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A fed-batch strategy is proposed to produce microalgae biomass under non-axenic heterotrophic conditions. The strategy induces the alternation of N-deplete (Glucose-replete) and N-replete (Glucose-deplete) cultivation phases by the periodic and uncoupled supply of glucose and NO3− to the culture. Cultivation of the microalga T. obliquus with this strategy reduced the ratio of the bacteria to microalgae cell concentration from 1.6, attained by conventional photoautotrophic cultivation, to 0.03. During the N-deplete phase, microalgae duplication stopped and biomass concentration increased 1.9 times, while during the N-replete phase, microalgae duplicated halving their average size and losing about 25% of their weight. The process proved to be effective under several consecutive cycles. Biomass productivity until 6.1 g/Ld and biomass concentration until 26 g/L were achieved. The results demonstrate that the proposed strategy can effectively prevent bacterial contamination, paving the way to the large scale production of microalgae biomass under non-axenic heterotrophic conditions.

An empirical model for prediction of microalgal growth in outdoor photobioreactors cultivation, using Principal Component Analysis (PCA) and Partial Least Squares (PLS) regression method, is implemented. Experimental data of biomass production were collected over 1 year of operation of a bubble column prototype, monitoring light and temperature and changing cultivation's conditions. PCA isolates 2 Principal Components that explain 80% of the variance and are associated with Environmental Conditions and Cultivation Conditions. Moreover, the PLS regression model showed positive results in term of responses (R2 = 0.84) and residuals, following the experimental trends of outputs as specific growth rate (μ(d−1)) and productivity calculated at Cmax (Pmax (g L−1 d−1)), giving also good prediction results in its validation test. This method could be easily used for other purpose, by changing the input values of the specific cultivation used (including CO2 uptake or wastewater dilution ratio in the culture medium), obtaining as outputs the desired variables (lipid production rate, etc.).

Li primary batteries are currently treated along with other Li batteries in several big pyro- metallurgical plants in Northern EU countries. Nevertheless, pyro-metallurgical processes do not allow for Mn and Li recycling and present negative environmental impacts, on the other hand hydrometallurgical processing can potentially ensure the integral recovery of all materials in Li primary batteries. In this work, preliminary experimental findings obtained in the LIFE-LIBAT project (LIFE16 ENV/IT/000389) are reported. In this project, end of life Li(0)-MnO2 batteries were cryo-mechanically treated and then the metals were recovered by a hydrometallurgical process. Representative samples of end of life Li(0) batteries were characterized by type and composition. Batteries were stabilized in an N2 bath and then crushed, sieved, and magnetically separated in the SEVal pilot units. Separated fractions (fine fraction, magnetic coarse fraction, and non-magnetic coarse fraction) were chemically characterized for target metal content (Li and Mn). Fractions were first treated for Li extraction and recovery, then the fine fraction was also leached for Mn recovery. Mass balances evidenced a 55% recycling rate and process simulations outlined profitability in the potentiality range in agreement with battery collection fluxes.

Experimental results of leaching tests using waste fractions obtained by mechanical pretreatment of lithium ion batteries (LIB) were reported. Two physical pretreatments were performed at pilot scale in order to recover electrodic powders: the first including crushing, milling, and sieving and the second granulation, and sieving. Recovery yield of electrodic powder was significantly influenced by the type of pretreatment. About 50% of initial LIB wastes was recovered by the first treatment (as electrodic powder with size0.5mm, Sample 1), while only 37% of powder with size1mm (Sample 2) can be recovered by the second treatment. Chemical digestion put in evidence the heterogeneity of recovered powders denoting different amounts of Co, Mn, and Ni. Leaching tests of both powders were performed in order to determine optimized conditions for metal extraction. Solid/liquid ratios and sulfuric acid concentrations were changed according to factorial designs at constant temperature (80°C). Optimized conditions for quantitative extraction (99%) of Co and Li from Sample 1 are 1/10g/mL as solid/liquid ratio and +50% stoichiometric excess of acid (1.1M). Using the same solid/liquid ratio, +100% acid excess (1.2M) is necessary to extract 96% of Co and 86% of Li from Sample 2. Best conditions for leaching of Sample 2 using glucose are +200% acid excess (1.7M) and 0.05M glucose concentration. Optimized conditions found in this work are among the most effective reported in the literature in term of Co extraction and reagent consumption.

Different kinds of panels (Si-based panels and CdTe panels) were treated according to a common process route made up of two main steps: a physical treatment (triple crushing and thermal treatment) and a chemical treatment. After triple crushing three fractions were obtained: an intermediate fraction (0.4–1 mm) of directly recoverable glass (17%w/w); a coarse fraction (>1 mm) requiring further thermal treatment in order to separate EVA-glued layers in glass fragments; a fine fraction (

End of life photovoltaic panels of different technologies (poly crystalline Si, amorphous Si, and CdTe) were treated mechanically in pilot scale by single shaft shredder minimizing the production of fine fractions below 0.4 mm (18% weight). Grounded material was sieved giving: an intermediate fraction (0.4-1 mm) of directly recoverable glass (18% weight); a coarse fraction (which should be further treated for encapsulant removal), and fine fractions of low-value glass (18%), which can be treated by leaching for the removal of metal impurities. Encapsulant removal from coarse fraction was successfully performed by solvent treatment using cyclohexane at 50 °C for 1 h giving high-grade glass (52% weight), which can be reused for panel production. Experimental results of solvent treatment were compared with those from thermal treatment by economic analysis and Life Cycle Assessment, denoting in both cases the advantages of solvent treatment in recovering high-value glass.

Hydrotreating catalysts (HTCs) are a waste byproduct of the petroleum refining industry. The recovery of intrinsic and sorbed metals from spent catalysts is desirable for meeting environmental disposal regulations, as well as for the metal resell value. In this study, innovative process schemes for metal recovery from end-of-life (i.e., spent) HTCs were tested in laboratory experiments and compared by process analysis. Synthetic leach liquors containing Al, Mo, Ni, and V were prepared resembling both chemical leaching and bioleaching methods for metal extraction from spent catalysts. Subsequently, metals in the leach liquor were recovered individually according to two pH-dependent process schemes: (i) Mo and Ni were separated first and Al was removed last, and (ii) Al was removed first. The second metal separation process gave the best results in terms of selectivity, whereby 65% of Al was recovered by precipitation at pH 4.0, 87% of Mo was precipitated by sulfide addition at pH 0.5, 52% of Ni was precipitated by sulfide addition at pH 3.5, and 65% of V was recovered by hydroxide complexation at pH 6.0. Experimental data of metal precipitation were used to perform a process analysis comparing chemical leaching and bioleaching for different input flow rates and product depreciation in a simulated commercial-scale plant. Simulation results indicate that chemical leaching is of superior performance over biological leaching in terms of metal recovery, which decrease the payback time for the capital investment to build the plant. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 703–712, 2015

Co and Li recovery by acid-reducing leaching of lithium ion battery powder was investigated evidencing that glucose efficiency changes depending on leaching procedure. Postponing glucose addition metal extractive yields were higher (88% for Co and 92% for Li) than adding glucose at the beginning (60% for both). Chromatographic analyses evidenced that glucose degradation occurred preferentially via glucaric acid when its addition is postponed, while gluconic via is favored if glucose is added initially. Dynamic evolution of particle area showed particle fragmentation occurring during acid preleaching determining an increase of specific surface area available for further reaction when glucose is added.

In this work experimental results of potentiometric titration and Cr removal at different ionic strength using a heterotrophically-grown biomass of Chlorella vulgaris were reported for the first time in the literature. Biomass cell wall was characterized by potentiometric titrations and IR spectra. Titration modeling denoted the presence of four kinds of sites with acid–base properties: hydroxyl, carboxylic, phenolic and amino groups. IR spectra confirmed such assignment and also showed the presence of sulfonates. Kinetic tests of Cr(VI) removal were performed according to a full factorial design with two factors (Cr(VI) concentration and ionic strength) at two levels: all tests can be represented by pseudo-first and pseudo-second order models. Analysis of variance showed significant negative effects of ionic strength and of ionic strength–time interaction on sorbed Cr, and positive effect of ionic strength on reduced Cr. These findings along with characterization results were elaborated according to a conceptual model for Cr(VI) biosorption-mediated reduction: protonated hydroxyl and amino groups can be involved in Cr(VI) sorption, hydroxyl groups can reduce sorbed Cr(VI) giving Cr(III) and new carboxyl groups. Cr(III) can be bound by labile electrostatic interactions to sulfonates. Competition with Na+ determined the release of Cr(III) and favored further Cr(VI) reduction.

Background A major obstacle to the application of microalgae for bio-fuel production is light intensity reduction in high density cultures. Mixotrophic operation can solve this problem by exploiting the ability of microalgae to grow on organic carbon in dark conditions. In this article, mixotrophic growth of Nannochloropsis oculata and Chlorella vulgaris is analyzed. The influence of nitrate and glucose concentration on cell growth in 300 mL Erlenmeyer flasks was investigated using an experimental factorial design. The analysis was extended and validated by analyzing mixotrophic growth in a 6 L bubble column. Results The addition of glucose at concentration 0.1 g L-1 inhibited or enhanced the growth of Chlorella depending on nitrate concentration, while it increased the growth rate of Nannochloropsis at all nitrate concentrations tested. Statistically significant interaction between glucose and nitrate concentration was revealed for Chlorella; negligible interaction was found for Nannochloropsis. A kinetic characterization, shedding light on the influence of glucose on microalgal growth, was conducted through identification of a Monod-like model. Experimental tests in 6 L bubble column confirmed for both Chlorella and Nannochloropsis the possibility to significantly enhance growth in the presence of light deficiency through mixotrophic operation. Conclusions Mixotrophic growth is governed by the interaction between organic carbon and nitrogen. This can have a profound impact on kinetic modeling of microalgal growth and on the operation of cultivation systems. Controlling the C/N ratio is in particular fundamental to optimize reactor operation. © 2013 Society of Chemical Industry

In 2014, the European Union defined a list of 20 raw materials critical for economic importance and high supply risk. The aim of this work is to present the main results achieved within the EU-FP7 Project HydroWEEE-Demo dealing with the recovery of indium and cobalt, metals included in such European list, from LCD scraps and end of life Li-ion batteries, respectively. A complete indium recovery was achieved carrying out an acidic leaching, followed by a zinc cementation. Cobalt was extracted from the electrodic powder according to the following main operations: leaching (by acid reducing conditions), primary purification (by precipitation of metal impurities), solvent extraction with D2EPHA (for the removal of metal impurities), solvent extraction with Cyanex 272 (for the separation of cobalt from nickel), cobalt recovery (by precipitation as cobalt hydroxide). Co products with 95% purity were obtained by implementation of the solvent extraction with D2EHPA and Cyanex 272.

An innovative process was optimized to recover Co from portable Lithium Ion Batteries (LIB). Pilot scale physical pretreatment was performed to recover electrodic powder from LIB. Co was extracted from electrodic powder by a hydrometallurgical process including the following main stages: leaching (by acid reducing conditions), primary purification (by precipitation of metal impurities), solvent extraction with D2EPHA (for removal of metal impurities), solvent extraction with Cyanex 272 (for separation of cobalt from nickel), cobalt recovery (by precipitation of cobalt carbonate). Tests were separately performed to identify the optimal operating conditions for precipitation (pH 3.8 or 4.8), solvent extraction with D2EHPA (pH 3.8; Mn/D2EHPA = 4; 10% TBP; two sequential extractive steps) and solvent extraction with Cyanex 272 (pH 3.8; Cyanex/Cobalt = 4, 10% TBP, one extractive step). The sequence of optimized process stages was finally performed to obtain cobalt carbonate. Products with different degree of purity were obtained depending on the performed purification steps (precipitation with or without solvent extraction). 95% purity was achieved by implementation of the process including the solvent extraction stages with D2EHPA and Cyanex 272 and final washing for sodium removal.

In this paper the recycling of nickel metal hydride (NiMH), lithium ion (Li-ion) and primary lithium batteries was examined. Three mechanical routes of treatment were developed for each type recovering mainly three fractions: ferrous metals, non-ferrous metals and electrodic powders. The above mentioned types of spent batteries were also treated together by a unique mechanical route, obtaining in this way a powder enriched in cobalt, nickel and manganese which can be further extractable by chemical leaching. Experimental tests of solvent extraction were performed on synthetic leach liquors simulating a feed mixture of spent devices with weight composition 40% NiMH, 40% primary lithium, and 20% Li-ion (as determined by manual sorting of 3 tons of end of life batteries collected in Northern Italy). Under these conditions nickel and cobalt can be easily separated by using Cyanex 272 (stoichiometric ratio Cyanex/Co = 4, pH 5–6), but in presence of manganese Cyanex 272 loses its selectivity towards cobalt. Thus manganese must be preliminarily removed by using D2EHPA (stoichiometric ratio D2EHPA/Mn = 2, pH 4). Mechanical treatments and hydrometallurgical section to recover metals from electrodic powder are unavoidable operations in order to recover at least 50% of batteries as weight according to European Guideline 2006/66/EC.

The control and inhibition of pyrite bioleaching involved in the generation of acid mine drainage was studied. Inhibition of pyrite bioleaching was performed by varying the pyrite concentration in the medium (substrate inhibition) and/or by addition of limestone (inhibition by pH increase) and olive pomace (inhibition by organic compounds). Inhibition tests of pyrite bioleaching were performed according to a full factorial design with three factors (pyrite, limestone and olive pomace) taken at two levels. Preliminary pyrite bioleaching tests showed the ability of the available inoculum to oxidise the mineral. Subsequently, experimental data for total soluble iron denoted strong inhibition under all the different operating conditions of the factorial design, except when larger pyrite concentrations were used. In particular, inhibition by limestone was due to the increase in pH which negatively affects microorganisms, while inhibition by olive pomace may be related to the antioxidant properties of polypheno...

In this study olive pomace was used as a source of binding substances for the development of composite biosorbents to be used in heavy metal removal from aqueous solutions. The aim was to obtain biosorbent material with an increased concentration of binding sites. The effects of two different extraction procedures (one using only methanol and the other one hexane followed by methanol) on the binding properties of olive pomace were tested by potentiometric titrations and batch biosorption tests for copper and cadmium removal. Titration modelling evidenced that both kinds of extractions generated a solid with a reduced amount of protonatable sites. Biosorption tests were organized according to full factorial designs. Analysis of variance denoted that both kinds of extractions determined a statistically significant negative effect on metal biosorption. In the case of cadmium extractions also determined a significant decrease of selectivity with respect to olive pomace. When the acid-base and binding properties of the substances extracted were determined, they were adsorbed onto a synthetic resin (octadecylsilane) and calcium alginate beads. In this way two kinds of composite biosorbents have been obtained both having an increased concentration of binding substances with respect to native olive pomace, also working more efficiently in metal removal.

Biosorbing properties of sulphate reducing bacteria were tested to distinguish the amount of cadmium removed by bioprecipitation from that bound onto biomass surface (biosorption). Experimental results of cadmium abatement in batch growth tests (bioprecipitation tests) were then compared with metabolism-independent binding properties of SRB cell wall surface (biosorption tests performed with dead biomass). Experimental results showed that SRB inoculum removed 59 + or - 5% of sulphates in 21 days even in presence of cadmium (0-36 mmol L(-1)), while non-monotonous kinetic effects were observed for increasing Cd concentrations. Comparison between bioprecipitation and biosorption tests denoted a significant contribution of biosorption (77%) in total Cd removal (0.40 + or - 0.01 mmol g(-1)). Characterisation of bacterial acid-base surface properties by potentiometric titrations and mechanistic modelling denoted that carboxylic, phosphate and amino groups of cell wall are the main responsible of metal removal by biosorption mechanism.

Acid leaching of manganese from the powders of exhausted zinc alkaline batteries has been studied using carbohydrates as reducing agents. A mono-saccharide (glucose) and a di-saccharide (lactose) have been tested, the second as a template of industrial wastes. Manganese leaching was complete in the presence of both carbohydrates, along with zinc. Data from the factorial test with lactose have been analysed with ANOVA. The most significant effects for manganese extraction were sulphuric acid concentration, temperature, and lactose concentration.

This paper investigates the chemical mechanisms operating in cadmium and lead removal by activated sludge in sequencing batch reactors. Selective extraction and acid digestion of sludge samples denoted that both Cd and Pb are mainly present as surface-bound metals. Characterisation of sludge samples by potentiometric titrations and IR spectra suggested that carboxylic and amino groups are the main active sites responsible for the binding properties of the biomass. Simulation of metal speciation implemented with complexation constants determined in biosorption tests, showed that cadmium predominates as biosorbed species, while lead was mainly removed by precipitation.

The aim of the work was the comparison between a selected reactive mixture containing organic matter for SRB and other electron donors, such as ethanol and polysaccharides. The comparison was performed in order to select the best operating conditions in terms of organic sources for SRB. A continuously operating fixed-bed column was filled with a batch-optimised solid reactive mixture (6% leaves, 9% compost, 3% zero valent iron, 30% silica sand, 30% perlite, 22% limestone) and inoculated by SRB. At steady state 50±10% sulphate abatement was reached and metals were totally removed. Batch tests with ethanol showed the ability of SRB to grow on this substrate efficiently. Experimentation using ethanol was performed using two different column reactors filled with perlite, one inoculated by SRB and the other used as blank. Sulphate abatements of the inoculated column were 70±10% against 10±5% of the blank column. Preliminary batch tests with polysaccharides showed the ability of bacteria to grow on these substrates.

BACKGROUND: In this study a comparison between two continuously operating fixed-bed column systems was performed in order to select the best operating conditions in terms of organic sources for sulphate reducing bacteria (SRB). The first column system (solid substrate, SS) was filled with a solid reactive mixture containing the organic matter necessary for SRB growth, while the second one (liquid substrate, LS) was filled with inert material and continuously fed by ethanol. RESULTS: In the SS column 50 ± 10% sulphate abatement was reached at steady state, while metals were totally removed. Blank tests showed that biosorption was mainly responsible for both sulphate and metal removal. In the LS column, sulphate abatement was 70 ± 10% at steady state against 10 ± 5% of an identical column without inoculum (blank liquid substrate, BLS). Comparison with BLS showed that the main mechanism operating in this system was bioprecipitation. Estimated degradation rate constants for both SS and LS columns indicate similar performances (0.008 ± 0.001 and 0.0085 ± 0.0005 d ―1 for SS and LS, respectively). CONCLUSIONS: LS column systems offer a valid alternative to conventional SS systems, avoiding the use of potentially harmful wastes as organic sources for SRB metabolism.

Obligate autotrophic and acidophilic characteristics of iron oxidizing bacteria were exploited in order to prevent or attenuate the generation of acid mine drainage. Inhibition of biomass growth was performed by variation of 9K medium by increasing ferrous iron concentration (substrate inhibition), by addition of limestone (inhibition by pH increase) and olive pomace (inhibition by organic compounds). Inhibition tests of batch growth were performed according to a full factorial design with three factors (ferrous iron, limestone and olive pomace) taken at two levels. Blank tests were also performed in the same operating conditions but without inoculum. All tests were monitored by measuring cell and ferrous iron concentrations, pH and redox potential. Biomass characterization was performed by determining the sequence of 16S ribosomal RNA gene that denoted a 100% homology with the sequence of Acidithiobacillus ferrooxidans, one of the main bacteria responsible for acid mine drainage. Experimental data of cell growth denoted a strong inhibition in all the operating conditions, except the case when larger ferrous iron concentrations were used. Blank tests allowed isolation of the effect of chemical speciation from the effect due to metabolic activities. In particular, inhibition by limestone seemed to be due not only to pH increase, but also to a reduced availability of ferrous iron substrate, while inhibition by pomace may be related to the antioxidant properties of polyphenols. Interactions among operating conditions, biomass growth and chemical parameters were specifically assessed by analysis of variance. Estimates of significant effects (95%) for cell concentration denoted that only main effects related to limestone and pomace addition determined a significant diminution of cell concentration with a dynamic increasing trend.

We analyze the influence of surface heterogeneity, inducing a random ζ -potential at the walls in electroosmotic incompressible flows. Specifically, we focus on how surface heterogeneity modifies the physico-chemical processes (transport, chemical reaction, mixing) occurring in microchannel and microreactors. While the macroscopic short-time features associated with solute transport (e.g. chromatographic patterns) do not depend significantly on ζ -potential heterogeneity, spatial randomness in the surface ζ -potential modifies the spectral properties of the advection–diffusion operator, determining different long-term properties of transport/reaction phenomena compared to the homogeneous case. Examples of physical relevance (chromatography, infinitely fast reactions) are addressed.

The oxidation of glucose during the reductive leaching of pure MnO2 and manganese ore in sulphuric acid at 90 °C MnO2 was investigated. The aim was to identify the derivatives and the chemical pathway of glucose oxidation. Organic derivatives were monitored by HPLC using an Aminex HPX-78H column and UV detection. Chromatographic patterns of leaching solutions showed that major compound formed was formic acid. Minor quantities of glycolic, glyceric and traces of gluconic acids were identified. Results suggest that during the leaching reaction, the carbon chain of glucose is shortened by detachment of one carbon atom as formic acid.

Biosorption of copper by Sphaerotilus natans in different conditions of ionic strength and pH was studied by performing sorption tests in batch and membrane reactors. Equilibrium batch tests evidenced the negative effect of ionic strength and the positive effect of pH on biosorption performances: the highest determined value for copper specific uptake, q, was about 60 mg/g at pH 6 and about 15 mg/g at pH 4. A competitive equilibrium model was successfully fitted to experimental data at different ionic strength levels to account for copper-sodium competition. In membrane reactor tests, experimental profiles of copper concentration in the permeate vs. time did not evidence a significant effect of ionic strength at low pH values (4 and 5). On the other hand a more remarkable effect of ionic strength on copper concentration in the permeate was observed at pH 6. Experimental profiles of continuous biosorption in the membrane reactors were successfully simulated by developing a dynamic model accounting for Cu-Na competition and for binding ability of cells fragments.

A methodological approach for validation, optimization and lumping of mechanistic models for heavy metal sorption onto composite natural matrices is proposed. It follows a previously developed mechanistic model for biosorption onto olive pomace, based on potentiometric titrations and Cu, Pb and Cd sorption tests at different pH. This model assumes two main kinds of active sites (carboxylic and phenolic groups) and three surface complexation reactions among these sites and metallic species in solution. It is able to represent the biosorption of Cu, Cd and Pb according to a general-validity reaction scheme in both acid and basic pH ranges. The identification of the most significant contributions of surface complexes by model simulations, along with sensitivity analysis oriented towards a lumped model, assumes one kind of active site (carboxylic) and two complexation reactions occurring in the pH 3–5 range. Simultaneous regression of titration data, first derivative plot of titration, and sorption data according to this lumped model, allow an improvement of experimental data representation by using a reduced number of parameters (i.e. model discrimination by statistical analysis). Contributions of surface complexes and sensitivity analysis show that all the assumed reactions of this lumped model are significant and necessary to represent biosorption of Cu, Cd and Pb in pH range 3–5.

Heavy metal biosorption onto solid wastes from olive oil production plants, olive pomace, has been investigated. Acid-base properties of the active sites of olive pomace were determined by potentiometric titrations and represented by a continuous model accounting for two main kinds of active sites. Competition among protons and heavy metals in solution was considered by performing biosorption tests at different equilibrium pH with single (Cu and Cd) and binary metal systems (Cu-Cd). Both Langmuir extensions and non-ideal competitive adsorption models (NICA models) can be used to represent experimental data of Cu and Cd biosorption in single metal systems at different equilibrium pH. Nevertheless only NICA models, accounting for site heterogeneity and non-ideal adsorption of the different species simultaneously present in solution, can adequately simulate the competition among Cu and Cd in binary metal systems by using the parameters fitted to single system data.

Biosorption of heavy metals using membrane reactors as confining devise for free cells is an alternative process to remove these metallic pollutants from aqueous solution. In this paper, experimental data and modelling of heavy metal biosorption onto Sphaerotilus natans cells confined by a ultrafiltration/microfiltration (UF/MF) membrane reactor are reported. Biosorption tests using single and binary metallic solutions (Cu, Pb and Cu–Pb) denoted the biomass affinity (Pb>Cu), the competition among metals simultaneously present in the system, the filtrate flux decline and the change of metal retention coefficient on the membrane for pore plugging by cell fragments. Dynamic modelling is developed considering the unsteady mass balances of the metal in the system and the equilibrium parameters obtained by biosorption batch tests using Langmuir models. Experimental validation of the dynamic models denoted the importance of partial degradation of cells, which is specifically considered in modelling by introducing a time-depending profile for the biomass concentration.

This article develops a versatile structural model specifically suited to describe the dissolution kinetics in leaching processes involving nonporous ore particles. The model accounts explicitly for intraparticle heterogeneity by describing the interplay between the dissolution kinetics of the main solid reactant (e.g. metal oxide) and the dissolution/fragmentation of the solid matrix (gangue). The application to the dissolution of manganiferous ores is thoroughly addressed.

In this paper a comparison about kinetic behaviour, acid-base properties and copper removal capacities was carried out between two different adsorbent materials used for heavy metal removal from aqueous solutions: an aminodiacetic chelating resin as commercial product (Lewatit TP207) and a lyophilised bacterial biomass of Sphaerotilus natans. The acid-base properties of a S. natans cell suspension were well described by simplified mechanistic models without electrostatic corrections considering two kinds of weakly acidic active sites. In particular the introduction of two-peak distribution function for the proton affinity constants allows a better representation of the experimental data reproducing the site heterogeneity. A priori knowledge about resin functional groups (aminodiacetic groups) is the base for preliminary simulations of titration curve assuming a Donnan gel structure for the resin phase considered as a concentrated aqueous solution of aminodiacetic acid (ADA). Departures from experimental and simulated data can be interpreted by considering the heterogeneity of the functional groups and the effect of ionic concentration in the resin phase. Two-site continuous model describes adequately the experimental data. Moreover the values of apparent protonation constants (as adjustable parameters found by non-linear regression) are very near to the apparent constants evaluated by a Donnan model assuming the intrinsic constants in resin phase equal to the equilibrium constants in aqueous solution of ADA and considering the amphoteric nature of active sites for the evaluation of counter-ion concentration in the resin phase. Copper removal outlined the strong affinity of the active groups of the resin for this ion in solution compared to the S. natans biomass according to the complexation constants between aminodiacetic and mono-carboxylic groups and copper ions.

In this paper, the purification of liquor leach solutions obtained from low-grade manganese ores leached by carbohydrates in sulfuric medium was studied and developed. In particular, purification was made acting directly during the leaching process (simple or hydroalcoholic medium) and also using different down-stream purification technologies such as precipitation, solvent extraction and adsorption onto active carbon. The complexity of the aqueous system (due to the high concentration and heterogeneity of inorganic ionic species, but also to the presence of organic compounds as intermediates of glucose oxidation) affects metal speciation in solution in contrast with theoretical predictions. Leaching performed in hydroalcoholic medium combined with adsorption onto active carbon permits obtaining, after an evaporation phase, a final solution with specification concentrations of manganese, calcium and iron for food-additive production.

In this study, a microbial culture of Arthrobacter sp. was characterized and tested as heavy metal biosorbent in different experimental conditions (pH and biomass concentrations) and operative configurations (free cell in batch system and membrane reactor). Biosorption batch trials with free cells were carried out using an original procedure defined as “subsequent additions method” (SAM), consisting of successive additions of heavy metal concentrated solution to a cellular suspension at constant pH. Mechanistic models for copper and cadmium biosorption have been developed taking into account the acidic properties of the cell wall constituents derived from biomass characterization. These models reveal the complexity of the metal biosorption phenomenon and the need to consider different chemico-physical mechanisms operating simultaneously. A membrane reactor system is proposed as a means for confining biomass cells, thus permitting a semicontinuous operation and avoiding immobilization procedures. A mathematical model based on metal mass balance considering the effect of pH on equilibrium adsorption fitted well the experimental data at low pH values and biomass concentrations. In contrast, a mathematical model, considering partial cell disruption during the biosorption trial, was necessary to understand and analyze the system behavior at high biomass concentrations.

Copper biosorption by Sphaerotilus natans immobilised in polysulfone matrices has been studied. Firstly, a rough characterisation of biosorbent beads has been performed, and operating conditions for beads preparation aimed at biosorption have been optimised. Then, the equilibrium of the process was studied in order to determine the effect of pH and biomass concentration inside beads; experimental data were successfully fitted by the Langmuir equation, and the highest value for loading was 5.4 mg/g estimated at pH 5.5 and 0.18 g of lyophilised biomass per gram of beads. Biosorption kinetics has also been studied, and an original kinetic model was developed which is able to correlate experimental data. This model was developed from the Shrinking Core Model, considering a variable copper diffusion coefficient dependent on the process conversion. The estimated values for copper diffusion coefficient were obviously lower than copper diffusivity in water, and they depend on biomass concentration inside beads. Beads regeneration was studied using EDTA, HCl and CaCl 2 . Satisfactory biosorption performances were observed also after 10 sorption/desorption cycles, with CaCl 2 as regeneration solution. All the results confirmed the technical feasibility of the biosorption process by a polysulfone-entrapped biomass even though biosorption efficiency should be improved.

Biosorption of heavy metals is an innovative and alternative technology to remove these pollutants from aqueous solutions using inactive and dead biomasses such as agricultural and industrial wastes, algae and bacteria. In this study olive mill solid residue was used as heavy metal adsorbent material for its wide availability as agricultural waste and also for its cellulosic matrix, rich of potential metal binding active sites. Preliminary studies concerned with the removal of different heavy metals (Hg, Pb, Cu, Zn and Cd), the effect of pre-treatments by water and n-hexane and the regeneration possibility. Olive mill solid residue resulted able to remove heavy metals from aqueous solutions with an affinity series reflecting the hydrolytic properties of the metallic ions, but also a particular affinity for copper. It can be supposed that biosorption phenomenon occur by a general ion exchange mechanism combined with a specific complexation reaction for copper ions. Water pre-treatment is sufficient to reduce COD release in the effluent according to the law limit, while n-hexane pre-treatment strongly reduces also the adsorption properties of this material. Experimental isotherms obtained under different operating conditions were fitted using a non linear regression method for the estimation of the Langmuir parameters. Moreover a simple Scatchard plot analysis was performed for a preliminary investigation of the active sites, showing the presence of two different site affinities depending on the metal concentration, according to the previous hypothesis of two kinds of uptake mechanisms for copper biosorption. Regeneration tests gave good results in terms of yield of regeneration and also concentration ratios.

This article develops a modified version of the shrinking-core model accounting for the surface heterogeneity of solid particles. This model can be primarily used as a shortcut method for estimating the dependence of the kinetic rates on the concentration of fluid reactants and specifically the reaction order in the presence of a polydisperse solid mixture. This approach is tested numerically for model reactions involving polydisperse systems and is applied to the dissolution of MnO2 in sulphuric acid solutions containing glucose as the reductant agent.

This paper develops a closed-form solution for the population-balance equations describing the dissolution of polydisperse mixtures of spherical particles in the presence of external mass-transfer resistance. The general case, obtained by relaxing the assumption of an excess concentration of fluid reactants, is also considered. In mathematical terms, this leads to a nonlinear first-order functional equation that can be solved by making use of a warped-time transformation. The inclusion of the fragmentation dynamics of solid particles occurring during the chemical dissolution process is also briefly addressed.

Cobalt nanoparticles were synthesized by pulsed electrodeposition on copper substrate. Scanning electron microscopy and image analysis were used to determine morphology and particle size distribution of nanoparticle populations obtained in different operating conditions. After preliminary tests, ton and toff were set at 50 and 300 ms respectively to obtain distinct nanoparticles and avoid dendritic structures. Experimental tests were performed according to two partially superimposed factorial designs with two factors at two levels. First factorial design investigated the effect of current density (I = 10 and 50 mA/cm2) and discharged cobalt (Q = 2.5 × 10−3 and 1.0 × 10−2C); second factorial design investigated the effect of cobalt concentration (C0 = 0.01 and 0.1 M) for the same two levels of Q. For optimized value of ton/toff, square and hexagonal shaped nanoparticles were obtained. Statistical analysis evidenced that, for C0 = 0.1 mol/L, current density is the most influencing factor on mean size: increasing I from 10 to 50 mA/cm2 determined a diminution of mean size of 240 nm. For the same cobalt concentration, increasing the deposition time (Q) determined an increase of mean size of 60 nm. Diminishing the initial cobalt concentration from 0.1 to 0.01 mol/L determined an increase of mean size from 10 nm to 36 nm. For C0 = 0.01 mol/L nanoparticles grow reaching an optimal size (36 nm) and then, increasing the time of deposition, optimal sized subunits tend to aggregate. As for polydispersity of nanoparticles, statistical tests denoted that increasing I determined significant reduction of variance, while increasing the time of deposition determined a significant increase of variance.

Recycling of polycrystalline silicon, amorphous silicon and CdTe photovoltaic panels was investigated by studying two alternative routes made up of physical operations: two blade rotors crushing followed by thermal treatment and two blade rotors crushing followed by hammer crushing. Size distribution, X-ray diffraction and X-ray fluorescence analysis of obtained products were carried out in order to evaluate their properties as valuable products. Results showed that for all kinds of investigated photovoltaic modules the two blade rotors crushing followed by hammer crushing and eventually by a thermal treatment of d >1 mm fractions, was the best option aiming to a direct recovery of glass.

Photovoltaic (PV) technology for renewable energy utilisation is constantly growing throughout the world. Many recent efforts were devoted to the treatment of end-of-life panels, but only two full-scale processes were developed for crystalline silicon modules (Deutsche Solar) and CdTe panels (First Solar). Furthermore, recent developments concerned with new technologies designed for treating together more kinds of PV panels by automated processes. In this work, a picture of the PV world in terms of market, typology, waste dynamics and recoverable materials was given. A description of full-scale processes will be reported evidencing products and yields of recovery. A case study of process development for the simultaneous treatment of different kinds of PV panels was presented. In particular, experimental results in lab and pilot scale were described regarding the development and optimisation of a process including both physical pre-treatment and hydrometallurgical treatment for the recovery of target metal.

A dynamic model was developed for representing the abatement of sulfates and metals in column reactors inoculated with sulfate reducing bacteria. The model framework includes both bioactive mechanisms (bioreduction of sulfates and bioprecipitation of metals) and passive abiotic mechanism (sorption onto the column filling). Sorption capacities of column filling material were determined by dedicated tests of sulfate and cadmium removal. These experimental data implemented in model framework denoted that before steady state sorption mechanism could predominate over bioactive mechanism. Sensitivity analysis confirmed that, varying sorption and bioreduction parameters in typical range of laboratory scale systems, sorption cannot be neglected before steady state. An operative equation was obtained by literature data and model simulations showing that in the majority of works reported in the literature the operational times used for column experiments are not sufficient to saturate column sorption capacity. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 70–80, 2014

A kinetic model of manganiferous ore dissolution varying sulphuric acid and lactose as reducing agent was developed here. The Shrinking Core Model (SCM) was modified to take into account both the variable reagent concentrations and the reaction rate change with respect to the manganese dioxide conversion: this last aspect is due to several oxidation reactions of the carbohydrates in a hot sulphuric acid medium. The effects of three factors were investigated for three ore size fractions: temperature, lactose and sulphuric acid concentrations. The application of the kinetic model to different size ore fractions with and without the particle size effect shows that the best results in data fitting were gained by applying the model separately to each particle size fraction. The influence of the particle size in the kinetic model is discussed with the support of SEM analysis and BET surface measurements before and after leaching.