Obtaining and Characterization of Highly Crystalline Recycled Graphites from Different Types of Spent Batteries.

Spent batteries recycling is an important way to obtain low-cost graphite. Nevertheless, the obtaining of crystalline graphite with a rather low density of defects is required for many applications. In the present work, high-quality graphites have been obtained from different kinds of spent batteries. Black masses from spent alkaline batteries (batteries black masses, BBM), and lithium-ion batteries from smartphones (smartphone black masses, SBM) and electric and/or hybrid vehicles (lithium-ion black masses, LBM) were used as starting materials. A hydrometallurgical process was then used to obtain recycled graphites by acidic leaching. Different leaching conditions were used depending on the type of the initial black mass. The final solids were characterized by a wide set of complementary techniques. The performance as Li ion batteries anode of the sample with better structural quality was assessed.

Separation Iron(III)-Manganese(II) via Supported Liquid Membrane Technology in the Treatment of Spent Alkaline Batteries.

In this paper, the transport of iron(III) from iron(III)-manganese(II)-hydrochloric acid mixed solutions, coming from the treatment of spent alkaline batteries through a flat-sheet supported liquid membrane, is investigated (the carrier phase being of Cyanex 923 (commercially available phosphine oxide extractant) dissolved in Solvesso 100 (commercially available diluent)). Iron(III) transport is studied as a function of hydrodynamic conditions, the concentration of manganese and HCl in the feed phase, and the carrier concentration in the membrane phase. A transport model is derived that describes the transport mechanism, consisting of diffusion through a feed aqueous diffusion layer, a fast interfacial chemical reaction, and diffusion of the iron(III) species-Cyanex 923 complex across the membrane phase. The membrane diffusional resistance (Δm) and feed diffusional resistance (Δf) are calculated from the model, and their values are 145 s/cm and 361 s/cm, respectively. It is apparent that the transport of iron(III) is mainly controlled by diffusion through the aqueous feed boundary layer, this being the thickness of this layer calculated as 2.9 × 10-3 cm. Since manganese(II) is not transported through the membrane phase, the present system allows the purification of these manganese-bearing solutions.

Immobilized Forms of the Ophiostoma piceae Lipase for Green Synthesis of Biodiesel. Comparison with Eversa Transform 2.0 and Cal A.

In this work, we analyzed the suitability of a versatile recombinant lipase, secreted by Ophiostoma piceae (OPEr) and produced in Pichia pastoris, as a catalyst of the synthesis of biodiesel. The enzyme was immobilized by five covalent procedures and by hydrophobicity on functionalized nanoparticles of magnetite or of a novel Zn/Mn oxide named G1. Then, they were tested for green production of biodiesel by solventless enzymatic transesterification of discarded cooking oil and methanol (1:4) at 25 °C. The results were compared with those shown by free OPEr and the commercial lipases Eversa® and Cal A®. Several preparations with immobilized OPEr produced high synthesis yields (>90% transesterification), comparable to those obtained with Eversa®, the commercial enzyme designed for this application. Three of the biocatalysts maintained their catalytic efficiency for nine cycles. The process catalyzed by AMNP-CH-OPEr was scaled from 500 µL to 25 mL (50 times), improving its efficiency.

Obtention and Characterization of Ferrous Chloride FeCl2·4H2O from Water Pickling Liquors.

As a hazardous waste, water pickling liquors must be properly treated. An alternative consists of promoting the formation of ferrous salts from this residue due to their higher ferrous content. Since FeCl2·4H2O is widely used in several applications, obtaining pure crystals of this material appears to be an interesting prospect. However, this compound has scarcely been investigated. In the present work, FeCl2·4H2O crystals were obtained from water pickling liquors. Their structural and morphological characteristics were investigated by X-ray diffraction, scanning electron microscopy as well as Mössbauer spectroscopy. In addition, the photoluminescence study of the obtained samples was also assessed. It was observed that after some aging time, the obtained crystals changed in colour from green to more yellowish. As such, the aged sample was also evaluated, and their structural characteristics were compared with the original crystals. Despite this, the obtained crystals exhibit a FeCl2·4H2O structure, which is not modified with the aging of the sample.

Organic Dyes versus Adsorption Processing.

Even in the first quarter of the XXI century, the presence of organic dyes in wastewaters was a normal occurrence in a series of countries. As these compounds are toxic, their removal from these waters is a necessity. Among the separation technologies, adsorption processing appeared as one of the most widely used to reach this goal. The present work reviewed the most recent approaches (first half of the 2021 year) regarding the use of a variety of adsorbents in the removal of a variety of organic dyes of different natures.

Transport of Au(III) from HCl Medium across a Liquid Membrane Using R3NH+Cl-/Toluene Immobilized on a Microporous Hydrophobic Support: Optimization and Modelling.

By the use of the tertiary amine A327 and 1 M HCl solution as precursors, the ionic liquid A327H+Cl- was generated and used to investigate its performance in the transport of Au(III) from hydrochloric acid medium. The influence of the stirring speed (600-1800 min-1), ionic liquid concentration (1.25-50% v/v) in the membrane phase, and gold concentration (0.01-0.15 g/L) in the feed phase on metal transport have been investigated. An equation which included both equilibrium and kinetics parameters was derived, and the membrane diffusional resistance (Δm) and feed phase diffusional resistance (Δf) was estimated as 9.5 × 106 s/cm and 307 s/cm, respectively. At carrier concentrations in the 5-50% v/v range and gold concentrations in the 0.01-0.15 g/L range, metal transport is controlled by diffusion of metal species through the feed boundary layer, whereas at the lowest carrier concentrations, membrane diffusion is predominant. From the receiving solutions, gold can be recovered as gold nanoparticles.

Characterization of K6Ta10.8O30 Microrods with Tetragonal Tungsten Bronze-Like Structure Obtained from Tailings from the Penouta Sn-Ta-Nb Deposit.

In this work, a deep characterization of the properties of K6Ta10.8O30 microrods has been performed. The starting material used to grow the microrods has been recovered from mining tailings coming from the Penouta Sn-Ta-Nb deposit, located in the north of Spain. The recovered material has been submitted to a thermal treatment to grow the microrods. Then, they have been characterized by scanning electron microscopy, X-ray diffraction, micro-Raman and micro-photoluminescence. The results of our study confirm that the K6Ta10.8O30 microrods have a tetragonal tungsten bronze-like crystal structure, which can be useful for ion-batteries and photocatalysis.

Photocatalytic Activity of Zn x Mn3-x O4 Oxides and ZnO Prepared From Spent Alkaline Batteries.

Oxides with Zn x Mn3-xO4 stoichiometries and ZnO were synthesized from the "black mass" material recovered from spent alkaline batteries. The oxides were characterized by XRF, XRD with Rietveld refinement, SEM, and TEM methods. Optical characterization included diffuse reflectance (DRS) and photoluminescence (PL) measurements. ZnO presented a clear band edge in the UV region, and PL signals were detected. The Zn/Mn oxides showed strong absorption in the UV region and a continuous absorption band in the Vis-IR regions. There is a non-detected PL signal due to excited charges being trapped on sub-band energy states and/or transfer by non-radiative paths. Photocatalytic activity under both irradiation conditions was evaluated using the resazurin dye test, terephthalic acid fluorescence probe method, and NOx air purification evaluation. In the three photoactivity tests, ZnO performed well under both UV and Vis irradiation, whereas no evidence of any appreciable photocatalytic activity was observed for the Zn/Mn oxides. The results are discussed in terms of the findings of previously reported optical measurements.

Activated Carbons From Winemaking Biowastes for Electrochemical Double-Layer Capacitors.

Revalorizing organic biowaste is critical to achieve a full circular economy, where waste is transformed into resources. One of the main strategies is to produce activated carbons and use them as functional materials for electrochemical energy storage. In this study, winemaking wastes, bagasse (BAG), and cluster stalks (CS) were recovered and used in the preparation of activated carbons by a hydrothermal process. Then, they were chemically activated using KOH and investigated for electrochemical capacitor applications. The activation treatment resulted in microporous structures, characterized by a type I isotherm for low partial pressures (P/P 0), and a type IV for higher pressures, as observed by Brunauer-Emmett-Teller surface analysis, with specific surfaces of 1,861 and 2,662 m2·g-1 for BAG and CS, respectively. These microporous structures were also investigated by means of scanning electron microscopy, revealing a high porous degree. Micro-Raman spectroscopy and X-ray photoelectron spectroscopy measurements displayed bands associated to disorder of the structure of the carbonaceous material. The electrochemical performance of the resulting materials was investigated for electrochemical energy storage applications, as supercapacitor electrode, in 1 M KOH aqueous electrolyte. These biowaste-derived materials displayed electrochemical double-layer capacitance, with 129 F·g-1 at 10 A·g-1 in the 0.1 to -1.0 V vs. saturated calomel electrode. For that reason, they are pin-pointed as potential negative electrodes for electrochemical double-layer supercapacitors and hybrid or asymmetric supercapacitors.

Recovery of niobium and tantalum by solvent extraction from Sn-Ta-Nb mining tailings.

The slag from the extraction processes of metals from their ores may contain valuable components that, if adequately recovered, can be reintroduced in the technological life cycle. This is the case for the material obtained in Penouta mines in the North of Spain. These mineral sites are a main source of tin obtained from cassiterite. The mineral is submitted to a pyrometallurgical process to separate tin, however cassiterite is not the only mineral present in the veins, and large amounts of other minerals are normally discarded, constituting the slag. In the present case, besides cassiterite, one of the most abundant minerals in the ore is columbo tantalite, the source of the strategic coltan. In this work the raw material (slag) has been treated by acid leaching, using HF/H2SO4 as the leaching agent. Then liquid-liquid extraction of Nb and Ta was performed, with Cyanex®923 extractant, so that both metals were obtained separately. Then they were precipitated from the corresponding aqeuous solution, and calcined in order to yield Nb2O5 of 98.5% purity and tantalum salt, after calcination and purification, of 97.3% purity. The process described in this work opens a possibility to produce high quality materials that are considered critical by the EU from alternative sources exempt of criticality factors.

Extraction of polyphenols and synthesis of new activated carbon from spent coffee grounds.

A valorization process of spent coffee grounds (SCG) was studied. Thus, a two-stage process, the first stage of polyphenols extraction and synthesis of a carbonaceous precursor and a subsequent stage of obtaining activated carbon (AC) by means of a carbonization process from the precursor of the previous stage, was performed. The extraction was carried out with a hydro-alcoholic solution in a pressure reactor, modifying time, temperature and different mixtures EtOH:H2O. To optimize the polyphenols extraction, a two-level factorial experimental design with three replicates at the central point was used. The best results were obtained by using a temperature of 80 °C during 30 min with a mixture of EtOH:H2O 50:50 (v/v). Caffeine and chlorogenic acid were the most abundant compounds in the analysed extracts, ranging from 0.09 to 4.8 mg∙g-1 and 0.06 to 9.7 mg∙g-1, respectively. Similarly, an experimental design was realized in order to analyze the influence of different variables in the AC obtained process (reaction time, temperature and KOH:precursor ratio). The best results were 1 h, 850 °C, and a mixture of 2.5:1. The obtained activated carbons exhibit a great specific surface (between 1600 m2∙g-1 and 2330 m2∙g-1) with a microporous surface. Finally, the adsorption capacity of the activated carbons was evaluated by methylene blue adsorption.

Effect of the Immobilization Strategy on the Efficiency and Recyclability of the Versatile Lipase from Ophiostoma piceae.

The recombinant lipase from Ophiostoma piceae OPEr has demonstrated to have catalytic properties superior to those of many commercial enzymes. Enzymatic crudes with OPEr were immobilized onto magnetite nanoparticles by hydrophobicity (SiMAG-Octyl) and by two procedures that involve covalent attachment of the protein (mCLEAs and AMNP-GA), giving three nanobiocatalysts with different specific activity in hydrolysis of p-nitrophenyl butyrate (pNPB) and good storage stability at 4 °C over a period of 4 months. Free OPEr and the different nanobiocatalysts were compared for the synthesis of butyl esters of volatile fatty acids C4 to C7 in reactions containing the same lipase activity. The esterification yields and the reaction rates obtained with AMNP-GA-OPEr were in general higher or similar to those observed for the free enzyme, the mCLEAs-OPEr, and the non-covalent preparation SiMAG-Octyl-OPEr. The time course of the esterification of the acids C4 to C6 catalyzed by AMNP-GA-OPEr was comparable. The synthesis of the C7 ester was slower but very efficient, admitting concentrations of heptanoic acid up to 1 M. The best 1-butanol: acid molar ratio was 2:1 for all the acids tested. Depending on the substrate, this covalent preparation of OPEr maintained 80-96% activity over 7 cycles, revealing its excellent properties, easy recovery and recycling, and its potential to catalyze the green synthesis of chemicals of industrial interest.

From spent alkaline batteries to Zn x Mn3-x O4 by a hydrometallurgical route: synthesis and characterization.

A series of Zn/Mn binary oxides with different molar ratios (1.4-11) were synthesized via co-precipitation from a solution obtained through the acidic (HCl) leaching of a black mass originating from the mechanical recycling of spent alkaline and Zn-C batteries. The oxides obtained were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Magnetic properties of the samples were also investigated. The Raman spectroscopy results showed all the binary metallic oxides belong to the Zn x Mn3-x O4 (0.25 ≤ x ≥ 1.75) type. All showed a spinel crystalline structure. The saturation magnetization decreases with the Zn/Mn molar ratio; a maximum of 13.19 emu g-1 was found for the molar ratio of 11 at the Curie temperature (25.5 K). XPS showed that all the synthesized compounds contained Mn2+, Mn3+ and Mn4+. Mn2+ was the most prominent at a molar ratio of 11, Mn3+ was most common at a molar ratio of 2, and Mn4+ at 1.4.

Sustainable remediation of mercury contaminated soils by thermal desorption.

Mercury soil contamination is an important environmental problem that needs the development of sustainable and efficient decontamination strategies. This work is focused on the application of a remediation technique that maintains soil ecological and environmental services to the extent possible as well as search for alternative sustainable land uses. Controlled thermal desorption using a solar furnace at pilot scale was applied to different types of soils, stablishing the temperature necessary to assure the functionality of these soils and avoid the Hg exchange to the other environmental compartments. Soil mercury content evolution (total, soluble, and exchangeable) as temperature increases and induced changes in selected soil quality indicators are studied and assessed. On total Hg, the temperature at which it is reduced until acceptable levels depends on the intended soil use and on how restrictive are the regulations. For commercial, residential, or industrial uses, soil samples should be heated to temperatures higher than 280 °C, at which more than 80 % of the total Hg is released, reaching the established legal total Hg level and avoiding eventual risks derived from high available Hg concentrations. For agricultural use or soil natural preservation, conversely, maintenance of acceptable levels of soil quality limit heating temperatures, and additional treatments must be considered to reduce available Hg. Besides total Hg concentration in soils, available Hg should be considered to make final decisions on remediation treatments and potential future uses. Graphical Abstract Solar energy use for remediation of soils affected by mercury.

Oxidation and waste-to-energy output of aluminium waste packaging during incineration: A laboratory study.

This work reports the oxidation behaviour and waste-to-energy output of different semi-rigid and flexible aluminium packagings when incinerated at 850°C in an air atmosphere enriched with 6% oxygen, in the laboratory setting. The physical properties of the different packagings were determined, including their metallic aluminium contents. The ash contents of their combustion products were determined according to standard BS ISO 1171:2010. The net calorific value, the required energy, and the calorific gain associated with each packaging type were determined following standard BS EN 13431:2004. Packagings with an aluminium lamina thickness of >50µm did not fully oxidise. During incineration, the weight-for-weight waste-to-energy output of the packagings with thick aluminium lamina was lower than that of packagings with thin lamina. The calorific gain depended on the degree of oxidation of the metallic aluminium, but was greater than zero for all the packagings studied. Waste aluminium may therefore be said to act as an energy source in municipal solid waste incineration systems.

Mercury leaching from hazardous industrial wastes stabilized by sulfur polymer encapsulation.

European Directive 2013/39/EU records mercury as a priority hazardous substance. Regulation n° 2008/1102/EC banned the exportation of mercury and required the safe storage of any remaining mercury compounds. The present work describes the encapsulation of three wastes containing combinations of HgS, HgSe, HgCl2, HgO2, Hg3Se2Cl2, HgO and Hg(0), according to patent of Spanish National Research Council WO2011/029970A2. The materials obtained were subjected to leaching tests according to standards UNE-EN-12457 and CEN/TS 14405:2004. The results are compared with the criteria established in the Council Decision 2003/33/EC for the acceptance of waste at landfills. The Hg concentrations of all leachates were <0.01mgHg/kg for a liquid/solid ratio of 10l/kg. All three encapsulated materials therefore meet the requirements for storage in inert waste landfills.

Valorisation of waste ilmenite mud in the manufacture of sulphur polymer cement.

This paper reports the preparation of sulphur polymer cements (SPCs) incorporating waste ilmenite mud for use in concrete construction works. The ilmenite mud raw material and the mud-containing SPCs (IMC-SPCs) were characterised physico-chemically and radiologically. The optimal IMC-SPC mixture had a sulphur/mud ratio (w/w) of 1.05 (mud dose 20 wt%); this cement showed the greatest compressive strength (64 MPa) and the lowest water absorption coefficient (0.4 g cm(-2) at 28 days). Since ilmenite mud is enriched in natural radionuclides, such as radium isotopes (2.0·10(3) Bq kg(-1)(228)Ra and 5.0·10(2) Bq kg(-1)(226)Ra), the IMC-SPCs were subjected to leaching experiments, which showed their environmental impact to be negligible. The activity concentration indices for the different radionuclides in the IMC-SPCs containing 10% and 20% ilmenite mud met the demands of international standards for materials used in the construction of non-residential buildings.

Gasification of the char derived from distillation of granulated scrap tyres.

This work reports the effect of pressure on the steam/oxygen gasification at 1000°C of the char derived from low temperature-pressure distillation of granulated scrap tyres (GST). The study was based on the analysis of gas production, carbon conversion, cold gas efficiency and the high heating value (HHV) of the product. For comparison, similar analyses were carried out for the gasification of coals with different rank. In spite of the relatively high ash (≈12 wt.%) and sulphur (≈3 wt.%) contents, the char produced in GST distillation can be regarded as a reasonable solid fuel with a calorific value of 34MJkg(-1). The combustion properties of the char (E(A)≈50 kJ mol(-1)), its temperature of self-heating (≈264°C), ignition temperature (≈459°C) and burn-out temperature (≈676°C) were found to be similar to those of a semi-anthracite. It is observed that the yield, H(2) and CO contents and HHV of the syngas produced from char gasification increase with pressure. At 0.1 MPa, 4.6 Nm(3)kg(char)(-1) of syngas was produced, containing 28%v/v of H(2) and CO and with a HHV around 3.7 MJ Nm(-3). At 1.5 MPa, the syngas yield achieved 4.9N m(3)kg(char)(-1) with 30%v/v of H(2)-CO and HHV of 4.1 MJ Nm(-3). Carbon conversion significantly increased from 87% at 0.1 MPa to 98% at 1.5 MPa. It is shown that the char derived from distillation of granulated scrap tyres can be further gasified to render a gas of considerable heating value, especially when gasification proceeds at high pressure.

Microencapsulation of phosphogypsum into a sulfur polymer matrix: physico-chemical and radiological characterization.

The aim of this work is to prepare a new type of phosphogypsum-sulfur polymer cements (PG-SPC) to be utilised in the manufacture of building materials. Physico-chemical and radiological characterization was performed in phosphogypsum and phosphogypsum-sulfur polymer concretes and modeling of exhalation rates has been also carried out. An optimized mixture of the materials was obtained, the solidified material with optimal mixture (sulfur/phosphogypsum=1:0.9, phosphogypsum dosage=10-40 wt.%) results in highest strength (54-62 MPa) and low total porosity (2.8-6.8%). The activity concentration index (I) in the PG-SPC is lower than the reference value in the most international regulations and; therefore, these cements can be used without radiological restrictions in the manufacture of building materials. Under normal conditions of ventilation, the contribution to the expected radon indoor concentration in a standard room is below the international recommendations, so the building materials studied in this work can be applied to houses built up under normal ventilation conditions. Additionally, and taking into account that the PG is enriched in several natural radionuclides as (226)Ra, the leaching experiments have demonstrated that environmental impact of the using of SPCs cements with PG is negligible.

Distillation of granulated scrap tires in a pilot plant.

This paper reports the pyrolytic treatment of granulated scrap tires (GST) in a pilot distillation unit at moderate temperature (550°C) and atmospheric pressure, to produce oil, char and gas products. Tire-derived oil is a complex mixture of organic C(5)-C(24) compounds, including a very large proportion of aromatic compounds. This oil has a high gross calorific value (∼ 43 MJ kg(-1)) and N and S contents of 0.4% and 0.6%, respectively, falling within the specifications of certain heating fuels. The distillation gas is composed of hydrocarbons; methane and n-butane are the most abundant, investing the distillation gas with a very high gross calorific value (∼ 68 MJ Nm(-3)). This gas is transformed into electric power by a co-generation turbine. The distillation char is mostly made of carbon but with significant inorganic impurities (∼ 12 wt%). The quality of the solid residue of the process is comparable to that of some commercial chars. The quantity of residual solids, and the qualities of the gas, liquid and solid fractions, are similar to those obtained by conventional pyrolytic treatments of waste tires. However, the simplicity of the proposed technology and its low investment costs make it a very attractive alternative.