Aluminate Slag Research Articles

Recovery of iron and calcium aluminate slag from high-ferrous bauxite by high-temperature reduction and smelting process

A high-temperature reduction and smelting process was used to recover iron and calcium aluminate slag from high-ferrous bauxite. The effects of w(CaO)/w(SiO2) ratio, anthracite ratio, and reduction temperature and time on the recovery and size of iron nuggets and on the Al2O3 grade of the calcium aluminate slag were investigated through thermodynamic calculations and experiments. The optimized process conditions were the bauxite/anthracite/slaked lime weight ratio of 100:16.17:59.37, reduction temperature of 1450°C and reduction time of 20 min. Under these conditions, high-quality iron nuggets and calcium aluminate slag were obtained. The largest size and the highest recovery rate of iron nuggets were 11.42 mm and 92.79wt%, respectively. The calcium aluminate slag mainly comprised Ca2SiO4 and Ca12Al14O33, with small amounts of FeAl2O4, CaAl2O4, and Ca2Al2SiO7.

Thermodynamic design of electroslag remelting slag for high titanium and low aluminium stainless steel based on IMCT

The advantages of the electroslag remelting (ESR) process as to cleanness and homogeneity of the ingot structure are well known. As to homogeneity of composition, the control of titanium in stainless steel with high titanium and low aluminium contents during the ESR process has not been resolved well so far. The current work focuses on designing appropriate slag for controlling titanium content during 1Cr21Ni5Ti remelting based on the interaction of the slag/metal interface. Several kinds of slag containing different CaO contents combined with steel samples of 1Cr21Ni5Ti were employed to investigate the effect of slag on titanium content in an electrical resistance furnace, and metal samples were taken at different times for investigating the change of titanium and aluminium contents in steel. The results show that slag with low CaO content at low temperature has excellent capacity for avoiding loss of titanium content caused by its reaction with the alumina in slag, especially in case of remelting of stainless steel with high titanium and low aluminium contents. The CaO in slag has great effect on the activities of TiO2 and Al2O3, and thermodynamic analysis was applied to investigate the CaO behaviour based on the ion and molecule coexistence theory of slag. The thermodynamic analysis results show that the increases as CaO content in slag decreases, which is better for preventing loss of titanium caused by its reaction with the alumina in the ESR slag. The slag with low CaO content at low temperature is suitable for ESR of 1Cr21Ni5Ti.

Researches concerning influence of magnesium, aluminum and titanium lime on steel desulfurization

The paper presents the results of laboratory experiments on steel desulphurisation with slag from the system MgO-Al2O3-TiO2. To determine the influence, on the desulphurisation process, of the titanium oxide added in calcium aluminate slag, we experimented, in the laboratory phase, the steel treatment with a mechanical mixture consisting of lime, aluminous slag and slag obtained from the titanium making process through the aluminothermic technology. The steel melting was carried out in an induction furnace of 10 kg capacity, existent in the "Metallic Melts" laboratory of the Engineering Faculty of Hunedoara. During the research, we aimed to establish correlation equations between the sulphur distribution coefficient and the slag components (MgO, Al2O3, TiO2). The data obtained in the experiments were processed in MATLAB programs, resulting multiple correlation equations, which allowed the elucidation of some physical-chemical phenomena specific to the desulphurisation processes.

Effect of Basicity, Al2O3and MgO content on the softening and melting properties of the CaO-MgO-SiO2-Al2O3high alumina quaternary slag system

The flow characteristic temperatures of the selected quaternary CaO-MgO-SiO2 -Al2 O3 slags have been experimentally measured by performing softening and melting tests using a high temperature microscope in accordance with German standard 51730. An effective statistical model is developed through constructing empirical equations by regression analysis method to predict Softening temperature (ST), Hemispherical temperature (HT), and Flow temperature (FT) based on Al2 O3 (25%–30%) content, CaO/SiO2 (C/S ratio: 0.9–1.4), and MgO (4%–12%) content. The effect of basicity, MgO and Al2 O3 content on characteristic temperature are also studied. FactSage 6.4 data base is used to calculate liquidus temperature of the above quaternary slags and compared with the experimental and regression results. The experimental results show that, increase in Al2 O3 content increases ST and HT while decreases FT of the slags. The ST, HT and FT increase with increase in C/S ratio. Increase in MgO content decreases both ST and HT while increases FT of the slags. The liquidus temperature obtained from FactSage 6.4 are found to correspond well with the experimental and regression data. Under the range of composition examined, a high Al2 O3 (30%) and high C/S ratio (1.4) coupled with low MgO (4%) content is beneficial for the blast furnaces running with high Alumina slags, as it ensures the formation of a short slag.

Influence of Basicity and MgO on Fluidity and Desulfurization Ability of High Aluminum Slag

AbstractThe viscosity of experimental slag, which was mixed based on the composition of a practical blast furnace slag, was measured in this paper. The influence of Al2O3and MgO content, basicityR2=w(CaO)/w(SiO2) on the fluidity of slag was studied. The stepwise regression analysis in SPSS was used to reveal the relationship between sulfur distribution coefficientLSand slag composition as well as furnace temperature. The results show that increasing of MgO up to 12% can decrease the slag viscosity. Thew(MgO) should be controlled below 8% when there is 20% Al2O3in the slag. Temperature of hot metal and content of CaO in slag are the two dominant factors on the desulfurization capacity of slag.

Secondary reaction mechanism of leaching process of calcium aluminate slag

SiO2 in calcium aluminate slag exists in the form of γ-2CaO·SiO2 which is more stable than β-2CaO·SiO2. However, it is decomposed by sodium carbonate solution during leaching process, leading to the secondary reaction. The extent of secondary reaction and reaction mechanism of calcium aluminate slag were studied using XRD. The results show that the decomposition rate of γ-2CaO·SiO2 increases with the increase in leaching time and sodium carbonate concentration. The main products of secondary reaction are the mixture of hydrogarnet and sodium hydrate alumina–silicate. SiO2 concentration rises firstly and then drops with the increase of leaching temperature. XRD results indicate that the stable product of secondary reaction at low temperature is hydrogarnet. But hydrogarnet is transformed into sodium hydrate alumina–silicate at high temperature.

Reduction and melting behavior of carbon composite lateritic bauxite pellets

Direct reduction of low-grade lateritic bauxite was studied at high temperature to recover Fe and beneficiate Al2O3 slag. The results show that a metallization rate of 97.9% and a nugget recovery rate of 85.1% can be achieved when the reducing and melting temperatures are 1350 and 1480°C, respectively. Moreover, a higher-grade calcium aluminate slag (Al2O3 = 50.52wt%) can also be obtained, which is mainly composed of α-Al2O3, hercynite (FeAl2O4), and gehlenite (Ca2Al2SiO7). In addition, high-quality iron nuggets have been produced from low-grade lateritic bauxite. The nugget is mainly composed of iron (93.82wt%) and carbon (3.86wt%), with almost no gangue (slag).

Synthesis of geopolymer from industrial wastes

Aluminium and grey cast iron slags are produced in small industries and in spite of blastfurnace slag are considered as wastes. In this work, synthesis possibility of geopolymeric paste and concrete through alkali activation of different mixes of these slags is studied. Workability of the mixtures was achieved immediately after mixing and compressive strength tests were conducted on specimens cured at room temperature. Workability of all pastes and concrete specimens were in acceptable range for use in constructions. Maximum compressive strength for both paste and concrete specimens was achieved by using silica/alumina weight ratio of 3.0. By increasing the value of parameters of this study including sodium hydroxide concentration, age of curing and silica/alumina weight ratio, more silicon and aluminium ions dissolve from slag mixture into alkali activator and hence, compressive strength increases. It was concluded that among the considered parameters, silica/alumina weight ratio is the most important factor. The results indicated the possibility of production of geopolymers by utilizing appropriate ratios of aluminium slag (alumina source) and grey cast iron slag (silica source). In most related works reported in the literature, an aluminosilicate source or a mixture of two aluminosilicate sources with defined silica/alumina weight ratio are evaluated for possibility of geopolymerization. In the current study, each alumina and silica is provided from an individual source, and geopolymerization is performed by manipulating silica/alumina weight ratio.

Steel Reoxidation by Gunning Mass and Tundish Slag

Steel reoxidation in the tundish has a significant influence on the steel cleanliness and therefore on the mechanical properties of the final product. In the present work, the steel reoxidation by two types of gunning mass (GM), viz. magnesia- and alumina-based GM, and two types of tundish slag, viz. lime–alumina–silica and lime–alumina slags, has been investigated. The evolution of the steel composition during the test was analyzed and predicted based on thermodynamic and kinetic considerations. The calculated steel composition agrees well with measured values, when assuming the mass transfer in slag phase limits the reoxidation reactions. The oxidation capacity of the gunning mass and tundish slag is quantified by calculating the oxygen amount supplied from the GM and the slag to the steel phase. It was found that compared to alumina GM, magnesia GM exhibits a stronger oxidation capacity due to its higher content of reducible oxides (10 wt pct SiO2 + 6 wt pct FeO). Compared to lime–alumina–silica tundish slag, lime–alumina slag (with more FeO + MnO contents) provides more oxygen to the molten steel in the present experimental conditions and consequently shows a stronger oxidation capacity.

The Influence of Limestone and Al2O3 Content in the Slag on the Performance of the Composite Cements

In the present contribution, the interaction between limestone and slag is investigated by a multi-method approach using chemical shrinkage, thermogravimetry, scanning electron microscopy (SEM) techniques and compressive strength measurements. The impact of limestone was investigated in blends containing synthetic slags of different alumina content. The results are correlated with the thermodynamic modelling in order to gain further insights into the physical and chemical processes governing the interaction between limestone, slag and Portland cement.Beyond 28 days of hydration, slag composites exhibit higher compressive strength values than their equivalent with quartz. Increasing the Al2O3 content from 8 to 12% in slag influenced compressive strengths positively at all hydration times. Further increase of alumina in slag to 16% has no positive effect on strength. Addition of limestone, results positively only on early compressive strengths. After 28 days and longer effect of limestone is either slightly negative or neutral. Only in the case of the slag containing 16% of alumina, limestone has positive impact on the late compressive strength. The effect of limestone has two main components: physical, so called filler effect and chemical that depends on the slag composition.

Preparation and Coagulation Performance of Polymeric Aluminum Zinc Ferric (PAZF) from Galvanized Aluminum Slag

A new inorganic coagulant polymeric aluminum zinc ferric (PAZF) was prepared using a galvanized aluminum slag as the main material. Coagulation performance was evaluated by jar test on printing and dyeing wastewater and landscape water treatment, and the optimum conditions for the two tested water samples were investigated to be coagulant dosage of 70 and 210 mg/L, pH value of 8.0 and 9.0, and settling time of 15 and 20 min. The removal of turbidity, chroma and COD for printing and dyeing wastewater treatment were 93.8%, 83.32% and 62.19% respectively with turbidity, TP and COD removal for landscape water treatment as 86.98%, 82.39% and 86.82%.

Influence of MgO on Calcium Aluminate Slag System with Lower Calcium

The effect of MgO on phase composition, alumina leaching properties and the self-disintegrating rate of calcium aluminate slag were investigated by X-ray diffraction and another analysis method. And a feasible method is proposed to eliminate the negative effects of MgO. The results shows that: the phase of 2CaO·SiO2(C2S)、20CaO·13Al2O3·3MgO·3SiO2(Q phase) and 12CaO·7Al2O3(C12A7) are formed when there is MgO in slag with the C/A=1.4 and A/S=1.3. The content of Q phase increase and the leaching rate of slag reduce with increasing the temperature and the content of MgO. MgO would reduce self-disintegrating rate of slag. CaSO4·2H2O can improve the self-disintegrating the leaching properties of slag by promoting the synthesis of C12A7 and inhibit the synthesis of Q phase.

Hydrotalcite-like compounds: A way to recover a hazardous waste in the aluminium tertiary industry

Magnesium–aluminium hydrotalcite-like compounds at ratios of 2:1, 3:1 and 4:1 were prepared using a non-conventional aluminium source, the hazardous wastes from the aluminium tertiary industry. The method consisted in a conventional coprecipitation at constant pH10 with magnesium chloride hexahydrate and stable solutions of Al3+ from dispersions of the fine powder from the sleeve filter suction system in the aluminium slag milling process. The characterisation of the resulting materials indicated that hydrotalcites were strongly dependent on the presence of iron in the layers, as well as the carbonate and chloride content in the interlayer which affected the final properties. XRD and SAED indicated low crystallinity for these materials. Furthermore, as can be seen by SEM, the formation of disordered tiny nuclei was significant causing small spherical agglomerates. The infrared spectra showed a change of symmetry in the interlayer for the different ratios and the textural data suggested the “ink-bottle shaped” mesopores and type IIb isotherms, similar to the results obtained for pillared clays, and the transition to H2 type in the hysteresis loops as a function of the higher ratio.

Formation of Low-Melting-Point Inclusions in Al-Deoxidized Steel Refined by High-Basicity Calcium Aluminate Slag in ZrO2 Crucible Experiments

ZrO2 crucible experiments were carried out in the laboratory to study the formation of low-melting-point inclusions in steel, during which aluminum deoxidization and a high-basicity calcium aluminate refining slag (CaO/SiO2: 6 to 8, Al2O3 40 to 45 pct) were used. Four experiments were done with different slag/steel reaction times (30, 60, 90, and 180 minutes). It was found that inclusions were mainly composed of CaO-Al2O3-ZrO2 with very limited SiO2, in spherical morphology and with sizes mainly less than 5 μm. They can be classified into two types according to the ZrO2 content. The first type contained much lower ZrO2, whereas a much higher level of ZrO2 was detected in the other type. An evolution of inclusions with the reaction time was observed and studied. The obtained results indicated that chemical compositions of inclusions were widely scattered in the CaO-Al2O3-ZrO2 phase diagram after 30 min reaction. However, the composition of inclusions became much more uniform and concentrated in low-melting-temperature regions at 60, 90, and 180 minutes, which would be favorable to prevent nozzle clogging and fatigue problems. Compared with the authors’ previous results obtained in MgO crucible experiments, it was found that low-melting-temperature inclusions can be targeted in shorter time in ZrO2 crucible experiments, without any degradation of cleanliness.

The Application of Thermal Solar Energy to High Temperature Processes: Case Study of the Synthesis of Alumina from Boehmite

The aim of this paper is to evaluate the feasibility of obtaining alumina from boehmite using a free, clean, and unlimited power source as the solar energy. Boehmite was obtained by hydrothermal treatment of a hazardous waste coming from aluminum slag milling. The waste is considered as a hazardous substance because of it releasing toxic gases (hydrogen, ammonia, methane, and hydrogen sulfide) in the presence of water. The as-obtained boehmite was transformed into alumina, in air atmosphere, using a solar energy concentrator (Fresnel lens). The solar installation provides a power density of 260 W·cm−2 which allows reaching temperatures upper than 1000°C at few minutes of exposure. Tests were performed at different periods of time that ranged between 5 and 90 min. The percentage of transformation of boehmite into alumina was followed by the water content of samples after solar radiation exposure. Samples were characterized by X-ray diffraction, infrared spectroscopy, and thermogravimetry. Metastable aluminas started to appear at 5 min and the crystalline and stable phase corundum at 10 min of solar radiation exposure.

Development of mould fluxes based on lime–alumina slag system for casting high aluminium TRIP steel

With excellent strength and ductility properties, transformation induced plasticity (TRIP) steels are superior to ordinary commercial steels and have great application potential in the automobile industry. However, the continuous casting of TRIP steels is associated with challenges owing to its high aluminium content, approximately 0⋅5–1⋅8%. The reaction of aluminium near the steel/slag interface continuously changes the basicity of conventional lime–silica based mould fluxes causing variation in the flux physical properties between the solidifying shell and mould wall. Therefore, the heat transfer process is unstable and the surface quality of the as-cast slab is not guaranteed.To reduce the reactivity of aluminium in TRIP steel during casting, it is suggested to replace the lime–silica based fluxes with a lime–alumina based mould flux, based on laboratory measurements and industrial trials.The trials showed great improvement in the slab surface quality and no depression defect was noticed so far.

Testing Study of FA-ASP Binder Mortar

By using high-volume fly ash (FA), aluminum slag superfine powder (ASP) as raw materials to synthesize FA-ASP binder, this paper developed M10 masonry mortar. Comparing with the cement mortar and FA mortar, the FA-ASP mortar has not only good construction performance and mechanical performance, but also reduces the production cost obviously, which is a broad development prospect of green new building mortar.

Resource Recycling of Waste Slag of Aluminum Factory

In the last decade, The government and scientific researchers have payed a lot of attention to waste slag of aluminum factory . Many scholars have done a great deal of research and put forward many valuable resource recycling methods,Especially in ceramics field. This paper has reviewed the aluminum slag application ways that researched by our team and some other related scholars,and mainly overviews the application in ceramic filed.

Cleanup Case Study of Waste Printed Circuit Boards on Illegal Dumping Sites

This paper study was commenced to treat fatal contamination at the Er-Jen River, supplied water for agricultural irrigation, aquaculture and industrial in Kaohsiung and Tainan Area, when the Sixth River Management of Water Resources Agency (WRA) developed the project to build flood embankment. The fatal contamination was throw into the discard by illegal manufacturer which discarded the wastage of printed circuit boards, toxic heavy metal contained sludge, and waste aluminum slag. The treatment project was conducted by Industrial Technology Research Institute (ITRI) on preliminary tests, cleanup planning, and process supervision to ensure contamination removal, flood protection, and landscape improvement. The accumulative volume cleaned and screened on this site reached 45,159 cubic meters, whereas 378.25 tons of waste printed circuit boards, 12,833 tons of toxic heavy metal contained sludge, and 31,000 tons of general industrial wastages. The waste printed circuit boards through stripping/acid washing and screening, there are 334.653 tons valuable (including 0.143 tons of copper and 334.51 tons of wire casting materials) from the recycle extract and 43.597 tons of wastes that were not valuable for reutilize. Toxicity characteristic leaching procedure (TCLP) tests were conducted on the site after cleanup to verify the treatment work successful, because the rate of contamination removal was greater than 90%.

Interaction between Molten Steel, Alumina Lining Refractory and Slag Phase

AbstractLaboratory experiments exploring the interaction between molten steel, slag and lining refractory were performed. The transient erosion and reaction over time were investigated, and the transient change of the reaction layer and inclusions generated in the molten steel were evaluated using optical microscopy and SEM-EDS. Without slag addition before remelting, the FeO from reoxidation entered the space between the lining refractory and the steel and strengthened the erosion of the lining refractory. Several layers were found from the steel to the original lining refractory layer: steel phase, FeO layer, a FeO-rich lining layer and an Original Lining (OL)-rich lining layer. The thickness of the reaction layer increased nearly linearly with the reaction time at an erosion rate of 4.2 µm/min. With slag addition before remelting, the reaction layer between the steel and the original lining materials included several sub-layers: a gap, a slag layer, an FeO-rich lining layer and an Original Lining (OL)-rich lining layer. The thickness of the reaction layer nearly linearly increased with the reaction time and with an erosion rate of 5.7 µm/min. Slags were entrained into the steel occasionally.