Acid Pickling Research Articles

Temperature prediction for wire rod pickling plant management

The prediction of the temperature in the different tanks of a mixed acid pickling line of wire rod coils is described in this paper. The goal is to develop a robust model-based prediction tool that allows prospective development of pickling bath states and adjustments in the management of a pickling line. The temperature of the pickling bath is a critical variable for the efficiency of the pickling process. Excessive temperatures can have an unfavorable effect on the pickling results and can complicate the decontamination of the exhaust gases. Root mean square error values lower than 0.2∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{\\circ }$$\\end{document}C were obtained when treating martensitic and ferritic steels, which are precisely the most problematic types of steel in the control of pickling temperature. The model software was installed on a computer for online operation at the pickling plant. Relevant information is predicted and transmitted such as the temperature pickling bath trend with the sequence of the wire coils to be treated. Plant personnel are able to change this sequence or modify pickling retention times based on this information. The economic benefits come mainly from better use of the production line, reducing coil waiting times.Graphical abstract

Development of a tool for predicting oxides scales and tensile properties of Stelmor-cooled wire rod

In industrial practice, it is known that the wire rod coils need to be descaled before drawing. Acid pickling by hydrochloric or sulphuric acidic solutions is the most common method. However, mechanical descaling could be preferred. According to this choice, the oxides type and morphology shall be different. The oxides nature can be controlled by the Stelmor parameters, that is, the temperature at the laying head and the cooling rate on the Stelmor conveyor. International standards and customer specifications prescribe precise requirements not only for the scale features, but also for the material mechanical resistance and deformability. So, a complicated plant set-up is needed to satisfy all the requirements. This research work is aimed at developing processing maps for the correct selection of the Stelmor parameters able to guarantee the required mechanical strength and surface scale suitable for acid pickling or mechanical descaling.

Metal-organic-framework-derived Fe, Co, N-tri-dopped porous carbon as oxygen electrocatalysts for Zn-air batteries

To commercialize the rechargeable zinc-air (Zn-air) battery, it is desirable but challenging to design highly active, low-cost, stable, and earth-rich bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) to replace rare, expensive, and unstable noble-metal electrocatalysts. Herein, two MOFs are combined under electrostatic interaction and pressure by the way of Ball milling. Then, after post-processing including calcination, acid pickling, and N doping, the bimetal (Fe and Co) and N triple-doped porous carbon electrocatalyst (MIL/ZIF-4-700 °C-NH3) is prepared. Noteworthily, the MIL/ZIF-4-700 °C-NH3 has bimetallic active sites, high contents of pyridine N and graphite N, large surface area, mesoporous structure, and conductive carbon skeletons, which decide the excellent ORR performance. For ORR, the half-wave potential (E1/2 = 0.902 V vs. RHE) of MIL/ZIF-4-700 °C-NH3 is 27 mV higher than that of 20 wt% Pt/C (E1/2 = 0.875 vs. RHE). And the catalyst has also excellent methanol tolerance and stability. The Zn-air battery with MIL/ZIF-4-700 °C-NH3 as cathode catalyst has higher peak power density (176.5 mW cm−2) than that with 20 wt% Pt/C (141.8 mW cm−2) and 20 wt% Pt/C + RuO2 (94.4 mW cm−2) as cathode catalyst. Meanwhile, the Zn-air battery with MIL/ZIF-4-700 °C-NH3 as cathode catalyst exhibits perfect charge-discharge stability (longer than 540 h).

Tailoring poly(2-ethyl-2-oxazoline) towards effective mitigation of chloride-induced dissolution of S235JR steel: The synergistic contributions of potassium iodide and myristyl trimethylammonium bromide

Organic compounds that exhibit little or no toxicity, have high solubility properties, and are affordable are highly sought after as metal corrosion inhibitors. The key to formulating an effective and economically viable corrosion inhibitor is the identification of compounds with strong synergistic effects. The synergistic inhibition of S235JR carbon steel in 1 M HCl by poly(2-ethyl-2-oxazoline) (PO), KI, and myristyl trimethylammonium bromide (MTAB) is studied. The durability of the PO + KI + MTAB blend is examined for up to 72 h. Results reveal an average inhibition efficiency (η) of 80 % for PO at 1000 mg/L. Adding 5 mg/L KI or MTAB to 1000 mg/L PO raised η to 97 % or 94 % from EIS measurements. PO(1000 mg/L) + KI(5 mg/L) + MTAB(5 mg/L) produced ∼ 99 % inhibition and kept the corrosion rate at 0.09 mm/y for up to 72 h. Spectroscopic and computational studies reveal PO interacted with the steel surface making use of the carbonyl functional group. The DFT calculations and MD simulations confirm the favorable tendency of the PO molecule to adsorb on the metal surface and the synergistic adsorption with KI and MTAB. Furthermore, SEM and AFM results confirm the high inhibitive performance of the blend. PO + KI + MTAB blend is highly recommended for long-term acid pickling of a metal surface and acid cleaning of plants.

Natural gums as green corrosion inhibitors for mild steel

In this study the corrosion inhibition efficiency of Guar gum and Arabic gum are investigated on mild steel in concentrated chlorohydric acid. Weight loss and electrochemical methods, potentiondynamic polarization and electrochemical impedance spectroscopy were used to determine the optimum concentration of each gum. The results show that there is a direct correlation between concentration of inhibitor and corrosion inhibition efficiency, therefore the best efficiency was obtained at the highest concentration, 3.3 g/l. When comparing the two polysaccharides Guar gums has a better inhibition effect than Arabic gum at the same concentration. The inhibition mechanism was analysed by fitting the electrochemical results to an adsorption isotherm. This research offers a green alternative to the synthetic inhibitors used in today’s industry during acid pickling in the manufacturing process of mild steel. Both substances are naturally obtained and considered green corrosion inhibitors due to their negligible impact on the environment. Future research on the topic will include more natural compounds tests in the same experimental conditions and comparing them to market inhibitors in terms of efficiency.

Study on dechlorination salt characteristics of pickling sludge by a water-washing process.

Steel hydrochloric acid pickling sludge (SHPS), containing the heavy metals Fe, Zn, and Ni and a high chloride salt content, is considered a hazardous solid waste. With the gradual reduction of high-grade metal mineral resources such as Fe, Zn and Ni, it is particularly urgent to recycle valuable metals such as Fe, Zn and Ni in solid waste SHPS in order to realize the resource utilization of SHPS and reduce the environmental harm caused by SHPS. In addition, SHPS usually contains different amounts of alkali chloride, which will have a serious adverse impact on the subsequent extraction and smelting process of Fe, Zn and other metals. Therefore, the removal of chloride plays an important role in the resource utilization of valuable metals in SHPS. Thus, in this study, the effects of water washing dechlorination process parameters such as liquid-solid (L/S) ratio, SHPS particle size, washing time and washing frequency on the chloride removal rate were investigated. The best experimental parameters of SHPS washing were obtained. At the same time, the microscopic morphology and crystal phase composition of SHPS before and after washing were explored. The results showed that the optimized conditions were as follows: room temperature, a L/S ratio of 3 : 1, an SHPS particle size of 100 mesh, and 10 min of water washing, repeated two or three times; under these conditions, the removal rate of Cl, Na, Ca, K, Mg, and S reached 96.64-99.68%, 97.38-99.89%, 36.40-60.37%, 49.11-54.82%, 39.18-40.22%, and 36.98-42.13% respectively. The contents of Cl, K, and Na in filter residue (FR) meets the requirements in GB/T 36144-2018 and GB/T 32545-2016. Conversely, the contents of Fe, Zn, Mn and Ni in the FR are enriched, which is more conducive to the subsequent resource utilization of SHPS. The scanning electron microscope (SEM) image shows the particle size of the FR particles is reduced after washing. The X-ray diffractometer (XRD) results proved that the chlorine salt content in the FR after washing was significantly reduced, the diffraction peaks of Al2O3 appeared in the FR, and the diffraction peak intensity of CaCO3, Fe2O3 and SiO2 increased.

Functionalized magnetic chitosan-based adsorbent for efficient tetracycline removal: Deep investigation of adsorption behaviors and mechanisms

As removal performance of tetracyclines in traditional wastewater treatment plants cannot satisfy the increasingly strict discharge requirements, developing an efficient approach to overcome this problem is quite urgent. Herein, a novel functionalized magnetic chitosan-based adsorbent (Fe3O4@CAA) with core-shell structure and unique magnetic responsiveness was facilely prepared by ultrasound-initiated radical grafting copolymerization and cross-link reaction. The as-prepared Fe3O4@CAA was fully characterized with TEM, SEM, BET, FTIR, TGA, XRD, VSM, and served as an efficient adsorbent for tetracycline hydrochloride (TCH) removal. Adsorption behaviors of TCH by Fe3O4@CAA were deeply evaluated at different adsorption time, initial TCH concentration, reaction temperature, solution pH, and background pollutant concentration. Results showed that Fe3O4@CAA presented a more competitive adsorption capacity of 325.04 mg g−1 compared with Fe3O4@CS and other reported adsorbent, due to the introduction of more active adsorption sites by abundant functional groups, including amino groups, hydroxyl groups, and sulfonic acid groups. After saturated adsorption, TCH loaded Fe3O4@CAA was easily collected by magnetic separation, and recycled after acid pickling. Fe3O4@CAA was successfully reused in five adsorption-desorption cycles, without obvious adsorption capacity loss. In binary pollutant systems, inorganic cations and Pb(II) restrained TCH adsorption by competitive effect, while proper amount of Cu(II) promoted TCH adsorption by bridge effect. FTIR and XPS analyses revealed that the adsorption mechanism of TCH by Fe3O4@CAA mainly included electrostatic interaction and hydrogen bonding, and Cu(II) could play a “mediator” role to form a strong Cu(II)-TCH complex to enhance TCH removal performance. This study provides an effective strategy for the design of magnetic chitosan-based adsorbents and valuable guidance for the removal of tetracyclines from wastewater.

Analysis of Pre-Treatment Processes to Enable Electroplating on Nitrided Steel

Nitrided steel is being used to increase the lifetime and wettability of selective soldering nozzles. In this environment, the liquid solder wets to the surface of the nozzle to enable control of the solder flow during the soldering process. Pre-treatment is a key step in the processing of parts for electroplating. Pre-treatment usually involves degreasing and acidic pickling steps in order to remove adsorbed oil-based compounds and oxides respectively. These steps ensure a well-structured and adherent electroplated coating to the part.Surface treatments such as nitriding alter the surface composition of steels and thereby change the conductivity/surface activity. Typically, a nitrided surface contains a dual-phase surface layer followed by a diffusion zone consisting of the formed nitrides and finally a transition zone to the bulk material. Generally, this surface treatment is performed to harden materials without the risk of dimensional changes. For a selective soldering application, it reduces the dissolution of material into the solder during operation while also improving the wetting of the nozzle.The electroplated coatings for the selective soldering nozzles consist of 10 microns of nickel and 10 microns of tin. This structure allows for near-instant wetting and use of the nozzle. Furthermore, the electroplated layers provide corrosion protection for the nozzle ensuring no oxide or scale layers will form that may require flux for cleaning.A range of chemical and electrochemical pre-treatment steps were explored to prepare and optimally activate the nitride-hardened steel surfaces for electroplating. The processes included: hot degreasing and electrolytic degreasing with alkaline detergents; electrolytic descaling in a solution containing sodium hydroxide; chemical pre-descaling process with potassium permanganate; varying the compositions of pickling in inorganic acids; different formulations for nickel strike electrolytes for plating onto ferrous alloys.Mass loss measurements provided an estimation of the thickness of the material removed due to acid pickling. Scanning electron microscopy was employed to assess changes in the surface due to the pre-treatment. Open circuit potential measurements were applied to measure the surface activity before any pre-treatment and also the change in surface conductivity/activity post-treatment. Nanoindentation measurements were used to assess the change in surface hardness as a result of the nitriding treatment and also to check for the presence of the remaining hardened nitrided layer after pre-treatment. Glow discharge optical emission spectroscopy was utilised to study the elemental depth profile of the nitrided parts. Crystalline structure was studied through x-ray diffraction. After pre-treatment, a Woods nickel strike was applied to prepare the surface for further electroplating with bright tin. SEM analysis of the cross-sections of the coated specimens was used to analyse the coating microstructure. Thickness of the electrodeposited coatings were confirmed with x-ray fluorescence. Thermal shock tests were performed to confirm that the adhesion of the coating was sufficient.Approximately half of the nitrided layer was removed by pre-treatment in order to activate the surface for electroplating. More severe pre-treatment was required compared to electroplating non-hardened parts to activate the surface. Surface conductivity/surface activity was altered as measured by OCP resulting from the pre-treatment.This work has analysed the surface modification of nitride-hardened steels during the pre-treatment steps required to initiate electroplating and has shown that it is possible to prepare nitride-treated steels for electroplating. The results can be used to develop more optimal pre-treatment processes for electroplating nitrided steels.

The Corrosion Inhibition Performance of Eco-Friendly bis-Schiff Bases on Carbon Steel in a Hydrochloric Solution

Corrosion inhibitors are widely used as an important tool for the prevention and remediation of different materials exposed to corrosive industrial processes. Corrosion inhibitors are usually added to acid pickling solutions to reduce the deterioration of metallic materials and particularly, corrosion due to hydrochloric acid. In this work, three bis-Schiff bases (BS2, BS4 and BS8) were synthesized and characterized using spectroscopic methods, and their anti-corrosive effects on AISI 1020 carbon steel in a hydrochloric acid solution were studied using gravimetric and electrochemical techniques and quantum chemical methods. The results showed that all substances act as potential corrosion inhibitors as BS8 exhibited the highest efficiency (98%) of all methods. The compounds adsorbed on the metal surface were as per the El-Awady adsorption isotherm. Morphological aspects of the metal were observed upon applying SEM, and the theoretical results acquired from the quantum chemical calculation for molecular properties and the Fe(110) surface adsorption proved to be compatible with the experimental results.

The chemical state of iron species influence on the performance of Fe–N–C bifunctional electrocatalyst for Zn–air batteries

Fe–N–C materials have emerged as promising alternatives to precious metals for oxygen reduction reaction/oxygen evolution reaction (ORR/OER). In this study, a strategy is presented to investigate the influence of different chemical states of iron species in Fe–N–C materials on their electrocatalytic performance. Three Fe–N–C catalysts, containing either zero-valent Fe or Fe3O4 nanoparticles, are synthesized using acid pickling, high-speed centrifugation and ultrasound-assisted hydrothermal methods, respectively. The findings manifest that the chemical state of iron significantly affects the electrocatalytic activity of Fe–NX active sites, namely zero-valent Fe enhancing Fe–NX activity while Fe3O4 weakening its activity. Notably, the Fe@FeNC catalyst containing only zero-valent iron, demonstrates the only 0.621 V potential difference between the ORR half-wave potential and the OER potential at 10 mA cm−2. Furthermore, the rechargeable Zn–air battery assembled with Fe@FeNC as the air cathode exhibits a remarkable peak power density of 179.0 mW cm−2, excellent cycling stability over 210 h (with a cycle frequency of one every 10 min), and the minimal voltage gap of 0.710 V. These results reveal the significance of different chemical states of metal-based nanoparticles in Fe–NX activity of Fe–N–C catalysts and offer insights into the rational design of electrocatalysts with exceptional activity and versatile applications.

Microwave-assisted hydrothermal synthesis of lithium ion-sieve for adsorption of lithium ion in coal gangue leaching solution

A two-step method involving microwave-assisted hydrothermal synthesis and solid-phase calcination was employed to prepare the Li1.6Mn1.6O4 (LMO) precursor. Material characterization demonstrated the structural stability of LMO even after acid pickling, resulting in the creation of the ion-sieve H1.6Mn1.6O4 (HMO) with the most notable Li+ adsorption capacity of 29.45 mg·g−1. The adsorption isotherm of HMO adhered to the Langmuir isothermal model (R2 = 0.9929), indicating a smooth and monolayer adsorption process. Simultaneously, the adsorption kinetics of HMO was consistent with the pseudo-second-order kinetic model (R2 = 0.9911), indicative of chemisorption. Upon undergoing five adsorption-desorption cycles, HMO's adsorption capacity remained above 22.32 mg·g−1. Evaluation of the distribution coefficient (Kd) and the separation factor (αMeLi) for HMO in both coal gangue leaching solution and simulated salt lake brine highlighted its exceptional selectivity. Notably, HMO achieved a remarkable 99.9% adsorption rate in the coal gangue leaching solution. These outcomes underscore the efficacy of the synthesized HMO in highly selective Li+ recovery from both coal gangue and salt lake brine, additionally emphasizing the potential of coal gangue as a valuable lithium resource with significant prospects for future development and utilization.

Novel Approach to Address Brownish Edge Band in Low Alloy Cold Rolled Steel Used in Tin Plate

Thin film formation of lubricant plays a key role in supporting lubrication and abating wear. During cold rolling of steel, esters, or film formers in rolling oil play an important role in the mixed lubrication regime. The property of the lubricant holds the key to achieving the mean film thickness during the mixed lubrication regimen. Band formation in cold rolling is often related to inadequate acid pickling. During cold rolling operation, the film formation between asperities plays an important role in controlling friction and coil temperatures. A well formulated lubricant ensures smooth transition of lubrication throughout the range of roll bite temperature and also across the lubrication regimes. A sudden spike in coefficient of friction (CoF) can often lead to increased wear and abnormal increase in coil temperatures resulting in band formation. The study highlights degradation of oil sample leading to the problem and the role of key lubricant properties in esters in mitigating the problem.

Effect of pretreatment on the interfacial bonding strength between modified polyolefin and aluminum foil treated with trivalent chromium chemical conversion: Experimental, quantum chemical calculations and molecular dynamics simulation

Good adhesive strength and joint durability are necessary for aluminum (Al)/polymer laminated film for lithium-ion battery packages. A pretreatment method involving alkaline degreasing followed by acid pickling was employed to treat the Al foil surface to facilitate the deposition of trivalent chromium [Cr(III)] conversion coating on the surface. The adhesive strength between propylene-based elastomer grafted glycidyl methacrylate (GMA-g-PBE) and Cr(III)-converted Al foil pretreated with 0.5 M HF pickling was 51% higher than Cr(III)-converted Al foil without pretreatment. Moreover, the effect of different pretreatments on the interfacial bond strength of GMA-g-PBE/Cr(III)-converted Al foil was studied from macroscopic to microscopic perspectives. The results indicate that the pretreatment of 0.5 M HF pickling results in complete coverage of the Cr(III) compounds and the formation of a thicker Cr(III) conversion coating on the Al foil compared to other pretreatments. A higher content of Cr(III) compounds results in an increased surface free energy of Cr(III)-converted Al foil, improving the wettability of adhesive melt on the substrate and enhancing the adhesion strength. Moreover, quantum chemical calculations and molecular dynamics simulations were used to investigate the interface bonding mechanism, and the results indicate that GMA in the adhesive exhibits a higher binding energy with Cr(III) oxides and hydroxides compared to Al oxides and hydroxides.

Surface analysis and interface properties of a newly synthesized quinoline-derivative corrosion inhibitor for mild steel in acid pickling bath: Mechanistic exploration through electrochemical, XPS, AFM, contact angle, SEM/EDS, and computational studies

The two novel heterocyclic quinoline derivatives, 5-(methoxymethyl)-2-methylquinolin-8-ol (QO) and 5-((2-hydroxyethoxy)methyl)-2-methylquinolin-8-ol (QOOH) are examined in this work for their ability to adsorb against the corrosion of mild steel (MS) in a molar hydrochloric acid (HCl) media. After the synthesis of these two compounds, we proceeded some analytical methods such as the nuclear magnetic resonance of the proton and the carbon (1H NMR and 13C NMR). Potentiodynamic polarization (PDP), electrochemical frequency modification (EFM), and impedance spectroscopy (EIS) were the methods used in the experimental examination. The results indicated that the inhibitory efficacy of QO and QOOH increases with concentration. Both inhibitors exhibit mixed type behavior, according to the findings of polarization. Following that order was QO's and QOOH's inhibitory efficiencies 93.20% (QO) > 88.84% (QOOH). The Langmuir adsorption model is used in the adsorption process of these two chemicals. A barrier layer encasing the MS was shown to exist by Scanning electron microscope (SEM), energy dispersive X-ray analysis (EDS), atomic force microscopy (AFM), contact angle, and X-ray photoelectron spectroscopy (XPS) were all used in the examination of the surface characterization. The Density functional theory (DFT) findings suggest that inhibitors with electron-accepting capabilities exhibit the strongest interactions with the iron surface.

The Production of Hematite Powder from Spent Pickling Hydrochloric Acid

This research aimed to study the recycling process and the feasibility of recovering iron as hematite or red oxide powder (Fe2O3) from spent pickling acid (hydrochloric acid). The spent hydrochloric acid waste from the pickling bath in the sheet rolling steel industry contains approximately 233 g of iron dissolved in one liter of the spent acid. To recover iron, 2 M NaOH was added to the spent acid until reaching pH 7. The iron was precipitated as iron oxide and/or hydroxide. Next, the oxidation of ferrous oxide was carried out by adding H2O2 35%v/v to control the shade color. The precipitates were subsequently separated from the acid solution by a filter press. The precipitates were dried at 110°C for 24 h and calcined at 700°C for 2 h to synthesize and modify the crystallinity of ferric oxide. Ferric oxide was subject to water washing, where contaminating sodium chloride could be dissolved and filtered out. After drying at 110°C for 24 h, high-purity hematite was achieved. Hematite recovered from the spent pickling acid via this process provided more than 97% purity at 94.4% recovery.

Effect of acid pickling treatment of stainless steel substrate on adhesion strength of electrodeposited copper coatings using non-cyanide electrolyte

In recent years, copper-based antimicrobial coatings have gained popularity in healthcare and public recreation facilities. The morphology, topography, and adhesion strength are decisive properties for copper coatings to have long-term antimicrobial effectiveness in hospital environments. This work explores the effect of multistage acid pickling treatment of AISI 304 stainless steel substrate on the adhesion strength of the copper coating. The copper coating was obtained by electrodeposition using an alkaline non-cyanide electrolyte. After the fourth stage of acid pickling, the copper coating had an excellent adhesion strength, up to 9 MPa. Glow discharge optical emission spectroscopy (GDOES) examination revealed no oxide scales or other contaminants on the SS surface after the fourth (final) stage of acid pickling. Using a non-contact optical profilometer, it was observed that the roughness of the substrate increased with each stage of the pickling treatment. The surface topography analysis confirms the increased density of the interlocking sites, which favors the adhesion of the coating. On the other hand, the microstructure of the copper coating showed a cauliflower-like morphology with an average nodule size of 28 nm. Transmission electron microscopy confirmed that the coatings have nano-scaled crystallites with internal twins inside the grains of copper coatings.

Correlation between experimental and theoretical approaches in the performance of new epoxy resin as an effective corrosion inhibitor for mild steel in acid pickling bath

In this recent work, novelty epoxy resin namely 1,3,4,5,6-pentaglycidyloxy hexan-2-one (PGH) was synthesized characterized and studied as a potential anticorrosive protection for mild steel (MS) in 1 M HCl solution. The corrosion inhibition for MS was examined by “potentiodynamic” polarization (PDP), electrochemical impedance spectroscopy (EIS), electrochemical frequency modulation measurements (EFM), scanning electron microscope coupled with energy dispersive X-ray spectroscopy (MES/EDS) and theoretical approaches (DFT and MD simulation). PGH elaborated was investigated by the Fourier transform infrared (FTIR) spectroscopy. Additionally, the inhibitory efficiencies found at higher concentration (10−3 M of the PGH) are 85.5% (EIS) and 88.6% (PDP), respectively. PDP results indicated that the PGH acted as a mixed-type inhibitor in 1 M HCl medium. SEM/EDS characterization represents a terrific decrease in corrosion of the MS surface within 10−3 M of PGH compared with the 1.0 M HCl pure. DFT calculation provided molecular level insights on the nature and the active centres of the corrosion inhibition efficiency of the PGH elaborated. MD simulation showed that the PGH has the maximum inhibition efficiencies at oxygen atoms.

Perspectives on Corrosion Inhibition Features of Novel Synthesized Gemini-Fluorinated Cationic Surfactants Bearing Varied Spacers for Acid Pickling of X60-Steel: Practical, and In Silico Calculations.

Through our present study, three novel Gemini-fluorinated cationic surfactants bearing different spacers (FSG6-2, FSG6-4, and FSG6-6) were synthesized, and their structures were explained via different spectroscopic instruments such as 1H, 13C, and 19F NMR spectra. The surface activity of the as-prepared surfactants was examined. The inhibiting influence of FSG6 molecules on the X60 steel corrosion in the pickling solution (HCl) was examined by diverse methods comprising electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), and X-ray photoelectron spectroscopy (XPS) experimentations, and computational calculations. The inhibition effectiveness of FSG6 surfactants followed the order of 93.37% (FSG6-2) < 96.74% (FSG6-4) < 98.37% (FSG6-6) at 2.0 × 10-4 M. The FSG6 surfactants function as mixed-type inhibitors, according to PDP investigations. The H2O molecules that adsorbed on the steel interface were substituted with surfactant molecules, and the surfactant's inhibitory activity is likely caused by the improvement in an adsorptive layer on the steel substrate, as specified by the EIS results. The Langmuir isotherm describes the absorption of FSG6 molecules on the metal surface. The XPS investigations validate the steel interface's extremely protective nature. The mechanism of interaction between FSG6 molecules with an X60-steel employing the DFT calculations and MC simulations methods was also examined and discussed.

The Color Formation of “Lumu Stone” in the Weathering Processes: The Role of Secondary Hematite and Goethite

Rocks and minerals buried in the earth’s surface usually undergo weathering processes and change color in the burying environment. A kind of yellow Chinese stamp stone named “Lumu stone”, which is buried in a yellowish weathering crust (yellowish soil), was selected to investigate its color changes in the weathering processes. In this study, the appearance features, mineral components, micromorphology, spectroscopy characteristics, and color causation of the “Lumu stone” were studied by using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), an electron probe microanalyzer (EPMA), a laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS), and a UV-Visible (UV-Vis) spectrum. The “Lumu stone” usually exhibits a darker yellow outer layer and a lighter yellow core, suggesting that yellow color permeated into the stone from the surface to the core gradually and the color is secondary forming. The results from XRD and SEM show the studied samples are mainly composed of dickite and illite. The individual particles of the dickite and illite are about 2–5 μm, randomly distributing in the three-dimensional space and constituting voids among the particles. The acid pickling experiments using HCl coupled with KSCN confirmed that the mineral phases that caused the yellow color of the matrix are iron oxide and hydroxide. On the other hand, goethite and hematite were observed gathering in the yellow and brown-red cracks on the “Lumu stone” by SEM study. However, iron oxide and hydroxide in the matrix were difficult to observe and detect among the dickite and illite aggregates by SEM and XRD methods. It indicates that they may be nanoscale in size and very low in content. According to the calculation of the second derivative of Kubelka-Munk (K-M) transformed diffuse reflection spectroscopy (DRS) curves obtained from UV-Vis, the characteristic peaks of goethite and hematite were found in the yellow matrix, and their contributions to the color were confirmed. The concentrations of goethite and hematite were calculated to be 0.32 to 1.87 g/kg and 0.22 to 0.93 g/kg in the studied samples, respectively. In this study, a series of methods were employed to detect very low levels of goethite and hematite in the samples undergoing weathering processes. Additionally, nanoscale goethite and hematite were considered newly formed minerals when buried in the weathering processes and may gradually move into the voids among phyllosilicate particles. Therefore, they turned the “Lumu stone” yellow.

The recovery of high purity iron phosphate from the spent lithium extraction slag by a simple phosphoric acid pickling

Recycling metal resources from spent lithium-ion batteries is promising for resource reuse and environmental conservationis, but there are challenges in obtaining high purity recovered materials. The alkaline solutions (NaOH) is employed to precipitate FePO4 from spent LiFePO4, however, the introduction of sodium leads to low purity and lattice defects in the recovered FePO4. Here, we propose an ultrasonic-centrifugal H3PO4 pickling method able to regenerate battery-grade FePO4 in the low Na/Fe environment. In a weak acid environment, the potential of NaH2PO4 increases and the NaH2PO4 attached to the outer layer of FePO4 is converted to FePO4 by H3PO4 pickling. When Na/Fe ≤ 0.8, sodium exists in the form of NaH2PO4, which can be removed by H3PO4 pickling to obtain perfectly crystalline FePO4. When Na/Fe ≥ 2, sodium co-exists in the form of NaH2PO4, NaFe3P3O12 and NaFeP2O7. The latter two impurities are too stable to be removed by pickling, resulting in lattice distortion of FePO4. In addition, the electrochemical performance of regenerated 0.8Na-FePO4 reached the level of commercial FePO4 (C-FePO4), meanwhile the cost of 0.8Na-FePO4 was calculated to be $2.08/kg. This is about 15 % lower than the cost of C-FePO4 ($2.45/kg). This work proposes a high value recovery method of FePO4 with considerable economic advantages and environmental benefits for engineering applications.