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Content archived on 2024-04-16



Improvement of the processing of the Iberian belt complex sulphide.
Research has been carried out in order to improve the grades and recoveries of the concentrates being produced at Apirsa (Aznalcollar, Spain), Almagrera and Piritas Alentejanas (Aljustrel, Portugal). It has been shown that the losses to the tailings in the processing operation are not predominantly caused through poor mineral liberation but the difficulty of selective flotation of fine particles. It is in the slimes fractions that the vast majority of the liberated minerals are being lost to the tailings.

It ensued from the tests run on Sotiel and Aljustrel sulphide ores that:
a new synthetic reagent, collector C (5-methyl-2-mercaptobenzooxazole) is more selective than conventional reagents where copper and silver minerals are concerned, mainly with respect to pyrite and galena (the structure of the collector and the method of synthesizing it can not be revealed at present);
the flotation rate of collector C is faster than that of PAX;
the new synthetic reagent can operate at neutral pH, ensuring recoveries comparable with those of PAX and with better grades;
collector C seems to be more selective towards silver minerals, though further tests are needed to confirm this idea;
whatever the particle size of the feed, the products of rougher copper flotation are always finer than 15 to 20 um, thus confirming that the recovery of copper minerals is only possible if they are completely free.

This led to the idea that although enhancement of the rougher flotation stage (by increasing collector quantity or flotation time) might result in higher recovery of metal, it would not result in any improvement in final recovery, because the finished product would contain only the completely free grains, while the circulating load would be increased.

The new reagent has been produced on a semicommercial scale for in plant flotation tests on a complex sulphide ore over a 1 month period at the Sotiel plant.
The results obtained on the copper concentrate demonstrate that the new reagent is more efficient than xanthate and dithiophosphate as regards copper grade and recovery, while also being more selective in eliminating penalty elements. These results were obtained in a plant where it was necessary to maintain the existing flowsheet while continuing to produce marketable concentrates. As this reagent acts in a different way to conventional collectors, a more suitable flow sheet should really be designed to achieve the best results.
The aim of the project is 2 fold: to increase yields and grades of the metallic concentrates produced at APIRSA (at Aznacollar, Spain) and ALMAGRERA (at Sotiel, Spain) flotation plants and to develop optimal conditions of flotation for the future Aljustrel (Portugal) plant.

In order to achieve the above mentioned objective the following milestones have to be reached. The corresponding tasks to be carried out are also described.

Mineralogical characterization and analyses of ores and processed materials. Sufficient mineralogical analysis (by X-ray and chemical analysis) will be carried out on an appropriate number of samples to get an overall statistical knowledge of the different mineral species (and their estimated percentages) present in the Spanish and Portuguese complex sulphide ores. Quantitative analysis of the liberation sizes obtained in the plants after grinding will be carried out (image processing). Mineralogical characterization and chemical analysis of the different solid streams of the flotation plants will also be studied in order to get a better interpretation of the reagents effects. Special analytical techniques will be used (eg Fourier transform infrared(FTIR) and scanning electron microscopy(SEM)) to study the microscopic interaction between the collector and the mineral superficies.

New reagents will be synthesized with the purpose of increasing their selectiveness regarding copper(2+) cations, lead(2+) cations and zinc(2+) cations. The molecular structure will be selected through the utilization of a statistical model taking into account the mineralogical characterization and all the experimental data. There will be interaction and feedback actions between this work programme and the flotation experimentation work programme that will be carried out in parallel in order to optimize the reagents molecular composition.

Laboratory flotation experiments with Sotiel and Aljustrel ores. Set up of the appropriate laboratory procedure that will take into account the whole flotation process. Set up of the corresponding appropriate laboratory equipment. Experiments will be planified through satisfactory design of experiments in order to explore all the experimental factors (chemical, mechanical and mineralogical) and get statistical mathematical models of the results. Study of the collector behaviour with respect to each distinct sulphur, comparison with the conventional reagents and interpretation of the mechanism involved. The different flotation curves obtained will be used to define the selectivity of each reagent (Gaudin selectivity).

Grinding technology of ores and flotation cells at Sotiel and Aljustrel being different, a comparison study between the results is necessary and effects related to these equipment differences will be studied and interpreted.

Pilot plant continuous experimentation will be carried out in Aljustrel with new reagents selected. Complete material balance will be calculated to find the different yields obtained for copper lead and zinc.

If the final reagent selected can be obtained in sufficient quantity (around 2 to 3 tons will be necessary for a process of 1900 tons/day running approximately 10 days), industrial experimentation will be carried out in the Sotiel plant. Economic feasibility study and conclusions will follow.


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Almagrera SA
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Centro Sotiel
21300 Calañas

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