Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Rare earth metal
Patent
1985-04-16
1987-06-02
Metz, Andrew H.
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Rare earth metal
423166, 423175, 423263, 423431, C01F 1700
Patent
active
046702288
DESCRIPTION:
BRIEF SUMMARY
In nature there are several examples of the occurence of valuable metals in large or small amounts under such conditions that their recovery in an economical manner is difficult or practically impossible. An example of such conditions is the presence of valuable metals in finely divided form in a matrix which contains considerable amounts of calcium carbonate, i.e. so-called carbonatites. Due to the finely divided form the valuable metals cannot be recovered by ordinary ore dressing, such as flotation. Efforts to recover by extraction with acid will normally lead to an unacceptably high acid consumption since a considerable part of the acid employed is consumed for the neutralisation of calcium carbonate.
Valuable metals which are of particular interest and which are connected to such deposits, are e.g. rare earths and similar metals such as scandium and yttrium, and metals which occur together with these such as niobium, tantalum and uranium. Further, other interesting metals are germanium, indium, vanadium and rhenium. In addition, nickel, cobalt, chromium and other metals may also occur under the conditions as mentioned above.
The problem with valuable metals of the above type is primarily to get them into a suitably concentrated solution from a matrix from which they are difficult to recover. As soon as they have been obtained in a concentrated solution, there are no problems involved in the separation and preparation in pure form, such as e.g. described for rare earths in Revue du Centainaire de l'Ecole Superieure de Physic et Chimie Industrielle (ESPCI, Paris 1982).
From i.a. Report of Investigations 8006 "Lime Roast-Leach Method for Treating Chalcopyrite Concentrate", F. P. Haver and M. M. Wong, Reno Metallurgy Research Center, Reno, Nev. for United Stated Department of the Interior, Bureau of Mines (1975) it is known to roast chalcopyrite together with burnt lime to form insoluble anhydrite so that SO.sub.2 is bound and does not escape to the athmosphere.
Norwegian Pat. No. 148.774 describes the use of i.a. sulphur as fuel for reactions which in addition to energy also consumes sulphur oxides, sulphuric acid and/or sulphate.
It has now been found that the problem mentioned initially with the recovery of valuable metals may be solved in a surprising and elegant manner so that deposits which were previously not workable, may be exploited in an economical manner.
According to the invention there is provided a process for the recovery of valuable metals which occur distributed in a calcium carbonate-containing raw material from which they cannot be recovered directly in an economical manner by ore dressing or acid leaching. The process is characterized in that the raw material with the valuable metals is subjected to vigorous heating and is allowed to react with sulphur oxides, particularly SO.sub.2, and in that the valuable metals are extracted from the calcine by extraction with dilute acid or water, whereafter the valuable metals are recovered from the extract in a per se known manner.
The heating and the addition of sulphur oxides, particularly SO.sub.2, may take place in several ways.
One possibility is to mix the raw material with a sulphurous material to a finely pulverized mixture and then heat this mixture by combustion of the sulphurous material. In the heating calcium carbonate is decomposed to burnt lime and CO.sub.2, and in the combustion sulphur oxides are formed, particularly SO.sub.2. The SO.sub.2 formed will then react directly with CaO formed, to form anhydrite, CaSO.sub.4, which is practically insoluble in water and dilute acid. The reactions involved and the total reaction may be illustrated as follows (with pyrite as sulphurous material): +4CO.sub.2 ( 4)
The heat evolved during the strongly exothermic reaction 1 brings about the decomposition reaction 2, and SO.sub.2 from reaction 1 reacts with CaO from reaction 2 to form CaSO.sub.4, according to reaction 3 which is also exothermic.
Like CaSO.sub.4 the Fe.sub.2 O.sub.3 formed is also practically insoluble in water and dilute acids.
REFERENCES:
patent: 2900231 (1959-08-01), Kremers et al.
patent: 3025131 (1962-03-01), Lerner
patent: 3722867 (1973-03-01), Butler
patent: 4220631 (1980-09-01), Serbent et al.
patent: 4464344 (1984-08-01), Saikkonen
A/S Megon & Co.
McFarlane Anthony
Metz Andrew H.
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