Hello colleagues, I would like to start a new research about stones and rocks, please can you tell me if there is a technical method to decompose the rock to its raw elements?
Dear Ishraq: there's no feasible or economic method to decompose a rock, mainly made of silicates, into its constituent elements. Actually, XRF and other analyses can give the chemical composition of rocks in terms of constituents oxides, which, except the minerals quartz (SiO2), hematite (Fe2O3), and rarely corundum (Al2O3), really don't exist in any rock, except as chemical constituents of the silicates which make them, like TiO2, FeOt, MgO, CaO, Na2O, K2O, and others. Even in granites, most of the SiO2 forms part of the structure of feldspars, micas and amphiboles, it is not free silica! The reason is simple: the chemical bonds in silicates are controlled by the strong Si-O and Al-O bonds in tetrahedra, the first one 50% ionic and 50% covalent, the other one is also quite strongly covalent, both bonds cannot be destroyed easily. Feldspar can be desilicated in tropical weathering first to kaolinite (Al-phyllosilicate), and lastly, to gibbsite (Al hydroxide). But, to obtain Al2O3, gibbsite (or other Al-oxi-hydroxides) should be dessicated, and the purified alumina should be fused with cryolite, so that a huge electric current passes through the melt, and Al is freed at the anode (this is the Bayer process). Indeed, to make free silicon for solar cells, chips, and the like, pure quartz powder should be mixed with coke coal, and put in a voltaic arc or other source of high temperature (laser), usually around 3,000 °C. A simple reaction takes place:
SiO2 + C = CO2 + Si. Only some soluble elements, lke alkalis, Mg and Ca, could be separated in solution as cations from a rock containing the respective silicates, but is a hard thing to do, and very expensive too.
As ouy can see, separating the most abundant cations from silicates, Si and Al, is no easy task! Not even talk about the rest!
Regards, Sebastián
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