In order to establish a sustainable society, with practical material recycling, it is appropriate to focus on a range of guiding "Earth Principles", including the character and application of hydrothermal processes. In this paper, it is demonstrated that information obtained from the study of fundamental Earth Principles can be used to inspire the development of new methods for material recycling, such as the following: (1) Hydrothermal hot-pressing processes, simulating the formation of sedimentary rock sequences, can be used for the solidification of toxic and hazardous materials. (2) Organic materials could be formed from CO 2 under hydrothermal conditions (using Fe and Ni metals, and low valence Fe oxides), at temperature and pressure conditions consistent with a subduction (tectonic) setting, such as (under Japan) where the Pacific Plate sinks beneath the (Eurasian) continental plate. (3) Diamond-structured carbon may be formed from toxic chlorinated hydrocarbon, in very high pressure regions of the Earth, and at high alkaline hydrothermal conditions, where magma formation may occur. (4) High temperature dry steam in rock fractures (at near critical conditions - i.e. below saturated vapor pressure, but relatively high pressure) is not only a source/carrier of noble metals, including gold, silver and copper, but also ceramic materials, silica and alumina. Its laboratory simulation may also be a guide for the formation of thin layer silicate ceramics on metal plates (e.g. SUS-304 nickel alloy). (5) To design an underground boiler in hot dry rock, non-equilibrium dissolution and deposition hydrothermal processes may be studied using a tube reactor, which simulates fluid flow and temperature gradients in fractured hot rock. .
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