Study on Sulfuric Acid Leaching and Purification of Zinc Ferrite by Roasting Zinc-Containing Gossan Ore

Sulfuric acid leaching of high iron-bearing zinc calcine

The simultaneous effect of temperature and sulfuric acid concentration on the degradation of FRP composites has been studied using the weight loss technique. The immersion tests were designed using RSM methodology based on Design Expert software. ICP-Mass tests were performed to analyze the ion concentration in sulfuric acid solution after immersion. Additionally, the morphology of FRP samples was studied through SEM-EDS analysis. Furthermore, the mechanical properties of the immersed samples were assessed through mechanical bending and micro-hardness tests. The study proposed a three-dimensional view of the variation in FRP weight loss as a response to changes in temperature and sulfuric acid concentration. The results showed that the maximum weight loss occurred at 60°C and 6% sulfuric acid concentration. A linear model for the variation of FRP weight loss was proposed based on independent parameters and ANOVA variance analysis. The effect of sulfuric acid concentration on FRP weight loss was found to be more significant than temperature in the range of investigated parameters. It was concluded that immersion of FRP in sulfuric acid resulted in corrosion and degradation, followed by weight loss and a decrease in flexural bending strength and Vickers micro-hardness.

In this paper, zinc ferrite was prepared from zinc calcine by sulfuric acid leaching, and its properties were studied by the methods of XRD, XRF and SEM/EDS. The results show that sulfuric acid leaching of zinc ferrite from zinc calcine is mainly affected by the initial concentration of sulfuric acid and leaching temperature. If the initial concentration of sulfuric acid and leaching temperature are too low, the soluble oxides in zinc calcine can not be completely dissolved. The prepared zinc ferrite was not suitable for application for too many impurities. However, the higher initial concentration of sulfuric acid and leaching temperature are, the lower recovery of zinc ferrite is. The suitable conditions for preparation of zinc ferrite from zinc calcine by sulfuric acid leaching are liquid-solid ratio 7:1, stirring speed 400rpm, sulfuric acid concentration 160g/L, leaching temperature 85°C, leaching time 120min. The particle size of zinc ferrite is fine, most of them is between 2~5μm. The impurity content of zinc ferrite is less. Zinc ferrite particles are composed of spherical and irregular shape, and they are agglomerate and encase each other.

Rare earth element recovery in molten salt electrolysis is approximately between 91 and 93%, whereof 8% is lost in waste molten salt slag. Presently, minimal research has been conducted on the technology for recycling waste rare earth molten salt slag, which is either discarded as industrial garbage or mixed with waste slag into qualified molten salt. The development of a new approach toward the effective treatment of rare earth fluoride molten salt electrolytic slag, which can recycle the remaining rare earth and improve the utilization rate, is essential. Herein, weak magnetic iron separation, sulfuric acid leaching transformation, water leaching, hydrogen fluoride water absorption, and cycle precipitation of rare earth are used to recover rare earth from their fluoride molten salt electrolytic slag, wherein the thermodynamic and kinetic processes of sulfuric acid leaching transformation are emphatically studied. Thermodynamic results show that temperature has a great influence on sulfuric acid leaching. With rising temperature, the equilibrium constant of the reaction gradually increases, and the stable interval of NdF3 decreases, while that of Nd3+ increases, indicating that high temperature is conducive to the sulfuric acid leaching process, whereof the kinetic results reveal that the activation energy E of Nd transformation is 41.57 kJ/mol, which indicates that the sulfuric acid leaching process is controlled by interfacial chemical reaction. According to the Nd transformation rate equation in the sulfuric acid leaching process of rare earth fluoride molten salt electrolytic slag under different particle size conditions, it is determinable that with the decrease of particle size, the reaction rate increases accordingly, while strengthening the leaching kinetic process. According to the equation of Nd transformation rate in the sulfuric acid leaching process under different sulfuric acid concentration conditions, the reaction series of sulfuric acid concentration K = 6.4, which is greater than 1, indicating that increasing sulfuric acid concentration can change the kinetic-control region and strengthen the kinetic process.

In the production of titanium dioxide pigment via the sulfuric acid process, maintaining a high sulfuric acid concentration (85%) is essential for efficient titanium leaching. However, this conventional approach generates substantial waste acid (20% sulfuric acid). By reducing the reactive sulfuric acid concentration, the waste acid recycling rate can be increased, thereby decreasing waste acid production and conserving fresh sulfuric acid consumption. In this paper, ultrasonic activation is employed to enhance the premixing process of ilmenite. The effects of sulfuric acid concentration, ultrasonic power, and ultrasonic time on the ilmenite leaching rate were studied using an L9 (33) orthogonal test. In order of significance, the primary factors influencing the ilmenite leaching rate are sulfuric acid concentration, ultrasonic power, and ultrasonic time. The optimal conditions for ilmenite leaching are as follows: a sulfuric acid concentration of 80%, an ultrasonic power of 800 W, and an ultrasonic time of 5 min. Under these conditions, the ilmenite leaching rate can reach 93.07%. Ultrasonic cavitation can reduce the size of ilmenite while increasing its surface area and surface reactivity. Furthermore, the ultrasonic strengthening effect can enhance the porosity of the reactive solid phase, promote the diffusion of sulfuric acid on the surface of the ilmenite, and improve the acid hydrolysis rate of ilmenite concentrate at low concentrations.

Natural graphite is classified as a strategic critical raw material by the European Union due to its strategic significance. The demand is steadily increasing, but the current purification methods are not environmentally sustainable, highlighting the need for greener alternatives. This study investigates the effects – sulfuric acid (H2SO4) leaching, thermal treatment, and their combination – on natural graphite from a flotation pilot plant. In the sulfuric acid leaching, the influences of reaction time (60–300 min), temperature (70–100°C), sulfuric acid concentration (0.5–3 mol/L), and liquid-to-solid ratio (10–20 mL/g) were systematically studied using experimental design. Leaching effectively removed 91.4% iron and 52.9% aluminum, but was ineffective against silicon-containing phases. A short 15 min thermal treatment at 2400°C in an argon atmosphere using induction annealing eliminated most silicon phases and other impurities, although residual 2.65 mg/g iron and 1.27 mg/g silicon remained. The combined approach reduced iron and silicon contents to 0.24 and 0.25 mg/g, respectively, and increased the carbon content from 78.4 to 97.6 wt% to near commercial battery-grade levels (98.0 wt%). Additionally, the combination-treated graphite exhibited the lowest degree of structural defects, offering a more sustainable route for purifying natural graphite to high-purity levels compared to conventional halogen-containing techniques.

Localized electrochemical deposition (LECD) is a promising method for three-dimensional micro-/nanofabrication and, thus, the factors influencing LECD have been intensively investigated. This study examined the effect of sulfuric acid concentration on copper microcolumns deposited by LECD using a microanode with a diameter of 20 μm. With 0.05 mol l−1 sulfuric acid, the deposition voltage of the optimal deposited morphology of copper microcolumns was at 2.9 V, but the column diameter was larger than the anode diameter. With 0.5 and 2.0 mol l−1 sulfuric acid, the optimal deposited morphology of copper microcolumns were at 3.2 V and 3.4 V, respectively, but the diameters of the copper microcolumns were smaller than the anode diameter. In the LECD process, the deposition rate is proportional to the deposition voltage. Because of the hydrogen evolution, the deposition rates of copper microcolumns at high sulfuric acid concentration were lower than those at low and medium sulfuric acid concentrations. The results of this study indicated that the deposition rate obtained the optimal surface topography was 0.22 to 0.327 um s−1, which had reference significance to improve the quality of the copper microcolumns. The effect of sulfuric acid on the LECD was demonstrated using a competitive reduction mechanism.

The purpose of this study was to use acid hydrolysis of cotton linter to generate nanocrystal-line cellulose (NCC). Based on a 2^4 factorial design, the effects of sulfuric acid concentration, temperature, hydrolysis time, and the solid/liquid ratio on the NCC yield were examined. NCC specimens obtained from different sulfuric acid concentrations were subjected to a battery of analyses, including dynamic light scattering (DLS), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), 13C solid-state nuclear magnetic resonance (13CSNMR), and a thermal gravimetric analysis (TGA) to probe the particle size distribution, morphology, functional group shifts, position of the carbon, and thermal degradation properties of the ensuing NCC. The results indicated that the sulfuric acid concentration and solid/liquid ratio at higher levels, and temperature and reaction time at lower levels were significantly conducive to increases in NCC yields. The main effects in diminishing order were the acid concentration, temperature, hydrolysis time, and solid/liquid ratio. Results of DLS and TEM observations suggested that the NCC had a size distribution centered around 20~200 nm, with length-to-width ratios ranging 1:1~1:30. The FTIR analysis indicated that absorption peaks at 1010~1080 and 1150~1260 cm^(-1) were derived from sulfate ester bonds on the cellulosic chains. Solid state 13CNMR spectra indicated that the C4 atoms along the cellulosic chain were shifted from 87.4 ppm to a lower magnetic domain, indicating the sulfonic ester bonding position. The TGA indicated that the lower-sulfuric-acid NCC specimen began step 1 weight loss at ca. 149℃, whereas its starting temperature of step 2 weight loss was generally higher than the mid- and high-acid NCC, at 337 and 205℃, respectively. The high-acid NCC only showed marked weight loss at 243℃. The study found that a sulfuric acid concentration of 60%, a solid/liquid ratio of 1:20, a hydrolysis temperature of 45℃, and a hydrolysis time of 5 min produced the best yield of 54.4%.

This study examined the effects of sulfuric acid concentrations on the corrosion behaviors of three types of commercial steels, conventional carbon steel (SA192), sulfuric acid dew resistant steel (S-TEN), and duplex stainless steel (S32205), considered to be potential materials for the heat recovery steam generator (HRSG) in combined cycle power plants. Based on the results of electrochemical polarization, immersion and wet-dry cycle tests, when exposed to a high sulfuric acid concentration (50%), SA192 and S-TEN exhibited higher corrosion resistance than S32205, which was due to the formation of a stable FeSO4 scale on the carbon steel materials. With prolonged exposure, S-TEN with slightly higher concentrations of Cu and Sb showed lower weight loss than SA192. Conversely, when subjected to low sulfuric acid concentrations (5 and 10%), S32205 exhibited passivation behavior, and showed significantly superior corrosion resistance (i.e., much smaller weight loss) than the other two steel samples. The examination of localized corrosion damages through cross-section observation using a scanning electron microscope revealed also that S32205 suffered less damages from the wet-dry cycling. The long-term superior corrosion resistance of duplex stainless steel in low sulfuric acid concentrations, compared to carbon steel and sulfuric acid due resistant steel, make it a promising candidate material for the HRSG in combined cycle power plants.

Effect of sulfuric acid concentration on the yield and properties of the bio-oils obtained from the auger and fast pyrolysis of Douglas Fir

Zinc ferrite, a by-product of zinc hydrometallurgy, is a typical secondary resource. This paper focuses on investigating the factors influencing the sulfuric acid leaching process of zinc ferrite and analyzes the leaching kinetics. The research indicates that the zinc leaching rates of both pure zinc ferrite and zinc ferrite within zinc calcine exhibit positive correlations with individual influencing factors. Moreover, a strong positive synergistic effect exists between leaching temperature and leaching time. The differential impact of various factors on the two zinc leaching rates lies in the interaction involving sulfuric acid concentration, where sulfuric acid concentration acts as a limiting factor for the zinc leaching rate from zinc calcine. Kinetic studies on zinc leaching revealed that the rate-controlling step for zinc leaching from pure zinc ferrite is the surface chemical reaction, with an apparent activation energy of 54.22 kJ/mol. At leaching temperatures of 55 °C, 85 °C, and 95 °C, the zinc leaching rate from zinc ferrite in zinc calcine showed high conformity with both the diffusion model and the surface chemical reaction model, suggesting that the leaching process may be influenced by both kinetic mechanisms at these temperatures.

Environmentally friendly preparation of exfoliated graphite

Iron rust was an iron oxide compound that was less attractive, dirty, brown in color, and could pollute the environment, causing water to turn brown. To minimize iron contamination, conversion was carried out into iron (III) sulfate which was useful as an adsorbent for textile dyes. The purpose of this study was to determine the effect of sulfuric acid concentration and volume of H2O2 10% used to convert iron rust into optimal iron (III) sulfate compounds. The method used was a laboratory experiment on a batch scale and the hydrate content in iron (III) sulfate was carried out by the gravimetric method and its ability as an adsorbent was carried out based on the adsorption of dyes using the spectrophotometric method. The results showed that a reactor filled with 3 grams of iron rust powder and 100 mL of sulfuric acid was stirred at 425 rpm at 80 0C for 30 minutes, added 15 ml 10% H2O2 followed by stirring and heating until the solution was saturated, cooled to form crystals. The crystalline yield in these conditions was the increase in sulfuric acid concentration which resulted in low process efficiency, namely 30.34% at 50% sulfuric acid concentration and 15 mL 10% H2O2. The addition of 10% H2O2 solution to 50 mL of 20% sulfuric acid solution and 3.0 grams of a carat as much as 5 mL-10 mL 10% H2O2 produced iron (III) sulfate with 26.53% process efficiency. Iron (III) sulfate is a white, light gray crystal with the chemical formula Fe2 (SO4)3.5 H2O which was a rhombic shaped crystal. and able to absorb the dye which showed that 1.0 g of iron (III) sulfate was able to absorb the highest amount of red dye in a volume of 100 mL of textile dye solution.
 Keywords: Iron rust, synthesis, iron (III), sulfuric acid, textile dyes

The dissolution kinetics of hemimorphite with low sulfuric acid solution was investigated at high temperature. The dissolution rate of zinc was obtained as a function of dissolution time under the experimental conditions where the effects of sulfuric acid concentration, temperature, and particle size were studied. The results showed that zinc extraction increased with an increase in temperature and sulfuric acid concentration and with a decrease in particle size. A mathematical model able to describe the process kinetics was developed from the shrinking core model, considering the change of the sulfuric acid concentration during dissolution. It was found that the dissolution process followed a shrinking core model with “ash” layer diffusion as the main rate-controlling step. This finding was supported with a linear relationship between the apparent rate constant and the reciprocal of squared particle radius. The reaction order with respect to sulfuric acid concentration was determined to be 0.7993. The apparent activation energy for the dissolution process was determined to be 44.9 kJ/mol in the temperature range of 373 K to 413 K (100 °C to 140 °C). Based on the shrinking core model, the following equation was established: $$ 1.21\ln \left( {1 - 0.83x} \right) - \left[ {1.02\ln \frac{{0.35 + \left( {1 - x} \right)^{{{2 \mathord{\left/ {\vphantom {2 3}} \right. \kern-0pt} 3}}} - 0.59\left( {1 - x} \right)^{{{1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-0pt} 3}}} }}{{0.35 + \left( {1 - x} \right)^{{{2 \mathord{\left/ {\vphantom {2 3}} \right. \kern-0pt} 3}}} + 1.18\left( {1 - x} \right)^{{{1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-0pt} 3}}} }} + 3.52\arctan \left( {1.96\left( {1 - x} \right)^{{{1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-0pt} 3}}} - 0.58} \right)} \right] + 2.06 = 42,192.59{\text{e}}^{{ - \frac{44,900}{{{\text{R}}T}}}} t. $$

An analysis of the composition of brass metallurgical waste was carried out using X-ray fluorescence analysis (XRF). The results showed that the copper content in the slag reaches 15 wt. %, and the zinc content – 83 wt. %. Sulfuric acid leaching was performed to separate zinc from the metallurgical dust. Optimal process parameters were selected: leaching duration – 60 minutes, sulfuric acid concentration – 0.1 M. After sulfuric acid leaching, the acid solution was subjected to electrochemical treatment to recover copper and zinc, and the copper cake (copper in unoxidized form) was subjected to copper-ammonia leaching for 40 minutes. The concentration of copper in the copper-ammonia solution reached 35 g/L. At the final stage, solvent extraction of copper from the copper-ammonia leach solutions was carried out, for which the most effective extractant was selected. Extractants of different nature and classes were studied: D2EHPA (a strong acidic organophosphorus extractant), DХ510А and LIX54 (belonging to the class of β-diketones). The concentration of extractants ranged from 50 to 100%, the diluent was kerosene. Copper stripping from the copper-ammonia extract was performed using 2M sulfuric acid. The best extractant was found to be LIX54 at 50% concentration in kerosene. The final stage was copper electrowinning from the stripping solutions at a current density of 3 A/dm, with a current efficiency of 65%. Based on the conducted research, a process flowsheet was developed for the recovery of copper and zinc from brass metallurgical dust.