Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Radioactive metal
Patent
1981-06-29
1984-08-07
Kyle, Deborah L.
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Radioactive metal
423 211, 423 45, 423 49, 423 99, 423111, 423138, 423155, 423557, 423 3, 75 1R, 75116, C01G 110, C01F 1500, C22B 106
Patent
active
044643446
DESCRIPTION:
BRIEF SUMMARY
A process for recovering non-ferrous metal values from ores, concentrates, oxidic roasting products or slags.
The present invention relates to a process for recovering non-ferrous metal values from ores, concentrates, oxidic roasting products, or slags by converting them into sulphates by using principally mixture of solid matters and molten salts as the sulphating agent. Said sulphating agent consists of alkali metal sulphate and iron (III) sulphate and one or more preferred non-ferrous metal sulphates.
The process described in this invention thus relates to a method that is widely used by the metallurgical industry for converting selectively particular non-ferrous metal values, which will be referred to as Me in the text, into their sulphates. These sulphates can then be separated from the tailings and in soluble hematite by a simple water leaching procedure. The non-ferrous values in the solution can thereafter be recovered by method known per se.
However, the known method, i.e. the sulphating roasting, involves some disadvantages which have often made it unfeasible for more extensive use. The main disadvantages have been difficulties in controlling reaction conditions, such as the SO.sub.3 partial pressure and temperature, so that it is practically impossible to achieve the maximum yield of the wanted water-soluble metal sulphate and, simultaneously, the maximum conversion of iron to non-soluble hematite in a reasonable reaction time, and further on, to avoid the thermodynamically and, especially in higher temperatures, also kinetically favourable conversion reaction between hematite and said metal oxide into the ferrites. Another serious disadvantage is the forming of a sulphate layer on the reacting particle which, in certain cases, strongly affects the reaction rate.
In general, it is presently believed that during the course of the roast, the metal value Me is converted first into the oxide form in the following manner: of the wanted metal value MeO and the iron oxide Fe.sub.2 O.sub.3. Thus, there are prerequisites for the ferrite formation, in other words for the reaction:
In general, it has been shown that all the sulphation reactions have occurred through the sulphate shell which has grown on the surface of the MeO particle during the course of the sulphation. It is through this shell that the reacting ions have to migrate before they can react further. The solid-state diffusion is, as well-known, a very slow phenomenon, especially when the migrating ionic species is large, such as an oxygen ion (see, for example, W. Jost and K. Hauffe: Diffusion. 2nd ed. Steinkopf Verlag, Darmstadt, 1972). On the other hand, the aforesaid formation reaction of ferrites is also a solid-state reaction when the oxides are diffusing into each other by counterdiffusion mechanism. The latter phenomenon is often considerably faster than the sulphation reaction. A commonly believed explanation for this is that in the ferrite formation reaction, only those ionic species with small dimensions (for example, metal ions) are migrating into each other in a relatively loosepacked oxygen lattice (see, for example, K. Hauffe: Reaktionen in und an der festen Stoffen, Springer Verlag, Berlin, 1955, p. 582 and H. Schmalzried: Solid State Reactions, Verlag Chemie, Weinheim, 1954, p. 90).
As the most important argument in favour of the previous review remains the experimental fact that from the competing reactions involving the Me-oxide, that is the reactions (3) and (4), reaction (4) occurs when there are thermodynamically favourable conditions, while the sulphation reaction (3) is normally very slow because it requires the diffusional migration of the reacting species through the growing sulphate shell.
It is well-known that, for example, the sulphation of nickel compounds is very difficult to perform because of the nonporous sulphate shell which does not offer any new reaction paths for the gas phase, for example, in the form of cracks or pores. It has been experimentally observed that the nonsulphated nickel has been mainly in t
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CIM Bulletin, Apr. 1975, p. 71-83.
Kyle Deborah L.
Thexton Matthew A.
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