Abstract: The invention provides a method for the formation of small-size iron oxide particles comprising the steps of preparing a starting aqueous solution comprising at least one of ferric ions and complexes thereof, at a concentration of at least 0.1% W/W iron and a pH greater than about 1.5; maintaining said solution at a temperature lower than 55° C. for a retention time in which hydrolysis takes place, the extent of said hydrolysis being insufficient to decrease the pH by at least 0.2 units, wherein said time does not exceed 14 days, to form a system containing a modified solution; and adjusting the conditions in said system by at least one of the steps of heating the modified solution to elevate the temperature thereof by at least 10° C; elevating the pH of the modified solution by at least 0.3 units; and diluting the modified solution by at least 20%; whereby there are formed particles; wherein the majority of the particles formed are between about 2 nm and about 500 nm in size.

Abstract: The invention provides a hydrometallurgical process for treating metal-containing sulfide ores and concentrates, comprising reacting said metal-containing sulfide with concentrated sulfuric acid at a temperature of between about 300° C. and 400° C. in the presence of oxygen to produce a solid metal sulfate product and a gaseous product which is primarily SO3, wherein said metal is selected from the group consisting of iron, copper, zinc, nickel, cobalt and manganese. Said metal sulfate product is then leached with dilute sulfuric acid to form a metal-containing solution, from which the metal values are separated by precipitation at raised H2SO4 concentrations obtained by saturating the solution with the gaseous SO3 from the sulfatization reaction step.