In the production of base metals pyrotechnical processes have traditionally been used. Because of environmental reasons hydrometallurgical methods are today increasingly employed where concentrates are leached with acid and oxygen at high temperature to dissolve the metals. In this way atmospheric pollution can largely be avoided.
Japrotek Oy Ab designs and manufactures leaching autoclaves for mixing oxygen into dense acid concentrate slurries at high pressure and temperature. The highly corrosive conditions mostly require that all parts of the autoclave in contact with the contents are made of titanium. As the working pressure of the autoclave is 20-40 bar the autoclave, that can have a volume of several hundred cubic meters, can’t be built out of solid titanium due to cost reasons. The solution is to build the pressure bearing autoclave shell of carbon steel plated with a titanium layer with the thickness of only a few millimeters. The titanium has been fixed to the carbon steel either by rolling or exploding. The shell sections and heads are joined to each other using the so called batten strap welding technology.
For producing metals such as nickel or gold the autoclaves mostly are horizontal vessels divided into several sections where the concentrate slurry flows from one compartment to the other. In this way a long and controlled residence time is achieved. Oxygen can be added and the slurry heated in each compartment using a powerful agitator and heating coils. In the precious metals recovery processes of melting plants one compartment autoclaves with one single agitator normally is enough because of the small process volumes.
The task of the agitators in an autoclave is to disperse oxygen into the slurry and prevent solids from settling in the autoclave. This mixing task requires high intensity, which is why the agitators normally are heavy duty special agitators.