Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group ib metal
Reexamination Certificate
1999-06-03
2001-08-14
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group ib metal
C423S037000, C423S042000, C423S049000, C423S050000, C423S099000, C423S100000, C423S101000, C423S104000, C423S138000, C423S139000, C423S146000, C423S147000, C075S419000, C075S424000, C075S425000, C075S429000, C075S430000, C075S431000
Reexamination Certificate
active
06274104
ABSTRACT:
The invention relates to a method for recovering non-ferrous metals, particularly nickel, cobalt, copper, zinc, manganese and magnesium, from materials containing said metals by converting said non-ferrous metals into sulphates by means of melt and melt coating sulphation, i.e. by a thermal treatment under oxidizing conditions within a temperature range of 400 to 800° C., during which a reaction mixture is formed containing at least one said non-ferrous metal, iron(III)sulphate and alkali metal sulphate, and appropriate reaction conditions are selected to substantially prevent iron(III)sulphate from thermally decomposing to hematite, and finally, said non-ferrous metals are recovered as metallic compounds. In the method of the invention, a process is formed around the melt and melt coating sulphation, which comprises the following steps:
a) if necessary, the material is pre-treated to convert it into oxidized and ferritic form for easier treatment with melt and melt coating sulphation,
b) after the pre-treatment or in a related step, a sufficient amount of iron(III)sulphate is formed and, if required, the iron compound formed in the process is recycled to this step and further, the alkali metal (Na, K(sodium and/or potassium)) sulphate—water mixture concentrated in the process is recycled to this step,
c) the mixture formed during the previous steps and adjusted to a suitable composition now containing iron(III)sulphate and alkali metal (Na, K) sulphate in a sufficient quantity and in due proportion to the amount and composition of the original material, is directed to a melt and melt coating sulphation step in which melt conditions favourable to sulphation are created and maintained long enough to produce as complete sulphation as possible, and, if necessary, a thermal after-treatment is added to this step to decompose the iron(III)sulphate of the sulphate melt into hematite (Fe
2
O
3
) and sulphur trioxide to reduce the amount of water-soluble iron,
d) the mixture formed by the sulphate melt and solid phase is lead to a leaching step in which the soluble sulphates dissolve in water; after the leaching step, the non-dissolved solids are separated from the solution, washed and removed from the process, and the washing water is returned to the process,
e) if required, the thus formed solution is lead to an iron removal step in which iron(III) is precipitated as alkali metal (Na, K) jarosite, jarosite is separated from the liquid phase, washed, if necessary, and recycled into the process step described in item 2, and the washing water is returned to the process,
f) if required, the solution is lead (the original material contains aluminium) to an aluminium removal step in which aluminium is precipitated as hydroxide or alunite, separated from the liquid phase, washed and removed from the process, and the washing water is returned to the process,
g) the solution is lead to an Me removal step (Me=Ni, Co, Cu, Zn, Mn), in which the metals, Me, and if required also iron and aluminium, are separated by mixed hydroxide or sulphide precipitation, ion exchange or liquid-liquid-extraction, and the compounds of said metals are removed from the process and reprocessed in a manner known per se into pure metallic compounds or metals,
h) the solution is lead to a magnesium removal step in which magnesium is precipitated as hydroxide in a manner known per se, magnesium hydroxide is separated from the liquid phase and reused as a neutralizing agent in the steps described in items 5, 6 and 7, and excess magnesium hydroxide is removed from the process, and
i) the solution is lead to an alkali metal (Na, K) sulphate concentration step in which the concentration is performed by evaporation, the concentrated alkali metal (Na, K) sulphate—water mixture is recycled to the step described in item 2, excess alkali metal (Na, K) sulphate is removed from the process and the water evaporated during the concentration step and then re-condensed is mainly directed to the step described in item 4 and to a lesser extent to the steps described in items 5 and 6, particularly to their washing steps.
The method of the invention is characterized in that before the melt and melt coating sulphation step (step 3), the initial mixture is pelletized and iron(III)sulphate is created using a sulphuric acid solution and, if necessary, roasting is performed before this treatment (step 1).
The invention is especially characterized by the manner of pelletizing the material fed into step 2 with an alkali metal (Na, K) sulphate—sulphuric acid—water solution, during which the hematite (Fe
2
O
3
) in the feed material will at a suitable temperature react immediately with sulphuric acid and form hydrous iron(III)sulphate which together with sodium sulphate also acts as a bonding agent required in the pelletizing.
A central feature of the invention is thus a step where oxidic (or silicated) material or material which has undergone an oxidizing treatment is pelletized and a step related hereto, where iron(III)sulphate is formed, and an entire process formed around these steps and the steps preceding them enabling the recovery of for example said metals in an advantageous and technically simple manner.
Finnish Patent 65088 discloses a method which in Finnish Patent 83335 is called melt and melt coating sulphation. Thus, melt coating sulphation refers to a situation in which a molten phase containing a sulphating reagent forms a coating or film around the particles to be sulphated while the mixture containing molten and solid phase behaves mechanically like a pulverised or paste-like material depending on the quantity of melt, as opposed to melt sulphation in which the material is substantially in molten form and contains varying quantities of solid phase. The above-mentioned definitions have no significance as to the chemical reactions in the system. The melt and melt coating sulphation disclosed in Finnish Patent 65088 comprises a method to recover non-ferrous metals from their minerals, mineral concentrates, roasted oxidic intermediates or slags by converting them into sulphates using substantially as the sulphating agent a sulphate mixture comprising alkali metal sulphate, iron(III)sulphate and sulphates of one or more desired non-ferrous metals. In the referred method, the reagent used in sulphation is substantially an iron(III)sulphate contained in the reaction mixture, and the method uses a temperature range in which this reagent, Fe
2
(SO
4
)
3
, stays substantially stable in the molten sulphate phase. Generally, when applying melt or melt coating sulphation, the important part is the sulphation of oxides or, as often is the case in practice, ferrites (MeFe
2
O
4
in which Me=Ni, Co, Cu, Zn, . . . ) contained in the processed oxidic material or material which has undergone an oxidizing treatment, using a ferric sulphate, Fe
2
(SO
4
)
3
, in sulphate melt in accordance with the reaction described in the main claim of patent 65088 or correspondingly the reaction (1).
3MeFe
2
O
4
(s)+Fe
2
(SO
4
)
3
(melt)→3MeSO
4
(melt)+Fe
2
O
3
(s) (1)
The particular mechanism and kinetics of the reaction between the Me ferrites and the sulphate melt are described in the article: P. J. Saikkonen, J. K. Rastas, The Role of Sulfate Melts in Sulfating Roasting, 25
th
Annual Conference of Metallurgists, Proceedings Nickel Metallurgy, Ed. E. Ozberk and S. W. Macuson, Series 25-7/6/1/3, No. 3 (Vol. 1) (1986) 278-290.
The thorough-sulphation of the ferrite particles, MeFe
2
O
4
, occurs in a counter-diffusion during which the Me
2+
ion moves through a growing Fe
2
O
3
phase formed between the ferrite phase and sulphate melt phase to the sulphate melt, and the Fe
3+
ion moves from the sulphate melt through the hematite (Fe
2
O
3
) phase in the opposite direction, and the entire occurrence can be presented in general with the reaction equation (2),
3Me
2+
(ferrite)+2Fe
3+
(melt)→3Me
2+
(melt)+2Fe
3+
(hematite) (2)
The thorough-sulphation of the ferrite parti
Rastas Jussi
Saikkonen Pekka
Andrus Sceales Starke & Sawall LLP
Bos Steven
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