Journal of Chemical Technology and Metallurgy

FROM STRUCTURE TO ACTIVITY: A COMPREHENSIVE REVIEW OF THE ANTIBACTERIAL PEPTIDE ANOPLIN

Heba Mzik — 2026-07-01

Biologically active peptides are a promising alternative of the existing medical drugs used in the medicinal practice. Especially, antimicrobial peptides are such an alternative to conventional antibiotics considering the growing prevalence of antimicrobial resistance. Anoplin, a short decapeptide isolated from the venom of the solitary wasp Anoplius samariensis, has attracted attention due to the simple structure and membrane - targeting feature. This review summarizes current knowledge on the synthesis, structural characteristics, and biological activity of anoplin, with emphasis on structure - activity relationships and modification strategies. The activity of anoplin is closely related to its cationic and amphipathic nature. This allows interaction with bacterial membranes and leads to membrane disruption and cell death. Various modification approaches, including amino acid substitution, lipidation, and structural stabilization, have been applied to improve anoplin’s antimicrobial activity, selectivity, and stability. In addition, environmental factors such as ionic strength, pH, and proteolytic degradation significantly affect biological performance and bioavailability. Although anoplin shows relatively low susceptibility to resistance development, limitations related to stability and cytotoxicity is still a main disadvantage. Therefore, further optimization is required to enhance its therapeutic potential. Anoplin can serve as a useful model for the rational design of new antimicrobial peptides and peptide - based therapeutic agents.

ALKENYL SUCCINIC ANHYDRIDE AS A COMPOUND TO REDUCE WATER ABSORPTION IN THE PRODUCTION OF FIBERBOARD WITH PHENOL FORMALDEHYDE RESIN

Stoyko Petrin — 2026-07-01

This study investigates the effect of alkenyl succinic anhydride (ASA) as an additive for improving the water resistance of wood fiberboard produced with urea-formaldehyde (UF) resin. The modulus of elasticity (MOE) showed a decreasing trend with increasing ASA content with reductions of 17 % to 35 % at 2 - 8 wt. % ASA, respectively, suggesting insufficient interfacial adhesion between the resin and ASA. However, at 10 wt. % ASA, no significant decrease in MOE was observed, indicating an improvement in crosslinking at higher additive levels. A similar trend was observed for bending strength (MOR), which decreased by an average of 1.77 - fold with increasing ASA content. In contrast, the addition of ASA significantly improved water - related properties. Water absorption decreased by up to 3 - fold and thickness swelling decreases 5 - fold.

ADSORPTION OF Cu(II) IONS ON NEWLY PREPARED ACTIVATED CARBON FROM HAZELNUT SHELLS: TEXTURAL ANALYSIS AND EFFICIENCY EVALUATION

Liliya Manoilova — 2026-07-01

The present study aims to obtain and characterize activated carbon obtained from hazelnut shells and evaluate its adsorption capacity towards Cu2+ ions. The synthesis includes pyrolysis at 700оC and subsequent chemical activation with KOH (1:1 ratio) at 500оC. The obtained activated carbon (ACH) was characterized by elemental analysis, nitrogen adsorption (BET method), FT-IR spectroscopy and scanning electron microscopy (SEM). The results show the formation of carbon with a well-developed microporous structure and high specific surface area. The performed FT-IR analysis confirms the presence of oxygen-containing functional groups on the surface. Adsorption tests demonstrate high efficiency of ACH in removing Cu2+ ions from aqueous solutions. The obtained data prove that hazelnut shells are a suitable raw material to produce activated carbon, which appears as a promising and sustainable adsorbent
for water purification from heavy metals.

CHARACTERIZATION OF ACTIVATED CHARCOAL FROM NUTMEG SHELL PYROLYSIS (Myristica fragrans houut) USING ACTIVATORS CaCl2 AND ZnCl2

Johny Zeth Lombok — 2026-07-01

A study was conducted on the characterization of activated carbon from pyrolyzed nutmeg shells (Myristica fragrans houut) using CaCl₂ and ZnCl₂ solution activators. This study aims to determine activated carbon’s surface morphology and composition from nutmeg shells activated with CaCl₂ and ZnCl₂ solutions. The research stages include pyrolysis, activation, and characterization. The results showed that the pyrolysis of 6 kg of nutmeg shells produced a charcoal yield of 3.2 kg, liquid smoke of 1.1 L, tar of 65 g, and non-condensed gas. The pore diameter data using Scanning Electron Microscopy (SEM) of activated carbon activated with CaCl₂ and ZnCl₂ solutions were 3.72 and 3.02 μm, respectively. In comparison, the pore diameter of nutmeg shell carbon before activation was 3.09 μm. The composition data of activated carbon activated with CaCl₂ and ZnCl₂ solutions using Energy Dispersive Spectroscopy (EDS) showed the presence of Carbon, Oxygen, Aluminium, and Calcium elements, with the most significant composition being carbon at 58.36 % and 67.10 %. In comparison, nutmeg shell carbon before activation showed the presence of carbon of 64.39 %. The spectrum data of Fourier Transform-Infra Red analysis indicates that nutmeg shell carbon before activation and activated carbon activated with CaCl₂ and ZnCl₂ solutions show the presence of absorption areas of functional groups at relatively the exact wavenumber, namely O-H, aromatic C-H, aliphatic C-H, C=C, and C-O.

PRODUCTION AND PROPERTIES OF OXIDATIVE-ORGANOSOLVENT

Iryna Trembus — 2026-07-01

The article presents the results of research on the production of cellulose from non-wood plant raw material - Miscanthus giganteus stems - using the oxidative-organosolv pulping method. It was established that, in terms of the content of major components (cellulose and lignin), the raw material is comparable to wood, although it exhibits higher ash content and increased pentosan levels. Optimal delignification parameters in the acetic acid - water - hydrogen peroxide system at a temperature of 100°C and a duration of 180 min provide a cellulose yield of 57.92 % with a residual lignin content of 1.84 %. Morphological and fractional analysis revealed a decrease in fiber length after refining and an increase in the proportion of fine fractions. The experimental results substantiate the feasibility of using citric acid as a catalyst, with an optimal concentration of 0.5 % relative to the oven-dry weight of the raw material. It was determined that the residual concentration of peracetic acid after cooking is only 27 % of the initial level, which prevents the effective reuse of spent liquor in subsequent delignification of plant biomass. The obtained results confirm the potential of miscanthus as a promising raw material for pulp and paper production.

KINETICS OF [Co(tpy)2]2+ DISSOCIATION IN AOT/HEPTANE AND CTAB/CHLOROFORM/HEXANE REVERSE MICELLES: A COMPARATIVE STUDY

Leela Kumari Bodasingi — 2026-07-01

A comparative study of the kinetic study of dissociation of [Co(tpy)₂]²⁺ was carried out in two distinct reverse micellar environments, namely AOT/heptane and CTAB/hexane/chloroform. The observed reaction rates were significantly higher in the reverse micellar media compared to an aqueous medium, where the reaction was notably slow and incomplete {k_CTAB = 6.9×10^-5 s^-1 < k_AOT = 31.5×10^-3 s^-1}. The enhanced reaction rate in reverse micelles was explained in terms of the lower dielectric constant of water present in the reverse micelles. Analysis revealed that, the rate of reaction decreases with increasing the W {= [H₂O]/[surfactant]}in both the reverse micellar media. The reaction rate increases with the concentration of the anionic surfactant (AOT) but independent of the concentration of the cationic surfactant (CTAB). The dependence of rate of reaction on surfactant concentration in the case of AOT
has been explained on the basis of electrostatic interactions between electro positively charged complex [Co(tpy)₂]²⁺ and charge of anionic micellar interface.

А COMPLETE NMR DATA ASSIGNMENT FOR THREE DISPIROCOMPOUNDS

Marin Marinov — 2026-07-01

The synthesis of three new dispirocompounds containing imidazolidine dione and isatin fragments as main building blocks each bonded to different ring substituents (i.e. tetraline, 1,4-diazepine, 1,5-benzothiazepine, fluorene) by a spirocarbon was reported. The heterocyclic compounds were obtained with high yields by applying novel and efficient synthetic procedures accompanied with melting point determination. The structures of the synthesized spirocompounds were verified by using a combination of 1D (¹H, ¹³C, DEPT 135) and 2D NMR techniques (¹H-¹H COSY, HSQC, HMBC). Fully assigned NMR data was presented for each heterocyclic derivative supported by partially assigned ATR-IR data. Cycloalkanespirohydantoins possess anticonvulsant properties similarly to benzothiazepines. Thus, it is expected that the newly synthesized compounds would be biologically active.

SYNTHESIS OF TiO2 NANOPARTICLES USING DURIAN PEEL EXTRACT FOR INDIGO CARMINE DYES PHOTOCATALYTIC DEGRADATION

Dosi Novita Sari — 2026-07-01

TiO₂ nanoparticles were successfully synthesized via a sol - gel using Durian (Durio zibethinus) peel extract as a green and sustainable approach for photocatalytic applications. The peel extract acted as a natural stabilizing and capping agent, with its bioactive compounds promoting the formation of nanocrystalline anatase (5 - 10 nm) exhibiting good colloidal stability and a bandgap of 3.2 eV. Photocatalytic evaluation showed that the bio-based TiO₂ nearly achieved ± 99 % degradation of indigo carmine within 60 min, comparable to commercial TiO₂. According to the result, utilization of durian peel extract for TiO₂ synthesis offers a sustainable strategy with potential application in textile wastewater treatment and contributing to circular economy practices.

SONO-ELECTROCHEMICAL PULSE DEPOSITION OF NiP COMPOSITE COATINGS

Katya Ignatova — 2026-07-01

The growth rate, elemental composition and morphology of electrodeposited NiP composite coatings in pulse mode with ultrasound stirring were investigated. NiP(C) composite coatings include graphite (C) and NiP(Prts) coatings - oxide bimetallic particles Prts, mainly of SnO and NiO. When increasing the temperature to 60 - 70 oC at a concentration of graphite in the solution of 2 g L^-1, the growth rate of the coatings decreases compared to that at room temperature (from 11 - 13 to 8 9 mg cm^-2 h^-1). The application of ultrasonic stirring and higher temperatures (60 - 70^oC) increases the phosphorus content in the NiP(C) coatings to 16.38 wt. % Р. In the same conditions, a coarsening of the structure of NiP(C) coatings is observed. NiP(Prts) coatings grow slower than those with graphite
particles and are composed of nanosized spheroidal crystals. At higher content of bimetallic oxide particles in the solution, deposited NiP(Prts) coatings double their tin content at the expense of nickel (33.12 wt. % Ni, 15.95 wt. % P, 42.34 wt. % Sn), making the coating suitable for application as an anode material in Li-ion batteries.

CORROSION AND CAVITATION IN TUBE FURNACES DURING THE HEATING OF WATER - CONTAMINATED OIL

Serhiy Nesterenko — 2026-07-01

In coking plants, tube furnaces are used to heat tar and oils, playing a crucial role in steam conservation. As a relatively expensive installation, they require careful maintenance to ensure serviceability and safe operation. Heating water-contaminated oil in a tubular furnace leads to severe metal corrosion, characterized by hemispherical cavities. The study of metal structure was carried out by light microscopy (metallographic method) on specially made micro disks. While intergranular corrosion is absent, signs of cavitation-induced damage are evident. Water contamination significantly increases the vapor phase fraction, particularly at reduced flow pressure and elevated temperatures, promoting cavitation and erosion within the tube bundle. Hydraulic calculations indicate that under turbulent flow conditions, with a pressure of 1 bar, 20 % water content, and a temperature of 160°C, cavitation becomes inevitable. This phenomenon accelerates corrosion, especially in the presence of aggressive compounds such as ammonium chloride. Electrochemical analysis confirms a high corrosion rate in oil contaminated with water.

Gravimetric measurements reveal the aggressive nature of oil vapours toward carbon steel due to the release of corrosive coke oven gas components (H₂S, NH₃, HCN). The findings highlight the critical role of cavitation in corrosion processes and emphasize the need for controlling water contamination in oil heating systems to mitigate equipment degradation.

CLIMATIC VARIABILITY AND ITS IMPACT ON HYDRAULIC LOAD AND OPERATIONAL RISK IN ACID MINE DRAINAGE TREATMENT IN AN OPEN-PIT COPPER MINE

Aleksandar Grigorov — 2026-07-01

This study presents a long-term assessment of acid mine wastewater treatment at an open-pit copper mine in the Republic of Bulgaria, with the aim of evaluating treatment efficiency, the influence of climatic factors on hydraulic loading, and associated operational risks. A comprehensive dataset covering the period 2015 - 2025 was analysed, including pH, concentrations of Cu, Mn and SO₄^2-, mine water flow, and key meteorological parameters. The results demonstrate stable neutralization and consistently high removal efficiency of copper and manganese (> 93 %), with effluent concentrations remaining below regulatory limits. In contrast, sulfate removal remains limited and variable, reflecting the inherent constraints of neutralization-based treatment processes. A moderate positive relationship
between monthly precipitation and generated mine water flow was identified (r = 0.5592, Pearson), enabling the development of an empirical regression model for predicting hydraulic loading. Based on this relationship, a three-tier hydraulic risk classification was proposed, incorporating a conservative safety factor to define operational thresholds under variable precipitation conditions. The proposed approach enables the use of forecasted precipitation as an early indicator of hydraulic load, supporting proactive and adaptive management of treatment facilities. The results highlight the importance of integrating monitoring and meteorological data to improve predictability, optimize resource use, and ensure stable system performance under changing climatic conditions.

CHARACTERIZATION AND POSSIBILITIES FOR UTILIZATION OF INDUSTRIAL WASTES FROM PROCESSING, BENEFICIATION OF MINERALS, AND SMELTING

Ilian Djobov — 2026-07-01

The aim of this study is the characterization of some of main inorganic wastes for Bulgaria as slag and ash from lignite - fired power plants, clinker and lead slag from the lead and zinc smelting industry, and fayalite waste from copper smelting production. The chemical and phase compositions and particle size distribution of the waste materials were determined using XRF, XRD and laser diffraction, respectively. Hot stage microscope was used to evaluate the thermal behaviour of the samples. SEM was used to study the microstructure of the sample.
The studied wastes contain mainly oxides of silica, aluminium, calcium and iron which also are basic for the building ceramics. In addition, they are finely dispersed with particle sizes below 1 mm, so they can be used without crushing or milling. However, due to the various and complex mineralogical composition the samples are characterized with different thermal behaviour.
The fly ash contains high percentage of amorphous phase, together with plagioclase, magnesium ferrite, quartz and some gypsum. As a result, it is chartered with wide firing interval at about 1200°C and can be considered as a main raw material for new building ceramics.
The lead slag contains less aluminium and silica and main crystal phases from the melilite group. It easy forms liquid phase at lower temperatures, so that can be considered as an alternative flux.
Finally, the waste from copper smelting production, which mainly contain fayalite and magnetite, melts at the highest temperature. It cannot be considered as a flux but can be used as a filler in ceramic batches or as raw material for geopolymers as well.
From the studied wastes only the bottom ash, due to the extremely high gypsum content, and the clinker slag, because of presence of high amount carbon and metal iron, are not appropriate for direct usage in ceramic industry.

EU CONSUMER LAW AND PLANNED OBSOLESCENCE: A BULGARIAN PERSPECTIVE ON SUSTAINABILITY AND RIGHT OF REPAIR

Petya Romanova — 2026-07-01

Planned obsolescence is a practice used by companies to make a product intentionally unusable after a certain period of time or otherwise make it obsolete, in order to increase sales by requiring premature product replacement. This phenomenon has a negative impact on sustainability, as it leads to waste of resources, pollutes the environment and increases the consumption of raw materials for new production processes. This article aims to analyze the legal problem of planned obsolescence in the context of consumer sales, in light of the current European regulatory framework, including its implementation in Bulgaria. With a particular focus on sustainability, the article aims to illustrate the problems and proposed solutions.

EXPLORING ALKALINE PERIODATE SALTS AS ECO-FRIENDLY OXIDIZERS FOR SOLID ROCKET PROPELLANTS

Hristofor Skandaliev — 2026-07-01

The development and experimental characterization of composite solid rocket propellants utilizing alkaline metaperiodates (KIO₄ and NaIO₄) as alternative oxidizing agents are presented. The physicochemical, mechanical, and sensitivity properties of these formulations were systematically evaluated. Differential thermal analysis was conducted to investigate high-temperature decomposition behaviour and to identify the dominant reaction mechanisms. Limited ballistic testing, including laboratory-scale ground tests and experimental rocket flights, was conducted to assess the practical feasibility of these systems. Comparative analysis with conventional composite propellant formulations demonstrates that periodate-based systems can achieve functional energetic and ballistic performance within specific application domains, while potentially offering environmental benefits. These findings indicate that alkaline metaperiodates constitute a promising class of oxidizers for environmentally focused energetic material systems.

COMPARATIVE STUDY OF FLAME BEHAVIOR IN INDUSTRIAL KILN SYSTEMS

Adnan Ghareeb Tuaamah Al-Hasnawi — 2026-07-01

Annular ring burners are widely used in industrial kilns, such as tunnel, shaft, and rotary kilns, because they provide consistent and controlled burning. To investigate how operational parameters, such as air to fuel ratio, air velocity, O₂ concentration in combustion gases, and air inlet diameter, affect flame behaviour, including temperature distribution and flame length, this study uses ANSYS Fluent to simulate non - premixed methane flames in a rotary kiln. The results show that lower intake diameters are associated with increased air velocity, which leads to shorter flames. Additionally, compared to flames in combustion gas conditions, flames in ambient air have higher peak temperatures and longer durations.

INVESTIGATION OF THE FUNCTIONAL PROPERTIES OF STRONTIUM HEXAFERRITE SrFe12-xCrxO19, DOPED WITH CHROMIUM, WITH A DEGREE OF SUBSTITUTION X UP TO 7.5

Alena Zykova — 2026-07-01

Strontium hexaferrite with a high degree of iron substitution by chromium (SrFe_12-xCr_x O₁₉, at x = 6.5 - 7.5 with a step of x(Cr) = 0.5) was obtained by solid - phase synthesis at an isothermal exposure temperature of 1500°C. Analysis of the results of XRD X - ray diffraction and scanning electron microscopy (SEM) confirmed the formation of single - phase hexagonal M - type ferrites upon substitution with Cr ions from x = 6.5 to x = 7.5. Previously, using the same method at a temperature of 1400°C, we synthesized and obtained the results of X - ray, morphology, elemental analyses and magnetic properties for single-phase samples of SrFe_12-xCr_xO₁₉ with x = 0 - 6 [1]. This article studies the effect of doping with Cr 3+ ions on the structural and functional properties of hexaferrite SrFe_12-x Cr_xO₁₉ x = 0 - 7.5. The temperature and frequency dependences of the initial magnetic permeability of the obtained ferrites have been studied. It was found that the substitution of iron with chromium leads to a decrease in the Curie temperature. Studies of the electrical properties of the obtained materials were carried out in the frequency range of 25 Hz - 3 MHz at room temperature. An analysis of the dielectric properties showed that an increase in the content of Cr³⁺ ions in SrFe_12-xCr_xO₁₉ leads to a decrease in the dielectric constant, dielectric losses, the tangent of the dielectric loss angle and an increase in the complex resistance. The results of the study demonstrate the dependence of electrical properties on the frequency of the applied field and the concentration of dopant.

CHARACTERIZATION ASSESSMENT OF COLUMBITE ORE FOR NIOBIUM PENTOXIDE VALUE ADDITION FOR ORTHOPEDIC APPLICATION

Kenneth Kanayo Alaneme — 2026-07-01

The demand for stable source for niobium pentoxide has market prospects for orthopedic implants, especially if economically sourced and processed. Columbite ore was extracted and sampled from four pits in Kuru mine site in Jos South Local Government Area, Nigeria. The columbite was processed using a three-disc rapid magnetic separator, and characterized using ED-XRFS, XRD, and SEM/EDS. The magnetic samples were mainly iron with impurities, while the ferromagnetic samples were columbite with niobium pentoxide, and the non-magnetic samples were more of silica. The crude was found to contain 32.1 % ZrO₂, 3.42 % ThO₂, 12.31 % Nb₂O₅, 6.65 % Fe₂O₃, 52.19 % SiO₂, and 1.61 % TiO₂, along with other trace compounds. The 45 A current application yielded the highest ferromagnetic product with a high grade of Niobium pentoxide, with a recovery rate of 67.67 %. The sample morphology showed coarse interlocking within crystal aggregates in the ore matrix. The elements present were Ti, Al, Mn, O, B, Ta, and Nb. The processed concentrate sample contained 1.8414 % SiO₂, 13.9485 % TiO₂, 20.9295 % Fe₂O₃, 46.5767 % Nb₂O₅, 7.9113 % Ta₂O₅, and other constituent compounds in trace form. The processed tailings sample contained 12.1418 % MgO, 4.3061 % Al₂O₃, 1.3150 % SO₃, 40.8441 % SiO₂, 4.8829 % CaO, 6.4475 % Cr₂O₃, 25.9409 % Fe₂O₃, and 1.0330 % NiO.

DELING OF THE MICROSTRUCTURE EVOLUTION OF A STEEL BILLET DURING THE VARIOUS TYPES OF ROLLING IN RELIEF ROLLS

Dmitry Panin — 2026-07-01

The paper presents the results of microstructure evolution obtained by finite element modeling in the DEFORM program for various types of rolling in relief rolls: symmetric rolling, asymmetric rolling with an asymmetry coefficient of 1.5 due to the roll diameters of 200 and 300 mm, as well as single-drive rolling, in which one of the rolls is driven and the other roll is idling. After rolling in relief rolls, the billet undergoes two-stage leveling in smooth rolls. The presence of a single driven roll with the ability to adjust its rotational speed allows for a higher asymmetry coefficient. The microstructure evolution was evaluated using the Cellular Automata method, which allows for the assessment of changes in both the size and shape of the grains. It was found that using a billet with a heating temperature of 700°C is the most preferable option in all cases, as it eliminates the negative effect of static recrystallization, and the implementation of single-drive rolling allows for the highest degree of grain refinement.