The expansion of industrialization and household use of synthetic compounds has generated significant wastewater containing toxic heavy metals. In developing countries, this wastewater is often discharged untreated due to the high cost of advanced treatment technologies. This study used sodium hydroxide as a low-cost, readily available precipitation agent to remove selected metal ions from mono- and binary-component solutions. Unlike most studies focusing on pH and initial ion concentration, this work investigated operational parameters such as stirring speed (0–800 rpm) and time (0–30 min) while keeping pH and concentration constant. Results showed that higher stirring speeds and longer stirring times enhanced metal ion removal, with Pb(II) efficiency increasing from 86.64% at 100 rpm to 94.33% at 800 rpm. In binary mixtures, similar improvements were observed. These findings highlight that simple, low-cost operational adjustments can significantly improve metal removal efficiency, which is particularly relevant for water treatment in resource-limited settings. The two-way ANOVA without replication showed that the type of metal or mixture had a significant effect on removal efficiency, while stirring speed and time within the investigated ranges did not have a statistically significant effect. These results indicate that differences in removal efficiency are primarily due to the metals’ chemical properties rather than the operational parameters.

Maleic anhydride is a key intermediate in the chemical industry, predominantly produced through the partial oxidation of n-butane over vanadium-phosphorus-oxide (VPO) catalysts. This reaction is accompanied by side reactions that lead to the formation of undesired by-products, primarily CO and CO₂. In this work, a previously developed mathematical model of a fixed-bed tubular reactor was extended to include a catalyst activity function accounting for catalyst deactivation, and the kinetic parameters were optimized using experimental data from an industrial reactor at Koksara d.o.o. Lukavac. The model describes the partial oxidation of n-butane to maleic anhydride through multiple reactions, with reaction rates expressed as functions of temperature, partial pressures, and catalyst activity. Numerical simulations were performed using MATLAB, employing a nonlinear least-squares solver to minimize the deviation between the predicted and measured temperature profiles along the reactor. The validated model showed good agreement with experimental data, demonstrating its capability to accurately simulate reactor behavior under typical industrial conditions. Parametric studies were conducted to analyze the effects of inlet n-butane and oxygen flow rates, reaction mixture temperature, and pressure on the formation of CO and CO₂. The results indicate that by-product formation is strongly influenced by the oxygen/n-butane ratio, temperature, pressure, and the catalyst oxidation state. Higher oxygen flow rates and elevated temperatures increase CO and CO₂ formation, while lower values reduce their production. Changes in n-butane flow have a minor effect on CO₂, but more pronounced effects on CO due to the interplay between partial and complete oxidation at different catalyst sites. Increasing the inlet pressure enhances by-product formation by increasing reactant concentrations, whereas reduced pressure decreases CO and CO₂ formation. The developed model provides a practical tool for understanding and optimizing industrial maleic anhydride production. It offers insights into the effects of key process parameters on by-product formation, supporting improved reactor operation, reduced trial-and-error experimentation, and more efficient industrial process design.

Optimal process conditions for carbonate precipitation of selected heavy metal ions were tested in laboratory conditions using Na2CO3. To the prepared synthetic monocomponent and binary multicomponent solutions of heavy metals with initial concentrations of 500 mg/L, Na2CO3 was added in certain doses at selected mixing speeds (0, 100, 300 and 800 rpm) and mixing time (0, 15, and 30 minutes). The results show the removal efficiency at optimal mixing speeds for monocomponent metal solutions were: Cu(II) 96.394% (300 rpm), Ni(II) 94.594% (0 rpm and 800 rpm), Pb(II) 75.968% (0 rpm ), Zn (II) 99.311% (0 rpm). In binary multicomponent mixtures Cu(II)-Ni(II) and Pb(II)-Zn(II) the removal efficiency results at optimal mixing speeds were: Cu(II) 96.394% (100 rpm), Ni(II) 95.528% (800 rpm), Pb(II) 99.536% (300 rpm), Zn(II) 98.945% (100 rpm). Also, the results of the efficiency of heavy metal removal due to the influence of the contact time of the precipitant and heavy metal ions in monocomponent solutions show the following values: Cu(II) 99.940% (0 min), Ni(II) 94.612 % (0 min), Pb(II) 77.925 % (15 min), Zn(II) 99.324% (30 min), while in binary multicomponent mixtures Cu(II)-Ni(II) and Pb(II)-Zn(II) they were for Cu(II) 96.247% (30 min), Ni(II) 95.521% (0 min), Pb(II) 99.350% (30 min) and Zn(II) 98.944% (0 min). Examination of the influence of the mixing speed of monocomponent solutions showed that the efficiency of removing heavy metal ions was in most cases the best without mixing. Effect of metal-precipitant contact time on the efficiency of heavy metal ion removal showed that in half of the examined metals, the optimal values ​​were chosen as the best (0 and 30 min). It can be concluded that this method based on chemical precipitation using Na2CO3 with optimal parameters such as contact time and mixing speed, can be used in the treatment of industrial wastewater.

The incorporation of waste glass as a component in clinker production presents a sustainable approach to addressing critical challenges in the cement industry, including the reduction of CO2 emissions and effective waste management. Waste glass, characterized by its high silica content and alkali properties, can serve as an alternative alkali source in clinker manufacturing, replacing traditional raw materials and regulating the alkali-sulphur ratio. This dual functionality not only optimizes the chemical balance in the kiln process but also enhances clinker quality by controlling phase formation. The utilization of waste materials in industrial processes is increasingly significant in promoting circular economy principles. Integrating waste glass reduces the dependence on natural raw materials such as limestone and clay, which are associated with high energy and CO2 emission intensities during production. Furthermore, waste glass contributes to a reduction in the carbon footprint of cement production by facilitating lower-temperature clinkering, thus cutting energy consumption and greenhouse gas emissions. This study highlights the potential of waste glass as a viable alternative in clinker production, emphasizing its importance in achieving sustainability goals. Beyond the environmental benefits, adopting waste materials in industrial applications contributes to waste diversion from landfills, resource conservation, and cost efficiencies, aligning with global efforts to mitigate climate change and promote sustainable development.

In this paper a mathematical model for the soda ash drying process in a pneumatic dryer was presented. The model presents a macroscopic aspect of the drying process, for a two-phase, gas-solid system. The model is based on mass and heat transfer between the gas phase and the particle, movement of air and particles through the system, and geometric characteristics of the drying system (fan, air heater, pneumatic dryer, and cyclone). The effects of the process parameters, such as airflow, inlet air temperature, and relative humidity, temperature at the inlet of the dryer, etc., have been studied by solving the model. Also, the model was tested for different values of the capacity of wet soda and different values of the operating parameters of the heating medium. The model was implemented in MATLAB and solved with a nonlinear equations solver. Data obtained by the model were compared with industrial pneumatic dryer data for drying wet soda ash particles with good agreement.

A simulation of a single-stage evaporator system integrated with a mechanical com- pressor for a case study (concentrating the electrolytic system KNO3 – H2O) was performed. A mathematical model of the subsystem of a single-stage evaporator, a mechanical compressor, and superheated steam seeding is presented. Microsoft Excel with VBA (Visual Basic for Application) was used to solve the mathematical model. The model was solved by an iterative method where the values of the in- let stream temperature and the salt concentration in the concentrated stream at the evaporator outlet were assumed. The process parameters of the system have been determined. Since the goal of any industrial process is to minimize costs and maximize products, the impact of mean temperature difference changes on satu- ration water consumption and molar salt content in the concentrated stream was presented. 106.92 kg/h of freshwater are required to obtain 18% by weight of salt in a concentrated stream, while 432.30 kg/h of fresh water are required to obtain 25% by weight of salt in a concentrated stream. Consumption of heating steam ranged from 1760.31 to 4473.4 kg/h depending on the average temperature dif- ference. By increasing the temperature differences from 10 to 25 ◦C, the amount of transferred upper lines increases from 1025 to 2750 kW, which is an advantage of increasing the mean temperature difference. The disadvantage of the larger tem- perature difference is the increase in the power of the mechanical compressor from 97.02 to 384.12 kW.

The aims of this study were to determine improved kineticparameters in five kinetic models for oxidation of n-butane intomaleic anhydride in an industrial fixed-bed reactor, and tosimulate the reactor performance. On the basis of the measuredprocess parameters, inlet and outlet concentrations of n-butanewere calculated and then used to fit the kinetic models. Theindustrial fixed-bed reactor was approximated by 10 continuousstirred tank reactors (CSTR) connected in series. Based on thecalculated outlet concentration of n-butane from the industrialreactor, the outlet concentration of n-butane from thepenultimate reactor was calculated. Then the concentrations ofn-butane were calculated until the inlet concentration of nbutanein the first reactor was obtained. Kinetic parameterswere determined by comparing the inlet concentrations of nbutanein the first reactor with the inlet concentration of nbutaneobtained on the basis of the measured processparameters in the industrial fixed-bed reactor. Kinetic modelswith improved kinetic parameters showed better simulationresults compared to kinetic models with the existing kineticparameters. The best agreement of simulation results andmeasured values was achieved with application of the kineticmodel 2 (Equations (2a-c)). The smallest deviations ofnumerical simulation in comparison with measured values of theoutlet pressure of reaction mixture were 0.45, 0.75 and 0.75%for application of the kinetic model 3 (Equations (3a-c)). Thepercentage deviations of numerical simulation with improvedkinetic parameters and the existing kinetic parameters incomparison with measured values of inside reactor temperaturewere in the range 0.90-5.36% and in the range 4.17-9.78%(kinetic model 2, Equations (2a-c)), respectively.

The objectives of this study were to develop and validate the mathematical model (kinetic and reactor model) of composting process, as well to used validated model in order investigate the effects of the air flow rate on organic matter conversion, carbon dioxide concentration and mixture temperature. The mathematical model incorporated two microbial populations that metabolized composting material which was split into two different fractions according to its degradability (easily-degradable and hardly-degradable). Comparisons of simulation and experimental results for five dynamic state variables demonstrated that the model has very good predictions of the composting process. Simulations with validated model showed that among three dynamic state variables (organic matter conversion, carbon dioxide concentration, mixture temperature), carbon dioxide concentration is the most sensitive while organic matter conversion is the least sensitive to the change of air flow rate.

The aim of this study was to determine the composting kinetics for mixture of poultry manure and wheat straw based on the volatile solids content. Experimental data was fitted with the first-order and the nth-order kinetic model. The nth-order kinetic model showed better prediction performance than the firstorder kinetic model. For the first-order kinetic model, maximum and mean differences between experimental and simulation results for the content of volatile solids were 5.43% and 3.00%, for the first reactor, and 4.68% and 2.12% for the second reactor, respectively, for the nth-order kinetic model, maximum and mean differences were 4.92% and 1.68%, for the first reactor, and 4.09% and 1.42% for the second reactor, respectively.