The geochemical environment of the formation of magnesite (substratum) is ultramafic (dunite’s olivine content >90%). In ultramafic rocks the dunite substratum is usually partially or completely altered, due to seawater circulation that took place during placement of the ophiolitic rocks in Earth’s crust. This alteration (transformation) occurs at temperatures around 300-500 oC and takes place mineralogically, meaning that a significant part of the olivine (considered as an mixture of equal quantities of forsterite and phagialite) is converted to serpentine, through the strong exothermic reactions 1 and 2.
In these processes the dunite rock is altered either serpentinized peridotite (with a small degree of alteration) or serpentinite (with extensive to complete alteration), while the degree of serpentinization depends on the composition of the substratum, as well as on the possibility of some ions advection or diffusion mainly Ca and Mg through the release of water content. At the same time, serpentinization can lead to the formation of talc, magnesite and asbestos.
3Mg2SiO4 + SiO2 + 4H2O -> 2Mg3Si2O5(OH)4
Forsterite + Silicon dioxide + Water -> Serpentinite
2Mg2SiO4 + 3H2O -> Mg3Si2O5(OH)4 + Mg(OH)2
Forsterite + Water -> Serpentinite + Brusite
Partial or complete serpentinization results in the alteration of substratum’s physical chemical properties. During this process the ultramafic ores/rocks can absorb large quantities of water, resulting to the increasing of rocks' volume up to 40%, with consequent decrease in the density of these rocks and the respective hardness. In addition decrease in rock density (from 3.3 to 2.7 g/cm3) and in its hardness (from ~6.5 to ~4 on the mohs scale) is observed. Based on the properties of the serpentinized rock, its uses are from limited to zero. In particular, it is a fact that, when the above rocks are intended to be used as construction materials, special attention is required to the state of the rock and the degree of alteration of olivine, which leads to loss of rock cohesion and degradation of the required mechanical properties.
In the magnesite mine of “Grecian Magnesite SA (e.g., in Gerakini, Halikidiki), the initial extraction of the ore follows a series of processes in order to separate the barren rock (waste) from the substratum. The separated substratum, is the waste of the separation process and, as already mentioned, is degraded to various degrees, up to 100%. The separation either takes place during the extraction stage (selective exploitation), or during the various stages of leukolite enrichment. In other words, this is a solid waste, which should be managed accordingly by the respective mining companies, with currently, the possibility of economic and commercial exploitation being very limited to non-existent.
The main objectives of the project are the detailed investigation of the main geochemical and thermodynamic variables, which affect the process of serpentinization and the development and application of a reverse process, resulting as effectively as possible to the conditions prior to serpentinization.
This process is expected to reduce the serpentine content of industrial solid waste, so that the percentage of olivine rises above 80%, i.e., the altered waste rock could be converted into (useful) dunite again.
Moreover, during the project the utilization of the produced transformed dunite in refractory applications, such as firebricks and magnesium-olivine masses, will also be examined in laboratory and in industrial scale tests. The developed products will be innovative and are expected to show upgraded properties than the corresponding olivine products currently on the market. The transformation of serpentine into thermally-treated dunite is important not only in terms of environmental management (solid waste management) but also from an economic point of view.