Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group va metal or arsenic
Patent
1987-03-26
1988-04-12
Doll, John
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group va metal or arsenic
204DIG13, 423 24, C01B 2700
Patent
active
047373504
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process for separating arsenic from acid solutions which contain it.
More particularly, the invention relates to a process for separating arsenic from sulphuric solutions of copper and other ions.
Still more particularly, the invention relates to a process for separating pentavalent arsenic from acid solutions, in particular sulphuric solutions of copper or other ions.
Almost all commercial copper is produced by electrolytically refining a raw material comprising about 99.5% of Cu and containing As together with many other extraneous elements. This raw material (blister copper), after suitably remelting and casting into slabs, forms the anode of an electrolytic cell, the cathode of which can be a slab of copper or, in more modern plants, stainless steel or titanium.
The electrolyte is a copper sulphate solution containing much free sulphuric acid.
On passage of electric current, copper dissolves from the anode and simultaneously deposits on the cathode. Of the impurities contained in the anode, some remain undissolved and form the so-called "anode mud", whereas others (elem-ents less nobel than copper) dissolve electrochemically. One of these is arsenic, which therefore constantly increases in concentration and has to be removed in order to prevent product contamination.
There are also other metallurgical problems in which arsenic control and removal are very important. This problem exists in the case of copper recovery by sulphuric electrolysis with insoluble anodes from residues such as the copper froth originating from purification operations in the primary metallurgy of lead.
The input-output equilibrium of arsenic (and of the other impurities) must therefore be controlled, and in a known method a part of the copper electrolyte is periodically deviated from the cycle, and this is subjected to multi-stage electrolytic separation to eliminate the As in the form of a Cu-As alloy. However, when solutions poor in coper but rich in arsenic are electrolysed, there is the risk of arsine evolution, an extremely toxic gas, and special arrangements and precautions are therefore required.
In addition, the subsequent recycling of the alloy sometimes gives rise to problems of a technical and cost nature. A more simple process for selectively removing arsenic from the copper electrolyte or in any event from strongly acid solutions is therefore of particular interest.
Methods are already known, consisting of extracting arsenic from the copper electrolyte using suitable organic solutions, which have tributylphosphate as their main active component. The arsenic can be re-extracted from these solutions with water or acid or alkaline aqueous solutions, and separated by precipitation either as the sulphide by using hydrogen sulphide or alkaline sulphides, or as arsenic trioxide by using sulphur dioxide or sulphites.
For example, German patent application No. 2603874 claims substantially the separation of arsenic from copper in acid solutions containing sulphuric acid, by carrying out the extraction with hydrocarbon solutions containing between 50 and 75% of tributylphosphate together with 5% or less of a high-boiling alcohol, the explicitly stated purpose of which is to prevent the formation of a third phase thus increasing the arsenic concentration in the organic phase.
German patent application No. 2615638 claims the use of a trialkyl, triaryl or triarylalkylphosphate, preferably tributylphosphate, diluted in a hydrocarbon medium and containing small quantities of isodecanol as an emulsion inhibitor.
British Pat. No. 1551023 claims the use of a solution in the form of a hydrocarbon medium containing between 40 and 75% of tributylphosphate and up to 15% of a quaternary ammonium salt, preferably tricaprylylmethylammonium chloride (Aliquat 336) or a mixture of methyl tri(C.sub.8 -C.sub.10)alkylammonium chlorides (Adogen 464).
All the three cited cases use substantial quantities of tributylphosphate, a considerably toxic substance, and in the third case there is a further increase in toxicity of t
REFERENCES:
patent: 4411698 (1983-10-01), Badesha
patent: 4547346 (1985-10-01), Guerriero et al.
Baradel Agostino
Guerriero Renato
Doll John
Langel Wayne A.
Nuova Samim S.p.A.
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