Formation Of Solid Products Research Articles

EFFECT OF DIDODECANOYL PEROXIDE ON TRANSFORMATIONS OF HIGH-SULFUR VACUUM RESIDUE COMPONENTS IN THE PROCESS OF INITIATED CRACKING

This paper presents the results of the study of the composition of cracking products of high-sulfur tar obtained from oil of Zyuzeyevskoye field in the presence of radical-forming additive – didodecanoyl peroxide. Thermal treatment of the mixture of vacuum residue with different amounts of didodecanoyl peroxide was carried out at a temperature of 500 °C. The duration of the process was 15 min. Characteristic features of changes in the material balance of the process, group composition of liquid cracking products, qualitative and quantitative composition of newly formed sulfur compounds were established. The use of additive in the amount of 0.5 – 0.75%wt. allows to reduce thermal stability of high-molecular components of tar (resins and asphaltenes), and also promotes change in direction of reactions. Processes of condensation of resins and asphaltenes into solid coke-like products are slowed down, and cracking reactions are initiated with formation of low-molecular components, which fall into the composition of oils, as a result of which it is possible to obtain additional amounts of distillate fractions. It is shown that thiophene, benzo- and dibenzothiophene derivatives, which are absent in the initial tar, are intensively formed and accumulated in the composition of liquid cracking products, which worsens the quality of the obtained distillate fractions. Among the identified sulfur compounds benzothiophene homologs prevail. It was found that cracking of tar in the presence of additive didodecanoyl peroxide promotes deep destruction of sulfur-containing fragments of vacuum residue and asphaltene molecules. Sulfur compounds formed under these conditions not only get into the composition of oils, but also participate in condensation reactions with the formation of solid products, which leads to an increase in the degree of sulfur removal from the composition of liquid cracking products. For citation: Goncharov A.V., Krivtsov E.B. Effect of didodecanoyl peroxide on transformations of high-sulfur vacuum residue components in the process of initiated cracking. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 8. P. 121-128. DOI: 10.6060/ivkkt.20246708.15t.

On the role of hydrogen inhibition in gas-phase methane pyrolysis for carbon capture and hydrogen production in a tubular flow reactor

The thermal pyrolysis of methane enables economically competitive hydrogen production without direct CO2 emissions. Although several mechanisms for the process have already been proposed, especially the inhibitory effect of hydrogen as well as the process operation at increased pressure have not yet been fully clarified. In this context, the present work investigates the influence of hydrogen and argon as inert gas on product composition, methane conversion, and hydrogen selectivity as a function of temperature (1000 °C to 1600 °C), residence time (1 s to 7 s), molar dilution ratio (1:1–4:1), and pressure (1 bar to 4 bar) in a high-temperature reactor. Within the scope of this work, total differences in CH4 conversion of up to 50 % could be observed at equal process parameters between an argon and hydrogen dilution, underlining the potential impact of diluents on the overall process. Moreover, increasing the pressure from 1 bar to 4 bar reduces the formation of byproducts significantly for both H2 and Ar as diluent, however, with different mechanistic characteristics. The most remarkable difference is the formation of propylene that exclusively takes place in argon-diluted reaction gas mixtures. This occurrence persists unabated, even under elevated pressures and temperatures reaching as high as 1600 °C. We ascribe this phenomenon to the interaction of methyl and ethyl radicals, establishing it as an impasse to further reactions leading to the formation of solid products. Herewith, the study provides novel insights from a reaction engineering perspective as well as from a process development perspective and clarifies the role of the dilution gases hydrogen and argon on the methane pyrolysis reaction.

Isocyanate-free urethanediol itaconates as biobased liquid monomers in photopolymerization-based 3D printing

Nowadays, most of the commercial resins for VP are composed of (meth)acrylated urethanes, as they are cheap and provide good mechanical properties to the thermosets produced by their photocuring. However, such urethanes are still produced using toxic and polluting isocyanates, though alternative pathways exploiting cyclic carbonates and biobased amines are arising. Unfortunately, the use of biobased amines and carbonates to produce (meth)acrylate urethanes often leads to the formation of solid products that display poor solubility in the liquid components of photocurable resins. In this work, we describe the synthesis of fully biobased diurethanediols using a biobased diamine and bioderived carbonates functionalized with itaconic acid moieties that are liquid at room temperature and that can be efficiently formulated with (meth)acrylic and itaconic acid-based formulations for VP leading to 3D printed materials with good mechanical properties, comparable to those of commercially available non-biobased alternatives. In fact, depending on the resin formulations, the addition of diurethanediols diitaconates led to the obtainment of 3D printed materials with elastic moduli as high as 1 GPa, and tensile strengths over 30 MPa, and biobased contents as high as 90 wt.%. These products may serve as candidates for the replacement of isocyanate-based components with the aim of increasing the sustainability of resins’ manufacturing for VP.

Chemical stability and reactivity of electrochemically grown manganese oxide films

The fundamental scientific challenge in fully harnessing the potential of manganese oxide compounds lies in understanding the interplay between microstructure, surface properties, and electrochemical reactivity. In this study, manganese oxides were synthesized via two distinct methods: electrodeposition trough anodic oxidation of Mn2+ in solution and direct anodic oxidation of metallic Mn. Employing electrochemical quartz crystal microbalance measurements under flow conditions, the deposited compounds were successfully identified as function of the applied anodic potentials, revealing a transition from Mn3O4 to Mn2O3. Furthermore, the MnO → Mn(OH)2 conversion was determined to be a critical step in the degradation process of manganese oxides. For the anodic oxidation process, the mere alkaline "pH effect" (solid product formation predicted from Pourbaix Diagram) was demonstrated to be insufficient to form a protective oxide/hydroxide layer on top of metallic Mn. Indeed, the addition of phosphate proved necessary for achieving this protective passive layer formation, particularly in pH 12.0 Na3PO4 electrolyte solution. Potentiostatic growth in the presence of phosphates demonstrated the progressive stabilization of the protective layer consisting of a mix of manganese oxide, hydroxide, and phosphate, as confirmed by Raman and X-ray photoemission spectroscopy. To provide a comprehensive framework for our findings, a revised Pourbaix Diagram for the Mn-H2O-PO43− system is proposed and discussed.

Carbon Dioxide Reduction on Alloyed Galinstan

Solar powered electrochemical CO₂ reduction to disposable products is presently being developed as one of negative carbon emission technologies1. State-of-the-art electrocatalysts are mainly developed for the CO2 reduction to hydrogen rich products or chemical feedstock materials while for the above-mentioned application solid carbon-rich products are desired (best pure carbon). Even though the formation of solid products is sometimes observed on catalysts (coking effect), this usually leads to an undesirable irreversible deactivation of their solid interfaces.Thus, the development of next generation CO2 electrocatalysts is demanded based on liquid metal alloys such as galinstan (GaInSn). The advantage of using liquid phase electrodes is to eliminate coking and coarsening limitations that are associated with solid catalysts. For example, it has been reported that ceria-supported liquid galinstan can electrochemically produce carbonaceous materials from CO2 gas2. This shows, that doping with additional active elements can change the CO2 reduction activity of GaInSn in the direction of other desired products.Our work investigates the activity of galinstan for the electroreduction of CO2 depending on alloying with additional metals (such as Ce, Ag, Pb). While pure GaInSn shows a predominant activity for the formation of C1 products (CO, HCOOH) in DMF/H2O electrolyte, we are mainly interested in the formation of solid carbon or oxalate. Therefore, our investigations aim at finding suitable modifications of GaInSn that achieve high selectivity for these products. Electrochemical analysis coupled with in-line gas chromatography and in-line mass spectroscopy are used to characterize the reactivity. Furthermore, the influence of the water content of the organic electrolyte on the product selectivity will be investigated. In particular, to suppress the observed low hydrogen evolution as a by-product even more efficiently. May, M. M.; Rehfeld, K., Negative Emissions as the New Frontier of Photoelectrochemical CO2 Reduction. Advanced Energy Materials 2022, 2103801.Esrafilzadeh, D.; Zavabeti, A.; Jalili, R.; Atkin, P.; Choi, J.; Carey, B. J.; Brkljača, R.; O’Mullane, A. P.; Dickey, M. D.; Officer, D. L.; MacFarlane, D. R.; Daeneke, T.; Kalantar-Zadeh, K., Room Temperature CO2 Reduction to Solid Carbon Species on Liquid Metals Featuring Atomically Thin Ceria Interfaces. Nature Communications 2019, 10 (1), 865. Figure 1

Kinetic and thermodynamic evidences of the Diels-Alder cycloaddition and Pechmann condensation as key mechanisms of hydrochar formation during hydrothermal conversion of Lignin-Cellulose

We investigated the kinetics and thermodynamics of the Diels-Alder cycloaddition and Pechmann condensation to evaluate the significance of both mechanisms toward hydrochar formation during hydrothermal carbonization and liquefaction of biomass. We performed well-designed experiments of semi-continuous hydrothermal conversion of pure compounds representative of lignin-cellulose fractions (i.e., D-(+)-cellobiose and 1-(3,4-dimethoxyphenyl)-2-(4-hydroxy-2-methoxyphenoxy)propane-1,3-diol) and corresponding hydrochar precursors at 220–370 °C for 60 min. We developed thermodynamically-feasible multi-phase reaction pathways and specified the kinetic and thermodynamic parameters of each pathway by fitting the reversible power-law kinetic model, Arrhenius equation, and correlation between conventional definition of Gibbs free energy and the Gibbs free energy isotherm equation into experimental data of time evolution of chemical species concentration measured using GC–MS, XRD, and μGC. Reaction pathways of mixtures of pure compounds were a combination of those for individual pure compounds. We discovered that endothermic Diels-Alder cycloaddition involving dienes and dienophile was prominent in D-(+)-cellobiose conversion pathways and functioned as an intermediate reaction producing precursors for various endothermic and exothermic precipitation mechanisms. The temperature dependence of solid organics formation via this indirect route depended on the net ΔH of a set of reaction pathways after Diels-Alder cycloaddition. In contrast, we found that the Pechmann condensation involving phenols and β-ketoester/β-ketoacid was significant in the conversion pathway of 1-(3,4-dimethoxyphenyl)-2-(4-hydroxy-2-methoxyphenoxy)propane-1,3-diol and facilitated direct precipitation of organics including 4,10-dimethyl-2,7-dioxo-2,7-dihydropyrano[2,3-g]chromene-5-carbaldehyde and 4,5-dimethoxy-2,7-dioxo-6,7-dihydro-2H-benzo[g]chromene-10-carboxylic acid. The endothermic nature of Pechmann condensation preferred higher temperatures for a higher equilibrium conversion toward solid product formation. Results in this study contributed to the improved understanding of fundamentals of hydrochar formation.

Hydrogen production by kraft black liquor supercritical water gasification: Reaction pathway and kinetic

Kraft black liquor (KBL) supercritical water gasification (SCWG) has significant implications for carbon emission reduction and energy efficiency improvement in the pulp industry. This research focuses on investigating the SCWG of KBL under different reaction conditions, including reaction times (5–30 min), temperatures (450–650 °C), and feed concentrations (5%–20%), utilizing a high heating rate batch reactor. The performance of the gasification process is evaluated by analyzing gaseous, liquid, and solid products. Remarkable achievements in carbon gasification efficiency (CGE) of 95.28% and COD removal of 99.90% are attained at 650 °C, 30 min, and 10 wt% feed concentration. The liquid-phase products primarily comprise aromatic compounds, particularly phenolics, with the possible presence of reactive nonaromatic compounds such as cyclopentanone. Lower temperatures favor the formation of solid products, which result from phenolic agglomeration reactions leading to char formation. The research also explores the SCWG reaction pathway of KBL and develops a comprehensive twelve-lumped quantitative kinetic model. This work provides valuable engineering parameters for reactor design, optimization, and numerical simulations, facilitating advancements in SCWG of KBL technology.

CFD-aided optimization of the decomposition kinetics of cement raw meals under high CO2 concentrations

Oxy-fuel combustion technology is a promising option for CO2 capture in the cement industry, as the cement raw meal decomposes to generate large amounts of CO2. Exploring the decomposition kinetics of raw meal under high CO2 concentrations is crucial for the design and operation optimization of precalciners. In this work, a new method is proposed to obtain the decomposition kinetics of cement raw meals. First, a real decomposition atmosphere, including the temperature and CO2 concentration in an actual precalciner, is simulated in an electric-heated down firing furnace (E-DFF), and the decomposition characteristics of raw meal at various temperatures (850–1050 °C) and CO2 concentrations (0–90 vol%) are investigated. Second, a detailed decomposition model of raw meal under high CO2 concentrations is developed, and this model considers gas adsorption and surface reactions, structural changes due to solid product formation, gas diffusion around the particle and particle temperature changes due to heat transfer and endothermic reactions. Third, the prediction model of raw meal decomposition is implemented into CFD software, and the kinetic parameters are determined via a CFD-aided optimization method in which a direct search algorithm is used to accelerate the optimization process. Finally, the optimized kinetics are verified over wide ranges of temperatures, residence times, and CO2 concentrations. The simulation results agree well with the experimental data, indicating that the developed model and obtained kinetic parameters could be applied for the application of oxy-fuel combustion technology in the cement industry.

Pyrolysis of mixed plastic waste: Predicting the product yields

The predictability of pyrolysis yields and product composition of mixed plastics has been studied. To do so, pyrolysis of virgin polymers (HDPE, LDPE, PP, PS and PET) and eight individual sorting categories from a real waste DKR-350 stream (PE rigid/film, PP rigid/film, PET, PS, multilayer flexibles, and clogged materials) was performed in a batch reactor at 500 °C at laboratory scale. The obtained oil/wax, gas, and solid yields and the composition of oil/wax of those individual feedstocks were used as input of a superposition model to predict the corresponding pyrolysis yields and oil/wax composition of mixed feeds, which were later compared with the experimentally measured product yields from the pyrolysis of those mixed streams. This linear model predicts the oil/wax yield of the mixed streams to a reasonable extent, with a maximum yield deviation (overestimation) of 8 percentage points. However, the presence of significant amounts of PET (above 33 wt%) in the mixed plastic streams negatively impacts the production of the condensable product and promotes the formation of solid products beyond the expected predicted values. Quantification of the type of carbon (aliphatic, aromatic and carbonyl) present in all the oil/wax products was done using 13C NMR spectroscopy. A linear model could also predict the aliphatic carbon yield in the condensable product from plastic waste streams with high accuracy (maximum yield difference of 6 percentage points). However, the aromatic carbon yield could not be predicted, probably due to the observed behavior of PET, which interacts with other polymers to promote solid product formation.

Where Does Sulfur Precipitate in Lithium Sulfur Batteries? an Operando SANS Experiment

In-situ and operando measurements are done to gain a better understanding of the precipitation mechanisms during charge and discharge in lithium sulfur batteries. In this work we used a carbon felt networked with microfibers consisting of pores, 2 nm and smaller, as a freestanding sulfur host. First, three different infiltration methods of sulfur infiltration are explored to determine the best method. Second, in-situ electrochemical impedance spectroscopy measurements were done that showed a solid product formation occurring at the sulfur cathode, both during the high voltage plateau and at the end of discharge. In an additional 3-electrode EIS measurement, a similar solid product formation on the Li counter electrode due to its reaction with polysulfides is also observed. Operando small angle neutron scattering measurements show the solid product formation, in the carbon, both near the beginning and at the end of discharge, confirming the precipitation data via contrast changes as a function of charge and discharge. We will show in this presentation that Li2S precipitates in the pores at the beginning and the end of discharge, whereas S8 precipitates on the surface of the carbon felt.

Boron removal from synthetic brines and oilfield produced waters using aluminum electrocoagulation

High boron (B) levels in oil and gas produced waters prevent its beneficial reuse as irrigation water without proper treatment. Aluminum (Al) electrocoagulation (EC) is a promising technology for B removal, but further research and development is needed to optimize EC for use in removing B from produced waters. To this end, B removal by adsorption onto insoluble aluminum hydroxide solids, generated by EC in simulated brines (up to 50,000 mg/L NaCl) and real oilfield produced waters, was studied. B removal during EC was greater than when aluminum hydroxide solids formed by EC were subsequently exposed to B containing solutions. Working parameters affecting B removal during the EC process, including current, total dissolved solid (TDS), temperature, pH, scale-forming cations and organic matter, were investigated to explore ways to achieve higher B removal. Boron removal increased with increased current loading and time, and with the concomitant increased Al solids concentration. However, too high a current loading limited B removal because of a change in the structure of the aluminum hydroxide solids. Higher TDS decreased B removal slightly, but lower TDS concentrations limited the use of higher current loadings. Temperature increased during EC treatment, particularly at higher current loadings, and this inhibited B removal due to an accelerated aggregation of amorphous Al solids into larger, denser, and presumably more crystalline particles. The best B removal occurred at pH 8, corresponding to a slightly positive zeta potential for aluminum hydroxide and a small but significant fraction of negatively charged B species. Scale-forming cations such as Ba2+ and Sr2+ had no obvious effect on the EC process. The presence of high concentrations of Mg2+ and Ca2+ resulted in low bulk pH values during the EC process and greater formation of solid products, but B removal did not decrease during a pH-controlled (pH = 8) EC process with these divalent cations present. Two produced water samples collected from oilfields in Kansas, US were treated using EC for 1 h, resulting in up to ~70 % B removal from solution with a current loading of 6.67 A/L, and up to 78 % with 13.33 A/L.

Enabling Total Process Digital Twin in Sugar Refining through the Integration of Secondary Crystallization Influences

Crystallization is the main thermal process resulting in the formation of solid products and, therefore, is widely spread in all kinds of industries, from fine chemicals to foods and drugs. For these high-performance products, a quality by design (QbD) approach is applied to maintain high product purity and steady product parameters. In this QbD-context, especially demanded in the foods and drugs industry, the significance of models to deepen process understanding and moving toward automated operation is steadily rising. To reach these aspired goals, besides major process influences like crystallization temperature, other impacting parameters have to be evaluated and a model describing these influences is sought-after. In this work, the suitability of a population balance-based physico-chemical process model for the production of sugar is investigated. A model overview is given and the resulting model is compared to a statistical DoE scheme. The resulting process model is able to picture the effects of secondary process parameters, alongside temperature or temperature gradients, the influences of seed crystal size and amount, stirrer speed, and additives.

Real-Time Monitoring Polymerization Reactions Using Dipolar Echoes in 1H Time Domain NMR at a Low Magnetic Field.

1H time domain nuclear magnetic resonance (1H TD-NMR) at a low magnetic field becomes a powerful technique for the structure and dynamics characterization of soft organic materials. This relies mostly on the method sensitivity to the 1H-1H magnetic dipolar couplings, which depend on the molecular orientation with respect to the applied magnetic field. On the other hand, the good sensitivity of the 1H detection makes it possible to monitor real time processes that modify the dipolar coupling as a result of changes in the molecular mobility. In this regard, the so-called dipolar echoes technique can increase the sensitivity and accuracy of the real-time monitoring. In this article we evaluate the performance of commonly used 1H TD-NMR dipolar echo methods for probing polymerization reactions. As a proof of principle, we monitor the cure of a commercial epoxy resin, using techniques such as mixed-Magic Sandwich Echo (MSE), Rhim Kessemeier—Radiofrequency Optimized Solid Echo (RK-ROSE) and Dipolar Filtered Magic Sandwich Echo (DF-MSE). Applying a reaction kinetic model that supposes simultaneous autocatalytic and noncatalytic reaction pathways, we show the analysis to obtain the rate and activation energy for the epoxy curing reaction using the NMR data. The results obtained using the different NMR methods are in good agreement among them and also results reported in the literature for similar samples. This demonstrates that any of these dipolar echo pulse sequences can be efficiently used for monitoring and characterizing this type of reaction. Nonetheless, the DF-MSE method showed intrinsic advantages, such as easier data handling and processing, and seems to be the method of choice for monitoring this type of reaction. In general, the procedure is suitable for characterizing reactions involving the formation of solid products from liquid reagents, with some adaptations concerning the reaction model.

Co-hydrothermal carbonization of swine manure and cellulose: Influence of mutual interaction of intermediates on properties of the products

Co-hydrothermal carbonization (HTC) of livestock manure and biomass might improve the fuel properties of the hydrochar due to the high reactivity of the biomass-derived intermediates with the abundant oxygen-containing functionalities. However, the complicated compositions make it difficult to explicit the specific roles of the individual components of biomass played in the co-HTC process. In this study, cellulose was used for co-HTC with swine manure to investigate the influence on the properties of the hydrochar. The yield of hydrochar obtained from co-HTC reduced gradually with the cellulose proportion increased, and the solid yield was lower than the theoretical value. This was because the cellulose-derived intermediates favored the stability of the fragments from hydrolysis of swine manure. The increased temperature resulted in the reduction of the hydrochar yield whereas the prolonged time enhanced the formation of solid product. The interaction of the co-HTC intermediates facilitated the formation of O-containing species, thus making the solid more oxygen- and hydrogen-rich with a higher volatility. In addition, the co-HTC affected the evolution of functionalities like -OH and CO during the thermal treatment of the hydrochar and altered its morphology by stuffing the pores from swine manure-derived solid with the microspheres from HTC of cellulose. The interaction of the varied intermediates also impacted the formation of amines, ketones, carboxylic acids, esters, aromatics and the polymeric products in distinct ways.

Quantifying the chemical, electrochemical heterogeneity and spatial distribution of (poly) sulfide species using Operando SANS

In-situ and operando measurements are done to gain a better understanding of the precipitation mechanisms during charge and discharge in lithium sulfur batteries. A carbon felt networked with microfibers consisting of pores, 2 nm and smaller, is used as a freestanding sulfur host. Three different methods of sulfur infiltration are explored in order to determine the best one to fill most of the pores. It was identified to be a melt infiltration method in a vacuum oven, where the pores including the ultra-micropores, are successfully filled. In-situ electrochemical impedance spectroscopy measurements show a solid product formation occurring at the sulfur cathode, both during the high voltage plateau and at the end of discharge. In a 3-electrode EIS measurement, a similar solid product formation on the Li counter electrode due to its reaction with polysulfides is also observed. Operando small angle neutron scattering measurements show the solid product formation, in the carbon, both near the beginning and at the end of discharge, confirming the precipitation data via contrast changes as a function of charge and discharge. It is shown that Li2S precipitates in the pores at the beginning and the end of discharge, whereas S8 precipitates on the surface of the carbon felt. This lithium sulfur system shows both the quasi-solid-state and the solid-liquid-solid reactions in a typical ethereal electrolyte solution with a two-plateau discharge profile.

Co-hydrothermal carbonization of swine and chicken manure: Influence of cross-interaction on hydrochar and liquid characteristics

Swine and chicken manures are abundant solid wastes that can be converted into carbonaceous materials through hydrothermal carbonization (HTC). Owing to their unique biochemical compositions, co-HTC of these two types of manures may have significant implications for the generated products. We investigated the co-HTC of swine manure and chicken manure to understand the influence of the interaction between contrasting manures on the properties of the derived products. The results indicated that co-HTC treatment enhanced the formation of solid product and improved the C and N contents, heating value, and energy yield of the resulting hydrochar. Regarding the ignition temperature and comprehensive combustion index, the combustion properties of the hydrochar were enhanced owing to the mutual effect of the HTC intermediates. Additionally, the interaction of the intermediates significantly impacted the transfer of nitrogenous species and generation of organic acids and organic polymers with fused-ring structures. Therefore, co-HTC processing of animal manures could potentially provide a sustainable pathway for the conversion of animal waste into solid products with improved characteristics compared to those produced by treating the two feedstocks separately.

Complex chemical kinetic mechanism reduction for simultaneous catalytic oxidation and desulphurization of hydrogen sulphide

Complex chemical kinetic mechanism complicates simulation of advancedadsorption column, particularly inthe coupling of simultaneous catalytic oxidation and desulphurization of hydrogen sulphide. In the present study, a new reduction method of the detailed chemical kinetic mechanism was postulated based on genetic algorithm and least square error to solve for both reactions class-based global sensitivity and path sensitivity analyses. During the reduction process, the influence of the species and reactions was determined according to the contribution of their corresponding reaction classes to the prediction uncertainties by calculating the normalized sensitivity index (NSI) and the path sensitivity coefficient (PSC) of each reaction class from the detailed mechanism. Through solving both NSI and PSC with MATLAB coding incorporating genetic algorithm and least square error, a reduced hydrogen sulphide mechanism with 15 species and 7 reactions is obtained. By comparing the calculated value from reduced mechanism with experimental data, 16 useful kinetic parameters were estimated and validated through the root mean square error (RMSE). Good agreements for the predicted data between the reduced and experimental data indicate the advantages of the present reduction method. Furthermore, the validated reduced mechanism also suggests that the exponential-like diffusion coefficient is suitable to explain the behaviour of pore blockage due to solid product formation. Lastly, the interaction between significant operating variables such as temperature, concentration, flow rate, and mass of adsorbent were also studied and presented under the umbrella of response surface method and analysis of variance (ANOVA).

О кинетике извлечения примесей из железного концентрата, полученного в ходе гидрометаллургической переработки чернового медного концентрата

The purpose of the paper is to study the physical and chemical features of high-quality iron concentrate precipitation from nitric acid leaching solutions of low-grade copper-sulfide raw materials, and to obtain a highly profitable product which is suitable for direct processing at ferrous metallurgy enterprises. To conduct the experiments on obtaining impurity rich and depleted iron concentrate a hydrolytic precipitate containing 54.6% iron and numerous impurities obtained as a result of processing of nitric acid leaching solutions of rough copper sulfide concentrate from the Zhezkazgan deposit is used. Analytical studies of initial materials and resulting products of the processes under investigation are conducted using the modern certified methods including the x-ray spectral, x-ray phase, atomic absorption analysis, mass spectrometry method with inductively coupled plasma. We have obtained a high-quality iron concentrate containing minimal amounts of silicon, aluminum, phosphorus and sulfur as well as partial and generalized equations that give an idea of the influence of the studied factors on the indicators of the iron concentrate production process. The apparent activation energy of the process has been calculated - 46.77 kJ/mol. It probably indicates the presence of diffusion complications caused by the formation of solid products passivating the surface of the material being dissolved. The principal possibility of obtaining high-quality iron concentrate from processing poor copper-sulfide concentrate middlings of the Zhezkazgan deposit is shown. The mathematical processing of experimental data has resulted in the determination of equations that characterize the degree of influence of the studied factors on the process indicators. It is found out that the production process of the saleable iron concentrate proceeds in the mode of diffusion restrictions. It is the first time, when multivariate generalized dependencies are obtained for the process under consideration and their analytical transformations are performed. These methods can be used to study the analogous processing of similar metallurgical raw materials.

Electrocoagulation with Polarity Reversal for Treatment of Produced Water

Electrocoagulation (EC) is a cost-effective and reliable technology to treat water and wastewater and has the ability to remove many types of contaminants. Studies have shown that EC operated with aluminum or iron electrodes exhibits higher treatment efficiencies than traditional chemical coagulation with aluminum sulfate or ferric chloride salts [1], [2]. EC involves the in-situ generation of metal hydroxide coagulant by the electrochemical dissolution of sacrificial metal anodes using a direct current, combined with generation of hydroxide ions at the cathode. However, material precipitation on the electrodes associated with long term operation is a major problem hindering the scale up of EC [3]. The growth of electrode surface layers increases passivation, which reduces the treatment efficiency and increases operating costs [4]. Polarity reversal during electrocoagulation, i.e. intermittently changing the direction of the current, is a method that can remove passivation layers on the electrodes formed during direct current operation [5]. The main goal of this study was to investigate the effect of polarity reversal on the reaction and electrode fouling mechanisms as well as the performance of electrocoagulation for the treatment of SAGD produced water.Total organic carbon and silicon removal efficiencies were measured to evaluate treatment performance. Laser scanning confocal microscopy was used to monitor the pH distribution close to electrodes as well as the formation of solid products in an electrocoagulation cell. Customized polycarbonate bench scale reactors were used to study the relationship between coagulant production, polarity reversal frequency, solution composition, and flowrate. The cycle time of the polarity reversals was varied from 5 to 600 s, and the Reynolds numbers was varied between 30 to 200. The Faradaic efficiencies for the coagulant dissolution at different operating conditions were determined by digesting the solid products followed by elemental analysis.The evolution of pH during polarity reversal revealed that at higher frequencies or higher flow rates, the thickness of the interfacial pH boundary layer was lower. The quantification of pH was used to study the effect of pH on passivation layer stability. It was found that at higher frequencies, Faradaic efficiencies were lower for EC with iron electrodes, whereas increased efficiencies were observed for aluminum electrodes due to increased susceptibility to non-Faradaic corrosion. EC using aluminum electrodes (Al-EC), employing polarity reversal at all frequencies led to a reduction in cell voltage and therefore a reduction in the required energy for treatment.

The electrochemistry of chalcopyrite in alkaline solutions

This paper summarizes the results of a study of the anodic characteristics of chalcopyrite in alkaline hydroxide and carbonate solutions. The cathodic reduction of oxygen, peroxide and hypochlorite have also been investigated as possible oxidants in a two-stage process for the heap leaching of chalcopyrite under alkaline conditions.Mixed potential measurements of chalcopyrite in alkaline solutions showed that the reactivity of the common oxidants is in decreasing order hypochlorite > peroxide > oxygen >> chlorate.Anodic oxidation of chalcopyrite involves active oxidation at low potentials followed by a passivation peak and transpassive oxidation at higher potentials. The kinetics of oxidation is favoured by increasing pH in both hydroxide and carbonate solutions. The formation of solid products of oxidation does not prevent continued oxidation for up to 18 h at potentials below the peak. Coulometric measurements suggest that both thiosulfate and sulfate ions are produced by oxidation in sodium hydroxide solutions while thiosulfate is the main product in carbonate and bicarbonate solutions.At potentials close to the mixed potentials, the rate of reduction of hypochlorite is approximately first-order in hypochlorite concentration and is greater at low hydroxide ion concentrations. The rate of the cathodic reduction of peroxide is also greater at lower pH values but is complicated by the surface catalysed disproportionation of peroxide to water and oxygen.Rates of oxidation of chalcopyrite by both hypochlorite and peroxide in sodium hydroxide solutions have been estimated. The rates in hypochlorite are an order of magnitude greater than those in peroxide solutions and are of the same order of magnitude as those previously measured for the dissolution of chalcopyrite in ammoniacal solutions with copper(II) ions as the oxidant.