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New strategies implementing a resource-efficient and competitive economy, which transforms environmental problems into opportunities, are encouraged at global scale (UN Sustainable Development Goals, SDG). In recent years, mine residues are attracting scientific interest, since they can turn into viable sources of secondary and critical raw materials (SRMs and CRMs). Planning the sustainable supply and circular use of resources, integrating incomplete information, providing environmentally sound technologies for the simultaneous reduction of environmental risks and recovery of SRMs and CRMs are the key steps for overcoming such ambitious challenges. In this study, a multidisciplinary and eco-sustainable strategy is presented for the characterization, mapping, classification and valorization of mine residues.

Mining and mineral-processing wastes have been giving a lot of concern in recent times. We have evaluated an integrated multidisciplinary strategy for mining residues characterization, as well as for the recovery of secondary (e.g., Fe, Mn) and critical (e.g., Ga) raw materials. After the in situ sampling campaigns in Bichakundi Joda West iron and manganese mine (Keonjhar district, State of Odisha, India), residues have been characterized and the acquired mineralogical, chemical and spectral information have been used to create a map of mining residue deposits by means of the new multispectral satellite Sentinel-2A classification. Furthermore, mycorrhizal-assisted phytoextraction of metals from previously classified soils, based on sunflowers colonized by an AM fungal strain GA5 Rhizophagus intraradices, was carried out in the perspective of subsequent recovery of Ga, Fe and Mn from biomass using hydrometallurgical and electrochemical techniques. The bioconcentration factors in aerial and radicular parts (BCS and BCR, respectively), and translocation factors (TF) followed the order Ga>Mn>Fe for BCS and TF, while for BCR was Ga>Fe>Mn. The results were used to estimate the bioextracting potential by phyto-mycoremediation into a Vegetable Depuration Module (VDM): the highest extraction was estimated for Fe (60 g/VDM), followed by Mn (35 g/VDM) and Ga (1.02 g/VDM), thus confirming a good potential for their subsequent recovery by hydrometallurgical techniques with final purification by selective electrodeposition. Results are encouraging and the application of such multidisciplinary approach can be important to develop a circular model for sustainable exploitation of mining residues.

During the past 30 years the gold leaching in thiosulphate media has attracted renewed interest of numerous researchers caused by fast kinetics in the presence of some oxidants/ligands and adaptability to carbonaceous and copper gold ores, inappropriate for direct cyanidation. The overall reaction of gold leaching is Au + Cu(II) = Au(I) + Cu(I). The paper presents a thermodynamic approach to studying mixed ligand complex formation reactions in the ammonia - thiosulfate aqueous system under real conditions. Its quintessence consists in the thermodynamic analysis of concurrent reactions in the system Au(I) - NH3 - S2O32- - H2O on the basis of the introduced notion of the generalized reaction equation (GRE). The formation of mixed ligand complex species is characterized usually by certain peculiarities in the behavior of two-phase heterogeneous systems.

The consumption of batteries has continually accelerated trend. Disposal of spent batteries represent severe environmental problem due to the metallic content, being considered as hazardous waste. Reutilization and recycling of spent batteries are appearing in order to minimize the wastes as well as to preservation of raw materials. The present experimental work involves the new bio-hydrometallurgical application, considering the integration of physical-chemical and biological-chemical methods for Mn-Zn recovery from spent alkaline batteries. The main aims of the research were: - to develop the preliminary experimental work to recover selectively MnO2 and Zn from bioleaching solutions containing Mn and Zn by electrolysis, with the scope to apply electrochemical technologies for Zn and Mn recovery from spent batteries; - to verify the possibility of spent batteries processing by bioleaching with Acidithiobacillus ferrooxidans together with the molasses coming, as waste materials, from agro-food industry. Average content of Zn in alkaline batteries was about 22.00%. The average Mn content was similar (21.00%). Average content in K was 4.9%, while Ni 0.65% and Fe 0.6%. Experimental results have demonstrated the technical feasibility of the application of bio-hydrometallurgical processes - integrated by electrochemical technologies - for Zn and Mn recovery from exhaust batteries. According to the experimental results, a preliminary flow-sheet has been proposed.

The metals and industrial minerals contained in the tailings produced by mining and quarrying activities, are cause of environmental damage. The objective of this experimental work is the application of innovative technologies for the treatment and exploitation of mining tailings in Romania, in order to recover materials high grade raw to be placed on the market, reducing the volume of the wastes. The study is focused on hydrometallurgical process for the recovery of gold. The innovative treatment chosen is the thiosulphate process that, compared to conventional cyanide, has several advantages, first of all the most eco-friendly and non- toxic to humans. The conventional processes - such as cyanidation - show operating limits in the case of auriferous minerals refractory materials, such as Romanian wastes object of the study. Another fundamental characteristic of the ammoniacal thiosulphate solutions, is the best selectivity towards gold, not attacking the majority of the gangue mineral constituents. The objective of the investigation, is to optimize some parameters relating to the dissolution of gold and the subsequent recovery from purified solutions, determining beforehand the technical feasibility of the scheme of process developed on a laboratory scale. The dissolution rates of gold reached a final value of 65% Au - working at room temperature - with recoveries of the global process of about 65%, in line with the conventional process.

Disposal of spent batteries constituted a serious environmental problem in terms of heavy metals content when these devices are disposed off in inadequate way. Alkaline and zinc-carbon batteries represent about 80% of the market. In particular, alkaline batteries, have an average content of manganese dioxide (MnO2) of 37%, while zinc content is of 16%. The high Mn and Zn content justify the interest to recover the metals. The present experimental work involves the utilisation of technologies well know in the framework of the mineral processing and the metal dissolution by bio-hydrometallurgical processes for Mn-Zn recovery from wastes. The wastes were constituted from spent alkaline batteries. Main aim of the research was to develop a preliminary experimental work to recover selectively MnO2 and Zn from leaching and/or bioleaching solutions containing Mn and Zn by electrolysis, with the scope to apply electrochemical technologies for Zn and Mn recovery from exhaust batteries. Results have demonstrated the technical feasibility of the application of electrochemical technologies for Zn and Mn recovery from exhaust batteries, after leaching and/or integrated bio-leaching of the powders achieved by manual dismantling and subsequent grinding and milling. About 98% of MnO2 and Zinc recovery from the leaching and/or bioleaching solutions has been achieved. In all the operative conditions, a MnO2 and Zn deposit at high grade of purity has been attained; this fact was demonstrated from the results of the analyses conducted by diffractometric techniques.

The main aim of this experimental work is to investigate remediation biohydrometallurgical processes for toxic metals removal (Zn, Cu, Mn, Al and Fe) from Acid Mine Drainage (AMD), recovering purified useful metals. The main cause of river water pollution in Western and Central European regions (Albania, Kosovo, FYR of Macedonia, Slovakia, Romania) and in South America regions (Perù, Bolivia, Argentina, Brasile....) is undoubtedly represented by metal sulphide (copper, zinc, iron, SO4 etc.) ore deposits and tailings abandoned near to closed and/or open mines. The aim of environmental protection policy of the region is devoted to the reduction of the content of heavy metals in the rivers. Water drainages have an appreciable metal content over the permitted standard. The metals of primary concern are Cu, Cr, Fe, Al, Mn, Hg, Ni, Pb, As and Zn. The processes studied are innovative, intended to reaching a specific purpose, economically and environmentally. These could be integrated with physical treatments, with the dual aim of reducing pollution of inland waters at the same time producing useful metals (copper, nickel, zinc, etc.). The benefit for the environment will result in the reduction of toxic effects on living organisms. Biohydrometallurgical applications - constituted by bioprecipitation/electrowinning - have demonstrated the technical feasibility of the process aimed at the removal of toxic metals from AMD samples; in fact, at the end of the process, the metals' concentration decreased under the recommended legislation limit, achieving metals at high degree of purity (about 95%).

The main aim was to demonstrate the technical feasibility of the remediation processes by electrowinning and bioprecipitation, for toxic metals removal from acid mine drainage (AMD) coming from a zinc mine located in Tùnel Kingsmill outlet of the Rio Yaulì (district of Yauli - Perù). The study consists in a preliminary work: the experimental tests have been conducted by synthetic solutions. Electrowinning tests have been carried out after chemical iron-aluminum precipitation, that permitted a complete Fe-Al removal. By electrochemical experiments, high metals removal, with a low energetic consumption, has been achieved: in particular, by Zn and Mn electrodeposition, it was possible to achieve 80-90% Zn and Mn removal, with a low energetic consumption. The culture of sulphate-reducing bacteria (SRB) of genera Desulfovibrio sp. was used for the bioprecipitation tests. The treatment of AMD by SRB is based on the ability of SRB to reduce sulphates to hydrogen sulphide, which binds readily with metals to form sparingly soluble precipitates. The kinetic of the selective precipitation of Fe, Zn, Al and Cu has been investigated. This method has been performed in two interconnected reactors. Achieved results demonstrate the 98-99% elimination of Cu by bacterially produced H2S.

In the framework of the project solving were achieved next main results: 1) Deepening of theoretical knowledge on the possible technological applications of physicalchemical (electrochemical) and biological removal of toxic metals from municipal and industrial wastewater through literature searches. 2) Determination of the characteristics of geo-materials through mineral-petrographic analysis and chemical and waste water samples by chemical analysis. Collecting data on selected samples from polluted areas in the territory of Peru and on the Italian territory. 3) Development of methods of treatment of heavy metals present in urban waste water and industrial residue. Reducing direct and indirect metal with Sulphur-Reducing Bacteria (SRB) in a laboratory scale, identifying the appropriate process to different types of contamination. 4) Development of biohyrometallurgical treatments of sulphides containing antimony and arsenic by iron and sulfur-oxidizing bacteria (Acidithiobacillus ferrooxidans, Thiobacillus ferrooxidans, Thiobacillus Thiooxidans) and sulfate-reducing (Desulfovibrio desulfuricans, Desulfotomaculum). 5) Development of an electrochemical circuit, with the identification of critical process parameters. 6) Determination of the electrochemical process on a laboratory scale with the study of relevant parameters. 7) Optimization of physical and chemical processes (electrowinning) and biological on laboratory scale. 8) Scale-up of the processes. The main purpose of the studies was to clean up the toxic metals from municipal wastewater and industrial waters such as acid mine drainage (AMD), by applying the processes of electrowinning and bioprecipitation. The samples were collected from zinc mines located in Italy and lead and zinc deposit in Perù. The electrochemical process has allowed a high removal of heavy metals, allowing, with low energy consumption, significant recoveries (90-99% Zn). Culture of sulphate-reducing bacteria (SRB) of genera Desulfovibrio sp. and Desulfotomaculum sp. were used for the bioprecipitation tests. The kinetic of the selective precipitation of Cu and Zn of AMD by SRB has been investigated. This method has been performed in two interconnected reactors. Achieved results demonstrate the about 95-99% elimination of Cu and Zn by bacterially produced H2S. Both the electrowinning and bioprecipitation processes have been demonstrated the technical feasibility to decrease the heavy metals concentration.

The main aim was to demonstrate the technical feasibility of the remediation processes by electrowinning and bioprecipitation, for toxic metals removal from acid mine drainage (AMD) coming from a zinc mine located in Tùnel Kingsmill outlet of the Rio Yaulì (district of Yauli - Perù). The study consists in a preliminary work: the experimental tests have been conducted by synthetic solutions. Electrowinning tests have been carried out after chemical iron-aluminum precipitation, that permitted a complete Fe-Al removal. By electrochemical experiments, high metals removal, with a low energetic consumption, has been achieved: in particular, by Zn and Mn electrodeposition, it was possible to achieve 80-90% Zn and Mn removal, with a low energetic consumption. The culture of sulphate-reducing bacteria (SRB) of genera Desulfovibrio sp. was used for the bioprecipitation tests. The treatment of AMD by SRB is based on the ability of SRB to reduce sulphates to hydrogen sulphide, which binds readily with metals to form sparingly soluble precipitates. The kinetic of the selective precipitation of Fe, Zn, Al and Cu has been investigated. This method has been performed in two interconnected reactors. Achieved results demonstrate the 98-99% elimination of Cu by bacterially produced H2S.

On a resource management level, batteries could be considered as an ore of secondary raw materials, because of their high content in useful metals, such as zinc and manganese; moreover, disposal of spent batteries constituted a serious environmental problem in terms of heavy metals content, when these devices are disposed off in inadequate way. Main processes applying for treatment of the batteries are the pyrometallurgical processes, that involve high energetic consumption and pollution problems, and hydrometallurgical processes, chipper and at low energetic cost. The experimental activity of the present work involve the utilisation of technology well know in the framework of the mineral processing and the metal dissolution by hydrometallurgical processes for Mn-Zn recovery from wastes, constituted by spent alkaline batteries. The results have demonstrated the technical feasibility of the application of the mentioned technologies; in fact, high recovery of manganese and zinc dissolved in solution were achieved (over 90%).

The main scope of this study was to remediate Acid Mine Drainage (AMD) by application of biohydrometallurgical processes, environmentally friendly, to remove heavy metals such as Zn, Cu, Mn, Cd, Al and Fe. The processes studied have been electrowinning and bioprecipitation. The samples utilised were collected from the zinc mine located in Italy and from a cooper - iron ore deposit in Slovakia. By electrochemical experiments, high metals removal, with a low energetic consumption, has been achieved: in particular, by Zn electrodeposition, it was possible to achieve 95-99% Zn removal. Culture of sulphatereducing bacteria (SRB) of genera Desulfovibrio sp. was used for the bioprecipitation tests. The precipitation kinetic of metals at the original pH of aforementioned AMD by SRB has been investigated. This method has been performed in two interconnected reactors. Achieved results indicate the 98-99% selective elimination of Cd from AMD - Italian mine, and the 98-99% selective elimination of Cu from AMD - Slovak mine by bacterially produced H2S. Both the electrowinning and bioprecipitation processes have been demonstrated the technical feasibility to decrease the heavy metals concentration. The experimental work has been carried out in the framework of the agreement of scientific cooperation between the Institute of Environmental Geology and Geoengineering of the CNR, Italy and the Institute of Geotechnics of Slovak Academy of Sciences, Slovakia (years 2007-2009).

This paper deals with bioleaching of metals from hazardous spent hydro-processing catalyst by means of iron/sulphur oxidizing bacteria. The effects on nickel, vanadium and molybdenum extraction yields of elemental sulphur, ferrous iron and actions contrasting a possible metal toxicity (either the presence of powdered activated charcoal or the simulation of a cross current process by means of filtration stages in series) was investigated. Ferrous iron resulted to be essential for metals extraction and for bacteria adaptation. Nickel and vanadium were successfully bioleached in the presence of iron, reaching extraction yields of 83% and 90%, respectively; on the other hand extractions around 50% for nickel and vanadium were observed both in biological systems in the absence of iron and in the chemical controls with iron. As concerns molybdenum, the highest extraction yields experimentally observed for molybdenum was about 50%, after 26 days bioleaching in the presence of iron, while a maximum extraction of 25 % was observed in the other treatments. In conclusion, a bio-oxidative attack with iron could successfully extract nickel, vanadium and partially molybdenum. Further actions aimed at contrasting a possible metal toxicity resulted not to be effective. The obtained results supported the important role of the indirect mechanism in bioleaching of LC-Finer catalysts and allowed the authors to propose a flowsheet for metal extraction from such waste by means of biohydrometallurgical technologies.

The present experimental work has been carried out in the framework of the agreement of scientific cooperation between the Institute of Environmental Geology and Geoengineering of the CNR, Italy and the Institute of Geotechnics of Slovak Academy of Sciences, Slovakia (years 2007-2009). The main scope was to remediate Acid Mine Drainage (AMD) by application of biohydrometallurgical processes, environmentally friendly, to remove heavy metals such as Zn, Cu, Mn, Cd, Al and Fe. The processes studied have been electrowinning and bioprecipitation. The samples utilised were collected from a zinc mine located in Italy and from a cooper - iron ore deposit in Slovakia. By electrochemical experiments, high metals removal, with a low energetic consumption, has been achieved: in particular, by Zn electrodeposition, it was possible to achieve 95-99% Zn removal. Culture of sulphate-reducing bacteria (SRB) of genera Desulfovibrio sp. was used for the bioprecipitation tests. The kinetic of the selective precipitation of Cu and Zn of AMD by SRB has been investigated. This method has been performed in two interconnected reactors. Achieved results demonstrate the about 98-99% elimination of Cu and Zn by bacterially produced H2S. Both the electrowinning and bioprecipitation processes have been demonstrated the technical feasibility to decrease the heavy metals concentration.

The application of hydrometallurgical processes have been experimented starting from spent alkaline batteries. Main aim of the research was to develop a preliminary experimental work to recover selectively MnO2 and Zn from leaching solution containing Mn and Zn, both at concentration of 10 g dm-3, by electrolysis, with the scope to apply electrochemical technologies for Zn and Mn recovery from exhaust batteries. The results have demonstrated the technical feasibility of the application of the mentioned technologies; in fact, high recoveries of manganese and zinc dissolved in solution were achieved (97 % MnO2 and 98.50 % Zn).

The present experimental work involves the application of electrohydrometallurgical processes for Mn-Zn recovery from wastes originated by spent batteries. Disposal of spent batteries constitutes a serious environmental problem in terms of heavy metals content when these devices are disposed off under inadequate way. Alkaline and zinc-carbon batteries represent about 80% of the market. In particular, alkaline batteries have an average content of manganese dioxide (MnO2) of 35%, while zinc content is of 14%. The high Mn and Zn content justify the interest to recover the metals. Main processes applied are the pyrometallurgical processes, that involve high energetic consumption and pollution problems; and hydrometallurgical processes, chipper and at low energetic cost. In this work, hydrometallurgical processes have been applied, starting from spent alkaline batteries. Zn and Mn recovery from the aqueous solutions has been carried out electrochemically. The composition of the alkaline batteries utilised was 14 % Zn and 27 % Mn, as MnO2. Main aim of the research was the development of an experimental work to recover selectively MnO2 and Zn from leaching solution containing Mn and Zn, both at concentration of 10 g dm-3, by electrolysis, with the scope to apply electrochemical technologies for Zn and Mn recovery from exhaust batteries. The results have demonstrated the technical feasibility of the application of the mentioned technologies; in fact, high recovery of manganese and zinc dissolved in solution were achieved (96% MnO2 and 98% Zn).

Results of studies carried out by different institutes of National Research Council (CNR) in the field of waste treatment, recovery and disposal are shown in this paper. The above institutes are included in the CNR Departments of Earth and Environment, Energy and Transports and Molecular Design. The research activities are related to waste incineration, production of a solid recovered fuel (SRF) by means of an innovative process, monitoring of gas produced by landfill sites, recovery of metallurgical waste and of metals from electronic and exhaust batteries, and recovery of wastes produced by the gold industry.

In this work, hydrometallurgical processes have been applied starting from spent alkaline batteries. Main aim of the research was to develop a preliminary experimental work to recover selectively MnO2 and Zn from leaching solution containing Mn and Zn, both at concentration of 10 g dm-3, by electrolysis, with the scope to apply electrochemical technologies for Zn and Mn recovery from exhaust batteries. The results have demonstrated the technical feasibility of the application of the mentioned technologies; in fact, high recoveries of manganese and zinc dissolved in solution were achieved (97 % MnO2 and 98.50 % Zn).

Extraction of Vanadium and Nickel from waste material was investigated using alkaline and acidic leaching systems. Spent catalyst coming from manufacture of sulfuric acid (3.5% V and 0.63% Ni) and boiler ash (25% V and 13% Ni) can be used as a secondary source of metals. Statistical design of experiments and analysis of variance (ANOVA) were performed in order to determine the main effects and interactions of the investigated factors, which were temperature of roasting and leaching; concentration of the leaching reagent (H2SO4/NaOH); pulp concentration and process time. ANOVA shows that roasting step is the main factor with positive effect on the recovery of metals, whereas pulp concentration shows a negative effect probable due to the inefficient mixing.

Main aim of the present experimental work was the development of hydrometallurgical innovative and environmentally friendly technologies, to re-use agro-industrial wastes. Manganese is an important commodity for application in the steel industry, in the battery manufacturing and as a fine chemical. The processes of manganiferous minerals are carried out by means of pyrometallurgical and hydrometallurgical treatments: the first ones present a more serious environmental impact especially considering the atmospheric emissions. The study started to develop a production process of manganiferous products of industrial interest, such as MnO2, by using an innovative chemical leaching, at low environmental impact, in presence of waste biomasses coming from agro-industrial activities (milk whey, molasses, vegetation waters and paper mill sludges). Important goal of this experimental work is to achieve products of industrial interest, such as electrolytic manganese dioxide (EMD), starting from manganiferous ores not treatable by conventional processes. The application of a chemical leaching in presence of carbohydrates as lactose was carried out. The study of the electrolytic process has been conducted utilising synthetic leaching solutions. The results show that it is possible to achieve high MnO2 recovery by hydrometallurgical processes (90%).

The main aim of the present experimental work - carried out in the framework of the S&T Cooperation Programme between Italy and Slovakia (years 2004-2007) - was to remediate Acid Mine Drainage (AMD) by the application of new technologies, chip and environmentally friendly, to eliminate the heavy metals content (Zn, Cu, Mn, Al and Fe). The processes studied have been electrowinning and bioprecipitation. The samples utilised were collected from the abandoned and flooded deposit of Smolník, located in Slovak Republic and from the zinc mine located in Montevecchio (Italy). Electrowinning tests have been carried out after chemical iron-aluminum precipitation, that permitted a complete Fe-Al removal. By electrochemical experiments, high metals removal, with a low energetic consumption, has been achieved: in particular, by Zn electrodeposition, it was possible to achieve about 95% Zn removal. The culture of sulphate-reducing bacteria (SRB) of genera Desulfovibrio sp. was used for the bioprecipitation tests. The treatment of AMD by SRB is based on the ability of SRB to reduce sulphates to hydrogen sulphide, which binds readily with metals to form sparingly soluble precipitates. The kinetic of the selective precipitation of Cu and Zn has been investigated. This method has been performed in two interconnected reactors. Achieved results demonstrate the 98-99% elimination of Cu and Zn by bacterially produced H2S. Both the electrowinning and bioprecipitation processes have been demonstrated the technical feasibility to decrease the heavy metals concentration.