Chloride Sulfate Solutions Research Articles

Fracture behavior and mechanical properties of engineered cementitious composites exposed to long-term sulfate and chloride environments

The fracture properties of engineered cementitious composites (ECC) exposed to dry-wet cycles in sulfate and sulfate-chloride solutions were studied by three-point bending (TPB) beams at the corrosion periods of 0, 30, 90, 130, 180, 270, and 360 days. The digital image correlation (DIC) technique was used to understand the whole fracture process. The fracture toughness and fracture energy were calculated using the proposed method, and the evolution of the horizontal strain field, displacement field, and fracture process zone (FPZ) were investigated. Meanwhile, the compressive and tensile performance of the specimens at the same corrosion periods were analyzed. The results showed that (1) Compared to water immersion, the environments of sulfate and sulfate-chloride were beneficial in improving the compressive and tensile strength, and weakening the tensile ductility. (2) With increasing the corrosion time, the evolution of the unstable fracture toughness can be distinguished into three phases: a stable phase, an increasing phase, and a rapidly decreasing phase, and the initial fracture toughness followed an increasing and then decreasing trend. The fracture energy initially decreased and tended to stabilize after 130 days. (3) By using DIC technology, as the corrosion time increased, the horizontal opening displacement at the notch tip showed a decreasing trend and stabilized after 90 days generally. The fracture path determined through horizontal displacement was well matched with the macrocrack trajectory. (4) The addition of chloride ions helped to improve the mechanical properties of ECC under long-term corrosion, such as compressive strength, unstable fracture toughness, fracture energy, and opening displacement at the notch tip. Compare to concrete, ECC exhibited greater resistance to sulfate corrosion.

Chemical Mechanisms Involved in the Coupled Attack of Sulfate and Chloride Ions on Low-Carbon Cementitious Materials: An In-Depth Study

This study aims to analyze the individual and combined chemical attacks of sulfate and chloride ions on cementitious materials and assess the efficiency of some selected additives (fly ash, blast furnace slag, and metakaolin) in countering this combined attack. This research is conducted in the context of construction in marine environments, where reinforced concrete structures are often subject to significant challenges due to early exposure to sulfate and chloride ions. This early exposure results in concrete expansion, cracking, and, ultimately, the corrosion of steel reinforcements. Nevertheless, the interaction between sulfate ions, chloride ions, and the cementitious matrix remains poorly understood. Previous research has drawn conflicting conclusions, with some suggesting that sulfate ions mitigate chloride attacks, while others have come to the opposite conclusion. During this study, experimental investigations were conducted by immersing powders obtained from crushed ordinary Portland cement (CEM I) paste specimens, as well as binary, ternary, and quaternary blends, in sulfate, chloride, and sulfate–chloride solutions over the course of 25 days at an early age. Results from different characterization techniques (thermogravimetric analysis, Fourier Transform Infrared spectroscopy, Raman spectroscopy, etc.) indicate that chloride ions delay the formation of ettringite, while the presence of sulfate ions accelerates the chloride attack by limiting the formation of Friedel’s salt. The Mercury Intrusion Porosimetry test confirmed these results by showing a pronounced increase in specimens’ porosity after exposure to solely sulfate after 25 days, compared to the ones exposed to both sulfate and chloride ions. Furthermore, the incorporation of multiple additives, particularly in ternary and quaternary blends, demonstrates the enhanced durability of the studied samples. This was confirmed by a Fourier Transform Infrared spectroscopy analysis, which indicated a delayed ettringite formation in these mixtures. This delay was further affirmed by the complete depletion of sulfate ions in the sulfate solutions upon contact with powders derived from the 100% CEM I paste.

Comparative analysis of the corrosion resistance of Bos taurus and Cocos nucifera–reinforced 1170 aluminum alloy in chloride-sulfate solution

Comparative analysis of the corrosion resistance of Bos taurus and Cocos nucifera–reinforced 1170 aluminum alloy in chloride-sulfate solution

Chloride effect on sulfate attack in hydrated Portland-limestone cement assessed by 29Si NMR spectroscopy and thermal analysis

Structural alterations in the C-S-H phase of hydrated Portland-limestone cements, caused by magnesium sulfate attack, were quantitatively assessed using 29Si MAS NMR spectroscopy, considering the presence of sodium chloride in the corrosive medium and the limestone content in cement. Quantitative information about crystalline deterioration products (ettringite, thaumasite, gypsum, brucite) was retrieved from thermogravimetric analysis. Scanning electron microscopy combined with elemental analysis indicated their accumulation areas. Formation of cross-linked silicate chains and reduction of bridging/pairing SiO4 tetrahedra in C-S-H was noted. The presence of chlorides decreased cross-linking of SiO4 tetrahedra and reduced gypsum formation and Ca depletion from the matrix. Precipitation of brucite at the edge of the specimens possibly inhibited the promotion of the attack process. Chlorides penetrated deeper into the matrix compared to sulfates. Increasing limestone content in cement led to a higher mean chain length of cross-linked chains and AlO4/SiO4 ratio in the sulfate-bearing environment. The extent of C-S-H degradation in the cement pastes with the highest limestone content was independent of the exposure conditions. Cement with approx. 12% limestone content can be considered of equal performance to ordinary Portland cement in severe sulfate–chloride solutions.

Thermodynamic and experimental study on chloride binding of limestone containing concrete in sulfate-chloride solution

Concrete's durability where sulfate and chloride ions coexist is a challenging issue. In addition, utilization of limestone powder (LS) in blended cements tended to result in physically and chemically different hydration processes compared with other cements. The present study aims to evaluate Cl− ingress into concrete samples containing LS in the presence of sulfates in exposure environment. In this regard, 3 different exposure conditions of 165 g/l NaCl, 27.5 g/l Na2SO4 + 165 g/l NaCl, and 55 g/l Na2SO4 + 165 g/l NaCl solutions have been designated. Compressive strength, capillary water absorption, surface electrical resistivity, and rapid chloride ions migration tests have been carried out and the total and water-soluble Cl− penetration profiles were determined. Besides these experimental studies, thermodynamic modelling was conducted to simulate the phase assemblage of samples before and after exposure to NaCl and Na2SO4 solutions. According to the results, using LS in concretes is followed by an increase in permeability and a decrease in compressive strength, which agree well with the outcomes of thermodynamic modelling. In the case of single Cl− attack, adding LS results in up to 60.7% and 36.0% increase in apparent and non-steady state Cl− diffusion coefficients, respectively. In addition, both thermodynamic modelling and experimental studies show that the presence of sulfate ions decreases the chemical Cl− binding ability of binders, and the Cl− diffusion coefficient of samples exposed to the combined condition increases. However, by increasing the sulfate ions concentration, the Cl− ingress may be retarded.

The deterioration mechanisms of hardened cement paste exposed to combined action of cyclic wetting–drying, salt attack and carbonation

In saline soil or salt lake regions, cement-based materials suffer from combined action of salt attack (SA), carbonation, and cyclic wetting–drying (CWD), and its deterioration mechanism remains an open question. Taking advantage of multiple techniques, this study is dedicated to unveiling the deterioration mechanism of hardened cement paste (HCP) exposed to combined action of SA (sulfate salt or sulfate–chloride salt), carbonation (natural carbonation, 0.035 vol.% CO2 or accelerated carbonation, 20 vol.% CO2) and CWD. The results show that, when exposed to combined action of SA, carbonation and CWD, HCP exhibits distinct deterioration mechanisms depending on the concentration of carbon dioxide: chemical sulfate attack (i.e., formation of ettringite and gypsum) is mainly responsible for the deterioration of HCP in the case of natural carbonation, whereas decomposition of C-S-H and formation of gypsum are both responsible for the deterioration of HCP in the case of accelerated carbonation. The presence of sodium chloride in sulfate–chloride solution inhibits the sulfate attack as well as carbonation attack of HCP.

Corrosion behaviour of maize husk reinforced aluminium (1070) metal matrix composites in chloride-sulphate solution

The effect of maize husk (MH) particulates on the corrosion resistance of 1070 aluminium alloy (AA70) matrix at 5% and 15% wt. content, and 150 μm and 300 μm particle size (AA70/MH composites) was studied in 3.5% NaCl, 0.0125 M H2SO4 and 3.5% NaCl/0.0125 M H2SO4 solutions. Potentiodynamic polarization technique, open circuit potential measurement, weight loss analysis, optical microscopy characterization, x-ray fluorescence and x-ray diffractometry were used for the investigation. Results show increase in MH %wt. content and particle size decreases the corrosion rate of AA70/MH composite. Data from potentiodynamic polarization and weight loss analysis shows AA70/MH composite at 15% wt. content and 300 μm particle size exhibited the lowest corrosion values of 0.135 mm y−1, 0.156 mm y−1 and 1.445 mm y−1, and −0.00043 mm y−1, 0.001 04 mm y−1 and 0.00218 mm y−1 in 3.5% NaCl, 0.0125 M H2SO4 and 3.5% NaCl/0.0125 M H2SO4 solutions. Optical representative images of the composites showed the presence of micro-pits on samples from NaCl solution, macro-pits and extensive surface deterioration from H2SO4 solution, and combined localized and total surface deterioration from NaCl-H2SO4 solution. Weight loss plots showed oxide formation significantly influenced the corrosion behavior of the alloys with respect to time. Open circuit potential plots showed AA70/MH composite at 5% wt. content and 150 um particle size was the most electronegative with the highest thermodynamic tendency to corrosion. Significant X-ray diffraction peaks from AA70/MH composite at 15% wt. content and 300 μm particle size showed the presence of corrosion resistant phase compounds of Al2O3 and Al(ZnS2) before and after corrosion.

Enhanced selectivity of platinum group metals concentrates at Kola MMC’s chemical and metallurgical shop

An upgrade of the nickel refining circuit realized in 2019 by Kola MMC when the plant adopted an electrowinning process for extracting nickel from sulphate-chloride solutions resulting from chlorine dissolution of tube furnace nickel powder, led to a considerable decrease in the amount of nickel sludge generated. The latter is treated at the Chemical and Metallurgical Shop by liquid phase sulphation in the presence of sulphuric acid. Other materials containing precious metals are now used in the sulphation process. For example, the concentrate obtained as a result of flotation of the tube furnace nickel powder chlorine dissolution residue. The main purpose of sulphation is to obtain selective concentrates of platinum group metals. The products include platinum-palladium concentrate and a concentrate of concomitant metals that contains at least 20 % of rhodium. The qualitative and quantitative characteristics of the concentrates define the process to be applied, as well as the recovery of base metals during further refining. A change in the feedstock supplied to the Chemical and Metallurgical Shop affected the distribution of rhodium between the target concentrates leading to a greater loss of concomitant metals in the refining process. The high demand for platinum group metals at the global market, the drawbacks of the current process, as well as the new type of feedstock supplied created a need for the process parameters to be studied and adjusted. The paper examines the process flowsheet and looks at ways to raise the selectivity of the final products by means of liquid phase sulphation in the presence of sulphuric acid.Contributors to this paper include M. A. Lastochkina, who oversees the precious metals section at the Hydrometallurgical Laboratory of Gipronikel Institute.

Effect of Combined Chloride-Sulfate Solutions and Associated Cation Types with Sulfate Ions on Corrosion Performance of Steel Rebar in Concrete

Abstract The rapid deterioration of reinforced concrete structures located in marine environment because of chloride-generated corrosion remains a matter of serious concern. The marine environment mainly comprises chloride (Cl−) ions, sodium (Na+) ions, sulfate (SO42−) ions, and magnesium (Mg2+) ions. The existence of SO42− ions with Cl− ions influences the chloride-generated corrosion behavior because of the binding of these ions with hydrated C3A in concrete. In this research, an experimental study has been conducted to assess the performance of embedded rebar (carbon steel) against corrosion in normal concrete subjected to chloride (NaCl) and combined chloride-sulfate (NaCl with MgSO4 and NaCl with Na2SO4) solutions for 27 months of exposure periods. The results showed that the corrosion performance of the embedded rebar was influenced by SO42− ions and its associated cation (Na+ and Mg2+) type. The SO42− ions associated with Na+ cation resulted in higher corrosion current density (Icorr) as compared to Mg2+ cation in the concomitant presence of Cl− ions. The presence of Cl− ions significantly increased the corrosion rate of steel rebar, whereas the presence of SO42− ions (irrespective of associated cation, i.e., Na+ and Mg2+) in the exposure solution hindered the effect of Cl− ions on increasing the corrosion rate of steel. The established empirical relationship obtained between half-cell potential (E0), and Icorr predicted well the Icorr values obtained from ordinary portland cement with 20 % fly ash concrete used in the present research work and with the results obtained by different researchers in the literature.

Yttrium speciation in sulfate-rich hydrothermal ore-forming fluids

Rare Earth elements (REE) are gaining importance due to their increasing industrial applications and usefulness as petrogenetic indicators. REE-sulfate complexes are some of the most stable REE aqueous species in hydrothermal fluids, and may be responsible for REE transport and deposition in a wide variety of geological environments, ranging from sedimentary basins to magmatic hydrothermal settings. However, the thermodynamic properties of most REE-sulfate complexes are derived from extrapolation of ambient temperature data, since direct information on REE-sulfate complexing under hydrothermal conditions is only available for Nd, Sm and Er to 250 °C (Migdisov and William-Jones, 2008, 2016).We employed ab initio molecular dynamics (MD) simulations to calculate the speciation and thermodynamic properties of yttrium(III) in sulfate and sulfate-chloride solutions at temperatures and pressures up to 500 °C and 800 bar. The MD results were complemented by in situ X-Ray Absorption Spectroscopy (XAS) measurements. Both MD and XAS show that yttrium(III) sulfate complexes form and become increasingly stable with increasing temperature (≥200 °C). The MD results also suggest that mixed yttrium-sulfate-chloride complexes (that cannot be distinguished from mixtures of chloride and sulfate complexes in XAS experiments) form at ≥ 350 °C. Two structures with two different Y(III)-S distances (monodentate and bidentate) are observed for Y(III)-sulfate bonding. The formation constants, derived via thermodynamic integration, for the Y(III) mono- and di-sulfate complexes parallel the trends for those of Nd, Sm and Er determined experimentally to 250 °C.The derived formation constants were used to fit revised Helgeson-Kirkham-Flowers equation-of-state parameters that enabled calculation of formation constants for Y(SO4)+ and Y(SO4)2− over a wide range of temperatures and pressures. The presence of sulfate increases the solubility of Y(III) under specific conditions. Since the stability of sulfate is redox sensitive, Y(III) solubility becomes highly redox-sensitive, with rapid precipitation of Y minerals upon destabilisation of aqueous sulfate.

Evaluation of macro- and meso-mechanical properties of concrete under the aggressiveness of landfill leachate

Current researches on the mechanical properties of concrete are mainly concentrated on the aggressiveness of sulfate, chloride ion, acid and freeze–thaw cycles. However, the evolution of concrete mechanical properties aggressived by landfill leachate remains to be revealed. As the micro-nano indentation test is a new method to measure the fine/micro mechanical behavior of materials, it is used in this research to evaluate the micro-mechanics of the landfill leachate of the concrete sample surface and different aggressived depths. In addition, the evolution of the macro-mechanical properties of concrete aggressived by the landfill leachate was studied through uniaxial compression tests. The results show that the hydration products with high elastic modulus are consumed by the aggressiveness of landfill leachate, which results in a large number of microscopic cracks on the surface of the concrete. Moreover, the longer the aggressive time, the shallower the aggressive depth, and the more severe the deterioration of the micromechanical properties of the sample surface. It is also notable that the uniaxial compressive strength of the concrete samples aggressived by landfill leachate showed a linear increase and then gradually decrease. Comparing with the sodium chloride and sodium sulfate solutions, the landfill leachate has the most significant weakening effect on the elastic modulus of concrete.

Evaluation of the influence of alumina nano-particle size and weight composition on the corrosion resistance of monolithic AA1070 aluminium

Corrosion resistance of AA1070 aluminium alloy (AA1070) was compared to AA1070 reinforced with alumina at weight composition (wt. %) of 5% and 10%, and grain size of 150 nm and 600 nm. Potentiodynamic polarization and open circuit potential analysis were employed in 0.0125 M H2SO4, 3.5% NaCl and 0.0125 M H2SO4-3.5% NaCl solutions. Data showed 0.0125 M H2SO4-3.5% NaCl solution was the most deleterious with peak corrosion rate value of 6.682 mm/y while 3.5% NaCl solution was the weakest with peak value of 0.084 mm/y. AA1070 at 5% (wt. %) and 150 nm particle size generally displayed the highest corrosion rate with values between 0.084 and 6.682 mm/y. However, visible decrease in corrosion rate occurred with increase in alumina weight fraction and particle size due to growth of the protective oxide on the composite and reduction of discontinuities to minimal values between 0.031 and 2.192 mm/y at 10% alumina weight fraction and 600 nm particle size. Cathodic and anodic reaction mechanisms significantly differs with respect to the electrolyte. Anodic reaction mechanism appeared under activation control in the sulphate-chloride and chloride solution, compared to cathodic reaction mechanism in the sulphate and sulphate-chloride solutions. Significant anodic degradation reaction was prevalent on the anodic polarization plot in the sulphate solution. Plots from open circuit potential analysis shows the composites and monolithic Al were the most thermodynamically stable in H2SO4 solution. In the sulphate-chloride solution, significant potential transients coupled with high corrosion tendency are conspicuous. The plot showed chaotic thermodynamic behaviour active passive transition behaviour of the passive film.

Behaviour of SiO2 during a new process applied to nickel concentrate from matte separation at Kola MMC

Kola MMC has built a new nickel site that relies on chlorine leaching of nickel powder followed by electrowinning of nickel with insoluble anodes. After the new site had been commissioned, the operations of the refining facility saw changes, the electric anode furnaces were taken out of service, and a magnetic separation section was commissioned. The latter helps remove unreacted coal, metal oxides and other non-magnetic components from the tube kiln nickel powder thus ensuring its optimized quality. At the same time, once the electric furnaces had been removed from the process, it created the need for strict control over carbon and slag-forming constituent concentration in the nickel powder that goes to the chlorine leaching section. This paper looks at the history of the process behind the production of roasted nickel – the product of fluidized-bed furnaces – and describes the revamping stages witnessed by the Kola MMC site. The paper also analyzes certain features related to the current processing of nickel concentrates – from nickel matte separation to the production of nickel metal powder. The latter is further sent for chlorine leaching and in the presence of chlorine gas it gets dissolved. Then copper, iron, zinc and cobalt are removed from the resultant liquor and the purified sulphate-chloride solution goes in the electrolysis cells where high-purity nickel cathodes are produced. The authors analyzed the compositions of the key components in the studied materials of the nickel processing line. Special attention is given to the behaviour of silicon dioxide as one of the impurities causing most problems in the new process.

The Use of the Electrochemical Impedance Technique to Predict the Resistance to Chloride Ingress in Silica Fume and Fly Ash-Reinforced Blended Mortars Exposed to Chloride or Chloride–Sulfate Solutions

The Use of the Electrochemical Impedance Technique to Predict the Resistance to Chloride Ingress in Silica Fume and Fly Ash-Reinforced Blended Mortars Exposed to Chloride or Chloride–Sulfate Solutions

The Resistance of Novel Concrete Prepared by Gap-Graded Blended Cement under Chloride-Sulfate Attack

The resistance of concrete under chloride-sulfate attack dominates the durability of marine constructions. The binder played a more important role in chloride-sulfate resistance of concrete due to the dynamic hydration process. Incorporating supplementary cementitious materials (SCMs) was beneficial to the microstructure densification of cement paste, but the low hydraulic activities of SCMs resulted in the decrease of mechanical properties, activating activities of SCMs would raise the cracking risk of cement paste. On the basic of close packing theory, a gap-graded blended cement contained calcined hydrotalcite and metakaolin was adopted to prepare concrete with high resistance under chloride-sulfate attack in present study. The gap-graded blended cement concrete presented comparable strength with Portland cement concrete, even though only 25% clinker used in the blended cement. Because of the continuous hydration of alumina-rich SCMs and functional components, the secondary hydration products with high chloride binding capacity helped blocking ions ingress, resulting in the one-magnitude decrease of chloride diffusivity. At the early period of soaking duration in chloride-sulfate solution, the sulfate ions were beneficial to delaying the migration of chloride. And the cracks introduced by expansive products from sulfate attack would observably accelerate the release and continuous ingress of chloride at late period.

A chemo-thermo-damage-transport model for concrete subjected to combined chloride-sulfate attack considering the effect of calcium leaching

Reinforced concrete structures can be seriously deteriorated under combined chloride-sulfate attack. To study the deterioration process of concrete under such condition, based on the chemo-physical–mechanical method, a coupled chemo-thermo-damage-transport model was proposed. Corrosive (i.e., acidic) environments and presence of chloride and sulfate ions in solution can promote the leaching and chemical transformation of solid-phase calcium from cement-based materials. Meanwhile, the change of temperature further affects the diffusivity and reaction rate of ions worsening the situation. Numerical results of the proposed model in this paper are in good agreement with the experimental results previously reported by Maes, suggesting that the proposed chemo-thermo-damage-transport model is reliable. During the experiment, the chloride distribution of Portland cement-based mortars immersed in 165 g / L NaCl and 50 g / L Na2SO4 solution for 28 weeks at 20 and 35 °C was investigated. Results show that, without accelerated effect, the diffusivity of chloride in mortar increases with diffusion depth. After 180 days exposure, the degradation depth of the specimens immersed in the combined chloride-sulfate solution is almost 3 times of that of deionized water. By incorporating the temperature and calcium leaching effects into the numerical exploration, the conclusions can provide a technical guidance for the engineering practice of long-term chloride-sulfate attack.

Corrosion resistance and passivation behavior of 3004 AlMnMg and 4044AlSi aluminum alloys in acid-chloride electrolytes

Corrosion resistance of 3004 and 4044 aluminium alloys (3004Al and 4044Al) in neutral chloride (0.5%–4.5% concentration), sulphate (0.00625M-0.1 M concentration), and chloride-sulphate (0.00625 M H2SO4/0.5%–4.5% chloride concentration) solutions was studied with potentiodynamic polarization, open circuit potential, cyclic polarization, and optical microscopy. Results show 4044Al exhibited higher resistance to general corrosion while 3004Al was more resistant to localized corrosion. Corrosion of 4044Al decreases with increase in chloride concentration while 3004 Al increases. Corrosion rate values for 3004Al and 4044Al in sulphate solution were generally similar between 0.061–0.395 mm y−1 and 0.168–0.213 mm y−1, respectively. In chloride-sulphate solution, corrosion rate of 3004Al increased from 0.130 mm y−1 to 1.563 mm y−1 at peak chloride concentration whereas the corrosion rate of 4044Al is near constant. The passive film on 4044Al is found to weaken significantly with increase in chloride concentration. Passivation values varied from 0.39 V at 0.5% chloride concentration to 0.01 V at 4.5% concentration while the potential at which stable pitting occurred increased. The passivation range values for 3004Al are relatively stable with respect to chloride concentration. Results from cyclic polarization experiments show the deterioration rate of both alloys in NaCl solution is subject to chloride concentration. The results show the alloys corrode at all NaCl concentrations (0.5%–4.5%) with the lowest pitting corrosion risk in 0.5% and 1.5%NaCl solutions. The highest pitting corrosion risk of the alloys occurred in 3.5% NaCl solution. Significant localized morphological deterioration is visible throughout the entirety of 4044Al relative to the adjacent Al alloy matrix compared to total surface deterioration on 3004Al.

Assessment of the corrosion susceptibility of 434 ferritic stainless steel in chloride-sulphate solution

The corrosion polarization behaviour of 434 ferritic stainless (434ST) was studied in 1 M H2SO4 at 0.25% to 2% NaCl concentration through potentiodynamic polarization techniques and open circuit potential analysis. Results showed corrosion rate of 434ST at in 1 M H2SO4 solution at 0% NaCl concentration is 5.51 mm/y. However, at 0.25% NaCl concentration corrosion output decreased to 1.31 mm/y due to competitive adsorption mechanism with dissolved O2 atoms. Increment in NaCl concentration causes increase in corrosion rate till 1% NaCl concentration at 5.97 mm/y. After 1% NaCl concentration, the corrosion of 434ST attained threshold deterioration mechanism with values varying between 6.20 mm/y and 6.56 mm/y. Shift in corrosion potential plot with respect to 434ST at 0% NaCl concentration indicates anodic corrosion and passivation mechanism on the steel surface which was also proven from the anodic Tafel slope values. Open circuit potential plots showed plots at 2% NaCl concentration showed the least thermodynamic tendency to corrode with the strongest shift to electropositive potentials which culminated at -0.439 V at 5400 s of observation. The plot at 0% NaCl solution exhibited the most electronegative plot configuration by reason of the deteriorating reaction of SO4 2- on the steel.

Sorption Recovery of Platinum Metals from Production Solutions of Sulfate-Chloride Leaching of Chromite Wastes

This paper discusses the scientific rationale for methods of platinum metals sorption centralization from saturated solutions with a high content of macrocomponents. Methods of sorption centralization of platinum and iridium using local anionites such as AH-31, AB-17-8, Purolite S985 are described. The sorbents used were conditioned to remove organic and mineral impurities. The sorption isotherms of platinum group metals 1/EC=f(1/Cp) at a temperature of 20 °C and a duration of 24 h were plotted. The data on the sorption recovery of platinum and iridium from individual and combined sulfate-chloride solutions were determined. Isotherms of iridium sorption from sulfate-chloride solution are formed. Results of the apparent sorption equilibrium constant and values of standard Gibbs energy (ΔG, kJ/mol) of ion exchange for sorption of platinum and iridium from individual and combined sulfate-chloride solutions are presented. Linearized isotherms and kinetic curves of joint sorption of platinum and iridium from sulfate-chloride solution are described. Comparative sorption of the platinum-group metals (PGM) by anionites AB-17-8 and Purolite S985 from sulfate-chloride solutions is shown. The sorption diagram of platinum and iridium from sulfate-chloride product solutions is presented. It has been revealed that complete recovery is achieved using chelation ion-exchange resin Purolite S985, with recovery of Pt up to 95% and Ir more than 73%. The sorption process is accompanied by intradiffusion constraints that are confirmed by the analysis of kinetic curves using Schmukler and Boyd–Adams models.

Chloride Diffusion Property of Hybrid Basalt-Polypropylene Fibre-Reinforced Concrete in a Chloride-Sulphate Composite Environment under Drying-Wetting Cycles.

The effect of fibre reinforcement on the chloride diffusion property of concrete is controversial, and the coupling effect of sulphate erosion and drying–wetting cycles in marine environments has been neglected in previous studies. In this study, the chloride diffusion property of hybrid basalt–polypropylene fibre-reinforced concrete subjected to a combined chloride–sulphate solution under drying–wetting cycles was investigated. The effects of basalt fibre (BF), polypropylene fibre (PF), and hybrid BP–PF on the chloride diffusion property were analysed. The results indicate that the presence of sulphate inhibits the diffusion of chloride at the early stage of erosion. However, at the late stage of erosion, sulphate does not only accelerate the diffusion of chloride by causing cracking of the concrete matrix but also leads to a decrease in the alkalinity of the pore solution, which further increases the risk of corrosion of the reinforcing steel. An appropriate amount of fibre can improve the chloride attack resistance of concrete at the early stage. With the increase in erosion time, the fibre effectively prevents the formation and development of sulphate erosion microcracks, thus reducing the adverse effects of sulphate on the resistance of concrete to chloride attack. The effects of sulphate and fibre on the chloride diffusion property were also elucidated in terms of changes in corrosion products, theoretical porosity, and the fibre-matrix interface transition zone.