https://www.tandfonline.com/doi/pdf/10.1080/21870764.2020.1815348

Sustainable ceramics derived from solid wastes: a review

Metallurgical slags are a mass-produced industrial solid waste, often destined to landfills; the volumes disposed represent an environmental burden. Over the last three decades, applications have been found for these wastes, mainly as a low-cost additive in building materials. More recently, their unique chemical properties have attracted attention to produce high-added-value materials for environmental applications, to be used as adsorbents, catalysts, or a source of reactive species in environmental engineering. Such uses can be classified as a function of the added value generated, technological complexity, and environmental impact. This review will focus specifically on the modification and use of slags for catalysis, photocatalysis, and photocatalytic production of hydrogen, which have received relatively little attention in literature. A summary will be presented about the general requirements for using unmodified slags as well as slag processed under alkaline or acidic conditions for advanced oxidation processes. Then, an overview will be given of the use of slags as photocatalysts in water treatment, organized according to the origin of the product (steel, copper, magnesium, ferromanganese), as well as emerging reports on the photocatalytic production of hydrogen, in contrast to the use of highly specific titania-based products developed for the same purpose.

https://www.mdpi.com/2071-1050/11/9/2470/pdf

Metallurgical Wastes Employed as Catalysts and Photocatalysts for Water Treatment: A Review

Experimental determination of the 1300 °C and 1400 °C isotherms for CaO–SiO2–TiO2-10 wt% Al2O3 system in air

Silicon production by the reduction of quartzite in furnaces is accompanied by copious dust emissions containing a high proportion of valuable silica (86%, on average). It is of great interest to capture that dust for reuse in the process. The dust captured in the gas-purification system consists of particles no larger than 120 μm, with a predominance of the 20–50 μm fraction. In order to use such dust in silicon production, it must be aggregated, so as to prevent its entrainment from the furnace by the gas fluxes. Since the batch pieces must be strong enough to withstand transportation, the binder employed is liquid glass with the addition of electrofilter dust from aluminum production, which contains tars (polyaromatic hydrocarbons). Strength tests of batch samples permit the recommendation of the following composition (by mass): 24–27% dust from silica production; 51–53% carbon reducing agent (a 1: 1 mixture of petroleum coke and charcoal); 4–5% silicon siftings; 14–15% binder (a 4:1 mixture of liquid glass and electrofilter dust from aluminum production). For such batch, the strength in drop tests is 82.5%, on average. Research shows that the batch pieces obtained by this method have a porous structure (45.5%) for the formation of a well-developed active surface and corresponding apparent density (1100 kg/cm3). That supports stable furnace operation. Trials in an HTF 17/10 high-temperature furnace yield an intermediate product containing more than 44 wt % silicon carbide. On that basis, such dust aggregates may be added to the main batch in silicon production.

Utilization of Dust from Silicon Production

The effect of 15 wt%Al2O3 addition on the equilibrium phase relations of CaO–SiO2–TiO2 system at 1400 °C in air

Global silicon-carbide production and consumption is assessed. It is expedient to produce silicon carbide from industrial microsilica by furnace synthesis and plasma metallurgy. The balance of silicon-monoxide formation is considered on the basis of the physicochemical interactions in ore furnaces during the melting of silicon and ferroalloys, and the processes responsible for microsilica formation are analyzed. The synthesis of silicon carbide by furnace heating with carbon and its plasma-metallurgical production are discussed.

Silicon-carbide production from steel-plant wastes

In the production of steel, as the productivity rises and the resource and energy consumption declines, improvements in converter design are required to ensure preliminary scrap and batch heating and to intensify redox processes in the liquid bath and exhaust-gas combustion above the bath, without impairing the durability of the injection systems and the converter lining. The use of fuel–oxygen combustion flames in the converter resolves numerous technological problems. The hydrodynamics in the reaction zones and in the liquid bath may be greatly changed by fuel combustion in the converter’s working space with jet formation or by means of submersible combustion flames. In the present work, thermodynamic methods are used to analyze the dynamics of gaseous-fuel combustion and the oxidation of elements in the converter bath on interaction with high-temperature combustion products. The interaction of the combustion flame and chemical elements in the converter bath is calculated for equilibrium conditions. The use of the combustion flames is found to change the composition of the gas phase in the converter’s working space (above the bath), which contains H2 and H2O in addition to the traditional components associated with oxygen injection: O2, CO, CO2. The presence of H2 and H2O changes the thermal conditions and oxidative properties of the gas phase. In the combustion of gas–oxygen fuel, the optimal composition of the initial gas mixture (natural gas + oxygen) must correspond to the ratio 100% CH4 + 69% O2. The oxidation product is gaseous phase consisting of 40% CO2 + 60% H2O. The total enthalpy of combustion of the gas–oxygen fuel at converter temperatures, with an oxygen excess greater than 1.0 (up to 2.0), is about 200 kJ per mole of the initial reagents. In the oxidation of methane by carbon dioxide, the total enthalpy of combustion is between–7 and–14.5 kJ/mol of initial reagents at 1800 K. The process becomes endothermal at temperatures above 2000 K: ΔH
 2200 = 7.7–15.4 kJ/mol. In the oxidation of natural gas by water vapor, ΔH
 1800–2200 = 19.5–70 kJ/mol. Thus, flame temperatures above 1800 K may only be attained in the oxidation of methane by oxygen. The use of air, carbon dioxide, or water vapor as the oxidant does not yield the required thermal effect.

Oxidation of molten impurities in converters by means of combustion flames: Thermodynamic principles. 1. Thermodynamic analysis of processes in natural-gas combustion

Determining redox parameters in the Fe-C-O2-H2 system

The possibility of using iron-ore concentrates from the Bachkar field and lignite semicoke from the Talovskoye field (Tomsk region) to obtain highly reduced pellets is considered. The high tar yield in the heat treatment of lignite hinders its use as a reducing agent in industrial processes and necessitates its conversion to semicoke. Analysis of the properties of carbon-based reducing agents indicates that lignite semicoke is more reactive than metallurgical coke and has a more developed porous structure. Semicoking of the lignite is optimal at ∼600°C, with roasting for about 40 min. The tar is completely removed, and the residual quantity of volatiles is sufficient for reduction by carbon in a hydrogen-bearing atmosphere. The production of iron-ore pellets from lignite semicoke is studied; the conditions of reductive roasting and the characteristics of the process are determined. At 950°C, 90–92% reduction is achieved after around 1 h. A production system for reduced pellets based on iron-ore concentrates and lignite semicoke in shaft furnaces is developed. The gases formed in the reduction of oxides (CO + H2 + H2O) provide the heat required for the process.

Production of reduced pellets from lignite semicoke

The CaO · SiO2-CaO · Al2O3 · 2SiO2-CaO · TiO2 · SiO2 system is analyzed. Thermodynamic analysis of monovariant and invariant solidification shows that, for invariant equilibrium and for solidification along the boundary curve between the solidification fields of anorthite and sphene, peritectic processes are observed. The invariant-state parameters of the system are determined: t = 1513 K; a
 CaO = 0.0407; $$a_{SiO_2 } = 0.5268$$
 ; $$a_{Al_2 O_3 } = 0.00003$$
 , $$a_{TiO_2 } = 0.005$$
 ). A corrected phase diagram is presented.

Thermodynamic activity of the liquid-phase components in the CaO · SiO2-CaO · Al2O3 · 2SiO2-CaO · TiO2 · SiO2 system with four-phase invariant equilibrium

N. F. Yakushevich

Papers

Silicon-carbide production from steel-plant wastes

Oxidation of molten impurities in converters by means of combustion flames: Thermodynamic principles. 1. Thermodynamic analysis of processes in natural-gas combustion

Determining redox parameters in the Fe-C-O2-H2 system

Production of reduced pellets from lignite semicoke

Thermodynamic activity of the liquid-phase components in the CaO · SiO2-CaO · Al2O3 · 2SiO2-CaO · TiO2 · SiO2 system with four-phase invariant equilibrium