On the attainment of stable autothermal operation in continuous pressure leaching reactors

Abstract

The autothermal model of operation of a multi-stage oxidative pressure leaching reactor is analysed with the aid of a descriptive mathematical model. For this, the adiabatic heat balance equation of the reactor is solved along with the mass balance equations. The model considers the process system (pressure oxidation) to be controlled simultaneously by the kinetics of the two parallel exothermic leaching reactions (oxidation of FeS 2/FeAsS by O 2), and the gas-liquid mass transfer of oxygen. By maintaining the total pressure of the system constant, that is P tot(=P H 2 O + P O 2 ∗ )= constant , enhanced thermal and kinetic stability is achieved at the autothermal steady-state operating temperature. The combined S/As content of the feed is of crucial importance to the thermal economy of the process. Feeds with sulphur content above 5.5 wt% can be processed without any preheating with either a 4 stage autoclave (equal size compartments), or a 5 stage autoclave having the first double the size of the rest. The higher the sulphur content the lower the concentration of solids in the feed slurry has to be in order to attain autothermal operation. For feeds with low sulphur content (<5 wt%), autoclaves with the first compartment substantially larger than the rest have to be employed for optimum thermal balance results.