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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 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.

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.

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.

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.

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, 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.

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.

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.

This work reports the kinetic study of a manganiferous ore leaching in acid media by sucrose as reducing agent. A shrinking core model with variable activation energy was found to successfully fit experimental data of manganese extraction yields vs leaching time. This model finds a physical confirmation both in the complex reactions that take place during manganese leaching and the different reactivity and accessibility of the mineralogical forms present in the ores. A non linear regression analysis has been performed in order to estimate the adjustable model parameters and a statistical analysis has also been carried out in order to evaluate the significativity of the estimated values.

Reductive acid leaching of a manganese dioxide ore has been carried out in a fixed bed column in order to monitor and evaluate the effect of some process parameters on the manganese, iron and calcium extraction yields: although manganese is the metal of interest, iron and calcium were selected as representative of the most significant contaminants of the leach liquor. A two-level fractional factorial design was planned to study the effect of five process factors: temperature, reagent concentration, ore particle size, solid/liquid ratio and flow rate of leaching solution were taken in consideration in the experimental tests. The main effects and the interaction among the factors investigated were obtained by ANOVA, carried out for each selected leaching time, taking into consideration manganese, iron and calcium extraction yields as response of the process. This analysis permitted to establish temperature and reagent concentration exerting the most important positive effect on the manganese extraction yield: 93% of manganese dissolution was obtained after 4 h of leaching in the following experimental conditions: temperature 70°C, S/L ratio 1/2, specific flow rate 1223 L/m 2 h, +50% of reagent excess (H 2 SO 4 and glucose) and 208–252 μm as ore size fraction. Each statistically significant main and interaction effects, evaluated in the selected leaching time, were correlated by empirical models in order to build a general model to perform simulation studies valid in the investigated range of experimental conditions but helpful for further modelling studies. Besides these experimental and simulation studies, the potential application of column leaching conditions in the extraction of manganiferous ores has been shown, although further work should be carried out in order to investigate a much more wide range of process conditions.

In this paper two hydrometallurgical processes were analyzed for recovery of lithium and cobalt from lithium ion batteries. The effect of adding a secondary purification step by solvent extraction was evaluated in terms of product purity and economical feasibility of the process. Process routes were made of the following steps: mechanical pretreatment, leaching, primary (and secondary) purification, product recovery. Electrodic material used in leaching experiments was produced in a large scale pre-treatment plant for waste recycling. Leaching tests were performed both using chloridric acid and sulphuric acid plus glucose. In optimized conditions quantitative extraction of Co and Li were obtained for both tested systems. Iron, aluminum and copper were removed by precipitation as hydroxides, while Ni can be separated only using solvent extraction. Process simulations showed that, for the same input flow rate of batteries, the addition of solvent extraction improves the economical feasibility of the process for lithium ion battery recovery.

Cyanide leaching is the wide-spread process for the extraction of gold from primary raw-materials. However when gold is associated with metal sulphides, an oxidative thermal or a chemical pretreatment is often needed to access precious metal particles. Bacterial oxidative leaching may be an interesting alternative — low cost and environmentally friendly — to liberate gold from the sulphide matrix and then make it amenable to cyanidation. Bioleaching with Thiobacillus ferroxidans has been investigated at 30°C at bench scale on a gold-bearing arsenopyrite (2 g/t Au) ore coming from Golcuck Mine in Turkey. The study was concerned with the influence of the age of the inoculum, pH, pulp density and time of the bacterial leaching at 30°C on the recovery of gold during the subsequent standard cyanide attack. Direct cyanide leaching of the arsenopyrite ground to −74 μm showed no gold dissolution at all, but with fine grinding to −30 μm, gold recovery increased to about 55.3% after 48 hours of cyanidation. On the contrary, cyanidation performed for 2 days on a bioleached arsenopyrite allowed 90% of gold to be solubilized in 2 hours.

The aim of this work was developing a hydrometallurgical process to recover metals from automobile shredded residue (or car fluff). Automobile shredded residue (ASR) was characterised by particle size distribution, total metal content and metal speciation in order to guide the choice of target metals and the operating conditions of leaching. Characterisation results showed that Fe is the most abundant metal in the waste, while Zn was the second abundant metal in the fraction with diameter lower than 500 μm. Sequential extractions denoted that Zn was easily extractable by weak acid attack, while Fe and Al required a strong acid attack to be removed. In order to recover zinc from

Leaching of manganese with aqueous SO 2 has been investigated at a laboratory scale by percolation at room temperature as a function of acid concentration solution flow-rate and time. The critical parameters were ascertained to be pH and redox potential in order to ensure the best conditions for the dissolution of MnO 2 . With the proper choice of the process variables, maximum manganese recovery is achieved in 15–20 days of leaching. A bioleaching process was also developed using different microorganism for extracting manganese from low grade domestic resources. The quantitative dissolution of manganese dioxide catalyzed by heterotrophic microorganisms was obtained in 20 days. The oxidation state of manganese in liquor was determined by polarographic techniques to be divalent. The consumption of ore and the presence of microorganisms was detected by scanning electron microscopy. The effect of the biotreatment of the ore was also investigated in petri plates.

This article develops a structural model for the dissolution of non-porous ore particles, referred to as “sporulation” kinetics. This model is based on the assumption that the particulate can be modelled as an ensemble of reactive solid grains (e.g. metallic oxides) embedded into a solid matrix (gangue). The solid matrix may not be chemically inert with the result that, during the dissolution of the ore particle, the solid matrix “sporulates”, i.e. grains of the reactive solid are progressively released from the ore particle into the liquid solution, due either to mechanical fragmentation or to chemical dissolution of the matrix itself. This model is applied in order to interpret the dissolution kinetics of manganiferous ores, which differs significantly from the corresponding kinetic behaviour of pure MnO2 particles.

A kinetic study of a manganiferous ore leaching in acid media by glucose as the reducing agent is here reported. The shrinking-core model opportunely modified was used to describe the kinetics of the manganese dissolution. Considering the complex network of chemical reaction involved in this process, a variable activation energy term was introduced in the kinetic model to take into consideration the different chemical reaction evolution. A nonlinear regression analysis was performed in order to estimate the modeling parameters, and their related statistical analysis was carried out as well. The proposed model was verified at low and high ore content (10 and 200 g/L, respectively). This comparison showed a quite good agreement between the experimental data and the theoretical prevision, confirming the possible application of the estimated kinetic parameters in a wide range of ore content.

The effect of alcohols on the dissolution of manganese, calcium, and iron from manganiferous ore is reported. The extractive process was studied in sulphuric acid solution by using glucose as reducing agent. The alcohols were employed in order to evaluate their effect on the leaching performance with and without glucose as reducing agent. Three different alcohols MeOH, EtOH, and n-BuOH, were tested in order to investigate the influence of the organic chain length on the metal dissolution during the leaching process. Two different test sequences were followed. The first one was based on the leaching of manganiferous ore by using glucose as reducing agent and a mixture of alcohol/H2O/H2SO4 as reaction media. In the second one, leaching was carried out by using glucose in the H2O/H2SO4 reaction media and after leaching, the aqueous solution was separated from the solid by filtration. Successively, alcohols were added to the leach liquor. The experimental results of Mn, Ca, and Fe dissolution obtained by using the latter procedure were compared with those obtained in the former one. In both the experimental sequences, methyl alcohol gave better results as compared to ethyl and n-butyl alcohol. MeOH showed a notable negative effect on calcium dissolution, thereby decreasing its concentration with respect to manganese and iron extraction. The effect was larger in the runs performed by alcohol addition to the leach liquor than that obtained in the mixed solvent leaching tests. The decrease in calcium dissolution caused by the presence of alcohol has been analysed and modelled.

The aim of the present investigation was to study the biooxidation of a refractory gold-bearing pyrrhotite, in order to increase the gold recovery during the subsequent conventional cyanidation. Bacterial cultures utilised in the biological test consisted predominantly of Thiobacillus genus. Tests were conducted at laboratory scale. The gold content of the ore sample, coming from Bolivia, was of 10 g t−1 Au. After 24 h leaching time by direct cyanidation, low gold recovery was obtained (

In the present work, the use of lactose and whey as reducing agents for the acid leaching of manganiferous ores was investigated. The target of the leaching tests performed by using whey was to simulate the possible use of the byproducts of cheese industries as reducing agents for metal extractions. The experimental results were analyzed by the “response surface methodology” (RSM) to find empirical models suitable to predict metal extraction yields as functions of the main operative conditions. A preliminary process analysis has been performed and a flow-sheet for MnSO4 has been proposed.

The experimental results of a leaching process of different manganiferous ores are here reported. The leaching treatment showed a satisfactory selectivity of manganese extraction in comparison of other metals such as Al, Si and Na. XRD analyses have been done on the ores before and after the leaching treatment. The experimental results showed a good technical feasibility of the process which can use alternative feedstocks (containing carbohydrates) to treat different manganese ores.

A kinetic study of the batch leaching of a pyrrhotite ore by a sulfooxidans strain is reported in this work. A mathematical model consistent with experimental data has been developed which takes into account both direct and indirect mechanism. The study has been performed from a separate study of micro-organisms' adsorption on the solid surface and of chemical leaching of pyrrhotite by ferric iron. The representative equations of these phenomena (Langmuir equation and a kinetic model with variable activation energy, respectively) have been combined with material balances of total iron, ferric iron and biomass. The final model consists of a system of three ordinary differential equations, where the independent variable is time and dependent variables are total iron, ferric iron and biomass concentrations in solution.

Cyanide leaching is the traditional process for the extraction of gold from primary raw materials. When the gold host rock contains high concentrations of sulphides, an oxidative thermal or a chemical pretreatment is often needed to access precious metal particles. Biooxidative leaching may be an interesting alternative, if compared with the environmental effects and costs of the conventional pretreatment processes, to liberate gold from the sulphide matrix and then to make it amenable to cyanidation. In this work, bioleaching with Thiobacillus ferrooxidans and Thiobacillus thiooxidans has been investigated at a bench scale on a refractory gold-bearing arsenopyrite (2 g/t Au) ore coming from the Golcuck mine (Turkey). The factors influencing the biooxidative pretreatment, in order to enhance the gold recovery in a conventional cyanidation process, were tested using a factorial plan of experiments. Direct cyanide leaching of the arsenopyrite ground to −74 μm showed no gold dissolution at all, but with fine grinding to −30 μm, gold recovery reached about 55.3% after 48 h of cyanidation. On the contrary, cyanidation accomplished on a 72 h bioleached arsenopyrite has allowed 84.3% of gold to be solubilized in 2 h, using the following bioleaching conditions: 20% pulp density, pH 2, stirring conditions 200 rpm, temperature 30°C, time 3 days. Under these conditions, the preliminary tests in a semi-continuous lab-scale microfermentor have been performed to evaluate the scale-up of the biooxidative process. It was possible to solubilise 95.2% Au after 48 h cyanidation for the samples bioleached during 3 days, and 96.8% Au when the time of bioleaching was 7 days.

A reductive leaching process for manganese dioxide using sucrose as the reducing agent in sulphuric acid solution was studied. Fractional factorial experiments have been used to test the main effects and the interactions among the factors investigated; 16 unreplicated tests have been carried out to study 5 factors at two levels: sulphuric acid concentration, sucrose concentration, particle size range of the mineral, mixing conditions and temperature. A 94% extraction yield of Mn 2+ was been obtained at 50°C with 1 M H 2 SO 4 (0.98 g acid/g of mineral) and 10g/l of sucrose (0.1 g of sucrose/g of mineral) after 150 min. of treatment. The experimental results show the potential application of the reductive process to manganese recovery from minerals not treatable by conventional pyrometallurgical processes.

A chalcopyrite concentrate of industrial interest was bioleached in shaken batch cultures using Thiobacillus ferrooxidans S8 as the promotor of the leaching. Over a period substrains of micro-organisms with improved technical properties were developed by treating batches for a two-year period with increasing contents of chalcopyrite pulp. Iron, copper and sulphide solubilization was detected with increasing chalcopyrite content and at different stages of microbial growth. Chemical analysis data were used as the method for checking the bioleaching process. The elemental chemical composition of the particle surface residues were investigated with a micro-analytical scanning electron microscope.