Metal recovery process

#The present invention relates to a process for recovering a metal from metallurgical waste such as process slag waste produced during smelting and refining processes. In particular, the invention relates to a process for recovering a metal of interest in the form of a metal chloride from slag waste materials produced in base metal smelting and refining processes and optionally subsequently extracting the metal from the metal chloride.

#When metalliferous ore deposits are formed in the Earth's crust they are rarely composed of just one metalliferous element; indeed it is well documented that certain combinations of metals commonly occur together. For example lead deposits are commonly associated with zinc and so as the lead concentrate is formed at the mine processing plant, zinc is inherently present in the concentrate as an impurity. It is not until the primary metal is won from the concentrate at a smelter that the impurities are removed.

#Many methods are known for extracting metals and their compounds from ores, including methods which involve liberating the metal in the form of its chloride. Such methods have not previously been applied to the recovery of metals such as zinc from slag wastes, reflecting the very different nature of these materials.

#The method of the invention is applicable to the recovery of metals chlorides from a variety of smelter slag wastes and may suitably be applied to any slag waste from lead, copper or zinc smelting or refining processes which has sufficiently high levels of metal containing constituents of interest to be economically worthwhile recovering.

#It will be appreciated, of course, that the composition and levels of potentially recoverable metal containing constituents will vary considerably depending on the origin of the slag waste. As discussed above, slag wastes from lead smelting processes commonly comprise zinc containing constituents, typically in the form of oxides and silicates for example. Other valuable metals which are commonly found in lead smelter slags include iron, copper, silver, indium, gold, molybdenum, tin, gallium and germanium. As copper deposits are commonly associated with nickel, copper smelter slags are a useful potential source of nickel compounds. The method of the present invention therefore affords the possibility of recovering a wide variety of valuable metals of interest.

#Heating of the solid waste material in the process according to the invention may conveniently be performed in a fluidised bed reactor. The fluidised bed reactor will desirably be provided with heat insulation to keep the solid material molten. It will be appreciated that the solid feed material should be of an appropriate size so as to permit fluidisation with the bed of the reactor; large particles may require screening and crushing, whereas finer materials may require agglomeration. Typically, the fluidised bed will be maintained with compressed air to ensure a homogenous bed.