Ppm SO42 Research Articles

Deterioration of Mortar Bars Using Binary and Ternary Mixtures Immersed in Sodium Sulfate Solutions

In this study, the performance of several binary and ternary mixtures containing high-calcium fly ash and other pozzolans, such as Class F fly ash and silica fume, were investigated for their sulfate resistance using different sodium sulfate solutions. The mortar bars were placed in a similar sulfate solution as per modified ASTM C 1012/1012M (33,800 ppm SO42−) with a less severe sulfate solution (6000 ppm SO42−) has been tested to resemble actual field performance for a duration of 18 months. The phase composition of the mortar samples was investigated using X-ray diffraction and scanning electron microscope coupled with energy dispersive spectroscopy (SEM/EDS). Results show that the mortar bars placed in the moderate sulfate concentration experience less expansion and deterioration than the same bars placed in the higher sulfate concentration. Storage in sodium sulfate solutions resulted in the formation of ettringite and gypsum in both sulfate concentrations. Replacement of cement by high-calcium fly ash showed significantly higher amounts of ettringite formation, especially for the mortar bars stored in the higher sulfate concentration. SEM analysis revealed ettringite to be the primary cause of disruption and deterioration observed in the mortar bars.

Preparation of Battery Grade Li2CO3 from Defective Product by the Carbonation‐Decomposition Method

AbstractBattery grade Li2CO3 is successfully synthesized by the carbonation‐decomposition method using defective crude Li2CO3 with the purity of 98.56 wt% containing 5873 ppm SO42− and other impurities such as Na, K, Ca, Fe, and Mg. Filter operation is found to be very important to improve quality of products. The purified Li2CO3 precipitation acquired by filtering the LiHCO3 solution possesses a higher purity of 99.65 wt% and greater whiteness with lower amounts of SO42− (222.0 ppm) and Fe (6.6 ppm). For further purification, ethylenediaminetetraacetic acid disodium salt is added into the LiHCO3 solution then Ca and Fe contents in purified Li2CO3 are reduced to 2.9 and 0.7 ppm, respectively. The removal efficiencies obtained for Ca, Fe, and SO42− are of 80.05%, 99.4%, and 97.5%, respectively. The research of reaction kinetics shows that the rate‐determining step of the carbonation process is diffusion control and the generated HCO3− ions can resist the further dissolution of CO2. The theoretical thermal decomposition temperature is 277.10 K by the thermodynamic calculation. SO42− impurity comes from absorbed Na2SO4 and doped Li2SO4. This work is of great significance to economically and simply treat defective product with high impurity content in the actual Li2CO3 production process.

A new type of silica-induced “moundless” pitting corrosion in copper observed in Japan

A new type of pitting corrosion in copper, namely “moundless” corrosion, has recently been reported in Japan. This type of pitting corrosion has some unique morphological features that differ from ordinary types of pitting corrosion, such as type I or type II. Firstly, this type of pitting corrosion has no mound of corrosion products that cover the mouth of the pit. In addition, a glassy verdigris exists around the pit. Furthermore, the pit measures <1 mm in diameter, but is extremely deep. In our study, we reproduced moundless pits by field testing in an area where moundless pits have often occurred. Moundless pits were also generated in synthetic freshwater through the dissolution of some selected components in a laboratory test. This synthetic freshwater contained 40 ppm SiO2, 50 ppm SO42−, 10 ppm Cl−, and 10 ppm HCO3−. Surface analysis of the moundless pit revealed that the mouths of the pits were covered with thin films that were mainly composed of silica.

Efficacy of glyphosate on David Spurge (Euphorbia davidii Subils) control under different levels of P and S / Eficácia do glyphosate no controle David Spurge (Euphorbia davidii Subils) em diferentes níveis de P e S

Euphorbia davidii Subils is one of the main weed species present in the central area of Argentina. The objective of this work was to evaluate the efficacy of glyphosate on E. davidii control, under different phosphorus and sulfur content in the soil. The aim of this study was to evaluate the influence of the P and S contents in the soil on the efficacy of glyphosate to control E. davidii. Two independent experiments were conducted in 2014 and 2015 in a completely randomized design with four replications, using three doses of glyphosate (0, 712, 1068 and 1424 g a.e. ha-1) on plants growing with three levels of P and S (5, 10 and 15 ppm P and SO4-2 respectively). At 5 ppm SO4-2, the 712 g a.e. ha-1 dose of glyphosate showed phytotoxicity ≤50% and evidenced differences with the 1068 and 1424 g a.e. ha-1 doses of the herbicide. The shoot dry weight showed only differences between the doses of glyphosate applied at low levels of phosphorus (5 ppm P). Besides, we observed that nutritional deficiency causes a delay in the onset of symptoms of phytotoxicity related to glyphosate. We can conclude that the nutritional status of E. davidii plants influenced the efficacy of glyphosate treatments. Finally, we suggest to check and control the nutritional status of agricultural plots and include fertilization practices as part of the information for decision-making within integrated weed management.

Behavior of iodate substituted ettringite during aqueous leaching

Ettringite [Ca6Al2(SO4)3(OH)12·26H2O] found in cementitious waste forms (CWFs) is known to immobilize iodate (IO3−) via sulfate (SO42-) substitution; however, limited studies have investigated the effects of leaching on the long-term fate and behavior of IO3− retained in ettringites. In this study, ettringite mineral transformation and iodine release from IO3−-incorporated ettringite ((IO3−)-Ett) were investigated using batch experiments to determine the mechanisms likely to drive IO3− release/retention within ettringite in environmentally relevant solutions of varying composition, pH, and alkalinity. (IO3−)-Ett was leached in six simulated solutions relevant to the Hanford Site (Washington State, USA) for a period of 56 days: double deionized water, 24 ppm CO32-, 1400 ppm SO42-, Hanford groundwater, Hanford vadose zone porewater and a cement-equilibrated solution. By monitoring IO3− uptake and removal and characterizing changes in the solid material, incongruent dissolution of ettringite to calcite and oxyanion substitution into the ettringite structure (e.g., SO42- or CO32-) were identified as contributing IO3− release mechanisms. However, the formation of calcium carbonates, e.g., calcite, may re-incorporate IO3− (pH < 10) or prevent the release of IO3− when formed on solution-exposed surfaces of ettringite. These results provide valuable insights into iodine release from CWFs that may be used to improve current CWF formulations for the treatment of iodine-containing nuclear waste.

A novel layered double hydroxide coupled with zero valent iron system for selenate removal under anaerobic condition: Batch and continuous studies

Batch and continuous stirred tank reactor (CSTR) tests were conducted to evaluate Se (VI) removal in a hybridized Fe(II)-Al(III)-Cl− layered double hydroxide/zero valent iron system (Fe-Al-Cl-LDH/ZVI) under anaerobic condition. This novel system was created by employing a nitrate-AlCl3 pretreatment method to coat the ZVI grains with an LDH surface and produce discrete LDH suspended solids (SS) with diameter of 475.3 nm through a rapid ZVI-AlCl3-nitrate reaction. In batch test, Se (VI) was quickly removed by Fe-Al-Cl-LDH/ZVI grains through adsorption via electrostatic attraction, anion exchange by releasing 1.7 mM Cl−/mM Se (VI) and Se (VI) reduction to Se (IV), Se (0) and Se (-II) by ZVI. In CSTR test, the anaerobic Fe-Al-Cl-LDH/ZVI system created a self-sustaining highly-reactive mixture that steadily reduced 2 ppm Se (VI) to below EPA discharge limit (50 ppb) in a single-stage reactor, where 200–300 ppm Cl− and 6.5–20 ppm SO42− coexisted. Externally-supplied FeCl2 and AlCl3 were essential to maintain LDH as the iron corrosion product and thus the high reactivity of ZVI. This study suggests that the Fe-Al-Cl-LDH/ZVI system could overcome ZVI passivation and thus provide an effective platform for Se (VI) and potentially other water contaminants removal.

Effect of chloride and sulfate ions on crevice corrosion behavior of low-pressure steam turbine materials

Crevice corrosion behavior between homogeneous and dissimilar materials of 13Cr and 3.5NiCrMoV steels was investigated in simulated boiler waters containing chloride ions (Cl−) and sulfate ions (SO42−), using open circuit potential (OCP) measurements in addition to morphology analysis. Pitting occurred inside the crevice not only on 13Cr steel but also on 3.5NiCrMoV steel in the test water containing 100 ppm Cl−, while it was suppressed by the coexistence of 50 ppm SO42− in the water with the 100 ppm Cl−. However, the presence of 50 ppm SO42− in the test waters promoted uniform corrosion on 3.5NiCrMoV steel inside the crevice.

Anodizing of aluminium and AA 2024-T3 alloy in chromic acid: Effects of sulphate on film growth

Chromic acid anodizing is important for the corrosion protection of aerospace aluminium alloys. Previous study has demonstrated that SO42− impurity in the chromic acid affects the film growth on aluminium at a voltage of 100V. The present work further investigates aluminium and extends the study to industrial anodizing conditions (Bengough-Stuart (B-S) process) and to the AA 2024-T3 alloy. It is shown that SO42− concentrations between ~38–300ppm reduce the film growth rate for aluminium anodized at 100V in comparison with an electrolyte than contains ≤1.5ppm SO42−, whereas ~1500–3000ppm SO42 have an opposite effect and lead to an unstable pore diameter. Under the B-S process, the film growth depends on the substrate composition, the SO42− content of the film, the film morphology and, for the alloy, oxygen generation. Corrosion tests of the alloy in 3.5% NaCl solution revealed better protection with films formed in chromic acid containing 38ppm SO42− compared with ≤1.5ppm SO42−, which are within the specified limits for sulphate impurity for chromic acid anodizing. The difference in corrosion protection is proposed to be related to the observed differences in the film morphologies; it is speculated that this may influence the retention of residues of chromate ions in the films.

Effect of sulfates on passivation in alkaline environments

Studies investigating passivation behaviour and corrosion resistance in simulated alkaline environments have typically been conducted in solutions containing sodium hydroxide (NaOH), potassium hydroxide (KOH) and calcium hydroxide (Ca(OH)2), with limited study of the effect of sulfates (SO42−). These sulfates are known to be present in the pore solution of materials like Portland cement-based concrete and may also ingress by the exposure to sulfate-rich environments. This study investigates the passivation behaviour and potentiodynamic polarisation behaviour of a high-strength carbon steel and high-strength stainless steels (austenitic and duplex) in saturated calcium hydroxide solutions containing up to 2000 ppm SO42−. Results indicate a negligible impact on the passivation behaviours of single-phase carbon steel and austenitic stainless steels. However, in duplex stainless steels, 1000 ppm of SO42− promotes passivation, whereas higher concentrations of 2000 ppm inhibit passivation. Additional research is necessary to correlate the altered passivation behaviour resulting from the presence of SO42− with chloride-induced corrosion resistance.

The effect of temperature on the rate of sulfate attack of Portland cement blended mortars in Na2SO4 solution

Sulfate attack on Portland cement and Portland blended cement concretes is a well-researched field. However, the effect of varying temperature on the rate of sulfate attack requires further attention. This laboratory experiment studied temperatures of 23°C, 10°C, 5°C, and 1°C. Both Portland and Portland limestone cements were studied in combination with several supplementary cementing materials. The mortar bars were submerged in 5% Na2SO4 (33,800ppm SO42−) solution for 15–30 months. At higher temperatures the supplementary cementing materials, particularly the fly ashes, greatly improved the resistance to external sulfate attack. At lower temperatures the metakaolin improved the resistance to sulfate attack; the fly ashes had little to no effect on the low-temperature sulfate resistance. The alterations to sulfate resistance are attributed to: dilution of Portland cement in the presence of supplementary cementing materials; additional nucleation sites provided by finely ground SCMs; and the pozzolanic and hydraulic reactions of the SCMs.

The potential use of serpentinite in the passive treatment of acid mine drainage: batch experiments

The efficiency of serpentinite as an alternative alkalinity generating material for the passive treatment of acid mine drainage (AMD) was assessed in the laboratory. Three series of batch experiments were designed for the passive treatment of a low pH (1.6) AMD synthetic solution containing 2,500 ppm Fe2+, 6,600 ppm SO42−, 10.5 ppm Al, 15 ppm Ni, and traces of Cr, Mn and Cu. The influencing factors studied were: the effect of water/rock ratio, residence time, type of the alkalinity generating material (dolomite, magnesite, marble, serpentinite), and nature of the system (open vs. closed cells). The variations in solution chemistry observed in the open cells indicate that a lower water/rock ratio (0.33 ml/g) was the most efficient for metals removal. The optimal residence time in open cells was 24 h to reach the higher pH values. In the closed cells laboratory setup, synthetic AMD was placed in contact with the various alkaline materials for three different contact times (24, 48, 72 h). The optimal pH was reached after 48 h and did not change appreciably for longer contact time, and the best results for metal removals were obtained with marble and serpentinite. Single treatment efficiency was compared with a successive treatment approach. The most promising results were obtained with a five step treatment: (1) pre-treatment in a closed cell using serpentinite, (2) aeration and settling, (3) treatment in an open cell using marble, (4) final aeration and settling, and (5) filtration with a coarse silica sand. With this configuration, the final pH was 6.5 and pronounced metals depletion was achieved (100% for Al, 99.95% for Fe, 85.7% for Ni).

Activation of Pozzolanic Reaction of Hydrated Portland Cement Fly Ash Pastes in Sulfate Solution

The activation of the pozzolanic reaction of fly ash in portland cement paste immersed in sulfate solution has been studied. Mixtures of two Spanish fly ashes (ASTM class F) with 0%, 15%, and 35% replacement of portland cement by fly ash were immersed in Na2SO4 solution, of 2880 ppm SO42− concentration, for a period of 90 days. The resistance of the different mixtures to the sulfate attack was evaluated using the Koch‐Steinegger test. The results showed that all of the mixtures were sulfate resistant, despite the high Al2O3 content of the fly ash. The diffusion of SO42− and Na+ ions through the pore solution activated the pozzolanic reactivity of the fly ashes, causing microstructural changes, which were characterized by X‐ray diffraction (XRD), mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM). As a result, the flexural strength of the mixtures increased, principally for the fly ash of a lower particle size and 35% of addition.

Low Chromate Corrosion Inhibitor with Borate and Hexametaphosphate

Chromate, despite being an efficient and versatile inhibitor for aqueous systems, is being phased out primarily because of its toxicity and carcinogenic nature. An effort is made in this work to substitute chromate by borate using Cr-51 and radioactive tracer technique. Mild steel is found to develop a thicker Cr containing protective film as chromate is systematically reduced from 100 to 60%, and substituted by borate. The film thickness decreased as chromate is reduced further, but the inhibitor still protects mild steel up to 5% chromate, at 303 K, at least up to 6 h. The open circuit potential shows predominance of anodic plarization.On attempting to reduce chromate further by substituting with hexametaphosphate, the Cr-uptake on the sample surface increases further showing the synergistic effect. The combination of inhibitors protects mild steel best at the ratio of chromate, borate and hexametaphosphate of 5:40:55 even in the presence of 500 ppm Cl− and 200 ppm SO42− ions, with predominance of cathodic polarization. The inhibitor formulation is more effective, less costly and contains chromate within the permissible limit.

Localised corrosion of high chromium superferritic alloys

AbstractThe general and pitting corrosion resistance of a selection of alloys based on a composition of Fe–40Cr were studied. These alloys have been investigated for corrosion resistant applications, specifically by microalloying with platinum group metals (PGM) to induce cathodic modification. The corrosion environments considered were a 10% H2SO4solution, and a synthetic mine water containing 500 ppm Cl− + 300 ppm SO42−. The effects of three metallurgical variables on the localised corrosion processes were investigated, these being: prestraining by cold work to increase the strain energy; recovery annealing to give a dislocation substructure; and alloying with 0·2 wt-% ruthenium. Prestraining by cold deformation of ∼5% does not impair the passivity or pitting resistance. However, a recovered dislocation substructure promotes localised attack which destabilises the passivity in a reducing acid medium. The addition of the cathodic element ruthenium increases the resistance to localised attack, but promote...

Geochemische Untersuchungen an Travertinen der Slowakei

Travertines are characterized by high rates of deposition. Waters from which travertines are precipitated have more than ten times the calcium concentration of mean continental surface waters. Calcium has been dissolved at some depth as sulfate and as carbonate the latter in bicarbonate rich waters. 38 samples from the important travertine deposits of Slovakia have been analyzed for the major elements including sulfate and 4 minor elements (Sr, Mn, Zn, Cu). Strontium and magnesium are correlated with the sulfur content. Due to its isotopic composition sulfate can be of Triassic origin. 9 out of 16 spring waters from the areas of travertine deposition contain more than 1000 ppm HCO 3 − +H2CO3 and 10 out of 16 more than 500 ppm SO 4 2− . A high carbonate content of waters is correlated with isotopically heavy carbon of travertines. Heavy carbonate carbon occurs also in travertines from CO2 discharging areas in Italy, Persia and Jugoslavia. A magmatic or metamorphic source of carbon dioxide can be considered for the carbonate of the majority of the Slovakian travertine deposits.