hydrothermal treatment of BOF steel slags.

Bacterial leaching of critical metal values from Polish copper metallurgical slags using Acidithiobacillus thiooxidans

Global economy faces an increasing problem of the supply risk of critical raw materials, therefore the search for secondary resources has become an urgent issue. Copper orebodies in Poland contain substantial amounts of metals deemed critical (e.g. Co, Mo, rare earth elements (REE) or V), which are not recovered during processing. The metals of interest are concentrated in metallurgical waste residues that should be classified as a secondary resource rather than as a waste. Bioleaching is a frontier technology promising for environment-friendly treatment of slags. Therefore, the objective of this work was to study the feasibility of metal (Co, Mo, REE, V) bioleaching from copper metallurgical wastes employing Acidithiobacillus thiooxidans bacterial strain as the leaching agent. The effect of particle size (fractions <0.25 mm and 0.25–0.5 mm) and pulp density (1%, 2%) was studied using three different slag samples (lead slag - LS, shaft furnace slag - SFS and granulated slag - GS). The bioleaching experiment was set up for 28 days under acidic conditions (pH t0 = 2.5). The results revealed that the microorganisms can catalyze metal extraction from slags as compared to leaching achieved under abiotic conditions. The optimal bioleaching yield was achieved under conditions at 0.25–0.5 mm particle size and 1% pulp density, regardless of used type of slag. After 28 days, the extracted amounts of metals were: 88% Co, 40% Mo, 83% REE and 55% V from LS, 100% Co, 44% Mo, 70% REE and 70% V from SFS and 95% Co, 70% Mo, 99% REE and 93% V from GS. All examined slags showed good potential for bioleaching of valuable elements. However, optimization of initial parameters is still needed for further efficiency improvement, especially in terms of the process duration.

Control of silica polymerisation during ferromanganese slag sulphuric acid digestion and water leaching

A major obstacle to the hydrometallurgical treatment of ferromanganese slags is the way in which silica polymerisation is controlled during sulphuric acid digestion and water leaching. In an acidic medium, silica enters in solution and forms silicic acid, which polymerises into silica gel and makes solid-liquid separation difficult.This article will show that the quick leach model, also called the water-starved system, limits silica solubilisation and its subsequent polymerisation during manganese extraction from ferromanganese slags by rejecting most of the ferromanganese slag silica content in the leach residue. It will further illustrate that the silica content in the residue is dependent on the acid concentration used during acid digestion. It will also show that dissolved silica in the pregnant leach solution is high when an unrestricted quantity of water is used and low when the water quantity is restricted during water leaching. Furthermore, a method for silica gel recovery from ferromanganese slag will be presented, as well as the silica gel analysis, in order to confirm the theory presented in this article.Manganese extraction of up to 90% is obtained and the leach residue presents good latent hydraulic properties, which can be used as an addition to Portland cement or a gypsum replacement. More than 95% of the initial silica content of the slag is rejected in the leach residue, and a residue silica content of more than 27% is obtained. Thus, silica solubilisation and polymerisation are controlled and solid-liquid separation is accelerated.

Disposal of High-Temperature Slags: A Review of Integration of Heat Recovery and Material Recycling

Nowadays with the continuous urbanization in China, the carbon emission and resource shortage have been serious issues, for which the disposal of blast furnace slags (BFS) and steel slags (SS) discharged from the metallurgical industry make up a significant strategy. The output of crude steel reached 823 Mt in China in 2014 and the thermal heat in these slags was equivalent to ~18 Mt of standard coal. Herein, the recent advances were systemically reviewed and analyzed, mainly from two respects, i.e., integration of heat recovery and material recycling and crystallization control of the slags. It was first found that for the heat recovery from BFS, the most intensively investigated physical method and chemical method were centrifugal granulation and gasification reaction, respectively. Furthermore, a two-step approach could contribute to a promising strategy for the treatment of slags, i.e., the liquid slags were first granulated into small particles, and then other further treatment was performed such as gasification reaction. With regard to SS, the effective disposal could be achieved using a selective crystallization and phase separation (SCPS) method, and moreover, the solid solution of 2CaO·SiO2 and the target phases could act as a promising enriched phase to extract the valuable elements.

Swelling Behavior of Electric Arc Furnace Aggregates for Unbound Granular Mixtures in Road Construction

Artificial aggregates, which result from the treatment of electric arc furnace slags (EAF aggregates), represent a very interesting technological solution to replace natural aggregates in different road construction applications. In spite of excellent mechanical properties, the swelling nature of some expansive compounds present in their mineralogy could be detrimental to volumetric stability of civil works. In light of these considerations, the main objective of this research was to analyze the volume stability of different unbound granular mixtures composed by EAF aggregates (aged and fresh) through two accelerated swelling procedures: water-bath swelling test (ASTM D4792/D4792M-13) and steam test (EN 1744-1). The results demonstrated how the expansive developmental process follows, in general, three different progressive phases. Both expansion development and final swelling extent were a function of preliminary exposition to aging treatment and different physical factors, such as particle size, grain size distribution, and degree of compaction. The expansive behavior was more evident for fresh slag aggregates, which did not undergo any type of stabilization procedure. Specifically, the residual voids content, which is in close correlation with the degree of compaction, can be considered the main factor affecting swelling ratio. All specimens analyzed, however, showed appropriate expansion values according to ASTM and EN standard requirements.

New Developments in Pyrometallurgy

Research and development in pyrometallurgy continue to attract attention from the scientific and engineering community as a result of the irreplaceable role of pyrometallurgy in the extraction and processing of metals for society. Development of energy-efficient and environmentally friendly pyrometallurgical processes continues to be pursued in the advancement of metallurgical technology and to contribute to continuous innovations in the field. In this section of the journal, ten articles are presented to address many new and diverse fields in pyrometallurgy. In the first article titled ‘‘Highlights of the Salt Extraction Process,’’ Aida Abbasalizadeh et al. discuss the characteristics, achievements, and future potential of a new process using molten (chloride) salts for the recovery of metals from several primary and secondary resources. The process has been identified for application in a broad range of areas, such as the treatment of metallurgical slags, recovery of lead from cathode ray tube glass, and recovery of rare earth metals from magnet scrap. It is considered a promising process for the recovery of strategic metals with the apparent advantage of being environmentally friendly. This could be one technology to watch. In the next article, Mohassab Yousef MohassabAhmed and Hong Yong Sohn report on the effect of water vapor on slag chemistry associated with a novel flash ironmaking technology in their article titled ‘‘Application of Spectroscopic Analysis Techniques to the Determination of Slag Structures and Properties: Effect of Water Vapor on Slag Chemistry Relevant to a Novel Flash Ironmaking Technology.’’ The University of Utah has been studying this process for many years, and this article serves as an update on aspects of this important work. The CaOMgO-SiO2-Al2O3-FeO-MnO-P2O5 slag system with the CaO/SiO2 ratio ranging from 0.8 to 1.4 was selected for the new flash process operating temperatures between 1550 C and 1650 C. It shows that water vapor significantly affects the chemistry of the slag and strongly affects the phase equilibria in the slag as well as the equilibrium distribution of elements (e.g., S, P, and Mn) between slag and molten metal. These results may provide a useful guide for controlling the quality of the produced iron, the iron loss into the slag, and the lining erosion. The next article titled ‘‘Thermodynamic Analysis of Looping Sulfide Oxidation Production of MoO2 from Molybdenite for Energy Capture and Generation’’ by Joseph D. Lessard et al. reports on the new looping sulfide oxidation process. Building on an earlier JOM article, it describes the selective and efficient production of MoO2 from MoS2 concentrates through the conversion of MoS2 to MoO2 with O2 and MoO3. The fourth article is concerned with new developments in nickel laterite technology. In this article titled ‘‘Carbothermic Reduction of Nickeliferous Laterite Ores for Nickel Pig Iron Production in China: A Review,’’ Mingjun Rao et al. review new developments in laterite metallurgy, in particular, in the so-called Krupp Renn process for producing a type of nickel pig iron from several nickel laterite ores. It shows that the relatively low temperature (below approximately 1300 C) solid-state reduction of nickeliferous laterite ores followed by magnetic separation offers an interesting route for producing a ferronickel at potentially lower cost by eliminating high-temperature electric furnace smelting. Conventional technologies are also reviewed. The article includes several interesting graphs presenting statistical data on the nickel market. The measurement and control of pyrometallurgical processes are vitally important issues. Jan Matousek, in the fifth article in this series titled ‘‘Oxidation Potentials in Iron and Steel Making,’’ Zhiwei Peng and Phillip J. Mackey are the guest editors for the Pyrometallurgy Committee of the TMS Extraction & Processing Division, and coordinators of the topic ‘‘New Developments in Pyrometallurgy’’ in this issue. JOM, Vol. 65, No. 11, 2013

Recent Development in Slag Treatment and Dust Recycling

Slags from metallurgical processes are widely used in different fields of application, e.g. in the building industry and as fertilisers. Nevertheless, also these by-products have to be improved to ensure their sustainable use. The treatment of liquid slags, e.g. by changing their composition outside of the steel production process, will lead to interesting new properties of the newly formed products and thus guarantee their use in the future. Moreover, dust and sludges from off-gas cleaning of metallurgical processes are becoming promising resource for coating and alloying elements. The very important element Zn for surface coating is enriched in the dusts, due to the recycling of Zn coated scrap. On the other hand, Zn might run short in the future, so that recovering of Zn from dusts and sludges may become necessary. To improve the efficiency of Zn recovery a dust re-cycling process has been developed for EAF steelmaking by FEhS-Institute. Some interesting side effects are supported by the dust recycling. It has been proved that the slag foaming can be enhanced by dust recycling, even for stainless steelmaking processes. Finally it can be shown that recovery of valuable elements from residues of iron and steelmaking is becoming more and more important. New developed processes are ready to be implemented into the daily steelmaking practise.

SEPARATION OF MICROLITE FROM ZIRCON BY FLOTATION

Tantalum, an important raw material, is produced mainly from tin slags, while some is extracted from tantalite, colombite and microlite. However, treatment of tin slags for tantalum production is an expensive process. Separation of microlite in zircon concentrates is important from technological and economical points of view. By-products of cassiterite concentration include colombite, tantalite, monazite, zircon, ksenotim, microlite, wolframite, rutile and ilmenite. Zircon concentrates thus produced may contain up to 30% Ta2O5 included in microlite. However, separation of microlite from zircon is not achieved in most cases. In this investigation, flotation separation of microlite from zircon was studied. Tests showed that microlite could be succesfully separated from zircon by floating zircon and leaving microlite in the non-float fraction using Porocoll SAM as the collector.Etant la matiere premiere importante, tantalium s’est obtenue principalement en grande quantite, a l’aide de scories d’ etain. Reciproquement, le reste de la production de tantalium provient par l’extraction des mineraux de tantalite, de colombite et de microlithe. Cependant, l’operation de l’extraction de tantalium se trouvant dans les scories est une processe tres expensive. Pour cette raison, la separation de microlithes qui existent dans dans la concentree de zircon, se montre comme un probleme important au point de vue technologique et economique. Pendant la concentration des mineraux de cassiderite, on obtient aussi les mineraux de colombite, de tantalite, du monazite, du zircon, du xenotime, du microlithe, de wolframite de rutile et d’ ilmenite sous forme de by product. La concentree de zirkonium ainsi obtenue, peut contenir plus de % 30 Ta2O5 avec des mineraux de microlithes inclus. Pourtant l’ operation de la separation du microlithe et du zirconium devient impossible dans beaucoup de conditions. Dans cette recherche, on a etudie la possibilite de la separation des mineraux de microlithe et du zirconium, par la methode de flotation. Les resultats des testes nous montrent qu’ on peut separer avec succes, les mineraux de microlithe et du zircon. Pendant la concentration avec le flottation, on flotte les mineraux de zirconium, en utilisant Porocoll SAM comme collecteur et e meme temps, on deprime les mineraux de microlithes.

Solubility and speciation of sulfur in silicate melts: The Conjugated Toop-Samis-Flood-Grjotheim (CTSFG) model

A Conjugated Toop-Samis-Flood-Grjotheim (CTSFG) model is developed by combining the framework of the Toop-Samis polymeric approach with the Flood-Grjotheim theoretical treatment of silicate melts and slags. Electrically equivalent ion fractions are computed over the appropriate matrixes (anionic and cationic) in a Temkin notation for fused salts, and are used to weigh the contribution of the various disproportionation reactions of type: M 2/ ν O (melt) + ½ S 2(gas) ⇔ M 2/ ν S (melt) + ½ O 2(gas) M 2/ ν O (melt) + ½ S 2(gas) + 3 2 O 2,(gas) ⇔ M 2/ ν SO 4(melt) ν being the charge of the generic M ν+ cation. The extension of the anionic matrix is calculated in the framework of a previously developed polymeric model (Ottonello et al., 2001), based on a parameterization of Lux-Flood acid-base properties of melt components. Model activities follow the Raoultian behavior implicit in the Temkin notation, without the needs of introducing adjustable parameters. The CTSFG model is based on a large amount of data available in literature and exhibits a satisfactory heuristic capability, with virtually no compositional limits, as long as the structural role given to each oxide holds. The model may be employed to compute gas-melt equilibria involving sulfur and allows computing sulfide and sulfate contents of silicate melts whenever the fugacity of a gaseous sulfur species and oxygen are known. Alternatively, the model calculates the oxidation state of the system (i.e., oxygen fugacity), whenever an analytical determination of either sulfide/sulfate or ferrous/ferric ratios in the melt is provided. Calculated sulfide and sulfate capacities allow the estimates of sulfur abundance in various melts of geological interest, both under anhydrous and hydrous conditions or, alternatively, of fS 2, given fO 2 and the bulk sulfur content. In this case, fSO 2 and fH 2S may be eventually computed along the water-sulfur-melt boundary provided fH 2O is known.

Effect of liquid and supercritical carbon dioxide treatments on the leaching performance of a cement-stabilised waste form

Cement-based stabilisation processes are frequently used for immobilising wastes containing a variety of toxic compounds. In order to improve and extend cement-based stabilisation processes, research has been carried out to examine the role of carbonation (i.e. the interaction of cement-based materials with atmospheric CO 2) on the leaching of inorganic contaminants from cementitious waste forms. Because supercritical CO 2 has a high diffusivity and a density over 2 orders of magnitude higher than gaseous CO 2, carbonation reactions in cementitious materials can be strongly accelerated by using supercritical CO 2 as the carbonating atmosphere, rather than using CO 2 gas under ambient pressure. In this paper, therefore, the effect of subcritical (liquid) and supercritical CO 2 treatments on the leaching behaviour of a cementitious waste form is presented. Different CO 2 pressure and temperature conditions ( 100 bar<p<250 bar, 20 ° C<T<50 °C) were applied. Two different leaching tests were performed to study the effect of the CO 2 treatments on the leaching of different elements (As, Ca, Cd, Cr, Cu, K, Mo, Na, Ni, Sb, Pb, V, Zn, chloride, fluoride and sulphate). The results indicated that liquid and supercritical carbonation of cement-immobilised slags indeed affected the leaching of the different contaminants investigated, but the different CO 2 treatments did not affect the leaching in the same manner all the time. It was found that the leachability (i.e. the leaching under normal environmental conditions) of the elements Cr, Cu, Mo, Sb, chloride and sulphate did not decrease (and even increased considerably under some conditions) upon treatment of the cement-immobilised slags with liquid and scCO 2. For the elements Pb, Ca, K, Na and fluoride, the effect of a liquid and scCO 2 treatment on their leachability appeared to be more beneficial for the environmental quality of the cement-immobilised slag material, since (for most contact times) these treatments resulted in a decrease of the leaching of these elements. In addition, it was found that the availability (i.e. leaching under extreme environmental conditions) of the element V increased considerably upon treatment of the cement-immobilised slags with liquid and scCO 2. For the elements Cd, Pb, Zn, Na and Sb, the effect of a liquid and scCO 2 treatment on their availability appeared to be more beneficial, since (for most contact times) these treatments resulted in a decrease of the availability of these elements. For the elements Ca, K, Mo, chloride and sulphate, the effect of liquid and scCO 2 treatments on their availability appeared to be negligible. For some other contaminants (such as As, Cr, Cu, Ni and fluoride), the effect on the availability was strongly dependent on the type of CO 2 treatment. In general, however, there was no clear relation between the extent of carbonation and the leachability or availability of the different contaminants. Further research should indicate if this new recycling technology will be justifiable, both in technical and economical terms, to reduce waste arisings.

Resurrection of the iron and phosphorus resource in steel-making slag

This research focused on the treatment of steel-making slags to recycle and recover iron and phosphorus. The carbothermal reduction behavior of both synthesized and factory steel-making slag in microwave irradiation was investigated. The slags were mixed with graphite powder and heated to a temperature higher than 1873 K to precipitate a lump of Fe–C alloy with a diameter of 2–8 mm. The larger the carbon equivalent (Ceq, defined in the text), the higher the fractional reduction of iron and phosphorus. An increase in the SiO2 content of slag led to a considerable improvement in the reduction for both iron and phosphorus because of the improvement in the fluidity of the slags and an increase in the activity coefficient of P2O5 in the slags. The extraction behavior of phosphorus from Fe–P–Csatd alloy was also investigated at 1473 K by carbonate flux treatment. For all the experiments with a processing time longer than 10 min, the phosphorus in the fluxes could be concentrated to more than 9% (w/w) showing that it could be used as a phosphorus resource. Compared with K2CO3 flux treatment, that using Na2CO3 was more effective for the extraction of phosphorus, and this was attributed to the lower evaporation of Na2CO3. Finally, a recycling scheme for steel-making slag is proposed.

Research of Processes and Development of Separatorsfor Metal Recovery From Metallurgical Slags

This article relates to the analysis of formation and the metal content of slag, generalised data from enterprises on yield and treatment of slags. Test results of the metal content determination in slag dumps, slag granulometric composition, its physical and chemical properties, as well as results of experimental investigation of metal recovery process from slags are presented. Dependences of metal recovery on slagging, granulometric composition and magnetic field parameters of separators were obtained. Electromagnetic separators were developed. Results of technological research carried out under industrial conditions of metal removal from slags, metal scrap cleaning from mineral component are examined in this article.

Effectiveness of the treatment of blast-furnace slags in the plants of the ministry of ferrous metallurgy of the Ukrainian SSR

Effectiveness of the treatment of blast-furnace slags in the plants of the ministry of ferrous metallurgy of the Ukrainian SSR