Simultaneous solvent extraction of cobalt and magnesium in the presence of nickel from sulfate solutions by Ionquest 801

The simultaneous extraction of Co(II) and Mg(II) from nickel sulfate solutions has been carried out using the organophosphonic extractant Ionquest 801 diluted in Exxsol D‐80. Statistical design and analysis of experiments were used in order to determine the main effects and interactions of the solvent extraction parameters, which were the extraction pH at equilibrium, the temperature, the extractant concentration and the organic/aqueous phase ratio. A statistically designed experiment was also carried out to study the stripping of the Ionquest 801 organic phase loaded with cobalt and magnesium by sulfuric acid solution. The number of stages required for both extraction and stripping processes of cobalt and magnesium was evaluated. The results of continuous counter‐current mini‐plant tests demonstrated the simultaneous recovery of cobalt and magnesium from nickel sulfate solution. Copyright © 2005 Society of Chemical Industry     

Properties and hydration of blended cements with steelmaking slag

The present research study investigates the properties and hydration of blended cements with steelmaking slag, a by-product of the conversion process of iron to steel. For this purpose, a reference sample and three cements containing up to 45% w/w steel slag were tested. The steel slag fraction used was the “0-5 mm”, due to its high content in calcium silicate phases. Initial and final setting time, standard consistency, flow of normal mortar, autoclave expansion and compressive strength at 2, 7, 28 and 90 days were measured. The hydrated products were identified by X-ray diffraction while the non-evaporable water was determined by TGA. The microstructure of the hardened cement pastes and their morphological characteristics were examined by scanning electron microscopy. It is concluded that slag can be used in the production of composite cements of the strength classes 42.5 and 32.5 of EN 197-1. In addition, the slag cements present satisfactory physical properties. The steel slag slows down the hydration of the blended cements, due to the morphology of contained C₂S and its low content in calcium silicates.     

Characterization of various cement grinding aids and their impact on grindability and cement performance

The aim of the present research work was the evaluation of six commercial grinding additives, which were used for the production of Portland cement (ground in a ball mill at a laboratory stage). For this purpose, a reference sample was also produced without using any admixture. The characterization of the grinding aids (GA) was carried out by Fourier transform infra-red spectroscopy (FT-IR) and gas chromatography/mass spectrometry (GC/MS). All the cement mixtures were tested for initial and final setting times, consistency of standard paste, flow of normal mortar and compressive strengths after 2, 7 and 28 days. In all cases the addition of grinding aids resulted in improvement of the specific surface and grindability index, a fact that was attributed to the additive ability not only to reduce resistance to comminution, but also to prevent agglomeration and powder coatings of ball and mill. The mortars made with cements ground with the addition of commercial additives, which contained triisopropanolamine (TIPA), exhibited higher strength at any age and higher setting times. On the other hand, the presence of triethanolamine (TEA) on the commercial grinding additives did not affect the mechanical properties of the produced cements but slightly decreased their setting times.     

Optimal management of hydrogen storage in stochastic smart microgrid operation

This paper presents an energy management and reserve scheduling scheme in order to optimally operate a 17-bus Low Voltage (LV) grid-tied microgrid, powered by photovoltaics, a wind turbine and a Fuel Cell (FC) utilizing on site hydrogen production and storage. Since high Renewable Energy Resources (RES) penetration is assumed, the expected deviations due to their intermittency are accounted for by the reserve provision by the FC system, in order to deviate as little as possible from the scheduled energy demand injected by the upstream grid. All these are incorporated into the operating cost of the microgrid assuming penalization of unscheduled power injections from the grid. The intermittency of RES and load are incorporated in the model by assuming known probability density functions for the forecasting errors. Then, energy and reserve scheduling is performed utilizing the Harmony Search algorithm in order to minimize the expected operating costs of the examined system by optimal reserve and energy provision from the stored/generated hydrogen. For that purpose, hourly optimizations are performed for a given year to assess the value on-site hydrogen generation and FC technologies add to microgrid operation and Distributed Generation (DG) in general. The purpose is to prove the use of hydrogen storage systems in effective uncertainty balancing. The hydrogen storage system appears to effectively counter the intermittency of renewables in moderate penetration, reducing the uncertainty costs. In higher renewable penetrations, due to uncertainty being already accounted for by the storage, the benefits of the RES penetration are even greater.     

Titanium leaching from red mud by diluted sulfuric acid at atmospheric pressure

Laboratory-scale research has focused on the recovery of titanium from red mud, which is obtained from bauxite during the Bayer process for alumina production. The leaching process is based on the extraction of this element with diluted sulfuric acid from red mud under atmospheric conditions and without using any preliminary treatment. Statistical design and analysis of experiments were used, in order to determine the main effects and interactions of the leaching process factors, which were: acid normality, temperature and solid to liquid ratio. The titanium recovery efficiency on the basis of red mud weight reached 64.5%. The characterization of the initial red mud, as well as this of the leached residues was carried out by X-ray diffraction, TG-DTA and scanning electron microscopy.     

Use of gypsum/brucite mixed precipitate instead of gypsum in Portland cement

The possibility of replacing the natural gypsum used in cement production by a chemical precipitate consisting of gypsum (CaSO₄ ·2H₂O) and brucite (Mg(OH)₂), was investigated. This precipitate is a by‐product of a new hydrometallurgical process, which was developed in order to treat economically low‐grade nickel oxide ores. More specifically, it is obtained by hydrolytic precipitation of magnesium at temperatures not exceeding 80 °C, from sulfate solutions which result from heap leaching of nickel oxide ores with dilute sulfuric acid at ambient temperature, using calcium hydroxide as a neutralizing agent. The mixture generally consists of 20–30% non‐fibrous magnesium hydroxide, 60–75% gypsum and any excess of calcium hydroxide, depending on the precipitation conditions. In the present work, a mixture was produced by hydrolytic precipitation at 25 °C, using 1.1 times the stoichiometric quantity of Ca(OH)₂ required to precipitate all of the magnesium. The possibility of using the above precipitate as a substitute for gypsum in cement was examined by testing four different cement mixtures, one reference sample, containing 4.5% gypsum and 0.5% anhydrite ((PC)_Ref) and another three with 4.1%, 5.2% and 6.3% of gypsum/brucite mixed precipitate ((PC)_B/G), in the place of gypsum. All samples were tested by determining the grindability, setting time, expansion and compressive strength. The results of the physico‐mechanical tests showed that the replacement of natural gypsum by the above precipitate did not affect negatively the quality of the produced cements. Copyright © 2005 Society of Chemical Industry     

A techno-economic analysis of biodiesel biorefineries: Assessment of integrated designs for the co-production of fuels and chemicals

In this work we explore the concept of integrated biorefineries, and we examine alternative schemes for the co-production of biofuels (biodiesel) and chemicals (succinic acid). Four different biorefinery schemes considering the different uses of crude glycerine from the biodiesel process are simulated and compared: (i) the disposal of crude glycerine as a waste, (ii) the purification (through distillation) of crude glycerine to 80%, (iii) the purification of glycerine to 95%. and (iv) the production of succinic acid from glycerine through fermentation. For the latter, we consider the bioprocess that converts the glycerol to succinate, and a downstream separation process that purifies and crystallises our product to the final succinic acid crystals. To apply complex kinetics for the fermentation we have linked Aspen Plus (2006.5) with Matlab (R2007b), where we have used the experimentally-based unstructured model from Vlysidis et al., 2009 and 2010. We first determine the operating parameters of the fermentor that have a significant effect on the economics of this scenario, i.e. the cycle time of the batch fermentation and the water flowrate entering the bioreactor. Subsequently, we perform single- and multi-objective optimisation to maximise the profit and/or to minimise the environmental impact of the overall process. We then analyse and compare the economics of the four different biorefinery schemes by using well-known profitability and/or emission criteria. Furthermore, we carry out sensitivity analysis that takes into consideration price variations for the most important materials and we extract firm conclusions about the profitability of each scenario. It is found that succinic acid co-production can enhance the profit of the overall biorefinery by 60% for a 20 years plant lifetime. These results indicate the importance of glycerol when it is utilised as a key renewable building block for the production of commodity chemicals.     

Cobalt recovery from mixed Co–Mn hydroxide precipitates by ammonia–ammonium carbonate leaching

The research work presented in this paper focused on the recovery of cobalt from mixed Co–Mn hydroxide precipitates (obtained from sulphate leach liquors of nickel oxide ore), using ammonia–ammonium carbonate leaching. The characterization of the initial mixed hydroxide precipitates, as well as the corresponding leached residue was carried out by X-ray Diffraction, TG–DTA and Scanning Electron Microscopy.Cobalt and manganese precipitation was based on the statistical design and analysis of experiments, in order to determine the main effects and interactions of the precipitation factors, which were the equilibrium pH and the temperature. Co and Mn were precipitated as hydroxides at pH = 10.5 and T = 25 °C, using 5 M NaOH as a neutralizing agent, by 99.9% and 99.5%, respectively. The main mineralogical phases were, Mn₃O₄ (Hausmannite), γ-Mn₃O₄ and CoMn₂O₄, while Co(OH)₂ and Mn(OH)₂ (Pyrochroite) were also present as minor constituents.Cobalt and manganese separation was based on selective cobalt recovery by ammonia–ammonium carbonate leaching of the produced mixed hydroxide precipitate. The factors studied were the ammonia–ammonium carbonate concentration and the solid to liquid ratio. The cobalt recovery efficiency reached 93%. Mn₃O₄ (Hausmannite) was the main mineralogical phase of the leached residue, while MnCO₃ (Rhodochrosite) and Mn₂O₃ were also present. Small quantities of cobalt were also observed in the residue as CoMn₂O₄.     

Hydrometallurgical Treatment of Steelmaking Electric Arc Furnace Dusts (EAFD)

The aim of the current research study was the development of a hydrometallurgical process for the recovery of metals from electric arc furnace dust. The behaviors of zinc, cadmium, iron, and lead in sulfuric acid were investigated. The recovery of the zinc (from zinc oxide) and cadmium is possible with a relatively high yield, as iron and lead remain in the solid residue after two stages of leaching at room temperature. In a third stage, zinc recovery from the zinc ferrite (in the leached residue) was carried out by pressure leaching. Under the optimum conditions of treatment and after three stages of processing, the total extractions of zinc and cadmium were 99 and 94 pct, respectively. Lead and the main part of iron remain in the residue. The proposed process also resulted in the reduction of the initial residue mass by 30 pct.     

Reinforcement learning agents providing advice in complex video games

This article introduces a teacher–student framework for reinforcement learning, synthesising and extending material that appeared in conference proceedings [Torrey, L., & Taylor, M. E. (2013)]. Teaching on a budget: Agents advising agents in reinforcement learning. {Proceedings of the international conference on autonomous agents and multiagent systems}] and in a non-archival workshop paper [Carboni, N., &Taylor, M. E. (2013, May)]. Preliminary results for 1 vs. 1 tactics in StarCraft. {Proceedings of the adaptive and learning agents workshop (at AAMAS-13)}]. In this framework, a teacher agent instructs a student agent by suggesting actions the student should take as it learns. However, the teacher may only give such advice a limited number of times. We present several novel algorithms that teachers can use to budget their advice effectively, and we evaluate them in two complex video games: StarCraft and Pac-Man. Our results show that the same amount of advice, given at different moments, can have different effects on student learning, and that teachers can significantly affect student learning even when students use different learning methods and state representations.