Solvent extraction

Details Solvent extraction Solvent extraction

1996-04-25

1998-11-10

Ludlow, Jan

Chemistry: analytical and immunological testing

Including sample preparation

Liberation or purification of sample or separation of...

210551, 210634, 210638, 210639, 436 73, 436 75, 436 79, 436 81, 436 82, 436 83, 436 84, 436103, 436119, 436161, G01N 118

Patent

active

058343164

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to the solvent extraction.


BACKGROUND OF THE INVENTION

Solvent extraction is used in a variety of analytical and industrial applications particularly in the chemical engineering and waste treatment fields. For example, hazardous radioactive and non-radioactive species present in a solid or liquid medium may be extracted into a solvent system and subsequently isolated and disposed of or recycled as appropriate.
A known technique which has been used for solvent extraction of metal containing species is supercritical fluid extraction (SFE). This technique is reported in a number of papers for example: and Technology--Theoretical and Applied Approaches to Analytical Chemistry", Bright F V and McNally M E, Eds.; ACS Symposium Series 488; Amer. Chem. Soc., Washington, D.C., 1991, p 206-220. In SFE the extractant solvent comprises a supercritical fluid such as carbon dioxide together with a complexant or chelant which serves to dissolve the metal species by forming a soluble complex. In the SFE processes described in the prior art the complexant provides a negatively charged ligand to facilitate metal ion extraction.


SUMMARY OF THE INVENTION

According to the present invention there is provided a method of extracting ionic species from a host medium containing such species which comprises contacting the medium with an extractant solvent which comprises a supercritical fluid and a complexant for solubilising and extracting the ionic species present in the said medium wherein the complexant comprises a positively charged ligand.
The method according to the present invention may therefore be employed to extract anions from a host medium containing such species.
The extractant solvent may also include a conditioning agent which may comprise an oxidising agent or a reducing agent and is present to assist dissolution of the metal species in the complexant by changing the oxidation state thereof. The presence of the conditioning agent thereby beneficially increases the efficiency of the solvent system in dissolving the anions to be extracted.
Where the conditioning agent is an oxidising agent it may be selected from a peroxide such as H.sub.2 O.sub.2, a perchlorate such as NaClO.sub.3, oxygen, ozone and potassium permanganate or a plurality of oxidising agents.
Where the conditioning agent is a reducing agent it may be selected from hydrogen, hydrazine or a solution containing an oxidisable metal species such as Fe++ or Cu+, or a plurality of reducing agents.
The medium from which anions are desired to be removed by the method according to the present invention may be a solid or liquid medium. Where the medium is a solid it may comprise a particulate material such as soil, sludge, an industrial process residue, an industrial process slag or the like. The metal species may be contained on the surface of the particles and/or bound within the particles. The medium could alternatively be a material to be decontaminated, e.g., a metal or concrete structure, waste building materials such as rubble or contaminated waste materials such as rubber, plastics or textiles materials. Where the medium is a liquid it may for example comprise a process solvent or an industrial effluent stream.
The method of the present invention may for example be employed to analyse the concentration of anion species of interest in liquid or solid samples. For example, when analysing for the presence of anion contaminants it may be desirable to produce a stock solution which is subsequently divided into multiple samples for different analyses.
The present invention may alternatively be employed to decontaminate surfaces contaminated with radioactive or non-radioactive anion species.
The present invention may for instance be employed for soil clean-up for land remediation purposes.
The present invention may alternatively be employed in processes which employ conventional solvent extraction, e.g., dissolution of lanthanide- or actinide-containing anions produced in reprocessing of irradiated nucl

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