Abstract: Gold and/or silver is leached from comminuted ore with an alkaline cyanide lixiviant at a superatmospheric pressure of at least 25 bar and with high purity oxygen (at least 90% pure) to reduce the residence time at high yield.

Abstract: A method for continuously extracting uranium from ores comprises the steps of forming a slurry of ore in a leaching solution; heating the slurry while pumping it through a tube reactor at high turbulences characterized by Reynolds numbers in excess of 50,000; supplying gaseous oxygen at high pressures of at least 30 bar into the tube reactor such that the uranium is substantially completely oxidized in a soluble form but impurities in the slurry are substantially kept from becoming soluble; recovering the uranium oxide solute which is substantially free of impurities.

Abstract: A fluid medium is conveyed along a conduit. During its passage through the conduit, the fluid medium undergoes temperature change. The change in temperature of the fluid medium is performed in a step-wise manner by indirect heat-exchange with a fluid flowing countercurrent to the fluid medium, that is, by means of a plurality of heat-exchangers arranged along the conduit. The fluid medium forms incrustations and the rate at which incrustations form is different at different temperatures. This is taken into account by providing for the ratio between the lengths of any two heat-exchangers to approximate the ratio between the rates at which incrustations form at the temperatures of the respective heat-exchangers. Of particular interest is the extraction of bauxite with sodium aluminate lye.

Abstract: A fluid medium is conveyed along a conduit. During its passage through the conduit, the fluid medium undergoes temperature change. The change in temperature of the fluid medium is performed in a step-wise manner by indirect heat-exchange with a fluid flowing countercurrent to the fluid medium, that is, by means of a plurality of heat-exchangers arranged along the conduit. The fluid medium forms incrustations and the rate at which incrustations form is different at different temperatures. This is taken into account by providing for the ratio between the lengths of any two heat-exchangers to approximate the ratio between the rates at which incrustations form at the temperatures of the respective heat-exchangers. Of particular interest is the extraction of bauxite with sodium aluminate lye.