The overall aim of the project is to develop low cost, environmental consistent biometallurgical technique for the exploitation of community manganese resources.
A low cost and environmentally friendly process has been developed for the exploitation of domestic European manganese resources which involves biometallurgical procedures.
The research covered the following steps:
localization, collection and preparation of the manganese ore samples from selected deposits and mines;
chemical, mineralogical and petrographic characterization of the raw materials; identification of the liberation functions of the minerals in the various comminution classes;
concentration by magnetic and gravimetric separation methods of the manganese ore;
bioleaching tests at laboratory scale on the different ores by computerized factorial design of experiments. Various species of microorganism (in pure or mixed cultures) were tested for the dissolution of manganese.
Heterotrophic microorganisms (Aspergillus niger) have proved to be robust and effective (40% yield after 7 days) unlike autotrophic (Thiobacillus species) that have shown only reduced manganese dissolution (20% yield after 15 days).
The best results have been generally achieved when using mixed cultures, where the most active species was represented by Agrobacter radiobacter.
The chemical reactions involved in the process were identified and a factorial design of experiments was applied to the bioleaching tests using mixed cultures. The behaviour of manganese oxide was easily detected by the disappearance of the typical brown colour. The leached manganese was distributed partially in the solution (30%), on the microorganisms (20%) and the remaining 50% in the precipitated manganese carbonate.
The influence of the particle size, medium composition, sucrose concentration on the dissolution of manganese has been evaluated. Manganese extraction was greatly affected by a decrease of particle size in the range 65 to 200 um. Sucrose and ammonium nitrate and yeast extract had a remarkable positive effect on manganese dissolution.
Significant differencies have been experimentally as certained when comparing the shaken flasks system with the biofermentator. In fact more high recoveries have been obtained in the first type of reactor. Whilst manganese dissolution occurs in reducing conditions, it has been emphasized that the biochemical reduction of manganese if favoured in aerobic conditions.
At present, there are only 2 EEC countries with manganese resources large and rich enough to be of commercial interest namely, Italy (Northern Lazio and Sardinia) and Greece (Drama area in Macedonia). The economic assessment of the overall results of the process will be evaluated together with the possible impact that this new process can bring about to other manganese deposits.
The work will involve the following stages.
Indispensable personnel, materials and means will be disposed for the appropriate collection and preparation of the manganese ore samples from the selected mines to be used in the project.
A complete minero-petrographic and chemical analysis of the ore will be performed by means of inductive coupled plasma spectrophotometry and plasma mass spectroscopy. Mineralogical analysis will utilize X-ray diffractometry and surface analysis will use X-ray photoelectron spectroscopy(XPS) and fourier transform infrared(FTIR).
Identification of the liberation function of the minerals in the various classes of the comminution products.
Design of bioleaching experiments for the 2 manganese ores will be performed by means of computerized fractional factorial designs of experiments. Different microorganisms from several bearing ores will be collected, cultivated and isolated to perform a preliminary study for the identification of the most capable and efficient manganese ore leacher. Different bioleaching tests will be performed in order to identify the best operation conditions of such process. The overall process will be optimized by taking advantage of the statistical analysis (computerized variance analysis, evaluation of single and cross factors contribution) of the data obtained experimentally. Mechanism of manganese dissolution during bioleaching tests as well as kinetic aspects will also be investigated.
Samples from occurrences or from the existing plant will be treated by gravimetric and magnetic separation methods. Both the residues and the head samples will be treated by microorganisms.
After completion of laboratory scale bioleaching experiments, pilot plant tests will be scheduled to be run on the installations at the University of L'Aquila on 300 kg samples.
According to the pilot plant tests, a preliminary economic evaluation of the overall results of the method (conventional and bioleaching or bioleaching) will be undertaken in order to assess the economic feasibility of such a process.
Funding SchemeCSC - Cost-sharing contracts
09016 Iglesias Cagliari