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Various metallurgical dust contains Fe2O3 and CaO, which catalyze the carbon–oxygen reaction and exhibit variable distributions and relative contents. Herein, we probe the interactions between Fe2O...

Nickel slags can be produced through ferronickel preparation by the pyrometallurgical processing of laterite nickel ores, however, such techniques are underutilized at present, and serious environmental problems arise from the stockpiling of such nickel ores. In this study, a modification to the process of ferronickel preparation by the direct reduction of carbon bases in laterite nickel ores is proposed. The gangue from the ore is used as a raw material to prepare a cementitious material, with the main components of tricalcium silicate and tricalcium aluminate. By using FactSage software, thermodynamic calculations are performed to analyze the reduction of nickel and iron and the effect of reduction on the formation of tricalcium silicate and tricalcium aluminate. The feasibility of a coupled process to prepare ferronickel and cementitious materials by the direct reduction of laterite nickel ore and gangue calcination, respectively, is discussed under varying thermodynamic conditions. Different warming strategies are applied to experimentally verify the coupled reactions. The coupled preparation of ferronickel and cementitious materials with calcium silicate and calcium aluminate as the main phases in the same experimental process is realized.

Oxy-fuel combustion of coal pyrolysis gas has recently been proposed to serve as internal heat source of a vertical low-temperature pyrolysis furnace, in order to make the output pyrolysis gas nearly free of nitrogen and widely useful. To keep the pyrolysis temperature and the heat carrier gas volume unchanged from air combustion to oxy-fuel combustion, the equivalence ratio has to be increased up to 8. To explore the flame temperature and species variation at this ultra-rich condition, freely propagating premixed oxy-fuel flames of a typical coal pyrolysis gas at equivalence ratios of 0.5–10 are numerically studied with detailed chemistry. It is found that super-adiabatic flame temperatures (SAFT) occur at equivalence ratios larger than 3 for the considered pyrolysis gas and the SAFT magnitude is 294 K at equivalence ratio of 8. Due to the high H2 mole fraction (46%) in the pyrolysis gas, preferential diffusion plays a negligible role in the SAFT feature. Global net production of CO and H2 by the rich combustion only occurs at moderate equivalence ratio ranges, which are 1.5–8 and 3–5.5 respectively for the two species. At equivalence ratio of 8, the three fuel components are all net consumed following the mole ratio of CH4:CO:H2 = 1:0.07:0.84. Kinetic analysis reveals three factors responsible for the reaction mechanism change with the increase in equivalence ratio. Firstly, the lack of H-radical and the decrease in temperature result in the disappearance of the H2 production peak in the initial stage. Secondly, HO2 attack to CO prevails and hence contribution of CO oxidation in the initial stage increases. Thirdly, the long lasting OH attack to CO and H2 leads to the weakened CO and H2 production rate in the final stage.

Large quantities of residual slag with high Fe content are left behind in pyrometallurgical nickel processing. How to separate and recover iron from the high fayalite residue is still a problem because iron mainly exists as iron-magnesium silicate in slag. This article suggests that the slag for nickel smelting is adjusted by increasing the amount of lime, partly instead of quartz, to form liable reduction compounds for subsequent Fe extraction. Based on the thermodynamic analysis and phase diagram of the FeO-SiO2-CaO-MgO slag system, the new slag composition was chosen, the suitable melting point of relevant slags was measured, and the phase change was observed. The new slag with a composition of 7 to 9 pct MgO, 10 to 15 pct CaO and 1.5 to 1.8 Fe/SiO2 was found to work well for nickel matte smelting. With the increase of CaO and decrease of SiO2 content in slag, Ca(Fe, Mg)Si2O6 and Mg(Ca)Fe2O4 are the main existing phases instead of (Fe, Mg)2SiO4 in the residual smelting slag. More than 50 pct of Fe-containing phases are in the form of MgFe2O4 when 15 pct CaO is added, which is what we want because the MgFe2O4 is much better for magnetic separation and reduction than the original (Fe, Mg)2SiO4. In this way, Fe can be much more easily extracted from residual slag and have multipurpose benefits.

An industrial experiment was carried out by classifying the waste cathodes of aluminum electrolytic cells in Shanxi Province and investigating the effect of particle size and temperature on the leaching of soluble fluoride. It was discovered that NaF was the main dissolvent and could be effectively dissolved by four-stage leaching at 348 K and that the soluble fluorine could be decreased to the limit for hazardous solid waste. After the leaching of discarded water, the fluoride concentration in the final water was enriched to 17.69 g/L, and the effective enrichment of fluoride ion was realized.

The reduction of iron in hematite and process coupling of cementing material generated from gangue components are explored in this paper, and a technical proposal for preparing directly reduced iron and cementing materials considering the processes of energy and material flows is proposed. An experimental study preparing cementing materials, such as tricalcium silicate and dicalcium silicate, by roasting the components, was performed. In this study, hematite was used as the raw material and powdered carbon was added, as the reducing agent, with CaO, at the same time, the gangue components of iron ore were used as the principal raw materials for the process of directly reduced iron preparation by direct reduction of iron ore. The FactSage software package was used to perform thermodynamic calculations of the reduction of iron and its influence on the formation of tricalcium silicate and dicalcium silicate. The feasibility of the direct reduction of iron to elemental iron and preparation of cementing materials by roasting of gangue components under the studied thermodynamic conditions was discussed. Different temperature control strategies were used to verify the reaction coupling test. The results showed that zero-valent iron could be produced by roasting and reducing hematite under certain experimental conditions, and cementing materials, such as tricalcium silicate and dicalcium silicate, could be produced simultaneously by reacting the gangue components with CaO. Fe2O3 exerted an adverse effect on the formation of tricalcium silicate, and sufficient reduction of the iron was a precondition for the formation and stability of tricalcium silicate.

When applied for desulfurization in the coal combustion process, traditional sulfur sorbents have very low sorbent utilization and normally have a negative effect on combustion efficiency. A new type of sulfur sorbent, calcium peroxide (CaO2), synthesized from natural limestone, is proposed and its effects on desulfurization and combustion efficiency are investigated in this paper. The first series of experiments were carried out in a drop tube furnace (DTF). The results showed that CaO2 captured more sulfur than limestone and improved the burnout behavior of coal. To investigate the sulfur removal efficiency of CaO2, the second experiment was carried out in a fixed bed. The results indicated that the sulfur capture capability of CaO2 definitely exceeds that of limestone no matter whether in a low or high temperature range. Moreover, the combustion behavior of coal with and without CaO2 addition was investigated using thermogravity (TG) and differential scanning calorimetric (DSC) analysis. An inc...