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TECHNOLOGIES ADAPTED FOR THE VALORIZATION OF A SMALL MINE, THE MONTE AVANZA POLYMETALLIC SULPHIDE (TETRAHEDRITE) MULTIBODY DEPOSIT, PART 2 : MINERAL PROCESSING AND EXTRACTIVE METALLURGY

Objective

The project is to define an efficient processing route for the polymetallic sulphide ore of Monte Avanza mine (north Italy) in order both to obtain products acceptable to smelters and to optimize the valorization of the metal values.
Interest has grown in a deposit of polymetallic sulphide ore containing copper, silver, antimony, mercury, arsenic and other metals in north Italy (Monte Avanza Mine).
The metals copper, silver, antimony, mercury and arsenic associated with a monomineralic polymetallic sulphide (tetrahedrite) cannot be separated using classical physical or physicochemical methods of mineral processing. Therefore, in spite of the high grade of the ore and the high value of the metals contained in the ore, the bulk concentrate obtainable by these methods is not acceptable to classical copper smelter particularly due to the presence of mercury and arsenic, which are considered as impurities.

Research has been carried out concerning the development of novel processing routes which allow the valorization not only of the copper and the silver, but also of the other metals (antimony, mercury and arsenic) most of which, at present, are considered as impurities. These include studies on the characterization of the different types of ore of Monte Avanza Mine and concentration tests concerning, in particular, gravity concentration. Also preliminary flotation tests have been carried out. The characterization of the ore has shown that the useful mineral in the ore body is argentiferous tetrahedrite and that the associated minerals (sulphides as pyrite, chalcopyrite, sphalerite, etc) are in such small quantities that they do not have economic relevance. The tetrahedrite mineral composition varies considerably with respect to whether the ore originates from the Carboniferous flyschoid or the Devonic limestone.

The heavy liquid tests have shown that the preconcentration of the ore by the dynamic dense medium separation system is feasible and that on the size range -8 + 0.5 mm, from ores having 3 to 4% copper, approximately 0.5% zinc and 1.5 to 2.2% antimony, preconcentrates having 6 to 7% copper, approximately 1% zinc and 3 to 5% antimony can be obtained with metal recoveries over 95%. By pr econcentration about 50% weight of the feed can be rejected as low grade tailings, thus reducing the requested capacity of the grinding and flotation plant.

Preliminary flotation tests have shown that the ore can be upgraded by flotation which produces adequate concentrate grades and metal recoveries.
Results would be of general interest for small mines having such complex ores. In this ore copper, silver, antimony, mercury and arsenic are associated in a single sulphide and cannot be separated using classical mineral processing methods. Despite the ore high grade and the value of the metals it contains, bulk concentrate obtainable by such methods is not acceptable to the classical copper smelter, particularly as a consequence of the mercury and arsenic presence which are considered impurities instead of values.

In particular the deposit is composed of various ore bodies having different mineralogical characteristics and shapes (vein, column, etc). These ore bodies are located in the Devonian limestone near the vertical contact with the carboniferous flysch (height 250 m, length 500 m). The mine is located in a mountain area (east Alps) over 1600 m above sea level.

The different work phases are as follows.

Systematic sampling of the ore body and supplying of samples to the contractors.

Characterization of the ore by chemical analysis, optical methods and electron microprobe analysis.

Beneficiation studies for preparing tetrahedrite concentrates involving:
gravity concentration tests;
flotation tests applied to an extended number of ore types;
determination of the best flowsheet;
production of a sufficient amount of concentrate for the metallurgical tests;
and analysis of the concentrates.

Studies of the pyrometallurgical processing of the concentrates by performing tests under different operating conditions to separate and recover mercury and possibly arsenic and antimony. The objective is to obtain a concentrate of copper silver or copper silver antimony acceptable to the smelters (ie according to the different required specifications) and recovering as much as possible of the remaining elements.

Economic evaluation of the best process. Preliminary evaluation of the investment and operating costs, with the aim of obtaining the maximum added value of the products.

Coordinator

Finsepol SpA
Address
Via Bonomo 4
34126 Trieste
Italy

Participants (2)

Métaleurop Recherche SA
France
Address
1 Avenue Albert Einstein
78193 Trappes
UNIVERSITA DEGLI STUDI DI TRIESTE
Italy
Address
Piazzale Europa 1
34127 Trieste