Edgel P. Stambaugh

Hydrothermal processing — An emerging technology

Abstract Hydrothermal processing involves the chemistry of hot water under pressure to carry out leaching and precipitation reactions. These reactions are usually conducted at temperatures ranging from 100 to 350°C and pressures in the range from a few to 3000 psig. The reaction medium may be water alone or in combination with inorganic and/or organic acids and bases. The chemistry of this technology permits selective dissolution (leaching) or selective precipitation of metal species to be achieved leading to potentially novel treatment methods using a wide variety of ores and raw materials to produce high quality inorganic products. Thus, hydrothermal technology offers alternate or new approaches which can be technically superior to conventional processing for producing a wide variety of high technology inorganic oxides for specific applications, recovery of valuable components from low grade ores, and converting waste material to marketable products. Furthermore, because of short reaction times, simplicity of the reactor and recycle of reagents, the application of hydrothermal technology frequently leads to processes which can be less energy intensive, less pollutant and/or less capital intensive. Hydrothermal technology has already been used in many successful commercial processes. Now, with the combination of feedstock shortages, rising energy costs, more restrictive pollution abatement regulations, inflationary pressures, need for higher quality products and a better understanding of the chemistry of hot water, this technology is emerging as a viable alternative to more conventional high temperature processing. The technology is expected to impact on several industrial areas, including primary and secondary ferrous and non-ferrous metals, ceramics, electronics, pigments, petroleum, utilities, refractories and inorganic chemicals.