350 u00b0 and 450 u00b0 f must be removed this removal of heat is accomplished by removing a stream of vapor composed of water vapor oxygen and nitrogen through conduit 28 this stream enters condenser 30 where water vapor is condensed on the outside of tubes 32 by a cooling medium such as water which is circulated from a source not shown through the inside of the tubes if desired as for example where corrosion is a factor condenser 30 could be constructed to have the water vapor condense on the inside of the condenser tubes and the cooling medium circulate on the outside of the tubes in either case after removal of heat from the stream by condensation and removal of the water vapor the residual oxygen nitrogen and uncondensed water vapor are returned to the autoclave through conduit 34 the condensate discharged through conduit 36 is not returned directly to the autoclave since this water is removed from the system in order to increase the copper concentration in the slurry it will be recognized that removal of heat by use of condenser 30 avoids the loss of oxygen from the system in a preferred embodiment it is desired to reduce the iron content of the final leach liquor to less than about 5 grams per liter in order to accomplish this it is necessary that virtually all of the iron be precipitated as fe 2 o 3 equation 3 however as noted in equation 3 this reaction is reversible therefore to insure the reaction proceeding to the right and obtaining the greatest amount of iron removal possible it is necessary to remove some of the sulfuric acid h 2 so 4.