• Energy Research

In the present work the influence of accelerated mineral carbonation on the leaching behaviour of basic oxygen furnace steel slag was investigated. The environmental behaviour of the material as evaluated through the release of major elements and toxic metals under varying pH conditions was the main focus of the study. Geochemical modelling of the eluates was used to derive a theoretical description of the underlying leaching phenomena for the carbonated material as compared to the original slag. Among the investigated elements, Ca and Si were most appreciably affected by carbonation. A very clear effect of carbonation on leaching was observed for silicate phases, and lower-Ca/Si-ratio minerals were found to control leaching in carbonated slag eluates as compared to the corresponding untreated slag sample as a result of Ca depletion from the residual slag particles. Clear evidence was also gained of solubility control for Ca, Mg and Mn by a number of carbonate minerals, indicating a significant involvement of the original slag constituents in the carbonation process. The release of toxic metals (Zn, V, Cr, Mo) was found to be variously affected by carbonation, owing to different mechanisms including pH changes, dissolution/precipitation of carbonates as well as sorption onto reactive mineral surfaces. The leaching test results were used to derive further considerations on the expected metal release levels on the basis of specific assumptions on the relevant pH domains for the untreated and carbonated slag.

Microalgae may be exploited in water or wastewater treatment facilities to reduce excess concentrations of nutrients and metals to comply with regulatory limits. In this study, we characterized the growth and phosphorus (P) removal capacity of an isolated strain of Tetradesmus obliquus VRUC280. Investigations were carried out from laboratory scale (50 mL) up to a 100 L outdoor photobioreactor (PBR). After 10 days, batch cultures removed up to 74% of the media P, while in the PBR, 95% removal was achieved within five days. The harvested biomass was then inactivated (freeze-dried) and used for metal adsorption tests, employing solutions containing 6.0 mg Cu L-1 or 4.8 mg Ni L-1. Metal removal rates were evaluated after 15, 30, 60 and 120 min by the analysis of liquid and biomass metal contents. For the latter, a specific biomass digestion method was developed. Cu removal ranged between 50% and 65%, while for Ni, removal varied between 30% and 50%. 300-400 mg Cu Kg DW-1 and 130-250 mg Ni Kg DW-1 were rapidly adsorbed on the cell surface of T. obliquus (ca. 15-30 min incubations). This study demonstrates the potential of microalgae, in this case T. obliquus, to remove sequentially P and metals from aqueous media.

Abstract This paper presents the results of characterization investigations carried out on the solid residues produced during coal gasification tests performed in the Zecomix (Zero Emission of CarbOn with MIXed technology) research infrastructure. In this pilot-scale plant, coal is gasified in a steam/oxygen-blown bubbling fluidized bed containing olivine. The solid residues, collected both directly from the solid bed (bed ash) and downstream from it (mixed ash), were characterized in terms of their main physical, chemical and mineralogical properties with the aim of identifying suitable management strategies for each of them within the Zecomix process. Thus, an experimental protocol was also developed to separate the organic and inorganic fractions of both ash types. The main constituents of the bed ash were Mg, Si and Fe, which represent the elemental components of olivine. The total organic carbon content of the bulk bed ash was of 5%, while that of the bulk mixed ash proved to be significantly higher (24–27%). Finally, the particle size and density separation procedure developed in this work showed to be effective for separating the organic and inorganic fractions of the bulk samples of both types of residues, allowing to reach separation efficiencies higher than 90%.

This paper investigates the effects of accelerated carbonation on the characteristics of bottom ash from refuse derived fuel (RDF) incineration, in terms of CO(2) uptake, heavy metal leaching and mineralogy of different particle size fractions. Accelerated aqueous carbonation batch experiments were performed to assess the influence of operating parameters (temperature, CO(2) pressure and L/S ratio) on reaction kinetics. Pressure was found to be the most relevant parameter affecting the carbonation yield. This was also found to be largely dependent on the specific BA fraction treated, with CO(2) uptakes ranging from approximately 4% for the coarse fractions to approximately 14% for the finest one. Carbonation affected both the mineralogical characteristics of bottom ash, with the appearance of neo-formation minerals, and the leaching behaviour of the material, which was found to be mainly related to the change upon carbonation in the natural pH of the ash.

This work reports the results of the life cycle assessment (LCA) of two carbonation processes aimed at permanent CO2 storage, employing Basic Oxygen Furnace (BOF) slag from steel manufacturing as a ...

AbstractSeveral bio-based and biodegradable polymers have been lately introduced on the market as potential substitutes for conventional plastics in order to decrease the environmental impacts related to plastics manufacturing and especially end of life disposal. The most applied route for the management of these types of bioplastics once they enter the waste stream is co-treatment with biowaste in anaerobic digestion and/or composting plants that may lead to their recycling as digestate and/or compost. Several studies however, have reported the incomplete biodegradation of these materials at lab-scale and/or in conventional treatment plants and the significant content of small inert particles, including microplastics, in the final products. This could represent an obstacle to the agricultural use of the produced digestate and/or compost. It is therefore necessary to study all the possible options for the recycling of these types of materials based on the specific characteristics of the polymers that constitute them. In this study, four different types of bio-based biodegradable plastics were characterized by chemical-physical analysis. In particular, the main properties investigated included the content of volatile and non-volatile phases, crystallinity, main elemental composition, content of different phases by spectroscopic investigation using Fourier Transform InfraRed spectra and of metals and metalloids of potential environmental concern. The results of the thermogravimetry analysis indicated that all of the recycling/recovery options considered (compost production via biodegradation, chemical recycling and energy recovery) could be potentially applicable for the examined bioplastics, since they showed to contain polymers that volatilize below 550 °C. The highest volatile matter contents were measured for PLA cups and starch-based films, while the highest ash contents were found for the other two types of rigid bioplastics, which also showed the highest concentrations of elements of potential environmental concern, that were anyhow quite limited, and reduced higher heating values estimated by elemental analysis compared to PLA or starch-based films. In addition, the rigid bioplastics tested exhibited a higher degree of crystallinity, which could be associated to a lower biodegradability. With regard to chemical recycling processes, the results of the chemical-physical investigations indicated that pyrolysis could be a technically viable process to apply for the treatment of all of the bioplastic samples examined. Thus, PLA, which is manufactured through lactic acid condensation, chemical recycling by rapid depolymerization through pyrolysis was evaluated applying a numerical model implemented in Aspen plus®. Results indicated that the best yields in terms of lactide recovery could be obtained at an temperature of 400 °C and 10 s residence time and that other valuable products may be obtained potentially by fractional condensation. Graphical Abstract

AbstractAn assessment of the energetic requirements of slurry‐phase accelerated carbonation for CO2 sequestration using steelmaking slag was conducted. The results of dedicated lab‐scale carbonation experiments in which the CO2 sequestration yield of basic oxygen furnace slag was investigated at different operating conditions were used for the energy requirement calculations. The operating variables of the process and the associated values adopted were total gas pressure, temperature, and CO2 concentration in the gas phase. The energy duties of the slurry‐phase carbonation layout were calculated for the different unit operations, which included slag milling, mixing, slurry pumping, heating, CO2 compression, solid/liquid separation, and CO2 capture (when required). The estimated energy requirements were found to lie in the range 980−6300 MJ t−1 CO2 sequestered, where the lower end of the range was associated with the use of diluted CO2. In all cases, the use of a concentrated CO2 flow proved largely energetically unfavorable over the use of diluted gas streams, since the energy duty of the required CO2 capture stage by far overcame the benefits associated with improved sequestration yields at increased CO2 concentrations in the gas phase. The calculated energy requirements were also processed to derive a second‐order model accounting for the main effects and interactions between the operating variables of the carbonation process. The model developed is meant to predict the expected energy demand of the carbonation process under different operating conditions and to define the optimal combination of these in terms of the energetic profile of the process itself. © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd.