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IRON CONTROL BY HYDROLYTIC STRIPPING IN COMPLEX ORE PROCESSING.

Objective

A PRELIMINARY ENGINEERING STUDY HAS SHOWN THAT THE PROPOSED PROCESS SHOULD BE ECONOMIC IF THE IRON OXIDE PRODUCT CAN BE MARKETED FOR A MODEST PRICE.
IN ORDER TO ASCERTAIN THE POTENTIAL VALUE OF THE OXIDE PRODUCT, TESTS WILL BE CARRIED OUT OF A SIZE SUFFICIENT FOR OBTAINING MEANINGFUL DATA. THE CONTINUOUS MINIPLANT WORK ENVISAGED IN THIS STUDY WILL ENABLE SUITABLE SAMPLES TO BE PREPARED FOR THIS PURPOSE AND SO TO EVALUATE THE ECONOMICS OF THE PROCESS.

ADDITIONAL BASIC RESEARCH WILL IMPROVE THE KNOWLEDGE OF THE VARIOUS MECHANISMS HAVING A ROLE IN THE IRON STRIPPING OPERATION WHICH IS CONTAINED IN COMPLEX ORE SOLUTIONS.
Separate kinetic and mass transfer information has been used to build up a kinetic model of oxidative extraction of iron in a batch stirred gas liquid liquid reactor, and to determine the best conditions for extraction. The calculated variations of ferrous and extracted iron concentrations and the pH behaviour for different ferrous concentrations and acidity, Versatic acid concentrations, stirring speed and air flow, are in fairly good agreement with the experimental values.
The rate of extraction is mainly increased by a higher stirring speed and a lower initial acidity, and is slightly increased by a higher ferrous species concentration.
The kinetic model is able to explain kinetic behaviour in both the MINEMET and the CUPREX processes where the driving force, and the limiting factor, of iron extraction is the consumption of acidity by oxidations.

The main objective of the research was to improve the knowledge of the various mechanisms having a role in the iron stripping operation which is contained in complex ore solutions.

It was prossible to produce hematite powders of different colour shades and particle sizes by the hydrolytic stripping process, suitable for sale into the pigment market. The colour shade and particle size of the hematite depended on the preparation method of the iron loaded organic solution and the rate of precipitation. Higher rates favoured precipitation of fine powders of brighter red shades, while lower rates tended to produce coarser powders of deeper brown appearance.

The rate of precipitation of hematite during hydrolytic stripping can be controlled by varying the reaction temperature, and by using formic acid solutions instead of water as the hydrolyzing agent. It is essential to have good gas dispersal in the reactor when using formic acid in order to achieve a chemically controlled reaction and fast rates of precipitation.

The solvent extraction section accounted for more than half of the capital and operating costs of an industrial scale plant if the hydrolytic stripping process is combined into MINEMET type processes for copper recovery from complex ores, where iron is loaded into the organic phase by the oxidative extraction method.

The novel iron oxidization extraction technique already used for iron elimination from liquours typical of Minemet hydrometallurgical process, where the leaching reagent is cupric chloride, was tested on liquors encounterd in the Cuprex process, using ferric chloride as leaching reagent.
13% of the aqueous iron was extracted in 130 min. Using pressurized air or oxygen and a counter current (both gas and organic solution upwards) continuous operation will improve this yield.

The kinetic study of iron (III) extraction from acidic and chloride media by versatic acid solutions in a known interfacial area cell showed the paradoxal decrease of the extraction rate for higher iron concentrations, because of an important production of acidity by iron (III) hydrolysis and a high sensitivity of extraction to the pH, which leads to a minus third order with respect to 10{-pH} in the rate expression elaborated.

A set of mass balance equations was written and solved numerically to simulate the development of oxidations and iron extraction in the oxidizing extraction experiments achieved in the stirred semibatch reactor. For this purpose, the separately eleaborated quantitative information on the rate of chemical reactions and on mass transfer parameters was used. Agreement was found despite the lack of accurate thermodynamical representations for both aqueous and organic solutions. Such a tool is useful to predict both iron oxidation and extraction yields in gas aqueous organic contactors for iron elimination in hydrometallurgical liquors.
THE RESEARCH WORK IS DIVIDED INTO THE FOLLOWING STEPS:

- STUDIES OF KINETICS OF OXIDATION OF SOLUTIONS CONTAINING MIXTURES OF FERROUS, FERRIC, CUPROUS, CUPRIC IONS;
- STUDY OF FERRIC ION EXTRACTION KINETICS BY VERSATIC ACID;
- EXPERIMENTAL AND DESIGN STUDY OF CONTINUOUS STIRRED THREE-PHASE REACTORS.
- SIMILAR STUDY WILL BE DONE USING TABULAR CONTACTORS;
- STUDY OF EXTRACTION KINETICS OF OTHER METALS (NI, CO);
- CONSTRUCTION OF A CONTINUOUS AUTOCLAVE MINIPLANT SYSTEM;
- HEMATITE PRECIPITATION;
- PHYSICAL AND CHEMICAL CHARACTERIZATION OF HEMATITE PRODUCED;
- FEASIBILITY STUDY FOR INDUSTRIAL UTILIZATION OF HEMATITE.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

IMPERIAL COLLEGE OF SCIENCE, TECHNOLOGY AND MEDICINE
Address
South Kensington Campus
London
United Kingdom

Participants (1)

ASSOCIATION POUR LA RECHERCHE ET LE DEVELOPPEMENT DES METHODES ET PROCESSUS INDUSTRIELS
France
Address
Boulevard Saint-michel 60
75272 Paris