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The recycling of spent batteries and recovery of metals from them is of great scientific and economic interest, on account of recycling requirement of these wastes and recovery of valuable materials (De Michellis et al., 2007). Usage of recycled materials is diminishing the energy consumption and pollution. It is important that the recycling process to be environmentally friendly, practical and cost-effective. Tests for the process of manganese removal from spent battery leaching solutions, with ammonium peroxodisulfate, prior to recovery of zinc by electrolysis are presented. The experiments were carried out according to a 23 full factorial design as a function of ammonium peroxodisulfate concentration, temperature and pH. Because the excessive manganese in the spent batteries leach solutions can cause problems in the process of Zn recovery by electrolysis the main focus of this study is the manganese removal without altering the concentration of zinc in solutions. Data from XRF and AAS during the reaction at different time are presented. Manganese is obtained with high extraction degree as MnO2, which is economic and commercial important with applications in battery industry, water treatment plants, steel industry and chemicals (Pagnanelli et al., 2007). The analysis of variance (ANOVA) was carried out on the extraction yields of Zn after 30min, 1h, 2h and 3h of reaction. The preliminary results denoted that by chemical oxidation with ammonium peroxodisulfate is a suitable method for manganese removal as MnO2 prior zinc recovery by electrolysis, from spent batteries solutions and it could be used in a plant for recycling batteries.

Recycling the valuable metals found in spent permanent magnets (REPMs) poses a significant global challenge for the future. This study examines the efficiency of back extraction of rare earth elements (REEs) by oxalic acid solution from di-(2-ethylhexyl) phosphoric acid (D2EHPA) in recycling REPMs. To evaluate the efficiency of this process, several experiments were carried out using designed BOX-Behnken methodology to investigate the effects of various operational and chemical parameters, including stripping solution to loaded organic phase volume ratio (in the range of 1.0-2.0), oxalic acid concentration (ranging from 0.25 to 0.75 M), the stirring rate (ranged between 150 and 350 rpm), and stripping time (ranging from 15 to 45 min) on the REEs recovery and the purity of final production. Analysis of variance was applied to rigorously examine the results statistically. The results showed that more than 85 % of light and 80 % of heavy REEs can be recovered under optimal conditions. Moreover, the final product contained 43.5 % REEs and approximately 0.1 % iron. The stripping experiment using phosphoric acid as the reagent demonstrated ∼57 % light and ∼4 % heavy REEs recovery. Additionally, the recyclability of the organic phase showed its effective reuse for up to four cycles. This study underscores significant progress in the selective recovery of rare earth elements through a relatively straightforward process consuming mild reagents., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

Permanent magnets are fundamental constituents in key sectors such as energy and transport, but also robotics, automatization, medicine, etc. High-performance magnets are based on rare earth elements (RE), included in the European list of critical raw materials list. The volatility of their market increased the research over the past decade to develop RE-free magnets to fill the large performance/cost gap existing between ferrites and RE-based magnets. The improvement of hard ferrites and Mn-Al-C permanent magnets plays into this important technological role in the near future. The possible substitution advantage was widely discussed in the literature considering both magnetic properties and economic aspects. To evaluate further sustainability aspects, the present paper gives a life cycle assessment quantifying the environmental gain resulting from the production of RE-free magnets based on traditional hexaferrite and Mn-Al-C. The analysis quantified an advantage of both magnets that overcomes the 95% in all the considered impact categories (such as climate change, ozone depletion, human toxicity) compared to RE-based technologies. The benefit also includes the health and safety of working time aspects, proving possible reduction of worker risks by 3-12 times. The results represent the fundamentals for the development of green magnets that are able to significantly contribute to an effective sustainable transition., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

The present work aims to describe and review the available technologies and the recent advancements in treating industrial wastewater containing tetramethylammonium hydroxide (TMAH). It is a quaternary ammonium salt and widely used in the microelectronics industry; this kind of company produces large quantities of wastewater containing TMAH. The exhausted solutions must be treated appropriately since TMAH is corrosive, toxic to human health, and ecotoxic. Regarding the concentration at discharge, currently there are no European regulations. Still, it has been indicated that the substance has a negative influence on the oxygen balance and cause eutrophication, and fall into the relevant categories. In the first part of the work, the available technologies and the recent advancements for the treatment of TMAH contained in industrial wastewater are reviewed. Separation methods as such adsorption, ion exchange, membrane processes, and destruction technologies classified as advanced oxidation processes and biological processes have been considered. In the second part of the manuscript, industrial patented wastewater treatments have been described. Biological processes are those more used, being more economically feasible, require very long times not always sustainable., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The current paper presents an innovative hydrometallurgical methodology for recovery of precious metals from different waste streams. The used hydrometallurgical process, which has been already patented (Birloaga and Francesco Veglio, 2019), consists of a single leaching system (HCl, H 2 O 2 and C 2 H 4 O 2 ) of all elements and then selective recovery of elements from solution by chemical reduction/processes. About 99% of Au dissolution efficiency was achieved using: 3.5 M HCl; 1.96 M H 2 O 2 ; 1.67 M of C 2 H 4 O 2 ; 5 h without stirring; room temperature; 20% of solid concentration. The same conditions have resulted recovery of over 95% of Au from spent mobile phones PCBs. Over 80% of Au was achieved by three steps of leaching of ceramic Intel CPU. The influences of hydrochloric acid concentration and process time have been evaluated for Pd and Pt leaching from spent autocatalyst. Over 89% of Pt and 100% of Pd recovery were obtained from spent catalyst using: 5 M HCl; 1.96 M H 2 O 2 ; 1.67 M of C 2 H 4 O 2 ; 250 rpm of stirring for 3 h; room temperature; 10% of solid concentration. More than 98% of Pd recovery was achieved from the turbine residue after 20 min of reaction. The almost complete recovery of Au (99%) from solution was achieved by reduction with ascorbic acid. Complete recovery of Pd and about 79% of Pt have been obtained by cementation with ion metal powder from the leaching solution of spent autocatalyst. The application of reduction process with iron metal on the solution of turbine residues led to over 99% of Pd recovery. This efficient process provides a new way to recycle precious metals and to effectively prevent environmental pollution from different e-waste and other waste streams., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Hydrometallurgical processes for the treatment and recovery of metals from waste electrical and electronic equipment produce wastewaters containing heavy metals. These residual solutions cannot be discharged into the sewer without an appropriate treatment. Specific wastewater treatments integrated with the hydrometallurgical processes ensure a sustainable recycling loops of the electrical wastes to maximize the metals recovery and minimize the amount of wastes and wastewaters produced. In this research activity the efficiency of ultrafiltration combined with surfactant micelles (micellar-enhanced ultrafiltration) was tested to remove metals form leach liquors obtained after leaching of NiMH spent batteries. In the micellar-enhanced ultrafiltration, a surfactant is added into the aqueous stream containing contaminants or solute above its critical micelle concentration. When the surfactant concentration exceeding this critical value, the surfactant monomers will assemble and aggregate to form micelles having diameter larger than the pore diameter of ultrafiltration membrane. Micelles containing contaminants whose diameter is larger than membrane pore size will be rejected during ultrafiltration process, leaving only water, unsolubilized contaminants and surfactant monomers in permeate stream. The experiments are carried out in a lab-scale plant, where a tubular ceramic ultrafiltration membrane is used with adding a surfactant to concentrate heavy metals in the retentate stream, producing a permeate of purified water that can be reused inside the process, thus minimizing the fresh water consumption., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

In this paper, the efficiency of micellar enhanced ultrafiltration technique (MEUF) was tested for the removal of yttrium and zinc ions from synthetic industrial liquid wastes. UF membranes (monotubular ceramic membranes of 210 kDa and 1 kDa molecular weight cut-off) were used with adding an anionic surfactant, sodium dodecyl sulfate (SDS). A two - level full factorial design was performed in order to evaluate the effect of molecular weight cut-off, sodium dodecyl sulfate concentration and pressure on the permeate flux and rejection yields. It was found that the single factors presented the largest influence on the permeate flux: the membrane pore size and the pressure had positive effect, instead the SDS had negative effect. Regarding the metal rejection yields the main relevant factors were the membrane pore size with a negative effect, followed by the surfactant concentration with a positive effect. The effect of the pressure seemed to be almost negligible, for zinc removal experiments had a positive effect in the interactions with the surfactant and membrane pore size. The results showed that very good removal percentages up to 99% were achieved for both metals under the following conditions: 1 kDa membrane MWCO, in the presence of the surfactant at a concentration above CMC independently of the investigated pressure., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Aerobic treatment of wastewater containing Tetramethylammonium hydroxide (TMAH) and photoresist was investigated using a lab scale reactor inoculated with activated sludge coming from urban wastewater treatment that never received TMAH before. The consumption of TMAH was monitored by liquid ion chromatography. Biodiversity indices were calculated from Denaturing Gradient Gel Electrophoresis (DGGE) bands distribution and used to estimate changes in community composition related to adaptation to the new feeding compound. The first week of adaptation was crucial, and it was analyzed in detail: many organisms died, and the microbial community suffered a great shock. TMAH levels remained constant through the first four days, and then suddenly dropped to undetectable, and at the same time NH₄⁺ increased. When the community showed complete adaptation, predominant groups of bacteria were obtained by the Illumina sequencing of 16s rDNA amplicons, to provide insights on ecology of the adapted community, focusing on the main actors of TMAH abatement. Richness of species ( Rr ) peaks suggest that the development of TMAH-consuming bacteria leads to persistent consortia that maintain toxicity resistance over time. This showed adaptation and changes of the population to the different feeding conditions, and it opens new perspectives in the in situ treatment of these important residues of industrial processes without relying on external processing plants., Competing Interests: The authors declare no conflict of interest.

The present paper deals with physico-mechanical pre-treatments for dismantling of spent liquid crystal displays (LCDs) and further recovery of valuable fractions like plastic, glass and indium. After a wide experimental campaign, two processes were designed, tested and optimized. In the wet process, 20%, 15% and 40% by weight of the feeding panels are recovered as plastic, glass and indium concentrate, respectively. Instead, in the dry process, only two fractions were separated: around 11% and 85% by weight are recovered as plastic and glass/indium mixture. Indium, that concentrated in the -212μm fraction, was completely dissolved by sulphuric acid leaching (0.75molL -1 H 2 SO 4 solution, 80°C, 10%vol H 2 O 2 , pulp density 10%wt/vol, leaching time 3h). 100% of indium can be extracted from the pregnant solution with 5%wt/vol Amberlite™ resin, at room temperature and pH 3 in 24h. Indium was thus re-extracted from the resin by means of a 2molL -1 H 2 SO 4 solution, at room temperature and S/L of 40%wt/vol., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Terbium and rare earths recovery from fluorescent powders of exhausted lamps by acid leaching with hydrochloric acid was the objective of this study. In order to investigate the factors affecting leaching a series of experiments was performed in according to a full factorial plan with four variables and two levels (4 2 ). The factors studied were temperature, concentration of acid, pulp density and leaching time. Experimental conditions of terbium dissolution were optimized by statistical analysis. The results showed that temperature and pulp density were significant with a positive and negative effect, respectively. The empirical mathematical model deducted by experimental data demonstrated that terbium content was completely dissolved under the following conditions: 90 °C, 2 M hydrochloric acid and 5% of pulp density; while when the pulp density was 15% an extraction of 83% could be obtained at 90 °C and 5 M hydrochloric acid. Finally a flow sheet for the recovery of rare earth elements was proposed. The process was tested and simulated by commercial software for the chemical processes. The mass balance of the process was calculated: from 1 ton of initial powder it was possible to obtain around 160 kg of a concentrate of rare earths having a purity of 99%. The main rare earths elements in the final product was yttrium oxide (86.43%) following by cerium oxide (4.11%), lanthanum oxide (3.18%), europium oxide (3.08%) and terbium oxide (2.20%). The estimated total recovery of the rare earths elements was around 70% for yttrium and europium and 80% for the other rare earths., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Saffron from the province of L'Aquila, in the Abruzzo region of Italy, is highly prized and has been awarded a formal recognition by the European Union with EU Protected Designation of Origin (PDO) status. Despite this, the saffron regions are abandoned by the younger generations because the traditional cultivation of saffron (Crocus sativus L.) is labour intensive and yields only one crop of valuable saffron stamens per year. Petals of the saffron Crocus have had additional uses in traditional medicine and may add value to the crops for local farmers. This is especially important because the plant only flowers between October and November, and farmers will need to make the best use of the flowers harvested in this period. Recently, the petals of C. sativus L., which are considered a waste material in the production of saffron spice, were identified as a potential source of natural antioxidants. The antioxidants crocin and kaempferol were purified by flash column chromatography, and identified by thin layer chromatography (TLC), HPLC-DAD, infrared (IR), and nuclear magnetic resonance ((1)H &(13)C NMR) spectroscopy. The antioxidant activity was determined with the ABTS and DPPH tests. The antioxidant activities are mainly attributed to carotenoid and flavonoid compounds, notably glycosides of crocin and kaempferol. We found in dried petals 0.6% (w/w) and 12.6 (w/w) of crocin and kaempferol, respectively. Petals of C. sativus L. have commercial potential as a source for kaempferol and crocetin glycosides, natural compounds with antioxidant activity that are considered to be the active ingredients in saffron-based herbal medicine., (Copyright © 2015 Elsevier B.V. All rights reserved.)

With the increase in environmental awareness, the disposal of any form of hazardous waste has become a great concern for the industrial sector. Spent catalysts contribute to a significant amount of the solid waste generated by the petrochemical and petroleum refining industry. Hydro-cracking and hydrodesulfurization (HDS) catalysts are extensively used in the petroleum refining and petrochemical industries. The catalysts used in the refining processes lose their effectiveness over time. When the activity of catalysts decline below the acceptable level, they are usually regenerated and reused but regeneration is not possible every time. Recycling of some industrial waste containing base metals (such as V, Ni, Co, Mo) is estimated as an economical opportunity in the exploitation of these wastes. Alkali roasted catalysts can be leached in water to get the Mo and V in solution (in which temperature plays an important role during leaching). Several techniques are possible to separate the different metals, among those selective precipitation and solvent extraction are the most used. Pyrometallurgical treatment and bio-hydrometallurgical leaching were also proposed in the scientific literature but up to now they did not have any industrial application. An overview on patented and commercial processes was also presented., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Indium is a critical element mainly produced as a by-product of zinc mining, and it is largely used in the production process of liquid crystal display (LCD) panels. End-of-life LCDs represent a possible source of indium in the field of urban mining. In the present paper, we apply, for the first time, cross-current leaching to mobilize indium from end-of-life LCD panels. We carried out a series of treatments to leach indium. The best leaching conditions for indium were 2M sulfuric acid at 80°C for 10min, which allowed us to completely mobilize indium. Taking into account the low content of indium in end-of-life LCDs, of about 100ppm, a single step of leaching is not cost-effective. We tested 6 steps of cross-current leaching: in the first step indium leaching was complete, whereas in the second step it was in the range of 85-90%, and with 6 steps it was about 50-55%. Indium concentration in the leachate was about 35mg/L after the first step of leaching, almost 2-fold at the second step and about 3-fold at the fifth step. Then, we hypothesized to scale up the process of cross-current leaching up to 10 steps, followed by cementation with zinc to recover indium. In this simulation, the process of indium recovery was advantageous from an economic and environmental point of view. Indeed, cross-current leaching allowed to concentrate indium, save reagents, and reduce the emission of CO2 (with 10 steps we assessed that the emission of about 90kg CO2-Eq. could be avoided) thanks to the recovery of indium. This new strategy represents a useful approach for secondary production of indium from waste LCD panels., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

This study refers to two chemical leaching systems for the base and precious metals extraction from waste printed circuit boards (WPCBs); sulfuric acid with hydrogen peroxide have been used for the first group of metals, meantime thiourea with the ferric ion in sulfuric acid medium were employed for the second one. The cementation process with zinc, copper and iron metal powders was attempted for solutions purification. The effects of hydrogen peroxide volume in rapport with sulfuric acid concentration and temperature were evaluated for oxidative leaching process. 2M H2SO4 (98% w/v), 5% H2O2, 25 °C, 1/10 S/L ratio and 200 rpm were founded as optimal conditions for Cu extraction. Thiourea acid leaching process, performed on the solid filtrate obtained after three oxidative leaching steps, was carried out with 20 g/L of CS(NH2)2, 6g/L of Fe(3+), 0.5M H2SO4, The cross-leaching method was applied by reusing of thiourea liquid suspension and immersing 5 g/L of this reagent for each other experiment material of leaching. This procedure has lead to the doubling and, respectively, tripling, of gold and silver concentrations into solution. These results reveal a very efficient, promising and environmental friendly method for WPCBs processing., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Yttrium is important rare earths (REs) used in numerous fields, mainly in the phosphor powders for low-energy lighting. The uses of these elements, especially for high-tech products are increased in recent years and combined with the scarcity of the resources and the environmental impact of the technologies to extract them from ores make the recycling waste, that contain Y and other RE, a priority. The present review summarized the main hydrometallurgical technologies to extract Y from ores, contaminated solutions, WEEE and generic wastes. Before to discuss the works about the treatment of wastes, the processes to retrieval Y from ores are discussed, since the processes are similar and derived from those already developed for the extraction from primary sources. Particular attention was given to the recovery of Y from WEEE because the recycle of them is important not only for economical point of view, considering its value, but also for environmental impact that this could be generated if not properly disposal., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

In this paper, yttrium recovery from fluorescent powder of lamps and cathode ray tubes (CRTs) is described. The process for treating these materials includes the following: (a) acid leaching, (b) purification of the leach liquors using sodium hydroxide and sodium sulfide, (c) precipitation of yttrium using oxalic acid, and (d) calcinations of oxalates for production of yttrium oxides. Experimental results have shown that process conditions necessary to purify the solutions and recover yttrium strongly depend on composition of the leach liquor, in other words, whether the powder comes from treatment of CRTs or lamp. In the optimal experimental conditions, the recoveries of yttrium oxide are about 95%, 55%, and 65% for CRT, lamps, and CRT/lamp mixture (called MIX) powders, respectively. The lower yields obtained during treatments of MIX and lamp powders are probably due to the co-precipitation of yttrium together with other metals contained in the lamps powder only. Yttrium loss can be reduced to minimum changing the experimental conditions with respect to the case of the CRT process. In any case, the purity of final products from CRT, lamps, and MIX is greater than 95%. Moreover, the possibility to treat simultaneously both CRT and lamp powders is very important and interesting from an industrial point of view since it could be possible to run a single plant treating fluorescent powder coming from two different electronic wastes., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

This work is focused on the recovery of yttrium and zinc from fluorescent powder of cathode ray tube (CRT). Metals are extracted by sulphuric acid in the presence of hydrogen peroxide. Leaching tests are carried out according to a 2(2) full factorial plan and the highest extraction yields for yttrium and zinc equal to 100% are observed under the following conditions: 3M of sulphuric acid, 10% v/v of H2O2 concentrated solution at 30% v/v, 10% w/w pulp density, 70°C and 3h of reaction. Two series of precipitation tests for zinc are carried out: a 2(2) full factorial design and a completely randomized factorial design. In these series the factors investigated are pH of solution during the precipitation and the amount of sodium sulphide added to precipitate zinc sulphide. The data of these tests are used to describe two empirical mathematical models for zinc and yttrium precipitation yields by regression analysis. The highest precipitation yields for zinc are obtained under the following conditions: pH equal to 2-2.5% and 10-12%v/v of Na2S concentrated solution at 10%w/v. In these conditions the coprecipitation of yttrium is of 15-20%. Finally further yttrium precipitation experiments by oxalic acid on the residual solutions, after removing of zinc, show that yttrium could be recovered and calcined to obtain the final product as yttrium oxide. The achieved results allow to propose a CRT recycling process based on leaching of fluorescent powder from cathode ray tube and recovery of yttrium oxide after removing of zinc by precipitation. The final recovery of yttrium is 75-80%., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The present study dealt with the whole valorization process of exhaust refinery catalysts, including metal extraction by ferric iron leaching and metal recovery by precipitation with sodium hydroxide. In the leaching operation the effects on metal recovery of the concentration and kind of acid, the concentration of catalyst and iron (III) were determined. The best operating conditions were 0.05 mol L(-1) sulfuric acid, 40 g L(-1) iron (III), 10% catalyst concentration; almost complete extraction of nickel and vanadium, and 50%extraction efficiency of aluminium and less than 20% for molybdenum. Sequential precipitation on the leach liquor showed that it was not possible to separate metals through such an approach and a recovery operation by means of a single-stage precipitation at pH 6.5 would simplify the procedures and give a product with an average content of iron (68%), aluminium (13%), vanadium (11%), nickel (6%) and molybdenum (1%) which would be potentially of interest in the iron alloy market. The environmental sustainability of the process was also assessed by means of life cycle assessment and yielded an estimate that the highest impact was in the category of global warming potential with 0.42 kg carbon dioxide per kg recovered metal.

The present lab-scale experimental study presents the process of leaching waste printed circuit boards (WPCBs) in order to recover gold by thioureation. Preliminary tests have shown that copper adversely affects gold extraction; therefore an oxidative leaching pre-treatment was performed in order to remove base metals. The effects of sulfuric acid concentration, hydrogen peroxide volume and temperature on the metal extraction yield were studied by analysis of variance (ANOVA). The highest copper extraction yields were 76.12% for sample A and 18.29% for sample D, after leaching with 2M H2SO4, 20 ml of 30% H2O2 at 30°C for 3h. In order to improve Cu removal, a second leaching was performed only on sample A, resulting in a Cu extraction yield of 90%. Other experiments have shown the negative effect of the stirring rate on copper dissolution. The conditions used for the process of gold extraction by thiourea were: 20 g/L thiourea, 6g/L ferric ion, 10 g/L sulfuric acid, 600 rpm stirring rate. To study the influence of temperature and particle size, this process was tested on pins manually removed from computer central processing units (CPUs) and on waste CPU for 3½ h. A gold extraction yield of 69% was obtained after 75% of Cu was removed by a double oxidative leaching treatment of WPCBs with particle sizes smaller than 2 mm., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Life cycle assessment (LCA) was applied to hydrometallurgical treatments carried out using a new portable prototype plant for the recovery of valuable metals from waste electrical and electronic equipment (WEEE). The plant was fed with the WEEE residues from physical processes for the recycling of fluorescent lamps, cathode ray tubes (CRTs), Li-ion accumulators and printed circuit boards (PCBs). Leaching with sulfuric acid was carried out, followed by metal recovery by selective precipitation. A final step of wastewater treatment with lime was performed. The recovered metals included yttrium, zinc, cobalt, lithium, copper, gold, and silver. The category of global warming potential was the most critical one considering the specifications for southern European territories, with 13.3 kg CO(2)/kg recovered metal from the powders/residues from fluorescent lamps, 19.2 kg CO(2)/kg from CRTs, 27.0 kg CO(2)/kg from Li-ion accumulators and 25.9 kg CO(2)/kg from PCBs. Data also show that metal extraction steps have the highest load for the environment. In general, these processes appear beneficial for the environment in terms of CO(2) emissions, especially for metal recovery from WEEE residues from fluorescent lamps and CRTs.

The present work deals with the application of biotechnology for the mobilization of metals from different solid wastes: end of life industrial catalysts, heavy metal contaminated marine sediments and fluorescent powders coming from a cathode ray tube glass recycling process. Performed experiments were aimed at assessing the performance of acidophilic chemoautotrophic Fe/S-oxidizing bacteria for such different solid matrices, also focusing on the effect of solid concentration and of different substrata. The achieved results have evidenced that metal solubilization seems to be strongly influenced by the metal speciation and partitioning in the solid matrix. No biological effect was observed for Ni, Zn, As, Cr mobilization from marine sediments (34%, 44%, 15%, 10% yields, respectively) due to metal partitioning. On the other hand, for spent refinery catalysts (Ni, V, Mo extractions of 83%, 90% and 40%, respectively) and fluorescent powders (Zn and Y extraction of 55% and 70%, respectively), the improvement in metal extraction observed in the presence of a microbial activity confirms the key role of Fe/S oxidizing bacteria and ferrous iron. A negative effect of solid concentration was in general observed on bioleaching performances, due to the toxicity of dissolved metals and/or to the solid organic component., (Copyright © 2011 Elsevier Ltd. All rights reserved.)