Interaction mechanism between arsenate and fayalite-type copper slag at high temperatures

The interaction mechanism between sodium arsenate and fayalite-type copper slag at 1200℃was investigated through XRD,XPS,HRTEM,TCLP and other technical means and methods.The results indicated that the proportions of sodium arsenate in the slag and flue gas phases were approximately 30%and 70%,respectively.The addition of sodium arsenate depolymerized the fayalite structure and changed it from a crystalline state to an amorphous state.The fayalite structural changes indicated that the[AsO_(4)]tetrahedron in sodium arsenate combined with the[SiO_(4)]tetrahedron and[FeO_(4)]tetrahedron through bridging oxygen to form a silicate glass structure.The TCLP test results of the samples before and after the high temperature reaction of fayalite and sodium arsenate showed that after high temperature reaction,fayalite could effectively reduce the leaching toxicity of sodium arsenate,reducing the leaching concentration of arsenic from 3025.52 to 12.8 mg/L before and after reaction,respectively.

Corrosion mechanism of magnesia-chromite refractories by ZnO-containing fayalite slags: Effect of funnel glass addition

An efficient approach for lead extraction from waste funnel glass through the lead smelting process has been proposed. To clarify the effect of funnel glass addition on the degradation of magnesia-chromite refractories by ZnO-containing fayalite slag, the corrosion behavior of magnesia-chromite refractories in lead smelting slags with different funnel glass additions from 0wt% to 40wt% was tested. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) was used to acquire the microstructural information of the worn refractory samples. Experimental results showed that the corrosion of magnesia-chromite refractory consisted predominantly of the dissolution of MgO into slag. ZnO and FeO reacted with periclase and chromite to form (Zn,Fe,Mg)O solid solution and (Zn,Fe,Mg)(Fe,Al,Cr)2O4 spinel, respectively. With the addition of funnel glass, the solubility of MgO increased whereas ZnO levels remained stable, thereby resulting in a reduced Mg content and an elevated Zn and Fe content in the (Zn,Fe,Mg)O solid solution and the (Zn,Fe,Mg)(Fe,Al,Cr)2O4 spinel. Considering the stability of the (Zn,Fe,Mg)O solid solution layer and the penetration depth of the slag, the optimal funnel glass addition for lead smelting was found to be 20wt%.

First-principles calculations of structure and elasticity of hydrous fayalite under high pressure

The structures, elasticities, sound velocities, and electronic properties of anhydrous and hydrous fayalite （Fe2SiO4 and Fe1.75H0.5SiO4） under high pressure have been investigated by means of the density functional theory within the generalized gradient approximation （GGA） with the on-site Coulomb energy being taken into account （GGA＋U）. The optimized results show that H atoms prefer to substitute Fe atoms in the Fe1 site. Compared with the anhydrous fayalite Fe2SiO4, the mass density, elastic moduli, and sound velocities of Fe1.75H0.5SiO4 slightly decrease. According to our data, adding 2.3 wt% water into fayalite leads to reductions of compressional and shear wave velocities （VP and VS） by 3.4%-7.5% and 0.3%-3.4% at pressures from 0 GPa to 25 GPa, respectively, which are basically in agreement with the 2%-5% reductions of sound velocity obtained by the experimental measurement in the low velocity zones （LVZ）. Based on the electronic structure, the valence and conduction bands are slightly broader for hydrous fayalite. However, hydrous fayalite keeps the insulation characteristics under the pressures up to 30 GPa, which indicates that hydration has little effect on its electronic structure.

Exploring the potential of olivine-containing copper-nickel slag for carbon dioxide mineralization in cementitious materials

Water-quenched copper-nickel metallurgical slag enriched with olivine minerals exhibits promising potential for the production of CO_(2)-mineralized cementitious materials.In this work,copper-nickel slag-based cementitious material(CNCM)was synthesized by using different chemical activation methods to enhance its hydration reactivity and CO_(2) mineralization capacity.Different water curing ages and carbonation conditions were explored related to their carbonation and mechanical properties development.Meanwhile,thermogravimetry differential scanning calorimetry and X-ray diffraction methods were applied to evaluate the CO_(2) adsorption amount and carbonation products of CNCM.Microstructure development of carbonated CNCM blocks was examined by backscattered electron imaging(BSE)with energy-dispersive X-ray spectrometry.Results showed that among the studied samples,the CNCM sample that was subjected to water curing for 3 d exhibited the highest CO_(2) sequestration amount of 8.51wt%at 80℃and 72 h while presenting the compressive strength of 39.07 MPa.This result indicated that 1 t of this CNCM can sequester 85.1 kg of CO_(2) and exhibit high compressive strength.Although the addition of citric acid did not improve strength development,it was beneficial to increase the CO_(2) diffusion and adsorption amount under the same carbonation conditions from BSE results.This work provides guidance for synthesizing CO_(2)-mineralized cementitious materials using large amounts of metallurgical slags containing olivine minerals.

Recovery of valuable metals from spent lithium ion batteries by smelting reduction process based on FeO-SiO_2-Al_2O_3 slag system

NA novel smelting reduction process based on FeO-SiO2-Al2O3 slag system for spent lithium ion batteries with Al cans was developed, while using copper slag as the only slag former. The feasibility of the process and the mechanism of copper loss in slag were investigated. 98.83% Co, 98.39% Ni and 93.57% Cu were recovered under the optimum conditions of slag former/battery mass ratio of 4.0：1, smelting temperature of 1723 K, and smelting mass ratio of time of 30 min. The FeO-SiO2-Al2O3 slag system for the smelting process is appropriate under the conditions of m（FeO）：m（SiO2）=0.58：1？1.03：1, and 17.19%？21.52% Al2O3 content. The obtained alloy was mainly composed of Fe-Co-Cu-Ni solid solution including small amounts of matte. The obtained slag mainly consisted of fayalite and hercynite. Meanwhile, the mechanism of copper loss is the mechanical entrainment from strip-like fayalite particles in the main form of copper sulfide and metallic copper.

Improvement of carbothermic reduction of nickel slag by addition of CaCO3

The effect of CaCO3 addition on the carbothermic reduction of nickel slag was studied,and the mechanism of CaCO3 in improving the reduction was analyzed.The results showed that when the CaCO3 content added to the slag was increased from 0 to 8 wt.%,initiation temperature of the carbothermic reaction decreased from 1100 to 1000℃,the temperature reaching the maximum reduction rate decreased from 1150 to 1100℃,and the reduction degree of the nickel slag increased from 58%to 88%.The iron particles in the reduced nickel slag were coarsened and the X-ray diffraction intensity of metallic iron peaks increased,confirming that the addition of CaCO3 was beneficial to the reduction of nickel slag and recovery of iron.

Enhancement of the nickel converter slag-cleaning operation with the addition of spent potlining

The slag cleaning(or matte settling) process was experimentally investigated at 1573 K using a fayalitic nickel converter slag containing spinel and matte/alloy particles.The addition of various amounts of spent potlining(SPL) was studied in terms of its influence on matte settling and the overall metal recoveries.The slags produced were characterized by scanning electron microscopy,energy-dispersive spectroscopy,and wet chemical analysis using inductively coupled plasma optical emission spectrometry.The presence of solid spinel particles in the molten slag hindered coalescence and settling of matte/alloy droplets.Matte settling was effectively promoted with the addition of as little as 2 wt% SPL because of the reduction of spinel by the carbonaceous component of the SPL.The reduced viscosity of the molten slag in the presence of SPL also contributed to the accelerated matte settling.Greater metal recoveries were achieved with larger amounts of added SPL.Fast reduction of the molten slag at 1573 K promoted the formation of highly dispersed metal particles/clusters via accelerated nucleation in the molten slag,which increased the overall slag viscosity.This increase in viscosity,when combined with rapid gas evolution from accelerated reduction reactions,led to slag foaming.

Effects of oxygen content on the oxidation process of Si-containing steel during anisothermal heating

The oxidizing behavior of Si-containing steel was investigated in an O2 and N2 binary-component gas with oxygen contents ranging between 0.5 vol% and 4.0 vol% under anisothermal-oxidation conditions. A simultaneous thermal analyzer was employed to simulate the heating process of Si-containing steel in industrial reheating furnaces. The oxidation gas mixtures were introduced from the commencement of heating. The results show that the oxidizing rate remains constant in the isothermal holding process at high temperatures; therefore, the mass change versus time presents a linear law. A linear relation also exists between the oxidizing rate and the oxygen content. Using the linear regression equation, the oxidation rate at different oxygen contents can be predicted. In addition, the relationship between the total mass gain and the oxygen content is linear; thus, the total mass gain at oxygen contents between 0.5 vol%–4.0 vol% can be determined. These results enrich the theoretical studies of the oxidation process in Si-containing steels.

Effect of Si Content and Temperature on Oxidation Resistance of Fe-Si Alloys

Hot-rolled Fe-（0.75-2.20）Si （mass%） alloys were oxidized in dry air at 600-1200 ℃. The oxidation process was carried out by thermal gravimetric analysis （TGA）. At 600- 1 150 ℃, oxidation gain curves were approximately parabolic. Electron probe mieroanalysis （EPMA） was applied to investigate cross-section morphology of oxide layer and element distribution across the layer. At lower temperature of 700 ℃, the oxide layer consisted of internal oxidation zone （IOZ）, inner Si-rich layer （conglomerate of fayalite and magnetite） and outer hematite layer, while at higher temperature of 1200 ℃, fayalite and wustite were observed in external oxide scale. Liquidus temperature of fayalite was detected by differential scanning calorimetry （DSC）. Through comparing the oxidation mass gain and parabolic rate constant of the alloys, it was found that oxidation resistance of Fe-Si alloy was enhanced by increasing Si content below 1 150 ℃ while increasing Si content of the alloy resulted in higher oxidation rate above 1150 ℃ owing to the liquid fayalite formation.

Direct Reduction Experiment on Iron-Bearing Waste Slag

A lot of iron-bearing slags were produced,and whose grade is much more than that of industrial iron ore grade.Chemical analysis and phase identification shows that the iron-bearing slag is amorphous,has fayalite main phase,iron grade is 36.10%,and is difficult to recover iron from the slag.Thermodynamic calculation indicates that CO cannot reduce fayalite at high temperature and carbon direct reduction can be effective.Moreover,the reaction begins at 770 ℃ and the temperature can be reduced down to 500℃ when CaO is added.On this basis,a method is put forward to making direct enrichment of iron by taking carbon contained pellets to realize the rapid reduction of fayalite,and the direct reduction process were studied in this paper.Experiments show that xC/xO should be less than 1.5 for the need of reduction and carburization,and CaO and Al2O3 can spur the reduction of fayalite.On conditions that xC/xO is 1.2,metallization rate can be 77% when temperature is 1 250 ℃ and only carbon is added,and metallization rate can be 74% when temperature is 1 200 ℃ and only CaO is added.Moreover the addition of Al2O3 can get a higher metallization rate（10% or so） than usual as R is between 0.4 and 1.0.Under the optimized condition of R equals to 0.6,temperature of 1 250 ℃,slag melting point of 1 320 ℃,and time of 30 min,the metallization rate can reach 88.43%.

The influence of curing conditions on the mechanical properties and leaching of inorganic polymers made of fayalitic slag

This study reports on the impact of the curing conditions on the mechanical properties and leaching of inorganic polymer （IP） mortars made from a water quenched fayalitic slag. Three similar IP mortars were produced by mixing together slag, aggregate and activating solution, and cured in three different environments for 28 d： a） at 20℃ and relative humidity （RH） - 50% （T20RH50）, b） at 20℃and RH≥90% （T20RH90） and c） at 60℃ and RH - 20% （T60RH20）. Compressive strength （EN 196-1） varied between 19 MPa （T20RH50） and 31 MPa （T20RH90）. This was found to be attributed to the cracks formed upon curing. Geochemical modelling and two leaching tests were performed, the EA NEN 7375 tank test, and the BS EN 12457-1 single batch test. Results show that Cu, Ni, Pb, Zn andAs leaching occurred even at high pH, which varied between 10 and 11 in the tank test＇s leachates and between 12 and 12.5 in the single batch＇s leachates. Leaching values obtained were below the requirements for non-shaped materials of Flemish legislation for As, Cu and Ni in the single batch test.