Ore-processing systems including rotary kilns

In a charge processing system including a rotary kiln for heat-treating the charge in a controlled atmosphere, the kiln comprising a main cylindrical processing section in which the charge may be reacted with suitable reagents under elevated temperature and pressure, an inlet zone including a charge-receiving port disposed upstream of the main processing section, an outlet zone including a charge-withdrawal port disposed downstream of the main processing section, means for heating the interior of the main processing zone, first conduit means for introducing reagents into the main processing zone, second conduit means for withdrawing spent reaction gases from the main processing zone, and means for rotating the kiln, the improvement in which the upstream and downstream ends of the main processing section respectively comprise first and second self-contained hollow spiral ducts, the inner ends of the hollow interior of each of the first and second ducts communicating in gas-tight fashion with the interior of the main processing section, the outer ends of the hollow interior of the first and second spiral ducts individually communicating with the charge-receiving port and the charge-withdrawal port whereby charge introduced into the inlet zone enters the main processing section via the hollow interior of the first spiral duct and charge exiting from the main processing section is conducted to the outlet zone via the hollow interior of the second spiral duct, the charge passing through the hollow interior of the respective first and second spiral ducts completely filling such hollow interior to augment the gas-tight seal between the interior of the main processing section and the respective inlet and outlet zone.