Stabilization of MgCr₂O₄ spinel in slags of the<br />SiO₂-CaO-MgO-Cr₂O₃ system

Abstract

The objective of this study is to analyze the effect of MgO content and the slag basicity on the stability of the mineralogical species of the SiO 2 -CaO-MgO-Cr 2 O 3 system. Slag samples were prepared in equilibrium at 1600 °C under reducing conditions (pO 2 = 10 -9 atm). The MgO content ranged from 0 to 12 mass%, Cr 2 O 3 was 10 % and the slag basicity was held at 1 and 1. ResumenEl objetivo de este estudio es analizar el efecto del contenido de MgO y la basicidad de la escoria sobre la estabilidad de las especies mineralógicas del sistema de escoria SiO 2 -CaOMgO-Cr 2 O 3 . Se realizaron ensayos al equilibrio a 1600 °C bajo condiciones reductoras (pO 2 =10 -9 atm). El contenido de MgO fue de 0 a 12 % masa, el Cr 2 O 3 de 10% y la basicidad de 1 y 1,5. También se realizó un análisis termodinámico para determinar las fases mineralógicas más estables en la escoria. Los resultados experimentales y calculados muestran que el Cr 2 O 3 se encuentra principalmente ligado en una fase espinela MgCr 2 O 4 , incluso a bajos contenidos de MgO. Los resultados obtenidos por microscopia electrónica de barrido (MEB-EDS), muestran la evidencia de tres estructuras cristalinas: (A) Octaedros, los cuales corresponden a la espinela MgCr 2 O 4 , (B) Cristales alargados que corresponden a la formación de silicatos cálcicos y (C) Matriz de silicatos cálcicos con impurezas de Mg y Cr que no cristalizaron por completo.

The effect of chemical composition on the leaching behaviour of electric arc furnace (EAF) carbon steel slag during a standard leaching test

“…For example, MgO 58 concentration in the slag seems to be favourable for Cr 59 immobilization but detrimental for the leaching of other 60 polluting elements, i.e. Ba and V [19]. The solution behaviour 61 of these elements have a parabolic law as a function of CaO and 62 MgO concentration, whereas their dependence on silica concen-63 tration is generally described by a linear law [20].…”

“…The identification of leaching behaviour 18 is mandatory for slag use in unbound applications, i.e. unpaved 19 roads, armourstone or gabions, because in such conditions, slag is 20 subject to a continuous cycle of wetting and drying. Several studies 21 [5][6][7][8][9] have investigated the leaching behaviour of slag aggregates, 22 and highlight that such aggregates could potentially release 23 dangerous chemical elements (especially Ba, V and Cr), as well 24 as unbound slag, when coming into contact with water.…”

Effect of Low Oxygen Partial Pressure on the Chromium Partition in CaO–MgO–SiO2–Cr2O3–Al2O3 Synthetic Slag at Elevated Temperatures

“…wüstite, spinel, and glass are, on other hand, considered as resistant to dissolution. While the wüstite and glass formation were studied by earlier researchers,1–12 very little effort has been made toward an understanding of the precipitation of spinel phase in the slag. Mineralogical phases present in a slag system are highly dependent on slags composition and heat treatment history 1–14…”

“…Adding relatively large amount of silica, for example, quartz sand or waste glass, is another way to control the slag composition (basicity) and prevent slag disintegration 4–8…”

Extracting Chromium from Stainless Steel Slags by NaOH‐Added Pellet Roasting Followed by Water Leaching

“…However, the thus obtained Cr 3+ is mixed with the slag of blast furnace and cannot be separated, which limited the application of this method. Some researchers studied the partial enrichment of Cr from the SSL slag to more stable spinel phases by adding some phase‐altering chemicals, such as MgO, Al 2 O 3 , FeO, B 2 O 3, and so on to SSL slags under the conditions of high smelting temperature . Some studies focused on the solidification/stabilization of SSL slag through the use of cementitious materials such as portland cement or pozzolime .…”