Abstract
Serpentine heat treatment at temperatures of 650–750 °C yields magnesium–silicate reagent with high chemical activity. Precise and express control of roasting conditions in laboratory kilns and industrial aggregates is needed to derive thermally activated serpentines on a large scale. Color change in serpentines with a high iron content during roasting might be used to indicate the changes in chemical activity in the technological process. This study gives a scientific basis for the express control of roasting of such serpentines by comparing the colors of the obtained material and the reference sample. Serpentines with different chemical activity were studied by X-ray diffraction, Mössbauer spectroscopy, and optical spectroscopy. The color parameters were determined using RGB (red, green, blue), CIELAB (International Commission on Illumination 1976 L*a*b), and HSB (hue, brightness, saturation) color models. The color of heat-treated samples was found to be affected by changes in the crystallochemical characteristics of iron included in the structure of the serpentine minerals. The color characteristics given by the CIELAB model were in good coherence with the acid-neutralizing ability and optical spectra of heat-treated serpentines. Thus, in contrast to the long-term analysis by these methods, the control by color palette provides an express assessment of the quality of the resulting product.
Highlights
Serpentine minerals are widespread in the Earth’s crust, including the overburden and host rocks of deposits of magnesian raw materials such as magnesite, olivenite, phlogopite, etc
Serpentinites are of interest as a raw material source for obtaining various products based on magnesium, silicon, iron, nickel, and chromium oxides
The goal of this study is to provide a scientific justification for the method of the express control of serpentine thermal activation
Summary
Serpentine minerals are widespread in the Earth’s crust, including the overburden and host rocks of deposits of magnesian raw materials such as magnesite, olivenite, phlogopite, etc. Serpentinites are of interest as a raw material source for obtaining various products based on magnesium, silicon, iron, nickel, and chromium oxides. Serpentine minerals belong to the hydrous magnesium group silicates and have the chemical formula 3MgO2 ·2SiO2 ·2H2 O. Isomorphic substitutions of magnesium and silicon are possible, and the general formula can be represented as Mg3-x (M)x Si2-y (T)y O5 (OH) , where M-Mg2+ , Fe2+ , Fe3+ , Al3+ , Ni2+ , Mn2+ , Zn2+ , and T-Si4+ , Al3+ , Fe3+ [4]. Practically unlimited reserves of serpentines, including mining waste, stimulate the search for new ways to use them
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