Analysis on the stability of chromium in mineral phases in stainless steel slag

2017 ◽  
Vol 115 (1) ◽  
pp. 114 ◽  
Author(s):  
Long-hu Cao ◽  
Cheng-jun Liu ◽  
Qing Zhao ◽  
Mao-fa Jiang
Keyword(s):  
Aqueous Solution ◽  
Stainless Steel ◽  
Spinel Phase ◽  
Steel Slag ◽  
Dicalcium Silicate ◽  
Limiting Factor ◽  
Leaching Test ◽  
Stainless Steel Slag ◽  
Mineral Phases ◽  
The Stability

Stainless steel slag from high alloy steel is hardly used in the construction industry. The chromium leaching in unstable phase is the limiting factor for the application in the slag. The aim of this study is to investigate the stability of mineral phases in stainless steel slag. In this work, the mineral phases were firstly confirmed through experimental results by SEM-EDS and XRD. Thermodynamic calculation and leaching test were adopted to characterize the theoretical stability of mineral phases in aqueous solution. The results showed that the main phases in the stainless steel slag were spinel, melilite [solid solution of gehlenite (Ca2Al2SiO7) and akermanite (Ca2MgSi2O7)], dicalcium silicate, merwinite and periclase phases. It can be concluded that the minerals behave differently when dissolving in aqueous solution and the dissolution of dicalcium silicate (Ca2SiO4), merwinite (Ca3MgSi2O8), akermanite (Ca2MgSi2O7) and periclase phase could be generally higher, especially at lower pH values. In addition, the solubility of chromium in the spinel phase is considered low. The leaching test demonstrated that the formation of spinel phase can limit the leaching of chromium and the chromium existing in the silicate and periclase phases can facilitate the chromium leaching.

scholarly journals Effect of Lime on Stability of Chromium in Stainless Steel Slag

Minerals ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 424 ◽  
Author(s):  
Qing Zhao ◽  
Chengjun Liu ◽  
Longhu Cao ◽  
Xiang Zheng ◽  
Maofa Jiang
Keyword(s):  
Stainless Steel ◽  
Phase Transformation ◽  
Layer Structure ◽  
Steel Slag ◽  
Product Layer ◽  
Dicalcium Silicate ◽  
Slag Basicity ◽  
Stainless Steel Slag ◽  
Living Organisms ◽  
The Stability

The stabilization of chromium is of great importance to the use of stainless steel slag (SSS), and the influence of lime on the stability of chromium is currently unclear. In this work, the variation of phase transformation and chromium distribution with slag basicity (CaO/SiO2) were investigated experimentally, and the leaching ability of chromium was evaluated. Results showed that chromium-bearing phases were glass, dicalcium silicate (C2S), spinel, and periclase, while the degree of enrichment of chromium in these phases was found to be closely related to the basicity. The optimal basicity obtained in this research was 1.5, with the chromium mainly present in the stable spinel and exhibiting the lowest leaching ability. The product layer structure of unmelted lime was studied as well, showing a periclase layer and a Ca2SiO4 layer. Some CaCr2O4 had formed in the periclase layer, which is potentially hazardous for the environment and living organisms.

scholarly journals Stability of Chromium in Stainless Steel Slag during Cooling

Minerals ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 445 ◽  
Author(s):  
Qing Zhao ◽  
Chengjun Liu ◽  
Longhu Cao ◽  
Xiang Zheng ◽  
Maofa Jiang
Keyword(s):  
Stainless Steel ◽  
Molten Slag ◽  
Steel Slag ◽  
Dicalcium Silicate ◽  
Cooling Process ◽  
Stainless Steel Slag ◽  
Chromium Release ◽  
Elution Behavior ◽  
The Stability ◽  
Chromium Enrichment

The chromium elution behavior of stainless steel (SS) slag depends highly on the chromium distribution, and the molten modification process proved to effectively improve the chromium enrichment in stable phases. However, the phase transformation and variation of chromium stability during the subsequent cooling process is still poorly understood. In this work, the phase composition and chromium distribution of SS slag from different quenching temperatures were experimentally studied, and the stability of chromium-bearing phases was evaluated using standard leaching tests. The results indicated that dicalcium silicate and spinel phases had formed in the molten slag at 1600 °C, while the dicalcium silicate disappeared and the phases of merwinite and melilite precipitated when the temperature decreased from 1600 to 1300 °C (at a rate of 5 °C/min). During this cooling process, the chromium migrated from other phases into the spinel, significantly suppressing the chromium elution. The leaching results also demonstrated that the potential chromium-bearing phases of glass, dicalcium silicate and merwinite are unstable and are presumably the main source of chromium release. The treated SS slag meets the requirements for the utilization of chromium-bearing slag in the cement and brick industries.

scholarly journals Experimental Study on Precipitation Behavior of Spinels in Stainless Steel-Making Slag under Heating Treatment

Processes ◽  
2019 ◽  
Vol 7 (8) ◽  
pp. 487 ◽  
Author(s):  
Jianli Li ◽  
Qiqiang Mou ◽  
Qiang Zeng ◽  
Yue Yu
Keyword(s):  
Particle Size ◽  
Stainless Steel ◽  
Steel Slag ◽  
Calcium Content ◽  
Heating Time ◽  
X Ray Diffraction ◽  
Stainless Steel Slag ◽  
Steel Making ◽  
Heating Treatment ◽  
The Stability

The stability of chromium in stainless steel slag has a positive correlation with spinel particle size and a negative correlation with the calcium content of the spinel. The effect of heating time on the precipitation of spinel crystals in the CaO-SiO2-MgO-Al2O3-Cr2O3-FeO system was investigated in the laboratory. Scanning electron microscopy with energy-dispersive and X-ray diffraction were adopted to observe the microstructure, test the chemical composition, and determine the mineral phases of synthetic slags, and FactSage7.1 was applied to calculate the crystallization process of the molten slag. The results showed that the particle size of the spinel crystals increased from 9.42 to 10.73 μm, the calcium content in the spinel crystals decreased from 1.38 at% to 0.78 at%, and the content of chromium in the spinel crystal increased from 16.55 at% to 22.78 at% with an increase in the heating time from 0 min to 120 min at 1450 °C. Furthermore, the species of spinel minerals remained constant. Therefore, an extension in the heating time is beneficial for improving the stability of chromium in stainless steel slag.

scholarly journals Study of the Dissolution of Stainless-Steel Slag Minerals in Different Acid Environments to Promote Their Use for the Treatment of Acidic Wastewaters

2021 ◽  
Vol 11 (24) ◽  
pp. 12106
Author(s):  
Mattia De Colle ◽  
Ross Kielman ◽  
Andreas Karlsson ◽  
Andrey Karasev ◽  
Pär G. Jönsson
Keyword(s):  
Stainless Steel ◽  
Steel Slag ◽  
Dicalcium Silicate ◽  
The Other ◽  
Experimental Conditions ◽  
Stainless Steel Slag ◽  
Ph Values ◽  
Neutralizing Capacity ◽  
Mineral Compositions ◽  
Do So

Several stainless-steel slags have been successfully employed in previous studies as substitutes for lime in the treatment of industrial acidic wastewaters. This study deepens the knowledge of such application, by analyzing the neutralizing capacity of different slags related to their mineral compositions. To do so, firstly the chemical and mineral compositions of all the slag samples are assessed. Then, 0.5 g, 1 g, 2 g of each slag and 0.25 g and 0.5 g of lime are used to neutralize 100 g of 0.1 M HCl or HNO3 solutions. After the has neutralization occurred, the solid residues are extracted and analyzed using XRD spectroscopy. Then, the solubility of the minerals is assessed and ranked, by comparing the XRD spectra of the residues with the obtained pH values. The results show that minerals such as dicalcium silicate and bredigite are highly soluble in the selected experimental conditions, while minerals such as merwinite and åkermanite, only partially. Moreover, Al-rich slags seem to perform poorly due to the formation of hydroxides, which generate extra protons. However, when the weight of slag is adequately adjusted, Al-rich slags can increase the pH values to higher levels compared to the other studied slags.

scholarly journals Occurrence and Leaching Behavior of Chromium in Synthetic Stainless Steel Slag Containing FetO

Minerals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1055
Author(s):  
Qiang Zeng ◽  
Jianli Li ◽  
Yue Yu ◽  
Hangyu Zhu
Keyword(s):  
Stainless Steel ◽  
Crystal Size ◽  
Spinel Phase ◽  
Steel Slag ◽  
Utilization Rate ◽  
Leaching Behavior ◽  
Stainless Steel Slag ◽  
Minimum Concentration ◽  
Edge Structure ◽  
Line Scanning

Stainless steel slag has been applied to other silicate materials due to its CaO-SiO2-based system. This is done to improve the utilization rate of stainless steel slag and apply it more safely. This paper investigated the occurrence of chromium in synthetic stainless steel slag containing FetO and its leaching behavior. The phase composition of the equilibrium reaction was calculated by FactSage 7.3 Equlib module. XRD, SEM-EDS and IPP 6.0 were used to investigate the phase compositions, microstructure and count the size of spinel crystals. The results indicate that the increase of Fe2O3 content can promote the precipitation of spinel phases and effectively inhibit the formation and precipitation of α-C2S in a CaO-SiO2-MgO-Cr2O3-Al2O3-FeO system. Fe2O3 contents increased from 2 wt% to 12 wt%, and the crystal size increased from 4.01 μm to 6.06 μm, with a growing rate of 51.12%. The results of SEM line scanning show the Cr-rich center and Fe-rich edge structure of the spinel phase. Comparing the TRGS 613 standard with the HJ/T 299-2007 standard, the leaching of Cr6+ in the FetO samples is far lower than the standards’ limit, and the minimum concentration is 0.00791 mg/L in 12 wt% Fe2O3 samples.

scholarly journals Carbonation of EAF Stainless Steel Slag and Its Effect on Chromium Leaching Characteristics

Crystals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1498
Author(s):  
Ya-Jun Wang ◽  
Meng-Jie Tao ◽  
Jun-Guo Li ◽  
Ya-Nan Zeng ◽  
Song Qin ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Steel Slag ◽  
Co2 Uptake ◽  
Stainless Steel Slag ◽  
Carbonation Process ◽  
Mineral Phases ◽  
Slurry Phase ◽  
Soluble Calcium ◽  
Eaf Slag ◽  
Identification Analysis

EAF stainless steel slag (EAF slag) is one kind of chromium-bearing metallurgical solid waste, which belongs to alkaline steel slag, and contains a large number of alkaline mineral phases. The carbonation activity of these minerals gives EAF slag the capability to effectively capture CO2. In this paper, EAF slag samples with different carbonation degrees were prepared by the slurry-phase accelerated carbonation route. The mineralogical identification analysis was used to qualitatively and semi-quantitatively determine the types and contents of the carbonatable mineral phases in the EAF slag. The sequential leaching test was used to study the chromium leachabilities in EAF slags with different carbonation degrees. The results showed that the main minerals with carbonation activity in EAF slag were Ca3Mg(SiO4)2 and Ca2SiO4, with mass percentages of 56.9% and 23%, respectively. During the carbonation process, Ca2SiO4 was the main reactant and calcite was the main product. As the degree of carbonation increased, the pH of the EAF slags’ leachate gradually decreased while the redox potential (Eh) gradually increased. At the same time, a large amount of Ca2+ in the EAF slag combined with CO2 to form slightly soluble calcium carbonate, which led to a significant decrease in the conductivity of the leachate. With the gradual increase in carbonation ratio, the leachability of chromium in the EAF slag first decreased and then increased, and reached its lowest value when the CO2 uptake ratio was 11.49%.

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