OPTIMIZATION OF LEACHING OF COPPER FROM OXIDIZED COPPER ORE IN NH3-(NH4)2SO4 MEDIUM

Studies were carried out for selective leaching of Cu with simultaneous avoidance of iron dissolution during leaching of oxidized copper ore in an aqueous NH₃-(NH₄)₂SO₄ system. The effects of leaching parameters, such as ammonia concentration, ammonium sulphate concentration, leaching time, and solid-to-liquid ratio, were investigated on leaching of copper. A 2ⁿ factorial experimental design method in the dissolution experiments was used. In addition, the “Steepest Ascent” method was also applied to determine the optimum leaching conditions. It was observed that the most effective parameters on the leaching of copper were ammonia concentration and leaching time. Only 0.17% of iron in ore was dissolved in ammonia and ammonium sulphate medium. The optimum conditions established for maximum copper recovery were: ammonia concentration 2.824 mol L^?1, ammonium sulphate concentration 0.236 mol L^?1, solid-to-liquid ratio 0.167 g mL^?1, leaching time 2 h. Fixed parameters chosen in the experiments were: room temperature, average particle size 2.8 mm, stirring speed 500 rpm. Under the optimum conditions established for maximum copper recovery, the percentage of leached copper was 98.87.     

EVALUATION OF LEACHING CONDITIONS FOR DISSOLUTION OF PYRITE IN CHLORINE-SATURATED WATER

The optimum leaching conditions for the dissolution of pyrite in water saturated with chlorine gas were investigated. Reaction temperature, solid-to-liquid ratio, reaction time, and particle size were selected as the leaching parameters. 2ⁿ factorial experimental design and orthogonal central-composite design methods were used. A mechanical stirring speed of 500 rpm and chlorine gas-flow rate of 1379 mL/minute were chosen as the fixed parameters in all experiments. The degrees of effectiveness from high to low were found to be, in respective order, the particle size, the reaction temperature, the solid-to-liquid ratio, and leaching time. A reaction temperature of 30°C, solid-to-liquid ratio of 0.167 g/mL, particle size of 150–212 μm, and reaction time of 360 minutes were found to be the optimum leaching conditions. The dissolution yield of iron from pyrite was 98.4% under optimal leaching conditions.     

Determination of the Optimum Conditions for Leaching of Malachite Ore in H2SO4 Solutions

The Taguchi method has been used to determine the optimum conditions for the dissolution of malachite ore in H₂SO₄ solutions. The chosen experimental parameters and their range were (i) reaction temperature: 15 to 45 °C, (ii) solid‐to‐liquid ratio: 1/10 to 1/3 g cm^–3, (iii) acid concentration (in weight): 2 % to 10 %, (iv) particle size: –40 to –3.5 mesh, (v) stirring speed: 240 to 720 rpm, and (vi) reaction time: 5 to 45 minutes. The optimum conditions were found to be reaction temperature: 40 °C, solid‐to‐liquid ratio: 1/3 g cm^–3, acid concentration (in weight): 10 %, particle size: –30 mesh, stirring speed: 480 rpm, and reaction time: 45 minutes. Under these optimum working conditions, the dissolution of copper and iron in malachite ore was 100 % and 58 %, respectively. Besides, alternative working conditions reducing the total cost and dissolution of iron were found.     

PRECIPITATION CONDITIONS OF CHEVREUL'S SALT FROM SYNTHETIC AQUEOUS CuSO4 SOLUTIONS

In this study, synthetic aqueous CuSO₄ solution was prepared at various concentrations. Chevreul's salt was precipitated by passing SO₂ through these solutions. Chevreul's salt, a mixed valence copper sulfite, Cu₂SO₃·CuSO₃·2H₂O, was characterized by XRD and SEM. The effects of parameters such as initial solution concentration, SO₂ feeding rate, reaction time, and initial solution pH on precipitation of Chevreul's salt were investigated. 2ⁿ factorial experimental design and orthogonal central composite design methods in the precipitation experiments were used. It was observed that the effective parameters on the precipitation of Chevreul's salt were initial solution concentration, SO₂ feeding rate, and initial solution pH. The optimum conditions obtained for maximum copper precipitation were: initial solution concentration 1.14 M, SO₂ feeding rate 329.35 L.h.^?1, reaction time 25 min, and initial solution pH 8.5. Constant parameters chosen at the initial stage of the reaction were: temperature 62°C, stirring speed 600 rpm, and reaction pH 3 (Çalban et al., 2006). Under these optimum conditions, the percentage of precipitated copper from synthetic aqueous CuSO₄ solutions was 99.95.     

Optimization of desulphurization of Artvin–Yusufeli lignite with acidic hydrogen peroxide solutions

In this study in which the Taguchi method was used, the optimization of sulphur removal by H₂O₂/H₂SO₄ solutions was carried out over lignite with higher content of sulphur from Artvin/Yusufeli, Turkey. In experiments, the ranges of experimental parameters were between 0.25 and 6.0 mol L⁻¹ for H₂O₂ concentration, 0.25–4 mol L⁻¹ for H₂SO₄ concentration, 10–60 °C for reaction temperature, 0.01–0.08 g mL⁻¹ for solid-to-liquid ratio, 15–120 min for reaction time, 200–300 rpm for stirring speed and 710–120 μm for particle size. The optimum conditions for these parameters have found to be 60 °C of temperature, 0.06 g mL⁻¹ of solid-to-liquid ratio, 60 min of reaction time, 250 rpm of stirring speed and −250 + 180 μm of particle size.A statistical experimental arrangement, L₂₅(5⁶) was prepared to determine optimum sulphur removal and ash removal ratios. The obtained yields were 97.85% in removal of total sulphur, 56.54% in removal of pyritic sulphur, 21.33% in removal of organic sulphur and 61.52% in removal of ash. According to variance analysis, it was seen that all parameters were effective in removal of pyritic and total sulphur, reaction temperature, solid-to-liquid ratio, reaction time, stirring speed, H₂O₂ and H₂SO₄ concentrations in removal of organic sulphur, and other parameters except acid concentration in removal of ash.     

Optimization of the Dissolution of Tincal Ore in Phosphoric Acid Solutions at High Temperatures

The aim of the study was to investigate the optimization of the dissolution of tincal ore in phosphoric acid solutions at high temperatures in a batch reactor. The effect of the following parameters on the dissolution process was investigated: the reaction temperature, the phosphoric acid concentration, the particle size, and the solid-to-liquid ratio. The best conditions for the dissolution were determined using the 2⁴ factorial experimental design method. The optimum values of the parameters were experimentally determined. The effective parameters were the reaction temperature, the phosphoric acid concentration, the particle size, and the solid-to-liquid ratio. The optimum conditions resulted in the maximum boron dissolution at an acid concentration of 1 M, reaction temperature of 85°C, particle size of 4.75 mesh, and solid-to-liquid ratio of 1/6 g · mL^?1. Under these optimum conditions, the best dissolution yield was 98.26%.     

Determination of Optimal Conditions for Retention of Sulfur Dioxide by Waste Ulexite Ore in an Aqueous Medium

The main aim of this study was to remove sulfur dioxide (SO₂), which is one of the most significant air pollutants emitted from thermal power stations, using waste ulexite ore, which cannot be recycled industrially and poses a risk for the environment. In experiments conducted at atmospheric pressure in an aqueous environment, the optimization of holding SO₂ with waste ulexite ore has been investigated comprehensively and determined how much SO₂ could be retained in solid waste. The Taguchi method was used to determine the optimal conditions, and the effectiveness of the parameters was identified by variance analysis. The selected parameters and their ranges were defined as temperature (293–333?K), solid to liquid ratio (0.4–0.6?g?mL^?1), particle size (150–600?µm), time (10–30?min), pH (5.5–7.5), and stirring speed (350–800?rpm). The optimal conditions for these parameters were determined to be 333?K, 0.45?g?mL^?1, ?250?µm, 15?min, pH 6, and 350?rpm, respectively. Among all the parameters, temperature and pH were found to be the most effective. The results of the study revealed that SO₂ can be retained in solid waste with calcium content of the boron minerals as CaSO₃?·?0.5H₂O and nearly whole B₂O₃ in the waste ulexite passes into solution. Under the optimum conditions, 86% of B₂O₃ passed into the solution and 75.2?L SO₂ was retained by 1?kg waste ulexite ore. Thus, both B₂O₃ recovery and SO₂ removal were materialized, while waste ulexite ore was evaluated and removed, simultaneously.     

Zinc deposition and dissolution in sulfuric acid onto a graphite–resin composite electrode as the negative electrode reactions in acidic zinc-based redox flow batteries

Electrodeposition and dissolution of zinc in sulfuric acid were studied as the negative electrode reactions in acidic zinc-based redox flow batteries. The zinc deposition and dissolution is a quasi-reversible reaction with a zinc ion diffusion coefficient of 4.6 × 10^?6 cm² s^?1 obtained. The increase of acid concentration facilitates an improvement in the kinetics of zinc electrodeposition–dissolution process. But too high acid concentration would result in a significant decrease in charge efficiency. The performance of the zinc electrode in a three-electrode system with magnetic stirring was also studied as a function of Zn(II) ion concentration, sulfuric acid concentration, current density, and the addition of additives in 1 M H₂SO₄ medium. The optimum electrolyte composition is suggested at high zinc(II) concentration (1.25 M) and moderate sulfuric acid concentration (1.0–1.5 M) at a current density range of 20–30 mA cm^?2. Whether in acid-free solution or in sulfuric acid solution with or without additives, no dendrite formation is observed after zinc electrodeposition for 1 h at 20 mA cm^?2. The energy efficiency is improved from 77 % in the absence of additives in 1 M H₂SO₄ medium to over 80 % upon the addition of indium oxide or SLS–Sb(III) combined additive as hydrogen suppressants.     

Ultrasonic Pretreatment Transesterification for Solid Basic-Catalyzed Synthesis of Fatty Acid Methyl Esters

Generally, ultrasound irradiation is required throughout the reaction for fatty acid methyl esters (FAME, namely, biodiesel) production, which is energy-consuming and difficult to scale-up. In order to improve the industrial application of ultrasonic technology, a systematic study of ultrasonic pretreatment solid basic (Na₂SiO₃)-catalyzed transesterification for FAME production from cottonseed oil was carried out, and the effect of ultrasonic waves on the properties of Na₂SiO₃ catalyst was assessed by X-ray diffraction (XRD), Fourier transform Infrared (FTIR) and scanning electron microscopy (SEM) characterization of fresh and collected catalysts. An ultrasonic frequency of 30 kHz, ultrasonic power of 200 W and ultrasonic pretreatment irradiation time of 30 min was determined to guarantee a satisfactory degree of transesterification. The optimum production was achieved in the reaction system at 45 °C with methanol/cottonseed oil molar ratio 5:1, catalyst dosage 3% and stirring speed 350 rpm resulting in a FAME yield of above 97% after 60 min of reaction under mechanical stirring with the ultrasonic pretreatment process. The new process has a shorter reaction time, a more moderate reaction temperature, a less amount of methanol and catalyst than only the mechanical stirring process without essential damage to activity and the structure of catalyst. These results are of great significance for applying the ultrasonic pretreatment method to produce FAME.     

Equilibrium Isotherms,Thermodynamics, and Kinetic Studies for the Adsorption of Food Azo Dyes onto Chitosan Films

The adsorption of FD&C red 2 and FD&C yellow 5 onto chitosan films (CFs) was evaluated by equilibrium isotherms, thermodynamics, and kinetic studies. The effects of temperature (298–328 K), initial dye concentration (50–300 mg L^?1), stirring rate (50–350 rpm), and contact time (0–120 min) were investigated at pH of 2.0 and 100 mg L^?1 of CFs. The dye concentration was determined by spectrophotometry. Freundlich and Langmuir models were used to represent the equilibrium data. The Langmuir model was the more adequate to represent the equilibrium data (R² > 0.99 and average relative error <2.50%) and the maximum adsorption capacities were 494.13 and 480.00 mg g^?1 for FD&C red 2 and FD&C yellow 5, respectively, obtained at 298 K. The R_L values ranged from 0.044 to 0.145. The adsorption was exothermic, spontaneous, and favorable. For the FD&C red 2, 90% of saturation was attained at 120 min and the Elovich model was the more appropriate. For the FD&C yellow 5, 95% of saturation was attained at 20 min and the pseudo first-order model was the more adequate to fit the kinetic data. CFs were easily separated from the liquid phase after the adsorption process, providing benefits for industrial applications, and its application range can be extended for azo dyes.     

OPTIMIZATION OF LEACHING OF COPPER FROM OXIDIZED COPPER ORE IN NH3-(NH4)2SO4 MEDIUM

Studies were carried out for selective leaching of Cu with simultaneous avoidance of iron dissolution during leaching of oxidized copper ore in an aqueous NH₃-(NH₄)₂SO₄ system. The effects of leaching parameters, such as ammonia concentration, ammonium sulphate concentration, leaching time, and solid-to-liquid ratio, were investigated on leaching of copper. A 2ⁿ factorial experimental design method in the dissolution experiments was used. In addition, the “Steepest Ascent” method was also applied to determine the optimum leaching conditions. It was observed that the most effective parameters on the leaching of copper were ammonia concentration and leaching time. Only 0.17% of iron in ore was dissolved in ammonia and ammonium sulphate medium. The optimum conditions established for maximum copper recovery were: ammonia concentration 2.824 mol L^-1, ammonium sulphate concentration 0.236 mol L^-1, solid-to-liquid ratio 0.167 g mL^-1, leaching time 2 h. Fixed parameters chosen in the experiments were: room temperature, average particle size 2.8 mm, stirring speed 500 rpm. Under the optimum conditions established for maximum copper recovery, the percentage of leached copper was 98.87.     

Dissolution kinetics of lead from a lead-oxide ore that consists mainly of cerussite by trichloroacetic acid and optimization of dissolution conditions

The dissolution kinetics of lead-bearing ore in trichloroacetic acid (TCA) solution were investigated. The effects of various parameters were studied to optimize the dissolution conditions and to determine the leach kinetics. An increase in leaching time, temperature, and TCA concentration, and a decrease in particle size enhanced the conversion rate. The results show that 99.26% of lead content was extracted from the samples with particle size range of –90 + 75 µm after 24 min leaching in 0.4 mol/L TCA at 800 rpm and 40°C. The following expression based on the Jander (three-dimensional) model can be described: [1–(1–x)^1/3]2 = 22.36 × 10^?3 (C_TCA)^1.1516(P)^0.55117(r)^0.92609exp (–20899/RT) t.     

Flue gas desulfurization by citrate process and optimization of working parameters

In this study, model flue gas was bubbled into 0.25 L tribasic sodium citrate (TSC) solution being in 0.5 L glass absorber to remove its SO₂ content. Size of gas bubbles, absorption temperature, gas flow rate, solution concentration and stirring rate were taken as working parameters to investigate their effect on SO₂ removal from flue gas. The Taguchi's experimental design method was used to obtain optimum values of working parameters for SO₂ saturation time of the TSC solution selected as a quality characteristic. The optimum levels of parameters to maximize the SO₂ saturation time of TSC solution were coarse bubbles for gas delivery, 35 °C for absorption temperature, 1.5 slm for gas flow rate, 0.5 M for TSC solution concentration and 500 rpm for stirring rate. Under these conditions, the SO₂ saturation time of the TSC solution was achieved as 511 min in average. The most effective parameters on the absorption of SO₂ in TSC solutions were ranked to the least as solution concentration, gas flow rate, size of gas bubbles, absorption temperature and stirring rate.     

Modeling of the nanocrystalline-sized mesoporous zinc oxide catalyst using an artificial neural network for efficient biodiesel production

The sulfonated mesoporous zinc oxide catalyst (SO₃H–ZnO) was hydrothermally fabricated and functionalized by sulfonation to catalyze the palm fatty acid distillate (PFAD) to esters. The effect of different reaction parameters including reaction time, reaction temperature, metal ratio, and calcination temperature was modeled by artificial neural networks (ANNs) to find out the possible relative optimum conditions of the synthesized mesoporous SO₃H–ZnO catalyst for the prediction of the nanocrystalline size. Under the optimized conditions of calcine temperature 700?°C, 18?min reaction time, 160?°C reaction temperature, and 4?mmol of Zn concentration predicted a 56.41?nm size of the mesoporous SO₃H–ZnO catalyst. The acquired model was statistically verified for its utility. The quick propagation model with four nodes in the input layer, six nodes in the hidden layer and one node in the output layer (QP-4-6-1) was chosen as the final model due to its optimum statistical characteristics. Furthermore, the most effective parameter was found to be the zinc concentration whilst the reaction time demonstrated the least influence. The optimized mesoporous SO₃H–ZnO catalyst was further utilized for esterification of PFAD, depicting a high fatty acid methyl ester yield (96.11%). It shows a valuable application for the conversion of discarded oils/fats containing high free fatty acids for the production of renewable green biodiesel.     

Preparation of a Sulfonated Porous Carbon Catalyst with High Specific Surface Area

A sulfonated (SO₃H-bearing) carbon catalyst with mesoporous structure and high specific surface area is successfully prepared by impregnating the cellulosic precursor (wood powder) with ZnCl₂ prior to activation and sulfonation. The specific surface area of the porous carbon catalyst thus prepared is also found to increase with carbonization temperature to a maximum of 1,560 m² g^?1 at ca. 773 K. Structural analyses reveal that the porous carbon catalysts carbonized at temperatures higher than 723 K contain high densities of micro- and mesopores. The porous carbon catalyst exhibits high catalytic performance for the esterification of acetic acid (343 K), the activity for which is dependent only on the acid density. The porous carbon catalyst also exhibits high catalytic activity for the benzylation of toluene, whereas non-porous sulfonated carbon has very limited activity for this reaction. The activity for the benzylation of toluene is dependent on both the specific surface area and the acid density of the sulfonated porous carbon catalyst.     

Epoxidation of waste used-oil biodiesel: Effect of reaction factors and its impact on the oxidative stability

Epoxidation of waste used-oil biodiesel (WUO-B) was performed to test the feasibility of properties improvement. The effects of the reaction temperature (30–50 °C) and time (2–12 h), molar ratio of H₂O₂: HCOOH (1: 7 to 1: 1) and the stirring rate (100–300 rpm) on the level of unsaturated carbon bond conversion and the epoxy compound selectivity were identified using a 2 ^k (two levels) factorial design. Besides epoxy biodiesel as the main product, only one by-product, hydroxyl-biodiesel, was generated. The conversion of unsaturated carbon bonds was positively affected by the molar ratio of H₂O₂: HCOOH and the stirring rate, while the reaction temperature and time had no significant affect (in the investigated ranges). In contrast, with respect to the epoxy compound selectivity, the stirring rate had a positive effect, while both the reaction temperature and time each had a negative effect. The oxidative stability (OS) of the epoxy waste used-oil biodiesel (EWUO-B) revealed a linear relationship to the unsaturated carbon bond conversion level, but no significant relationship to the epoxy compound selectivity. EWUO-B prepared from a 1: 1 molar ratio of H₂O₂: HCOOH at 50 °C with stirring at 300 rpm for 12 h exhibited a higher OS (around 37.85 h) than that of the WUO-B. Except for the cold flow properties and methyl ester content, all other key properties of the EWUOB were within the specifications of the EN14214 standard set by the Department of Energy Business.     

Investigation of selective leaching and kinetics of copper from malachite ore in aqueous perchloric acid solutions

In this study, the leaching kinetics of malachite in perchloric acid solutions was investigated. The dissolution behaviors of copper, zinc, and iron in the ore matrix were determined at different acid concentrations and reaction temperatures. It was observed that the concentration of perchloric acid had a major effect on the dissolution of copper, zinc, and iron. It was determined that the effect of temperature on the dissolution of these species was not as significant as concentration impact. The results obtained shown that copper in the ore matrix was completely leached while zinc and iron were partially dissolved in perchloric acid solutions. In addition, the effects of the acid concentration, reaction temperature, stirring speed, particle size, and solid-to-liquid ratio on the leaching of malachite were researched. In these experiments, it was observed that the leaching rate of copper increased with increasing solution concentration, stirring speed, and reaction temperature, and with decreasing solid-to-liquid ratio and particle size. A kinetic analysis was performed, and it was found that the rate of leaching reaction obeyed the mixed kinetic control model in the unsteady state. The activation energy of the leaching process was calculated to be 34.69 kJ/mol.     

Application of Taguchi method in the optimization of dissolution of ulexite in NH4Cl Solutions

The Taguchi method was used to determine optimum conditions for the dissolution of ulexite in NH₄Cl solutions. The ranges of experimental parameters were between 50–87 ‡C for reaction temperature, 0.05-0.20 gmL^-1 for solid-to-liquid ratio, 1–4 M for NH₄Cl concentration, 5–25 min for reaction time, and (-850+600)-(-90) Μm for particle size. The optimum conditions for these parameters were found to be 87 ‡C, 0.05 gmL^-1, 4M, (-300+212) Μm, and 18 minutes, respectively. Under these conditions, the dissolution percentage of ulexite in NH₄Cl solution was 98.37. Reaction products were found to be boric acid, ammonium tetraborates, sodium tetraborate decahydrate, calcium chloride, and sodium chloride.     

Application of Response Surface Methodology to Optimize Roasting Conditions in Cocoa Beans Subjected to Superheated Steam Treatments in Relevance to Antioxidant Compounds and Activities

Roasting is an essential technological process used to produce high-quality cocoa-based products. Response surface methodology (RSM) was employed to optimize the roasting conditions in cocoa beans based on antioxidant compounds (total phenolic, total flavonoids) and their activity (percentage inhibition of 1,1-diphenyl-2-picrylhydrazyl [DPPH] radical and ferric-reducing antioxidant power assay) using two variables: temperature and time. Cocoa beans were roasted at temperature ranging between 150 and 250°C for 10–50 min using superheated steam. The effects of the roasting conditions on the antioxidant properties of cocoa beans were investigated using a second-order central composite design. Results showed that roasting temperature and time significantly affect antioxidants in cocoa beans. Numerical optimization and superimposed contour plots suggested the optimal roasting conditions to be 192°C for temperature with 10 min of roasting time (R ² = 0.99). These conditions can be used for roasting of cocoa beans to produce high-quality cocoa products in terms of antioxidant properties.     

GAS PERMEANCE BEHAVIOR AT ELEVATED TEMPERATURE IN MESOPOROUS ANODIC OXIDIZED ALUMINA SYNTHESIZED BY PULSE-SEQUENTIAL VOLTAGE METHOD

Mesoporous anodic oxidized alumina (MAOA) capillary tubes with and without a barrier layer have been synthesized by applying a pulse-sequential voltage. The single gas permeances at an elevated temperature and the thermal and hydrothermal stabilities of MAOA were investigated. A highly oriented radial mesopore channel with pore sizes from 40 to 4 nm was formed in the MAOA tubes. Micropores with sizes from 0.4 to 0.8 nm were formed in the barrier layer. The H₂ permeance of MAOA with a barrier layer (barrier type) was approximately 540 times lower than that of MAOA without a barrier layer (block type) at 773 K. The H₂/N₂ permselectivity of the barrier type in the temperature range from 333 to 673 K was 3.4; those of the barrier type at 773 and 823 K were 4.4 and 11, respectively. On the other hand, the H₂/N₂ permselectivities of the block type were from 3.1 to 3.6 in the temperature range from 333 to 773 K. The H₂ permeance and the H₂/N₂ permselectivity of the amorphous silica membrane on the block type were 1.1 × 10^?7 mol/m² · s · Pa and 40 at 773 K, respectively. MAOA synthesized by the pulse-sequential voltage method can be applied to the mesoporous support of the gas separation membrane at elevated temperatures.